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Sample records for half-metallic heusler alloys

  1. Anisotropy in layered half-metallic Heusler alloy superlattices

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    Azadani, Javad G.; Munira, Kamaram; Sivakumar, Chockalingam; Butler, William H. [Center for Materials for Information Technology, University of Alabama, Tuscaloosa, Alabama 35487 (United States); Department of Physics and Astronomy, University of Alabama, Tuscaloosa, Alabama 35487 (United States); Romero, Jonathon [Department of Physics and Astronomy, University of Alabama, Tuscaloosa, Alabama 35487 (United States); Ma, Jianhua; Ghosh, Avik W. [Department of Electrical and Computer Engineering, University of Virginia, Charlottesville, Virginia 22904 (United States)

    2016-01-28

    We show that when two Heusler alloys are layered in the [001], [110], or [111] directions for various thicknesses to form a superlattice, the Slater-Pauling rule may still be satisfied and the resulting superlattice is often half-metallic with gaps comparable to or larger than those of its constituents. In addition, uniaxial magnetocrystalline anisotropy is induced because of the differences in the electronic structure of the two Heuslers in the superlattice. Various full-full, full-half, and half-half Heusler superlattices are studied, and potential half-metallic superlattices with perpendicular magnetocrystalline anisotropy are identified.

  2. Spin-electronic devices with half-metallic Heusler alloys

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    Huetten, A. [Institute of Nanotechnology, Forschungszentrum Karlsruhe GmbH, P.O. Box 3640, D-76021 Karlsruhe (Germany)]. E-mail: Andreas.Huetten@fzk.de; Schmalhorst, J. [Fakultaet fuer Physik, Universitaet Bielefeld, D-33615 Bielefeld (Germany); Thomas, A. [Fakultaet fuer Physik, Universitaet Bielefeld, D-33615 Bielefeld (Germany); Kaemmerer, S. [Fakultaet fuer Physik, Universitaet Bielefeld, D-33615 Bielefeld (Germany); Sacher, M. [Fakultaet fuer Physik, Universitaet Bielefeld, D-33615 Bielefeld (Germany); Ebke, D. [Fakultaet fuer Physik, Universitaet Bielefeld, D-33615 Bielefeld (Germany); Liu, N.-N. [Fakultaet fuer Physik, Universitaet Bielefeld, D-33615 Bielefeld (Germany); Kou, X. [Fakultaet fuer Physik, Universitaet Bielefeld, D-33615 Bielefeld (Germany); Reiss, G. [Fakultaet fuer Physik, Universitaet Bielefeld, D-33615 Bielefeld (Germany)

    2006-10-26

    We have integrated Co{sub 2}MnSi as a representative of the full-Heusler compound family as one magnetic electrode into technological relevant magnetic tunnel junctions. The resulting tunnel magnetoresistance at 20 K currently achieved is 108% associated with a Co{sub 2}MnSi spin polarization of 70% clearly proving that Co{sub 2}MnSi is already superior to 3d-based magnetic elements or their alloys. The corresponding room temperature value of the tunnel magnetoresistance is 42%. The presence of a step like tunnel barrier which is already created during plasma oxidation, while preparing the AlO {sub x} tunnel barrier, has been identified as the current limitation to achieve larger tunnel magnetoresistance and hence larger spin polarization and is a direct consequence of the oxygen affinity of the Co{sub 2}MnSi-Heusler element Mn. In addition preliminarily results on Co{sub 2}FeSi as a new full-Heusler compound integrated as magnetic electrode into technological relevant magnetic tunnel junctions are shown and discussed.

  3. Disorder dependent half-metallicity in Mn{sub 2}CoSi inverse Heusler alloy

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    Singh, Mukhtiyar [Department of Physics, Kurukshetra University, Kurukshetra, 136119 Haryana (India); Saini, Hardev S. [Department of Physics, M.M. University, Mullana, Ambala, 133207 Haryana (India); Thakur, Jyoti [Department of Physics, Kurukshetra University, Kurukshetra, 136119 Haryana (India); Reshak, Ali H. [Institute of Complex systems, FFPW, CENAKVA, University of South Bohemia in CB, 37333 Nove Hrady (Czech Republic); Center of Excellence Geopolymer and Green Technology, School of Material Engineering, University Malaysia Perlis, Kangar, 01007 Perlis (Malaysia); Kashyap, Manish K., E-mail: manishdft@gmail.com [Department of Physics, Kurukshetra University, Kurukshetra, 136119 Haryana (India)

    2013-12-15

    Heusler alloys based thin-films often exhibit a degree of atomic disorder which leads to the lowering of spin polarization in spintronic devices. We present ab-initio calculations of atomic disorder effects on spin polarization and half-metallicity of Mn{sub 2}CoSi inverse Heusler alloy. The five types of disorder in Mn{sub 2}CoSi have been proposed and investigated in detail. The A2{sub a}-type and B2-type disorders destroy the half-metallicity whereas it sustains for all disorders concentrations in DO{sub 3a}- and A2{sub b}-type disorder and for smallest disorder concentration studied in DO{sub 3b}-type disorder. Lower formation energy/atom for A2{sub b}-type disorder than other four disorders in Mn{sub 2}CoSi advocates the stability of this disorder. The total magnetic moment shows a strong dependence on the disorder and the change in chemical environment. The 100% spin polarization even in the presence of disorders explicitly supports that these disorders shall not hinder the use of Mn{sub 2}CoSi inverse Heusler alloy in device applications. - Graphical abstract: Minority-spin gap (E{sub g↓}) and HM gap (E{sub sf}) as a function of concentrations of various possible disorder in Mn{sub 2}CoSi inverse Heusler alloy. The squares with solid line (black color)/dotted line (blue color)/dashed line (red color) reperesents E{sub g↓} for DO{sub 3a}-/DO{sub 3b}-/A2{sub b}-type disorder in Mn{sub 2}CoSi and the spheres with solid line (black color)/dottedline (blue color)/dashed line (red color) represents E{sub sf} for DO{sub 3a}-/DO{sub 3b}-/A2{sub b}-type disorder in Mn{sub 2}CoSi. - Highlights: • The DO{sub 3}- and A2-type disorders do not affect the half-metallicity in Mn{sub 2}CoSi. • The B2-type disorder solely destroys half-metallicity in Mn{sub 2}CoSi. • The A2-type disorder most probable to occur out of all three types. • The total spin magnetic moment strongly depends on the disorder concentrations.

  4. Peculiarities of the electronic transport in half-metallic Co-based Heusler alloys

    OpenAIRE

    Marchenkov, V. V.; Perevozchikova, Yu. A.; Kourov, N. I.; Irkhin, V. Yu.; Eisterer, M.; Gao, T.

    2017-01-01

    Electrical, magnetic and galvanomagnetic properties of half-metallic Heusler alloys of Co$_2$YZ (Y = Ti, V, Cr, Mn, Fe, Ni, and Z = Al, Si, Ga, Ge, In, Sn, Sb) were studied in the temperature range 4.2--900 K and in magnetic fields of up to 100 kOe. It was found that varying Y in affects strongly the electric resistivity and its temperature dependence $\\rho(T)$, while this effect is not observed upon changing Z. When Y is varied, extrema (maximum or minimum) are observed in $\\rho(T)$ near the...

  5. Half-metallic ferrimagnetism in Full-Heusler alloy Mn{sub 2}CuMg

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    Wei Xiaoping; Deng Jianbo; Chu Shibing; Mao Geyong; Lei Tao [Department of Physics, LanZhou University, Lanzhou 730000 (China); Hu Xianru, E-mail: huxianru@lzu.edu.c [Department of Physics, LanZhou University, Lanzhou 730000 (China)

    2011-01-15

    In the paper Ab initio electronic structure calculations are applied to study the electronic structure and magnetism properties of a new Mn-based Heusler alloy Mn{sub 2}CuMg. We take into account both possible L 2{sub 1} structures (CuHg{sub 2}Ti and AlCu{sub 2}Mn types). The CuHg{sub 2}Ti-type structure is found to be energetically more favorable than the AlCu{sub 2}Mn-type structure and presents half-metallic ferrimagnetism. However, the case of exchanging X with Y atoms in generic formula loses its half-metallicity due to the symmetric surroundings. Calculations show that their total spin moment is -1{mu}{sub B} for a wide range of equilibrium lattice constants and the total spin magnetic moment is attributed mainly to the two Mn atoms, while the Cu atom is almost non-magnetic. A small total spin moment origins from the antiparallel configurations of the Mn partial moments. The CuHg{sub 2}Ti-type Mn{sub 2}CuMg alloy keeps a 100% of spin polarization of conduction electrons at the Fermi level, thus opening the way to engineer new half-metallic alloys with the desired magnetic properties.

  6. A half-metallic half-Heusler alloy having the largest atomic-like magnetic moment at optimized lattice constant

    Directory of Open Access Journals (Sweden)

    R. L. Zhang

    2016-11-01

    Full Text Available For half-Heusler alloys, the general formula is XYZ, where X can be a transition or alkali metal element, Y is another transition metal element, typically Mn or Cr, and Z is a group IV element or a pnicitide. The atomic arrangements within a unit-cell show three configurations. Before this study, most of the predictions of half-metallic properties of half-Heusler alloys at the lattice constants differing from their optimized lattice constant. Based on the electropositivity of X and electronegativity of Z for half-Heusler alloys, we found that one of the configurations of LiCrS exhibits half-metallic properties at its optimized lattice constant of 5.803Å, and has the maximum atomic-like magnetic moment of 5μB. The challenges of its growth and the effects of the spin-orbit effect in this alloy will be discussed.

  7. Electronic structure, magnetism and robust half-metallicity of new quaternary Heusler alloy FeCrMnSb

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    Singh, Mukhtiyar [Department of Physics, Kurukshetra University, Kurukshetra 136 119, Haryana (India); Saini, Hardev S. [Department of Physics, National Institute of Technology, Kurukshetra 136 119, Haryana (India); Thakur, Jyoti [Department of Physics, Kurukshetra University, Kurukshetra 136 119, Haryana (India); Reshak, Ali H. [Institute of Complex Systems, FFPW, CENAKVA, University of South Bohemia in CB, Nove Hrady 37333 (Czech Republic); Center of Excellence Geopolymer and Green Technology, School of Material Engineering, University Malaysia Perlis, 01007 Kangar, Perlis (Malaysia); Kashyap, Manish K., E-mail: manishdft@gmail.com [Department of Physics, Kurukshetra University, Kurukshetra 136 119, Haryana (India)

    2013-12-15

    Highlights: •A new quaternary Heusler alloy FeCrMnSb is identified with robust half metallicity. •The stability of FeCrMnSb has been examined using elastic constants. •Effect of uniform and tetragonal strains on half metallicity has been studied. -- Abstract: A new quaternary Heusler alloy FeCrMnSb is identified by employing ab initio electronic structure calculations. It is stable in Y-structure which is also verified by various conditions governed by elastic constants c{sub ij}. It is a true half-metallic (HM) ferromagnet with integer magnetic moment of 2.00 μ{sub B} per formula unit. The values of minority band gap and HM gap are found to be 0.65 eV and 0.1 eV, respectively. The HM character of FeCrMnSb sustains for −6% to 9% of uniform strain and −9% to 12% of tetragonal strain. This new quaternary Heusler alloy can be proved as an ideal candidate for spin valves and magnetic tunnel junction applications (MTJs)

  8. Half-metallicity and anisotropy magnetoresistance properties of Heusler alloys Fe2Co1-xCrxSi

    Science.gov (United States)

    Du, Y.; Xu, G. Z.; Liu, E. K.; Li, G. J.; Zhang, H. G.; Yu, S. Y.; Wang, W. H.; Wu, G. H.

    2013-06-01

    In this paper, we investigate the half-metallicity of Heusler alloys Fe2Co1-xCrxSi by first principles calculations and anisotropy magnetoresistance measurements. It is found that, with the increase of Cr content x, the Fermi level of Fe2Co1-xCrxSi moves from the top of valence band to the bottom of conduction band, and a large half-metallic band gap of 0.75 eV is obtained for x=0.75. We then successfully synthesized a series of Heusler Fe2Co1-xCrxSi polycrystalline ribbon samples. The results of X-ray diffraction indicate that the Fe2Co1-xCrxSi series of samples are pure phase with a high degree of order and the saturation magnetic moment follows half-metallic Slater-Pauling rule. Except for the two end members, Fe2CoSi and Fe2CrSi, the anisotropic magnetoresistance of Fe2Co1-xCrxSi (x=0.25, 0.5, and 0.75) shows a negative value suggesting they are stable half-metallic ferromagnets.

  9. Half-metallicity and magnetism at Heusler alloy surfaces: Co{sub 2}MSi(001)(M=Ti,Cr)

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    Jin, Ying Jiu [Department of Physics, Inha University, Incheon (Korea); Department of Physics, College of Science, Yanbian University, Yanji, Jilin (China); Lee, Jae Il [Department of Physics, Inha University, Incheon (Korea)

    2008-08-15

    We investigated the electronic structures, magnetism, and half-metallicity at the (001) surfaces of full-Heusler alloys, Co{sub 2}MSi (M=Ti,Cr), by using the all-electron full-potential linearized augmented plane wave method within the generalized gradient approximation. Both the Co-terminated (Co-term) and the MSi-terminated (MSi-term) surfaces were considered. From the calculated atom-resolved density of states, we found that the half-metallicity was destroyed at the Co-term surfaces for both alloys. The electronic structures at the MSi-term surfaces of the two alloys showed much different behavior. The half-metallicity was retained at the TiSi-term for Co{sub 2}TiSi(001) but the minority spin gap was much reduced due to surface states located just below the Fermi level. On the other hand the half-metallicity was destroyed at the CrSi-term of Co{sub 2}CrSi(001) due to the surface states located at the Fermi level. The calculated magnetic moment of the surface Co atom of the Co-term for Co{sub 2}CrSi(001) was increased slightly to 1.05 {mu}{sub B} with respect to that of the deep inner layers ({proportional_to}1.00{mu}{sub B}), while that for Co{sub 2}TiSi(001) was decreased to 0.88 {mu}{sub B}. Large enhancement of the magnetic moment was found for the surface Ti atoms at TiSi-term of Co{sub 2}TiSi(001) and Cr atoms at CrSi-term of Co{sub 2}CrSi(001) with values of 0.07 {mu}{sub B} and 2.91({mu}{sub B}), respectively. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  10. Large half-metallic gaps in the quaternary Heusler alloys CoFeCrZ (Z = Al, Si, Ga, Ge): A first-principles study

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    Gao, G.Y., E-mail: guoying_gao@163.com [School of Physics and Wuhan National High Magnetic Field Center, Huazhong University of Science and Technology, Wuhan 430074 (China); Hu, Lei; Yao, K.L.; Luo, Bo; Liu, Na [School of Physics and Wuhan National High Magnetic Field Center, Huazhong University of Science and Technology, Wuhan 430074 (China)

    2013-02-25

    Highlights: Black-Right-Pointing-Pointer Half-metallic ferromagnetism in quaternary Heusler alloys CoFeCrZ (Z = Al, Si, Ga, Ge). Black-Right-Pointing-Pointer The influence of Coulomb interaction on the half-metallicity of CoFeCrZ. Black-Right-Pointing-Pointer Half-metallicity is destroyed at the (0 0 1) surface of CoFeCrSi. - Abstract: The high Curie temperatures and compatible lattice structure with conventional semiconductors for half-metallic Co{sub 2}FeZ and Co{sub 2}CrZ (Z = Al, Si, Ga, Ge) inspired us to design new quaternary Heusler half-metallic ferromagnets CoFeCrZ. Our first-principles calculations show that, within generalized gradient approximation for the electronic exchange-correlation functional, both CoFeCrGa and CoFeCrGe are nearly half-metals, while both CoFeCrAl and CoFeCrSi exhibit excellent half-metallic ferromagnetism with the large half-metallic gaps of 0.16 and 0.28 eV, respectively. The half-metallicity of CoFeCrAl and CoFeCrSi is robust against the lattice compression (up to 7% and 4%, respectively). We also reveal that the half-metallicity is lost for both CoFeCrAl and CoFeCrGa but retentive for both CoFeCrSi and CoFeCrGe when the Coulomb interactions are considered. In addition, both CoFe- and CrSi-terminated (0 0 1) surfaces with and without antisite defects lose the bulk half-metallicity in CoFeCrSi.

  11. Tunable magnetization relaxation of Fe2Cr1 -xCoxSi half-metallic Heusler alloys by band structure engineering

    Science.gov (United States)

    He, Shikun; Liu, Yifan; Zheng, Yuhong; Qin, Qing; Wen, Zhenchao; Wu, Qingyun; Yang, Yi; Wang, Yupu; Feng, YuanPing; Teo, Kie Leong; Panagopoulos, Christos

    2017-11-01

    We report a systematic investigation on the magnetization relaxation properties of iron-based half-metallic Heusler alloy Fe2Cr1 -xCo xSi (FCCS) thin films using broadband angular-resolved ferromagnetic resonance. Band structure engineering through Co doping (x ) demonstrated by first-principles calculations is shown to tune the intrinsic magnetic damping over an order of magnitude, namely 1 ×10-2-8 ×10-4 . Notably, the intrinsic damping constants for samples with high Co concentration are among the lowest reported for Heusler alloys and even comparable to magnetic insulator yttrium iron garnet. Furthermore, a significant reduction of both isotropic and anisotropic contributions of extrinsic damping of the FCCS alloys was found in the FCCS films with x =0.5 -0.75 , which is of particular importance for applications. These results demonstrate a practical recipe to tailor functional magnetization for Heusler alloy-based spintronics at room temperature.

  12. Electron correlations and the minority-spin band gap in half-metallic Heusler alloys

    NARCIS (Netherlands)

    Chioncel, L.; Arrigoni, E.; Katsnelson, M.I.; Lichtenstein, A.I.

    2006-01-01

    Electron-electron correlations affect the band gap of half-metallic ferromagnets by introducing nonquasiparticle states just above the Fermi level. In contrast with the spin-orbit coupling, a large asymmetric nonquasiparticle spectral weight is present in the minority-spin channel, leading to a

  13. Electronic structure and half-metallicity in new Heusler alloys CoYO2 (Y = Sc, Ti, V, Cr, Mn, Fe, Ni, Cu, and Zn)

    Science.gov (United States)

    Esteki, S.; Ahmadian, F.

    2017-09-01

    First-principles calculations based on density functional theory (DFT) using the self-consistent full-potential linearized augmented plane wave (FPLAPW) method were applied to study the electronic structures and magnetic properties of new Heusler alloys CoYO2 (Y = Sc, Ti, V, Cr, Mn, Fe, Ni, Cu, and Zn). The calculated formation energies of these compounds were negative, therefore, they can be synthesized experimentally. All compounds were stable in ferromagnetic AlCu2Mn-type structure. In AlCu2Mn-type structure, CoScO2, CoFeO2, and CoNiO2 compounds were HM ferromagnets, CoCuO2 was a nearly half-metal, CoZnO2 was a spin gapless semiconductor, and other compounds were conventional ferromagnets. In CuHg2Ti-type structure, CoTiO2 compound had a nearly HM characteristic, CoVO2 was a spin gapless semiconductor, and other compounds were conventional ferromagnets. The origin of the half-metallic band gap for CoScO2 alloy Heusler alloy was well understood. The total magnetic moments of the three HM compounds obeyed Slater-Pauling rules (Mtot = 22-Ztot and Mtot = 32-Ztot). CoScO2 had the widest region of half-metallicity between the three half-metals indicating its high robustness of half-metallicity with respect to the variation of lattice constants.

  14. Density functional study of the half-metallic ferromagnetism in Co-based Heusler alloys Co{sub 2}MSn (M = Ti, Zr, Hf) using LSDA and GGA

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    Aguayo, Aaron, E-mail: aguayo@uady.mx [Facultad de Matematicas, Universidad Autonoma de Yucatan, Apartado Postal 172, Cordemex, 97110 Merida, Yucatan (Mexico); Murrieta, Gabriel, E-mail: murrieta@uady.mx [Facultad de Matematicas, Universidad Autonoma de Yucatan, Apartado Postal 172, Cordemex, 97110 Merida, Yucatan (Mexico)

    2011-12-15

    The half-metallic state in the Heusler alloys Co{sub 2}MSn (M = Ti, Zr, Hf) was studied by means of first principles calculation, using both, the Local Spin Density Approximation (LSDA) and the Generalized Gradient Approximation (GGA) to the exchange-correlation energy. While the GGA calculation shows that the three alloys are half-metallic ferromagnets, the LSDA results show that they are ferromagnetic but not half-metallic systems. The difference between the exchange-correlation functionals is analyzed through the electronic structure of the alloys. The origin of the gap in the minority spin channel for GGA calculations is discussed. - Highlights: > In Co{sub 2}MSn (M = Ti, Zr, and Hf) LSDA and GGA act differently on the orbitals. > LSDA and GGA results about their half-metallic estate differ. GGA are half-metallic. > LSDA miscalculated the occupied and unoccupied Co d orbitals. > The calculated magnetic moment also shows differences between the two functionals. > The Co-Co hybridization is central to explain the half-metallic state in these alloys.

  15. Half-metallicity and anisotropy magnetoresistance properties of Heusler alloys Fe{sub 2}Co{sub 1−x}Cr{sub x}Si

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    Du, Y.; Xu, G.Z.; Liu, E.K.; Li, G.J.; Zhang, H.G. [Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100080 (China); Yu, S.Y. [School of Physics, Shandong University, Jinan 250100 (China); Wang, W.H., E-mail: wenhong.wang@aphy.iphy.ac.cn [Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100080 (China); Wu, G.H. [Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100080 (China)

    2013-06-15

    In this paper, we investigate the half-metallicity of Heusler alloys Fe{sub 2}Co{sub 1−x}Cr{sub x}Si by first principles calculations and anisotropy magnetoresistance measurements. It is found that, with the increase of Cr content x, the Fermi level of Fe{sub 2}Co{sub 1−x}Cr{sub x}Si moves from the top of valence band to the bottom of conduction band, and a large half-metallic band gap of 0.75 eV is obtained for x=0.75. We then successfully synthesized a series of Heusler Fe{sub 2}Co{sub 1−x}Cr{sub x}Si polycrystalline ribbon samples. The results of X-ray diffraction indicate that the Fe{sub 2}Co{sub 1−x}Cr{sub x}Si series of samples are pure phase with a high degree of order and the saturation magnetic moment follows half-metallic Slater–Pauling rule. Except for the two end members, Fe{sub 2}CoSi and Fe{sub 2}CrSi, the anisotropic magnetoresistance of Fe{sub 2}Co{sub 1−x}Cr{sub x}Si (x=0.25, 0.5, and 0.75) shows a negative value suggesting they are stable half-metallic ferromagnets. - Highlight: ► We have investigated the half-metallicity of Fe{sub 2}Co{sub 1−x}Cr{sub x}Si Heusler alloys by first-principles calculations. ► We adjust the doping level x in Fe{sub 2}Co{sub 1−x}Cr{sub x}Si to move Fermi level from the top of valence band to the bottom of conduction band. ► Saturation magnetic moments of the samples follow half-metallic Slater–Pauling rule. ► The anisotropic magnetoresistance of Fe{sub 2}Co{sub 1−x}Cr{sub x}Si shows a negative value suggesting the half-metallic property.

  16. Ultrafast magnetization dynamics in the half-metallic Heusler alloy Co{sub 2}Cr{sub 0.6}Fe{sub 0.4}Al

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    Wuestenberg, Jan-Peter; Steil, Daniel; Alebrand, Sabine; Roth, Tobias; Aeschlimann, Martin; Cinchetti, Mirko [Department of Physics, Research Center OPTIMAS, University of Kaiserslautern, Erwin-Schroedinger-Str. 46, 67663 Kaiserslautern (Germany)

    2011-10-15

    Ultrafast demagnetization upon excitation with intense laser pulses has been observed for a variety of ferromagnetic materials. In half-metals, long demagnetization times are expected due to the band gap for one spin direction. We have investigated the theoretically half-metallic Heusler alloy Co{sub 2}Cr{sub 0.6}Fe{sub 0.4}Al (CCFA), using the time-resolved magnetooptical Kerr effect. A demagnetization time in the range of typical transition metal ferromagnets with lower spin polarization has been found, while magnetization recovery proceeds on a slower time scale. The results are discussed in the context of recent models and experimental results. We propose that for Heusler alloys the initial stage of recovery could be a better measure for the spin polarization than the demagnetization time. A simple estimate leads to a bulk spin polarization value of 0.86 for CCFA. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  17. Effect of atomic disorder on half-metallic ferromagnetism in Fe3-xCrxSi (x= 0, 0.25, 0.75, 1) heusler alloys

    Science.gov (United States)

    Singh, Mukhtiyar; Singh, Hardev; Kashyap, Manish K.

    2012-06-01

    Full potential linearized augmented plane wave (FPLAPW) method has been employed to investigate the electronic and magnetic properties of Fe3-xCrxSi (x = 0, 0.25, 0.75, 1) Heusler alloys using supercell approach. We obtained a regular increase in the spin polarization (P) with increase of Cr concentration. The signature of half-metallicity significantly starts from x = 0.75 with an indirect pseudogap at Fermi level (EF) in minority spin channel along ΓX direction, which converted into a real gap for the next alloy, Fe2CrSi (x= 1). The magnitude of band gap totally depends upon the concentration of Cr atom present in the alloy. The magnetic moment in all cases is mainly comes from FeII or/and Cr site. The disordered system showing maximum spin polarization can also be used for tunnel magnetoresistance (TMR) device.

  18. Half-metallic ferromagnetism in {Ti}2 {IrZ} (Z = B, Al, Ga, and In) Heusler alloys: A density functional study

    Science.gov (United States)

    Sadeghi, K. H.; Ahmadian, F.

    2018-02-01

    The first-principle density functional theory (DFT) calculations were employed to investigate the electronic structures, magnetic properties and half-metallicity of {Ti}2 {IrZ} (Z = B, Al, Ga, and In) Heusler alloys with {AlCu}2 {Mn}- and {CuHg}2 {Ti}-type structures within local density approximation and generalised gradient approximation for the exchange correlation potential. It was found that {CuHg}2 {Ti}-type structure in ferromagnetic state was energetically more favourable than {AlCu}2 {Mn}-type structure in all compounds except {Ti}2 {IrB} which was stable in {AlCu}2 {Mn}-type structure in non-magnetic state. {Ti}2 {IrZ} (Z = B, Al, Ga, and In) alloys in {CuHg}2 {Ti}-type structure were half-metallic ferromagnets at their equilibrium lattice constants. Half-metallic band gaps were respectively equal to 0.87, 0.79, 0.75, and 0.73 eV for {Ti}2 {IrB}, {Ti}2 {IrAl}, {Ti}2 {IrGa}, and {Ti}2 {IrIn}. The origin of half-metallicity was discussed for {Ti}2 {IrGa} using the energy band structure. The total magnetic moments of {Ti}2 {IrZ} (Z = B, Al, Ga, and In) compounds in {CuHg}2 {Ti}-type structure were obtained as 2μ B per formula unit, which were in agreement with Slater-Pauling rule (M_{tot} =Z_{tot}-18). All the four compounds were half-metals in a wide range of lattice constants indicating that they may be suitable and promising materials for future spintronic applications.

  19. Structural stability, electronic structure and magnetic properties of the new hypothetical half-metallic ferromagnetic full-Heusler alloy CoNiMnSi

    Directory of Open Access Journals (Sweden)

    Elahmar M.H.

    2016-03-01

    Full Text Available We investigated the structural stability as well as the mechanical, electronic and magnetic properties of the Full-Heusler alloy CoNiMnSi using the full-potential linearized augmented plane wave (FP-LAPW method. Two generalized gradient approximations (GGA and GGA + U were used to treat the exchange-correlation energy functional. The ground state properties of CoNiMnSi including the lattice parameter and bulk modulus were calculated. The elastic constants (Cij and their related elastic moduli as well as the thermodynamic properties for CoNiMnSi have been calculated for the first time. The existence of half-metallic ferromagnetism (HM-FM in this material is apparent from its band structure. Our results classify CoNiMnSi as a new HM-FM material with high spin polarization suitable for spintronic applications.

  20. Electronic structure and half-metallicity of the heusler alloy Co{sub 2}ZrGe

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    Li, Songtao; Liu, Yang; Ren, Zhi; Zhang, Xiaohong [North China Electric Power University, Baoding (China); Liu, Guodong [Hebei University of Technology, Tianjin (China)

    2014-10-15

    The site preference, the electronic structure and the magnetic properties of Co{sub 2}ZrGe have been studied by using first-principles calculations, and the stabilities of the Cu{sub 2}MnAl-type and the Hg{sub 2}CuTi-type structures have been tested in this respect. The Cu{sub 2}MnAltype structure is more favorable than the Hg{sub 2}CuTitype structure for the Co{sub 2}ZrGe compound, and the equilibrium lattice parameter of the Cu{sub 2}MnAl type Co{sub 2}ZrGe alloy is 6.06 A. The Co{sub 2}ZrGe alloy is found to have an energy gap in the minority spin direction at the Fermi level (E{sub F} ) and the majority spin band shows strongly metallic characteristic. As a result, the Co{sub 2}ZrGe alloy is predicted to be a half-metal with 100% spin polarization of the conduction electrons at the E{sub F}. The calculated total magnetic moment is 2.00 μ{sub B} per unit cell, which is in line with the Slater-Pauling curve of M{sub t} = Z{sub t} - 24. The Co atom-projected spin moment is 1.02μ{sub B}, which mainly determines the total moment. Simultaneously, the Zr and the Ge atom moments are - 0.08μ{sub B} and 0.04μ{sub B}, respectively. The Co{sub 2}ZrGe alloy may be a promising material for application in future spintronics devices.

  1. Possible half-metallicity and variable range hopping transport in Sb-substituted Fe2TiSn Heusler alloys

    Science.gov (United States)

    Chaudhuri, S.; Bhobe, P. A.; Nigam, A. K.

    2018-01-01

    The investigation of the magnetotransport properties on Fe2 TiSn1-x Sb x with 0 ≤slant x ≤slant 0.6 are presented in this paper. The substitution of Sb in place of Sn decreases the anti-site disorder as evident from x-ray diffraction patterns as well as from transport properties measurement. The much-disputed upturn in low temperature electrical resistivity of Fe2 TiSn has been demonstrated to be a result of weak localization induced by anti-site disorder. With increased Sb substitution (⩾25%) the metallic transport behavior of Fe2 TiSn changes to semiconductor-like. At low temperature, carrier transport in such compositions occurs via the variable range hopping mechanism. Moreover, a systematic increase in the anomalous Hall voltage is observed with increasing Sb-content, attributable to a side jump or Berry phase curvature effect. Electrical resistivity in the entire temperature regime hints towards half metallicity of the system. Our ab initio electronic structure calculations using generalised gradient approximation formalism further supports the results of our magnetotransport study.

  2. Robust half-metallic properties in inverse Heusler alloys composed of 4d transition metal elements: Zr{sub 2}RhZ (Z=Al, Ga, In)

    Energy Technology Data Exchange (ETDEWEB)

    Wang, X.T.; Lin, T.T. [School of Material Sciences and Engineering, Hebei University of Technology, Tianjin 300130 (China); Rozale, H. [Condensed Matter and Sustainable Development Laboratory, Physics Department, University of Sidi-Bel-Abbès, 22000 Sidi-Bel-Abbès (Algeria); Dai, X.F., E-mail: xuefangdai1976@163.com [School of Material Sciences and Engineering, Hebei University of Technology, Tianjin 300130 (China); Liu, G.D., E-mail: gdliu1978@126.com [School of Material Sciences and Engineering, Hebei University of Technology, Tianjin 300130 (China)

    2016-03-15

    A first-principles approach is used to study the electronic and magnetic properties of Zr{sub 2}RhZ (Z=Al, Ga, In) alloys in the Hg{sub 2}CuTi-type structure. The Zr{sub 2}RhZ (Z=Al, Ga, In) alloys are found to be half-metallic ferrimagnets. The half-metallicity is quite robust against hydrostatic strain and tetragonal deformation in Zr{sub 2}RhZ (Z=Al, Ga, In) alloys. The magnetization of Zr{sub 2}RhZ (Z=Al, Ga, In) alloys mainly originates from the 4d electrons of Zr atoms and follows the rule: M{sub t}=Z{sub t}−18. Zr{sub 2}Rh-based alloys do not contain any 3d transition metal element, which implies a wider field to search for new half-metallic materials. - Highlights: • Some HM materials containing 4d transition metal elements, Zr{sub 2}RhZ, have been found. • Zr{sub 2}RhZ alloys are HM ferrimagnets at their equilibrium lattice constants. • Their half-metallicity is robust against hydrostatic and tetragonal strains. • Zr{sub 2}RhZ with the Hg{sub 2}CuTi-type structure follows the SP rule M{sub t}=Z{sub t}−18. • Our results may trigger Zr-based HM materials applying in future spintronics field.

  3. Vacancy induced half-metallicity in half-Heusler semiconductors

    KAUST Repository

    Zhu, Zhiyong

    2011-09-28

    First-principles calculations are performed to investigate the effect of vacancies on the electronic structure and magnetic properties of the two prototypical half-Heusler semiconductors NiTiSn and CoTiSb. The spin degeneracy of the host materials is broken for all types of isolated vacancies under consideration, except for Ni-deficient NiTiSn. A half-metallic character is identified in Sn-deficient NiTiSn and Co/Ti/Sb-deficient CoTiSb. We can explain our findings by introducing an extending Slater-Pauling rule for systems with defects. A ferromagnetic ordering of the local moments due to double exchange appears to be likely.

  4. The half-metallicity of LiMgPdSn-type quaternary Heusler alloys FeMnScZ (Z=Al, Ga, In: A first-principle study

    Directory of Open Access Journals (Sweden)

    Y. C. Gao

    2015-05-01

    Full Text Available Based on the first-principles calculations, quaternary Heusler alloys FeMnScZ (Z=Al, Ga, In including its phase stability, band gap, the electronic structures and magnetic properties has been studied systematically. We have found that, in terms of the equilibrium lattice constants, FeMnScZ (Z=Al, Ga, In are half-metallic ferrimagnets, which can sustain the high spin polarization under a very large amount of lattice distortions. The half-metallic band gap in FeMnScZ (Z=Al, Ga, In alloys originates from the t1u-t2g splitting instead of the eu-t1u splitting. The total magnetic moments are 3μB per unit cell for FeMnScZ (Z=Al, Ga, In alloys following the Slater–Pauling rule with the total number of valence electrons minus 18 rather than 24. According to the study, the conclusion can be drawn that all of these compounds which have a negative formation energy are possible to be synthesized experimentally.

  5. Ferromagnetism in half-metallic quaternary FeVTiAl Heusler compound

    Energy Technology Data Exchange (ETDEWEB)

    Bhat, Tahir Mohiuddin; Bhat, Idris Hamid; Yousuf, Saleem; Gupta, Dinesh C., E-mail: sosfizix@yahoo.co.in [Condensed Matter Theory Group, School of Studies in Physics, Jiwaji University, Gwalior – 474 011 (MP) (India)

    2016-05-23

    The electronic structure and magnetic properties of FeVTiAl quaternary Heusler alloy have been investigated within the density functional theory framework. The material was found completely spin-polarized half-metallic Ferromagnet in the ground state with F-43m structure. The structural stability was further confirmed by calculating different elastic constants in the cubic phase. Present study predicts an energy band gap of 0.72 eV calculated in localized minority spin channel at an equilibrium lattice parameter of 6.0Å. The calculated total spin magnetic moment of 2 µ{sub B}/f.u. is in agreement with the Slater-Pauling rule for full Heusler alloys.

  6. Effect of site preference of 3d atoms on the electronic structure and half-metallicity of Heusler alloy Mn2YAl

    Science.gov (United States)

    Luo, Hongzhi; Zhu, Zhiyong; Ma, Li; Xu, Shifeng; Zhu, Xiaoxi; Jiang, Chengbao; Xu, Huibin; Wu, Guangheng

    2008-03-01

    The site preference of 3d atoms Y in Mn2YAl (Y = V, Fe, Co) alloys and its influence on their electronic structures and magnetism have been studied by first-principles calculations. The results prove that elements with more valence electrons than Mn tend to enter the A (0, 0, 0) and C (½, ½, ½) sites and elements with fewer electrons prefer the B (¼, ¼, ¼) site (Wyckoff positions). Meanwhile, it is found that for Mn2VAl and Mn2FeAl, a high spin polarization can be obtained whether the Y atom enters the (A, C) or the B site. In particular, Mn2VAl is half-metallic whether it forms the Cu2MnAl type or the Hg2CuTi type of structure. And a 100% spin polarization can be retained even when a 25% Mn-V antisite disorder occurs. This is quite preferable in practical applications. It is also found that the higher-valent element such as Co at the B (¼, ¼, ¼) site has opposite effects and tends to close the energy gap. Finally, a systemic summarization on the electronic and magnetic properties of Mn2YAl (Y = Ti, V, Cr, Mn, Fe and Co) alloys was made. All of them except for Mn2TiAl are predicted as half-metals. The calculated total spin moment is an integral value and increases from -3µB/f.u. for Mn2TiAl to +2µB/f.u. for Mn2CoAl with increasing number of valence electrons. This agrees with the Slater-Pauling curve quite well. All the Mn2YAl alloys studied here are ferrimagnets.

  7. Half-metallic ferromagnetism in Ti2IrZ (Z= B, Al, Ga, and In) Heusler ...

    Indian Academy of Sciences (India)

    Home; Journals; Pramana – Journal of Physics; Volume 90; Issue 2. Half-metallic ferromagnetism in T i 2 I r Z ( Z = B , A l , G a , a n d I n ) Heusler alloys: A density functional study. K H SADEGHI F AHMADIAN. Research Article Volume 90 Issue 2 February 2018 Article ID 16 ...

  8. Half-metallic Fe2CrSi and non-magnetic Cu2CrAl Heusler alloys for current-perpendicular-to-plane giant magneto-resistance: First principle and experimental study

    Science.gov (United States)

    Ko, V.; Qiu, J.; Luo, P.; Han, G. C.; Feng, Y. P.

    2011-04-01

    We present results of our first principle and experimental study on new Heusler alloys candidates for half-metallic electrode and nonmagnetic spacer in current-perpendicular-to-plane giant magneto-resistance devices. The electronic structures of Fe2CrSi and Cu2CrAl are characterized by high density of states at the Fermi level in the majority spin band with a good match in their majority band structures near the Fermi level. The calculated interfacial spin polarization in Fe2CrSi/Cu2CrAl (100) superlattice is ˜80%. We have also epitaxially grown ferromagnetic A2 Fe-Cr-Si and nonmagnetic L21 Cu-Cr-Al (100) films on Cr-buffered MgO(100) substrates.

  9. First-principles study on the magnetic and half-metallic properties in bulk and (001) surface of Ti{sub 2}CoSn Heusler alloy

    Energy Technology Data Exchange (ETDEWEB)

    Yan, Peng-Li [College of Physics and Information Technology, Shaanxi Normal University, Xian 710119, Shaanxi (China); Zhang, Jian-Min, E-mail: jmzhang@snnu.edu.cn [College of Physics and Information Technology, Shaanxi Normal University, Xian 710119, Shaanxi (China); Xu, Ke-Wei [College of Physics and Mechanical and Electronic Engineering, Xian University of Arts and Science, Xian 710065, Shaanxi (China)

    2016-06-30

    For the bulk and (001) surface of Ti{sub 2}CoSn Heusler alloy, the electronic and magnetic properties in bulk and the surface effect on the structural, electronic and magnetic properties of the alloy for different terminations of (001) surface have been studied by using first-principles calculations. The spin-gapless semiconductor (SGS) ferromagnetism with the magnetic moment of 3.00 μ{sub B}/f.u. is confirmed in the bulk Ti{sub 2}CoSn alloy with Hg{sub 2}CuTi-type structure. For two ideal terminations (TiCo, TiSn) and three modified terminations (CoCo*, TiTi*, SnSn*), the density of states (DOS) indicates that all terminations destroy the SGS character. Furthermore, we find that the atomic magnetic moments (AMM) decrease for the most atoms on the outmost three layers due to structural relaxation of these atoms inward. Both the DOS and AMM of the central layer L{sub 9} are similar to the corresponding bulk characters because surface effects fade out at the position of the inner layer, 12 Å below the surface. - Highlights: • Bulk Ti{sub 2}CoSn is spin-gapless semiconductor (SGS) ferromagnetism with 3 μB/f.u. moment. • All terminations of the (001) surface of the Ti{sub 2}CoSn alloy lose the SGS character. • Atomic magnetic moments at the (001) surface are greatly different from the bulk values.

  10. First-principles study on the thermodynamic stability, magnetism, and half-metallicity of full-Heusler alloy Ti{sub 2}FeGe (001) surface

    Energy Technology Data Exchange (ETDEWEB)

    Hu, Yan; Zhang, Jian-Min, E-mail: jmzhang@snnu.edu.cn

    2017-05-10

    For the Ti{sub 2}FeGe Heusler alloy, the surface stability, electronic and magnetic properties of the various (001) surfaces have been studied by using first-principles calculations. The TiGe termination is the most stable one while the GeGe* termination is the most unstable one. Both the density of states (DOS) and atomic magnetic moments (AMMs) of the central layers are similar to the corresponding bulk characters due to no influence of surface effect as we expected. The TiGe termination has the highest spin polarization 96.67%, followed by the TiFe (67.17%), GeGe* (66.51%) and FeFe* terminations (62.02%). The TiTi* terminations has the lowest spin polarization 61.31%. The magnetic moments for atoms on the surfaces and subsurfaces of these terminations are different from the bulk case. - Highlights: • TiGe termination is the most stable while GeGe* termination is the most unstable. • TiGe termination has the highest spin polarization followed by TiFe, GeGe*, FeFe* and TiTi*. • Atomic magnetic moments at the (001) surfaces are greatly different from the bulk values.

  11. First-principles study of the half-metallic and magnetic properties for new yttrium-based full-Heusler alloys Y2CrZ (Z = Al, Ga, In)

    Science.gov (United States)

    Kang, Xu-Hui; Zhang, Jian-Min

    2017-09-01

    First-principles calculations have been performed on the structural, electronic and magnetic properties of new yttrium-based full-Heusler alloys Y2 CrZ (Z = Al, Ga, In) in Hg2 CuTi structure. For three Y2 CrZ (Z = Al, Ga, In) alloys, the ferromagnetic states are the most favorable states among the possible magnetic configurations. At equilibrium lattice constants of 7.079, 6.979 and 7.212 Å, the Y2 CrZ (Z = Al, Ga, In) alloys are half-metallic ferromagnets with spin-up band gaps of 0.622, 0.652 and 0.489 eV, respectively. The formation energies and the cohesion energies indicate the stability of the Y2 CrZ (Z = Al, Ga, In) alloys. The much higher Curie temperatures TC of 772.947, 842.512 and 966.184 K than room temperature show the Y2 CrZ (Z = Al, Ga, In) alloys are suitable for spintronics and magnetoelectronics applications. The origins of the spin-up band gaps are attributed to the d-d hybridization (especially) and covalent hybridization. The total magnetic moments of 3 μB / f.u . for these alloys satisfy the Slater-Pauling rule Mt = 18 -Zt . In addition, the HM characters are kept in the lattice constants range from 6.757 to 7.501 Å, 6.716 to 7.422 Å and 6.743 to 7.585 Å for Y2 CrZ (Z = Al, Ga, In) alloys, respectively.

  12. Prediction of half-metallic properties for the Heusler alloys Mn{sub 2}CrZ (Z=Al, Ga, Si, Ge, Sb): A first-principles study

    Energy Technology Data Exchange (ETDEWEB)

    Luo Hongzhi [Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100080 (China)], E-mail: luohz@aphy.iphy.ac.cn; Zhu Zhiyong; Liu Guodong; Xu Shifeng; Wu Guangheng [Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100080 (China); Liu Heyan; Qu Jingping; Li Yangxian [School of Material Science and Engineering, Hebei University of Technology, Tianjin 300130 (China)

    2008-02-15

    First-principles FLAPW calculations were performed on the Mn{sub 2}CrZ (Z=Al, Ga, Si, Ge and Sb) alloys. Based on these results we predict two half-metallic ferromagnets (HMFs) namely Mn{sub 2}CrAl and Mn{sub 2}CrSb, and also find an energy gap in Mn{sub 2}CrGa which lies near the Fermi level. The energy gap lies in the majority spin band for Mn{sub 2}CrAl and Mn{sub 2}CrGa, whereas in the minority one for Mn{sub 2}CrSb. The calculated total spin magnetic moments M{sub t}{sup cal} are -1{mu}{sub B} per unit cell for Mn{sub 2}CrAl and Mn{sub 2}CrGa, +1{mu}{sub B} per unit cell for Mn{sub 2}CrSb and zero for Mn{sub 2}CrSi and Mn{sub 2}CrGe, which agree with the Slater-Pauling rule. The calculation indicates a large and localized magnetic moment of Cr at B site. This is meaningful for searching for new half-metallic antiferromagnets in Heusler alloys. The magnetic moment of Cr is found to increase with increasing atomic number of Z and is antiparallel to that of Mn. The change of Mn and Cr spin moments compensates each other and keeps the total spin moment as an integer when the Z atom is changed.

  13. Investigation of electronic structure, magnetic and transport properties of half-metallic Mn{sub 2}CuSi and Mn{sub 2}ZnSi Heusler alloys

    Energy Technology Data Exchange (ETDEWEB)

    Bhat, Idris Hamid, E-mail: idu.idris@gmail.com; Yousuf, Saleem; Mohiuddin Bhat, Tahir; Gupta, Dinesh C., E-mail: sosfizix@gmail.com

    2015-12-01

    The electronic and magnetic properties of Mn{sub 2}CuSi and Mn{sub 2}ZnSi Heusler alloys have been investigated using full-potential linearized augmented plane wave method. The optimized equilibrium lattice parameters in stable F-43m configuration are found to be 5.75 Å for Mn{sub 2}CuSi and 5.80 Å for Mn{sub 2}ZnSi. Spin-resolved calculations show that the Mn atoms at inequivalent Wyckoff positions have different contributions to the total magnetic moment in the unit cell. The anti-parallel magnetic moments of inequivalent Mn atoms sum to an integer with total magnetic moment per unit cell. The 100% spin-polarization at Fermi energy together with the total magnetic moment of 1.0 µ{sub B} for Mn{sub 2}CuSi and 2.0 µ{sub B} for Mn{sub 2}ZnSi per unit cell, predict that the materials follow M{sub T}=Z{sub T} – 28 Slater–Pauling rule. Both the materials under study exhibit half-metallicity with an energy gap in the spin-down channels. In the study, we predict a rather fine value of Seebeck coefficient. Further, the decreasing electrical conductivity with temperature shows a metallic character in spin-up configurations, while the electrical conductivity of spin-down states follows a semiconductor-like trend. - Highlights: • Half-metallic materials. • Highly spin-polarized. • Possess large conductivity in spin-up and large resistivity in spin-down channels. • Large Seebeck coefficient makes them suitable thermoelectric materials.

  14. Surface half-metallicity of half-Heusler compound FeCrSe and interface half-metallicity of FeCrSe/GaP

    Energy Technology Data Exchange (ETDEWEB)

    Khalaf Al-zyadi, Jabbar M., E-mail: jabbar_alzyadi@yahoo.com [Department of Physics, College of Education for Pure Sciences, University of Basrah (Iraq); Jolan, Mudhahir H. [Department of Physics, College of Education for Pure Sciences, University of Basrah (Iraq); Yao, Kai-Lun, E-mail: klyao@mail.hust.edu.cn [School of Physics and Wuhan National High Magnetic Field Center, Huazhong University of Science and Technology, Wuhan 430074 (China); International Center of Materials Physics, Chinese Academy of Sciences, Shenyang 110015 (China)

    2016-04-01

    Recent studies showed that half-Heusler FeCrSe exhibits half-metallic ferromagnetism (Huang et al. [20]). In this paper, we investigate extensively the electronic, magnetic, and half-metallic properties of the half-Heusler alloy FeCrSe (111) and (001) surfaces and the interface with GaP (111) substrate by using the first-principles calculations within the density functional theory. The atomic density of states demonstrates that the half-me tallicity verified in the bulk FeCrSe is maintained at the CrSe-terminated (001) and Se-terminated (111) surfaces, but lost at both Cr- and Fe-terminated (111) surfaces and the Fe-terminated (001) surface. Alternatively, for the interface of FeCrSe/GaP (111), the bulk half-metallicity is destroyed at Se–P configuration while Se–Ga interface and subinterface show nearly 100% spin polarization. Moreover, the calculated interfacial adhesion energies exhibit that Se–Ga shape is more stable than the Se–P one. The calculated magnetic moments of Se, Ga at the Se–Ga (111) interface and P at the Se–P (111) interface increase with respect to the corresponding bulk values while the atomic magnetic moment of Se atom at the Se–P (111) interface decreases. We also notice that the magnetic moments of subinterface Fe at both Se–Ga and Se–P (111) interfaces decrease compared to the bulk values. - Highlights: • The half-metallicity verified in the bulk FeCrSe is kept at the CrSe-terminated (001) and Se-terminated (111) surfaces. • The calculated interfacial adhesion energies exhibit that Se–Ga shape is more stable than Se–P. • The magnetic moments of Se, Ga and P atoms at the interface increase. • The Se–Ga interface shows nearly 100% spin polarization.

  15. Ultrafast demagnetization for Ni{sub 80}Fe{sub 20} and half-metallic Co{sub 2}MnSi heusler alloy films

    Energy Technology Data Exchange (ETDEWEB)

    Mizukami, S; Watanabe, D; Miyazaki, T [WPI-Advanced Institute for Materials Research, Tohoku University, Katahira 2-1-1, Sendai 980-8577 (Japan); Tsunegi, S; Kubota, T; Oogane, M; Naganuma, H; Ando, Y, E-mail: mizukami@wpi-aimr.tohoku.ac.j [Department of Applied Physics, Graduate School of Engineering, Tohoku University, Aoba 5-5-06, Sendai 980-8579 (Japan)

    2010-01-01

    We investigated ultrafast demagnetization for NM/Ni{sub 80}Fe{sub 20} (Py)/NM (NM=Ta,Pt) and epitaxial half-metallic Co{sub 2}MnSi (CMS) films using an all-optical pump-probe technique to clarify the correlation between demagnetization time {tau}{sub M} and magnetic damping constant {alpha} or spin polarization. The signal from the all-optical time-resolved magneto-optical Kerr effect exhibited rapid decrease in the sub-ps time regime and damped oscillations for these films. Values of {tau}{sub M} and {alpha} were evaluated using the three- temperature model and the Landau-Lifshitz-Gilbert equation. The {alpha} values for the NM/Py/NM films depended on both the Py thickness and NM materials while {tau}{sub M} was almost constant. The {tau}{sub M} values for the epitaxial CMS films were almost independent of L2{sub 1}-ordering and a little shorter than those for NM/Py/NM films.

  16. Magnetism and structure of a half-metallic Heusler compound Co-Mn-Cr-Si

    Science.gov (United States)

    Huh, Yung; Joshi, Swarangi; Jain, Sanmati; Pathak, Ojas; Kharel, Parashu

    Half metallic ferromagnetic Heusler compounds have a potential in the development of spintronic devices for its high spin polarization at the Fermi level and lattice structure compatibility. Heusler compounds based on cobalt are considered a good candidate for room temperature half-metals due to their high Curie temperature. Co2CrSi is one of such predicted half-metal, but it is meta-stable and difficult to synthesize in the desired crystal structure. We have successfully synthesized a Heusler compound Co2Mn0.5Cr0.5Si by using arc melting and rapid quenching followed by thermal treatment under high vacuum to control any parasitic contamination. Crystal X-ray diffraction pattern shows the samples crystallize in a cubic Heusler structure with some degrees of structural disorder. Curie temperatures of the prepared samples are observed well beyond room temperature near 900 K. Magnetic anomalies present in as-prepared samples are cleared, and its magnetic properties are improved by thermal treatment. This research is supported by Academic and Scholarly Excellence Funds, and Research/Scholarship Support Fund, South Dakota State University.

  17. Investigation of electronic structure, magnetic properties and thermal properties of the new half-metallic ferromagnetic full-Heusler alloys Cr{sub 2}GdSi{sub 1−x}Ge{sub x}: An ab-initio study

    Energy Technology Data Exchange (ETDEWEB)

    Asfour, I. [Laboratoire des matériaux magnétiques, Département de physique, Faculté des Sciences, Université Djillali LIABES, Sidi-Bel-Abbès 22000 (Algeria); Rached, H., E-mail: habib_rached@yahoo.fr [Laboratoire des matériaux magnétiques, Département de physique, Faculté des Sciences, Université Djillali LIABES, Sidi-Bel-Abbès 22000 (Algeria); Département de physique, Faculté des Sciences, Université Hassiba BenBouali Chlef, Chlef 02000 (Algeria); Benalia, S.; Rached, D. [Laboratoire des matériaux magnétiques, Département de physique, Faculté des Sciences, Université Djillali LIABES, Sidi-Bel-Abbès 22000 (Algeria)

    2016-08-15

    We have studied the structural, electronic, elastic, magnetic, thermal and thermodynamic properties of the quaternary Heusler alloys Cr{sub 2}GdSi{sub 1−x}Ge{sub x} (x = 0, 0.25, 0.5, 0.75, 1) with the linearized augmented plane wave method based on density functional theory and implemented in WIEN2K code. For exchange correlation potential, we have used the generalized gradient approximation (GGA) within the Perdew-Burke-Ernzerhof (PBE 96) parameterization. Our results provide a theoretical study for the mixed Heusler Cr{sub 2}GdSi{sub 1−x}Ge{sub x} (0 < x < 1) in which no experimental or theoretical data are currently available. In their equilibrium L2{sub 1} structure, all concentrations are magnetic and metallic. However, there is linear variation of the lattice parameter. The bulk modulus, the elastic constants and the Debye temperature was studied with variation of composition x of Ge. A regular solution model is used to investigate the thermodynamic stability, which are essentially shows a miscibility gap phase by calculating the critical temperatures for our alloys. In addition, the quasi-harmonic Debye model is applied to determine the thermal properties. - Highlights: • Based on DFT, GGA calculations, Cr{sub 2}GdSi{sub 1−x}Ge{sub x} compound have been investigated. • Single and polycrystalline elastic parameters are predicted. • The electronic and magnetic structure reveals the HMF character of these compounds. • The thermodynamic and thermal properties are predicted.

  18. Large magneto-Seebeck effect in magnetic tunnel junctions with half-metallic Heusler electrodes.

    Science.gov (United States)

    Boehnke, Alexander; Martens, Ulrike; Sterwerf, Christian; Niesen, Alessia; Huebner, Torsten; von der Ehe, Marvin; Meinert, Markus; Kuschel, Timo; Thomas, Andy; Heiliger, Christian; Münzenberg, Markus; Reiss, Günter

    2017-11-20

    Spin caloritronics studies the interplay between charge-, heat- and spin-currents, which are initiated by temperature gradients in magnetic nanostructures. A plethora of new phenomena has been discovered that promises, e.g., to make wasted heat in electronic devices useable or to provide new read-out mechanisms for information. However, only few materials have been studied so far with Seebeck voltages of only some microvolt, which hampers applications. Here, we demonstrate that half-metallic Heusler compounds are hot candidates for enhancing spin-dependent thermoelectric effects. This becomes evident when considering the asymmetry of the spin-split density of electronic states around the Fermi level that determines the spin-dependent thermoelectric transport in magnetic tunnel junctions. We identify Co2FeAl and Co2FeSi Heusler compounds as ideal due to their energy gaps in the minority density of states, and demonstrate devices with substantially larger Seebeck voltages and tunnel magneto-Seebeck effect ratios than the commonly used Co-Fe-B-based junctions.

  19. New Half-Metallic Materials: FeRuCrP and FeRhCrP Quaternary Heusler Compounds

    Directory of Open Access Journals (Sweden)

    Jiannan Ma

    2017-11-01

    Full Text Available The electronic structures and magnetic properties of FeRuCrP and FeRhCrP quaternary Heusler compounds with LiMgPbSb-type structures have been investigated via first-principles calculations. The calculational results show that both FeRuCrP and FeRhCrP compounds present perfect half-metallic properties: Showing large half-metallic band gaps of 0.39 eV and 0.38 eV, respectively. The total magnetic moments of FeRuCrP and FeRhCrP are 3 μB and 4 μB per formula unit, respectively. The magnetism of them mainly comes from the 3d electrons of Cr atoms and follows the Slater-Paulig behavior of Heusler compounds: Mt = Zt − 24. Furthermore, the half-metallic properties of FeRuCrP and FeRhCrP compounds can be kept in a quite large range of lattice constants (about 5.44–5.82 Å and 5.26–5.86 Å, respectively and are quite robust against tetragonal deformation (c/a ratio in the range of 0.94–1.1 and 0.97–1.1, respectively. Moreover, the large negative cohesion energy and formation energy of FeRuCrP and FeRhCrP compounds indicate that they can be synthesized experimentally.

  20. Investigating half-metallicity in PtXSb alloys (X=V, Mn, Cr, Co) at ambient and high pressure

    Energy Technology Data Exchange (ETDEWEB)

    Habbak, Enas L., E-mail: enas_habbak@yahoo.com [Department of Physics, Faculty of Science, Damietta University (Egypt); Shabara, Reham M., E-mail: rehamph@hotmail.com [Department of Physics, Faculty of Science, Damietta University (Egypt); Aly, Samy H., E-mail: samy.ha.aly@gmail.com [Department of Physics, Faculty of Science, Damietta University (Egypt); Yehia, Sherif, E-mail: sherif542002@yahoo.com [Department of Physics, Faculty of Science, Helwan University, Cairo (Egypt)

    2016-08-01

    The structural, electronic, magnetic and elastic properties of half-Heusler alloys PtMnSb, PtVSb, PtCrSb and PtCoSb are investigated using first-principles calculation based on Density Functional Theory DFT. The Full Potential local Orbital (FPLO) method, within the General Gradient Approximation (GGA) and Local Spin Density Approximation (LSDA), have been used. The calculated structural, electronic and magnetic properties are in good agreement with available experimental and theoretical data. Using GGA approximation, only PtVSb shows a half-metallic behavior with a spin-down band gap and total magnetic moment of 0.802 eV and 2 µ{sub B} respectively. Both of PtVSb and PtMnSb alloys are half-metallic with spin-down band gaps of 0.925 eV and 0.832 eV and magnetic moments of 2 µ{sub B} and 4 µ{sub B} respectively using LSDA approximation. The bulk modulus and its first pressure-derivative of these alloys are calculated using the modified Birch–Murnaghan equation of state (EOS). The effect of pressure on the lattice constant, energy gap and bulk modulus is investigated. Under pressure, PtMnSb and PtCrSb turn into half-metallic alloys at nearly 6 GPa and 27 GPa respectively using GGA approximation.

  1. First principles study on Fe based ferromagnetic quaternary Heusler alloys

    Science.gov (United States)

    Amudhavalli, A.; Rajeswarapalanichamy, R.; Iyakutti, K.

    2017-11-01

    The study of stable half-metallic ferromagnetic materials is important from various fundamental and application points of view in condensed matter Physics. Structural phase stability, electronic structure, mechanical and magnetic properties of Fe-based quaternary Heusler alloys XX‧YZ (X = Co, Ni; X‧ = Fe; Y = Ti; Z = Si, Ge, As) for three different phases namely α, β and γ phases of LiMgPdSn crystal structure have been studied by density functional theory with generalized gradient approximation formulated by Perdew, Burke and Ernzerhof (GGA-PBE) and the Hubbard formalism (GGA-PBE + U). This work aims to identify the ferromagnetic and half-metallic properties of XX‧YZ (X = Co, Ni, X‧ = Fe; Y = Ti; Z = Si, Ge, As) quaternary Heusler alloys. The predicted phase stability shows that α-phase is found to be the lowest energy phase at ambient pressure. A pressure-induced structural phase transition is observed in CoFeTiSi, CoFeTiGe, CoFeTiAs, NiFeTiSi, NiFeTiGe and NiFeTiAs at the pressures of 151.6 GPa, 33.7 GPa, 76.4 GPa, 85.3 GPa, 87.7 GPa and 96.5 GPa respectively. The electronic structure reveals that these materials are half metals at normal pressure whereas metals at high pressure. The investigation of electronic structure and magnetic properties are performed to reveal the underlying mechanism of half metallicity. The spin polarized calculations concede that these quaternary Heusler compounds may exhibit the potential candidate in spintronics application. The magnetic moments for these quaternary Heusler alloys in all the three different phases (α, β and γ) are estimated.

  2. Investigation of half-metallic ferromagnetism in Heusler compounds Co2VZ (Z = Ga, Ge, As, Se)

    Science.gov (United States)

    Han, Jiajia; Wang, Zhengwei; Xu, Weiwei; Wang, Cuiping; Liu, Xingjun

    2017-11-01

    The electronic structures and magnetic properties of 3d transition metal-based full Heusler compounds Co2VZ (Z = Ga, Ge, As, Se) are investigated using the projector augmented wave (PAW) pseudopotential method. By considering the strong localization of Co 3d-states and V 3d-states at the Fermi level, these Co2VZ (Z = Ga, Ge, As, Se) compounds were treated in the framework of the generalized gradient approximation (GGA)+U method, and the results from the conventional GGA method are presented for comparison. The results that were obtained from the density of states with the GGA+U and GGA methods show that the Co2VGa compound is a half-metallic ferromagnet. For the Co2VGe and Co2VAs compounds, the GGA+U method predicts that these two compounds are half-metallic ferromagnetic by shifting the Fermi level to a lower value with respect to the gap in the minority states, when compared to the conventional GGA method. The energy gaps are determined to be 0.283 eV and 0.425 eV, respectively. However, these results show that the density of states of the Co2VSe compound has a metallic character, although the 3d states were corrected when using the GGA+U method. We found that the characteristic of half-metallic ferromagnetism is attributed to the interaction between the V 3d-states other than Co 3d-states. The calculated total magnetic moments are 2.046 μB, 3.054 μB and 4.012 μB respectively for the Co2VZ (Z = Ga, Ge, As) compounds with the GGA+U method. The relationship between total spin magnetic moment per formula unit and total number of valence electrons of these Heusler compounds is in agreement with the Slater-Pauling rule.

  3. The electronic and magnetic properties of quaternary Heusler alloy CoFeMnGe

    Energy Technology Data Exchange (ETDEWEB)

    Seema, K. [Department of Physics, Post Graduate Government College, Sector 11, Chandigarh (India)

    2016-05-23

    We present study of quaternary Heusler alloy CoFeMnGe using density functional theory. The compound is half-metallic with half-metallic gap of 0.13 eV. The total magnetic moment of this compound is 3.96 μ{sub B} which is in close agreement with Slater-Pauling rule. The effect of lattice compression and expansion shows the robustness of half-metallicity. A large value of half-metallic gap and 100% spin-polarization makes this material interesting for spin dependent applications.

  4. Effects of Ga substitution on the structural and magnetic properties of half metallic Fe{sub 2}MnSi Heusler compound

    Energy Technology Data Exchange (ETDEWEB)

    Pedro, S. S., E-mail: sandrapedro@uerj.br; Caraballo Vivas, R. J.; Andrade, V. M.; Cruz, C.; Paixão, L. S.; Contreras, C.; Costa-Soares, T.; Rocco, D. L.; Reis, M. S. [Instituto de Física, Universidade Federal Fluminense, Niterói-RJ (Brazil); Caldeira, L. [IF Sudeste MG, Campus Juiz de Fora - Núcleo de Física, Juiz de Fora-MG (Brazil); Coelho, A. A. [Instituto de Física Gleb Wataghin, Universidade Estadual de Campinas - Unicamp, Campinas-SP (Brazil); Carvalho, A. Magnus G. [Laboratório Nacional de Luz Sincrotron, CNPEM, Campinas-SP (Brazil)

    2015-01-07

    The so-called half-metallic magnets have been proposed as good candidates for spintronic applications due to the feature of exhibiting a hundred percent spin polarization at the Fermi level. Such materials follow the Slater-Pauling rule, which relates the magnetic moment with the valence electrons in the system. In this paper, we study the bulk polycrystalline half-metallic Fe{sub 2}MnSi Heusler compound replacing Si by Ga to determine how the Ga addition changes the magnetic, the structural, and the half-metal properties of this compound. The material does not follow the Slater-Pauling rule, probably due to a minor structural disorder degree in the system, but a linear dependence on the magnetic transition temperature with the valence electron number points to the half-metallic behavior of this compound.

  5. 55Mn NMR study of quaternary half-metallic ferromagnetic Co2Mn1-xFexSi Heusler compounds

    Science.gov (United States)

    Wurmehl, S.; Alfonsov, A.; Kohlhepp, J. T.; Swagten, H. J. M.; Koopmans, B.; Wójcik, M.; Balke, B.; Ksenofontov, V.; Blum, C. G. F.; Büchner, B.

    2013-10-01

    In this work, the 55Mn spin-echo nuclear magnetic resonance technique is used to systematically analyze the complete substitutional series Co2Mn1-xFexSi in terms of the resonance frequencies of the satellite structure and the corresponding hyperfine fields of the 55Mn nuclei. The frequency spacing between satellite lines is constant within a compound, but decreases with increasing Fe concentration x, which originates in changes in the band structure. These changes are also responsible for the altered resonance frequencies observed for the same third shell environment but corresponding to a different overall Fe concentration x. All modifications in the hyperfine field upon substitution of Mn by Fe can be uniquely assigned to an entirely random distribution of Mn and Fe limited to only one (4b) out of four fcc sublattices constituting the L21 Heusler structure, demonstrating that the complete substitutional series Co2Mn1-xFexSi is crystallographically very well defined. This very high degree of order sets the stage for the observation of stable half-metallic ferromagnetism which is typically very sensitive to the structural order.

  6. Half-metallic compensated ferrimagnetism with a tunable compensation point over a wide temperature range in the Mn-Fe-V-Al Heusler system

    Directory of Open Access Journals (Sweden)

    Rolf Stinshoff

    2017-10-01

    Full Text Available The cubic Heusler compound Mn1.5FeV0.5Al with the L21 Heusler structure is the first fully compensated half-metallic ferrimagnet with 24 valence electrons. The ferrimagnetic state can be tuned by changing the composition such that the compensation point appears at finite temperatures ranging from 0 K up to 226 K, while retaining half-metallicity in the system. In this paper, the structural, magnetic and transport properties of the Mn-Fe-V-Al system are discussed. Magnetic reversal and a change of sign of the anomalous Hall effect were observed at the compensation point, which gives rise to a sublattice spin-crossing. These materials present new possibilities for potential spintronic devices because of their advantageous properties such as imperceptibility to external fields, lower power consumption and ultrafast switching in the THz region.

  7. Half-metallic compensated ferrimagnetism with a tunable compensation point over a wide temperature range in the Mn-Fe-V-Al Heusler system

    Science.gov (United States)

    Stinshoff, Rolf; Fecher, Gerhard H.; Chadov, Stanislav; Nayak, Ajaya K.; Balke, Benjamin; Ouardi, Siham; Nakamura, Tetsuya; Felser, Claudia

    2017-10-01

    The cubic Heusler compound Mn1.5FeV0.5Al with the L21 Heusler structure is the first fully compensated half-metallic ferrimagnet with 24 valence electrons. The ferrimagnetic state can be tuned by changing the composition such that the compensation point appears at finite temperatures ranging from 0 K up to 226 K, while retaining half-metallicity in the system. In this paper, the structural, magnetic and transport properties of the Mn-Fe-V-Al system are discussed. Magnetic reversal and a change of sign of the anomalous Hall effect were observed at the compensation point, which gives rise to a sublattice spin-crossing. These materials present new possibilities for potential spintronic devices because of their advantageous properties such as imperceptibility to external fields, lower power consumption and ultrafast switching in the THz region.

  8. Magnetism of quaternary Heusler alloys

    Energy Technology Data Exchange (ETDEWEB)

    Kudrnovsky, Josef; Drchal, Vaclav [Institute of Physics, AS CR, Prague (Czech Republic); Bose, Shyamal [Brock University, St. Catharines (Canada); Turek, Ilja [Institute of Physics of Materials, AS CR, Brno (Czech Republic)

    2011-07-01

    The electronic properties, exchange interactions, finite-temperature magnetism and transport properties of random Ni{sub 2}MnSn quaternary Heusler alloys doped with Cu- and Pd-atoms are studied theoretically by means of first-principles calculations over the entire concentration range. While the magnetic moments are only weakly dependent on the alloy composition, the Curie temperatures exhibit strongly non-linear behavior with respect to Cu-doping in contrast with an almost linear concentration dependence in the case of Pd-doping. The residual resistivity obey the Nordheim rule while the dominating contribution to the temperature-dependent resistivity is due to thermodynamical fluctuations originating from the spin-disorder, which, according to our calculations, can be described reasonably well via the disordered local moments model. The present parameter-free theory agrees qualitatively and also reasonably well quantitatively with all available experiments.

  9. Pressure effect of magnetic and electronic properties of Mn2PtGa Heusler alloy

    Science.gov (United States)

    Xiao, Haibo; Wang, Ruilong; Xu, Linfang; Yang, Fujun; Yang, Changping

    2018-01-01

    First-principles calculations are performed to investigate pressure effects on structure, magnetism, martensitic phase transition and Curie temperatures of Mn2PtGa Heusler alloy in framework of the density functional theory. It is shown that Mn2PtGa prefer to crystallize in the inverse Heusler type structure. Besides, we predict an extraordinary occurrence of pressure induced metallic ferrimagnetism to half-metallic ferromagnetism transition in cubic phase of Mn2PtGa alloy under hydrostatic pressure up to 43 GPa and the half-metallic ferromagnetism is found to be robust even the lattice further compression to 90 GPa. However, with the pressure up to 100 GPa, the spin-down gap starts to close and the half metallicity begin to disappear, while with the pressure increasing from 100 GPa to 300 GPa, the alloy returns to metallic characteristic. In addition, the energy difference between the austenitic and martensitic phases is found to increase with increasing pressure followed by a decrease when pressure reaches to 43 GPa, which implies a variation trend of martensitic phase transition temperature. Furthermore, Curie temperatures in both austenitic and martensitic phases are estimated under pressure by using the standard mean-field approximation which agrees well with the theoretical results in literature. The robustness of the half metallicity, magnetic transition and the high Curie temperature under pressure make Mn2PtGa alloy a promising candidate for applications in spintronic devices.

  10. First-principles study of the thermal properties of half-metallic ferromagnetic systems

    Energy Technology Data Exchange (ETDEWEB)

    Sandratskii, L.M. [Max Planck Institute of Microstructure Physics, Weinberg 2, D-06120 Halle (Germany)], E-mail: lsandr@mpi-halle.de

    2009-04-15

    The origin of the half-metallicity is different in diluted magnetic semiconductors and Heusler alloys. I briefly review our earlier work on (GaMn)As and (GaMn)N focusing on the relation between the half-metallicity and the strength of the interatomic exchange interactions. This relation is governed by the properties of the valence-band holes. In Heusler alloys the factors determining the thermal behavior are distinct. Here the relation between half-metallicity and the longitudinal fluctuations of atomic moments is considered. The temperature dependence of the Ni magnetization in NiMnSb is studied.

  11. Equiatomic quaternary Heusler alloys: A material perspective for spintronic applications

    Energy Technology Data Exchange (ETDEWEB)

    Bainsla, Lakhan, E-mail: lakhanbainsla@gmail.com, E-mail: suresh@phy.iitb.ac.in; Suresh, K. G., E-mail: lakhanbainsla@gmail.com, E-mail: suresh@phy.iitb.ac.in [Magnetic Materials Lab, Department of Physics, Indian Institute of Technology Bombay, Mumbai 400076 (India)

    2016-09-15

    Half-metallic ferromagnetic (HMF) materials show high spin polarization and are therefore interesting to researchers due to their possible applications in spintronic devices. In these materials, while one spin sub band has a finite density of states at the Fermi level, the other sub band has a gap. Because of their high Curie temperature (T{sub C}) and tunable electronic structure, HMF Heusler alloys have a special importance among the HMF materials. Full Heusler alloys with the stoichiometric composition X{sub 2}YZ (where X and Y are the transition metals and Z is a sp element) have the cubic L2{sub 1} structure with four interpenetrating fcc sublattices. When each of these four fcc sublattices is occupied by different atoms (XX′YZ), a quaternary Heusler structure with different structural symmetries (space group F-43m, #216) is obtained. Recently, these equiatomic quaternary Heusler alloys (EQHAs) with 1:1:1:1 stoichiometry have attracted a lot of attention due to their superior magnetic and transport properties. A special class of HMF materials identified recently is known as spin gapless semiconductors (SGS). The difference in this case, compared with HMFs, is that the density of states for one spin band is just zero at the Fermi level, while the other has a gap as in the case of HMFs. Some of the reported SGS materials belong to EQHAs family. This review is dedicated to almost all reported materials belonging to EQHAs family. The electronic structure and hence the physical properties of Heusler alloys strongly depend on the degree of structural order and distribution of the atoms in the crystal lattice. A variety of experimental techniques has been used to probe the structural parameters and degree of order in these alloys. Their magnetic properties have been investigated using the conventional methods, while the spin polarization has been probed by point contact Andreev reflection technique. The experimentally obtained values of saturation magnetization are

  12. Electronic, magnetic, half-metallic and mechanical properties of a new quaternary Heusler compound ZrRhTiTl: Insights from first-principles studies

    Science.gov (United States)

    Wang, Xiaotian; Zhao, Weiqi; Cheng, Zhenxiang; Dai, Xuefang; Khenata, R.

    2018-01-01

    In this paper, we have investigated the electronic, magnetic, half-metallic and mechanical properties of a new Zr-based equiatomic quaternary Heusler (EQH) compound ZrRhTiTl by means of the first-principles calculations. With the help of the generalized gradient approximation (GGA) in the scheme of Perdew-Burke-Enzerhof (PBE), we reveal that the ZrRhTiTl is an excellent half-metallic material (HMM) at its equilibrium lattice constant 6.70 Å. In the minority-spin direction, a quite large band gap (Ebg) of 0.584 eV and a half-metallic band-gap (EHM) of 0.137 eV can be observed. For ZrRhTiTl, the formation energy of -1.18 eV and the cohesive energy of 19.35 eV suggest that it is a thermo-stabilized material in theory. The formation mechanism of EHM in the minority-spin direction has also been discussed by considering of the possible d-d hybridization between Zr, Ti and Rh elements. The total magnetic moment of ZrRhTiTl is 2 μB and it satisfies the famous Slater-Pauling rule Mt = Zt-18. Two types of strain, i.e., uniform strain and tetragonal deformation, have been taken into account to examine the magneto-electronic and half-metallic behaviors of ZrRhTiTl EQH compound. Finally, we show that ZrRhTiTl is mechanically stable, ductile and anisotropic.

  13. First principles study of a new half-metallic ferrimagnets Mn{sub 2}-based full Heusler compounds: Mn{sub 2}ZrSi and Mn{sub 2}ZrGe

    Energy Technology Data Exchange (ETDEWEB)

    Abada, A. [Laboratoire d’études physico-chimiques, Université Dr Moulay Tahar, Saida 20000 (Algeria); Amara, K., E-mail: kamaraphy@gmail.com [Laboratoire d’études physico-chimiques, Université Dr Moulay Tahar, Saida 20000 (Algeria); Hiadsi, S. [Département de Génie Physique, Université d’Oran des sciences et de la technologie Mohamed Boudiaf (Algeria); Amrani, B. [Département de Physique, Université d’Oran Es-Senia, Oran 31000 (Algeria)

    2015-08-15

    Half-metallic properties of new predicted Mn{sub 2}-based full Heusler alloys Mn{sub 2}ZrSi and Mn{sub 2}ZrGe have been studied by first-principles full-potential linearized augmented plane wave plus local orbital (FP-LAPW+lo) method based on density functional theory (DFT). Our investigation is focused on the structural, elastic, electronic and magnetic properties of these compounds. The AlCu{sub 2}Mn-type structure is found to be energetically more favorable than the CuHg{sub 2}Ti-type structure for both compounds and are half-metallic ferrimagnets (HMFIs) with total magnetic moments of 2.000µ{sub B} per formula unit, well consistent with Slater–Pauling rule (M{sub tot}=(24–Z{sub tot})µ{sub B}). Calculations show that both the alloys have an indirect band gaps, in the majority-spin channel, with values of 0.505 eV and 0.278 eV for Mn{sub 2}ZrSi and Mn{sub 2}ZrGe, respectively. It was found that Mn{sub 2}ZrSi and Mn{sub 2}ZrGe preserved their half-metallicity for lattice constants range of 5.85–6.38 Å and 6.05–6.38 Å, respectively, and kept a 100% of spin polarization at the Fermi level. Moreover, the calculated formation energies and elastic constants confirm that these compounds are stable chemically and mechanically, and the good crystallographic compatibility with the lattice of semiconductors used industrially makes them promising magnetic materials in spintronic applications. - Highlights: • For Mn{sub 2}ZrZ (Z=Si, Ge) the AlCu{sub 2}Mn-type structure is more favorable than the CuHg{sub 2}Ti-type. • The calculated elastic constants confirm their mechanical stability. • Their negative estimated formation energies means they can be synthesized. • Their lattice constants match well with those of many semiconductor substrates. • They are predicted to be true half-metallic ferrimagnets. • The band gaps of Mn{sub 2}ZrSi~0.51 eV and Mn{sub 2}ZrGe~0.28 eV are indirect along, the Γ–X.

  14. The effect of magnetocrystalline anisotropy on the domain structure of patterned Fe2CrSi Heusler alloy thin films

    Science.gov (United States)

    Miyawaki, T.; Foerster, M.; Finizio, S.; Vaz, C. A. F.; Mawass, M.-A.; Inagaki, K.; Fukatani, N.; Le Guyader, L.; Nolting, F.; Ueda, K.; Asano, H.; Kläui, M.

    2013-08-01

    The effects of magnetic anisotropy on domain structures in half-metallic Heusler alloy Fe2CrSi thin film elements were investigated using high resolution x-ray magnetic circular dichroism photoemission electron microscopy. The transition of the dominating contribution from the magnetocrystalline anisotropy to the shape anisotropy is observed in square-shaped elements when reducing the size below 2.0-2.5 μm. In particular, we identify in disk-shaped Heusler elements the vortex state as the ground state. The shape-anisotropy dominated, well-defined magnetization configuration shows the potential of the Fe2CrSi Heusler alloy for applications in vortex-core- or domain-wall-devices, where the high spin polarization is desirable.

  15. High spin polarization and spin splitting in equiatomic quaternary CoFeCrAl Heusler alloy

    Energy Technology Data Exchange (ETDEWEB)

    Bainsla, Lakhan; Mallick, A.I. [Department of Physics, Indian Institute of Technology Bombay, Mumbai 400076 (India); Coelho, A.A. [Instituto de Física “Gleb Wataghin”, Universidade Estadual de Campinas-UNICAMP, SP 6165, Campinas 13 083-859, Sao Paulo (Brazil); Nigam, A.K. [DCMPMS, Tata Institute of Fundamental Research, Mumbai 4000052 (India); Varaprasad, B.S.D.Ch.S.; Takahashi, Y.K. [Magnetic Materials Unit, National Institute for Materials Science, Tsukuba 305-0047 (Japan); Alam, Aftab [Department of Physics, Indian Institute of Technology Bombay, Mumbai 400076 (India); Suresh, K.G., E-mail: suresh@phy.iitb.ac.in [Department of Physics, Indian Institute of Technology Bombay, Mumbai 400076 (India); Hono, K. [Magnetic Materials Unit, National Institute for Materials Science, Tsukuba 305-0047 (Japan)

    2015-11-15

    In this paper, we investigate CoFeCrAl alloy by means of ab-initio electronic structure calculations and various experimental techniques. The alloy is found to exist in the B2-type cubic Heusler structure, which is very similar to Y-type (or LiMgPdSn prototype) structure with space group F-43m (#216). Saturation magnetization (M{sub S}) of about 2 µ{sub B}/f.u. is observed at 8 K under ambient pressure, which is in good agreement with the Slater–Pauling rule. M{sub S} values are found to be independent of pressure, which is a prerequisite for half-metals. The ab-initio electronic structure calculations predict half-metallicity for the alloy with a spin slitting energy of 0.31 eV. Importantly, this system shows a high current spin polarization value of 0.67±0.02, as deduced from the point contact Andreev reflection measurements. Linear dependence of electrical resistivity with temperature indicates the possibility of reasonably high spin polarization at elevated temperatures (~150 K) as well. All these suggest that CoFeCrAl is a promising material for the spintronic devices. - Highlights: • The ab-initio calculations predict half-metallic nature for the alloy. • Saturation magnetization (M{sub S}) gives characteristics of half-metallic nature. • Current spin polarization (P) value of 0.67±0.02 is deduced from PCAR measurements. • Deduced P is higher than those obtained for many ternary and/or quaternary alloys. • Resistivity behavior gives signature of high P at elevated temperatures.

  16. Quantitative analysis of anisotropic magnetoresistance in Co{sub 2}MnZ and Co{sub 2}FeZ epitaxial thin films: A facile way to investigate spin-polarization in half-metallic Heusler compounds

    Energy Technology Data Exchange (ETDEWEB)

    Sakuraba, Y., E-mail: SAKURABA.Yuya@nims.go.jp; Hirayama, Y.; Furubayashi, T.; Sukegawa, H.; Li, S.; Takahashi, Y. K.; Hono, K. [National Institute for Materials Science (NIMS), Sengen 1-2-1, Tsukuba, Ibaraki 305-0047 (Japan); Kokado, S. [Graduate School of Engineering, Shizuoka University, Hamamatsu 432-8561 (Japan)

    2014-04-28

    Anisotropic magnetoresistance (AMR) effect has been systematically investigated in various Heusler compounds Co{sub 2}MnZ and Co{sub 2}FeZ (Z = Al, Si, Ge, and Ga) epitaxial films and quantitatively summarized against the total valence electron number N{sub V}. It was found that the sign of AMR ratio is negative when N{sub V} is between 28.2 and 30.3, and turns positive when N{sub V} becomes below 28.2 and above 30.3, indicating that the Fermi level (E{sub F}) overlaps with the valence or conduction band edges of half-metallic gap at N{sub V} ∼ 28.2 or 30.3, respectively. We also find out that the magnitude of negative AMR ratio gradually increases with shifting of E{sub F} away from the gap edges, and there is a clear positive correlation between the magnitude of negative AMR ratio and magnetoresistive output of the giant magnetoresistive devices using the Heusler compounds. This indicates that AMR can be used as a facile way to optimize a composition of half-metallic Heusler compounds having a high spin-polarization at room temperature.

  17. First principles calculation of elastic and magnetic properties of Cr-based full-Heusler alloys

    Science.gov (United States)

    Aly, Samy H.; Shabara, Reham M.

    2014-06-01

    We present an ab-initio study of the elastic and magnetic properties of Cr-based full-Heusler alloys within the first-principles density functional theory. The lattice constant, magnetic moment, bulk modulus and density of states are calculated using the full-potential nonorthogonal local-orbital minimum basis (FPLO) code in the Generalized Gradient Approximation (GGA) scheme. Only the two alloys Co2CrSi and Fe2CrSi are half-metallic with energy gaps of 0.88 and 0.55 eV in the spin-down channel respectively. We have predicted the metallicity state for Fe2CrSb, Ni2CrIn, Cu2CrIn, and Cu2CrSi alloys. Fe2CrSb shows a strong pressure dependent, e.g. exhibits metallicity at zero pressure and turns into a half-metal at P≥10 GPa. The total and partial magnetic moments of these alloys were studied under higher pressure, e.g. in Co2CrIn, the total magnetic moment is almost unchanged under higher pressure up to 500 GPa.

  18. Half-metallic ferromagnetism in (Z B, Al, Ga, and In) Heusler alloys ...

    Indian Academy of Sciences (India)

    K H SADEGHI

    2018-01-03

    Jan 3, 2018 ... [10] and Cr-doped CdTe [11], and zincblende (ZB) transition-metal pnictides and ..... structures for FM and NM states using LDA and GGA. a (Е): lattice parameter, B (GPa): bulk module, B : derivative of bulk module, Ec (Ry): cohesive energy, and Ef (Ry): formation energy. Compound. Structure. State VXC.

  19. Effect of atomic disorder on magnetization and half-metallic character of Cr{sub 2}CoGa alloy

    Energy Technology Data Exchange (ETDEWEB)

    Deka, Bhargab, E-mail: d.bhargab@iitg.ernet.in; Modak, Rajkumar, E-mail: r.modak@iitg.ernet.in; Paul, Pralay, E-mail: p.pralay@iitg.ernet.in; Srinivasan, A., E-mail: asrini@iitg.ernet.in

    2016-11-15

    Crystallographic, magnetic and transport properties of bulk Cr{sub 2}CoGa alloy are reported in this work. The alloy exhibits inverse Heusler (or XA) structure. Analysis of XRD pattern reveals the presence of 10% Cr(B)–Ga disorder in the alloy. Lattice constant of the alloy was found to be 5.80 Å. The alloy exhibits ferrimagnetic behavior with Curie temperature (T{sub C}) of 320 K as obtained from the thermo-magnetic measurement and temperature dependent inverse susceptibility for the alloy. The saturation magnetization M{sub s} for the alloy was found to be 0.26 μ{sub B}/f.u. at 25 K against the value of 0 μ{sub B}/f.u. predicted by Slater-Pauling rule. This deviation is attributed to the presence of Cr(B)–Ga disorder along with a small amount of Cr(B)–Co disorder in the alloy. The temperature dependent resistivity data shows a T{sup 2} dependency in low temperature region predicting that the charge carriers are not completely spin polarized at Fermi level due to the presence of sub-lattice disorder. Linear variation of resistivity above 100 K indicates the main contribution is from scattering of electrons by phonons. The effective anisotropy of the alloy was low (1.2×10{sup 4} Jm{sup −3} at 25 K) mainly due to its low M{sub s}. - Highlights: • Low magnetic moment of 0.26μ{sub B}/f.u. is reported for for Cr{sub 2}CoGa alloy. • Amount of Cr(B)–Ga disorder in Cr{sub 2}CoGa is determined by XRD analysis. • Cr(B)–Ga and Cr(B)–Co disorders result in non-zero moment of the alloy.

  20. First principles calculation of elastic and magnetic properties of Cr-based full-Heusler alloys

    Energy Technology Data Exchange (ETDEWEB)

    Aly, Samy H., E-mail: samy.ha.aly@gmail.com; Shabara, Reham M., E-mail: rehamph@hotmail.com

    2014-06-01

    We present an ab-initio study of the elastic and magnetic properties of Cr-based full-Heusler alloys within the first-principles density functional theory. The lattice constant, magnetic moment, bulk modulus and density of states are calculated using the full-potential nonorthogonal local-orbital minimum basis (FPLO) code in the Generalized Gradient Approximation (GGA) scheme. Only the two alloys Co{sub 2}CrSi and Fe{sub 2}CrSi are half-metallic with energy gaps of 0.88 and 0.55 eV in the spin-down channel respectively. We have predicted the metallicity state for Fe{sub 2}CrSb, Ni{sub 2}CrIn, Cu{sub 2}CrIn, and Cu{sub 2}CrSi alloys. Fe{sub 2}CrSb shows a strong pressure dependent, e.g. exhibits metallicity at zero pressure and turns into a half-metal at P≥10 GPa. The total and partial magnetic moments of these alloys were studied under higher pressure, e.g. in Co{sub 2}CrIn, the total magnetic moment is almost unchanged under higher pressure up to 500 GPa. - Highlights: • This study is a novel study on properties of Ni{sub 2}CrIn, Cu{sub 2}CrIn, Cu{sub 2}CrSi and Fe{sub 2}CrSb. • We have calculated the lattice constant, bulk modulus, energy gap, and DOS. • Half-metallic property is found only in both Co{sub 2}CrSi and Fe{sub 2}CrSi alloys. • Total and partial magnetic moments were studied under high pressure.

  1. Structural stability, electronic and magnetic behaviour of spin-polarized YCoVZ (Z = Si, Ge) and YCoTiZ (Z = Si, Ge) Heusler alloys

    Energy Technology Data Exchange (ETDEWEB)

    Rasool, Muhammad Nasir, E-mail: nasir4iub@gmail.com [Department of Physics, The Islamia University of Bahawalpur, Bahawalpur, 63100 (Pakistan); Hussain, Altaf, E-mail: altafiub@yahoo.com [Department of Physics, The Islamia University of Bahawalpur, Bahawalpur, 63100 (Pakistan); Javed, Athar [Department of Physics, University of the Punjab, Lahore, 54590 (Pakistan); Khan, Muhammad Azhar; Iqbal, F. [Department of Physics, The Islamia University of Bahawalpur, Bahawalpur, 63100 (Pakistan)

    2016-11-01

    The structural stability, electronic and magnetic behaviour of YCoVZ (Z = Si, Ge) and YCoTiZ (Z = Si, Ge) Heusler alloys have been studied by first principle approach. Generalized gradient approximation (GGA) based on density functional theory (DFT) has been applied to investigate the properties of quaternary Heusler alloys. The YCoVSi, YCoVGe, YCoTiSi and YCoTiGe Heusler alloys of Type-3 structure are found to be stable in spin-polarized/magnetic phase. The YCoVSi and YCoVGe alloys exhibit nearly spin gapless semiconductor (SGS) behaviour while YCoTiSi and YCoTiGe alloys show half-metallic ferromagnetic (HMF) behaviour. For YCoVSi, YCoVGe, YCoTiSi and YCoTiGe alloys, the calculated energy band gaps in spin down (↓) channel are 0.60, 0.54, 0.68 and 0.44 eV, respectively. The YCoVZ and YCoTiZ alloys are found to have integral value of total magnetic moment (M{sub T}), thus obeying the Slater-Pauling rule, M{sub T} = (N{sub v}–18)μ{sub B}. - Highlights: • Four Heusler alloys i.e. YCoVZ (Z = Si, Ge) and YCoTiZ (Z = Si, Ge) are studied. • Type-3 crystal structure of all four alloys is stable in magnetic phase. • The compressibility (S) follows the order: S{sub YCoVSi} > S{sub YCoTiSi} > S{sub YCoVGe} > S{sub YCoTiGe}. • Half metallic ferromagnetic behaviour is observed in all four alloys. • All four alloys obey the Slater-Pauling rule, M{sub T} = (N{sub v} – 18)μ{sub B}.

  2. Magnetic properties and phase stability of Co{sub 2}Cr(Ga,Si) Heusler alloys

    Energy Technology Data Exchange (ETDEWEB)

    Umetsu, R.Y., E-mail: rieume@imr.tohoku.ac.jp [Institute for Materials Research, Tohoku University, Sendai 980-8577 (Japan); Japan Science and Technology Agency-Precursory Research for Embryonic Science and Technology (JST-PREST), Saitama 332-0012 (Japan); Okubo, A.; Xu, X.; Kainuma, R. [Department of Materials Science, Graduate School of Engineering, Tohoku University, Sendai 980-8579 (Japan)

    2014-03-05

    Highlights: • Phase diagram was first established in Co{sub 2}Cr(Ga{sub 1−x}Si{sub x}) Heusler alloys. • Existence region of the single phase in the L2{sub 1}-type was confirmed in x ⩽ 0.5. • Magnetic measurements predict Co{sub 2}Cr(Ga,Si) are half-metallic ferromagnets if the order degree is completely controlled. -- Abstract: The phase diagram, magnetic properties and the region over which the Heusler alloys Co{sub 2}Cr(Ga{sub 1−x}Si{sub x}) occur as a single phase have been established. A single phase was obtained in the composition range of x ⩽ 0.5, in which the order–disorder phase transition temperature from the L2{sub 1} to the B2 phase, T{sub t}{sup L21/B2}, increased almost linearly with increasing x. The value of T{sub t}{sup L21/B2} for the L2{sub 1}-type Co{sub 2}CrSi Heusler alloy, estimated by linear extrapolation from its concentration dependence, was about 1450 K, and therefore higher than that of Co{sub 2}CrAl and Co{sub 2}CrGa. The Curie temperature, T{sub C}, also increased with increasing x becoming 600 K at x = 0.5, thus reflecting an increase in the magnetic moment caused by the change in the number of the valence electrons. The concentration dependence of the spontaneous magnetic moment, M{sub s}, measured at 5 K increased with increasing x, almost following the generalized Slater–Pauling (S.P.) rule predicted by Galanakis et al.

  3. Half-Metallic Ferromagnetism in Chalcopyrite (AlGaMnP2 Alloys

    Directory of Open Access Journals (Sweden)

    Byung-Sub Kang

    2015-01-01

    Full Text Available We studied the electronic and magnetic properties of (Al1−yMnyGaP2 (Ga-rich and Al(Ga1−yMnyP2 (Al-rich with y = 0.03125, 0.0625, 0.09375, and 0.125 by using the first-principles calculations. The ferromagnetic Mn-doped AlGaP2 chalcopyrite is the most energetically favorable one. The spin polarized Al(GaMnP2 state (Al-rich system is more stable than spin polarized (AlMnGaP2 state (Ga-rich with the magnetic moment of 3.8 μB/Mn. The Mn-doped AlGaP2 yields strong half-metallic ground states. The states of host Al, Ga, or P atoms at the Fermi level are mainly a P-3p character, which mediates a strong interaction between the Mn-3d and P-3p states.

  4. Inverted spin polarization of Heusler alloys for spintronic devices

    Science.gov (United States)

    Thomas, Andy; Meyners, Dirk; Ebke, Daniel; Liu, Ning-Ning; Sacher, Marc D.; Schmalhorst, Jan; Reiss, Günter; Ebert, Hubert; Hütten, Andreas

    2006-07-01

    A magnetic logic concept overcomes the major limitations of field programmable gate arrays while having a 50% smaller unit cell than conventional designs utilizing magnetic tunnel junctions with one Heusler alloy electrode. These show positive and negative tunneling magnetoresistance values at different bias voltages at room temperature which generally add an additional degree of freedom to all spintronic devices.

  5. Study of structural, electronic and magnetic properties of CoFeIn and Co{sub 2}FeIn Heusler alloys

    Energy Technology Data Exchange (ETDEWEB)

    El Amine Monir, M. [Laboratoire de Physique Quantique de la Matière et de la Modélisation Mathématique (LPQ3M), Faculté des Sciences, Université de Mascara, Mascara 29000 (Algeria); Khenata, R., E-mail: khenata_rabah@yahoo.fr [Laboratoire de Physique Quantique de la Matière et de la Modélisation Mathématique (LPQ3M), Faculté des Sciences, Université de Mascara, Mascara 29000 (Algeria); Baltache, H. [Laboratoire de Physique Quantique de la Matière et de la Modélisation Mathématique (LPQ3M), Faculté des Sciences, Université de Mascara, Mascara 29000 (Algeria); Murtaza, G., E-mail: murtaza@icp.edu.pk [Materials Modeling Lab, Department of Physics, Islamia College University, Peshawar (Pakistan); Abu-Jafar, M.S., E-mail: mabujafar@najah.edu [Dipartimento di Fisica Universita di Roma ' La Sapienza' , Roma (Italy); Department of Physics, An-Najah N. University, Nablus, Palestine (Country Unknown); Bouhemadou, A. [Laboratory for Developing New Materials and their Characterization, Department of Physics, Faculty of Science, University of Setif, 19000 Setif (Algeria); Bin Omran, S. [Department of Physics and Astronomy, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451 (Saudi Arabia); and others

    2015-11-15

    The structural, electronic and magnetic properties of half-Heusler CoFeIn and full-Heusler Co{sub 2}FeIn alloys have been investigated by using the state of the art full-potential linearized augmented plane wave (FP-LAPW) method. The exchange-correlation potential was treated with the generalized gradient approximation (PBE-GGA) for the calculation of the structural properties, whereas the PBE-GGA+U approximation (where U is the Hubbard Coulomb energy term) is applied for the computation of the electronic and magnetic properties in order to treat the “d” electrons. The structural properties have been calculated in the paramagnetic and ferromagnetic phases where we have found that both the CoFeIn and Co{sub 2}FeIn alloys have a stable ferromagnetic phase. The obtained results of the spin-polarized band structure and the density of states show that the CoFeIn alloy is a metal and the Co{sub 2}FeIn alloy has a complete half-metallic nature. Through the obtained values of the total spin magnetic moment, we conclude that in general, the Co{sub 2}FeIn alloy is half-metallic ferromagnet material whereas the CoFeIn alloy has a metallic nature. - Highlights: • Based on DFT calculations, CoFeIn and Co2FeIn Heusler alloys were investigated. • The magnetic phase stability was determined from the total energy calculations. • Electronic properties reveal the metallic (half-metallic) nature for CoFeIn (Co2FeIn)

  6. Largest Magnetic Moments in the Half-Heusler Alloys XCrZ (X = Li, K, Rb, Cs; Z = S, Se, Te: A First-Principles Study

    Directory of Open Access Journals (Sweden)

    Xiaotian Wang

    2017-09-01

    Full Text Available A recent theoretical work indicates that intermetallic materials LiMnZ (Z = N, P with a half-Heusler structure exhibit half-metallic (HM behaviors at their strained lattice constants, and the magnetic moments of these alloys are expected to reach as high as 5 μB per formula unit. (Damewood et al. Phys. Rev. B 2015, 91, 064409. This work inspired us to find new Heusler-based half-metals with the largest magnetic moment. With the help of the first-principles calculation, we reveal that XCrZ (X = K, Rb, Cs; Z = S, Se, Te alloys show a robust, half-metallic nature with a large magnetic moment of 5 μB at their equilibrium and strained lattice constants in their most stable phases, while the excellent HM nature of LiCrZ (Z = S, Se, Te alloys can be observed in one of their metastable phases. Moreover, the effects of uniform strain in LiCrZ (Z = S, Se, Te alloys in type II arrangement have also been discussed.

  7. The effect of defects on the electronic structure and magnetic map of the Fe2CrSi Heusler alloy: ab-initio calculations

    Science.gov (United States)

    Hamad, B. A.

    2011-03-01

    Density functional theory (DFT) calculations are performed using the full-potential linearized augmented plane wave (FP-LAPW) and generalized gradient approximation (GGA) to study the electronic and magnetic properties of perfect and defected Fe2CrSi Heusler alloy. The perfect structure was found to be a half-metallic ferromagnet with a total magnetic moment of 2 μ B and a band gap 0.6 eV. The Fermi level is found to be in the middle of this gap, which is promising for fabricating tunneling magnetoresistance (TMR) devices. Among the studied defected structures FeSi and CrSi antisite defects as well as Fe-Si and Cr-Si defects destroyed the half metallicity. However the remaining antisite, swap and vacancy defects retained the half metallicity with band gaps lower than the perfect case.

  8. Magnetic and anomalous electronic transport properties of the quaternary Heusler alloys Co{sub 2}Ti{sub 1−x}Fe{sub x}Ge

    Energy Technology Data Exchange (ETDEWEB)

    Venkateswarlu, B.; Midhunlal, P.V. [Advanced Magnetic Materials Laboratory, Department of Physics, Indian Institute of Technology Madras, Chennai 600036 (India); Babu, P.D. [UGC-DAE Consortium for Scientific Research, Mumbai Center, R-5 shed, BARC, Trombay, Mumbai 400085 (India); Kumar, N. Harish, E-mail: nhk@iitm.ac.in [Advanced Magnetic Materials Laboratory, Department of Physics, Indian Institute of Technology Madras, Chennai 600036 (India)

    2016-06-01

    The half-metallic Heusler alloy Co{sub 2}TiGe has a ferromagnetic ground state with a low magnetic moment (2 μ{sub B}). It is free of atomic antisite disorder but has low Curie temperature (~390 K). In contrast the other cobalt based Heusler alloy Co{sub 2}FeGe has high Curie temperature (~980 K) and high magnetic moment (5.6 μ{sub B}) while exhibiting antisite disorder and lack of half-metallicity. Hence it is of interest to investigate the magnetic and transport properties of solid solutions of these two materials with contrasting characteristics. We report the structural, magnetic and electronic transport properties of quaternary Co{sub 2}Ti{sub 1−x} Fe{sub x}Ge (x=0.2, 0.4, 0.6, 0.8) Heusler alloys. The alloys crystallize in L2{sub 1} structure but with antisite disorder. The magnetization measurements revealed that the alloys were of soft ferromagnetic type with high Curie temperatures. Deviation from Slater-Pauling behavior and drastic change in electronic transport properties with some anomalous features were observed.The complex electronic transport properties have been explained using different scattering mechanisms. - Highlights: • Magnetic and transport properties of quaternary Heusler alloys Co{sub 2}Ti{sub 1−x}Fe{sub x}Ge. • Soft magnetic characteristics and high Curie temperatures. • Deviation from Slater-Pauling rule observed for higher Fe concentration (x>0.2). • Anomalous transport properties explained by different scattering mechanisms.

  9. Growth and characterization of high crystalline quality Co2FeAlxSi1-x Heusler alloy films on MgAl2O4(001) substrates

    Science.gov (United States)

    Peters, Brian; Blum, Christian; Woodward, Patrick; Wurmehl, Sabine; Yang, Fengyuan

    2013-03-01

    A number of Heusler alloys have been predicted to be half-metallic and are thus ideal candidates for use in spintronics. Co2FeAlxSi1-x has been predicted and shown to have some of the highest Tc, saturation magnetization and lowest magnetic damping constant among Heusler half-metals. Here we outline the growth and characterization of the highest crystalline quality epitaxial Heusler films using a novel off-axis UHV sputtering technique. We grow these films onto a closely lattice matched MgAl2O4(001) substrate, without the need for a Cr-buffer layer or post annealing, as has been done previously. This eliminates the diffusion of Cr across the interface, thus improving the purity and crystallinity of the films at the interface. X-ray diffraction results demonstrate epitaxial films with distinct Laue oscillations and rocking curves of FWHM as low as 0.0035°, which demonstrates the highest crystalline quality for Heusler films reported to date. Magnetic measurements show highly square hysteresis loops with a remanence of 95-98%, near ideal saturation magnetization, very small coercivities - between 3-8 Oe, pronounced magnetocrystalline anisotropy. Department of Chemistry, The Ohio State University

  10. Enhancement of spin polarization via Fermi level tuning in Co{sub 2}MnSn{sub 1−x}Sb{sub x} (x = 0, 0.25. 0.5, 0.75, 1) Heusler alloys

    Energy Technology Data Exchange (ETDEWEB)

    Singh, Mukhtiyar, E-mail: msphysik09@gmail.com; Thakur, Jyoti; Kashyap, Manish K. [Department of Physics, Kurukshetra University, Kurukshetra - 136119, Haryana (India); Saini, Hardev S. [Department of Physics, National Institute of Technology, Kurukshetra - 136119, Haryana (India)

    2014-04-24

    Full potential approach has been employed to tune Fermi level in Co{sub 2}MnSn{sub 1−x}Sb{sub x} (x = 0, 0.25, 0.5, 0.75, 1) Heulser alloys for enhancement of spin polarization and finding signature of half metallicity. Present density functional theory (DFT) based calculation indicates that stoichoimetric Heusler alloy, Co{sub 2}MnSn is not a half-metallic ferromagnet but the doping of Sb in it results in the shifting of E{sup F} in well-defined energy gap which leads the 100% spin polarization in the resultant alloys. The magnetism in present alloys is governed by localized moment on Mn atom mainly. The tuning of half-metallicity using doping can be proved as an ideal technique to search the new materials which can accomplish the need of spintronics.

  11. Electronic structure and magnetic properties of quaternary Heusler alloys CoRhMnZ (Z = Al, Ga, Ge and Si) via first-principle calculations

    Energy Technology Data Exchange (ETDEWEB)

    Benkabou, M. [Laboratoire des Matériaux Magnétiques, Faculté des Sciences, Université DjillaliLiabès de Sidi Bel-Abbès, Sidi Bel-Abbès 22000 (Algeria); Rached, H. [Laboratoire des Matériaux Magnétiques, Faculté des Sciences, Université DjillaliLiabès de Sidi Bel-Abbès, Sidi Bel-Abbès 22000 (Algeria); Département de Physique, Faculté des Sciences, Université Hassiba Benbouali, Chlef 02000 (Algeria); Abdellaoui, A. [Laboratoire des Matériaux Magnétiques, Faculté des Sciences, Université DjillaliLiabès de Sidi Bel-Abbès, Sidi Bel-Abbès 22000 (Algeria); Rached, D., E-mail: rachdj@yahoo.fr [Laboratoire des Matériaux Magnétiques, Faculté des Sciences, Université DjillaliLiabès de Sidi Bel-Abbès, Sidi Bel-Abbès 22000 (Algeria); Khenata, R. [Laboratoire de Physique Quantique et de Modélisation Mathématique de la Matière, (LPQ3M), Université de Mascara, Mascara 29000 (Algeria); and others

    2015-10-25

    First-principle calculations are performed to predict the electronic structure and elastic and magnetic properties of CoRhMnZ (Z = Al, Ga, Ge and Si) Heusler alloys. The calculations employ the full-potential linearized augmented plane wave. The exchange-correlations are treated within the generalized gradient approximation of Perdew–Burke and Ernzerhof (GGA-PBE). The electronic structure calculations show that these compounds exhibit a gap in the minority states band and are clearly half-metallic ferromagnets, with the exception of the CoRhMnAl and CoRhMnGa, which are simple ferromagnets that are nearly half metallic in nature. The CoRhMnGe and CoRhMnSi compounds and their magnetic moments are in reasonable agreement with the Slater-Pauling rule, which indicates the half metallicity and high spin polarization for these compounds. At the pressure transitions, these compounds undergo a structural phase transition from the Y-type I → Y-type II phase. We have determined the elastic constants C{sub 11}, C{sub 12} and C{sub 44} and their pressure dependence, which have not previously been established experimentally or theoretically. - Highlights: • Based on DFT calculations, CoRhMnZ (Z = Al, Ga, Ge and Si) Heusler alloys were investigated. • The magnetic phase stability was determined from the total energy calculations. • The mechanical properties were investigated.

  12. Understanding demagnetization dynamics in the Heusler alloy Co{sub 2}Mn{sub 1-x}Fe{sub x}Si

    Energy Technology Data Exchange (ETDEWEB)

    Steil, Daniel; Alebrand, Sabine; Roth, Tobias; Krauss, Michael; Schneider, Hans Christian; Aeschlimann, Martin; Cinchetti, Mirko [Department of Physics, Research Center OPTIMAS, University of Kaiserslautern, 67653 Kaiserslautern (Germany); Kubota, Takahide; Oogane, Mikihiko; Ando, Yasuo [Department of Applied Physics, Graduate School of Engineering, Tohoku University, Sendai 980-8579 (Japan)

    2011-07-01

    We have investigated ultrafast demagnetization in the half-metallic Heusler alloy system Co{sub 2}Mn{sub 1-x}Fe{sub x}Si (CMFS). The two investigated compounds CMS and CFS are predicted to be half metallic, with a different lineup of the minority band gap and the Fermi level. In CMS, the Fermi energy is lined up to the top of the valence band, while in CFS to the bottom. Despite such differences, both alloys show remarkably similar magnetization dynamics, as measured by the time-resolved magneto optical Kerr effect. Based on the experimental observations and our recent dynamical model that includes momentum- and spin-dependent carrier scattering, we show that magnetization dynamics are dominated by hole spin flips below the Fermi energy, which are not influenced by the band gap.

  13. First-principles study on half-metallic ferromagnetic properties of Zn{sub 1-x}V{sub x}Se ternary alloys

    Energy Technology Data Exchange (ETDEWEB)

    Khatta, Swati; Tripathi, S.K.; Prakash, Satya [Panjab University, Central of Advanced Study in Physics, Department of Physics, Chandigarh (India)

    2017-09-15

    The spin-polarised density functional theory along with self-consistent plane-wave pseudopotential is used to investigate the half-metallic ferromagnetic properties of ternary alloys Zn{sub 1-x}V{sub x}Se. The generalized gradient approximation is used for exchange-correlation potential. The equilibrium lattice constants, bulk modulus, and its derivatives are calculated. The calculated spin-polarised energy-band structures reveal that these alloys are half-metallic for x = 0.375 and 0.50 and nearly half-metallic for other values of x. The estimated direct and indirect bandgaps may be useful for the magneto-optical absorption experiments. It is found that there is strong Zn 4s, Se 4p, and V 3d orbital hybridization in the conduction bands of both the spins, while Se 4p and V 3d orbital hybridization predominates in the valence bands of both the spins. The s, p-d, and p-d orbital hybridization reduces the local magnetic moment of V atoms and small local magnetic moments are produced on Zn and Se atoms which get coupled with V atoms in ferromagnetic and antiferromagnetic phases, respectively. The conduction and valence-band-edge splittings and exchange constants predict the ferromagnetism in these alloys. The conduction band-impurity (s and p-d) exchange interaction is more significant for ferromagnetism in these alloys than the valence band-impurity (p-d) exchange interaction. (orig.)

  14. First-principles study of new series of quaternary Heusler alloys CsSrCZ (Z=Si, Ge, Sn, P, As, and Sb)

    Energy Technology Data Exchange (ETDEWEB)

    Bouabça, A. [Condensed Matter and Sustainable Development Laboratory (LMCDD), University of Sidi Bel-Abbes, Sidi Bel-Abbes 22000 (Algeria); Rozale, H., E-mail: hrozale@yahoo.fr [Condensed Matter and Sustainable Development Laboratory (LMCDD), University of Sidi Bel-Abbes, Sidi Bel-Abbes 22000 (Algeria); Amar, A. [Condensed Matter and Sustainable Development Laboratory (LMCDD), University of Sidi Bel-Abbes, Sidi Bel-Abbes 22000 (Algeria); Wang, X.T. [School of Physics and Electronic Engineering, Chongqing Normal University, Chongqing 400044 (China); Sayade, A. [UCCS, CNRS-UMR 8181, Université d’Artois, Faculté des Sciences Jean Perrin, Rue Jean Souvraz, SP 18, 62307 Lens Cedex (France); Chahed, A. [Condensed Matter and Sustainable Development Laboratory (LMCDD), University of Sidi Bel-Abbes, Sidi Bel-Abbes 22000 (Algeria)

    2016-12-01

    The structural, electronic, magnetic, and thermal properties of new quaternary Heusler alloys CsSrCZ (Z=Si, Ge, Sn, P, As, and Sb) were investigated using the full-potential linearized augmented plane wave (FPLAPW) within the generalized gradient approximation (GGA) and GGA plus modified Becke and Johnson as the exchange correlation. The results showed that all Heusler compounds were stable in Type (I) structure. The CsSrCZ (Z=Si, Ge, Sn) compounds had a nearly HM characteristic, and CsSrCZ (Z=P, As, Sb) compounds were true half-metallic (HM) ferromagnets. The strong spin polarization of p orbital for C, Si, Ge, Sn, P, As, and Sb atoms is found to be the origin of ferromagnetic. The half-metallicity is preserved up to a lattice contraction of 3.45%, 1.69%, 1.69%, 7.16%, 7.16%, and 11.2% for all six quaternary Heusler compounds. We also investigated the thermal effects using the quasi-harmonic Debye model. - Highlights: • Electronic, magnetic, and thermodynamic properties of CsSrCZ (Z=Si, Ge, Sn, P, As, and Sb) are investigated. • Until now, there have been no reports theoretical and experimental studies on d{sup 0} half-metals with quaternary structures. • The strong spin polarization of p orbital for C, Si, Ge, Sn, P, As, and Sb atoms is found to be the origin of ferromagnetic. • The half-metallicity is preserved up to a lattice contraction.

  15. A spin-gapless semiconductor of inverse Heusler Ti2CrSi alloy: First-principles prediction

    Science.gov (United States)

    Wang, Lei; Jin, Yingjiu

    2015-07-01

    Spin-gapless semiconductors (SGSs) have been recently identified as a new class of materials that have potential applications in spintronic devices. On the basis of first-principles calculations, an inverse Heusler Ti2CrSi alloy is predicted as a promising candidate for SGS. The Ti2CrSi alloy with equilibrium lattice parameter is an antiferromagnetic semiconductor with a total magnetic moment that satisfies the Mt =Zt - 18 rule. Ti2CrSi exhibits antiferromagnetic semiconductor → SGS → half-metallicantiferromagnet → nonmagnetic semiconductor (or conventional ferrimagnet) transitions under lattice distortions. Ti2CrSi achieves an SGS feature at -2.0% and +11.4% uniform strains and at ±1.8% tetragonal distortions. SGS to half-metallic antiferromagnet transitions occur at -2.4% and +11.8% uniform strains and at ±2.2% tetragonal distortions. The half-metallic feature persists up to -5.3% and +13.5% uniform strain, as well at -9.3% and +13.2% squeezed and elongated tetragonal distortions. Ti2CrSi is a nonmagnetic semiconductor at a uniform strain of less than -5.3% and is a conventional ferrimagnet at larger than +13.5% uniform strain. Moreover, beyond -9.3% to +13.2% tetragonal distortion range, the alloy behaves as a conventional ferrimagnet. With its diverse electronic and magnetic properties, Ti2CrSi makes a promising candidate for spintronic applications.

  16. Origin of magnetic circular dichroism in soft x-ray fluorescence of Heusler alloys at threshold excitation

    Energy Technology Data Exchange (ETDEWEB)

    Yablonskikh, M. V.; Yarmoshenko, Yu. M.; Grebennikov, V. I.; Kurmaev, E. Z.; Butorin, S. M.; Duda, L.-C.; Nordgren, J.; Plogmann, S.; Neumann, M.

    2001-06-15

    The results of investigations of the Heusler alloys NiMnSb and Co{sub 2}MnSb by magnetic circular dichroism in soft x-ray emission spectroscopy (SXEMCD) are presented. The data obtained are in a good agreement with theoretical calculations of x-ray emission. A very intense resonant inelastic peak in the Mn L{sub 3} spectra in the region of states above the nominal Fermi level was observed and attributed to x-ray reemission. The interplay between the theoretically predicted half-metallic character of the Mn 3d valence band and the Mn L{sub 2},L{sub 3} SXEMCD spectra is discussed.

  17. Tuning Fermi level of Cr{sub 2}CoZ (Z=Al and Si) inverse Heusler alloys via Fe-doping for maximum spin polarization

    Energy Technology Data Exchange (ETDEWEB)

    Singh, Mukhtiyar [Department of Physics, Kurukshetra University, Kurukshetra-136119, Haryana (India); Saini, Hardev S. [Department of Physics, Panjab University, Chandigarh-160014 (India); Thakur, Jyoti [Department of Physics, Kurukshetra University, Kurukshetra-136119, Haryana (India); Reshak, Ali H. [New Technologies—Research Center, University of West Bohemia, Univerzitni 8, 306 14 Pilsen (Czech Republic); Center of Excellence Geopolymer and Green Technology, School of Material Engineering, University Malaysia Perlis, 01007 Kangar, Perlis (Malaysia); Kashyap, Manish K., E-mail: manishdft@gmail.com [Department of Physics, Kurukshetra University, Kurukshetra-136119, Haryana (India)

    2014-12-15

    We report full potential treatment of electronic and magnetic properties of Cr{sub 2−x}Fe{sub x}CoZ (Z=Al, Si) Heusler alloys where x=0.0, 0.25, 0.5, 0.75 and 1.0, based on density functional theory (DFT). Both parent alloys (Cr{sub 2}CoAl and Cr{sub 2}CoSi) are not half-metallic frromagnets. The gradual replacement of one Cr sublattice with Fe induces the half-metallicity in these systems, resulting maximum spin polarization. The half-metallicity starts to appear in Cr{sub 2−x}Fe{sub x}CoAl and Cr{sub 2−x}Fe{sub x}CoSi with x=0.50 and x=0.25, respectively, and the values of minority-spin gap and half-metallic gap or spin-flip gap increase with further increase of x. These gaps are found to be maximum for x=1.0 for both cases. An excellent agreement between the structural properties of CoFeCrAl with available experimental study is obtained. The Fermi level tuning by Fe-doping makes these alloys highly spin polarized and thus these can be used as promising candidates for spin valves and magnetic tunnelling junction applications. - Highlights: • Tuning of E{sub F} in Cr{sub 2}CoZ (Z=Al, Si) has been demonstrated via Fe doping. • Effect of Fe doping on half-metallicity and magnetism have been discussed. • The new alloys have a potential of being used as spin polarized electrodes.

  18. Accelerated discovery of new magnets in the Heusler alloy family

    Science.gov (United States)

    Sanvito, Stefano; Oses, Corey; Xue, Junkai; Tiwari, Anurag; Zic, Mario; Archer, Thomas; Tozman, Pelin; Venkatesan, Munuswamy; Coey, Michael; Curtarolo, Stefano

    2017-01-01

    Magnetic materials underpin modern technologies, ranging from data storage to energy conversion to contactless sensing. However, the development of a new high-performance magnet is a long and often unpredictable process, and only about two dozen magnets are featured in mainstream applications. We describe a systematic pathway to the design of novel magnetic materials, which demonstrates a high throughput and discovery speed. On the basis of an extensive electronic structure library of Heusler alloys containing 236,115 prototypical compounds, we filtered those displaying magnetic order and established whether they can be fabricated at thermodynamic equilibrium. Specifically, we carried out a full stability analysis of intermetallic Heusler alloys made only of transition metals. Among the possible 36,540 prototypes, 248 were thermodynamically stable but only 20 were magnetic. The magnetic ordering temperature, TC, was estimated by a regression calibrated on the experimental TC of about 60 known compounds. As a final validation, we attempted the synthesis of a few of the predicted compounds and produced two new magnets: Co2MnTi, which displays a remarkably high TC in perfect agreement with the predictions, and Mn2PtPd, which is an antiferromagnet. Our work paves the way for large-scale design of novel magnetic materials at potentially high speed. PMID:28439545

  19. Structural and magnetic properties of antiferromagnetic Heusler Ru2MnGe Epitaxial thin films

    Science.gov (United States)

    Fukatani, Naoto; Fujita, Hirohito; Miyawaki, Tetsuya; Ueda, Kenji; Asano, Hidefumi

    2013-08-01

    Structural and magnetic properties were investigated for Heusler-type alloy Ru2MnGe thin films. Ru2MnGe films on MgO substrate were subjected to an in-plane compressive strain, and exhibited enhanced antiferromagnetic (AFM) transition temperature ( T N ) up to 353 K, which exceeds by 37 K from the cubic bulk material ( T N = 316 K). We also observed the exchange coupling between Ru2MnGe and Heusler-type ferromagnetic (FM) half-metal Fe2CrSi thin films. The present AFM Heusler alloy with relatively high T N is useful to fabricate high-quality all Heusler-type half-metal AFM/FM junctions and is a promising material for the emerging field of AFM spintronics.

  20. DFT investigations on mechanical stability, electronic structure and magnetism in Co2TaZ (Z = Al, Ga, In) heusler alloys

    Science.gov (United States)

    Khandy, Shakeel Ahmad; Gupta, Dinesh C.

    2017-12-01

    Ferromagnetic Heusler compounds have vast and imminent applications for novel devices, smart materials thanks to density functional theory (DFT) based simulations, which have scored out a new approach to study these materials. We forecast the structural stability of Co2TaZ alloys on the basis of total energy calculations and mechanical stability criteria. The elastic constants, robust spin-polarized ferromagnetism and electron densities in these half-metallic alloys are also discussed. The observed structural aspects calculated to predict the stability and equilibrium lattice parameters agree well with the experimental results. The elastic parameters like elastic constants, bulk, Young’s and shear moduli, poison’s and Pugh ratios, melting temperatures, etc have been put together to establish their mechanical properties. The elaborated electronic band structures along with indirect band gaps and spin polarization favour the application of these materials in spintronics and memory device technology.

  1. Atomic disorder in Heusler alloy Cr{sub 2}CoGa

    Energy Technology Data Exchange (ETDEWEB)

    Luo, Hongzhi, E-mail: luo_hongzhi@163.com [School of Material Science and Engineering, Hebei University of Technology, Tianjin 300130 (China); Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Yang, Ling; Liu, Bohua; Meng, Fanbin [School of Material Science and Engineering, Hebei University of Technology, Tianjin 300130 (China); Liu, Enke [Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China)

    2015-11-01

    Heusler alloy Cr{sub 2}CoGa with 24 valence electrons is a promising candidate for half-metallic completely compensated ferrimagnets. Its electronic structure and atomic disorder have been investigated by using a KKR–CPA method. The equilibrium lattice constant is 5.88 Å and the total moment is as small as 0.09 μ{sub B}. This near zero moment is mainly determined by the antiparallel aligned Cr (A) and Cr (B) spin moments, which are −2.16 μ{sub B} and 2.17 μ{sub B}, respectively and compensate each other. The calculated spin polarization ratio is as high as 95%. Three kinds of atomic disorder have been considered in Cr{sub 2}CoGa: Cr (B)-Co, Cr (A)-Co and Cr (B)-Ga. Among them, Cr (A)-Co and especially Cr (B)-Co disorder raise the total energy obviously. While Cr (B)-Ga disorder decreases the total energy by ~0.14 eV. So Cr (B)-Ga disorder is more energetically favored in the sample. The influence of Cr (B)-Ga disorder on the magnetic moment and electronic structure is small. The total moment only increases slightly to 0.16 μ{sub B}. The influence of Cr (A)-Co disorder on the magnetic properties is also not obvious. Whereas Cr (B)-Co disorder increases the total moment obviously, which is mainly related to the ferromagnetic coupling between the Cr spin moments at A, C sites.

  2. Electronic structure and magnetic properties of Fe{sub 2}YSi (Y = Cr, Mn, Fe, Co, Ni) Heusler alloys: a theoretical and experimental study

    Energy Technology Data Exchange (ETDEWEB)

    Luo Hongzhi [Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100080 (China); Zhu Zhiyong [Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100080 (China); Ma Li [Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100080 (China); Xu Shifeng [Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100080 (China); Liu Heyan [School of Material Science and Engineering, Hebei University of Technology, Tianjin 300130 (China); Qu Jingping [School of Material Science and Engineering, Hebei University of Technology, Tianjin 300130 (China); Li Yangxian [School of Material Science and Engineering, Hebei University of Technology, Tianjin 300130 (China); Wu Guangheng [Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100080 (China)

    2007-11-21

    A series of Fe{sub 2}YSi (Y = Cr, Mn, Fe, Co, Ni) alloys were synthesized and their electronic and magnetic properties were studied both theoretically and experimentally. In particular, a novel Heusler alloy Fe{sub 2}CrSi single phase was synthesized by means of the melt-spinning method. First principles FLAPW calculations were performed on Fe{sub 2}YSi alloys. Based on the results, Fe{sub 2}CrSi is predicted to be a half-metallic ferromagnet with a spin moment of 2{mu}{sub B}/f.u. and a gap of 0.42 eV. Fe{sub 2}MnSi is also half-metallic in the ferromagnetic state. The saturation magnetic moments at 5 K for this series of alloys fit the theoretical calculations well. Specifically, the saturation magnetic moment of Fe{sub 2}CrSi is 2.05{mu}{sub B}/cell, which agrees with the ideal value of 2{mu}{sub B} derived from the Slater-Pauling rule. The Curie temperatures of Fe{sub 2}YSi alloys are all higher than 500 K except for Fe{sub 2}MnSi, which has a T{sub C} below room temperature. Finally, the effect of lattice distortion on the electronic and magnetic properties of Fe{sub 2}CrSi and Fe{sub 2}CoSi was studied. It is found that Fe{sub 2}CrSi is half-metallic from -3% to +1% uniform lattice distortion, and this character is preferred in systems containing large strain, such as melt-spun ribbons or thin films.

  3. Magnetism and electronic structure of CoFeCrX (X = Si, Ge) Heusler alloys

    Energy Technology Data Exchange (ETDEWEB)

    Jin, Y.; O' Connell, A. [Department of Physics and Astronomy, University of Nebraska, Lincoln, Nebraska 68588 (United States); Kharel, P., E-mail: parashu.kharel@sdstate.edu [Department of Physics, South Dakota State University, Brookings, South Dakota 57007 (United States); Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln, Nebraska 68588 (United States); Lukashev, P., E-mail: pavel.lukashev@uni.edu; Staten, B.; Tutic, I. [Department of Physics, University of Northern Iowa, Cedar Falls, Iowa 50614 (United States); Valloppilly, S. [Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln, Nebraska 68588 (United States); Herran, J. [Department of Chemistry and Biochemistry, University of Northern Iowa, Cedar Falls, Iowa 50614 (United States); Mitrakumar, M.; Bhusal, B.; Huh, Y. [Department of Physics, South Dakota State University, Brookings, South Dakota 57007 (United States); Yang, K. [Department of Physics, South Dakota State University, Brookings, South Dakota 57007 (United States); College of Mechanical and Electrical Engineering, Hohai University, Changzhou (China); Skomski, R.; Sellmyer, D. J. [Department of Physics and Astronomy, University of Nebraska, Lincoln, Nebraska 68588 (United States); Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln, Nebraska 68588 (United States)

    2016-08-07

    The structural, electronic, and magnetic properties of CoFeCrX (X = Si, Ge) Heusler alloys have been investigated. Experimentally, the alloys were synthesized in the cubic L2{sub 1} structure with small disorder. The cubic phase of CoFeCrSi was found to be highly stable against heat treatment, but CoFeCrGe disintegrated into other new compounds when the temperature reached 402 °C (675 K). Although the first-principle calculation predicted the possibility of tetragonal phase in CoFeCrGe, the tetragonal phase could not be stabilized experimentally. Both CoFeCrSi and CoFeCrGe compounds showed ferrimagnetic spin order at room temperature and have Curie temperatures (T{sub C}) significantly above room temperature. The measured T{sub C} for CoFeCrSi is 790 K but that of CoFeCrGe could not be measured due to its dissociation into new compounds at 675 K. The saturation magnetizations of CoFeCrSi and CoFeCrGe are 2.82 μ{sub B}/f.u. and 2.78 μ{sub B}/f.u., respectively, which are close to the theoretically predicted value of 3 μ{sub B}/f.u. for their half-metallic phases. The calculated band gaps for CoFeCrSi and CoFeCrGe are, respectively, 1 eV and 0.5 eV. These materials have potential for spintronic device applications, as they exhibit half-metallic electronic structures with large band gaps, and Curie temperatures significantly above room temperature.

  4. A first principle study of phase stability, electronic structure and magnetic properties for Co{sub 2−x}Cr{sub x}MnAl Heusler alloys

    Energy Technology Data Exchange (ETDEWEB)

    Rached, H. [Laboratoire des Matériaux Magnétiques, Faculté des Sciences exactes, Université Djillali Liabès de Sidi Bel-Abbès, Sidi Bel-Abbès 22000 (Algeria); Rached, D., E-mail: rachdj@yahoo.fr [Laboratoire des Matériaux Magnétiques, Faculté des Sciences exactes, Université Djillali Liabès de Sidi Bel-Abbès, Sidi Bel-Abbès 22000 (Algeria); Khenata, R. [Laboratoire de Physique Quantique et de Modélisation Mathématique de la Matière, (LPQ3M), Université de Mascara, Mascara 29000 (Algeria); Abidri, B.; Rabah, M.; Benkhettou, N. [Laboratoire des Matériaux Magnétiques, Faculté des Sciences exactes, Université Djillali Liabès de Sidi Bel-Abbès, Sidi Bel-Abbès 22000 (Algeria); Omran, S. Bin [Department of Physics and Astronomy, College of Science, King Saud University, P.O.Box 2455, Riyadh 11451 (Saudi Arabia)

    2015-04-01

    The structural stabilities, electronic and magnetic properties of Co{sub 2−x}Cr{sub x}MnAl alloys with (x=0,1 and 2) were investigated using the full-potential linear muffin-tin orbital (FP-LMTO) method, in the framework of the density functional theory (DFT) within the generalized gradient approximation (GGA) for the exchange correlation functional. The ground state properties including lattice parameter, bulk modulus for the two considered crystal structures Hg{sub 2}CuTi-Type (X-Type) and Cu{sub 2}MnAl-Type (L2{sub 1}-Type) are calculated. The half-metallicity within ferromagnetic ground state starts to appear in CoCrMnAl and Cr2MnAl. In the objective for the proposition of the new HM-FM in the Full-Heusler alloys, our results classified CoCrMnAl as new HM-FM material with high spin polarization. - Highlights: • Based on DFT calculations, Co2-xCrxMnAl Heusler alloys have been investigated. • The magnetic phase stability was determined from the total energy calculations. • The LMTO calculations have classified CoCrMnAl as new HM-FM material with high spin polarization.

  5. Time-Reversal-Breaking Weyl Fermions in Magnetic Heusler Alloys

    Science.gov (United States)

    Wang, Zhijun; Vergniory, M. G.; Kushwaha, S.; Hirschberger, Max; Chulkov, E. V.; Ernst, A.; Ong, N. P.; Cava, Robert J.; Bernevig, B. Andrei

    2016-12-01

    Weyl fermions have recently been observed in several time-reversal-invariant semimetals and photonics materials with broken inversion symmetry. These systems are expected to have exotic transport properties such as the chiral anomaly. However, most discovered Weyl materials possess a substantial number of Weyl nodes close to the Fermi level that give rise to complicated transport properties. Here we predict, for the first time, a new family of Weyl systems defined by broken time-reversal symmetry, namely, Co-based magnetic Heusler materials X Co2Z (X =IVB or VB; Z =IVA or IIIA). To search for Weyl fermions in the centrosymmetric magnetic systems, we recall an easy and practical inversion invariant, which has been calculated to be -1 , guaranteeing the existence of an odd number of pairs of Weyl fermions. These materials exhibit, when alloyed, only two Weyl nodes at the Fermi level—the minimum number possible in a condensed matter system. The Weyl nodes are protected by the rotational symmetry along the magnetic axis and separated by a large distance (of order 2 π ) in the Brillouin zone. The corresponding Fermi arcs have been calculated as well. This discovery provides a realistic and promising platform for manipulating and studying the magnetic Weyl physics in experiments.

  6. Magnetic Properties of MnFe2Ga Heusler Alloys

    Science.gov (United States)

    Elgendy, Ahmed A.; Salehi-Fashami, Mohammad; Sellmyer, David; Hadjipanayis, George

    2015-03-01

    Recently, MnFe2Ga Heusler alloys have attracted significant attention due to their interesting physical properties such as large magnetic-field-induced strain, giant magnetocaloric effects,large magnetoresistance, and exchange bias behavior. These properties make them promising candidates for various practical applications in the field of smart materials, magnetic refrigeration and spintronics. In this work, we prepared MnFe2Ga alloys by melt-spinning and sputtering and studied the structural and magnetic properties. The melt-spun ribbons were prepared with a wheel speed of 30 m/s. The ribbons were annealed at different temperatures for 1 hour and grinded to make fine powders. The grinded powders were also used to make the target that is used in the cluster gun for the fabrication of MnFe2Ga nanoparticles. The structure of the as made, annealed ribbons, and powders displayed a face-centered-cubic structure. The microstructure of the as-made ribbons showed equiaxed grains with an average size of 3-5 μm while the annealed ribbons showed bigger grains with small particles covering homogeneously their surface. The magnetic properties show an enhancement of magnetization while coercivity remains the same with values M(3T) and HC of 85 emu/g and 150 Oe, respectively Transmission electron microscopy with elemental mapping is currently underway to determine the structure and composition of the surface nanoparticles. The work was supported by DOE-BES-DMSE (Grant No. DE-FG02-04ER4612).

  7. Measurements of spin polarization of Ru{sub 2-x}Fe{sub x}CrSi Heusler alloys by Andreev reflection

    Energy Technology Data Exchange (ETDEWEB)

    Shigeta, Iduru, E-mail: shigeta@sci.kagoshima-u.ac.j [Department of Physics and Astronomy, Kagoshima University, Kagoshima 890-0065 (Japan); Murayama, Osamu; Hisamatsu, Toru; Ito, Masakazu; Hiroi, Masahiko [Department of Physics and Astronomy, Kagoshima University, Kagoshima 890-0065 (Japan)

    2010-12-15

    We report spin polarization P of Ru{sub 2-x}Fe{sub x}CrSi Heusler alloys by Andreev reflection technique. Ru{sub 2-x}Fe{sub x}CrSi with the L2{sub 1}-type structure is theoretically predicted to be half-metals in the wide range of the composition x. The experimental results of saturation moment in Fe-rich compounds measurements also support the theoretical prediction. We have measured the differential conductance of Ru{sub 2-x}Fe{sub x}CrSi/Pb planar-type junctions. The P value of Ru{sub 2-x}Fe{sub x}CrSi was determined by fitting the differential conductance with the modified Blonder-Tinkham-Klapwijk theory. The behavior of P was independent of the composition x in the Fe-rich region; P=0.53 for x=1.5 and P=0.52 for x=1.7, respectively. We have found that the spin polarization of Ru{sub 2-x}Fe{sub x}CrSi in Fe-rich compounds was the similar values to Co-based Heusler alloys.

  8. The electronic structure and spin polarization of Co{sub 2}Mn{sub 0.75}(Gd, Eu){sub 0.25}Z (Z=Si, Ge, Ga, Al) quaternary Heusler alloys

    Energy Technology Data Exchange (ETDEWEB)

    Berri, Saadi, E-mail: berrisaadi12@yahoo.fr

    2016-03-01

    A first-principles approach is used to study the electronic and magnetic properties of Co{sub 2}Mn{sub 0.75}(Gd, Eu){sub 0.25}Z(Z=Si, Ge, Ga, Al) quaternary Heusler alloys. The investigation was done using the (FP-LAPW) method where the exchange-correlation potential was calculated with the frame of GGA-WC. At ambient conditions our calculated results of band structures reveal that for Co{sub 2}Mn{sub 0.75}(Gd, Eu){sub 0.25}Z(Z=Si, Ge) has a half-metallic (HM) band structure profile showing 100% spin polarization at the Fermi level. In contrast, Co{sub 2}Mn{sub 0.75}(Gd, Eu){sub 0.25}Z(Z=Ga, Al) alloys are found to be metallic. Finally, the half metallic compounds found in some structures of this series might be useful in spintronic devices. - Highlights: • The full potential linear augmented plane wave based on the density-functional theory is employed. • Some physical properties of Co{sub 2}Mn{sub 0.75}(Gd, Eu){sub 0.25}Z have been investigated. • Co{sub 2}Mn{sub 0.75}(Gd, Eu){sub 0.25}Z (Si,Ge) quaternary Heusler alloys are a HMF. • Exchange splitting of 3D-TMs and 4 f-Re electrons.

  9. PREFACE: Half Metallic Ferromagnets

    Science.gov (United States)

    Dowben, Peter

    2007-08-01

    Since its introduction by de Groot and colleagues in the early 1980s [1], the concept of half metallic ferromagnetism has attracted great interest. Idealized, half-metals have only one spin channel for conduction: the spin-polarized band structure exhibits metallic behavior for one spin channel, while the other spin band structure exhibits a gap at the Fermi level. Due to the gap for one spin direction, the density of states at the Fermi level has, theoretically, 100 & spin polarization. This gap in the density of states in one spin at the Fermi level, for example ↓ so N↓ (EF) = 0, also causes the resistance of that channel to go to infinity. At zero or low temperatures, the nonquasiparticle density of states (electron correlation effects), magnons and spin disorder reduce the polarization from the idealized 100 & polarization. At higher temperatures magnon-phonon coupling and irreversible compositional changes affect polarization further. Strategies for assessing and reducing the effects of finite temperatures on the polarization are now gaining attention. The controversies surrounding the polarization stability of half metallic ferromagnets are not, however, limited to the consideration of finite temperature effects alone. While many novel half metallic materials have been predicted, materials fabrication can be challenging. Defects, surface and interface segregation, and structural stability can lead to profound decreases in polarization, but can also suppress long period magnons. There is a 'delicate balance of energies required to obtain half metallic behaviour: to avoid spin flip scattering, tiny adjustments in atomic positions might occur so that a gap opens up in the other spin channel' [2]. When considering 'spintronics' devices, a common alibi for the study of half metallic systems, surfaces and interfaces become important. Free enthalpy differences between the surface and the bulk will lead to spin minority surface and interface states, as well as

  10. Preparation of Co2FeSn Heusler alloys by electrodeposition method

    Directory of Open Access Journals (Sweden)

    Nobuaki Watanabe

    2015-04-01

    Full Text Available We propose a new method for preparing Heusler alloys on the basis of the electrodeposition. The alloy composition is controllable by the deposition potential. The composition ratio of (Co, Fe and Sn is inversely proportional to the deposition potential. The effect of deposition potential on alloy composition, surface morphology, crystal structure, and magnetic properties of the samples was investigated. The (Co, Fe vs. Sn alloy composition displayed an inverse dependence on the deposition potential. According to the magnetic measurement, the obtained Co2FeSn composition alloy showed ferromagnetic properties. The coercivity shows the minimum value in the stoichiometric samples.

  11. Native defects in the Co2Ti Z (Z =Si ,Ge,Sn) full Heusler alloys: Formation and influence on the thermoelectric properties

    Science.gov (United States)

    Popescu, Voicu; Kratzer, Peter; Wimmer, Sebastian; Ebert, Hubert

    2017-08-01

    We have performed first-principles investigations on the native defects in the half-metallic, ferromagnetic full Heusler alloys Co2Ti Z (Z one of the group IV elements Si, Ge, Sn), determining their formation energies and how they influence the transport properties. We find that the Co vacancies (VcCo) and the TiSn as well as the CoZ or CoTi antisites exhibit the smallest formation energies. The most abundant native defects were modeled as dilute alloys, treated with the coherent potential approximation in combination with the multiple-scattering theory Green function approach. The self-consistent potentials determined this way were used to calculate the residual resistivity via the Kubo-Greenwood formula and, based on its energy dependence, the Seebeck coefficient of the systems. The latter is shown to depend significantly on the type of defect, leading to variations that are related to subtle, spin-orbit coupling induced changes in the electronic structure above the half-metallic gap. Two of the systems, VcCo and CoZ, are found to exhibit a negative Seebeck coefficient. This observation, together with their low formation energy, offers an explanation for the experimentally observed negative Seebeck coefficient of the Co2Ti Z compounds as being due to unintentionally created native defects.

  12. Magnetic transformation of Ni{sub 2}AlMn Heusler-type shape memory alloys

    Energy Technology Data Exchange (ETDEWEB)

    Gejima, F.; Sutou, Y.; Kainuma, R.; Ishida, K.

    1999-10-01

    It has recently been reported that the movement of twin (or variant) boundaries, induced by a magnetic field during the martensitic transformation, affects the magnetic properties and shape change in the ferromagnetic NiGaMn shape memory (SM) alloys. These observations suggest that the NiGaMn SM alloys with an L2{sub 1} (Ni{sub 2}GaMn: Heusler) structure have the potential for use as a new type of smart materials whose SM properties can be controlled not only by temperature and stress, but also by a magnetic field. Very recently, the present authors have detected that in the alloys with compositions near the stoichiometric Ni{sub 2}AlMn, the ferromagnetic L2{sub 1} phase appears on low-temperature aging and it transforms martensitically from B2 to 2M. This suggests that the NiAlMn Heusler alloys could also exhibit unique magnetic and SM properties similar to those of the NiGaMn alloys. It is the purpose of this article to report the results of investigations on the magnetic properties of the NiAlMn Heusler alloys.

  13. Ab-Initio Investigations of Magnetic Properties and Induced Half-Metallicity in Ga1−xMnxP (x = 0.03, 0.25, 0.5, and 0.75 Alloys

    Directory of Open Access Journals (Sweden)

    Amel Laref

    2017-07-01

    Full Text Available Ab-initio calculations are performed to examine the electronic structures and magnetic properties of spin-polarized Ga1−xMnxP (x = 0.03, 0.25, 0.5, and 0.75 ternary alloys. In order to perceive viable half-metallic (HM states and unprecedented diluted magnetic semiconductors (DMSs such as spintronic materials, the full potential linearized augmented plane wave method is utilized within the generalized gradient approximation (GGA. In order to tackle the correlation effects on 3d states of Mn atoms, we also employ the Hubbard U (GGA + U technique to compute the magnetic properties of an Mn-doped GaP compound. We discuss the emerged global magnetic moments and the robustness of half-metallicity by varying the Mn composition in the GaP compound. Using GGA + U, the results of the density of states demonstrate that the incorporation of Mn develops a half-metallic state in the GaP compound with an engendered band gap at the Fermi level (EF in the spin–down state. Accordingly, the half-metallic feature is produced through the hybridization of Mn-d and P-p orbitals. However, the half-metallic character is present at a low x composition with the GGA procedure. The produced magnetic state occurs in these materials, which is a consequence of the exchange interactions between the Mn-element and the host GaP system. For the considered alloys, we estimated the X-ray absorption spectra at the K edge of Mn. A thorough clarification of the pre-edge peaks is provided via the results of the theoretical absorption spectra. It is inferred that the valence state of Mn in Ga1−xMnxP alloys is +3. The predicted theoretical determinations surmise that the Mn-incorporated GaP semiconductor could inevitably be employed in spintronic devices.

  14. Compositional trends in Ni-Mn-Ga Heusler alloys: first-principles approach

    Directory of Open Access Journals (Sweden)

    Sokolovskiy Vladimir

    2015-01-01

    Full Text Available In this work we present a systematic investigation of magnetic and structural properties of a broad range of Ni-Mn-Ga alloys by means of the density functional theory. Calculations are carried out for the cubic austenitic phase. The effect of chemical disorder is simulated by using the single-site coherent-potential approximation and the spin-polarized generalized gradient approximation. Equilibrium lattice parameters, bulk moduli, total magnetic moments, and formation energies of a wide range of Heusler alloys have been mapped on compositional ternary diagrams that give a bigger picture of the variety of physical properties of this family of alloys.

  15. Effect of electron-electron correlation and site disorder on the magnetic moment and half-metallicity of Co{sub 2}FeGa{sub 1−x}Si{sub x} alloys

    Energy Technology Data Exchange (ETDEWEB)

    Deka, Bhargab, E-mail: d.bhargab@iitg.ernet.in; Kundu, Ashis, E-mail: k.ashis@iitg.ernet.in; Ghosh, Subhradip, E-mail: subhra@iitg.ernet.in; Srinivasan, A., E-mail: asrini@iitg.ernet.in

    2016-07-01

    X-ray diffraction studies on Co{sub 2}Fe(Ga{sub 1−x}Si{sub x}) alloys did not show the characteristic L2{sub 1} super-lattice peaks for alloys with x ≤ 0.5. The saturation magnetization (M{sub s}) of alloy compositions with x = 0.75 and x = 1.00 deviated from the values predicted by Slater-Pauling (S-P) rule. In order to understand this deviation in M{sub s} and its implication on the half-metallic character of these alloys, a systematic ab initio study was carried out using generalized gradient approximation (GGA) and GGA with on-site Coulomb interaction (GGA + U). Total magnetic moment obtained from the GGA calculation agrees well with S-P rule and experimental results obtained for alloys with high Ga concentration (i.e. for x = 0 and 0.25) and gets overestimated by the inclusion of U. However, the value predicted by the S-P rule is obtained for the alloys with x = 0.50, 0.75 and 1.00, only after the inclusion of U. Similar behavior was observed in the appearance of the energy gap in density of states of the spin-down band and hence the half-metallic nature of the alloys. The deviation in measured M{sub s} of the alloy with x = 1.00 is attributed to the presence of small amount of DO{sub 3} disorder in the alloy as revealed by the ab initio studies. Comparison of experimental and theoretically estimated properties of Co{sub 2}Fe(Ga{sub 1−x}Si{sub x}) alloys provides insight to the variation in electron-electron interaction and the influence on atomic site disorder in these alloys on their half-metallic character. - Highlights: • M{sub t} of Co{sub 2}FeGa{sub 1−x}Si{sub x} was determined by experimental and ab initio studies. • Need for GGA + U to estimate M{sub t} of x > 0.25, shows change in magnetic interaction. • Rhodes-Wohlfarth ratio and DoS show that half-metallicity is possible in all alloys.

  16. Observation of enhanced exchange bias behaviour in NiCoMnSb Heusler alloys

    Energy Technology Data Exchange (ETDEWEB)

    Nayak, Ajaya K; Suresh, K G [Magnetic Materials Laboratory, Department of Physics, Indian Institute of Technology Bombay, Mumbai-400076 (India); Nigam, A K [Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai-400005 (India)], E-mail: suresh@phy.iitb.ac.in

    2009-06-07

    We report the observation of large exchange bias (EB) in Ni{sub 50-x}Co{sub x}Mn{sub 38}Sb{sub 12} Heusler alloys with x = 0, 2, 3, 4, 5, which is attributed to the coexistence of ferromagnetic (FM) and antiferromagnetic (AFM) phases in the martensitic phase. The phase coexistence is possibly due to the supercooling of the high temperature FM phase and the predominant AFM component in the martensitic phase. The presence of EB is well supported by the observation of the training effect. The EB field increases with Co concentration. The maximum value of 480 Oe at T = 3 K is observed in x = 5 after field cooling in 50 kOe, which is almost double the highest value reported so far in any Heusler alloy system. Increase in the AFM coupling after Co substitution is found to be responsible for the increase in the EB.

  17. Magnetic transformation in Ni-Mn-In Heusler alloy

    Directory of Open Access Journals (Sweden)

    Kuzma Marian

    2015-07-01

    Full Text Available Magnetic properties of a Ni50Mn35.5In14.5 Heusler ribbon were studied by ferromagnetic resonance (FMR in the temperature range of 335–100 K. In the temperature region of 265–170 K, the FMR signal disappeared, in spite of the fact that this region comprised the main crystal transformation temperatures: Ms, Mf, As, Af. In the austenite crystal state, a weak antiferromagnetic interaction was observed, whereas ferromagnetism was detected in the low temperature martensitic state.

  18. On the Challenges of Reducing Contact Resistances in Thermoelectric Generators Based on Half-Heusler Alloys

    DEFF Research Database (Denmark)

    Pham, Hoang Ngan; Van Nong, Ngo; Le, Thanh Hung

    2016-01-01

    A method using fast hot pressing to join half-Heusler (HH) thermoelectric materials directly to an electrical current collector (Ag electrode) without using a third filler material is introduced. The compositions of the HH alloys used are Hf0.5Zr0.5CoSn0.2Sb0.8 and Ti0.6Hf0.4NiSn for p- and n-typ...... and better performance compared with the method of using active brazing filler alloy....

  19. A first-principle investigation of spin-gapless semiconductivity, half-metallicity, and fully-compensated ferrimagnetism property in Mn{sub 2}ZnMg inverse Heusler compound

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Xiaotian [School of Material Sciences and Engineering, Hebei University of Technology, Tianjin 300130 (China); Institute for Superconducting & Electronic Materials (ISEM), University of Wollongong, Wollongong 2500 (Australia); Cheng, Zhenxiang, E-mail: cheng@uow.edu.au [Institute for Superconducting & Electronic Materials (ISEM), University of Wollongong, Wollongong 2500 (Australia); Khenata, Rabah [Laboratoire de Physique Quantique, de la Matière et de la Modélisation Mathématique (LPQ3M), Université de Mascara, Mascara 29000 (Algeria); Rozale, Habib [Condensed Matter and Sustainable Development Laboratory, Physics Department, University of Sidi-Bel-Abbès, 22000 Sidi-Bel-Abbès (Algeria); Wang, Jianli [Institute for Superconducting & Electronic Materials (ISEM), University of Wollongong, Wollongong 2500 (Australia); Wang, Liying; Guo, Ruikang [School of Material Sciences and Engineering, Hebei University of Technology, Tianjin 300130 (China); Liu, Guodong, E-mail: gdliu1978@126.com [School of Material Sciences and Engineering, Hebei University of Technology, Tianjin 300130 (China)

    2017-02-01

    Recently, spin-gapless semiconductors (SGSs) and half-metallic materials (HMMs) have received considerable interest in the fields of materials sciences and solid-state physics because they can provide a high degree of spin polarization in electron transport. The results on band structure calculations reveal that the metallic fully-compensated ferrimagnet (M-FCF) Mn{sub 2}ZnMg becomes half-metallic fully-compensated ferrimagnet (HM-FCF), fully-compensated ferrimagnetic semiconductor (FCF-S) and fully-compensated ferrimagnetic spin-gapless semiconductor (FCF-SGS) if the uniform strain applied. However, the metallic fully-compensated ferrimagnetism property of the Mn{sub 2}ZnMg is robust to the tetragonalization. The structure stability based on the calculations of the cohesion energy and the formation energy of this compound has been tested. Furthermore, a magnetic state transition from antiferromagentic (AFM) state to non-magnetic (NM) state can be observed at the lattice constant of 5.20 Å. - Highlights: • Mn{sub 2}ZnMg is a M-FCF at its equilibrium lattice constant. • We study the effect of uniform strain on the physical nature transition of Mn{sub 2}ZnMg. • The M-FCF property of the Mn{sub 2}ZnMg is robust to the tetragonalization. • A magnetic phase transition occurs at 5.20 Å.

  20. Magnetic and Chemical Order in Heusler Alloys Containing Neodymium and Moiybdenum

    Directory of Open Access Journals (Sweden)

    N. A. Khalefa

    2015-12-01

    Full Text Available Saturation magnetization X-ray and neutron diffraction measurements have been made on alloys at the compositions Nd2MoCd’, Nd2MoZn’, Nd2MoCu, Nd2MoTi, Nd2MoAg, Nd2MoZr and NdMoZr. The alloys containing Cu and Ag have fully ordered Heusler, L21, Chemical structure. Nd2MoCd is similarly ordered but with some partial Mo-Cd disorder. The alloys Nd2MoZn and Nd2MoTi each contain a secondary phase in addition to the primary Heusler phase Nd2MoZr contains the two phases Nd122MoZr and Nd and NdMoZr is ordered in the Clb structure. The alloys containing the group IIIB or IVB elements Cd, Zn, Cu, Ti or Ag are ferromagnetically ordered, with the magnetic moment associated with the ordered Nd sites. The two alloys containing the group VB elements Zr have vacant chemically ordered ‘Nd’ sites but are paramagnetic.

  1. Defect-induced ferrimagnetism in the half-metallic Co{sub 2}CrAl and Co{sub 2}CrSi compounds

    Energy Technology Data Exchange (ETDEWEB)

    Oezdogan, Kemal; Aktas, Bekir [Department of Physics, Gebze Institute of Technology, 41400 Gebze, Kocaeli (Turkey); Galanakis, Iosif [Department of Materials Science, School of Natural Sciences, University of Patras, 26504 Patra (Greece); Sasioglu, Ersoy [Institut fuer Festkoerperforschung, Forschungszentrum Juelich, 52425 Juelich (Germany); Fatih University, Physics Department, 34500 Bueyuekcekmece, Istanbul (Turkey)

    2007-05-15

    Co{sub 2}CrAl and Co{sub 2}CrSi are amongst the most studied Heusler alloys due to their half-metallic character. These compounds are also well-known to present ferromagnetism with high Curie temperatures. We show using first-principles calculations that the creation of Cr antisites (Cr atoms at the Co sites) induces ferrimagnetism in these compounds without destroying the half-metallic character of these alloys. The reduction of the total spin moment causes lower external fields and thus smaller energy losses in realistic magnetoelectronic, also known as spintronic, devices. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  2. Martensitic transformation in Heusler alloys Mn{sub 2}YIn (Y=Ni, Pd and Pt): Theoretical and experimental investigation

    Energy Technology Data Exchange (ETDEWEB)

    Luo, Hongzhi, E-mail: luo_hongzhi@163.com [School of Material Science and Engineering, Hebei University of Technology, Tianjin 300130 (China); Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Liu, Bohua; Xin, Yuepeng; Jia, Pengzhong; Meng, Fanbin [School of Material Science and Engineering, Hebei University of Technology, Tianjin 300130 (China); Liu, Enke; Wang, Wenhong; Wu, Guangheng [Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China)

    2015-12-01

    The martensitic transformation and electronic structure of Heusler alloys Mn{sub 2}YIn (Y=Ni, Pd, Pt) have been investigated by both first-principles calculation and experimental investigation. Theoretical calculation reveals that, the energy difference ΔE between the tetragonal martensitic phase and cubic austenitic phase increases with Y varying from Ni to Pt in Mn{sub 2}YIn. Thus a structural transition from cubic to tetragonal is most likely to happen in Heusler alloy Mn{sub 2}PtIn. A single Heusler phase can be obtained in both Mn{sub 2}PtIn and Mn{sub 2}PdIn. A martensitic transformation temperature of 615 K has been identified in Mn{sub 2}PtIn. And in Mn{sub 2}PdIn, the austenitic phase is stable and no martensitic transformation is observed till 5 K. This indicates there may exist a positive relation between ΔE and martensitic transformation temperature. Calculated results show that Mn{sub 2}YIn are all ferrimagnets in both austenitic and martensitic phases. The magnetic properties are mainly determined by the antiparallel aligned Mn spin moments. These findings can help to develop new FSMAs with novel properties. - Highlights: • Positive relation between ΔE and martensitic transformation temperature has been observed. • Heusler alloy Mn{sub 2}PdIn has been synthesized successfully and investigated. • Martensitic transformation in Heusler alloys can be predicted by first -principles calculations.

  3. Structural, mechanical, electronic and magnetic properties of a new series of quaternary Heusler alloys CoFeMnZ (Z=Si, As, Sb): A first-principle study

    Energy Technology Data Exchange (ETDEWEB)

    Elahmar, M.H.; Rached, H.; Rached, D. [Laboratoire des Matériaux Magnétiques, Faculté des Sciences, Université Djillali Liabès de SidiBel-Abbès, SidiBel-Abbès 22000 (Algeria); Khenata, R., E-mail: khenata_rabah@yahoo.fr [Laboratoire de Physique Quantique et de Modélisation Mathématique, Université de Mascara, 29000 (Algeria); Murtaza, G. [Materials Modeling Lab, Department of Physics, Islamia College Peshawar, KPK (Pakistan); Bin Omran, S. [Department of Physics and Astronomy, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451 (Saudi Arabia); Ahmed, W.K. [ERU, College of Engineering, United Arab Emirates University, Al Ain, Abu Dhabi (United Arab Emirates)

    2015-11-01

    The structural, mechanical, electronic and magnetic properties of the series of Heusler alloys CoFeMnZ (Z=Si, As, and Sb) have been investigated theoretically. The objective is to seek for stable half-metallic ferromagnets materials with Curie temperatures higher than room temperature. The series of CoFeMnZ (Z=Si, As and Sb) is found to exhibit half-metallic ferromagnetism with high magnetic moment and the localized moment in these magnetic compounds resides at the Mn atom. It has been observed that all our compounds have high Curie temperatures with high spin polarizations. - Highlights: • Density functional calculations for CoFeMnZ (Z=Si, As, Sb) compounds are performed. • Half-metallic ferromagnetism in CoFeMnZ (Z=Si, As, Sb) compounds is established. • The magnetic and mechanical properties for CoFeMnZ (Z=As, Sb) are studied for the first time. • The studied compounds possess high Curie temperatures with high spin polarizations.

  4. Phase transition of Ni43Mn41Co5Sn11 Heusler alloy

    Science.gov (United States)

    Elwindari, N.; Kurniawan, C.; Manaf, A.

    2017-07-01

    In the recent years, Heusler alloy has been extensively studied. Among various the Heusler alloys, Ni-Mn-Sn has gained considerable interest due to their multifunctional properties like magnetoresistance, shape memory effect and magnetocaloric effect associated with a first order phase transition martensite to austenite. In this paper, we report the magneto-structural phase transitions under varying temperature of Ni43Mn41Co5Sn11 synthesized through vacuum arc-melting process. The magnetization of the sample was obtained after annealing process at 1173 K for 12 hours. It was evaluated by magnetic measurement using vibrating sample magnetometer (VSM250) up to a field of 21 kOe. The magnetic isotherm (M-H curves) shows the vicinity of the structural phase transition point. Magnetic saturation (Ms) of the NMCS alloy decreased and ferromagnetic transition shift towards higher temperature from 297-372 K. It might occur due to the alignment of the atomic magnetic moments depends on temperature. We discussed also the context of structural disorder and the ferromagnetic correlations in this study. The structural disorder of these alloys will explain the magnetic transition and the entropy change related magnetic properties.

  5. The half-metallic ferromagnetism character in Be{sub 1−x}V{sub x}Y (Y=Se and Te) alloys: An ab-initio study

    Energy Technology Data Exchange (ETDEWEB)

    Sajjad, M. [School of Electronic Engineering, Beijing University of Posts and Telecommunications, Beijing 100876 (China); Manzoor, Sadia [Department of Physics, University of the Punjab, Quaid-e-Azam Campus, 54590 Lahore (Pakistan); Zhang, H.X. [School of Electronic Engineering, Beijing University of Posts and Telecommunications, Beijing 100876 (China); Beijing Key Laboratory of Work Safety Intelligent Monitoring, Beijing University of Posts and Telecommunications, Beijing 100876 (China); Noor, N.A. [Department of Physics, University of the Punjab, Quaid-e-Azam Campus, 54590 Lahore (Pakistan); Alay-e-Abbas, S.M. [Department of Physics, GC University Faisalabad, Allama Iqbal Road, Faisalabad 38000 (Pakistan); Department of Physics, University of Sargodha, Sargodha 40100 (Pakistan); Shaukat, A. [Department of Physics, University of Sargodha, Sargodha 40100 (Pakistan); Khenata, R., E-mail: khenata_rabah@yahoo.fr [Laboratoire de Physique Quantique et de Modélisation Mathématique (LPQ3M), Département de Technologie, Université de Mascara, Mascara 29000 (Algeria)

    2015-04-01

    Ab-initio calculations for V-doped BeSe and BeTe semiconductors are performed by means of all-electrons full-potential linearized augmented plane wave plus local orbital (FP-LAPW+lo) method. The structural properties are optimized using the Wu-Cohen generalized gradient approximation functional, whereas modified Becke and Jhonson local density approximation functional has been employed for evaluating the spin-polarized electronic and magnetic properties. Magnetic stability at various doping concentrations in ferromagnetic (FM) and anti-ferromagnetic (AFM) ordering is investigated by comparing the minimum total energies and enthalpies of formation (ΔH). Studied band structures, density of states, total energy, exchange interactions and magnetic moments manifest both alloys with half-metallic ferromagnetic behavior. Moreover, their valance bands are found to be paired ferromagnetically with V atoms. Furthermore, it was observed that the magnetic moment of vanadium atom reduces from free space charge value due to p–d hybridization which yields small magnetic moments on the Be, Se and Te sites. - Highlights: • Density functional calculations for V-doped BeSe and BeTe are performed. • V-doped BeSe and BeTe are found to be stable half-metallic ferromagnetism. • Improved electronic properties are achieved using mBJLDA which confirm HMF. • The half-metallic gaps show non-linear variation with increasing dopant concentration.

  6. Electron dominated thermoelectric response in MNiSn (M: Ti, Zr, Hf) half-Heusler alloys

    KAUST Repository

    Gandi, Appala

    2016-05-09

    We solve the transport equations of the electrons and phonons to understand the thermoelectric behaviour of the technologically important half-Heusler alloys MNiSn (M: Ti, Zr, Hf). Doping is simulated within the rigid band approximation. We clarify the origin of the electron dominated thermoelectric response and determine the carrier concentrations with maximal figures of merit. The phonon mean free path is studied to calculate the grain size below which grain refinement methods can enforce ballistic heat conduction to enhance the figure of merit. © The Owner Societies 2016.

  7. High thermoelectric figure of merit by resonant dopant in half-Heusler alloys

    Directory of Open Access Journals (Sweden)

    Long Chen

    2017-06-01

    Full Text Available Half-Heusler alloys have been one of the benchmark high temperature thermoelectric materials owing to their thermal stability and promising figure of merit ZT. Simonson et al. early showed that small amounts of vanadium doped in Hf0.75Zr0.25NiSn enhanced the Seebeck coefficient and correlated the change with the increased density of states near the Fermi level. We herein report a systematic study on the role of vanadium (V, niobium (Nb, and tantalum (Ta as prospective resonant dopants in enhancing the ZT of n-type half-Heusler alloys based on Hf0.6Zr0.4NiSn0.995Sb0.005. The V doping was found to increase the Seebeck coefficient in the temperature range 300-1000 K, consistent with a resonant doping scheme. In contrast, Nb and Ta act as normal n-type dopants, as evident by the systematic decrease in electrical resistivity and Seebeck coefficient. The combination of enhanced Seebeck coefficient due to the presence of V resonant states and the reduced thermal conductivity has led to a state-of-the-art ZT of 1.3 near 850 K in n-type (Hf0.6Zr0.40.99V0.01NiSn0.995Sb0.005 alloys.

  8. Progress Report 2011: Understanding compound phase transitions in Heusler alloy giant magnetocaloric materials

    Energy Technology Data Exchange (ETDEWEB)

    Stadler, Shane

    2011-12-13

    Our goal is to gain insight into the fundamental physics that is responsible for magnetocaloric effects (MCE) and related properties at the atomic level. We are currently conducting a systematic study on the effects of atomic substitutions in Ni2MnGa-based alloys, and also exploring related full- and half-Heusler alloys, for example Ni-Mn-X (X=In, Sn, Sb), that exhibit a wide variety of interesting and potentially useful physical phenomena. It is already known that the magnetocaloric effect in the Heusler alloys is fundamentally connected to other interesting phenomena such as shape-memory properties. And the large magnetic entropy change in Ni2Mn0.75Cu0.25Ga has been attributed to the coupling of the first-order, martensitic transition with the second-order ferromagnetic paramagnetic (FM-PM) transition. Our research to this point has focused on understanding the fundamental physics at the origin of these complex, compound phase transitions, and the novel properties that emerge. We synthesize the materials using a variety of techniques, and explore their material properties through structural, magnetic, transport, and thermo-magnetic measurements.

  9. High thermoelectric figure of merit by resonant dopant in half-Heusler alloys

    Science.gov (United States)

    Chen, Long; Liu, Yamei; He, Jian; Tritt, Terry M.; Poon, S. Joseph

    2017-06-01

    Half-Heusler alloys have been one of the benchmark high temperature thermoelectric materials owing to their thermal stability and promising figure of merit ZT. Simonson et al. early showed that small amounts of vanadium doped in Hf0.75Zr0.25NiSn enhanced the Seebeck coefficient and correlated the change with the increased density of states near the Fermi level. We herein report a systematic study on the role of vanadium (V), niobium (Nb), and tantalum (Ta) as prospective resonant dopants in enhancing the ZT of n-type half-Heusler alloys based on Hf0.6Zr0.4NiSn0.995Sb0.005. The V doping was found to increase the Seebeck coefficient in the temperature range 300-1000 K, consistent with a resonant doping scheme. In contrast, Nb and Ta act as normal n-type dopants, as evident by the systematic decrease in electrical resistivity and Seebeck coefficient. The combination of enhanced Seebeck coefficient due to the presence of V resonant states and the reduced thermal conductivity has led to a state-of-the-art ZT of 1.3 near 850 K in n-type (Hf0.6Zr0.4)0.99V0.01NiSn0.995Sb0.005 alloys.

  10. Magnetostriction of Ni2Mn1−xCrxGa Heusler Alloys

    Directory of Open Access Journals (Sweden)

    Takuo Sakon

    2017-10-01

    Full Text Available Among the functionalities of magnetic Heusler alloys, magnetostriction is attracting considerable attention. The alloy Ni2MnGa has a premartensite phase, which is a precursor state to the martensitic transition. Some researchers have observed magnetostriction in this alloy in the premartensite phase. We performed magnetostriction studies on the premartensite phase of related Cr-substituted Ni2Mn1−xCrxGa alloys and measured the thermal strain, permeability, magnetisation, and magnetostriction of polycrystals. Our thermal expansion measurements show an anomaly that indicates the occurrence of lattice deformation below the premartensitic transition temperature TP. Our permeability measurements also showed an anomaly at the premartensitic transition. From our magnetisation results, we obtained the magnetic-anisotropy constant K1. In the martensite phase, we found that the magnetic-anisotropy constant of the x = 0.00 alloy is larger than that of the x = 0.15 alloy. At 0.24 MA/m, we obtained a magnetostriction of −120 ppm for the x = 0.15 alloy. Magnetostriction in the premartensite phase is larger than that in the austenite and martensite phases at low magnetic-field strength, thus indicating that it is related to lattice softening in the premartensite phase. The e/a is proportional to the magnetostriction and TP, which indicates that the electron energy, the magnetostriction, and the Tp are correlative each other.

  11. First-principal study of full Heusler alloys Co2VZ (Z = As, In)

    Science.gov (United States)

    Gupta, Dinesh C.; Ghosh, Sukriti

    2017-08-01

    We have used full-potential linearized augmented plane wave method in the stable Fm-3m phase to investigate the structural, elastic, magnetic and electronic properties of Co2VZ (Z = As, In). The optimized equilibrium lattice parameter in stable phase is 5.80 Å for Co2VAs and 6.01 Å for Co2VIn. Ferromagnetic behavior of both the alloys is explained by the spin resolved density of states. The exchange splitting due to Co and V atoms are responsible for the ferromagnetic behaviour. No energy gap is found in spin up state while an energy gap can be seen in spin down state, hence, showing half-metallic nature. Elastic stability is discussed through elastic constants. Thermodynamic properties of the alloys have been obtained by using the quasi-harmonic approximations. Boltzmann theory is employed to investigate the electronic transport properties of these alloys.

  12. Insights into Ultrafast Demagnetization in Pseudogap Half-Metals

    Directory of Open Access Journals (Sweden)

    Andreas Mann

    2012-11-01

    Full Text Available Interest in femtosecond demagnetization dynamics was sparked by Bigot’s experiment in 1996, which unveiled the elementary mechanisms that relate the electrons’ temperature to their spin order. Simultaneously, the application of fast demagnetization experiments has been demonstrated to provide key insight into technologically important systems such as high-spin-polarization metals, and consequently there is broad interest in further understanding the physics of these phenomena. To gain new and relevant insights, we performed ultrafast optical pump-probe experiments to characterize the demagnetization processes of highly spin-polarized magnetic thin films on a femtosecond time scale. Full spin polarization is obtained in half-metallic ferro- or ferrimagnets, where only one spin channel is populated at the Fermi level, whereas the other one exhibits a gap. In these materials, the spin-scattering processes is controlled via the electronic structure, and thus their ultrafast demagnetization is solely related to the spin polarization via a Fermi golden-rule model. Accordingly, a long demagnetization time correlates with a high spin polarization due to the suppression of the spin-flip scattering at around the Fermi level. Here we show that isoelectronic Heusler compounds (Co_{2}MnSi, Co_{2}MnGe, and Co_{2}FeAl exhibit a degree of spin polarization between 59% and 86%. We explain this behavior by considering the robustness of the gap against structural disorder. Moreover, we observe that CoFe-based pseudogap materials, such as partially ordered Co-Fe-Ge and Co-Fe-B alloys, can reach similar values of the spin polarization. By using the unique features of these metals we vary the number of possible spin-flip channels, which allows us to pinpoint and control the half-metals’ electronic structure and its influence on the elementary mechanisms of ultrafast demagnetization.

  13. Thermoelectric properties of ultra-low thermal conductivity half-Heusler alloy

    Energy Technology Data Exchange (ETDEWEB)

    Mallick, Md. Mofasser; Vitta, Satish, E-mail: satish.vitta@iitb.ac.in [Department of Metallurgical Engineering and Materials Science, Indian Institute of Technology Bombay, Mumbai 400076 (India)

    2016-05-23

    The half-Heusler alloy HfNiGe has been synthesized by arc melting from high purity elements followed by annealing at 1000 K for 6 days to homogenize completely. The X-ray diffraction pattern indicates the presence of mainly an orthorhombic phase with small amount of other binary phases. The electrical resistivity is found to be low and increases slightly with temperature from 14 µΩ-m to 24 µΩ-m, indicating a semi metallic behavior. As a result the Seebeck coefficient is found to be low and also increases with temperature from −11 µV K{sup −1} to −19.5 µV K{sup −1}. The thermal conductivity has been determined using a combination of heat capacity and thermal diffusivity. It decreases from ~ 1.9 Wm{sup −1}K{sup −1} at room temperature to ~ 0.007 Wm{sup −1}K{sup −1} at 843 K, an extremely low value for a half-Heusler alloy. The thermal conductivity reduction is found to be mainly due to a sharp decrease in heat capacity for T> 650 K. This leads to a divergence of figure of merit at high temperatures, >800 K, from ~0.05 to 2 at 843 K.

  14. Electron spin resonance probed competing states in NiMnInSi Heusler alloy

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Y.S. [Center for Condensed Matter Sciences, National Taiwan University, Taipei 10617, Taiwan (China); Lin, J.G., E-mail: jglin@ntu.edu.tw [Center for Condensed Matter Sciences, National Taiwan University, Taipei 10617, Taiwan (China); Titov, I.S.; Granovsky, A.B. [Faculty of Physics, Lomonosov Moscow State University, Vorob' evy Gory, 11999l Moscow (Russian Federation)

    2016-06-01

    Shape memory Heusler alloy Ni{sub 50}Mn{sub 35}In{sub 12}Si{sub 3} is investigated with electron spin resonance (ESR) technique in a temperature range of 200–300 K. ESR is a dynamic probe allowing us to separate the responses from various magnetic phases, thus to study the complex phase transitions. The sample shows three transition temperatures: T{sub c}{sup A} (271 K), T{sub M} (247 K) and T{sub c}{sup M} (212 K), where T{sub c}{sup A} is the Curie temperature of austenitic phase, T{sub M} and T{sub c}{sup M} are the temperatures of magnetostructural martensitic transition and the Curie temperature of martensitic phase, respectively. Furthermore, ESR data reveals the coexistence of two magnetic modes in whole temperature range of 200–300 K. Particularly in martensitic phase, two magnetic modes are attributed to two different kinds of lattice deformation, the slip and twinning deformations. - Highlights: • Electron spin resonance study on magnetocaloric Heusler alloy within 200–300 K. • Magnetic phase separation below and above the structural transition temperature. • Phase competing is in association with different types of lattice distortions. • Electron spin resonance results are complementary to the magnetization data.

  15. Structure and Magnetic Properties in Ruthenium-Based Full-Heusler Alloys: AB INITIO Calculations

    Science.gov (United States)

    Bahlouli, S.; Aarizou, Z.; Elchikh, M.

    2013-12-01

    In this paper, we present ab initio calculations within density functional theory (DFT) to investigate structure, electronic and magnetic properties of Ru2CrZ (Z = Si, Ge and Sn) full-Heusler alloys. We have used the developed full-potential linearized muffin tin orbitals (FP-LMTO) based on the local spin density approximation (LSDA) with the PLane Wave expansion (PLW). In particular, we found that these Ruthenium-based Heusler alloys have the antiferromagnetic (AFM) type II as ground state. Then, we studied and discussed the magnetic properties belonging to our different magnetic structures: AFM type II, AFM type I and ferromagnetic (FM) phase. We also found that Ru2CrSi and Ru2CrGe exhibit a semiconducting behavior whereas Ru2CrSn has a semimetallic-like behavior as it is experimentally found. We made an estimation of Néel temperatures (TN) in the framework of the mean-field theory and used the energy differences approach to deduce the relevant short-range nearest-neighbor (J1) and next-nearest-neighbor (J2) interactions. The calculated TN are somewhat overestimated to the available experimental ones.

  16. Thermoelectric properties of ultra-low thermal conductivity half-Heusler alloy

    Science.gov (United States)

    Mallick, Md. Mofasser; Vitta, Satish

    2016-05-01

    The half-Heusler alloy HfNiGe has been synthesized by arc melting from high purity elements followed by annealing at 1000 K for 6 days to homogenize completely. The X-ray diffraction pattern indicates the presence of mainly an orthorhombic phase with small amount of other binary phases. The electrical resistivity is found to be low and increases slightly with temperature from 14 µΩ-m to 24 µΩ-m, indicating a semi metallic behavior. As a result the Seebeck coefficient is found to be low and also increases with temperature from -11 µV K-1 to -19.5 µV K-1. The thermal conductivity has been determined using a combination of heat capacity and thermal diffusivity. It decreases from ~ 1.9 Wm-1K-1 at room temperature to ~ 0.007 Wm-1K-1 at 843 K, an extremely low value for a half-Heusler alloy. The thermal conductivity reduction is found to be mainly due to a sharp decrease in heat capacity for T> 650 K. This leads to a divergence of figure of merit at high temperatures, >800K, from ~0.05 to 2 at 843 K.

  17. Martensitic Transformation in Ni-Mn-Sn-Co Heusler Alloys

    Directory of Open Access Journals (Sweden)

    Alexandre Deltell

    2015-04-01

    Full Text Available Thermal and structural austenite to martensite reversible transition was studied in melt spun ribbons of Ni50Mn40Sn5Co5, Ni50Mn37.5Sn7.5Co5 and Ni50Mn35Sn10Co5 (at. % alloys. Analysis of X-ray diffraction patterns confirms that all alloys have martensitic structure at room temperature: four layered orthorhombic 4O for Ni50Mn40Sn5Co5, four layered orthorhombic 4O and seven-layered monoclinic 14M for Ni50Mn37.5Sn7.5Co5 and seven-layered monoclinic 14M for Ni50Mn35Sn5Co5. Analysis of differential scanning calorimetry scans shows that higher enthalpy and entropy changes are obtained for alloy Ni50Mn37.5Sn7.5Co5, whereas transition temperatures increases as increasing valence electron density.

  18. Study of electronic structure and magnetic properties of epitaxial Co{sub 2}FeAl Heusler Alloy Thin Films

    Energy Technology Data Exchange (ETDEWEB)

    Soni, S. [Department of Pure & Applied Physics, University of Kota, Kota 324007 (India); Dalela, S., E-mail: sdphysics@rediffmail.com [Department of Pure & Applied Physics, University of Kota, Kota 324007 (India); Sharma, S.S. [Department of Physics, Govt. Women Engineering College, Ajmer (India); Liu, E.K.; Wang, W.H.; Wu, G.H. [State Key Laboratory for Magnetism, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Kumar, M. [Department of Physics, Malviya National Institute of Technology, Jaipur-302017 (India); Garg, K.B. [Department of Physics, University of Rajasthan, Jaipur-302004 (India)

    2016-07-25

    This work reports the magnetic and electronic characterization of plane magnetized buried Heusler Co{sub 2}FeAl nano thin films of different thickness by X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) measurements. . The spectra on both Fe- and Co L{sub 2,3} edges show a pronounced magnetic dichroic signal in remanence, corresponding to a ferromagnetically-aligned moments on Fe and Co atoms conditioning the peculiar characteristics of the Co{sub 2}FeAl Heusler compound (a half-metallic ferromagnet). The detailed knowledge of the related magnetic and electronic properties of these samples over a wide range of thickness of films are indispensable for achieving a higher tunnel magnetoresistance ratio, and thus for spintronics device applications. - Highlights: • Electronic structure and Magnetic Properties of Epitaxial Co{sub 2}FeAl Heusler Films. • X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD). • Fe- and Co L{sub 2,3} edges show a pronounced magnetic dichroic signal in remanence. • Calculated Orbital, Spin and total magnetic moments of Fe and Co for 30 nm Co{sub 2}FeAl thin film. • The total magnetic moment of Fe at L{sub 2,3} edges increases with the thickness of the Co2FeAl films.

  19. High tunneling magnetoresistance ratio in perpendicular magnetic tunnel junctions using Fe-based Heusler alloys

    Science.gov (United States)

    Wang, Yu-Pu; Lim, Sze-Ter; Han, Gu-Chang; Teo, Kie-Leong

    2015-12-01

    Heulser alloys Fe2Cr1-xCoxSi (FCCS) with different Co compositions x have been predicted to have high spin polarization. High perpendicular magnetic anisotropy (PMA) has been observed in ultra-thin FCCS films with magnetic anisotropy energy density up to 2.3 × 106 erg/cm3. The perpendicular magnetic tunnel junctions (p-MTJs) using FCCS films with different Co compositions x as the bottom electrode have been fabricated and the post-annealing effects have been investigated in details. An attractive tunneling magnetoresistance ratio as high as 51.3% is achieved for p-MTJs using Fe2CrSi (FCS) as the bottom electrode. The thermal stability Δ can be as high as 70 for 40 nm dimension devices using FCS, which is high enough to endure a retention time of over 10 years. Therefore, Heusler alloy FCS is a promising PMA candidate for p-MTJ application.

  20. Thermoelectric Properties of the XCoSb (X: Ti,Zr,Hf) Half-Heusler Alloys

    KAUST Repository

    Gandi, Appala

    2017-09-18

    We investigate the thermoelectric properties of the half-Heusler alloys XCoSb (X: Ti,Zr,Hf) by solving Boltzmann transport equations and discuss them in terms of the electronic band structure. The rigid band approximation is employed to address the effects of doping. While many half-Heuser alloys show excellent thermoelectric performance, the materials under study are special by supporting both n- and p-doping. We identify the reasons for this balanced thermoelectric transport and explain why experimentally p-doping is superior to n-doping. We also determine the spectrum of phonon mean free paths to guide grain refinement methods to enhance the thermoelectric figure of merit.

  1. Growth of Co2FeAl Heusler alloy thin films on Si(100) having very small Gilbert damping by Ion beam sputtering

    National Research Council Canada - National Science Library

    Husain, Sajid; Akansel, Serkan; Kumar, Ankit; Svedlindh, Peter; Chaudhary, Sujeet

    2016-01-01

    The influence of growth temperature Ts (300-773 K) on the structural phase ordering, static and dynamic magnetization behaviour has been investigated in ion beam sputtered full Heusler alloy Co2FeAl (CFA...

  2. The zero-moment half metal: How could it change spin electronics?

    Directory of Open Access Journals (Sweden)

    Davide Betto

    2016-05-01

    Full Text Available The Heusler compound Mn2RuxGa (MRG may well be the first compensated half metal. Here, the structural, magnetic and transport properties of thin films of MRG are discussed. There is evidence of half-metallicity up to x = 0.7, and compensation of the two Mn sublattice moments is observed at specific compositions and temperatures, leading to a zero-moment half metal. There are potential benefits for using such films with perpendicular anisotropy for spin-torque magnetic tunnel junctions and oscillators, such as low critical current, high tunnel magnetoresistance ratio, insensitivity to external fields and resonance frequency in the THz range.

  3. The zero-moment half metal: How could it change spin electronics?

    Energy Technology Data Exchange (ETDEWEB)

    Betto, Davide; Rode, Karsten, E-mail: rodek@tcd.ie; Thiyagarajah, Naganivetha; Lau, Yong-Chang; Borisov, Kiril; Atcheson, Gwenael; Stamenov, Plamen; Coey, J. M. D. [CRANN, AMBER and School of Physics, Trinity College Dublin, Dublin 2 (Ireland); Žic, Mario; Archer, Thomas [CRANN, and School of Physics, Trinity College Dublin, Dublin 2 (Ireland)

    2016-05-15

    The Heusler compound Mn{sub 2}Ru{sub x}Ga (MRG) may well be the first compensated half metal. Here, the structural, magnetic and transport properties of thin films of MRG are discussed. There is evidence of half-metallicity up to x = 0.7, and compensation of the two Mn sublattice moments is observed at specific compositions and temperatures, leading to a zero-moment half metal. There are potential benefits for using such films with perpendicular anisotropy for spin-torque magnetic tunnel junctions and oscillators, such as low critical current, high tunnel magnetoresistance ratio, insensitivity to external fields and resonance frequency in the THz range.

  4. Structural phase transition, electronic structure and optical properties of half Heusler alloys LiBeZ (Z = As, Sb)

    Energy Technology Data Exchange (ETDEWEB)

    Amudhavalli, A.; Rajeswarapalanichamy, R., E-mail: rajeswarapalanichamy@gmail.com [PG and Research Department of Physics, N.M.S.S.V.N college, Madurai, Tamilnadu-625019 (India)

    2016-05-23

    Ab initio calculations are performed to investigate the structural stability, electronic structure, mechanical properties and optical properties of half Heusler alloys (LiBeAs and LiBeSb) for three different phases of zinc blende crystal structure. Among the considered phases, α- phase is found to be the most stable phase for these alloys at normal pressure. A pressure induced structural phase transition from α-phase to β- phase is observed for LiBeAs. The electronic structure reveals that these alloys are semiconductors. The optical properties confirm that these alloys are semiconductor in nature.

  5. Magnetic properties of Ni-Mn-Ga Heusler alloy films

    Science.gov (United States)

    Dubowik, J.; Gociaska, I.; Kudryavtsev, Y. V.; Lee, Y. P.; Sovák, P.; Kon, M.

    2006-01-01

    The films with composition Nix Mny Gaz (x = 50 +/- 5, y = 25 +/- 5, z = 25 +/- 5) were deposited by flash-evaporation or sputtering on mica and glass substrates and annealed in a high vacuum at 673-973 K. X-ray diffraction at room temperature reveals the presence of B2 (or L21) type of structure depending on annealing conditions. Magnetic properties were studied by ferromagnetic resonance at temperatures from 78 K to 400 K and compared with electric resistivity data. It is shown that the magnetic properties of the films critically depend on their structural ordering and microstructure. The films annealed at T 800 K show magnetic properties comparable with those of bulk Ni-Mn-Ga alloys.

  6. Structure and magnetic properties of Heusler alloy Co{sub 2}RuSi melt-spun ribbons

    Energy Technology Data Exchange (ETDEWEB)

    Xin, Yuepeng; Ma, Yuexing; Hao, Hongyue [School of Materials Science and Engineering, Hebei University of Technology, Tianjin 300130 (China); Luo, Hongzhi, E-mail: luo_hongzhi@163.com [School of Materials Science and Engineering, Hebei University of Technology, Tianjin 300130 (China); Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Meng, Fanbin; Liu, Heyan [School of Materials Science and Engineering, Hebei University of Technology, Tianjin 300130 (China); Liu, Enke; Wu, Guangheng [Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China)

    2017-08-01

    Highlights: • New Heusler alloy Co{sub 2}RuSi has been prepared by melt-spinning successfully. • Magnetic and electronic properties of Co{sub 2}RuSi were investigated. • Ru has a strong site preference for A, C sites in the lattice of Co{sub 2}RuSi. • Site preference of Ru cannot be determined by “number of valence electrons”. - Abstract: Heusler alloy Co{sub 2}RuSi has been synthesized by melt-spinning technology successfully. Co{sub 2}RuSi bulk sample after annealing is composed of an HCP Co-rich phase and a BCC Ru-Si phase, but melt-spinning can suppress the precipitation of the HCP phase and produce a single Co{sub 2}RuSi Heusler phase. In the XRD pattern, it is found that Ru has a strong preference for the (A, C) sites, though it has fewer valence electrons compared with Co. This site preference is different from the case in Heusler alloys containing only 3d elements and is supported further by first-principles calculations. Melt-spun Co{sub 2}RuSi has a M{sub s} of 2.67 μ{sub B}/f.u. at 5 K and a Tc of 491 K. An exothermic peak is observed at 871 K in the DTA curve, corresponding to the decomposition of the Heusler phase. Finally, the site preference and magnetic properties of Co{sub 2}RuSi were discussed based on electronic structure calculation and charge density difference.

  7. Electronic, magnetic and thermal properties of Co{sub 2}Cr{sub x}Fe{sub 1−x}X (X=Al, Si) Heusler alloys: First-principles calculations

    Energy Technology Data Exchange (ETDEWEB)

    Guezlane, M. [Department of Physics, Faculty of Science, University of Batna, 05000 Batna (Algeria); Baaziz, H., E-mail: baaziz_hakim@yahoo.fr [Physics Department, Faculty of Science, University of M' sila, 28000 M' sila (Algeria); El Haj Hassan, F., E-mail: hassan.f@ul.edu.lb [Université Libanaise, Faculté des Sciences (I), Laboratoire de Physique et d’Electronique (LPE), Elhadath, Beirut (Lebanon); Charifi, Z. [Physics Department, Faculty of Science, University of M' sila, 28000 M' sila (Algeria); Djaballah, Y. [Laboratoire d’étude Physico-Chimique des Matériaux, Département de Physique, Faculté des Sciences, Université de Batna, Rue Chahid Boukhlouf, 05000 Batna (Algeria)

    2016-09-15

    Density functional theory (DFT) based on the full-potential linearized augmented plane wave (FP-LAPW) method is used to investigate the structural, electronic, magnetic and thermal properties of Co{sub 2}Cr{sub x}Fe{sub 1−x}X (X=Al, Si) full Heusler alloys, with L2{sub 1} structure. The structural properties and spin magnetic moments are investigated by the generalized gradient approximations (GGA) minimizing the total energy. For band structure calculations, GGA, the Engel–Vosko generalized gradient approximation (EVGGA) and modified Becke–Johnson (mBJ) schemes are used. Results of density of states (DOS) and band structures show that these alloys are half-metallic ferromagnets (HMFS). A regular-solution model has been used to investigate the thermodynamic stability of the compounds Co{sub 2}Cr{sub x}Fe{sub 1−x}X that indicates a phase miscibility gap. The thermal effects using the quasi-harmonic Debye model are investigated within the lattice vibrations. The temperature and pressure effects on the heat capacities, Debye temperatures and entropy are determined from the non-equilibrium Gibbs functions. - Highlights: • We present electronic, magnetic and thermal properties of Co{sub 2}Cr{sub x}Fe{sub 1−x}X (X=Al, Si) Heusler alloys. • The calculated phase diagram indicates a significant phase miscibility gap. • The computed band structures of ternary compounds using GGA, EVGGA and mBJ schemes indicate an indirect band gap (Γ-X) for the ternary compounds Co{sub 2}FeAl, Co{sub 2}CrAl, Co{sub 2}FeSi and Co{sub 2}CrSi while both alloys have a direct band gap. • The quasi-harmonic Debye model is successfully applied to determine the thermal properties.

  8. Reducing the nucleation barrier in magnetocaloric Heusler alloys by nanoindentation

    Directory of Open Access Journals (Sweden)

    R. Niemann

    2016-06-01

    Full Text Available Magnetocaloric materials are promising as solid state refrigerants for more efficient and environmentally friendly cooling devices. The highest effects have been observed in materials that exhibit a first-order phase transition. These transformations proceed by nucleation and growth which lead to a hysteresis. Such irreversible processes are undesired since they heat up the material and reduce the efficiency of any cooling application. In this article, we demonstrate an approach to decrease the hysteresis by locally changing the nucleation barrier. We created artificial nucleation sites and analyzed the nucleation and growth processes in their proximity. We use Ni-Mn-Ga, a shape memory alloy that exhibits a martensitic transformation. Epitaxial films serve as a model system, but their high surface-to-volume ratio also allows for a fast heat transfer which is beneficial for a magnetocaloric regenerator geometry. Nanoindentation is used to create a well-defined defect. We quantify the austenite phase fraction in its proximity as a function of temperature which allows us to determine the influence of the defect on the transformation.

  9. Special Heusler compounds for spintronic applications

    Energy Technology Data Exchange (ETDEWEB)

    Balke, B.

    2007-07-01

    This work emphasizes the potential of Heusler compounds in a wide range of spintronic applications. Using electronic structure calculations it is possible to design compounds for specific applications. Examples for GMR and TMR applications, for spin injection into semiconductors, and for spin torque transfer applications will be shown. After a detailed introduction about spintronics and related materials chapter 5 reports about the investigation of new half-metallic compounds where the Fermi energy is tuned in the middle of the gap to result in more stable compounds for GMR and TMR applications. The bulk properties of the quaternary Heusler alloy Co{sub 2}Mn{sub 1-x}Fe{sub x}Si with the Fe concentration ranging from x=0 to 1 are reported and the results suggest that the best candidate for applications may be found at an iron concentration of about 50%. Due to the effect that in the Co{sub 2}Mn{sub 1-x}Fe{sub x}Si series the transition metal carrying the localized moment is exchanged and this might lead to unexpected effects on the magnetic properties if the samples are not completely homogeneous chapter 6 reports about the optimization of the Heusler compounds for GMR and TMR applications. The structural and magnetic properties of the quaternary Heusler alloy Co{sub 2}FeAl{sub 1-x}Si{sub x} with varying Si concentration are reported. From the combination of experimental (better order for high Si content) and theoretical findings (robust gap at x=0.5) it is concluded that a compound with an intermediate Si concentration close to x=0.5-0.7 would be best suited for spintronic applications, especially for GMR and TMR applications. In chapter 7 the detailed investigation of compounds for spin injection into semiconductors is reported. It is shown that the diluted magnetic semiconductors based on CoTiSb with a very low lattice mismatch among each other are interesting materials for spintronics applications like Spin-LEDs or other spin injection devices. Chapter 8 refers

  10. New Class of Materials : Half-Metallic Ferromagnets

    NARCIS (Netherlands)

    Groot, R.A. de; Mueller, F.M.; Engen, P.G. van; Buschow, K.H.J.

    1983-01-01

    The band structure of Mn-based Heusler alloys of the C1b crystal structure (MgAgAs type) has been calculated with the augmented-spherical-wave method. Some of these magnetic compounds show unusual electronic properties. The majority-spin electrons are metallic, whereas the minority-spin electrons

  11. Nature of electron correlation and hybridization in NixCu1−xMnSb Heusler alloys

    Directory of Open Access Journals (Sweden)

    I. Sarkar

    2016-08-01

    Full Text Available The electronic structure of Heusler alloys having mixed magnetic phases, comprising of vicinal anti-ferromagnetic and ferromagnetic orders, is of great significance. We present the results of an electronic structure study on NixCu1−xMnSb Heusler alloys, using Mn-2p core-level photoemission spectroscopy. Room temperature data in the paramagnetic phase reveal a non-monotonic variation of both electron correlation strength and conduction-band hybridization such that the former enhances while the latter weakens for compositions showing a mixed phase relative to compositions at the phase boundaries to the ordered phases. The results suggest a possible electronic driving force for settling mixed-magnetic phases.

  12. Magnetic properties of Heusler alloys Ru{sub 2-x}Fe{sub x}CrSi

    Energy Technology Data Exchange (ETDEWEB)

    Matsuda, Kazuhisa; Hiroi, Masahiko; Kawakami, Masayuki [Department of Physics, Faculty of Science, Kagoshima University, Kagoshima 890-0065 (Japan)

    2005-09-21

    We report on the structural and magnetic properties of newly synthesized Heusler alloys, Ru{sub 2-x}Fe{sub x}CrSi, which have quite recently been shown to be candidates for ferromagnetic metals with high spin polarization from band structure calculations. Polycrystalline samples of Heusler alloys Ru{sub 2-x}Fe{sub x}CrSi were prepared for 0.5{<=}x{<=}1.8. They were found to have L2{sub 1} structures for 0.5{<=}x{<=}1.5 and B2 for x = 1.8. Magnetic measurements showed that they are ferromagnets. The Curie temperature for x = 1.0 was found to be 370 K. The Curie temperature tends to increase with increasing Fe concentration x. The saturation magnetic moment increases almost linearly as x increases. For higher Fe concentration the saturation magnetic moment is close to 2 {mu}{sub B} per formula unit, which is theoretically expected.

  13. High performance p-type segmented leg of misfit-layered cobaltite and half-Heusler alloy

    DEFF Research Database (Denmark)

    Le, Thanh Hung; Van Nong, Ngo; Snyder, Gerald Jeffrey

    2015-01-01

    In this study, a segmented p-type leg of doped misfit-layered cobaltite Ca2.8Lu0.15Ag0.05Co4O9+δ and half-Heusler Ti0.3Zr0.35Hf0.35CoSb0.8Sn0.2 alloy was fabricated and characterized. The thermoelectric properties of single components, segmented leg, and the electrical contact resistance of the j......In this study, a segmented p-type leg of doped misfit-layered cobaltite Ca2.8Lu0.15Ag0.05Co4O9+δ and half-Heusler Ti0.3Zr0.35Hf0.35CoSb0.8Sn0.2 alloy was fabricated and characterized. The thermoelectric properties of single components, segmented leg, and the electrical contact resistance...

  14. Magnetic states stabilization in Ni51Mn33.4In15.6 Heusler alloy

    Directory of Open Access Journals (Sweden)

    Mohammadreza Ghahremani

    2015-12-01

    Full Text Available The rate-independent stabilization of magnetic states with iterations in a Heusler alloy has been studied. The direct measurement of the adiabatic temperature change, ΔTad, of a Ni51Mn33.4In15.6 alloy near the magnetostructural phase transition is presented. The adiabatic temperature change at a given temperature within the temperature range of the magnetostructural transition is history dependent and varies considerably with the iteration count of the field cycle. The data show the transition from the low magnetization state to the high magnetization state during low to high (L–H temperature change direction and from high magnetization to low magnetization state during high to low (H–L temperature change direction require several field cycles to stabilize the ΔTad measurement, similar to the accommodation phenomenon in hysteretic materials. In the mixed magnetic state inside the first-order transition, both low and high magnetization portions of the alloy exist and it varies considerably with the induced fields. This original observation emphasizes that it is incorrect to assess the performance of a magnetic refrigeration system through a single measurement, and that achieving a stable, utilizable, adiabatic temperature change requires several field-induced transitions.

  15. Development of antiferromagnetic Heusler alloys for the replacement of iridium as a critically raw material

    Science.gov (United States)

    Hirohata, Atsufumi; Huminiuc, Teodor; Sinclair, John; Wu, Haokaifeng; Samiepour, Marjan; Vallejo-Fernandez, Gonzalo; O'Grady, Kevin; Balluf, Jan; Meinert, Markus; Reiss, Günter; Simon, Eszter; Khmelevskyi, Sergii; Szunyogh, Laszlo; Yanes Díaz, Rocio; Nowak, Ulrich; Tsuchiya, Tomoki; Sugiyama, Tomoko; Kubota, Takahide; Takanashi, Koki; Inami, Nobuhito; Ono, Kanta

    2017-11-01

    As a platinum group metal, iridium (Ir) is the scarcest element on the earth but it has been widely used as an antiferromagnetic layer in magnetic recording, crucibles and spark plugs due to its high melting point. In magnetic recording, antiferromagnetic layers have been used to pin its neighbouring ferromagnetic layer in a spin-valve read head in a hard disk drive for example. Recently, antiferromagnetic layers have also been found to induce a spin-polarised electrical current. In these devices, the most commonly used antiferromagnet is an Ir-Mn alloy because of its corrosion resistance and the reliable magnetic pinning of adjacent ferromagnetic layers. It is therefore crucial to explore new antiferromagnetic materials without critical raw materials. In this review, recent research on new antiferromagnetic Heusler alloys and their exchange interactions along the plane normal is discussed. These new antiferromagnets are characterised by very sensitive magnetic and electrical measurement techniques recently developed to determine their characteristic temperatures together with atomic structural analysis. Mn-based alloys and compounds are found to be most promising based on their robustness against atomic disordering and large pinning strength up to 1.4 kOe, which is comparable with that for Ir-Mn. The search for new antiferromagnetic films and their characterisation are useful for further miniaturisation and development of spintronic devices in a sustainable manner.

  16. Half-metallic ferrimagnetism in Mn{sub 2}CuGe

    Energy Technology Data Exchange (ETDEWEB)

    Wei Xiaoping; Hu Xianru; Mao Geyong; Chu Shibing; Lei Tao; Hu Leibo [Department of Physics, LanZhou University, Lanzhou 730000 (China); Deng Jianbo, E-mail: dengjb@lzu.edu.c [Department of Physics, LanZhou University, Lanzhou 730000 (China)

    2010-10-15

    We study magnetism properties and the electronic structure of a new Mn-based Heusler alloys Mn{sub 2}CuGe using ab initio electronic structure calculations. We take into account both possible L 2{sub 1} structures (CuHg{sub 2}Ti and AlCu{sub 2}Mn types). The CuHg{sub 2}Ti-type structure is found to be energetically more favorable than the AlCu{sub 2}Mn-type structure and exhibits half-metallic ferrimagnetism. Calculations show that their total spin moment is -1{mu}{sub B} for a wide range of equilibrium lattice constants and magnetic moment mainly comes from the two Mn atoms, while the Cu atom is almost nonmagnetic. The small total moment comes from the antiparallel configurations of the Mn partial moments. And the CuHg{sub 2}Ti-type Mn{sub 2}CuGe alloy keeps a 100% of spin polarization at the Fermi level. Thus, the Mn{sub 2}CuGe is the compound of choice for further experimental investigations.

  17. First-principal study of full Heusler alloys Co{sub 2}VZ (Z = As, In)

    Energy Technology Data Exchange (ETDEWEB)

    Gupta, Dinesh C., E-mail: sosfizix@gmail.com [Condensed Matter Theory Group, School of Studies in Physics, Jiwaji University, Gwalior 474 011, M.P. (India); Ghosh, Sukriti [Department of Physics, Govt. K.R.G. Auto. P.G. College, Gwalior 474 001, M.P. (India); Condensed Matter Theory Group, School of Studies in Physics, Jiwaji University, Gwalior 474 011, M.P. (India)

    2017-08-01

    Highlights: • The present materials show magnetism and hence they can prove to be important in modern technology. • The materials show high spin polarization hence can be better candidates for spintronics. • It is the first attempt to predict the thermodynamic and transport properties by ab initio method. • They behave as metallic in spin-up and semiconductor-like behavior in spin-down states. • Their interesting properties will attract interest in such materials. - Abstract: We have used full-potential linearized augmented plane wave method in the stable Fm-3m phase to investigate the structural, elastic, magnetic and electronic properties of Co{sub 2}VZ (Z = As, In). The optimized equilibrium lattice parameter in stable phase is 5.80 Å for Co{sub 2}VAs and 6.01 Å for Co{sub 2}VIn. Ferromagnetic behavior of both the alloys is explained by the spin resolved density of states. The exchange splitting due to Co and V atoms are responsible for the ferromagnetic behaviour. No energy gap is found in spin up state while an energy gap can be seen in spin down state, hence, showing half-metallic nature. Elastic stability is discussed through elastic constants. Thermodynamic properties of the alloys have been obtained by using the quasi-harmonic approximations. Boltzmann theory is employed to investigate the electronic transport properties of these alloys.

  18. Enhancement of magnetic properties of Co2MnSi Heusler alloy prepared by mechanical alloying method

    Science.gov (United States)

    Rabie, Naeemeh; Gordani, Gholam Reza; Ghasemi, Ali

    2017-07-01

    Ferromagnetic Heusler alloys of Co2MnSi were synthesized by mechanical alloying method at low temperature. The effect of milling time and annealing process on structural and magnetic properties of ferromagnetic alloy samples were studied by X-ray diffraction, scanning electron microscopy and vibration sample magnetometer methods, respectively. Structural characteristics such as crystallite size, phase percentage, and lattice parameter determined using the Rietveld method. The values of these parameters were obtained 362.9 nm, 5.699 Å and 98.7%, respectively for annealed sample. Magnetization studies show that the Co2MnSi phase is formed at 15 h of milling and is optimized after 20 h of milling. VSM results showed that saturation magnetization (Ms) of milled samples reduces from 112 to 75 (emu/g) with increasing milling time and then increased gradually to 95 emu/g. The effect of post-annealing on the structural and magnetic properties of milled samples was also investigated. The saturation magnetization of annealed sample (120 emu/g) is higher than the optimum milled sample (95 emu/g) due to increasing preferential ordered L21 structure.

  19. Cooling-induced shape memory effect and inverse temperature dependence of superelastic stress in Co2Cr(Ga,Si) ferromagnetic Heusler alloys

    Science.gov (United States)

    Xu, Xiao; Omori, Toshihiro; Nagasako, Makoto; Okubo, Akinari; Umetsu, Rie Y.; Kanomata, Takeshi; Ishida, Kiyohito; Kainuma, Ryosuke

    2013-10-01

    Normally, shape memory effect (SME) is obtained by the reverse martensitic transformation, therefore only induced by heating a sample from the deformed martensite phase. In this study, we report a phenomenon of cooling-induced SME, observed in a Co2Cr(Ga,Si) Heusler alloy, where the normal heating-induced SME can be obtained at the same time. The cooling-induced SME is attributed to an abnormal martensitic transformation in Co2Cr(Ga,Si) Heusler alloy. Moreover, an inverse temperature dependence of superelastic stress was also observed. The discoveries of these phenomena provide application possibilities for shape memory alloys, especially at low temperatures.

  20. High tunneling magnetoresistance ratio in perpendicular magnetic tunnel junctions using Fe-based Heusler alloys

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Yu-Pu, E-mail: Vicky-sg1015@hotmail.com [Department of Electrical and Computer Engineering, National University of Singapore (Singapore); Data Storage Institute, Agency for Science, Technology and Research - A*STAR (Singapore); Lim, Sze-Ter; Han, Gu-Chang, E-mail: HAN-Guchang@dsi.a-star.edu.sg [Data Storage Institute, Agency for Science, Technology and Research - A*STAR (Singapore); Teo, Kie-Leong, E-mail: eleteokl@nus.edu.sg [Department of Electrical and Computer Engineering, National University of Singapore (Singapore)

    2015-12-21

    Heulser alloys Fe{sub 2}Cr{sub 1−x}Co{sub x}Si (FCCS) with different Co compositions x have been predicted to have high spin polarization. High perpendicular magnetic anisotropy (PMA) has been observed in ultra-thin FCCS films with magnetic anisotropy energy density up to 2.3 × 10{sup 6 }erg/cm{sup 3}. The perpendicular magnetic tunnel junctions (p-MTJs) using FCCS films with different Co compositions x as the bottom electrode have been fabricated and the post-annealing effects have been investigated in details. An attractive tunneling magnetoresistance ratio as high as 51.3% is achieved for p-MTJs using Fe{sub 2}CrSi (FCS) as the bottom electrode. The thermal stability Δ can be as high as 70 for 40 nm dimension devices using FCS, which is high enough to endure a retention time of over 10 years. Therefore, Heusler alloy FCS is a promising PMA candidate for p-MTJ application.

  1. Effects of disorder in the Heusler alloy Co{sub 2}MnSi and properties of the Co{sub 2}MnSi(100)/MgO interface; Effekte von Unordnung in der Heusler-Legierung Co{sub 2}MnSi und Eigenschaften der Co{sub 2}MnSi (100)/MgO-Grenzflaeche

    Energy Technology Data Exchange (ETDEWEB)

    Huelsen, Bjoern

    2009-02-13

    This work focuses on the Heusler alloy Co{sub 2}MnSi, a ferromagnetic half-metal. The experimental verification of the theoretically predicted band gap in the minority spin channel is still lacking. Previous studies have shown that structural disorder has a crucial impact on the electronic properties of half-metals. Defect-induced states may appear at the Fermi energy in the spin-down-band and decrease the spin polarization. Furthermore, heterostructures may show interface states reducing (dramatically) the spin polarization of tunneling or injection currents. Both aspects are investigated with calculations in the framework of density functional theory. The first part of this work adresses the influence of atomic defects on the electronic and magnetic properties of Co{sub 2}MnSi. Investigations of antisites, antistructure pairs and vacancies show that especially Co atoms at Mn or Si sites and Mn atoms at Co sites lead to dramatic deviations from the properties of the ideal compound. Co based defect states are a serious threat for the half-metallicity. Based on these results in the second part Co{sub 2-x}Mn{sub 1+x}Si (-1alloy where only the Co-Mn interactions are taken into account. Two separate cluster expansions (one for the formation energy ECE and one for the total spin moment MCE) that are parametrized with ab initio data are established. With the ECE several new ground states are predicted, with one of them (Co{sub 2}Mn{sub 4}Si{sub 2}) also having a band gap. The well-known Slater-Pauling rule for stochiometric Heusler alloys can be expanded to non-stochiometric Mn-rich compositions. With this new Slater-Pauling rule and the MCE a large region of potentially half-metallic Mn-rich compositions is identified. Monte Carlo simulations show that Co{sub 2}MnSi with ideal or slightly deviating ({+-}2%) stochiometry is nearly perfectly ordered. The Mn-rich structures are not thermally stable but decompose into Co{sub 2}MnSi and

  2. Structural, electronic, magnetic and optical properties of Ni,Ti/Al-based Heusler alloys. A first-principles approach

    Energy Technology Data Exchange (ETDEWEB)

    Adebambo, Paul O. [Univ. of Agriculture. Abeokuta (Nigeria). Dept. of Physics; McPherson Univ., Abeokuta (Nigeria). Dept. of Physical and Computer Sciences; Adetunji, Bamidele I. [Univ. of Agriculture. Abeokuta (Nigeria). Dept. of Physics; Bells Univ. of Technology, Oto (Nigeria). Dept. of Mathematics; Olowofela, Joseph A. [Univ. of Agriculture. Abeokuta (Nigeria). Dept. of Physics; Oguntuase, James A. [Univ. of Agriculture. Abeokuta (Nigeria). Dept. of Mathematics; Adebayo, Gboyega A. [Univ. of Agriculture. Abeokuta (Nigeria). Dept. of Physics; Abdus Salam International Centre for Theoretical Physics, Trieste (Italy)

    2016-05-01

    In this work, detailed first-principles calculations within the generalised gradient approximation (GGA) of electronic, structural, magnetic, and optical properties of Ni,Ti, and Al-based Heusler alloys are presented. The lattice parameter of C1{sub b} with space group F anti 43m (216) NiTiAl alloys is predicted and that of Ni{sub 2}TiAl is in close agreement with available results. The band dispersion along the high symmetry points W→L→Γ→X→W→K in Ni{sub 2}TiAl and NiTiAl Heusler alloys are also reported. NiTiAl alloy has a direct band gap of 1.60 eV at Γ point as a result of strong hybridization between the d state of the lower and higher valence of both the Ti and Ni atoms. The calculated real part of the dielectric function confirmed the band gap of 1.60 eV in NiTiAl alloys. The present calculations revealed the paramagnetic state of NiTiAl. From the band structure calculations, Ni{sub 2}TiAl with higher Fermi level exhibits metallic properties as in the case of both NiAl and Ni{sub 3}Al binary systems.

  3. Ab initio study of effect of Co substitution on the magnetic properties of Ni and Pt-based Heusler alloys

    Energy Technology Data Exchange (ETDEWEB)

    Roy, Tufan, E-mail: tufanroyburdwan@gmail.com [Theory and Simulations Lab, HRDS, Raja Ramanna Centre for Advanced Technology, Indore 452013 (India); Homi Bhabha National Institute, Training School Complex, Anushaktinagar, Mumbai 400094 (India); Chakrabarti, Aparna [Theory and Simulations Lab, HRDS, Raja Ramanna Centre for Advanced Technology, Indore 452013 (India); Homi Bhabha National Institute, Training School Complex, Anushaktinagar, Mumbai 400094 (India)

    2017-04-25

    Using density functional theory based calculations, we have carried out in-depth studies of effect of Co substitution on the magnetic properties of Ni and Pt-based shape memory alloys. We show the systematic variation of the total magnetic moment, as a function of Co doping. A detailed analysis of evolution of Heisenberg exchange coupling parameters as a function of Co doping has been presented here. The strength of RKKY type of exchange interaction is found to decay with the increase of Co doping. We calculate and show the trend, how the Curie temperature of the systems vary with the Co doping. - Highlights: • We discuss the effects of Co doping on magnetic properties of Ni/Pt based Heusler alloys. • Indirect RKKY interaction is maximum for shape memory alloy like systems. • We predict Pt{sub 2}MnSn as a probable ferromagnetic shape memory alloy.

  4. Local moments and electronic correlations in Fe-based Heusler alloys: Kα x-ray emission spectra measurements

    Energy Technology Data Exchange (ETDEWEB)

    Svyazhin, Artem, E-mail: svyazhin@imp.uran.ru [M.N. Mikheev Institute of Metal Physics, Russian Academy of Sciences – Ural Division, 620990 Yekaterinburg (Russian Federation); Kurmaev, Ernst; Shreder, Elena; Shamin, Sergey [M.N. Mikheev Institute of Metal Physics, Russian Academy of Sciences – Ural Division, 620990 Yekaterinburg (Russian Federation); Sahle, Christoph J. [ESRF – The European Synchrotron, CS40220, 38043 Grenoble Cedex 9 (France)

    2016-09-15

    Heusler alloys are a property-rich class of materials, intensively investigated today from both theoretical and real-world application points of view. In this paper, we attempt to shed light on the role of electronic correlations in the Fe{sub 2}MeAl group (where Me represents all 3d elements from Ti to Ni) of Heusler alloys. For this purpose, we have investigated the local moments of iron by means of the x-ray emission spectroscopy technique. To obtain numerical values of local moments, the Kα-FWHM method has been employed for the first time. In every compound of the group, the presence of a local moment on the Fe atom was detected. As has been revealed, the values of these moments are temperature-independent, pointing to an insufficiency of a pure itinerant approach to magnetism in these alloys. We also comprehensively compare the usage of Kβ main lines and Kα spectra as tools for the probing of local moments and point out the significant advantages of the latter. - Highlights: • Local spin moments of iron in Fe{sub 2}MeAl (Me = Ti … Ni) Heusler alloys were investigated by means of x-ray emission spectroscopy. • Independence of the local moments from temperature confirms their localized nature. • A local moment value of iron in Fe{sub 2}MeAl raises with the atomic number of element Me. • The applicability of the Kα x-ray emission line for extracting local moment values of 3d elements was established.

  5. Theoretical investigation of new Heusler alloys Ru{sub 2}VGa{sub 1−x}Al{sub x}

    Energy Technology Data Exchange (ETDEWEB)

    Abbassa, Hamza [Département de Physique, Université de Abdelhamid Ibn Badis de Mostaganem, Mostaganem (Algeria); Laboratoire de Physique des Couches Minces et Matériaux pour l’Electronique (LPC2ME), Université d’Oran, Es-Senia, Oran (Algeria); Hadjri-Mebarki, Soria [Laboratoire de Physique des Couches Minces et Matériaux pour l’Electronique (LPC2ME), Université d’Oran, Es-Senia, Oran (Algeria); Amrani, Bouhalouane, E-mail: amrani.bouhalouane@univ-oran.dz [Laboratoire de Physique des Couches Minces et Matériaux pour l’Electronique (LPC2ME), Université d’Oran, Es-Senia, Oran (Algeria); Belaroussi, Tayeb [Département de Physique, Université de Abdelhamid Ibn Badis de Mostaganem, Mostaganem (Algeria); Laboratoire de Physique de Plasmas des Matériaux Conducteur et leur Applications (LPPMCA), Université d’USTOMB, Oran (Algeria); Driss Khodja, Kouider [Laboratoire de Physique des Couches Minces et Matériaux pour l’Electronique (LPC2ME), Université d’Oran, Es-Senia, Oran (Algeria); Aubert, Pascal [Institut d’Electronique Fondamentale, Université Paris-Sud – CNRS, Orsay 91405 (France)

    2015-07-15

    Highlights: • Electronic and thermodynamic properties of new Heusler alloys Ru{sub 2}VGa{sub 1−x}Al{sub x} (x = 0, 0.25, 0.50, 0.75, and 1.00) are studied. • Elastic parameters and stability of Ru{sub 2}VGa{sub 1−x}Al{sub x} alloys. • A linear behavior of the lattice parameter, bulk modulus, elastic constants and Debye temperature on x has been observed. - Abstract: Results of first-principles full-potential linearized augmented plane wave calculations of elastic and related electronic and thermodynamic properties of the quaternary Heusler alloys Ru{sub 2}VAl{sub x}Ga{sub 1−x} (x = 0, 0.25, 0.5, 0.75, 1) are presented. These materials were found to have the L2{sub 1} structure for all concentrations. The agreement between the theoretical and experimental lattice parameters for both Ru{sub 2}VAl and Ru{sub 2}VGa at various temperatures was found to be satisfactory. Our results provide predictions for the remaining mixed more» Heusler alloys Ru{sub 2}VAl{sub x}Ga{sub 1−x} (0 < x < 1) for which no direct experimental or theoretical data are presently available. In their equilibrium L2{sub 1} structure, all concentrations are non-magnetic metals. A linear variation of the lattice parameter, bulk modulus, elastic constants and Debye temperature has been observed with x.

  6. sup 3 He neutron polarising filters -- theoretical comparison with supermirrors and Heusler alloy polarisers

    CERN Document Server

    Cussen, L D; Hicks, T J

    2000-01-01

    There is currently intense interest in the development of gaseous sup 3 He neutron polarising transmission filters. The key areas of development are increasing the currently achievable levels of nuclear spin polarisation, pi, within the sup 3 He gas and improving the reliability of the devices. Recent work has identified 'quality factors' which can be used to determine the optimum thickness of such filters under various experimental conditions. The best achievable quality factor for a sup 3 He polariser with a given pi is determined. It is demonstrated that the optimum filter thickness depends only weakly on pi and is always approximately given by the dimensionless expression rho sigma lambda t=3.4 where rho is the density of sup 3 He atoms in the filter, sigma is the absorption cross section at a wavelength of 1 A, lambda is the neutron wavelength in A and t is the filter thickness. Quality factors are calculated for existing types of neutron polariser (supermirrors and Heusler alloy monochromators) as a fun...

  7. Structural, transport, magnetic, magnetocaloric properties and critical analysis of Ni-Co-Mn-Ga Heusler alloys

    Science.gov (United States)

    Arumugam, S.; Devarajan, U.; Esakki Muthu, S.; Singh, Sanjay; Thiyagarajan, R.; Raja, M. Manivel; Rama Rao, N. V.; Banerjee, Alok

    2017-11-01

    In this work, we have investigated structural, transport, magnetic, magnetocaloric (MC) properties and critical exponents analysis of the (Ni2.1-xCox)Mn0.9 Ga (x = 0, 0.04, 0.12 and 0.2) Heusler alloys. For all compositions, cubic austenite (A) phase with metallic character is observed at room temperature (RT). With increasing of Co content, magnitude of resistivity decreases, whereas residual resistivity (ρ0) and electron scattering factor (A) increases linearly. Magnetic measurements exhibit that ferromagnetic (FM) Curie temperature (TCA) increases towards RT by increasing Co concentration. All samples show conventional MC and maximum magnetic entropy change (ΔSMpeak) of -2.8 Jkg-1 K-1 is observed for x = 0.12 at 147 K under 5 T. Further, hysteresis is observed between cooling and warming cycles around FM-PM (TCA) transition in x = 0, 0.04 samples, which suggests that first order nature of transition. However, there is no hysteresis across TCA for x = 0.12 and 0.2 samples suggesting second-order nature of the transition. The critical exponents are calculated for x = 0.12 sample around TCA using Arrott plot and Kouvel-Fisher method, the estimated critical exponents are found closer to the mean-field model reveals the long range ferromagnetic ordering in this composition.

  8. Perpendicular magnetic anisotropy in Fe2Cr1 - xCoxSi Heusler alloy

    Science.gov (United States)

    Wang, Yu-Pu; Qiu, Jin-Jun; Lu, Hui; Ji, Rong; Han, Gu-Chang; Teo, Kie-Leong

    2014-12-01

    Perpendicular magnetic anisotropy (PMA) was achieved in annealed Fe2Cr1 - xCoxSi (FCCS) Heusler alloys with different Co compositions x. The Co composition is varied to tune the Fermi level in order to achieve both higher spin polarization and better thermal stability. The PMA is thermally stable up to 400 oC for FCCS with x = 0, 0.3, 0.5 and 350 oC for FCCS with x = 0.7, 0.9, 1. The thickness of FCCS films with PMA ranges from 0.6 to 1.2 nm. The annealing temperature and FCCS thickness are found to greatly affect the PMA. The magnetic anisotropy energy density KU is 2.8  ×  106 erg cm-3 for 0.8 nm Fe2CrSi, and decreases as the Co composition x increases, suggesting that the PMA induced at the FCCS/MgO interface is dominated by the contribution of Fe atoms. There is a trade-off between high spin polarization and strong PMA by adjusting the Co composition.

  9. Thickness dependencies of structural and magnetic properties of cubic and tetragonal Heusler alloy bilayer films

    Science.gov (United States)

    Ranjbar, R.; Suzuki, K. Z.; Sugihara, A.; Ando, Y.; Miyazaki, T.; Mizukami, S.

    2017-07-01

    The thickness dependencies of the structural and magnetic properties for bilayers of cubic Co-based Heusler alloys (CCHAs: Co2FeAl (CFA), Co2FeSi (CFS), Co2MnAl (CMA), and Co2MnSi (CMS)) and D022-MnGa were investigated. Epitaxy of the B2 structure of CCHAs on a MnGa film was achieved; the smallest thickness with the B2 structure was found for 3-nm-thick CMS and CFS. The interfacial exchange coupling (Jex) was antiferromagnetic (AFM) for all of the CCHAs/MnGa bilayers except for unannealed CFA/MnGa samples. A critical thickness (tcrit) at which perpendicular magnetization appears of approximately 4-10 nm for the CMA/MnGa and CMS/MnGa bilayers was observed, whereas this thickness was 1-3 nm for the CFA/MnGa and CFS/MnGa films. The critical thickness for different CCHAs materials is discussed in terms of saturation magnetization (Ms) and the Jex .

  10. Chemical Potential Evaluation of Thermoelectric and Mechanical Properties of Zr2CoZ (Z = Si, Ge) Heusler Alloys

    Science.gov (United States)

    Yousuf, Saleem; Gupta, Dinesh C.

    2017-12-01

    The electronic, mechanical and thermoelectric properties of Zr2CoZ (Z = Si, Ge) Heusler alloys are investigated by the full-potential linearized augmented plane wave method. Using the Voigt-Reuss approximation, we calculated the various elastic constants, the shear and Young's moduli, and Poisson's ratio which predict the ductile nature of the alloys. Thermoelectric coefficients viz., Seebeck, electrical conductivity and figure of merit show Zr2CoZ alloys as n-type thermoelectric materials showing a linearly increasing Seebeck coefficient with temperature mainly because of the existence of almost flat conduction bands along L to D directions of a high symmetry Brillouin zone. The efficiency of conversion was measured as the figure of merit by taking into effect the lattice thermal part that achieves an upper-limit of 0.14 at 1200 K which may favour their use for waste heat recovery at higher temperatures.

  11. First-principles investigations of electronic, magnetic and thermodynamic properties of Heusler alloy Co{sub 2}Mn{sub 1−x}Ti{sub x}Sn

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Lu [Department of Physics, Nanjing University of Information Science and Technology, Nanjing 210044 (China); Zhu, Xingfeng, E-mail: zxf_physics@163.com [Department of Physics, Nanjing Normal University, Nanjing 210023 (China)

    2016-09-15

    Using first-principles density functional theory based method we have investigated the electronic, magnetic and thermodynamic properties of Heusler alloy Co{sub 2}Mn{sub 1−x}Ti{sub x}Sn. From analysis of elastic constants, we find that the cubic L2{sub 1} phase is stable and all the alloys prone to ductility for Co{sub 2}Mn{sub 1−x}Ti{sub x}Sn alloy. The total magnetic moment decreases with increasing x, in agreement with the generalized Slater-Pauling rule. Band structure calculations show that the minority DOS exhibits a gap around Fermi level confirming the half-metallic character of the material for all the concentrations studied and the Fermi level can be shifted within the minority spin gap by changing the Ti concentration. The Curie temperature T{sub C} estimated from the effective exchange constant J{sub 0} decreases with x, and qualitatively accords with the experimental values. Finally, by using a quasi-harmonic Debye model, the temperature dependent bulk modulus, heat capacity and coefficient of thermal expansion have been obtained in the present work. - Highlights: • The cubic L2{sub 1} phase is stable and all the alloys prone to ductility from analysis of elastic constants. • The total magnetic moments are in agreement with the generalized Slater-Pauling line. • The Fermi level can be shifted within the gap by changing the Ti concentration. • The T{sub C} estimated from J{sub 0} qualitatively accords with the experimental values. • The temperature dependent bulk modulus, heat capacity and coefficient of thermal expansion have been obtained.

  12. Density functional study of elastic and vibrational properties of the Heusler-type alloys Fe2VAl and Fe2VGa

    DEFF Research Database (Denmark)

    Kanchana, V.; Vaitheeswaran, G.; Ma, Yanming

    2009-01-01

    The structural and elastic properties as well as phonon-dispersion relations of the Heusler-type alloys Fe2VAl and Fe2VGa are computed using density functional and density-functional perturbation theory within the generalized-gradient approximation. The calculated equilibrium lattice constants...

  13. Effect of swap disorder on the physical properties of the quaternary Heusler alloy PdMnTiAl: a first-principles study

    Directory of Open Access Journals (Sweden)

    Guanhua Qin

    2017-07-01

    Full Text Available Heusler alloys crystallize in a close-packed cubic structure, having a four-atom basis forming a face-centred cubic lattice. By selecting different composite elements, Heusler alloys provide a large family of members for frontier research of spintronics and magnetic materials and devices. In this paper, the structural, electronic and magnetic properties of a novel quaternary Heusler alloy, PdMnTiAl, have been investigated using a first-principles computational materials calculation. It was found that the stable ordered structure is a non-magnetic Y-type1, in good agreement with the Slater–Pauling rule. From the band structure and the density of states, it is predicted that this Y-type1 configuration is a new gapless semi-metal material. Furthermore, it was discovered that the Pd–Mn swap-disordered structure is more stable than the Y-type1 structure. The present work provides a guide for experiments to synthesize and characterize this Heusler alloy.

  14. Unveiling the Mechanism for the Split Hysteresis Loop in Epitaxial Co2Fe1-xMnxAl Full-Heusler Alloy Films

    National Research Council Canada - National Science Library

    Tao, X D; Wang, H L; Miao, B F; Sun, L; You, B; Wu, D; Zhang, W; Oepen, H P; Zhao, J H; Ding, H F

    2016-01-01

    Utilizing epitaxial Co2Fe1-xMnxAl full-Heusler alloy films on GaAs (001), we address the controversy over the analysis for the split hysteresis loop which is commonly found in systems consisting of both uniaxial and fourfold anisotropies...

  15. Structural, electronic and magnetic properties of Fe{sub 2}-based full Heusler alloys: A first principle study

    Energy Technology Data Exchange (ETDEWEB)

    Dahmane, F., E-mail: fethallah05@gmail.com [Département de SM, Institue des sciences et des technologies, Centre universitaire de Tissemsilt, 38000, Tissemsilt (Algeria); Modelling and Simulation in Materials Science Laboratory, Physics Department, University of Sidi Bel-Abbes, 22000 Sidi Bel-Abbes (Algeria); Mogulkoc, Y. [Department of Engineering Physics, Ankara University, Ankara (Turkey); Doumi, B.; Tadjer, A. [Modelling and Simulation in Materials Science Laboratory, Physics Department, University of Sidi Bel-Abbes, 22000 Sidi Bel-Abbes (Algeria); Khenata, R. [Laboratoire de Physique Quantique de la Matière et de Modélisation Mathématique (LPQ3M), Université de Mascara, 29000 Mascara (Algeria); Bin Omran, S. [Department of Physics and Astronomy, College of Science, King Saud University, P.O Box 2455, Riyadh 11451 (Saudi Arabia); Rai, D.P. [Department of Physics, Pachhunga University College, Aizawl-796001 (India); Murtaza, G. [Materials Modeling Lab, Department of Physics, Islamia College University, Peshawar (Pakistan); Varshney, Dinesh [Materials Science Laboratory, School of Physics, Vigyan Bhavan, Devi Ahilya University, Khandwa Road Campus, Indore 452001 (India)

    2016-06-01

    Using the first-principles density functional calculations, the structural, electronic and magnetic properties of the Fe{sub 2}XAl (X=Cr, Mn, Ni) compounds in both the Hg{sub 2}CuTi and Cu{sub 2}MnAl-type structures were studied by the full-potential linearized augmented plane waves (FP-LAPW) method. The exchange and correlation potential is treated by the generalized-gradient approximation (GGA) where the results show that the Cu{sub 2}MnAl-type structure is energetically more stable than the Hg{sub 2}CuTi-type structure for the Fe{sub 2}CrAl and Fe{sub 2}MnAl compounds at the equilibrium volume. The full Heusler compounds Fe{sub 2}XAl (X=Cr, Mn) are half-metallic in the Cu{sub 2}MnAl-type structure. Fe{sub 2}NiAl has a metallic character in both CuHg{sub 2}Ti and AlCu{sub 2}Mn-type structures. The total magnetic moments of the Fe{sub 2}CrAl and Fe{sub 2}MnAl compounds are 1.0 and 2.0 μ{sub B}, respectively, which are in agreement with the Slater–Pauling rule M{sub tot}=Z{sub tot}− 24.

  16. Structural and magnetic properties of epitaxial Heusler alloy Fe2Cr0.5Co0.5Si

    Science.gov (United States)

    Wang, Yu-Pu; Han, Gu-Chang; Lu, Hui; Qiu, Jinjun; Yap, Qi-Jia; Teo, Kie-Leong

    2014-05-01

    This paper reports the study of structural and magnetic properties of Heusler alloy Fe2Cr0.5Co0.5Si (FCCS) thin film and its tunnel magnetoresistance (TMR) effect. The smooth quaternary Heusler alloy FCCS film with surface roughness of rms value of 0.25 nm measured by atomic force microscopy and partial L21 phase was obtained by magnetron sputtering at room temperature followed by in-situ annealing at 400 °C. The saturation magnetization and coercivity of FCCS are 410 emu/cm3 and 20 Oe, respectively. The magnetic tunnel junctions (MTJs) using FCCS as free layer were studied in detail as a function of post-annealing temperature. A TMR ratio of 15.6% has been achieved with 300 °C post-annealing. This is about twice the highest TMR ratio obtained in MTJs using Fe2CrSi. The enhancement of TMR ratio can be attributed to the successful tuning of the Fermi level of Fe2CrSi close to the center of the minority band gap by Co-doping.

  17. Enhanced current-perpendicular-to-plane giant magnetoresistance effect in half-metallic NiMnSb based nanojunctions with multiple Ag spacers

    Energy Technology Data Exchange (ETDEWEB)

    Wen, Zhenchao; Yamamoto, Tatsuya [Institute for Materials Research, Tohoku University, Sendai 980-8577 (Japan); Kubota, Takahide; Takanashi, Koki [Institute for Materials Research, Tohoku University, Sendai 980-8577 (Japan); Center for Spintronics Research Network (CSRN), Tohoku University, Sendai 980-8577 (Japan)

    2016-06-06

    Current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) heterostructure devices using half-metallic NiMnSb Heusler alloy electrodes with single, dual, and triple Ag spacers were fabricated. The NiMnSb alloy films and Ag spacers show (001) epitaxial growth in all CPP-GMR multilayer structures. The dual-spacer CPP-GMR nanojunction exhibited an enhanced CPP-GMR ratio of 11% (a change in the resistance-area product, ΔRA, of 3.9 mΩ μm{sup 2}) at room temperature, which is approximately twice (thrice) of 6% (1.3 mΩ μm{sup 2}) in the single-spacer device. The enhancement of the CPP-GMR effects in the dual-spacer devices could be attributed to improved interfacial spin asymmetry. Moreover, it was observed that the CPP-GMR ratios increased monotonically as the temperatures decreased. At 4.2 K, a CPP-GMR ratio of 41% (ΔRA = 10.5 mΩ μm{sup 2}) was achieved in the dual-spacer CPP-GMR device. This work indicates that multispacer structures provide an efficient enhancement of CPP-GMR effects in half-metallic material-based CPP-GMR systems.

  18. The effects of substituting Ag for In on the magnetoresistance and magnetocaloric properties of Ni-Mn-In Heusler alloys

    Directory of Open Access Journals (Sweden)

    Sudip Pandey

    2016-05-01

    Full Text Available The effect of substituting Ag for In on the structural, magnetocaloric, and thermomagnetic properties of Ni50Mn35In15−xAgx (x = 0.1, 0.2, 0.5, and 1 Heusler alloys was studied. The magnitude of the magnetization change at the martensitic transition temperature (TM decreased with increasing Ag concentration. Smaller magnetic entropy changes (ΔSM were observed for the alloys with larger Ag concentrations and the martensitic transition shifted to higher temperature. A shift of TM by about 25 K to higher temperature was observed for an applied hydrostatic pressure of P = 6.6 kbar with respect to ambient pressure. A large drop in resistivity was observed for large Ag concentration. The magnetoresistance was dramatically suppressed due to an increase in the disorder of the system with increasing Ag concentration. Possible mechanisms responsible for the observed behavior are discussed.

  19. Magnetostructural martensitic transformations with large volume changes and magneto-strains in all-d-metal Heusler alloys

    Energy Technology Data Exchange (ETDEWEB)

    Wei, Z. Y.; Liu, E. K., E-mail: ekliu@iphy.ac.cn; Xi, X. K.; Zhang, H. W.; Wang, W. H.; Wu, G. H. [State Key Laboratory for Magnetism, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Li, Y. [State Key Laboratory for Magnetism, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); School of Materials Science and Engineering, Hebei University of Technology, Tianjin 300130 (China); Han, X. L.; Du, Z. W. [National Center of Analysis and Testing for Nonferrous Metals and Electronic Materials, General Research Institute for Nonferrous Metals, Beijing 100088 (China); Luo, H. Z.; Liu, G. D. [School of Materials Science and Engineering, Hebei University of Technology, Tianjin 300130 (China)

    2016-08-15

    The all-d-metal Mn{sub 2}-based Heusler ferromagnetic shape memory alloys Mn{sub 50}Ni{sub 40−x}Co{sub x}Ti{sub 10} (x = 8 and 9.5) are realized. With a generic comparison between d-metal Ti and main-group elements in lowering the transformation temperature, the magnetostructural martensitic transformations are established by further introducing Co to produce local ferromagnetic Mn-Co-Mn configurations. A 5-fold modulation and (3, −2) stacking of [00 10] of martensite are determined by X-ray diffraction and HRTEM analysis. Based on the transformation, a large magneto-strain of 6900 ppm and a large volume change of −2.54% are observed in polycrystalline samples, which makes the all-d-metal magnetic martensitic alloys of interest for magnetic/pressure multi-field driven applications.

  20. Magnetostructural phase transition in off-stoichiometric Ni–Mn–In Heusler alloy ribbons with low In content

    Energy Technology Data Exchange (ETDEWEB)

    González-Legarreta, L. [Dept. de Física, Universidad de Oviedo, Calvo Sotelo s/n, 33007 Oviedo (Spain); González-Alonso, D. [Facultat de Física, Departament d’Estructura i Constituents de la Matèria, Universitat de Barcelona, Diag. 647, E-08028 Barcelona (Spain); Rosa, W.O. [Centro Brasileiro de Pesquisas Físicas, Rua Dr. Xavier Sigaud, 150 Urca., 22290-180 Rio de Janeiro, RJ (Brazil); Caballero-Flores, R. [Dept. de Física, Universidad de Oviedo, Calvo Sotelo s/n, 33007 Oviedo (Spain); Suñol, J.J. [Universidad de Girona, Montilivi edifici PII, Lluís Santaló s/n. 17003 Girona (Spain); González, J. [Department of Materials Physics, Faculty of Chemistry, University of the Basque Country, 20018 San Sebastian (Spain); Hernando, B. [Dept. de Física, Universidad de Oviedo, Calvo Sotelo s/n, 33007 Oviedo (Spain)

    2015-06-01

    We report features of microstructure, martensitic transformation, magnetic properties and magnetocaloric effect in three off-stoichiometric Ni{sub 45}Mn{sub 44}In{sub 11}, Ni{sub 47}Mn{sub 41}In{sub 12}and Ni{sub 48}Mn{sub 39}In{sub 13} (nominal-compositions) alloys ribbons. They were selected in the 7.8alloys near room-temperature. Although the real composition is shifted from nominal one in each sample, its influence on all here studied properties at the temperature range of 50–400 K is analyzed. Especially, the role played by Ni content in the decrease of magnetization observed in two alloys with respect to the third one with the lowest e/a. Ni content effect on the antiferromagnetic interaction present in the martensitic phase of the alloys ribbons is also evidenced. - Highlights: • Three off-stoiquiometric Ni–Mn–In Heusler alloys ribbons with low In content were prepared by melt spinning. • A drastic decrease in magnetization for the two alloys with e/a=7.9 and 8.0 in comparison with the alloy showing e/a=7.8 with less Ni content. • High spin freezing temperature around 300 K for the two alloys with e/a=7.9 and 8.0. • Exchange bias field at 5 K about 1.3 kOe and 1.8 kOe for alloys with a high at% of Ni, but 0.012 kOe for the ribbon with less Ni content. • Magnetocaloric effect enhanced for the alloy with less Ni content.

  1. Effect of short-range order on magnetic and transport properties of Fe2MnGa Heusler alloy films

    Science.gov (United States)

    Kudryavtsev, Y. V.; Melnyk, A. K.; Trachevskyi, V. V.; Gościańska, I.; Dubowik, J.

    2017-11-01

    Fe56Mn20Ga24, Fe46Mn35Ga19 and Fe39Mn25Ga36 Heusler alloy (HA) films are investigated. It is shown that as-deposited Fe-Mn-Ga films are fine crystalline with a body-centered cubic (BCC) structure. Annealing of the films leads to the formation of a face-centered cubic (FCC) structure. The BCC to FCC transformation results in a drastic increase in the magnetization, the Curie temperature as well as in a change of the sign of temperature coefficient of resistivity from negative to positive. These effects are discussed in terms of band structures of L21 and L12 phases of stoichiometric Fe2MnGa HA.

  2. Structural and magnetic properties of ion beam sputtered Co{sub 2}FeAl full Heusler alloy thin films

    Energy Technology Data Exchange (ETDEWEB)

    Husain, Sajid; Chaudhary, Sujeet, E-mail: sujeetc@physics.iitd.ac.in [Thin Film Laboratory (Spintronics), Indian Institute of Technology Delhi (India); Kumar, Ankit; Svedlindh, Peter [Department of Engineering Sciences, Uppsala University Sweden, 75121 Uppsala (Sweden)

    2016-05-06

    Co{sub 2}FeAl full Heusler alloy thin films grown at different temperatures on Si(100) substrates using ion beam sputtering system have been investigated. X-ray diffraction (XRD) patterns revealed the A2 disordered phase in these films. The deduced lattice parameter slightly increases with increase in the growth temperature. The saturation magnetization it is found to increase with increase in growth temperature. The magnetic anisotropy has been studied using angle dependent magneto-optical Kerr effect. In the room temperature deposited film, the combination of cubic and uniaxial anisotropy have been observed with weak in-plane uniaxial anisotropy which increases with growth temperature. The uniaxial anisotropy is attributed to the anisotropic interfacial bonding in these Co{sub 2}FeAl /Si(100) heterostructures.

  3. Structural and magnetic properties of ion beam sputtered Co2FeAl full Heusler alloy thin films

    Science.gov (United States)

    Husain, Sajid; Kumar, Ankit; Chaudhary, Sujeet; Svedlindh, Peter

    2016-05-01

    Co2FeAl full Heusler alloy thin films grown at different temperatures on Si(100) substrates using ion beam sputtering system have been investigated. X-ray diffraction (XRD) patterns revealed the A2 disordered phase in these films. The deduced lattice parameter slightly increases with increase in the growth temperature. The saturation magnetization it is found to increase with increase in growth temperature. The magnetic anisotropy has been studied using angle dependent magneto-optical Kerr effect. In the room temperature deposited film, the combination of cubic and uniaxial anisotropy have been observed with weak in-plane uniaxial anisotropy which increases with growth temperature. The uniaxial anisotropy is attributed to the anisotropic interfacial bonding in these Co2FeAl /Si(100) heterostructures.

  4. Anomalous Hall effect in ion-beam sputtered Co2FeAl full Heusler alloy thin films

    Science.gov (United States)

    Husain, Sajid; Kumar, Ankit; Akansel, Serkan; Svedlindh, Peter; Chaudhary, Sujeet

    2017-11-01

    Investigations of temperature dependent anomalous Hall effect and longitudinal resistivity in Co2FeAl (CFA) thin films grown on Si(1 0 0) at different substrate temperature Ts are reported. The scaling of the anomalous Hall conductivity (AHC) and the associated phenomenological mechanisms (intrinsic and extrinsic) are analyzed vis-à-vis influence of Ts. The intrinsic contribution to AHC is found to be dominating over the extrinsic one. The appearance of a resistivity minimum at low temperature necessitates the inclusion of quantum corrections on account of weak localization and electron-electron scattering effects whose strength reduces with increase in Ts. The study establishes that the optimization of Ts plays an important role in the improvement of atomic ordering which indicates the higher strength of spin-orbit coupling and leads to the dominant intrinsic contribution to AHC in these CFA full Heusler alloy thin films.

  5. L21 and XA Ordering Competition in Hafnium-Based Full-Heusler Alloys Hf2VZ (Z = Al, Ga, In, Tl, Si, Ge, Sn, Pb

    Directory of Open Access Journals (Sweden)

    Xiaotian Wang

    2017-10-01

    Full Text Available For theoretical designing of full-Heusler based spintroinc materials, people have long believed in the so-called Site Preference Rule (SPR. Very recently, according to the SPR, there are several studies on XA-type Hafnium-based Heusler alloys X2YZ, i.e., Hf2VAl, Hf2CoZ (Z = Ga, In and Hf2CrZ (Z = Al, Ga, In. In this work, a series of Hf2-based Heusler alloys, Hf2VZ (Z = Al, Ga, In, Tl, Si, Ge, Sn, Pb, were selected as targets to study the site preferences of their atoms by first-principle calculations. It has been found that all of them are likely to exhibit the L21-type structure instead of the XA one. Furthermore, we reveal that the high values of spin-polarization of XA-type Hf2VZ (Z = Al, Ga, In, Tl, Si, Ge, Sn, Pb alloys have dropped dramatically when they form the L21-type structure. Also, we prove that the electronic, magnetic, and physics nature of these alloys are quite different, depending on the L21-type or XA-type structures.

  6. L2₁ and XA Ordering Competition in Hafnium-Based Full-Heusler Alloys Hf₂VZ (Z = Al, Ga, In, Tl, Si, Ge, Sn, Pb).

    Science.gov (United States)

    Wang, Xiaotian; Cheng, Zhenxiang; Wang, Wenhong

    2017-10-20

    For theoretical designing of full-Heusler based spintroinc materials, people have long believed in the so-called Site Preference Rule (SPR). Very recently, according to the SPR, there are several studies on XA-type Hafnium-based Heusler alloys X₂YZ, i.e., Hf₂VAl, Hf₂CoZ (Z = Ga, In) and Hf₂CrZ (Z = Al, Ga, In). In this work, a series of Hf₂-based Heusler alloys, Hf₂VZ (Z = Al, Ga, In, Tl, Si, Ge, Sn, Pb), were selected as targets to study the site preferences of their atoms by first-principle calculations. It has been found that all of them are likely to exhibit the L2₁-type structure instead of the XA one. Furthermore, we reveal that the high values of spin-polarization of XA-type Hf₂VZ (Z = Al, Ga, In, Tl, Si, Ge, Sn, Pb) alloys have dropped dramatically when they form the L2₁-type structure. Also, we prove that the electronic, magnetic, and physics nature of these alloys are quite different, depending on the L2₁-type or XA-type structures.

  7. Fate of half-metallicity near interfaces: the case of NiMnSb/MgO and NiMnSi/MgO.

    Science.gov (United States)

    Zhang, Rui-Jing; Eckern, Ulrich; Schwingenschlögl, Udo

    2014-08-27

    The electronic and magnetic properties of the interfaces between the half-metallic Heusler alloys NiMnSb, NiMnSi, and MgO have been investigated using first-principles density-functional calculations with projector augmented wave potentials generated in the generalized gradient approximation. In the case of the NiMnSb/MgO (100) interface, the half-metallicity is lost, whereas the MnSb/MgO contact in the NiMnSb/MgO (100) interface maintains a substantial degree of spin polarization at the Fermi level (∼60%). Remarkably, the NiMnSi/MgO (111) interface shows 100% spin polarization at the Fermi level, despite considerable distortions at the interface, as well as rather short Si/O bonds after full structural optimization. This behavior markedly distinguishes NiMnSi/MgO (111) from the corresponding NiMnSb/CdS and NiMnSb/InP interfaces.

  8. Fate of half-metallicity near interfaces: The case of NiMnSb/MgO and NiMnSi/MgO

    KAUST Repository

    Zhang, Ruijing

    2014-08-27

    The electronic and magnetic properties of the interfaces between the half-metallic Heusler alloys NiMnSb, NiMnSi, and MgO have been investigated using first-principles density-functional calculations with projector augmented wave potentials generated in the generalized gradient approximation. In the case of the NiMnSb/MgO (100) interface, the half-metallicity is lost, whereas the MnSb/MgO contact in the NiMnSb/MgO (100) interface maintains a substantial degree of spin polarization at the Fermi level (∼60%). Remarkably, the NiMnSi/MgO (111) interface shows 100% spin polarization at the Fermi level, despite considerable distortions at the interface, as well as rather short Si/O bonds after full structural optimization. This behavior markedly distinguishes NiMnSi/MgO (111) from the corresponding NiMnSb/CdS and NiMnSb/InP interfaces. © 2014 American Chemical Society.

  9. Analysis of the Magnetocaloric Effect in Heusler Alloys: Study of Ni50CoMn36Sn13 by Calorimetric Techniques

    Directory of Open Access Journals (Sweden)

    Elias Palacios

    2015-03-01

    Full Text Available Direct determinations of the isothermal entropy increment, \\(-\\Delta S_T\\, in the Heusler alloy Ni\\(_{50}\\CoMn\\(_{36}\\Sn\\(_{13}\\ on demagnetization gave positive values, corresponding to a normal magnetocaloric effect. These values contradict the results derived from heat-capacity measurements and also previous results obtained from magnetization measurements, which indicated an inverse magnetocaloric effect, but showing different values depending on the technique employed. The puzzle is solved, and the apparent incompatibilities are quantitatively explained considering the hysteresis, the width of the martensitic transition and the detailed protocol followed to obtain each datum. The results show that these factors should be analyzed in detail when dealing with Heusler alloys.

  10. Recent Developments in Half-Metallic Magnetism

    NARCIS (Netherlands)

    Groot, R.A. de; Buschow, K.H.J.

    1986-01-01

    The compound PtMnSb is a half-metallic ferromagnet and its unusual band structure is intimately connected with the high Magneto Optical Kerr Effect (MOKE). In this paper it will be discussed how various types of substitutions can modify this band structure and lead to possible enhancement of the

  11. Perpendicular magnetic anisotropy in nearly fully compensated ferrimagnetic Heusler alloy Mn0.75Co1.25VIn: An ab initio study

    Science.gov (United States)

    Muthui, Zipporah; Musembi, Robinson; Mwabora, Julius; Kashyap, Arti

    2017-11-01

    First principles calculations are reported on perpendicular magnetic anisotropy (PMA) in nearly fully compensated ferrimagnetic Heusler compound Mn0.75Co1.25VIn. The structural, electronic and magnetic properties of Mn2-xCoxVIn Heusler compounds (x = 0.0, 0.25, 0.50, 0.75, 1.0, 1.25, and 1.75) have been investigated using Density Functional theory (DFT) as implemented in the Vienna ab initio simulation package (VASP). The Perdew Burke Ernzerhof parametrization of the generalized gradient approximation (GGA) was used to treat the exchange and correlation in the system. The crystal structure of the compounds with x = 0.75, 1.00 and 1.25 are found to be tetragonally distorted. While the former exhibits inplane magnetocrystalline anisotropy (IMA) energy of 0.035 meV, the latter two exhibit perpendicular magnetocrystalline anisotropy (PMA) energy of 11.700 meV and 96.800 meV respectively. Additionally, the magnetic moments for x = 0.75 and 1.25 are found to be ∼0.5 μB/f.u. while for x = 1.00, it is found to be ∼0 μB/f.u., in agreement with the Slater Pauling rule for half metallic systems. Through Co replacement of Mn in Mn2VIn which is not half metallic at the optimized volume, a composition whose crystal structure is tetragonally distorted is found, which is not only a highly spin polarized nearly fully compensated ferrimagnet but also exhibits PMA.

  12. Magnetocaloric effect in “reduced” dimensions: Thin films, ribbons, and microwires of Heusler alloys and related compounds: Magnetocaloric effect in “reduced” dimensions

    Energy Technology Data Exchange (ETDEWEB)

    Khovaylo, Vladimir V. [National University of Science and Technology MISiS, Moscow 119049 Russia; ITMO University, St. Petersburg 197101 Russia; Rodionova, Valeria V. [National University of Science and Technology MISiS, Moscow 119049 Russia; Innovation Park and Institute of Physics & Technology, Immanuel Kant Baltic Federal University, Kaliningrad 236041 Russia; Shevyrtalov, Sergey N. [Innovation Park and Institute of Physics & Technology, Immanuel Kant Baltic Federal University, Kaliningrad 236041 Russia; Novosad, Val [Materials Science Division, Argonne National Laboratory, Argonne IL 60439 USA

    2014-08-19

    Room temperature magnetic refrigeration is an energy saving and environmentally-friendly technology which has developed rapidly from a basic idea to prototype devices. The performance of magnetic refrigerators crucially depends on the magnetocaloric properties and the geometry of the employed refrigerants. Here we review the magnetocaloric properties of Heusler alloys and related compounds with a high surface to volume ratio such as films, ribbons and microwires, and compare them with their bulk counterparts.

  13. EDITORIAL: Cluster issue on Heusler compounds and devices Cluster issue on Heusler compounds and devices

    Science.gov (United States)

    Felser, Claudia; Hillebrands, Burkard

    2009-04-01

    This is the third cluster issue of Journal Physics D: Applied Physics devoted to half-metallic Heusler compounds and devices utilizing this class of materials. Heusler compounds are named after Fritz Heusler, the owner of a German copper mine, the Isabellenhütte, who discovered this class of materials in 1903 [1]. He synthesized mixtures of Cu2Mn alloys with various main group metals Z = Al, Si, Sn, Sb, which became ferromagnetic despite all constituents being non-magnetic. The recent success story of Heusler compounds began in 1983 with the discovery of the half-metallic electronic structure in NiMnSb [2] and Co2MnZ [3], making these and similar materials, in particular PtMnSb, also useful for magneto-optical data storage media applications due to their high Kerr rotation. The real breakthrough, however, came in 2000 with the observation of a large magnetoresistance effect in Co2Cr0.6Fe0.4Al [4]. The Co2YZ (Y = Ti, Cr, Mn, Fe) compounds are a special class of materials, which follow the Slater-Pauling rule [5], and most of them are half-metallic bulk materials. The electronic structure of Heusler compounds is well understood [6] and Curie temperatures up to 1100 K have been observed [7]. In their contribution to this cluster issue, Thoene et al predict that still higher Curie temperatures can be achieved. A breakthrough from the viewpoint of materials design is the synthesis of nanoparticles of Heusler compounds as reported in the contribution by Basit et al. Nano-sized half- metallic ferromagnets will open new directions for spintronic applications. The challenge, however, is still to produce spintronic devices with well defined interfaces to take advantage of the half-metallicity of the electrodes. Several groups have succeeded in producing excellent tunnel junctions with high magnetoresistance effects at low temperatures and decent values at room temperature [8-11]. Spin-dependent tunnelling characteristics of fully epitaxial magnetic tunnel junctions with a

  14. Half-Metallicity of (001) Film of Fe2CrSi

    Science.gov (United States)

    Fujii, Shinpei; Ishida, Shoji; Asano, Setsuro

    2012-03-01

    On the basis of the electronic structures obtained by first-principles calculations, we have studied the half-metallicity of a (001) film of the Heusler compound Fe2CrSi, which is predicted to be a half-metallic ferromagnet in its bulk. The result shows that a film with a surface consisting of Si and Cr atoms holds a high spin polarization (nearly 100%) and that the atomic disorder between Cr and Si atoms reduces spin polarization, but that the film holds a comparatively high spin polarization of 75%. We also show that, in a film with a surface consisting of Fe atoms, spin polarization decreases drastically from that of the bulk.

  15. Optimizing performance of half-metals at finite temperature

    NARCIS (Netherlands)

    Attema, J. J.; de Wijs, G. A.; de Groot, R. A.

    2007-01-01

    Several aspects of half-metallic magnetism at finite temperature are discussed. Since NiMnSb is the simplest half-metal and the longest known it will be used as an example. Also it is a half-metal with remarkable little on-site Coulomb repulsion. Consequently it is a half-metal that is not notably

  16. Effects of Annealing on the Martensitic Transformation of Ni-Based Ferromagnetic Shape Memory Heusler Alloys and Nanoparticles

    Directory of Open Access Journals (Sweden)

    Tina Fichtner

    2015-03-01

    Full Text Available We report on the effects of annealing on the martensitic phase transformation in the Ni-based Heusler system: Mn50Ni40Sn10 and Mn50Ni41Sn9 powder and Co50Ni21Ga32 nanoparticles. For the powdered Mn50Ni40Sn10 and Mn50Ni41Sn9 alloys, structural and magnetic measurements reveal that post-annealing decreases the martensitic transformation temperatures and increases the transition hysteresis. This might be associated with a release of stress in the Mn50Ni40Sn10 and Mn50Ni41Sn9 alloys during the annealing process. However, in the case of Co50Ni21Ga32 nanoparticles, a reverse phenomenon is observed. X-ray diffraction analysis results reveal that the as-prepared Co50Ni21Ga32 nanoparticles do not show a martensitic phase at room temperature. Post-annealing followed by ice quenching, however, is found to trigger the formation of the martensitic phase. The presence of the martensitic transition is attributed to annealing-induced particle growth and the stress introduced during quenching.

  17. Current perpendicular-to-plane giant magnetoresistance using an L 12 Ag3Mg spacer and Co2Fe0.4Mn0.6Si Heusler alloy electrodes: Spacer thickness and annealing temperature dependence

    Science.gov (United States)

    Kubota, Takahide; Ina, Yusuke; Wen, Zhenchao; Narisawa, Hiroyuki; Takanashi, Koki

    2017-09-01

    Spacer thickness tN and annealing temperature Tanneal dependence of current perpendicular-to-plane giant magnetoresistance effects were investigated in junctions using L 12Ag3Mg spacer and half-metallic Co2Fe0.4Mn0.6Si (CFMS) Heusler alloy electrodes. tN was changed from 2-12 nm and Tanneal was changed from 450 -650°C to promote the chemical ordering of the CFMS electrodes. Concerning the tN dependence, the magnetoresistance (MR) ratio and the change of the areal resistance (Δ R A ) exhibited the maximum values at tN=5 nm . The reasons for the decrease of the MR ratio for tN5 nm were possibly due to an unstable antiparallel magnetization configuration and to the increased occurrence of spin scattering inside the Ag3Mg spacer, respectively. The spin-diffusion length of the Ag3Mg spacer was also estimated using the tN dependence of Δ R A and it was found to be of the order of 10-30 nm. Concerning the Tanneal dependence, Δ R A and the MR ratio exhibited the maximum values at 550°C, which was the optimum point in terms of the degrees of order in the CFMS layers and the Ag3Mg layer, and the (001) orientation of the layered structure. The maximum Δ R A and the intrinsic MR ratio in which parasitic resistance contribution was eliminated were 25 m Ω μ m2 and 63%, respectively, at room temperature.

  18. The influence of chemical disorder enhancement on the martensitic transformation of the Ni{sub 50}Mn{sub 36}Sn{sub 14} Heusler-type alloy

    Energy Technology Data Exchange (ETDEWEB)

    Passamani, E.C., E-mail: edson@cce.ufes.br [Departamento de Fisica, Universidade Federal do Espirito Santo, 29075-910 Vitoria, ES (Brazil); Nascimento, V.P.; Larica, C.; Takeuchi, A.Y. [Departamento de Fisica, Universidade Federal do Espirito Santo, 29075-910 Vitoria, ES (Brazil); Alves, A.L.; Proveti, J.R. [Departamento de Ciencias Matematicas e Naturais, Universidade Federal do Espirito Santo, 29932-540, Sao Mateus, ES (Brazil); Pereira, M.C. [Instituto de Ciencia e Tecnologia, Universidade Federal dos Vales do Jequitinhonha e Mucuri (UFVJM), 39803-371 Teofilo Otoni, Minas Gerais (Brazil); Fabris, J.D. [Departamento de Quimica, UFVJM, 39100-000 Diamantina, Minas Gerais (Brazil)

    2011-07-28

    Highlights: > Chemical disorder affects martensitic transformation in Ni-Mn-Sn Heusler alloys. > Martensitic transition temperature depends on the L21-ferromagnetic fraction. > Grain boundaries induce drastic reduction of magnetization in milled Heusler alloys. > Magnetic properties of the milled Ni50Mn36Sn14 alloy get better after annealing. - Abstract: The effect of chemical disorder over the martensitic phase transformation of the Ni{sub 50}Mn{sub 36}Sn{sub 14} Heusler-type alloy was systematically investigated by performing X-ray diffractometry (DRX), DC magnetization and {sup 57}Fe-doping and {sup 119}Sn-Moessbauer spectroscopy measurements. DRX patterns are characteristics of a L2{sub 1}-type chemically disordered structure, where the presence of this disorder was first evaluated by analyzing the relative intensity of the (1 1 1) DRX reflection, which varies in the case of Fe-doped and practically disappears for the milled samples. In consequence, the magnetic properties of Fe-doped well-milled samples related to the martensitic phase transformation change substantially. 300 K {sup 57}Fe-Moessbauer spectroscopy data suggest that the changes in the magnetic properties related to the martensitic transformation are intrinsically correlated to the ferromagnetic and paramagnetic fractions, which are respectively associated with Fe atoms replacing Mn- and Sn-sites. In the case of milled samples, the drastic reduction of alloy magnetization was explained by the increase of the number of Mn atoms in the shell regions, which have a reduced magnetic moment comparatively to those in the grain cores. The magnetization change and the temperature transition in the martensitic transformation are governed by the grain core. The initial magnetic properties and martensitic transformation can be recovered by a subsequent annealing on the milled sample.

  19. Magnetic properties of Heusler alloy Rh{sub 2}NiGe

    Energy Technology Data Exchange (ETDEWEB)

    Kanomata, T. [Faculty of Engineering, Tohoku Gakuin University, Tagajo 985-8537 (Japan)]. E-mail: kanomata@tjcc.tohoku-gakuin.ac.jp; Adachi, Y. [Faculty of Engineering, Yamagata University, Yonezawa 992-8510 (Japan); Nishihara, H. [Faculty of Science and Technology, Ryukoku University, Otsu 520-2123 (Japan); Fukumoto, H. [Faculty of Science and Technology, Ryukoku University, Otsu 520-2123 (Japan); Yanagihashi, H. [Faculty of Engineering, Tohoku Gakuin University, Tagajo 985-8537 (Japan); Nashima, O. [Faculty of Engineering, Tohoku Gakuin University, Tagajo 985-8537 (Japan); Morita, H. [Faculty of Engineering, Yamagata University, Yonezawa 992-8510 (Japan)

    2006-06-29

    Rh{sub 2}NiGe crystallizes in Heusler L2{sub 1} structure. Precise magnetization measurements have been made on Rh{sub 2}NiGe. The spontaneous magnetic moment at 4.2 K and the Curie temperature T {sub C} are 0.57{mu} {sub B}/f.u. and 113 K, respectively. Below 30 K the decrease in the square of the spontaneous magnetization {sigma} {sub s}(T){sup 2} is proportional to T {sup 2}. However, over a temperature range from 89 K to the Curie temperature the decrease in {sigma} {sub s}(T){sup 2} is proportiona to T {sup 4/3}. The obtained results are analyzed using spin fluctuation theory.

  20. Magnetic properties and atomic ordering of BCC Heusler alloy Fe{sub 2}MnGa ribbons

    Energy Technology Data Exchange (ETDEWEB)

    Xin, Yuepeng; Ma, Yuexing; Luo, Hongzhi, E-mail: luo_hongzhi@163.com; Meng, Fanbin; Liu, Heyan

    2016-05-15

    The electronic structure, atomic disorder and magnetic properties of the Heusler alloy Fe{sub 2}MnGa have been investigated experimentally and theoretically. BCC Fe{sub 2}MnGa ribbon samples were prepared. Experimentally, a saturation magnetic moment (3.68 μ{sub B} at 5 K) much larger than the theoretical value (2.04 μ{sub B}) has been reported. First-principles calculations indicate that the difference is related to the Fe–Mn disorder between A, B sites, as can also be deduced from the XRD pattern. L2{sub 1} type Fe{sub 2}MnGa is a ferrimagnet with antiparallel Fe and Mn spin moments. However, when Fe–Mn disorder occurs, part of Mn moments will be parallel to Fe moments, and the Fe moments also clearly increase simultaneously. All this results in a total moment of 3.74 μ{sub B}, close to the experimental value.

  1. Tuning martensitic transformation, large magnetoresistance and strain in Ni50-xFexMn36Sn14 Heusler alloys

    Science.gov (United States)

    Liao, Pan; Jing, Chao; Zheng, Dong; Li, Zhe; Kang, Baojuan; Deng, Dongmei; Cao, Shixun; Lu, Bo; Zhang, Jincang

    2015-09-01

    We have investigated the martensitic transformation, exchange bias, magnetoresistance (MR) and strain in Ni50-xFexMn36Sn14 (x=1, 2, 3, 4) Heusler alloys. With the increase of Fe content, the austenite phase could be stabilized with L21 structure and hence the martensitic transition shifts to a lower temperature and finally disappears. This behavior can be understood by the weakening of Ni-Mn hybridization to suppress AFM interactions and enhancement of Fe-Fe ferromagnetic exchange interactions. The same reason can account for the slight decrease of exchange bias field (HEB) with the increase of the Fe content from x=1 to 2 and the disappearance of HEB for x=3. We observed MR effect for x=3, and a maximum MR value of -52% was achieved, which can be explained by the change in the electronic structure during martensitic transformation induced by the magnetic field. In addition, a large strain of 0.207% in Ni49Fe1Mn36Sn14 was observed due to the changes of lattice parameters during the martensitic transformation induced by temperature.

  2. Effect of As and Nb doping on the magnetic properties for quaternary Heusler alloy FeCoZrGe

    Energy Technology Data Exchange (ETDEWEB)

    Mao, Ge-Yong; Liu, Xiao-Xiong; Gao, Qiang; Li, Lei; Xie, Huan-Huan; Lei, Gang; Deng, Jian-Bo, E-mail: dengjb@lzu.edu.cn

    2016-01-15

    We investigate the effect of doping on FeCoZrGe. Electronic structure calculations reveal that doping of As or Nb into FeCoZrGe will transform it into half-metallic materials. They have half-metallic properties in a large range of proportion of As or Nb's doping. So by doping with different proportion of As or Nb, the controllable half-metallic gaps can be realized. In addition, this doped system can have higher Curie temperature. - Highlights: • The half-metallic properties of As- and Nb-systems of FeCoZrGe are studied. • We simulate the doped systems by supercell and virtual crystal approximations. • The magnetic, electronical and stabile properties are discussed. • The half-metallic gap variation with the doped proportion is shown.

  3. Moessbauer spectroscopic study of half-Heusler compounds

    Energy Technology Data Exchange (ETDEWEB)

    Ksenofontov, V., E-mail: v.ksenofontov@uni-mainz.de; Kroth, K.; Reiman, S.; Casper, F.; Jung, V. [Johannes Gutenberg Universitaet, Institut fuer Anorganische Chemie und Analytische Chemie (Germany); Takahashi, M.; Takeda, M. [Toho University, Department of Chemistry, Faculty of Science (Japan); Felser, C. [Johannes Gutenberg Universitaet, Institut fuer Anorganische Chemie und Analytische Chemie (Germany)

    2006-02-15

    The family of half-Heusler compounds offers a variety of half-metallic ferromagnetic materials. We have applied the Moessbauer spectroscopy to study the atomic order, local surroundings and hyperfine fields to several half-Heusler compounds. {sup 121}Sb Moessbauer study of the compound CoMnSb revealed the presence of two nonequivalent antimony positions in the elementary cell and enabled to identify the structure. {sup 119m}Sn, {sup 155}Gd and {sup 197}Au Moessbauer spectroscopic studies were used to characterize the properties of ferromagnetic granular material based on the half-Heusler ferromagnet MnAuSn in the antiferromagnetic GdAuSn matrix.

  4. Tetrahedrally coordinated half-metallic antiferromagnets

    Science.gov (United States)

    Nakao, Masao

    2006-11-01

    We explore the electronic structures of transition-metal-based chalcopyrites TMX2 ( X=S , Se, and Te) to establish a concept of half-metallic antiferromagnets (HM-AFM’s) within the class of tetrahedrally coordinated ternary systems. Using a full-potential muffin-tin approach and the spin-polarized density functional method, we find two series of HM-AFM’s: CrFeX2 and VCoX2 , where two constituent magnetic ions in a unit cell have antialigned local moments that cancel exactly by virtue of the integer filling of one spin channel. The bonding nature is interpreted in terms of the “ghost-bond-orbital model”; the T - X bonds are covalent while the M - X bonds are ionic, suggesting the magnetic interaction in each bond is due to ferromagnetic double exchange and antiferromagnetic superexchange, respectively, in the conventional scheme.

  5. Epitaxial Growth of Full-Heusler Alloy Co2MnSi Thin Films on MgO-Buffered MgO Substrates

    OpenAIRE

    Kijima, H; Ishikawa, T.; Marukame, T.; Koyama, H; Matsuda, K; Uemura, T.; Yamamoto, M.

    2006-01-01

    Full-Heusler alloy Co₂MnSi (CMS) thin films were epitaxially grown on MgO-buffered MgO substrates through magnetron sputtering. The films were deposited at room temperature and subsequently annealed in situ at 600℃. X-ray pole figure measurements of the annealed films showed 111 peaks with fourfold symmetry, providing direct evidence that these films were epitaxial and crystallized in the L2₁ structure. The annealed films had sufficiently flat surface morphologies with root-mean-squa...

  6. Unusual nature of the martensite and ferromagnetic transitions in Ni2Mn0.4-XFeXCr0.6Ga Heusler alloys

    Directory of Open Access Journals (Sweden)

    Jeffrey A. Brock

    2017-05-01

    Full Text Available An experimental study has been performed on a series of Ni2Mn0.4-xFexCr0.6Ga Heusler alloys. At room temperature, the alloys crystallize in either the tetragonal martensite (x < 0.1 or cubic L21 structure (x ≥ 0.1. Additionally, a Cr-Fe based face-centered cubic γ-Fe type secondary phase was found to co-exist in the samples. Magnetization and transport measurements revealed that the Curie and martensitic transition temperatures decrease as Mn is replaced with Fe. Atypical to other Ni2MnGa-derivative Heusler alloys, the transition temperatures decrease at the same rate with respect to x for x ≥ 0.1. Thus, the two transitions do not couple in to a single magnetostructural transition at any composition. Transport measurements revealed that all samples exhibit a sharp drop in resistivity during the martensitic phase transition (13 - 17 %, with the magnitude of this drop remaining relatively constant over the entire series. The possible origins of the observed experimental behavior are discussed.

  7. Design of Fatigue Resistant Heusler-strengthened PdTi-based Shape Memory Alloys for Biomedical Applications

    Science.gov (United States)

    Frankel, Dana J.

    The development of non-surgical transcatheter aortic valve implantation (TAVI) techniques, which utilize collapsible artificial heart valves with shape memory alloy (SMA)-based frames, pushes performance requirements for biomedical SMAs beyond those for well-established vascular stent applications. Fatigue life for these devices must extend into the ultra-high cycle fatigue (UHCF) regime (>600M cycles) with zero probability of failure predicted at applied strain levels. High rates of Ni-hypersensitivity raise biocompatibility concerns, driving the development of low-Ni and Ni-free SMAs. This work focuses on the development of biocompatible, precipitation-strengthened, fatigue-resistant PdTi-based SMAs for biomedical applications. Functional and structural fatigue are both manifestations of cyclic instability resulting in accumulation of slip and eventual structural damage. While functional fatigue is easily experimentally evaluated, structural fatigue is more difficult to measure without the proper equipment. Therefore, in this work a theoretical approach using a model well validated in steels is utilized to investigate structural fatigue behavior in NiTi in the UHCF regime, while low cycle functional fatigue is evaluated in order to monitor the core phenomena of the cyclic instability. Results from fatigue simulations modeling crack nucleation at non-metallic inclusions in commercial NiTi underscore the importance of increasing yield strength for UHCF performance. Controlled precipitation of nanoscale, low-misfit, L21 Heusler aluminides can provide effective strengthening. Phase relations, precipitation kinetics, transformation temperature, transformation strain, cyclic stability, and mechanical properties are characterized in both Ni-free (Pd,Fe)(Ti,Al) and low-Ni high-strength "hybrid" (Pd,Ni)(Ti,Zr,Al) systems. Atom probe tomography is employed to measure phase compositions and particle sizes used to calibrate LSW models for coarsening kinetics and Gibbs

  8. Electronic structure and magnetism in full-Heusler compound Mn{sub 2}ZnGe

    Energy Technology Data Exchange (ETDEWEB)

    Wei Xiaoping; Hu Xianru; Liu Bin; Lei Yi; Deng Hong; Yang Mingkun [Department of Physics, LanZhou University, Lanzhou 730000 (China); Deng Jianbo, E-mail: dengjb@lzu.edu.c [Department of Physics, LanZhou University, Lanzhou 730000 (China)

    2011-06-15

    The first-principle calculations within density functional theory are used to investigate the electronic structure and magnetism of the Mn{sub 2}ZnGe Heusler alloy with CuHg{sub 2}Ti-type structure. The half-metallic ferrimagnets (HMFs) in Mn{sub 2}ZnGe are predicted. The energy gap lies in the minority-spin band for the Mn{sub 2}ZnGe alloy. The calculated total spin magnetic moment is -2{mu}{sub B} per unit cell for Mn{sub 2}ZnGe alloy, the magnetic moments of Zn and Mn(B) are antiparallel to that of Mn(A), and we also found that the half-metallic properties of Mn{sub 2}ZnGe are insensitive to the dependence of lattice within the wide range of 5.69 and 5.80 A where exhibiting perfect 100% spin polarization at the Fermi energy. - Research highlights: The current investigation presents that the ferrimagnetic states of Mn{sub 2}ZnGe alloy in CuHg{sub 2}Ti-type structure are energetically more favorable than the non-magnetic ones. The states at the Fermi level keep a 100% of spin polarization. The calculated total spin magnetic moment arising from the antiparallel configurations of the Mn partial moments is -2{mu}{sub B} per unit cell for Mn{sub 2}ZnGe alloy. Effect of the lattice parameter shows that the half-metallic properties of Mn{sub 2}ZnGe are insensitive to the dependence of lattice within a wide range of lattice constant where it still exhibits a perfect 100% spin polarization at the Fermi energy.

  9. Molecular beam epitaxy growth and magnetic properties of Cr-Co-Ga Heusler alloy films

    Energy Technology Data Exchange (ETDEWEB)

    Feng, Wuwei, E-mail: wfeng@cugb.edu.cn; Wang, Weihua [School of Materials Science and Technology, China University of Geosciences, Beijing 100083 (China); Zhao, Chenglong [Key Laboratory for Renewable Energy, Beijing Key Laboratory for New Energy Materials and Devices, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Van Quang, Nguyen; Cho, Sunglae, E-mail: slcho@ulsan.ac.kr [Department of Physics, University of Ulsan, Ulsan 680-749 (Korea, Republic of); Dung, Dang Duc [Department of General Physics, School of Engineering Physics, Ha Noi University of Science and Technology, 1 Dai Co Viet Road, Ha Noi (Viet Nam)

    2015-11-15

    We have re-investigated growth and magnetic properties of Cr{sub 2}CoGa films using molecular beam epitaxy technique. Phase separation and precipitate formation were observed experimentally again in agreement with observation of multiple phases separation in sputtered Cr{sub 2}CoGa films by M. Meinert et al. However, significant phase separation could be suppressed by proper control of growth conditions. We showed that Cr{sub 2}CoGa Heusler phase, rather than Co{sub 2}CrGa phase, constitutes the majority of the sample grown on GaAs(001) at 450 {sup o}C. The measured small spin moment of Cr{sub 2}CoGa is in agreement with predicted HM-FCF nature; however, its Curie temperature is not as high as expected from the theoretical prediction probably due to the off-stoichiometry of Cr{sub 2}CoGa and the existence of the disorders and phase separation.

  10. Epitaxial Growth, Surface, and Electronic Properties of Unconventional Semiconductors: RE-V/III-V Nanocomposites and Semiconducting Half Heusler Alloys

    Science.gov (United States)

    2014-09-01

    groundwork for future studies on all-Heusler heterostructures . 2 UNIVERSITY of CALIFORNIA Santa Barbara Epitaxial growth, surface, and electronic...Schultz, and C. J. Palmstrøm. Growth and transport properties of epitaxial lattice matched Half Heusler Co- TiSb/InAlAs/InP(001) heterostructures . Appl...and nanowires via directed electrochemical nanowire assembly. Nano Lett., 11, 191901 (2011). 5. N. Ferralis, J. K. Kawasaki, R. Maboudian, and C

  11. Prediction of a new class of half-metallic ferromagnets from first principles

    Science.gov (United States)

    Griffin, Sinéad M.; Neaton, Jeffrey B.

    2017-09-01

    Half-metallic ferromagnetism (HMFM) occurs rarely in materials and yet offers great potential for spintronic devices. Recent experiments suggest a class of compounds with the ThCr2Si2 (122) structure (isostructural and containing elements common with Fe pnictide-based superconductors) can exhibit HMFM. Here, we use ab initio density functional theory calculations to understand the onset of half-metallicity in this family of materials and explain the appearance of ferromagnetism at a quantum critical point. We also predict new candidate materials with HMFM and potentially high Curie temperatures through A -site alloying.

  12. Exploration of new multifunctional magnetic materials based on a variety of Heusler alloys and rare-earth compounds

    Science.gov (United States)

    Pathak, Arjun Kumar

    2011-12-01

    Magnetic, magnetocaloric, magnetotransport and magnetoelastic properties of Ni-Mn-X (X = In, and Ga) Heusler alloys and La-Fe-Si based rare earth compounds have been synthesized and investigated by x-ray diffraction, magnetization, strain, and electrical resistivity measurements. The phase transitions, magnetic, magnetocaloric, magnetotransport and magnetoelastic properties strongly depend on the composition of these systems. In Ni50Mn50-xInx with x = 13.5, magnetocaloric and magnetotransport properties associated with the paramagnetic martensitic to paramagnetic austenitic transformation were studied. It was shown that magnetic entropy changes (DeltaSM) and magnetoresistance (MR) associated with this transformation are larger and the hysteresis effect is significantly lower when compared to that associated with paramagnetic-ferromagnetic transitions or ferromagnetic-antiferromagnetic/paramagnetic transitions in other systems. The Hall resistivity and the Hall angle shows unusual behavior in the vicinity of the martensitic phase transition for Ni50Mn 50-xInx with x = 15.2. The observed Hall resistivity and Hall angle are 50 μO·cm and tan-1 0.5, respectively. It was observed that the presence of Ge, Al and Si atoms on the In sites strongly affects the crystal structure, and the electric and magnetic behaviors of Ni50Mn35In15. It was found that the partial substitution of In atoms by Si in Ni50Mn35In15 results in an increase in the magnetocaloric effect, exchange bias and shape memory effect. In Ni50Mn35In15-xSi x, the peak values of positive DeltaSM for magnetic field changes H = 5 T were found to depend on composition and vary from 82 J·kg -1·K-1 for x = 1 (at T = 275 K) to 124 J·kg -1·K-1 for x = 3 (at T = 239 K). The partial substitution of Ni by Co in Ni50Mn35In15 significantly improves the magnetocaloric effect and MR in the vicinity of martensitic transition. In addition, significantly large inverse DeltaS M and MR were observed at the inverse

  13. High field magnetic behavior in Boron doped Fe{sub 2}VAl Heusler alloys

    Energy Technology Data Exchange (ETDEWEB)

    Venkatesh, Ch., E-mail: venkyphysicsiitm@gmail.com [Department of Physics, Indian Institute of Technology, Kharagpur (India); DCMP & MS, Tata Institute of Fundamental Research, Mumbai (India); Vasundhara, M., E-mail: vasu.mutta@gmail.com [Materials Science and Technology Division, National Institute for Interdisciplinary Science and Technology, CSIR, Trivandrum 695019 (India); Srinivas, V. [Department of Physics, Indian Institute of Technology, Chennai (India); Rao, V.V. [Cryogenic Engineering Centre, Indian Institute of Technology, Kharagpur (India)

    2016-11-15

    We have investigated the magnetic behavior of Fe{sub 2}VAl{sub 1−x}B{sub x} (x=0, 0.03, 0.06 and 0.1) alloys under high temperature and high magnetic field conditions separately. Although, the low temperature DC magnetization data for the alloys above x>0 show clear magnetic transitions, the zero field cooled (ZFC) and field cooled (FC) curves indicate the presence of spin cluster like features. Further, critical exponent (γ) deduced from the initial susceptibility above the T{sub c}, does not agree with standard models derived for 3 dimensional long range magnetic systems. The deviation in γ values are consistent with the short range magnetic nature of these alloys. We further extend the analysis of magnetic behavior by carrying the magnetization measurements at high temperatures and high magnetic fields distinctly. We mainly emphasize the following observations; (i) The magnetic hysteresis loops show sharp upturns at lower fields even at 900 K for all the alloys. (ii) High temperature inverse susceptibility do not overlap until T=900 K, indicating the persistent short range magnetic correlations even at high temperatures. (iii) The Arrott's plot of magnetization data shows spontaneous moment (M{sub S}) for the x=0 alloy at higher magnetic fields which is absent at lower fields (<50 kOe), while the Boron doped samples show feeble M{sub S} at lower fields. The origin of this short range correlation is due to presence of dilute magnetic heterogeneous phases which are not detected from the X-ray diffraction method. - Highlights: • Short range magnetic character has been confirmed by the critical exponents analysis. • Magnetoresistace is about −14% with non-saturating tendency even at 150 kOe for Fe{sub 2}VAl alloy. • Boron doped Fe{sub 2}VAl alloys show a weak magnetism even at T=900 K.

  14. Thermodynamic stability, magnetism and half metallicity of Mn2CoAl/GaAs(0 0 1) interface

    Science.gov (United States)

    Feng, Yu; Zhou, Ting; Chen, Xiaorui; Yuan, Hongkuan; Chen, Hong

    2015-07-01

    Interface properties of the heterojunction which is composed of the inverse Heusler alloy Mn2 CoAl and semiconductor GaAs are investigated by employing the first-principles density functional simulations. Two kinds of interface structures, namely the top-type and bridge-type structure by connecting termination of nine Mn2 CoAl layers to the top of the As-terminated GaAs layer and bridge site between interface As atoms are respectively built. Our calculations reveal that, as for the structure with the same interface atoms, different atoms sitting directly on top of the interface As atom will lead to different interface magnetism and electronic structures. The calculated phase diagram reveals that the top-type structure including natural MnCo or MnAl termination is stable only when the interface Mn or interface Al atom directly locates on top of the As atom. Besides, bridge-type and top-type structures containing a pure Mn interface are always thermodynamically accessible regardless of values of the chemical potential of Mn and Co. The atom-resolved spin magnetic moments of most interface magnetic atoms are enhanced due to the rehybridization caused by symmetry breaking at the interface. Further analyses on electronic structures indicate that, owing to the interface effect, the interface half metallicity of all structures are completely destroyed. However, the top-type structure with MnAl termination where the interface Al atom directly sits on top of the As atom preserves the highest interface spin polarization of 80%, indicating that it has more advantages in spintronics application than other atomic terminations.

  15. Structural stability, half-metallicity and magnetism of the CoFeMnSi/GaAs(0 0 1) interface

    Science.gov (United States)

    Feng, Yu; Chen, Xiaorui; Zhou, Ting; Yuan, Hongkuan; Chen, Hong

    2015-08-01

    The ferromagnet/semiconductor interface plays a crucial role in the performance of advanced magnetic tunnel junctions (MTJs) built of ferromagnetic electrodes and semiconductor as a spacer. We investigate the interface character between LiMgPbSb-type Heusler alloy CoFeMnSi and semiconductor GaAs by using the first-principles density functional simulations. In our calculations, we build two kinds of interface structures, namely the top-type and the bridge-type structure by connecting the termination of nine CoFeMnSi layers to the top of the As-terminated GaAs layer and the bridge site between interface As atoms, respectively. The calculated phase diagram indicated that the CoFe-terminated interface is more stable in the bridge-type structure than in the top-type structure, and a favored MnMn- or MnSi-terminated interface will appear in the top-type structure instead of the bridge-type structure under Fe-rich conditions. Besides, our calculation reveals that interface Mn and interface Fe atoms prefer to extend outward and their atom-resolved spin magnetic moments are enhanced due to the rehybridization caused by the symmetry breaking at the interface, while interface Co atoms shrink inward and their moments are decreased compared with the bulk value. Further analysis on DOS and PDOS indicates that owing to the interface effect, the half metallicity of CoFe-, MnSi-, and SiSi-terminated interfaces is completely destroyed. However, the MnMn-terminated interface in the top-type structure preserves 100% spin polarization, indicating that the CoFeMnSi/GaAs heterostructure with the top-type MnMn-terminated interface has more advantages than other atomic terminations in spintronics applications.

  16. Structure and properties of quarternary and tetragonal Heusler compounds for spintronics and spin transver torque applications

    Energy Technology Data Exchange (ETDEWEB)

    Zamani, Vajiheh Alijani

    2012-03-07

    This work is divided into two parts: part 1 is focused on the prediction of half-metallicity in quaternary Heusler compounds and their potential for spintronic applications and part 2 on the structural properties of Mn{sub 2}-based Heusler alloys and tuning the magnetism of them from soft to hard-magnetic for spin-transfer torque applications. In part 1, three different series of quaternary Heusler compounds are investigated, XX'MnGa (X=Cu, Ni and X'=Fe,Co), CoFeMnZ (Z=Al,Ga,Si,Ge), and Co{sub 2-x}Rh{sub x}MnZ (Z=Ga,Sn,Sb). All of these quaternary compounds except CuCoMnGa are predicted to be half-metallic ferromagnets by ab-initio electronic structure calculations. In the XX'MnGa class of compounds, NiFeMnGa has a low Curie temperature for technological applications but NiCoMnGa with a high spin polarization, magnetic moment, and Curie temperature is an interesting new material for spintronics applications. All CoFeMnZ compounds exhibit a cubic Heusler structur and their magnetic moments are in fair agreement with the Slater-Pauling rule indicating the halfmetallicity and high spin polarization required for spintronics applications. Their high Curie temperatures make them suitable for utilization at room temperature and above. The structural investigation revealed that the crystal structure of all Co{sub 2-x}Rh{sub x}MnZ compounds aside from CoRhMnSn exhibit different types of anti-site disorder. The magnetic moments of the disordered compounds deviate from the Slater-Pauling rule indicating that 100% spin polarization are not realized in CoRhMnGa, CoRhMnSb, and Co{sub 0.5}Rh{sub 1.5}MnSb. Exchange of one Co in Co{sub 2}MnSn by Rh results in the stable, well-ordered compound CoRhMnSn. This exchange of one of the magnetic Co atoms by a non-magnetic Rh atom keeps the magnetic properties and half-metallicity intact. In part 2, two series of Mn{sub 2}-based Heusler alloys are investigated, Mn{sub 3-x}Co{sub x}Ga and Mn{sub 2-x}Rh{sub 1+x}Sn. It has been

  17. Crystalline structure and magnetic properties of Fe2CrSi Heusler alloy films: New ferromagnetic material for high-performance magnetic random access memory

    Science.gov (United States)

    Yoshimura, S.; Asano, H.; Nakamura, Y.; Yamaji, K.; Takeda, Y.; Matsui, M.; Ishida, S.; Nozaki, Y.; Matsuyama, K.

    2008-04-01

    A new Heusler alloy, Fe2CrSi, which has high spin polarization (P), low saturation magnetization (Ms), and a low Curie temperature (TC), was investigated in order to fabricate high-performance magnetic tunnel junctions (MTJs) with a high tunnel magnetoresistance ratio and with low critical current for the spin-transfer switching method, or a low switching field for the thermally assisted magnetization reversal technique. The main results are as follows: (1) P and the magnetic moment of Fe2CrSi with an L21 structure were 0.98 and 1.98μB/f.u., respectively, according to density of states calculations. (2) Fe2CrSi films show the (100) orientation with a B2 structure on a MgO substrate upon a thermal treatment with optimum temperature and duration. (3) Fe2CrSi films have Ms and TC values of 385emu /cm3 and 630K, respectively. (4) The (100) oriented epitaxial MTJs are produced with Fe2CrSi films fabricated with the optimized thermal treatment condition. It is found that the Fe2CrSi Heusler alloy films are a suitable ferromagnetic material for high-performance magnetic random access memory.

  18. Structural and magnetic properties of epitaxial Heusler alloy Fe{sub 2}Cr{sub 0.5}Co{sub 0.5}Si

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Yu-Pu, E-mail: wangyupu@nus.edu.sg [Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, Singapore 117583 (Singapore); Data Storage Institute, Agency for Science, Technology and Research (A-STAR), 5 Engineering Drive 1, Singapore 117608 (Singapore); Han, Gu-Chang; Qiu, Jinjun; Yap, Qi-Jia [Data Storage Institute, Agency for Science, Technology and Research (A-STAR), 5 Engineering Drive 1, Singapore 117608 (Singapore); Lu, Hui; Teo, Kie-Leong [Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, Singapore 117583 (Singapore)

    2014-05-07

    This paper reports the study of structural and magnetic properties of Heusler alloy Fe{sub 2}Cr{sub 0.5}Co{sub 0.5}Si (FCCS) thin film and its tunnel magnetoresistance (TMR) effect. The smooth quaternary Heusler alloy FCCS film with surface roughness of rms value of 0.25 nm measured by atomic force microscopy and partial L2{sub 1} phase was obtained by magnetron sputtering at room temperature followed by in-situ annealing at 400 °C. The saturation magnetization and coercivity of FCCS are 410 emu/cm{sup 3} and 20 Oe, respectively. The magnetic tunnel junctions (MTJs) using FCCS as free layer were studied in detail as a function of post-annealing temperature. A TMR ratio of 15.6% has been achieved with 300 °C post-annealing. This is about twice the highest TMR ratio obtained in MTJs using Fe{sub 2}CrSi. The enhancement of TMR ratio can be attributed to the successful tuning of the Fermi level of Fe{sub 2}CrSi close to the center of the minority band gap by Co-doping.

  19. The Thermal Transformation Arrest Phenomenon in NiCoMnAl Heusler Alloys

    Directory of Open Access Journals (Sweden)

    Rie Y. Umetsu

    2013-08-01

    Full Text Available In this report, we present findings of systematic research on NiCoMnAl alloys, with the purpose of acquiring a higher thermal transformation arrest temperature (TA. By systematic research, TA in the NiCoMnAl alloy systems was raised up to 190 K, compared to the highest TA of 130 K in NiCoMnIn. For a selected alloy of Ni40Co10Mn33Al17, magnetization measurements were performed under a pulsed high magnetic field, and the critical magnetic field-temperature phase diagram was determined. The magnetic phase diagram for Ni50-xCoxMn50-yAly was also established. Moreover, from the discussion that the formerly called “kinetic arrest phenomenon” has both thermodynamic and kinetic factors, we suggest a terminology change to the “thermal transformation arrest phenomenon”.

  20. Pressure- and Temperature-Dependent Study of Heusler Alloys Cu2MGa (M = Cr and V)

    Science.gov (United States)

    Gupta, Dinesh C.; Ghosh, Sukriti

    2017-04-01

    Full-potential computation of the electronic, magnetic, elastic and thermodynamic properties of Cu2MGa (M = Cr and V) alloys has been performed in the most stable Fm-3 m phase. The equilibrium lattice parameter is 5.9660 Å for Cu2CrGa and 5.9629 Å for Cu2VGa in the stable state. The application of mBJ potential has also found no energy gap in these alloys in either of the spin channels, hence they are metallic. The total and partial density of states, second-order elastic constants and their combinations are computed to show the electronic, magnetic, stability and brittle or ductile nature of these alloys, which are reported for the first time. Cauchy's pressure and Pugh's index predict Cu2CrGa to be brittle and Cu2VGa to be ductile. Both the materials are stiff enough to break. We have found that both the compounds are anisotropic, ferromagnetic and metallic in nature. We have used quasi-harmonic approximations to study the pressure and temperature variation of the thermodynamic properties of these alloys.

  1. Effect of the Heusler phase formation on the magnetic behavior of the Cu–10 wt.%Mn alloy with Al and Ag additions

    Energy Technology Data Exchange (ETDEWEB)

    Carvalho, T.M., E-mail: thaisa.mary@gmail.com [Instituto de Química – UNESP, Caixa Postal 355, 14801-970 Araraquara, SP (Brazil); Adorno, A.T.; Santos, C.M.A. [Instituto de Química – UNESP, Caixa Postal 355, 14801-970 Araraquara, SP (Brazil); Silva, R.A.G. [Departamento de Ciências Exatas e da Terra – UNIFESP, 09972-270 Diadema, SP (Brazil); Magnani, M. [Instituto de Química – UNESP, Caixa Postal 355, 14801-970 Araraquara, SP (Brazil)

    2015-09-15

    Highlights: • The presence of the Cu{sub 2}MnAl phase was observed in annealed alloys. • Al and Ag additions shift the equilibrium concentration to higher Al values. • There is a correlation between the Ag-rich phase and the Cu{sub 2}MnAl phase. - Abstract: In this work, the formation of the Cu{sub 2}AlMn Heusler phase and its influence on the magnetic behavior of the Cu–Mn–Al–Ag alloys in the range of 8–10 wt.% of aluminum and 2–4 wt.% of silver were studied using differential scanning calorimetry (DSC), transmission electron microscopy (TEM), high-resolution TEM (HRTEM) and saturation magnetization measurements at 4 K. The results showed that there is a correlation between the presence of the Ag-rich phase and the formation of the Cu{sub 2}MnAl phase.

  2. Substitution effect on magnetic and electrical properties of half-Heusler alloy Ni{sub 1−x}Co{sub x}Mn{sub 1−y}Fe{sub y}Sb

    Energy Technology Data Exchange (ETDEWEB)

    Kushwaha, Varun, E-mail: varun300791@gmail.com; Sharma, Himanshu, E-mail: varun300791@gmail.com; Dixit, Dinesh, E-mail: varun300791@gmail.com; Tomy, C. V. [Department of Physics, Indian Institute of Technology Bombay, Mumbai-400 076 (India); Tulapurkar, Ashwin [Department of Electrical Engineering, Indian Institute of Technology Bombay, Mumbai-400 076 (India)

    2014-04-24

    We have studied the effects of Co and Fe doping on the magnetic and electrical properties of half-Heusler compound NiMnSb. The alloys were prepared by arc-melting method in the presence of Argon gas. The powder X-ray diffraction of the each alloy was performed in air at room temperature. The magnetic and electrical properties were performed in the temperature range 2–400 K and in magnetic field up to 1 T.

  3. Ti{sub 2}FeZ (Z=Al, Ga, Ge) alloys: Structural, electronic, and magnetic properties

    Energy Technology Data Exchange (ETDEWEB)

    Liping, Mao, E-mail: mlp_920306@163.com [Department of Medical Engineering and Technology, Xinjiang Medical University, Urumqi 830011, Xinjiang (China); Yongfan, Shi [Department of Medical Engineering and Technology, Xinjiang Medical University, Urumqi 830011, Xinjiang (China); Yu, Han [Xinjiang New Energy Research Institute, Urumqi 830011, Xinjiang (China)

    2014-11-15

    Using the first-principle projector augmented wave potential within the generalized gradient approximation taking into account the on-site Coulomb repulsive, we investigate the structural, electronic and magnetic properties of Ti{sub 2}FeZ (Z=Al, Ga, Ge) alloys with Hg{sub 2}CuTi-type structure. These alloys are found to be half-metallic ferrimagnets. The total magnetic moments of the Heusler alloys Ti{sub 2}FeZ follow the µ{sub t}=Z{sub t}−18 rule and agree with the Slater–Pauling curve quite well. The band gaps are mainly determined by the bonding and antibonding states created from the hybridizations of the d states between the Ti(A)–Ti(B) coupling and Fe atom. - Highlights: • Ti{sub 2}FeZ (Z=Al, Ga, Ge) are found to be half-metallic ferrimagnets. • The band gaps are mainly determined by the hybridizations of the d states between the Ti(A)–Ti(B) coupling and Fe atom. • The s–p elements play an important role in the half-metallicity of these Heusler alloys.

  4. Magnetocaloric effect in Ni-Fe-Ga Heusler alloys with Co and Al substitutions

    Directory of Open Access Journals (Sweden)

    Tolea F.

    2015-01-01

    Full Text Available The functionality of the ferromagnetic shape memory alloys is related to the martensitic and magnetic order-disorder transformations, both of which may be tailored by doping with other elements or by suitable thermal treatments, so that alloys with concomitant (or sequential but close structural and magnetic phase transitions may be obtained. Concerning the magnetocaloric applications, it is assumed that the thin melt-spun ribbons assure a more efficient heat transfer. In the present work we investigate the influence of Co and Al substitutions on magnetocaloric effect characteristics of NiFeGa in bulk and also in ribbons prepared by melt spinning method and subjected to different thermal treatments. X-ray diffraction, differential scanning calorimetry, magnetocaloric and magnetoresistive characterizations have been performed. The results highlight the differences between the bulk and the ribbons (both as prepared and annealed and the role of substitutions.

  5. Structure and magnetic properties of Co{sub 2}(Cr{sub 1−x}Fe{sub x})Al, (0 ≤ x ≤ 1) Heusler alloys prepared by mechanical alloying

    Energy Technology Data Exchange (ETDEWEB)

    Srivastava, Yogesh, E-mail: 123209001_yogesh@manit.ac.in [Department of Materials Science & Metallurgical Engineering, Ceramic & Powder Metallurgy Laboratory, Maulana Azad National Institute of Technology, Bhopal, Madhya Pradesh 462003 (India); Vajpai, Sanjay Kumar, E-mail: vajpaisk@gmail.com [Department of Materials Science & Metallurgical Engineering, Maulana Azad National Institute of Technology, Bhopal, Madhya Pradesh 462003 (India); Srivastava, Sanjay, E-mail: s.srivastava.msme@gmail.com [Department of Materials Science & Metallurgical Engineering, Maulana Azad National Institute of Technology, Bhopal, Madhya Pradesh 462003 (India)

    2017-07-01

    Highlights: • A series of nanocrystalline Co{sub 2}(Cr{sub 1−x}Fe{sub x})Al Heusler alloy by powder metallurgy. • Effect of substitution of Fe for Cr on the microstructure and magnetic properties. • Increasing amounts of B2 type disordered structure with increasing Fe content. • Enhanced Ms, Mr, Hc, and Tc with increasing Fe content. • Relative magnetic anisotropy decreased with increasing Fe content. - Abstract: In the present study, a series of nanocrystalline Co{sub 2}(Cr{sub 1−x}Fe{sub x})Al Heusler alloy powders were successfully prepared by high energy ball milling and the effect of substitution of Fe for Cr on the microstructure and magnetic properties was investigated in detail. The Co{sub 2}CrAl alloy powder consisted of only A2 type disordered structure whereas the substitution of Cr by Fe led to the appearance of increasing amounts of B2 type disordered structure along with A2 type structure. All the Co{sub 2}(Cr{sub 1−x}Fe{sub x})Al Heusler alloy powders demonstrated high spontaneous magnetization together with a very small hysteresis losses. The saturation magnetization, remanence, coercivity, and Curie temperature increased with increasing Fe content. The increasing magnetization with increasing Fe content was attributed to the replacement of antiferromagnetic Cr by strongly ferromagnetic Fe and an increasing amounts of relatively more ordered, atomically as well as ferromagnetically, B2 structure as compared to that of A2 phase. The increment in remanence and coercivity with increasing Fe content were associated with the variation in microstructural characteristics, such as grain size, lattice defects, and the presence of small amounts of magnetic/nonmagnetic secondary phases. The increment in Curie temperature with increasing Fe content was attributed to the enhancement of d-d exchange interaction due to the possible occupancy of vacant sites by Fe atoms. All the Heusler alloys indicated extremely low magnetic anisotropy and the

  6. Magnetic properties of Ni{sub 40+x}Mn{sub 39−x}Sn{sub 21} (x = 0, 2, 4, 6 and 8 at.%) Heusler alloys

    Energy Technology Data Exchange (ETDEWEB)

    Lázpita, P., E-mail: patricia.lazpita@ehu.es [BCMaterials and UPV/EHU, Bilbao (Spain); Barandiarán, J.M. [BCMaterials and UPV/EHU, Bilbao (Spain); Chernenko, V.A. [BCMaterials and UPV/EHU, Bilbao (Spain); Ikerbasque, Basque Foundation for Science, Bilbao (Spain); Valle García, B. [UPV/EHU, EUITI Bilbao, Dpto. Ing. Minera, Metalurgia y Ciencia de los Materiales, Bilbao (Spain); Díaz Tajada, E. [UPV/EHU, ETS Náutica y Máquinas Navales, Dpto. Ing. Minera, Metalurgia y Ciencia de los Materiales, Portugalete (Spain); Lograsso, T. [Division of Materials Science and Engineering, Ames Laboratory, Ames, IA (United States); Department of Materials Science and Engineering, Iowa State University, Ames, IA (United States); Schlagel, D.L. [Division of Materials Science and Engineering, Ames Laboratory, Ames, IA (United States)

    2014-05-01

    Highlights: • Curie temperature versus e/a dependence shows broad maximum in NiMnSn alloys. • Magnetic moment versus e/a < 7.75 dependence was determined. • The localized magnetic moment model is compatible with the magnetic moment evolution. • The values of the magnetic moments indicate an almost full atomic order. - Abstract: The low electron concentration region (e/a < 7.75) of the magnetic phase diagram of the off-stoichiometric Ni–Mn–Sn Heusler alloys was investigated in detail by DSC and magnetization measurements of the Ni{sub 40+x}Mn{sub 39−x}Sn{sub 21}(x = 0, 2, 4, 6 and 8 at.%) alloys. The alloys show a stable austenitic phase without any martensitic transformation down to 5 K even after heat treatment. The Curie temperature exhibits a broad maximum over a large composition range. The evolution of the magnetic moment with the electron concentration fits the data of previous studies and confirms the peak-like dependence in the extended range of e/a values predicted by ab initio calculations. The explored part of the moment versus e/a curve can be explained in terms of a localized magnetic moment model and full atomic order in the alloys.

  7. Chromium and iron contained half-Heusler MnNiGe-based alloys

    Energy Technology Data Exchange (ETDEWEB)

    Budzynski, M. [UMCS, Institute of Physics, 1 sq.M.Curie-Skłodowska, 20-031 Lublin (Poland); Valkov, V.I.; Golovchan, A.V.; Kamenev, V.I. [Donetsk Institute for Physics and Engineering, 72, R.Luxemburg str., 83114 Donetsk (Ukraine); Mitsiuk, V.I., E-mail: vmitsiuk@gmail.com [Scientific-Practical Materials Research Center of National Academy of Sciences of Belarus, 19 P.Brovky Str., 220072 Minsk (Belarus); Sivachenko, A.P. [Donetsk Institute for Physics and Engineering, 72, R.Luxemburg str., 83114 Donetsk (Ukraine); Surowiec, Z. [UMCS, Institute of Physics, 1 sq.M.Curie-Skłodowska, 20-031 Lublin (Poland); Tkachenka, T.M. [Scientific-Practical Materials Research Center of National Academy of Sciences of Belarus, 19 P.Brovky Str., 220072 Minsk (Belarus)

    2015-12-15

    The magnetic characteristics of chromium and iron containing MnNiGe-based alloys with several types of quenching and annealing were investigated. It was found that the quenched Mn{sub 0.89}Cr{sub 0.11}NiGe has a spontaneous and magnetic field induced magnetostructural first-order transitions at room temperature. These transitions might be accompanied by a large magnetocaloric effect. In general, Mn{sub 0.89}Cr{sub 0.11}NiGe can be classified as promising material for use in the magnetocaloric application at room temperatures. The first order magnetostructural phase transition from the ferromagnetic to paramagnetic state is not realized in MnNi0.90Fe0.10Ge. In contrast to Mn{sub 0.89}Cr{sub 0.11}NiGe, however, the FM state in quenched-on-wheel MnNi0.90Fe0.10Ge is preserved to the lowest temperatures. Based on the set of the magnetic properties, it has been concluded that the iron containing MnNiGe-based alloys are less promising for practical use.

  8. Effect of Spark Plasma Sintering on the Structure and Properties of Ti1−xZrxNiSn Half-Heusler Alloys

    Directory of Open Access Journals (Sweden)

    Ruth A. Downie

    2014-10-01

    Full Text Available XNiSn (X = Ti, Zr and Hf half-Heusler alloys have promising thermoelectric properties and are attracting enormous interest for use in waste heat recovery. In particular, multiphase behaviour has been linked to reduced lattice thermal conductivities, which enables improved energy conversion efficiencies. This manuscript describes the impact of spark plasma sintering (SPS on the phase distributions and thermoelectric properties of Ti0.5Zr0.5NiSn based half-Heuslers. Rietveld analysis reveals small changes in composition, while measurement of the Seebeck coefficient and electrical resistivities reveals that all SPS treated samples are electron doped compared to the as-prepared samples. The lattice thermal conductivities fall between 4 W·m−1·K−1 at 350 K and 3 W·m−1·K−1 at 740 K. A maximum ZT = 0.7 at 740 K is observed in a sample with nominal Ti0.5Zr0.5NiSn composition.

  9. Defects in half-metals and finite temperature

    NARCIS (Netherlands)

    Attema, JJ; Fang, CM; Chioncel, L; de Wijs, GA; Lichtenstein, AI; de Groot, RA

    2004-01-01

    The influence of intrinsic defects in half-metals is calculated in the case of NiMnSb. Of the 14 cases of intrinsic defects, five affect the half-metallic properties. They are energetically very unlikely to occur. Circumstances are discussed under which defects may even have a beneficial effect on

  10. Ab initio and Monte Carlo investigations of structural, electronic and magnetic properties of new ferromagnetic Heusler alloys with high Curie temperatures

    Energy Technology Data Exchange (ETDEWEB)

    Dannenberg, Antje

    2011-08-30

    The mechanism which causes many of the unusual thermomechanical properties of martensitic alloys, as for example, superelasticity and the shape-memory effect, is the martensitic transformation. The prototype ferromagnetic shape memory alloy (FSMA) is Ni{sub 2}MnGa. But a technological breakthrough is missing due to its poor ductility and low operation temperatures. The goal of this thesis is the proposal of new FSMA appropriate for future technological applications. I focus on X{sub 2}YZ Heusler alloys which are mainly based on Mn, Fe, Co, and Ni for the X and Y sites and Z=Ga or Zn. The big challenge of this work is to find material classes which combine the unique magnetomechanical properties of FSMA which are large recoverable magnetostrictive strains, high magnetocrystalline anisotropy energy, and highly mobile twin boundaries with transformation temperatures clearly above room temperature and a reduced brittleness. Such a study, providing material classes which from a theoretical point of view are promising candidates for future FSMA, will help the experimental physicists to select interesting subgroups in the vast number of possible chemical compositions of X{sub 2}YZ Heusler alloys. I have systematically varied the composition in the new Heusler alloys in order to find trends indicating generic tendencies of the material properties, for instance, as a function of the valence electron concentration e/a. A main feature of this thesis is the attempt to find the origin of the competing structural ordering tendencies between conventional X{sub 2}YZ and inverse (XY)XZ Heusler structures which are observed for all systems investigated. In the first part of this work the accuracy and predictive power of ab initio and Monte Carlo simulations is demonstrated by reproducing the experimental phase diagram of Ni-Mn-(Ga,In,Sn,Sb). The linear increasing and decreasing slopes of T{sub M} and T{sub C} can be reproduced by total and free energy calculations and the analysis

  11. Electronic and magnetic properties of zincblende half-metal superlattices

    Energy Technology Data Exchange (ETDEWEB)

    Fong, C Y; Qian, M C; Pask, J; Yang, L H; Dag, S

    2003-11-05

    Zincblende half-metallic compounds such as CrAs, with large magnetic moments and high Curie temperatures, are promising materials for spintronic applications. They explore layered materials, consisting of alternating layers of zincblende half-metals, by first principles calculations, and find that superlattices of (CrAs){sub 1}(MnAs){sub 1} and (CrAs){sub 2}(MnAs){sub 2} are half-metallic with magnetic moments of 7.0{mu}{sub B} and 14.0{mu}{sub B} per unit cell, respectively. They discuss the nature of the bonding and half-metallicity in these materials and, based on the understanding acquired, develop a simple expression for the magnetic moment in such materials. They explore the range of lattice constants over which half-metallicity is manifested, and suggest corresponding substrates for growth in thin film form.

  12. Synthesize and microstructure characterization of Ni{sub 43}Mn{sub 41}Co{sub 5}Sn{sub 11} Heusler alloy

    Energy Technology Data Exchange (ETDEWEB)

    Elwindari, Nastiti; Manaf, Azwar, E-mail: azwar@ui.ac.id [Physics Department, Faculty of Science, Universitas Indonesia, Depok 16424 (Indonesia)

    2016-06-17

    The ferromagnetic heusler alloys are promising materials in many technical applications due to their multifunctional properties such as shape memory effect, magnetocaloric effect, giant magnetoresistance, etc. In this work, synthesize and characterization of polycrystalline Ni{sub 43}Mn{sub 41}Co{sub 5}Sn{sub 11} (NMCS) alloy are reported. Alloy preparation was conducted by melting the constitute elements under an innert Argon (Ar) atmosphere in a vacuum mini arc-melting furnace. Homogenization of the microstructure of the as-cast ingot was obtained after annealing process at 750°C for 48 hours. It is shown that the dendrites structure has changed to equaixed grains morphology after homogenization. Microstructure characteristics of material by x-ray diffraction revealed that the alloy has a L{sub 21}-type cubic crystal structure as the main phase at room temperature. In order to induce the shape anisotropy, a forging treatment was applied to show the shape orientation of material. Various enhancements of magnetic properties in a longitudinal direction were observed at various degree of anisotropy. The microstructure changes of as-cast NMCS and effects of homogenization treatments as studied by scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS) are discussed in details.

  13. Magnetic and magnetocaloric properties of martensitic Ni{sub 2}Mn{sub 1.4}Sn{sub 0.6} Heusler alloy

    Energy Technology Data Exchange (ETDEWEB)

    Chernenko, Volodymyr A., E-mail: vladimir_chernenko@ehu.es [Universidad del Pais Vasco, Dept. Electricidad y Electronica, PO Box 644, Bilbao 48080 (Spain); Ikerbasque, Basque Foundation for Science, Bilbao 48011 (Spain); Barandiaran, Jose M. [Universidad del Pais Vasco, Dept. Electricidad y Electronica, PO Box 644, Bilbao 48080 (Spain); Rodriguez Fernandez, Jesus; Rojas, Daniel P. [CITIMAC, Fac. Ciencias, Univ. Cantabria, Santander 39005 (Spain); Gutierrez, Jon; Lazpita, Patricia [Universidad del Pais Vasco, Dept. Electricidad y Electronica, PO Box 644, Bilbao 48080 (Spain); Orue, Inaki [SGiker, Vicerrectorado de Inv. UPV/EHU, Sarriena s/n, Leioa 48940 (Spain)

    2012-10-15

    The evolutions of magnetic properties at low temperatures and the influence of magnetic field on the temperature dependence of specific heat in martensitic Ni{sub 2}Mn{sub 1.4}Sn{sub 0.6} Heusler alloy are studied. The frequency-dependent blocking temperature and considerable exchange bias below it are measured in the martensitic phase. From the analysis of the specific heat curves under magnetic field, a large inverse magnetocaloric effect manifested as the magnetic field induced rise of isothermal magnetic entropy and/or magnetic field induced adiabatic temperature decrease in the vicinity of the reverse magnetostructural transformation and a significant value of the conventional magnetocaloric effect at the Curie temperature are obtained. The Debye temperature and electronic coefficient equal to {Theta}{sub D}=310{+-}2 K and {gamma}= 16.6{+-}0.3 mJ/K{sup 2}mol, respectively, do not depend on the magnetic field.

  14. Suppression of the ferromagnetic order in the Heusler alloy Ni{sub 50}Mn{sub 35}In{sub 15} by hydrostatic pressure

    Energy Technology Data Exchange (ETDEWEB)

    Salazar Mejía, C., E-mail: Catalina.Salazar@cpfs.mpg.de; Mydeen, K.; Naumov, P.; Medvedev, S. A.; Wang, C.; Schwarz, U.; Felser, C.; Nicklas, M., E-mail: nicklas@cpfs.mpg.de [Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Str. 40, 01187 Dresden (Germany); Hanfland, M. [ESRF, BP220, 38043 Grenoble (France); Nayak, A. K. [Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Str. 40, 01187 Dresden (Germany); Max Planck Institute of Microstructure Physics, Weinberg 2, 06120 Halle (Germany)

    2016-06-27

    We report on the effect of hydrostatic pressure on the magnetic and structural properties of the shape-memory Heusler alloy Ni{sub 50}Mn{sub 35}In{sub 15}. Magnetization and x-ray diffraction experiments were performed at hydrostatic pressures up to 5 GPa using diamond anvil cells. Pressure stabilizes the martensitic phase, shifting the martensitic transition to higher temperatures, and suppresses the ferromagnetic austenitic phase. Above 3 GPa, where the martensitic-transition temperature approaches the Curie temperature in the austenite, the magnetization shows no longer indications of ferromagnetic ordering. We further find an extended temperature region with a mixture of martensite and austenite phases, which directly relates to the magnetic properties.

  15. Magnetic states of C-doped Ni43.75Co6.25Mn37.5In12.5 Heusler alloys

    Directory of Open Access Journals (Sweden)

    Buchelnikov Vasiliy

    2015-01-01

    Full Text Available In this study, we present the results of first principles calculations of structural and magnetic equilibrium states of carbon doped Ni1.75Co0.25Mn1.5In0.5 Heusler alloy. The pseudopotential method within spin-polarized generalized gradient approximation is used. Different distributions of Mn, In and C atoms as well as different spin reference states are discussed by using a supercell approach. The ferromagnetic cubic austenite with substitution of C for Mn is found to be energetically stable. The addition of carbon has promoted the martensitic transformation from a ferromagnetic cubic structure to a ferrimagnetic tetragonal structure with c/a ratio of 1.35.

  16. Observation of giant exchange bias in bulk Mn{sub 50}Ni{sub 42}Sn{sub 8} Heusler alloy

    Energy Technology Data Exchange (ETDEWEB)

    Sharma, Jyoti; Suresh, K. G., E-mail: suresh@iitb.ac.in [Magnetic Materials Laboratory, Department of Physics, Indian institute of Technology Bombay, Mumbai, Maharashtra 400076 (India)

    2015-02-16

    We report a giant exchange bias (EB) field of 3520 Oe in bulk Mn{sub 50}Ni{sub 42}Sn{sub 8} Heusler alloy. The low temperature magnetic state of the martensite phase has been studied by DC magnetization and AC susceptibility measurements. Frequency dependence of spin freezing temperature (T{sub f}) on critical slowing down relation and observation of memory effect in zero field cooling mode confirms the super spin glass (SSG) phase at low temperatures. Large EB is attributed to the strong exchange coupling between the SSG clusters formed by small regions of ferromagnetic order embedded in an antiferromagnetic (AFM) matrix. The temperature and cooling field dependence of EB have been studied and related to the change in unidirectional anisotropy at SSG/AFM interface. The training effect also corroborates with the presence of frozen (SSG) moments at the interface and their role in EB.

  17. Anti-phase boundaries and magnetic domain structures in Ni{sub 2}MnGa-type Heusler alloys

    Energy Technology Data Exchange (ETDEWEB)

    Venkateswaran, S.P. [Department of Materials Science and Engineering, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA 15213 (United States); Nuhfer, N.T. [Department of Materials Science and Engineering, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA 15213 (United States); De Graef, M. [Department of Materials Science and Engineering, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA 15213 (United States)]. E-mail: degraef@cmu.edu

    2007-05-15

    The microstructure and magnetic domain structure of austenitic Heusler Ni{sub 2}MnGa are investigated as a function of heat treatment to study the interplay of anti-phase boundaries and magnetic domain walls. Conventional electron microscopy observations on arc-melted polycrystalline samples show that anti-phase boundaries in this system are invisible for standard two-beam imaging conditions, due to the large extinction distance of the Heusler superlattice reflections. Lorentz Fresnel and Foucault observations on quenched samples reveal a wavy magnetic domain morphology, reminiscent of curved anti-phase boundaries. A close inspection of the domain images indicates that the anti-phase boundaries have a magnetization state different from that of the matrix. Fresnel image simulations for a simple magnetization model are in good agreement with the observations. Magnetic coercivity measurements show a decrease in coercivity with annealing, which correlates with the microscopy observations of reduced anti-phase boundary density for annealed samples.

  18. Ab initio studies of Co{sub 2}FeAl{sub 1−x}Si{sub x} Heusler alloys

    Energy Technology Data Exchange (ETDEWEB)

    Szwacki, N. Gonzalez, E-mail: gonz@fuw.edu.pl; Majewski, Jacek A., E-mail: jam@fuw.edu.pl

    2016-07-01

    We present results of extensive theoretical studies of Co{sub 2}FeAl{sub 1−x}Si{sub x} Heusler alloys, which have been performed in the framework of density functional theory employing the all-electron full-potential linearized augmented plane-wave scheme. It is shown that the Si-rich alloys are more resistive to structural disorder and as a consequence Si stabilizes the L2{sub 1} structure. Si alloying changes position of the Fermi level, pushing it into the gap of the minority spin-band. It is also shown that the hyperfine field on Co nuclei increases with the Si concentration, and this increase originates mostly from the changes in the electronic density of the valence electrons. - Highlights: • GGA+U calculations: μ and E{sub g} dependence on the value of U for Co{sub 2}FeAl and Co{sub 2}FeSi. • Behavior of magnetic hyperfine fields on the Co site of Co{sub 2}FeAl{sub 1−x}Si{sub x} versus x. • DFT proof of suppression of formation of antisites defects with x in Co{sub 2}FeAl{sub 1−x}Si{sub x}.

  19. Insight into mechanical properties and thermoelectric efficiency of Zr2CoZ (Z  =  Si, Ge) Heusler alloys

    Science.gov (United States)

    Yousuf, Saleem; Gupta, Dinesh C.

    2017-11-01

    We investigated the electronic, mechanical and thermoelectric properties of Zr2CoZ (Z  =  Si, Ge) Heusler alloys using the first-principles calculation. From the analysis of various elastic constants, the shear and Young’s moduli, Poisson’s ratio, the ductile nature of the alloys is predicted. Thermoelectric coefficients viz., Seebeck, electrical conductivity and figure of merit show Zr2CoZ alloys as n-type thermoelectric materials showing linearly increasing Seebeck coefficient with temperature. The value of total absolute Seebeck coefficients at 1200 K of Zr2CoSi and Zr2CoGe are 60 µV K‑1 and 40 µV K‑1 respectively mainly because of the existence of almost flat conduction bands along L to Г directions of high symmetry Brillouin zone. Further, the chemical potential variation of power factor confirms the n-type doping fruitful to increase their TE performance. The figure of merit achieves an upper-limit of 0.95 at 850 K and can favour their use for waste heat recovery at higher temperatures and thermoelectric spin generators.

  20. Basics and prospective of magnetic Heusler compounds

    Directory of Open Access Journals (Sweden)

    Claudia Felser

    2015-04-01

    Full Text Available Heusler compounds are a remarkable class of materials with more than 1000 members and a wide range of extraordinary multi-functionalities including halfmetallic high-temperature ferri- and ferromagnets, multi-ferroics, shape memory alloys, and tunable topological insulators with a high potential for spintronics, energy technologies, and magneto-caloric applications. The tunability of this class of materials is exceptional and nearly every functionality can be designed. Co2-Heusler compounds show high spin polarization in tunnel junction devices and spin-resolved photoemission. Manganese-rich Heusler compounds attract much interest in the context of spin transfer torque, spin Hall effect, and rare earth free hard magnets. Most Mn2-Heusler compounds crystallize in the inverse structure and are characterized by antiparallel coupling of magnetic moments on Mn atoms; the ferrimagnetic order and the lack of inversion symmetry lead to the emergence of new properties that are absent in ferromagnetic centrosymmetric Heusler structures, such as non-collinear magnetism, topological Hall effect, and skyrmions. Tetragonal Heusler compounds with large magneto crystalline anisotropy can be easily designed by positioning the Fermi energy at the van Hove singularity in one of the spin channels. Here, we give a comprehensive overview and a prospective on the magnetic properties of Heusler materials.

  1. Evolution of phase transformation and magnetic properties with Fe content in Ni55‑x Fe x Mn20Ga25 Heusler alloys

    Science.gov (United States)

    Zhang, Yuanlei; Li, Zhe; He, Xijia; Huang, Yinsheng; Xu, Kun; Jing, Chao

    2018-02-01

    A series of Ni55‑x Fe x Mn20Ga25 (0  ⩽  x  ⩽  5) Heusler alloys was prepared to investigate their phase transitions and magnetic properties. At room temperature, these alloys present various crystal structures, and the unit cell volume enlarges with increase of Fe content in both austenite and martensite. Multiple magneto-structural transformations were observed in the parent alloy (x  =  0). In the process of cooling, it undergoes martensitic transformation (MT) from L21-type paramagnetic austenite to L10-type ferromagnetic martensite, accompanying an intermartensitic transformation (IMT, 7M  →  L10). By establishing a detailed phase diagram, we found that both MT and IMT shift to lower temperature simultaneously, while the ferromagnetic (FM) transition of austenite moves to higher temperature as Fe increases. With the further increase of Fe content beyond a critical value, both the IMT and the FM transitions split off from MT, and the former follows with the transforming sequence of 7M  →  5M. Based on the experimental data, some key magnetic parameters have been obtained in this system. The calculated magnetocrystalline anisotropy constant ({{K}1} ) of martensite quickly increases as Fe increases, and then it almost reaches a saturated value (~5.5  ×  105 J m‑3) for the alloys with x  >  3. However, the spontaneous magnetic moment ({μs} ) attains a peak value of about 4.2 μ B/f.u. in the alloy with x  =  4, which is not consistent with the linear increasing of effective magnetic moment ({μef f} ). Further magnetic measurements with hydrostatic pressure indicate that such a discrepancy could be ascribed to the competition between the magnetic exchange interaction and the volume change of unit cell governed by the dopant Fe content.

  2. Structural characterization of half-metallic Heusler compound NiMnSb

    Energy Technology Data Exchange (ETDEWEB)

    Nowicki, L. E-mail: lech.nowicki@fuw.edu.pl; Abdul-Kader, A.M.; Bach, P.; Schmidt, G.; Molenkamp, L.W.; Turos, A.; Karczewski, G

    2004-06-01

    High resolution X-ray diffraction (HRXRD) and Rutherford backscattering/channeling (RBS/c) techniques were used to characterize layers of NiMnSb grown by molecular beam epitaxy (MBE) on InP with a In{sub x}Ga{sub 1-x}As buffer. Angular scans in the channeling mode reveal that the crystal structure of NiMnSb is tetragonally deformed with c/a=1.010{+-}0.002, in agreement with HRXRD data. Although HRXRD demonstrates the good quality of the pseudomorphic NiMnSb layers the channeling studies show that about 20% of atoms in the layers do not occupy lattice sites in the [0 0 1] rows of NiMnSb. The possible mechanisms responsible for the observed disorder are discussed.

  3. Half-metallicity in 2D organometallic honeycomb frameworks.

    Science.gov (United States)

    Sun, Hao; Li, Bin; Zhao, Jin

    2016-10-26

    Half-metallic materials with a high Curie temperature (T C) have many potential applications in spintronics. Magnetic metal free two-dimensional (2D) half-metallic materials with a honeycomb structure contain graphene-like Dirac bands with π orbitals and show excellent aspects in transport properties. In this article, by investigating a series of 2D organometallic frameworks with a honeycomb structure using first principles calculations, we study the origin of forming half-metallicity in this kind of 2D organometallic framework. Our analysis shows that charge transfer and covalent bonding are two crucial factors in the formation of half-metallicity in organometallic frameworks. (i) Sufficient charge transfer from metal atoms to the molecules is essential to form the magnetic centers. (ii) These magnetic centers need to be connected through covalent bonding, which guarantee the strong ferromagnetic (FM) coupling. As examples, the organometallic frameworks composed by (1,3,5)-benzenetricarbonitrile (TCB) molecules with noble metals (Au, Ag, Cu) show half-metallic properties with T C as high as 325 K. In these organometallic frameworks, the strong electronegative cyano-groups (CN groups) drive the charge transfer from metal atoms to the TCB molecules, forming the local magnetic centers. These magnetic centers experience strong FM coupling through the d-p covalent bonding. We propose that most of the 2D organometallic frameworks composed by molecule-CN-noble metal honeycomb structures contain similar half metallicity. This is verified by replacing TCB molecules with other organic molecules. Although the TCB-noble metal organometallic framework has not yet been synthesized, we believe the development of synthesizing techniques and facility will enable the realization of them. Our study provides new insight into the 2D half-metallic material design for the potential applications in nanotechnology.

  4. The effect of Pd on martensitic transformation and magnetic properties for Ni50Mn38−xPdxSn12Heusler alloys

    Directory of Open Access Journals (Sweden)

    C. Jing

    2016-05-01

    Full Text Available In the past decade, Mn rich Ni-Mn based alloys have attained considerable attention due to their abundant physics and potential application as multifunctional materials. In this paper, polycrystalline Ni50Mn38−xPdxSn12 (x = 0, 2, 4, 6 Heusler alloys have been prepared, and the martensitic phase transformation (MPT together with the shape memory effect and the magnetocaloric effect has been investigated. The experimental result indicates that the MPT evidently shifts to a lower temperature with increase of Pd substitution for Mn atoms, which can be attributed to the weakness of the hybridization between the Ni atom and excess Mn on the Sn site rather than the electron concentration. The physics properties study focused on the sample of Ni50Mn34Pd4Sn12 shows a good two-way shape memory behavior, and the maximum value of strain Δ L/L reaches about 0.13% during the MPT. The small of both entropy change Δ ST and magnetostrain can be ascribed to the inconspicuous influence of magnetic field induced MPT.

  5. Magnetic, thermal, and electrical properties of an Ni{sub 45.37}Mn{sub 40.91}In{sub 13.72} Heusler alloy

    Energy Technology Data Exchange (ETDEWEB)

    Batdalov, A. B.; Aliev, A. M., E-mail: lowtemp@mail.ru; Khanov, L. N. [Russian Academy of Sciences, Amirkhanov Institute of Physics, Dagestan Research Center (Russian Federation); Buchel’nikov, V. D.; Sokolovskii, V. V. [Chelyabinsk State University (Russian Federation); Koledov, V. V.; Shavrov, V. G.; Mashirov, A. V.; Dil’mieva, E. T. [Russian Academy of Sciences, Institute of Radio Engineering and Electronics (Russian Federation)

    2016-05-15

    The magnetization, the electrical resistivity, the specific heat, the thermal conductivity, and the thermal diffusion of a polycrystalline Heusler alloy Ni{sub 45.37}Mn{sub 40.91}In{sub 13.72} sample are studied. Anomalies, which are related to the coexistence of martensite and austenite phases and the change in their ratio induced by a magnetic field and temperature, are revealed and interpreted. The behavior of the properties of the alloy near Curie temperature T{sub C} also demonstrates signs of a structural transition, which suggests that the detected transition is a first-order magnetostructural phase transition. The nontrivial behavior of specific heat detected near the martensite transformation temperatures is partly related to a change in the electron density of states near the Fermi level. The peculiar peak of phonon thermal conductivity near the martensitic transformation is interpreted as a consequence of the appearance of additional soft phonon modes, which contribute to the specific heat and the thermal conductivity.

  6. Electronic structure and magneto-optical Kerr spectra of an epitaxial Ni54.3Mn31.9Sn13.8 Heusler alloy film

    Science.gov (United States)

    Uba, L.; Bonda, A.; Uba, S.; Bekenov, L. V.; Antonov, V. N.

    2017-07-01

    In this joint experimental and ab initio study, we investigated the influence of chemical composition and martensitic phase transition on the electronic, magnetic, optical and magneto-optical properties of ferromagnetic shape-memory Ni-Mn-Sn alloys. Optical properties and polar magneto-optical Kerr effect (MOKE) spectra for Ni-Mn-Sn alloy film of composition Ni54.3Mn31.9Sn13.8 deposited epitaxially on MgO(0 0 1) substrate were measured over the photon energy range 0.8≤slant hν ≤slant 5.8 eV, and the complete set of optical conductivity tensor elements were determined. To explain the microscopic origin of the optical and magneto-optical spectra, extensive first-principles calculations were made, using the spin-polarized fully relativistic linear-muffin-tin-orbital method. The electronic, magnetic and magneto-optical properties of Ni-Mn-Sn Heusler alloys were investigated for the cubic austenitic and 4O orthorhombic martensitic phases, in stoichiometric and off-stoichiometric compositions. The MOKE properties of Ni-Mn-Sn systems are very sensitive to deviation from stoichiometry. It was shown that the ab initio calculations reproduce experimental spectra well, and help to explain the microscopic origin of Ni-Mn-Sn optical and magneto-optical responses. The interband transitions responsible for the prominent structures in the Ni-Mn-Sn MOKE spectra have been identified—they come from relatively narrow energy intervals at several well-defined vicinities of high-symmetry directions of the Brillouin zone. Significant modification of the MOKE spectra can be considered as a fingerprint of martensitic phase transition in Ni-Mn-Sn alloys.

  7. Characterizing half-metallicity via magnetization dynamics on ultrafast timescales

    Energy Technology Data Exchange (ETDEWEB)

    Mann, Andreas; Ulrichs, Henning; Walowski, Jakob; Muenzenberg, Markus [I. Physikalisches Institut, Universitaet Goettingen (Germany); Schmalhorst, Jan; Thomas, Andy; Huetten, Andreas; Reiss, Guenter [Department of Physics, Universitaet Bielefeld (Germany)

    2009-07-01

    We study the magnetization dynamics of potential half-metals probed by the time-resolved magneto-optical Kerr effect (TRMOKE) using a femtosecond laser pump-probe setup (temporal resolution: 50 fs). Half metals are promising candidates for the development of so called 'spintronic' devices, because they possess a minority-spin band gap at the Fermi level and are therefore 100 % spin-polarized. The magnetization dynamics in ferromagnetic metals are generally marked by two characteristic timescales, a short demagnetization time {tau}{sub m} of several hundred fs and a relaxation time {tau}{sub e} in the ps range. In the special case of a half metal, the minority-spin band gap blocks the Elliot-Yafet scattering and thus slows down the demagnetization. The enlarged {tau}{sub m} of a few ps to ns which is governed by anisotropy fluctuations can be measured in our setup and indicates a half-metallic behaviour of the sample. More in detail, our experiments imply that the band gap of a half metal also has a subtle influence on the magnetization dynamics on the ultrafast timescale, evident in a steplike feature. We present an expansion of the three temperature model by Beaurepaire et al.

  8. Ni-Mn-Sn Heusler: milling and annealing effect on structural and magnetic properties

    Science.gov (United States)

    Popa, Florin; Florin Marinca, Traian; Florin Chicinaş, Horea; Isnard, Olivier; Chicinaş, Ionel

    2017-10-01

    Nanocrystalline Ni51Mn19Sn30 Heusler alloy was prepared in the form of powder by solid state reaction in a planetary ball mill under argon atmosphere. After 10 h of milling the samples exhibit a mixture of two phases: disordered Heusler structure and half-Heusler structure. The stability of the phases was studied and a transformation of the disordered Heusler phase into the ordered Heusler and Ni3Sn2 phase was observed after heat treatment. Magnetic properties strongly depend on the phases promoted during milling and annealing. The phase change after annealing leads to the increase of the sample’s magnetisation.

  9. Half-metallic magnetism in Ti3Co5-xFexB2

    Science.gov (United States)

    Pathak, Rohit; Ahamed, Imran; Zhang, W. Y.; Vallopilly, Shah; Sellmyer, D. J.; Skomski, Ralph; Kashyap, Arti

    2017-05-01

    Bulk alloys and thin films of Fe-substituted Ti3Co5B2 have been investigated by first-principle density-functional calculations. The series, which is of interest in the context of alnico magnetism and spin electronics, has been experimentally realized in nanostructures but not in the bulk. Our bulk calculations predict paramagnetism for Ti3Co5B2, Ti3Co4FeB2 and Ti3CoFe4B2, whereas Ti3Fe5B2 is predicted to be ferromagnetic. The thin films are all ferromagnetic, indicating that moment formation may be facilitated at nanostructural grain boundaries. One member of the thin-film series, namely Ti3CoFe4B2, is half-metallic and exhibits perpendicular easy-axis magnetic anisotropy. The half-metallicity reflects the hybridization of the Ti, Fe and Co 3d orbitals, which causes a band gap in minority spin channel, and the limited equilibrium solubility of Fe in bulk Ti3Co5B2 may be linked to the emerging half-metallicity due to Fe substitution.

  10. Half-metallic magnetism in Ti3Co5-xFexB2

    Directory of Open Access Journals (Sweden)

    Rohit Pathak

    2017-05-01

    Full Text Available Bulk alloys and thin films of Fe-substituted Ti3Co5B2 have been investigated by first-principle density-functional calculations. The series, which is of interest in the context of alnico magnetism and spin electronics, has been experimentally realized in nanostructures but not in the bulk. Our bulk calculations predict paramagnetism for Ti3Co5B2, Ti3Co4FeB2 and Ti3CoFe4B2, whereas Ti3Fe5B2 is predicted to be ferromagnetic. The thin films are all ferromagnetic, indicating that moment formation may be facilitated at nanostructural grain boundaries. One member of the thin-film series, namely Ti3CoFe4B2, is half-metallic and exhibits perpendicular easy-axis magnetic anisotropy. The half-metallicity reflects the hybridization of the Ti, Fe and Co 3d orbitals, which causes a band gap in minority spin channel, and the limited equilibrium solubility of Fe in bulk Ti3Co5B2 may be linked to the emerging half-metallicity due to Fe substitution.

  11. First Principles and Monte Carlo Calculations of Structural and Magnetic Properties of FexNi2-xMn1+yAl1-y Heusler Alloys

    Directory of Open Access Journals (Sweden)

    Zagrebin Mikhail

    2015-01-01

    Full Text Available The composition dependences of crystal lattice parameters, bulk moduli, magnetic moments, magnetic exchange parameters, and Curie temperatures in FexNi2-xMn1+yAl1-y (0.2 ≤ x ≤ 1.8; 0.0 ≤ y ≤ 0.6 Heusler alloys are investigated with the help of first principles and Monte Carlo calculations. It is shown that equilibrium lattice parameters and MnY-MnZ magnetic exchange interactions increase with increasing Fe content (x. A crossover from ferromagnetic to antiferromagnetic interaction between nearest neighbors MnY and MnZ atoms was observed in compositions with x ≥ 1.4 and 0.2 ≤ y ≤ 0.6. Such magnetic competitive behavior points to a complex magnetic structure in FexNi2-xMn1+yAl1-y. Calculated values of lattice parameters, magnetic moments, and Curie temperatures are in a good agreement with other theoretical results and available experimental data.

  12. Fabrication of MgAl2O4 Thin Films on Ferromagnetic Heusler Alloy Fe2CrSi by Reactive Magnetron Sputtering

    Science.gov (United States)

    Fukatani, Naoto; Inagaki, Keima; Mari, Kenichiro; Fujita, Hirohito; Miyawaki, Tetsuta; Ueda, Kenji; Asano, Hidefumi

    2012-02-01

    Epitaxial MgAl2O4 thin films were grown on Heusler alloy Fe2CrSi by reactive magnetron sputtering of a MgAl2 target in an O2+Ar atmosphere. To grow MgAl2O4 on Fe2CrSi, we inserted a protective layer of MgAl2 between Fe2CrSi and MgAl2O4 to prevent Fe2CrSi from being oxidized. Growth of MgAl2O4 was found to be very sensitive to the MgAl2 thickness and PO2 during deposition of MgAl2O4. A strong XRD peak of MgAl2O4 (004) was observed with an ultrathin (0.2 nm) MgAl2 layer. The saturation magnetic moment of Fe2CrSi was measured to be 370 emu/cm3 (1.84 µB/f.u.) at room temperature and it is expected to have a high spin polarization. The Fe2CrSi/MgAl2O4 heterostructure is promising for use in future spintronic devices.

  13. Moessbauer and NMR study of Heusler alloy Co{sub 2}Mn{sub 1-x}Fe{sub x}Si

    Energy Technology Data Exchange (ETDEWEB)

    Ksenofontov, Vadim; Kandpal, Hem C.; Balke, Benjamin; Felser, Claudia [Institut fuer Anorganische Chemie und Analytische Chemie, Johannes Gutenberg Univ. Mainz (Germany); Wojcik, Marek [Institute of Physics, Polish Academy of Sciences, Warszawa (Poland)

    2007-07-01

    The Heusler alloys Co{sub 2}Mn{sub 1-x}Fe{sub x}Si have recently attracted particular interest due to the unique possibility to tune the spin polarization by varying the Mn/Fe fraction. The calculated band structures show the shift of the Fermi energy from the top of the minority valence band for Co{sub 2}MnSi to the bottom of the minority conduction band for Co{sub 2}FeSi upon Fe doping. From computational results it has been predicted that a compound with an intermediate Fe concentration of about 50% should be best suited for spintronic applications. These theoretical findings still require experimental proofs. We report on 57 Fe Moessbauer spectroscopic, {sup 59}Co and {sup 55}Mn NMR studies of hyperfine magnetic fields (HFF) in Co{sub 2}Mn{sub 1-x}Fe{sub x}Si (0{<=}x{<=}1). The hyperfine magnetic field on Fe atoms is non-monotonic and shows maximum at x=0.5. We argue that the maximum value of the HFF found on Fe and Co atoms at x=0.5 is due to the existence of maximal spin-polarization in Co{sub 2}Mn{sub 0.5}Fe{sub 0.5}Si. Experimentally found HFF values are compared with results following from electronic band structure calculations taking into account electronic correlations (LDA+U).

  14. Thermomagnetic and magnetocaloric properties of metamagnetic Ni-Mn-In-Co Heusler alloy in magnetic fields up to 140 kOe

    Directory of Open Access Journals (Sweden)

    Kamantsev Alexander

    2014-07-01

    Full Text Available High cooling power of magnetocaloric refrigeration can be achieved only at large amounts of heat, which can be transferred in one cycle from cold end hot end at quasi-isothermal conditions. The simple and robust experimental method of direct measuring of the transferred heat of materials with magnetocaloric effect (MCE in thermal contact with massive copper block with definite heat capacity in quasi-isothermal regime was proposed. The vacuum calorimeter for the specific transferred heat ΔQ and adiabatic temperature change ΔT measurements of MCE materials in the fields of Bitter coil magnet up to H = 140 kOe was designed and tested on samples of Ni43Mn37.9In12.1Co7 Heusler alloy with inverse MCE in the vicinity of meta-magnetostructural phase transition (PT. It was found, that the magnetic field H = 80 kOe produces complete PT from martensite to austenite with ΔQ = - 1600 J/kg at initial temperature 273 K.

  15. Ab Initio and Monte Carlo Approaches For the Magnetocaloric Effect in Co- and In-Doped Ni-Mn-Ga Heusler Alloys

    Directory of Open Access Journals (Sweden)

    Vladimir Sokolovskiy

    2014-09-01

    Full Text Available The complex magnetic and structural properties of Co-doped Ni-Mn-Ga Heusler alloys have been investigated by using a combination of first-principles calculations and classical Monte Carlo simulations. We have restricted the investigations to systems with 0, 5 and 9 at% Co. Ab initio calculations show the presence of the ferrimagnetic order of austenite and martensite depending on the composition, where the excess Mn atoms on Ga sites show reversed spin configurations. Stable ferrimagnetic martensite is found for systems with 0 (5 at% Co and a c=a ratio of 1.31 (1.28, respectively, leading to a strong competition of ferro- and antiferro-magnetic exchange interactions between nearest neighbor Mn atoms. The Monte Carlo simulations with ab initio exchange coupling constants as input parameters allow one to discuss the behavior at finite temperatures and to determine magnetic transition temperatures. The Curie temperature of austenite is found to increase with Co, while the Curie temperature of martensite decreases with increasing Co content. This behavior can be attributed to the stronger Co-Mn, Mn-Mn and Mn-Ni exchange coupling constants in austenite compared to the corresponding ones in martensite. The crossover from a direct to inverse magnetocaloric effect in Ni-Mn-Ga due to the substitution of Ni by Co leads to the appearance of a “paramagnetic gap” in the martensitic phase. Doping with In increases the magnetic jump at the martensitic transition temperature. The simulated magnetic and magnetocaloric properties of Co- and In-doped Ni-Mn-Ga alloys are in good qualitative agreement with the available experimental data.

  16. Structural, magnetic and magnetocaloric properties of Heusler alloys Ni{sub 50}Mn{sub 38}Sb{sub 12} with boron addition

    Energy Technology Data Exchange (ETDEWEB)

    Nong, N.V., E-mail: ngno@risoe.dtu.dk [Fuel Cells and Solid State Chemistry Division, Riso National Laboratory for Sustainable Energy, Technical University of Denmark, 4000 Roskilde (Denmark); Tai, L.T. [Cryogenic Laboratory, Faculty of Physics, Hanoi University of Science, Vietnam National University, 334 Nguyen Trai, Hanoi (Viet Nam); Huy, N.T. [PetroVietnam University, 173 Trung Kinh, Hanoi (Viet Nam); Trung, N.T. [Fundamental Aspects of Materials and Energy, Faculty of Applied Sciences, TU Delft, Mekelweg 15, 2629 JB Delft (Netherlands); Bahl, C.R.H.; Venkatesh, R.; Poulsen, F.W.; Pryds, N. [Fuel Cells and Solid State Chemistry Division, Riso National Laboratory for Sustainable Energy, Technical University of Denmark, 4000 Roskilde (Denmark)

    2011-09-25

    Highlights: > We investigate the influence of the additional boron atoms on the structural, magnetic and magnetocaloric properties of Heusler alloys Ni{sub 50}Mn{sub 38}Sb{sub 12}B{sub x} with x = 1, 3, and 5. > We found that both the paramagnetic-ferromagnetic austenitic transition (T{sub C}) and the ferromagnetic-antiferromagnetic martensitic transition (T{sub M}) are tunable by varying the boron concentration. > Temperature dependent X-ray diffraction clearly shows a martensitic-austenitic magneto-structural transformation on heating. > Interestingly, the addition of boron atoms into the lattice favours the ferromagnetic ordering relatively to the antiferromagnetic arrangement below T{sub M}. This consequently affects on the magneto-structural transition as well as the size of magnetocaloric effect at T{sub M}. - Abstract: We report on the structural, magnetic and magnetocaloric properties of the Ni{sub 50}Mn{sub 38}Sb{sub 12}B{sub x} alloys in term of boron addition with x = 1, 3 and 5. We have found that both the paramagnetic-ferromagnetic austenitic transition (T{sub C}) and the ferromagnetic-antiferromagnetic martensitic transition (T{sub M}) are sensitively influenced by the boron addition: T{sub C} tends to increase, while T{sub M} decreases with increasing boron concentration. Temperature dependent X-ray diffraction in the range of 200-500 K clearly shows an evolution of the structural transformation from orthorhombic to cubic structure phase transition on heating for the x = 1 and 3 samples. Strikingly, the addition of boron atoms into the lattice favours the ferromagnetic ordering relatively to the antiferromagnetic arrangement below T{sub M}. This consequently affects on the magneto-structural transition as well as on the size of magnetocaloric effect.

  17. Electronic structure, magnetic properties and electrical resistivity of the Fe(2)V(1-x)Ti(x)Al Heusler alloys: experiment and calculation.

    Science.gov (United States)

    Slebarski, A; Goraus, J; Deniszczyk, J; Skoczeń, L

    2006-11-22

    The aim of this work is to investigate electronic structure, magnetic properties and electrical resistivity of Fe(2)V(1-x)Ti(x)Al Heusler alloys. Numerical calculations give a pseudogap at the Fermi level for the majority-spin band of Fe(2)TiAl and a magnetic moment larger than 0.9 μ(B), whereas the ground state of Fe(2)VAl is calculated as a nonmagnetic semimetal with a very low total density of states at the Fermi level. In our calculations the remaining alloys of the Fe(2)V(1-x)Ti(x)Al series are nonmagnetic for xmagnetic for 0.1magnetic moment μ of the series of Fe(2)V(1-x)Ti(x)Al compounds scales with the number of valence electrons and fits well to the Slater-Pauling curve. We also present a study of the electronic transport properties and magnetic susceptibility. The resistivities ρ(T) of Fe(2)VAl and Fe(2)V(0.9)Ti(0.1)Al are large and exhibit a negative temperature coefficient dρ/dT of the resistivity between 2 and 300 K. Below 20 K, ρ(T) also shows an activated character. The magnetic susceptibility of Fe(2)VAl and Fe(2)V(0.9)Ti(0.1)Al shows a maximum at ∼2 K which could reflect either the disorder effect or the hybridization gap, characteristic of Kondo insulators.

  18. First principles study of the structural properties of Ni1.75Co0.25Mn1.5-xCrxIn0.5 Heusler alloy

    Directory of Open Access Journals (Sweden)

    Pavlukhina Oksana

    2015-01-01

    Full Text Available In this work, the structural and magnetic properties of Cr – doped Ni1.75Co0.25MnCr0.5In0.5 Heusler alloys are investigated by using the density functional theory calculations. The chemical disorder is treated by the 16-atom supercell approach. Three compositions with substitution of 6.25%, 12.5 %, 18.75%, and 25% Cr for Mn are taken into consideration. The formation energy, magnetic moments and lattice parameters depending on the Cr content are found. It is shown that compositions with 6.25% and 12.5% of Cr are energetically stable in austenite.

  19. New type of half-metallic antiferromagnet: transition metal pnictides

    Science.gov (United States)

    Long, N. H.; Ogura, M.; Akai, H.

    2009-02-01

    The electronic structures of transition metal pnictides ABX2, where A and B are the transition metal elements and X = N, P, As, Sb, and Bi, with the total valence d-electron number of the transition metal ions being ten, are investigated in the framework of the first-principles KKR Green's function method. Some possible crystal structures such as NiAs-type, NaCl-type, chalcopyrite, zinc-blende, wurtzite, and MnP-type structures are assumed. Similarly to chalcogenides, a new type of spin-compensated half-metallic ferrimagnet is found for the case of nitrides. The stability and magnetic transition temperature of these nitrides indicate that they are good candidates for spintronics materials. For other cases of pnictides such as P, As, Sb, and Bi, the half-metallicity seems not to be realized.

  20. Intrinsic half-metallicity in fractal carbon nitride honeycomb lattices.

    Science.gov (United States)

    Wang, Aizhu; Zhao, Mingwen

    2015-09-14

    Fractals are natural phenomena that exhibit a repeating pattern "exactly the same at every scale or nearly the same at different scales". Defect-free molecular fractals were assembled successfully in a recent work [Shang et al., Nature Chem., 2015, 7, 389-393]. Here, we adopted the feature of a repeating pattern in searching two-dimensional (2D) materials with intrinsic half-metallicity and high stability that are desirable for spintronics applications. Using first-principles calculations, we demonstrate that the electronic properties of fractal frameworks of carbon nitrides have stable ferromagnetism accompanied by half-metallicity, which are highly dependent on the fractal structure. The ferromagnetism increases gradually with the increase of fractal order. The Curie temperature of these metal-free systems estimated from Monte Carlo simulations is considerably higher than room temperature. The stable ferromagnetism, intrinsic half-metallicity, and fractal characteristics of spin distribution in the carbon nitride frameworks open an avenue for the design of metal-free magnetic materials with exotic properties.

  1. Tunnel magnetoresistance effect in magnetic tunnel junctions using Fermi-level-tuned epitaxial Fe2Cr1-xCoxSi Heusler alloy

    Science.gov (United States)

    Wang, Yu-Pu; Han, Gu-Chang; Lu, Hui; Qiu, Jinjun; Yap, Qi-Jia; Teo, Kie-Leong

    2014-05-01

    This paper reports a systematic investigation on the structural and magnetic properties of Fe2Cr1-xCoxSi Heusler alloys with various compositions of x by co-sputtering Fe2CrSi and Fe2CoSi targets and their applications in magnetic tunnel junctions (MTJs). Fe2Cr1-xCoxSi films of high crystalline quality have been epitaxially grown on MgO substrate using Cr as a buffer layer. The L21 phase can be obtained at x = 0.3 and 0.5, while B2 phase for the rest compositions. A tunnel magnetoresistance (TMR) ratio of 19.3% at room temperature is achieved for MTJs using Fe2Cr0.3Co0.7Si as the bottom electrode with 350 °C post-annealing. This suggests that the Fermi level in Fe2Cr1-xCoxSi has been successfully tuned close to the center of band gap of minority spin with x = 0.7 and therefore better thermal stability and higher spin polarization are achieved in Fe2Cr0.3Co0.7Si. The post-annealing effect for MTJs is also studied in details. The removal of the oxidized Fe2Cr0.3Co0.7Si at the interface with MgO barrier is found to be the key to improve the TMR ratio. When the thickness of the inserted Mg layer increases from 0.3 to 0.4 nm, the TMR ratio is greatly enhanced from 19.3% to 28%.

  2. Evidence for the absence of electron-electron Coulomb interaction quantum correction to the anomalous Hall effect in Co2FeSi Heusler-alloy thin films

    Science.gov (United States)

    Hazra, Binoy Krishna; Kaul, S. N.; Srinath, S.; Raja, M. Manivel; Rawat, R.; Lakhani, Archana

    2017-11-01

    Electrical (longitudinal) resistivity ρx x, at H =0 and H =80 kOe, anomalous Hall resistivity ρxy A H, and magnetization M , have been measured at different temperatures in the range 5-300 K on the Co2FeSi (CFS) Heusler-alloy thin films, grown on Si(111) substrate, with thickness ranging from 12 to 100 nm. At fixed fields H =0 and H =80 kOe, ρx x(T ) goes through a minimum at T =Tmin (which depends on the film thickness) in all the CFS thin films. In sharp contrast, both the anomalous Hall coefficient RA and ρxy A H monotonously increase with temperature without exhibiting a minimum. Elaborate analyses of ρx x, RA, and ρxy A H establishes the following. (i) The enhanced electron-electron Coulomb interaction (EEI) quantum correction (QC) is solely responsible for the upturn in "zero-field" and "in-field" ρx x(T ) at T value of 103 S/cm when the Fermi level is located near the anticrossing of band dispersions split by spin-orbit interaction. This suppression is shown to correspond to one or both of the possibilities: the resonance condition is not satisfied, or the interband spin-flip inelastic electron-magnon scattering enhances the side-jump contribution at the expense of the intrinsic contribution. We demonstrate that RA, or equivalently ρxy A H, scales with ρx x T, the temperature-dependent part of ρx x, over a considerably wide temperature range (5-300 K) only when ρxy A H is corrected for the observed temperature dependence of spontaneous magnetization and ρx x for the EEI effects.

  3. The Effect of a Multiphase Microstructure on the Inverse Magnetocaloric Effect in Ni–Mn–Cr–Sn Metamagnetic Heusler Alloys

    Directory of Open Access Journals (Sweden)

    Paweł Czaja

    2017-07-01

    Full Text Available Two Ni–Mn–Sn alloys substituted with 0.5 and 1 at.% Cr have been studied. The first alloy shows an average composition of Ni49.6Mn37.3Cr0.7Sn12.4 (e/a = 8.107, whereas the second has a multiphase microstructure with the matrix phase of an average Ni52.4Mn32.7Cr1Sn14 composition (e/a = 8.146. Both alloys undergo a reversible martensitic phase transformation. The Ni49.6Mn37.3Cr0.7Sn12.4 alloy transforms to the martensite phase at 239 K and, under the magnetic field change of μ0·ΔH = 1.5 T, gives the magnetic entropy change equal to 7.6 J/kg·K. This amounts to a refrigerant capacity in the order of 48.6 J/kg, reducible by 29.8% due to hysteresis loss. On the other hand, the alloy with a multiphase microstructure undergoes the martensitic phase transformation at 223 K with the magnetic entropy change of 1.7 J/kg·K (1 T. Although the latter spreads over a broader temperature window in the multiphase alloy, it gives much smaller refrigerant capacity of 16.2 J/kg when compared to Ni49.6Mn37.3Cr0.7Sn12.4. The average hysteresis loss for a field change of 1.5 T in the multiphase alloy is 2.7 J/kg, reducing the effective refrigerant capacity by 16.7%. These results illustrate that the key to gaining a large effective refrigerant capacity is the synergy between the magnitude of the magnetic entropy change and its broad temperature dependence.

  4. Annealing effect on the crystal structure and exchange bias in Heusler Ni{sub 45.5}Mn{sub 43.0}In{sub 11.5} alloy ribbons

    Energy Technology Data Exchange (ETDEWEB)

    González-Legarreta, L. [Department of Physics, University of Oviedo, Calvo Sotelo s/n, 33007 Oviedo (Spain); Rosa, W.O. [Centro Brasileiro de Pesquisas Físicas, Rua Dr. Xavier Sigaud, 150 Urca., 22290-180 Rio de Janeiro, RJ (Brazil); García, J. [Department of Physics, University of Oviedo, Calvo Sotelo s/n, 33007 Oviedo (Spain); Ipatov, M.; Nazmunnahar, M. [Department of Materials Physics, Faculty of Chemistry, University of the Basque Country, 20018 San Sebastian (Spain); Escoda, L.; Suñol, J.J. [Department of Physics, Campus Montilivi s/n, University of Girona, 17071 Girona (Spain); Prida, V.M. [Department of Physics, University of Oviedo, Calvo Sotelo s/n, 33007 Oviedo (Spain); Sommer, R.L. [Centro Brasileiro de Pesquisas Físicas, Rua Dr. Xavier Sigaud, 150 Urca., 22290-180 Rio de Janeiro, RJ (Brazil); González, J. [Department of Materials Physics, Faculty of Chemistry, University of the Basque Country, 20018 San Sebastian (Spain); Leoni, M. [Department of Material Engineering and Industrial Technologies, University of Trento, Via Mesiano 77, I-38123 Trento (Italy); Hernando, B., E-mail: grande@uniovi.es [Department of Physics, University of Oviedo, Calvo Sotelo s/n, 33007 Oviedo (Spain)

    2014-01-05

    Highlights: • Preparation of Ni–Mn–In Heusler alloys by melt spinning technique in ribbon shape. • Short annealing effects on the crystal structure, microstructure and magnetic properties. • Influence of annealing on the martensitic transformation. • Enhancement of the exchange bias effect. -- Abstract: A Heusler Ni{sub 45.5}Mn{sub 43.0}In{sub 11.5} alloy has been prepared by arc melting and produced in a ribbon shape by rapid solidification using melt spinning technique. Structural properties have been investigated, at different temperatures, by using X-ray diffraction. Austenite is the stable phase at room temperature with a L2{sub 1} cubic crystal structure. Exchange bias effect was observed after field cooling by means of hysteresis loop measurements. At 5 K, hysteresis loop shifts along the axis of the applied magnetic field and that shift magnitude decreases significantly with increasing temperature. A piece of ribbon was annealed at 973 K during 10 min in order to investigate the influence of annealing on crystal structure and magnetic properties. After annealing, a martensitic phase with a monoclinic 10M structure at room temperature is observed. The onset of the martensitic phase transformation shifts to 365 K, temperatures associated with both martensitic and reverse transitions do not change noticeably under an applied magnetic field up to 30 kOe, and a drastic decrease on magnetization is observed in comparison with the as-quenched ribbon meanwhile the exchange bias effect is enhanced.

  5. Boron Triangular Kagome Lattice with Half-Metallic Ferromagnetism.

    Science.gov (United States)

    Kim, Sunghyun; Han, W H; Lee, In-Ho; Chang, K J

    2017-08-04

    Based on the first-principles evolutionary materials design, we report a stable boron Kagome lattice composed of triangles in triangles on a two-dimensional sheet. The Kagome lattice can be synthesized on a silver substrate, with selecting Mg atoms as guest atoms. While the isolated Kagome lattice is slightly twisted without strain, it turns into an ideal triangular Kagome lattice under tensile strain. In the triangular Kagome lattice, we find the exotic electronic properties, such as topologically non-trivial flat band near the Fermi energy and half-metallic ferromagnetism, and predict the quantum anomalous Hall effect in the presence of spin-orbit coupling.

  6. Structural, magnetic and magnetocaloric properties of Heusler alloys Ni50Mn38Sb12 with boron addition

    DEFF Research Database (Denmark)

    Van Nong, Ngo; Tai, N.T.; Huy, N.T.

    2011-01-01

    We report on the structural, magnetic and magnetocaloric properties of the Ni50Mn38Sb12Bx alloys in term of boron addition with x=1, 3 and 5. We have found that both the paramagnetic–ferromagnetic austenitic transition (TC) and the ferromagnetic–antiferromagnetic martensitic transition (TM...

  7. Investigation of multifunctional properties of Mn{sub 50}Ni{sub 40−x}Co{sub x}Sn{sub 10} (x = 0–6) Heusler alloys

    Energy Technology Data Exchange (ETDEWEB)

    Sharma, Jyoti; Suresh, K.G., E-mail: suresh@phy.iitb.ac.in

    2015-01-25

    Highlights: • Mn{sub 50}Ni{sub 40−x}Co{sub x}Sn{sub 10} Heusler alloys exhibit multifunctional properties. • Co doping results decrease in martensitic transition temperature and increase in T{sub C}{sup A}. • Ferromagnetic coupling increases with increase in Co concentration. • Large positive ΔS{sub M} of 10.5 J/kg K and large RCP of 125 J/kg was obtained for x = 1. • Large exchange bias field of 833 Oe was observed for Mn{sub 50}Ni{sub 39}Co{sub 1}Sn{sub 10} alloy. - Abstract: A series of Co doped Mn{sub 50}Ni{sub 40−x}Co{sub x}Sn{sub 10} (x = 0, 1, 2, 2.5, 3, 4 and 6) Heusler alloys has been investigated for their structural, magnetic, magnetocaloric and exchange bias properties. The martensitic transition temperatures are found to decrease with the increase in Co concentration due to the decrease in valence electron concentration (e/a ratio). The Curie temperature of austenite phase increases significantly with increasing Co concentration. A large positive magnetic entropy change (ΔS{sub M}) of 8.6 and 10.5 J/kg K, for a magnetic field change of 50 kOe is observed for x = 0 and 1 alloys, and ΔS{sub M} values decreases for higher Co concentrations. The relative cooling power shows a monotonic increase with the increase in Co concentration. Large exchange bias fields of 920 Oe and 833 Oe have been observed in the alloys with compositions x = 0 and 1, after field cooling in presence of 10 kOe. The unidirectional anisotropy arising at the interface between the frustrated and ferromagnetic phases is responsible for the large exchange bias observed in these alloys. With increase in Co, the magnetically frustrated phase diminishes in strength, giving rise to a decrease in the exchange bias effect for larger Co concentration. The exchange bias fields observed for compositions x = 0 and 1, in the present case are larger than that reported for Co doped Ni–Mn–Z (Z = Sn, Sb, and Ga) alloys. Temperature and cooling field dependence of the exchange bias

  8. Epitaxial growth and physical properties of Heusler/perovskite heterostructures

    Science.gov (United States)

    Kobayashi, K.; Ueda, K.; Fukatani, N.; Kawada, H.; Sakuma, K.; Asano, H.

    2013-08-01

    Multiferroic heterostructures of the ferromagnetic, half-metallic Heusler Fe2CrSi (FCS) and the ferroelectric perovskite Ba0.7Sr0.3TiO3 (BSTO) have been formed by magnetron sputtering, and their magnetic and ferroelectric properties have been investigated. FCS/BSTO bilayer structures were epitaxially grown on LaAlO3 substrates with epitaxial relationships of FCS (001)[110]//BSTO (001)[100]. Multiferroic properties with a remanent polarization of 10.6 µC/cm2 and a saturation magnetization of 417 emu/cc were observed for the FCS/BSTO heterostructures at room temperature. These results suggest that the Heusler/perovskite epitaxial heterostructure is a promising candidate for fabricating multiferroic devices.

  9. Structure and composition of layers of Ni-Co-Mn-In Heusler alloys obtained by pulsed laser deposition

    Directory of Open Access Journals (Sweden)

    Wisz Grzegorz

    2017-01-01

    Full Text Available In present work we were analysing thin layers of Ni-Co-Mn-In alloys, grown by pulsed laser deposition method (PLD on Si, NaCl and glass substrates. For target ablation the second harmonics of YAG:Nd3+ laser was used. The target had the composition Ni45Co5Mn34.5In14.5. The morphology of the layers and composition were studied by electron microscopy TESCAN Vega3 equipped with microanalyzer EDS – Easy EdX system working with Esprit Bruker software. The X-ray diffraction measurements (XRD, performed on spectrometer Bruker XRD D8 Advance system, reveals Ni2-Mn-In cubic phase having lattice constant a = 6.02Å.

  10. Transport measurements on superconducting iron pnictides and Heusler compounds; Transportmessungen an Supraleitenden Eisenpniktiden und Heusler-Verbindungen

    Energy Technology Data Exchange (ETDEWEB)

    Bombor, Dirk

    2014-09-05

    In this work, results of electronic transport measurements are discussed for superconducting iron pnictides as well as for ferromagnetic Heusler compounds. The iron pnictides are a recently discovered class of high temperature superconductors where magnetism might play a crucial role. While the 122-pnictides show antiferromagnetism and migrate to the superconducting state upon doping, ferromagnetism has been observed in doped LiFeAs. On the other hand, in the undoped state this material shows interesting superconducting properties. Among other properties, Heusler compounds are well known due to their ferromagnetism. Co{sub 2}FeSi, which was investigated in this work, is one of the strongest ferromagnets. Beside this, one predicts this compound to be a half-metallic ferromagnet with completely spin polarized electronic transport where all conducting electrons have the same spin. The here addressed properties can well be investigated with the method of electronic transport measurements, whose results on single crystals are discussed in this work.

  11. Martensitic transformation and magnetic properties of manganese-rich Ni-Mn-In and Ni-Mn-Sn Heusler alloys; Untersuchung der martensitischen Umwandlung und der magnetischen Eigenschaften Mangan-reicher Ni-Mn-In- und Ni-Mn-Sn-Heusler-Legierungen

    Energy Technology Data Exchange (ETDEWEB)

    Krenke, T.

    2007-06-29

    In the present work, the martensitic transition and the magnetic properties of Manganese rich Ni{sub 50}Mn{sub 50-x}Sn{sub x} and Ni{sub 50}Mn{sub 50-y}In{sub y} alloys with 5 at%{<=}x(y){<=}25 at% were investigated. Calorimetry, X-ray and neutron diffraction, magnetization, and strain measurements were performed on polycrystalline samples. It was shown that alloys close to the stoichiometric composition Ni{sub 50}Mn{sub 25}Sn{sub 25} and Ni{sub 50}Mn{sub 25}Sn{sub 25} do not exhibit a structural transition on lowering of the temperature, whereas alloys with x{<=}15 at% Tin and y{<=}16 at% Indium transform martensitically. The structural transition temperatures increase linearly with decreasing Tin or Indium content. The crystal structures of the low temperature martensite are modulated as well as unmodulated. Alloys with compositions close to stoichiometry are dominated by ferromagnetic interactions, whereas those close to the binary composition Ni{sub 50}Mn{sub 50} order antiferromagnetically. Ferromagnetic order and structural instability coexist in a narrow composition range between 13 at%{<=}x{<=}15 at% and 15 at%{<=}x{<=}16 at% for Ni{sub 50}Mn{sub 50-x}Sn{sub x} and Ni{sub 50}Mn{sub 50-y}In{sub y} respectively. As a consequence, interesting magnetoelastic effects are observed. The Ni{sub 50}Mn{sub 34}In{sub 16} alloy shows a magnetic field-induced structural transition, whereby application of an external magnetic field in the martensitic state stabilizes the high temperature L2{sub 1} structure. Evidence for this was given by neutron diffraction experiments in external magnetic fields. Moreover, the structural transition temperatures of this alloy show large magnetic field dependencies. By use of calorimetry, M(T), and strain measurements, changes in M{sub s} up to -11 K/Tesla are observed. Such large values have, until now, not been observed in Heusler alloys. Since during transformation the volume changes reversibly, magnetic field-induced strains of about

  12. Thermal and Structural Analysis of Mn49.3Ni43.7Sn7.0 Heusler Alloy Ribbons

    Directory of Open Access Journals (Sweden)

    Tarek Bachaga

    2015-02-01

    Full Text Available The martensitic transformation and the solidification structures of Mn49.3Ni43.7Sn7.0 alloy ribbons prepared by melt-spinning were investigated by means of scanning electron microscopy, X-ray diffraction and differential scanning calorimetry. In those experiments special attention was given to melt spinning processing parameters such as the linear surface speed of the copper wheel rotating, the injection overpressure and the distance between wheel and injection quartz tube. Transformation entropy was found higher when increasing linear surface speed or the distance from injection point to wheel. The resulting samples showed chemical compositions close to the nominal ones and, at room temperature, crystallized in a monoclinic single-phase martensite with 14M modulation (without a significant variation in the cell parameters. Strong dependence of ribbon thickness on processing parameters was found. The average grain size varied between 1.6 and 6.6 μm, while the start temperature of the martensitic temperature varied from 394 to 430 K.

  13. A first principles study on the full-Heusler compound Mn{sub 2}CuSi

    Energy Technology Data Exchange (ETDEWEB)

    Wei Xiaoping; Hu Xianru; Chu Shibing; Mao Geyong; Hu Leibo; Lei Tao [Department of Physics, Lanzhou University, Lanzhou 730000 (China); Deng Jianbo, E-mail: dengjb@lzu.edu.c [Department of Physics, Lanzhou University, Lanzhou 730000 (China)

    2011-03-01

    Using a state-of-the-art full-potential electronic structure method within the generalized gradient approximation (GGA), we study the electronic structure and magnetic properties of the Mn{sub 2}CuSi full-Heusler alloy. Calculations show that CuHg{sub 2}Ti-type structure alloy is a half-metallic ferrimagnet with the Fermi level ({epsilon}{sub F}) being located within a tiny gap of the minority-spin density of states. The conduction electron at {epsilon}{sub F} keeps a 100% spin polarization. A total spin moment, which is mainly due to the antiparallel configurations of the Mn partial moments, is -1.00{mu}{sub B} for a wide range of equilibrium lattice parameters. Simultaneously, the small spin magnetic moments of Cu and Si atoms are antiparallel. The gap mainly originates from the hybridization of the d states of the two Mn atoms. Thus, Mn{sub 2}CuSi may be the compound of choice for further experimental investigations.

  14. Large magnetoresistance in Heusler-alloy-based epitaxial magnetic junctions with semiconducting Cu(In{sub 0.8}Ga{sub 0.2})Se{sub 2} spacer

    Energy Technology Data Exchange (ETDEWEB)

    Kasai, S. [Research Center for Magnetic and Spintronic Materials, National Institute for Materials Science (NIMS), 1-2-1 Sengen, Tsukuba 305-0047 (Japan); Center for Emergent Matter Science, RIKEN, 2-1 Hirosawa, Wako 351-0198 (Japan); Takahashi, Y. K.; Ohkubo, T. [Research Center for Magnetic and Spintronic Materials, National Institute for Materials Science (NIMS), 1-2-1 Sengen, Tsukuba 305-0047 (Japan); Cheng, P.-H.; Ikhtiar,; Mitani, S.; Hono, K. [Research Center for Magnetic and Spintronic Materials, National Institute for Materials Science (NIMS), 1-2-1 Sengen, Tsukuba 305-0047 (Japan); Graduate School of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba 305-8577 (Japan); Kondou, K. [Center for Emergent Matter Science, RIKEN, 2-1 Hirosawa, Wako 351-0198 (Japan); Otani, Y. [Center for Emergent Matter Science, RIKEN, 2-1 Hirosawa, Wako 351-0198 (Japan); Institute for Solid State Physics, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa 277-8581 (Japan)

    2016-07-18

    We investigated the structure and magneto-transport properties of magnetic junctions using a Co{sub 2}Fe(Ga{sub 0.5}Ge{sub 0.5}) Heusler alloy as ferromagnetic electrodes and a Cu(In{sub 0.8}Ga{sub 0.2})Se{sub 2} (CIGS) semiconductor as spacers. Owing to the semiconducting nature of the CIGS spacer, large magnetoresistance (MR) ratios of 40% at room temperature and 100% at 8 K were obtained for low resistance-area product (RA) values between 0.3 and 3 Ω μm{sup 2}. Transmission electron microscopy observations confirmed the fully epitaxial growth of the chalcopyrite CIGS layer, and the temperature dependence of RA indicated that the large MR was due to spin dependent tunneling.

  15. Critical behavior and magnetocaloric effect in Co{sub 50−x}Ni{sub x}Cr{sub 25}Al{sub 25} (x = 0 and 5) full Heusler alloy system

    Energy Technology Data Exchange (ETDEWEB)

    Panda, J.; Saha, S.N.; Nath, T.K., E-mail: tnath@phy.iitkgp.ernet.in

    2015-09-25

    Highlights: • The Curie temperature of alloy series of Co{sub 50−x}Ni{sub x}Cr{sub 25}Al{sub 25} decreases with increasing x. • The critical exponents behavior and scaling relation of the alloy series have been investigated. • Using M–H data, employing Modified Arrott plot and Kouvel–Fisher plot exponents are estimated. • The estimated critical exponent values match very well with the mean field theory. • Under a magnetic field maximum up to 5 T, normal magnetocaloric effect has been observed. - Abstract: This work reports the investigation of critical behavior of Co{sub 50−x}Ni{sub x}Cr{sub 25}Al{sub 25} (x = 0 and 5) and magneto caloric effect (MCE) of bulk Co{sub 2}CrAl full Heusler alloy system. The alloy series of Co{sub 50−x}Ni{sub x}Cr{sub 25}Al{sub 25} (x = 0, 1, 2, 3, 4 and 5) have been prepared using arc melting technique. The magnetic properties of all the samples have been studied in the temperature range of 5–300 K. The value of Curie temperature (T{sub C}) is found to decrease with increasing doping concentration of the Ni (substitution of Ni at Co site). The critical exponents behavior and scaling relation have been investigated using magnetic isotherms in Co{sub 50−x}Ni{sub x}Cr{sub 25}Al{sub 25} (x = 0 and 5) alloys. The critical exponents are estimated by various techniques such as, Modified Arrott plot, Kouvel–Fisher plot and critical isotherm technique. The value of critical exponents vicinity to the second order magnetic phase transition of Co{sub 50}Cr{sub 25}Al{sub 25} were found to be β = 0.488 (7), γ = 1.144 (16) and δ = 3.336 (5) with T{sub C} = 328.64 (5) K whereas for Co{sub 50}Ni{sub 5}Cr{sub 25}Al{sub 25} the values are β = 0.522 (13), γ = 1.014 (6) and δ = 3.043 (7) with T{sub C} = 285.71 (11). The critical exponent values for both the samples are almost similar to the value as predicted by mean field theory. This has been best explained by long range mean field like ferromagnetic interaction in the

  16. Suppression of interfacial intermixing between MBE-grown Heusler alloy Ni2MnIn and (0 0 1)InAs or InAs-HEMT structures

    Science.gov (United States)

    Bohse, S.; Zolotaryov, A.; Kreuzpaintner, W.; Lott, D.; Kornowski, A.; Stemmann, A.; Heyn, Ch.; Hansen, W.

    2011-05-01

    This paper reports on the application of a thin MgO interlayer as a diffusion barrier between a Ni2MnIn Heusler film and the substrate consisting of either (0 0 1)InAs or a high electron mobility transistor structure with an InAs channel layer. The functionality of the MgO interlayers is studied in dependence of their layer thicknesses. Our studies reveal that MgO interlayers are effective diffusion barriers, which in conjunction with post-growth annealing significantly improve the structural and magnetic properties of the Heusler films. For all as-grown samples, a Curie temperature of 170 K was found indicating that the Ni2MnIn films are crystallized in the B2 phase. Post-growth annealing for 15 h at 350 °C of samples with MgO layer thicknesses smaller than 3 nm leads to a strong decrease in magnetisation. This film degradation may be attributed to the intermixing of the Heusler films with substrate material through not-completely closed MgO films. For samples with a MgO interlayer thickness of 3 nm, the Curie temperature increases up to 300 K. This Curie temperature is close to the value reported for bulk Ni2MnIn films in the desired L21 phase. Furthermore, an increase in saturation magnetisation by a factor of 2.4 was observed.

  17. Epitaxial growth and surface properties of half-metal NiMnSb films.

    Science.gov (United States)

    Borca, C N; Ristoiu, D; Jeong, H-K; Komesu, Takashi; Caruso, A N; Pierre, J; Ranno, L; Nozières, J P; Dowben, P A

    2007-08-08

    We present, herein, an extended study of the half-Heusler alloy NiMnSb, starting with the deposition technique, continuing with the basic structural and magnetic properties of the thin films, and finishing with the electronic and compositional properties of their surfaces. The experimental methods we apply combine magnetization and magnetoresistivity measurements, atomic force microscopy, ferromagnetic resonance, x-ray and neutron diffraction, low energy electron diffraction, angle resolved x-ray photoemission, extended x-ray absorption fine structure spectroscopy, soft x-ray magnetic circular dichroism and spin polarized inverse photoemission spectroscopy. We find that stoichiometric surfaces exhibit close to 100% spin polarization at the centre of the surface Brillouin zone at the Fermi edge at ambient temperatures. There is strong evidence for a moment reordering transition at around 80 K which marks the crossover from a high polarization state (T80 K). The results from the different experimental techniques are successively reviewed, with special emphasis on the interplay between composition and electronic structure of the NiMnSb film surfaces. Surface segregation, consistent with a difference in free enthalpy between the surface and the bulk, is induced by annealing treatments. This surface segregation greatly reduces the surface polarization.

  18. Epitaxial growth and surface properties of half-metal NiMnSb films

    Energy Technology Data Exchange (ETDEWEB)

    Borca, C N [Swiss Light Source and the Laboratory for Waste Management, Paul Scherrer Institute, Viligen PSI CH-5232 (Switzerland); Ristoiu, D [Laboratoire Louis Neel, CNRS, BP166X, 38042 Grenoble Cedex (France); Jeong, H-K [Department of Physics, SungkyunKwan University, Jangan Suwon 440-746 (Korea, Republic of); Komesu, Takashi [Department of Physics and Astronomy and the Center for Materials Research and Analysis, Behlen Laboratory of Physics, University of Nebraska, Lincoln, NE 68588-0111 (United States); Caruso, A N [Center for Nanoscale Science and Engineering, North Dakota State University, Fargo, ND 58047 (United States); Pierre, J [Laboratoire Louis Neel, CNRS, BP166X, 38042 Grenoble Cedex (France); Ranno, L [Laboratoire Louis Neel, CNRS, BP166X, 38042 Grenoble Cedex (France); Nozieres, J P [Laboratoire Louis Neel, CNRS, BP166X, 38042 Grenoble Cedex (France); Dowben, P A [Department of Physics and Astronomy and the Center for Materials Research and Analysis, Behlen Laboratory of Physics, University of Nebraska, Lincoln, NE 68588-0111 (United States)

    2007-08-08

    We present, herein, an extended study of the half-Heusler alloy NiMnSb, starting with the deposition technique, continuing with the basic structural and magnetic properties of the thin films, and finishing with the electronic and compositional properties of their surfaces. The experimental methods we apply combine magnetization and magnetoresistivity measurements, atomic force microscopy, ferromagnetic resonance, x-ray and neutron diffraction, low energy electron diffraction, angle resolved x-ray photoemission, extended x-ray absorption fine structure spectroscopy, soft x-ray magnetic circular dichroism and spin polarized inverse photoemission spectroscopy. We find that stoichiometric surfaces exhibit close to 100% spin polarization at the centre of the surface Brillouin zone at the Fermi edge at ambient temperatures. There is strong evidence for a moment reordering transition at around 80 K which marks the crossover from a high polarization state (T<80 K) to a more representative metallic ferromagnetic state (T>80 K). The results from the different experimental techniques are successively reviewed, with special emphasis on the interplay between composition and electronic structure of the NiMnSb film surfaces. Surface segregation, consistent with a difference in free enthalpy between the surface and the bulk, is induced by annealing treatments. This surface segregation greatly reduces the surface polarization.

  19. FCC Fe{sub 2}NiSi prepared by mechanical alloying and stabilization effect of L2{sub 1}B disorder on BCC Heusler structure

    Energy Technology Data Exchange (ETDEWEB)

    Luo, Hongzhi, E-mail: luo_hongzhi@163.com [School of Materials Science and Engineering, Hebei University of Technology, Tianjin 300130 (China); Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Xin, Yuepeng; Ma, Yuexing; Liu, Bohua; Meng, Fanbin; Liu, Heyan [School of Materials Science and Engineering, Hebei University of Technology, Tianjin 300130 (China); Liu, Enke; Wu, Guangheng [Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China)

    2016-12-01

    Fe{sub 2}NiSi FCC phase has been prepared by ball-milling successfully, which is different from the BCC Heusler phase prepared by arc-melting in previous literatures. The FCC Fe{sub 2}NiSi is a ferromagnet with a lattice constant of 3.58 Å. The phase stability of the FCC and BCC Fe{sub 2}NiSi has been compared by first-principles calculations. It has been found that the FCC structure has a lower total energy compared with the highly-ordered Heusler structures XA and L2{sub 1}, that is the reason why the FCC phase can be prepared by ball-milling. However, the Fe (A)–Ni (C) disorder in the BCC XA structure can lower its total energy further and make it smaller than the FCC phase. So the most stable structure in Fe{sub 2}NiSi is L2{sub 1}B, as has been observed in the arc-melting sample. This can be explained from their DOS structures. The calculated total moments for the FCC and BCC phases agree with their M{sub s} at 5 K quite well. - Highlights: • FCC Fe{sub 2}NiSi has been prepared by ball-milling successfully. • Phase stability of Fe{sub 2}NiSi with different structures has been investigated. • The BCC Heusler structure in Fe{sub 2}NiSi is stabilized by L2{sub 1}B disorder.

  20. Growth and transport properties of thin Co-based Heusler films; Wachstum und Transporteigenschaften duenner Co-basierter Heusler-Filme

    Energy Technology Data Exchange (ETDEWEB)

    Schneider, Horst

    2010-07-01

    half-metallic Heusler compounds. The availableness of these high quality quaternary alloy films allowed the systematic investigation of their electronic properties. Band structure calculations predict that the substitution of Mn by Fe leads to a shift of the Fermi energy over the minority energy gap, whereas the density of states remains nearly unchanged. The corresponding changes in the topology of the Fermi surface could be tested by electronic transport measurements. This is particularly obvious in the normal Hall effect. Here a transition from a hole-like charge transport in Co{sub 2}MnSi to an electron-like transport in Co{sub 2}FeSi could be demonstrated. This is in accordance with the corresponding band structure calculations. Additionally, with these samples comparative XMCD experiments were performed. The densities of states reconstructed from these spectra show the expected shift of the Fermi energy as well. Furthermore, the behavior of the anomalous Hall effect was studied. Here it could be seen that the effect is influenced by two mechanisms: On the one hand an intrinsic contribution, caused by the topology of the Fermi surface and on the other hand by temperature dependent impurity scattering. These two effects have an opposing influence on the anomalous Hall effect. This can lead to an observable sign reversal of the anomalous contribution. This behavior has been predicted just recently and was in this work systematically investigated for the first time for Heusler compounds. (orig.)

  1. Observation of strong ferromagnetism in the half-Heusler compound CoTiSb system

    Energy Technology Data Exchange (ETDEWEB)

    Sedeek, K., E-mail: KamiliaSedeek@yahoo.com; Hantour, H.; Makram, N.; Said, Sh. A.

    2016-06-01

    not obey the 18 valence electron/unit cell category of zero magnetic moment. Electronic structure calculations of the prepared stable multiphases CoTiSb is necessary to understand the origin of the detected strong half-metallic ferromagnetic behavior. - Highlights: • Synthesis by direct fusion yields stable multiphases CoTiSb half-Heusler alloy. • A mixture of well-ordered and distorted lattice planes characterizes the alloy. • De-mixing into multiphases altered the semiconducting CoTiSb to strong ferromagnet. • The alloy undergoes more than two ferromagnetic transitions with T{sub c} above 900 °K. • A proposed magnetic field diagram is given for the multiphases CoTiSb nano-system.

  2. Structure, magnetic properties and electrical resistivity of Co{sub 2}FeSi{sub 1−x}Ga{sub x} Heusler alloy thin films

    Energy Technology Data Exchange (ETDEWEB)

    Ramudu, M., E-mail: macrams2@gmail.com; Raja, M. Manivel; Chelvane, J. Arout; Kamat, S.V.

    2016-11-15

    The influence of Ga on the structural, magnetic and half-metallic properties of Co{sub 2}FeSi{sub 1−x}Ga{sub x} (0≤x≤1) thin films grown on Si (100) substrates using ultra high vacuum magnetron sputtering has been systematically investigated. The linear increase in cubic lattice parameter from 5.63 Å to 5.73 Å and the Curie temperature (T{sub C}) from 854 K to 941 K with x varying from 0 to 1 indicate the progressive substitution of Ga for Si. The coercivity (H{sub c}) was found to decrease from 26 Oe (x=0) to 3 Oe (x=1) at room temperature and is attributed to the decrease in magnetic anisotropy. The magnetic hysteresis loops measured from 300–873 K revealed that the film where Ga completely replaces Si exhibit better stability in both saturation magnetization (M{sub s}) and H{sub c} with temperature. The increase in coercivity at higher temperatures is attributed to the film to substrate interaction. The measured M{sub s} at 100 K decreases from 5.01 µ{sub B}/f.u. (x=0) to 4.49 µ{sub B}/f.u. (x=1) and follows the trend of Slater-Pauling rule. The indirect evidence of half-metallic nature is examined from the temperature dependent electrical resistivity measurements. - Highlights: • A linear dependence of lattice parameter and T{sub C} was observed with Ga content. • Indirect evidence of half-metallicity was examined from resistivity measurements. • Co{sub 2}FeSi{sub 1−x}Ga{sub x} films with higher Ga showed better magnetic and electrical properties.

  3. Ferromagnetic resonance study of the half-Heusler alloy NiMnSb. The benefit of using NiMnSb as a ferromagnetic layer in pseudo-spin-valve based spin-torque oscillators

    Energy Technology Data Exchange (ETDEWEB)

    Riegler, Andreas

    2011-11-25

    Since the discovery of spin torque in 1996, independently by Berger and Slonczewski, and given its potential impact on information storage and communication technologies, (e.g. through the possibility of switching the magnetic configuration of a bit by current instead of a magnetic field, or the realization of high frequency spin torque oscillators (STO)), this effect has been an important field of spintronics research. One aspect of this research focuses on ferromagnets with low damping. The lower the damping in a ferromagnet, the lower the critical current that is needed to induce switching of a spin valve or induce precession of its magnetization. In this thesis ferromagnetic resonance (FMR) studies of NiMnSb layers are presented along with experimental studies on various spin-torque (ST) devices using NiMnSb. NiMnSb, when crystallized in the half-Heusler structure, is a half-metal which is predicted to have 100% spin polarization, a consideration which further increases its potential as a candidate for memory devices based on the giant magnetoresistance (GMR) effect. The FMR measurements show an outstandingly low damping factor for NiMnSb, in low 10{sup -3} range. This is about a factor of two lower than permalloy and well comparable to lowest damping for iron grown by molecular beam epitaxy (MBE). According to theory the 100% spin polarization properties of the bulk disappear at interfaces where the break in translational symmetry causes the gap in the minority spin band to collapse but can remain in other crystal symmetries such as (111). Consequently NiMnSb layers on (111)(In,Ga)As buffer are characterized in respect of anisotropies and damping. The FMR measurements on these samples indicates a higher damping that for the 001 samples, and a thickness dependent uniaxial in-plane anisotropy. Investigations of the material for device use is pursued by considering sub-micrometer sized elements of NiMnSb on 001 substrates, which were fabricated by electron

  4. Effect of Coulomb interactions and Hartree-Fock exchange on structural, elastic, optoelectronic and magnetic properties of Co{sub 2}MnSi Heusler: A comparative study

    Energy Technology Data Exchange (ETDEWEB)

    Lantri, T. [Laboratory of Technology and Solid’s Properties, Faculty of Sciences and Technology, Abdelhamid Ibn Badis University, BP 227, Mostaganem 27000 (Algeria); Bentata, S., E-mail: sam_bentata@yahoo.com [Laboratory of Technology and Solid’s Properties, Faculty of Sciences and Technology, Abdelhamid Ibn Badis University, BP 227, Mostaganem 27000 (Algeria); Bouadjemi, B.; Benstaali, W. [Laboratory of Technology and Solid’s Properties, Faculty of Sciences and Technology, Abdelhamid Ibn Badis University, BP 227, Mostaganem 27000 (Algeria); Bouhafs, B. [Modelling and Simulation in Materials Science Laboratory, Djillali Liabès University of Sidi Bel-Abbès, 22000 Sidi Bel-Abbes (Algeria); Abbad, A. [Laboratory of Technology and Solid’s Properties, Faculty of Sciences and Technology, Abdelhamid Ibn Badis University, BP 227, Mostaganem 27000 (Algeria); Modelling and Simulation in Materials Science Laboratory, Djillali Liabès University of Sidi Bel-Abbès, 22000 Sidi Bel-Abbes (Algeria); Zitouni, A. [Laboratory of Technology and Solid’s Properties, Faculty of Sciences and Technology, Abdelhamid Ibn Badis University, BP 227, Mostaganem 27000 (Algeria)

    2016-12-01

    Using the first-principle calculations, we have investigated the structural, elastic, optoelectronic and magnetic properties of Co{sub 2}MnSi Heusler alloy. Based on the density functional theory (DFT) and hiring the full-potential linearized augmented plane wave (FP-LAPW) method, we have used five approaches: the Hybrid on-site exact exchange, the Local Spin Density Approximation (LSDA), the LSDA+U, the Generalized Gradient Approximation GGA and GGA+U; where the Hubbard on-site Coulomb interaction correction U is calculated by constraint local density approximation for Co and Mn atoms. Our results show that the highly-ordered Co{sub 2}MnSi alloy is a ductile, stiff and anisotropic material. It has a half-metallic ferromagnetic character with an integer magnetic moment of 5 µB which is in good agreement with the Slater-Pauling rule. - Highlights: • Each approach gives a half magnetic compound. • EECE gives the largest gap. • Elastic properties show a stiff, ductile and anisotropic material. • Electronic properties are similar for the five approaches. • Total magnetic moment is the same for the five approaches (5 µB).

  5. Temperature-dependence of current-perpendicular-to-the-plane giant magnetoresistance spin-valves using Co{sub 2}(Mn{sub 1−x}Fe{sub x})Ge Heusler alloys

    Energy Technology Data Exchange (ETDEWEB)

    Page, M. R.; Nakatani, T. M., E-mail: nakatani.tomoya@nims.go.jp; Stewart, D. A.; York, B. R.; Read, J. C.; Choi, Y.-S.; Childress, J. R. [San Jose Research Center, HGST, a Western Digital Company, 3403 Yerba Buena Road, San Jose, California 95135 (United States)

    2016-04-21

    The properties of Co{sub 2}(Mn{sub 1−x}Fe{sub x})Ge (CMFG) (x = 0–0.4) Heusler alloy magnetic layers within polycrystalline current-perpendicular-to-the plane giant magnetoresistance (CPP-GMR) spin-valves are investigated. CMFG films annealed at 220–320 °C exhibit partly ordered B2 structure with an order parameter S{sub B2} = 0.3–0.4, and a lower S{sub B2} was found for a higher Fe content. Nevertheless, CPP-GMR spin-valve devices exhibit a relatively high magnetoresistance ratio of ∼13% and a magnetoresistance-area product (ΔRA) of ∼6 mΩ μm{sup 2} at room temperature, which is almost independent of the Fe content in the CMFG films. By contrast, at low temperatures, ΔRA clearly increases with higher Fe content, despite the lower B2 ordering for increasing the Fe content. Indeed, first-principles calculations reveal that the CMFG alloy with a partially disordered B2 structure has a greater density of d-state at the Fermi level in the minority band compared to the Fe-free (Co{sub 2}MnGe) alloy. This could explain the larger ΔRA measured on CMFG at low temperatures by assuming that s-d scattering mainly determines the spin asymmetry of resistivity as described in Mott's theory.

  6. Large enhancement of bulk spin polarization by suppressing Co{sub Mn} anti-sites in Co{sub 2}Mn(Ge{sub 0.75}Ga{sub 0.25}) Heusler alloy thin film

    Energy Technology Data Exchange (ETDEWEB)

    Li, S.; Takahashi, Y. K.; Sakuraba, Y., E-mail: Sakuraba.Yuya@nims.go.jp; Furubayashi, T. [National Institute for Materials Science, Tsukuba 305-0047 (Japan); Tsuji, N.; Tajiri, H. [Japan Synchrotron Radiation Research Institute/SPring-8, Hyogo 679-5198 (Japan); Miura, Y. [Kyoto Institute of Technology, Kyoto 605-8585 (Japan); Chen, J.; Hono, K. [National Institute for Materials Science, Tsukuba 305-0047 (Japan); Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba 305-8571 (Japan)

    2016-03-21

    We have investigated the structure and magneto-transport properties of Co{sub 2}Mn(Ge{sub 0.75}Ga{sub 0.25}) (CMGG) Heusler alloy thin films with near-stoichiometric and Mn-rich compositions in order to understand the effect of Co-Mn anti-sites on bulk spin polarization. Anomalous x-ray diffraction measurements using synchrotron radiated x-rays confirmed that Co{sub Mn} anti-sites easily form in the near-stoichiometric CMGG compound at annealing temperature higher than 400 °C, while it can be suppressed in Mn-rich CMGG films. Accordingly, large enhancement in negative anisotropic magnetoresistance of CMGG films and giant magnetoresistance (GMR) in current-perpendicular-to-plane (CPP) pseudo spin valves were observed in the Mn-rich composition. A large resistance-area product change (ΔRA) of 12.8 mΩ μm{sup 2} was demonstrated in the CPP-GMR pseudo spin valves using the Mn-rich CMGG layers after annealing at 600 °C. It is almost twice of the maximum output observed in the CPP-GMR pseudo spin valves using the near-stoichiometric CMGG. These indicate that the spin polarization of CMGG is enhanced in the Mn-rich composition through suppressing the formation of Co{sub Mn}-antisites in CMGG films, being consistent with first-principle calculation results.

  7. First-principle investigation of structural, electronic and magnetic properties of Co2VIn and CoVIn Heusler compounds

    Science.gov (United States)

    Zipporah, Muthui; Rohit, Pathak; Robinson, Musembi; Julius, Mwabora; Ralph, Skomski; Arti, Kashyap

    2017-05-01

    Investigation of the structural, electronic and magnetic properties of full-Heusler Co2VIn as well as half-Heusler CoVIn Cobalt based Heusler compounds using density functional theory (DFT) leads to the general conclusion that Co2VIn and CoVIn are half-metallic materials with a gap at the Fermi level in the minority states and majority states respectively. A Hubbard-like Coulomb correlation term U has been included in the DFT (DFT+U) for the computation of the electronic and magnetic properties of the compounds. The structural properties have been calculated for the paramagnetic and ferromagnetic phases, and both Co2VIn and CoVIn are found to be stable in the ferromagnetic phase. The calculated magnetic moments are 2 μB and 0.9 μB per formula unit for Co2VIn and CoVIn respectively.

  8. Inducing half-metallicity with enhanced stability in zigzag graphene nanoribbons via fluorine passivation

    Energy Technology Data Exchange (ETDEWEB)

    Jaiswal, Neeraj K., E-mail: neerajkjaiswal@gmail.com [Discipline of Physics, Indian Institute of Information Technology Design & Manufacturing, Jabalpur 482005 (India); Tyagi, Neha [Department of Applied Physics, Delhi Technological University, Delhi 110042 (India); Kumar, Amit [Discipline of Physics, Indian Institute of Information Technology Design & Manufacturing, Jabalpur 482005 (India); Srivastava, Pankaj [Nanomaterials Research Group, ABV-Indian Institute of Information Technology & Management, Gwalior 474015 (India)

    2017-02-28

    Highlights: • F passivated zigzag graphene nanoribbon (F-ZGNR) are more favorable than pristine ones. • External electric field induces half metallicity in F-ZGNR. • The observed half metallicity is independent of ribbon widths. • Enhanced stability makes F-ZGNR preferable over pristine ribbon. - Abstract: Half metals are the primary ingredients for the realization of novel spintronic devices. In the present work, by employing density functional theory based first-principles calculation, we predict half metallic behavior in fluorine passivated zigzag graphene nanoribbons (F-ZGNR). Four different structures have been investigated viz. one edge F passivated ZGNR (F-ZGNR-1), both edges F passivated ZGNR (F-ZGNR-2), F passivation on alternate sites in first configuration (alt-1) and F passivation on alternate sites in second configuration (alt-2). Interestingly, it is noticed that F passivation is analogous to H passivation (pristine), however, F-ZGNR are reckoned energetically more stable than pristine ones. An spin induced band gap is noticed for all F-ZGNR irrespective of their widths although its magnitude is slightly less than the pristine counterparts. With an external transverse electric field, ribbons undergo semiconducting to half metallic transformation. The observed half metallic character with enhanced stability present F-ZGNR as a better candidate than pristine ZGNR towards the realization of upcoming spintronic devices.

  9. Tuning magneto-structural properties of Ni{sub 44}Co{sub 6}Mn{sub 39}Sn{sub 11} Heusler alloy ribbons by Fe-doping

    Energy Technology Data Exchange (ETDEWEB)

    Wójcik, Anna, E-mail: a.wojcik@imim.pl [Institute of Metallurgy and Materials Science, Polish Academy of Sciences, 25 Reymonta Street, 30-059 Kraków (Poland); Maziarz, Wojciech; Szczerba, Maciej J. [Institute of Metallurgy and Materials Science, Polish Academy of Sciences, 25 Reymonta Street, 30-059 Kraków (Poland); Sikora, Marcin [Academic Centre for Materials and Nanotechnology, AGH University of Science and Technology, Al. Mickiewicza 30, 30-059 Kraków (Poland); Dutkiewicz, Jan [Institute of Metallurgy and Materials Science, Polish Academy of Sciences, 25 Reymonta Street, 30-059 Kraków (Poland); Cesari, Eduard [Departament de Física, Universitat de les Illes Balears, Ctra. De Valldemossa, km 7.5, E-07122 Palma de Mallorca (Spain)

    2016-07-15

    Graphical abstract: - Highlights: • Fe substitution for Ni in Ni{sub 44}Co{sub 6}Mn{sub 39}Sn{sub 11} causes a drastic decrease of M{sub T} temperature. • The type of structure changes with increasing of iron (12M → 10M + L2{sub 1} → L2{sub 1}). • Content of Fe above 1 at.% has a negative influence on magneto-structural properties. - Abstract: Microstructure, martensitic transformation behavior and magnetic properties of Ni{sub 44−x}Fe{sub x}Co{sub 6}Mn{sub 39}Sn{sub 11} (x = 0, 1, 2 at.%) melt spun ribbons have been investigated. The influence of iron addition has been thoroughly studied by means of electron microscopy, X-ray diffraction and vibrating sample magnetometry. The results show that addition of 1 at.% of iron into quaternary Ni–Co–Mn–Sn Heusler alloy drastically decreases the martensitic transformation temperature by more than 100 K. Higher concentration of iron leads to complete suppression of martensitic transition. The structure of samples change from fully martensite (12 M) through mixed austenite-martensite (L2{sub 1} + 10 M) to fully austenite (L2{sub 1}) with increase of iron content. Addition of 1 at.% of iron leads to enhance magnetization of both austenitic and martensitic phases and also a small increase of Curie temperature occurs. The largest change of magnetic entropy under 15 kOe measured 2.9 and 0.65 J kg{sup −1} K{sup −1} for alloys where x = 0 and 1, respectively.

  10. Magnetic tunneling junctions with the Heusler compound Co{sub 2}Cr{sub 0.6}Fe{sub 0.4}Al

    Energy Technology Data Exchange (ETDEWEB)

    Conca Parra, A.

    2007-07-20

    Materials with large spin polarization are required for applications in spintronics devices. For this reason, major research efforts are directed to study the properties of compounds which are expected to be half metals, i.e. materials with 100% spin polarization. Half metals are expected to have a gap in the density of states at the Fermi energy for one spin band while the other spin band is metallic leading to a completely spin polarized current. The ferromagnetic full Heusler alloy Co{sub 2}Cr{sub 0.6}Fe{sub 0.4}Al (CCFA) has attracted great interest in the field of spintronics. The high Tc (800 K) and the expected half metallicity make CCFA a good candidate for applications in spintronic devices such as magnetic tunneling junctions (MTJs). This thesis presents the results of the study of the electronic and structural properties of CCFA thin films. The films were implemented in magnetic tunneling junctions and the tunneling magnetoresistance effect (TMR) was investigated. The main objectives were the measurement of the spin polarisation of the CCFA alloy and to obtain information about its electronic structure. The influence of the deposition conditions on the thin film properties and on the surface crystalline order and their respective influence on the TMR ratio was investigated. Epitaxial CCFA thin films with two alternative growth orientations were deposited on different substrates and buffer layers. An annealing step was used to improve the crystalline properties of the thin films. In the tunneling junctions, Al{sub 2}O{sub 3} was used as a barrier material and Co was chosen as counter electrode. The multilayer systems were patterned in Mesa structures using lithographic techniques. In the framework of the Julliere model, a maximum spin polarisation of 54% at 4K was measured in tunneling junctions with epitaxial CCFA electrodes. A strong influence of the annealing temperature on the TMR ratio was determined. The increase of the TMR ratio could be correlated

  11. The first ternary intermetallic Heusler nanoparticles: Co{sub 2}FeGa

    Energy Technology Data Exchange (ETDEWEB)

    Basit, Lubna; Yella, Aswani; Ksenofontov, Vadim; Fecher, Gerhard H.; Felser, Claudia [Institute of Inorganic and Analytical Chemistry, Johannes-Gutenberg-University, Mainz (Germany); Nepijko, Sergej A. [Institute of Physics, Johannes-Gutenberg-University, Mainz (Germany)

    2008-07-01

    Synthesis of materials with controlled particle size on the nanometer scale is an active area in the field of materials research. With the control over particle size, the electronic and magnetic properties of materials can be easily tuned. To study the effect of nanometer dimensions on the properties of Heusler alloys, a first example of Heusler nanoparticles is presented. Co{sub 2}FeGa Heusler nanoparticles were produced by reducing a methanol impregnated mixture of CoCl{sub 2}.6H{sub 2}O, Fe(NO{sub 3}){sub 3}.9H{sub 2}O, and Ga(NO{sub 3}){sub 3}.xH{sub 2}O after loading on fumed silica. The dried samples were heated under pure H{sub 2} gas at 900 C. The synthesized Co{sub 2}FeGa Heusler nanoparticles were characterized by HRTEM, XRD and Moessbauer spectroscopy. All peaks of the XRD pattern can be attributed to a L2{sub 1} Heusler structure with a lattice constant of a=4.37 A. The size of the particles, as determined by transmission electron microscopy, is between 16 nm and 20 nm. The ferromagnetic behaviour of the particles as determined by the SQUID measurements is presented and compared with the bulk Co{sub 2}FeGa Heusler alloy.

  12. Inhomogeneous strain-induced half-metallicity in bent zigzag graphene nanoribbons

    Science.gov (United States)

    Zhang, Dong-Bo; Wei, Su-Huai

    2017-08-01

    Realization of half-metallicity in low dimensional materials is a fundamental challenge for nano spintronics, which is a critical component for next-generation information technology. Using the method of generalized Bloch theorem, we show that an in-plane bending can induce inhomogeneous strains, which in turn lead to spin-splitting in zigzag graphene nanoribbons and results in the highly desired half-metallic state. Unlike the previously proposed scheme that requires unrealistically strong external electric fields, the obtained half-metallicity with sizeable half-metallic gap and high energetic stability of magnetic order of edge states requires only relatively low-level strain in the in-plane bending. Given the superior structural flexibility of graphene and the recent experimental advances in controllable synthesis of graphene nanoribbons, our design provides a hitherto most practical approach to the realization of half-metallicity in low dimensional systems. This work, thus paves a way towards the design of nanoscale spintronic devices through strain engineering.

  13. Uniaxial pressure-induced half-metallic ferromagnetic phase transition in LaMnO3

    Science.gov (United States)

    Rivero, Pablo; Meunier, Vincent; Shelton, William

    2016-03-01

    We use first-principles theory to predict that the application of uniaxial compressive strain leads to a transition from an antiferromagnetic insulator to a ferromagnetic half-metal phase in LaMnO3. We identify the Q2 Jahn-Teller mode as the primary mechanism that drives the transition, indicating that this mode can be used to tune the lattice, charge, and spin coupling. Applying ≃6 GPa of uniaxial pressure along the [010] direction activates the transition to a half-metallic pseudocubic state. The half-metallicity opens the possibility of producing colossal magnetoresistance in the stoichiometric LaMnO3 compound at significantly lower pressure compared to recently observed investigations using hydrostatic pressure.

  14. Design of half-metallic antiferromagnets: transition metal chalcogenides and pnictides

    Science.gov (United States)

    Akai, Hisazumi; Ogura, Masako; Hoang Long, Nguyen

    2010-03-01

    Half-metallic antiferromagnts are the materials that exhibit half-metallicity and antifirromagnetism (compensated ferrimagnetism) simultaneously. Such materials are especially useful for spintronics devices since they have 100 % spin-polarized Fermi surfaces despite of their robustness against a disturbance of external magnetic field. We found that (XY)Z2, where X and Y are transition metal elements and Z is a chalcogens or a pnictigen, show half-metallic antiferromagnetism when the sum of effective d electron numbers of X and Y is 10. Examples are (CrFe)S2 and (CrFe)Se2. We report a systematic investigation of the electronic structure and transport properties of these materials calculated by the KKR-Green's function method combined with the Kubo-Greenwood formula.

  15. Organometallic benzene-vanadium wire: A one-dimensional half-metallic ferromagnet

    DEFF Research Database (Denmark)

    Maslyuk, V.; Bagrets, A.; Meded, V.

    2006-01-01

    methods. We predict that the ground state of the wire is a 100% spin-polarized ferromagnet (half-metal). Its density of states is metallic at the Fermi energy for the minority electrons and shows a semiconductor gap for the majority electrons. We find that the half-metallic behavior is conserved up to 12......% longitudinal elongation of the wire. Ab initio electron transport calculations reveal that finite size vanadium-benzene clusters coupled to ferromagnetic Ni or Co electrodes will work as nearly perfect spin filters....

  16. Tunnel magnetoresistance effect in magnetic tunnel junctions using Fermi-level-tuned epitaxial Fe{sub 2}Cr{sub 1−x}Co{sub x}Si Heusler alloy

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Yu-Pu, E-mail: wangyupu@nus.edu.sg [Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, Singapore 117583 (Singapore); Data Storage Institute, Agency for Science, Technology and Research (A-STAR), 5 Engineering Drive 1, Singapore 117608 (Singapore); Han, Gu-Chang; Qiu, Jinjun; Yap, Qi-Jia [Data Storage Institute, Agency for Science, Technology and Research (A-STAR), 5 Engineering Drive 1, Singapore 117608 (Singapore); Lu, Hui; Teo, Kie-Leong [Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, Singapore 117583 (Singapore)

    2014-05-07

    This paper reports a systematic investigation on the structural and magnetic properties of Fe{sub 2}Cr{sub 1−x}Co{sub x}Si Heusler alloys with various compositions of x by co-sputtering Fe{sub 2}CrSi and Fe{sub 2}CoSi targets and their applications in magnetic tunnel junctions (MTJs). Fe{sub 2}Cr{sub 1−x}Co{sub x}Si films of high crystalline quality have been epitaxially grown on MgO substrate using Cr as a buffer layer. The L2{sub 1} phase can be obtained at x = 0.3 and 0.5, while B2 phase for the rest compositions. A tunnel magnetoresistance (TMR) ratio of 19.3% at room temperature is achieved for MTJs using Fe{sub 2}Cr{sub 0.3}Co{sub 0.7}Si as the bottom electrode with 350 °C post-annealing. This suggests that the Fermi level in Fe{sub 2}Cr{sub 1−x}Co{sub x}Si has been successfully tuned close to the center of band gap of minority spin with x = 0.7 and therefore better thermal stability and higher spin polarization are achieved in Fe{sub 2}Cr{sub 0.3}Co{sub 0.7}Si. The post-annealing effect for MTJs is also studied in details. The removal of the oxidized Fe{sub 2}Cr{sub 0.3}Co{sub 0.7}Si at the interface with MgO barrier is found to be the key to improve the TMR ratio. When the thickness of the inserted Mg layer increases from 0.3 to 0.4 nm, the TMR ratio is greatly enhanced from 19.3% to 28%.

  17. Epitaxial diodes of a half-metallic ferromagnet on an oxide semiconductor

    NARCIS (Netherlands)

    Postma, F.M.; Ramaneti, R.; Banerjee, T.; Gokcan, H.; Haq, E.; Blank, D.H.A.; Jansen, R.; Lodder, J.C.

    2004-01-01

    We report on the fabrication and electrical characterization of epitaxial Schottky diodes of a half-metallic ferromagnet on an oxide semiconductor. La0.67Sr0.33MnO3 thin films are grown by pulsed laser deposition on niobium-doped SrTiO3 semiconductor substrates with two doping concentrations and a

  18. Evidencing the existence of intrinsic half-metallicity and ferromagnetism in zigzag gallium sulfide nanoribbons

    Science.gov (United States)

    Zhou, Yungang; Li, Sean; Zhou, Weilie; Zu, Xiaotao; Gao, Fei

    2014-07-01

    The achievement of half-metallicity with ferromagnetic (FM) coupling has become a key technology for the development of one-dimensional (1D) nanoribbons for spintronic applications. Unfortunately, in previous studies, such a half-metallicity always occurs upon certain external constraints. Here we, for the first time, demonstrate, via density functional theory (DFT), that the recent experimentally realized gallium sulfide nanoribbons (GaSNRs) can display an intrinsic half-metallic character with FM coupling, raised from Ga-4s, Ga-4p and S-3p states at the Ga-dominated edge. Furthermore, the novel half-metallic behavior with FM coupling here is rather robust, especially for GaSNRs with large width and thickness, and can be sustained to the room temperature. Thus, our results accidentally disclose a new 1D spin nanomaterial, which allows us to go beyond the current scope limited to the graphene, boron nitride (BN), zinc oxide (ZnO) and molybdenum sulfide (MoS2) nanoribbons, toward more realistic spintronic applications.

  19. Robust band gap and half-metallicity in graphene with triangular perforations

    DEFF Research Database (Denmark)

    Gregersen, Søren Schou; Power, Stephen; Jauho, Antti-Pekka

    2016-01-01

    . The inclusion of spin polarization within a mean-field Hubbard approach gives rise to a large overall magnetic moment at each antidot due to the sublattice imbalance imposed by the triangular geometry. Half-metallic behavior arises from the formation of spin-split dispersive states near the Fermi energy...

  20. Half-metallic ferromagnets : From band structure to many-body effects

    NARCIS (Netherlands)

    Katsnelson, M. I.; Irkhin, V. Yu.; Chioncel, L.; Lichtenstein, A. I.; de Groot, R. A.

    2008-01-01

    A review of new developments in theoretical and experimental electronic-structure investigations of half-metallic ferromagnets (HMFs) is presented. Being semiconductors for one spin projection and metals for another, these substances are promising magnetic materials for applications in spintronics

  1. Ferromagnetism and Half-Metallicity in Atomically Thin Holey Nitrogenated Graphene Based Systems.

    Science.gov (United States)

    Choudhuri, Indrani; Pathak, Biswarup

    2017-09-06

    Metal-free half-metallicity has been the subject of immense research focus in the field of spintronic devices. By using density functional theoretical (DFT) calculations, atomically thin holey nitrogenated graphene (C2 N) based systems are studied for possible spintronic applications. Ferromagnetism is observed in all the C-doped holey nitrogenated graphene. Interestingly, the holey nitrogenated graphene (C2 N) based system shows strong half-metallicity with a Curie temperature of approximately 297 K when a particular C-doping concentration is reached. It shows a strong half-metallicity compared with any metal-free systems studied to date. Thus, such carbon nitride based systems can be used for a 100 % spin polarized current. Furthermore, such C-doped systems show excellent dynamical, thermal, and mechanical properties. Thus, we predict a metal-free planar ferromagnetic half-metallic holey nitrogenated graphene based system for room-temperature spintronic devices. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  2. Ferromagnetism and Half-Metallicity in a High-Band-Gap Hexagonal Boron Nitride System.

    Science.gov (United States)

    Choudhuri, Indrani; Pathak, Biswarup

    2018-01-05

    Metal-free half-metallicity is the subject of intense research in the field of spintronics devices. Using density functional theoretical calculations, atom-thin hexagonal boron nitride (h-BN)-based systems are studied for possible spintronics applications. Ferromagnetism is observed in patterned C-doped h-BN systems. Interestingly, such a patterned C-doped h-BN exhibits half-metallicity with a Curie temperature of approximately 324 K at a particular C-doping concentration. It shows half-metallicity more than metal-free systems studied to date. Thus, such a BN-based system can be used to achieve a 100 % spin-polarised current at the Fermi level. Furthermore, this C-doped system shows excellent dynamical, thermal, and mechanical properties. Therefore, a stable metal-free planar ferromagnetic half-metallic h-BN-based system is proposed for use in room-temperature spintronics devices. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  3. Work function anisotropy and surface stability of half-metallic CrO(2)

    NARCIS (Netherlands)

    Attema, J. J.; Uijttewaal, M. A.; de Wijs, G. A.; de Groot, R. A.

    Insight in the interplay between work function and stability is important for many areas of physics. In this paper, we calculate the anisotropy in the work function and the surface stability of CrO(2), a prototype half-metal, and find an anisotropy of 3.8 eV. An earlier model for the relation

  4. First principle prediction of half-metallic ferromagnetism in zinc-blende MBi (M=Ca, Sr, Ba)

    Energy Technology Data Exchange (ETDEWEB)

    Yao, K.L. [Department of Physics, Huazhong University of Science and Technology, Wuhan 430074 (China) and International Center of Materials Physics, Chinese Academy of Science, Shenyang 110015 (China)]. E-mail: klyao@hust.edu.cn; Jiang, J.L. [Department of Physics, Huazhong University of Science and Technology, Wuhan 430074 (China)]. E-mail: lianghust@126.com; Liu, Z.L. [Department of Physics, Huazhong University of Science and Technology, Wuhan 430074 (China); State Key Lab of Coordination Chemistry, Nanjing University, Nanjing 210093 (China); Gao, G.Y. [Department of Physics, Huazhong University of Science and Technology, Wuhan 430074 (China)

    2006-11-27

    The first-principle calculations have been performed to investigate the zinc-blende compounds of alkaline elements with the Bi atom to find new half-metallic ferromagnets. It is found that CaBi, SrBi and BaBi are true half-metallic ferromagnets with the magnetic moment of 1{mu}{sub B}/formula unit. Their half-metallicity can be maintained within a wide range of lattice constants.

  5. Effect of boron on the structural and magnetic properties of Co{sub 2}FeSi{sub 1-x}B{sub x} Heusler alloys

    Energy Technology Data Exchange (ETDEWEB)

    Ramudu, M., E-mail: macrams2@gmail.com; Raja, M. Manivel; Kamat, S. V. [Defence Metallurgical Research Laboratory (DMRL), Kanchanbagh, Hyderabad – 500058 (India)

    2016-05-23

    The partial substitution of Si with B on the structural and magnetic properties of Co{sub 2}FeSi{sub 1-x}Bx (x = 0-0.5) alloys was systematically investigated. X-ray and microstructural investigations show the presence of second phase at the grain boundaries which increases with increasing boron content. From thermal analysis studies, it was observed that L2{sub 1}-B2 ordering temperature remain constant whereas the melting point decreases with increase in boron addition and merges with ordering temperature at x = 0.5. The increase in T{sub C} for the alloys x ≥ 0.25 was attributed to the increase in second phase due to boron.

  6. Half-metallic perovskite superlattices with colossal thermoelectric figure of merit

    KAUST Repository

    Upadhyay Kahaly, M.

    2013-05-09

    Nowadays heavy experimental efforts are focussed on doped oxide thermoelectrics to increase the thermopower and thermoelectric performance. We propose a high thermoelectric figure of merit for half-metallic SrTi1−xCoxO3 (x = 0, 0.125, 0.25, 0.375, and 0.5) in a superlattice with SrTiO3, which is stable at high temperatures and in an oxygen environment. The maximal value of Z hardly depends on the doping, while the temperature at which the maximum occurs increases with the Co concentration. The easy tunability from being an insulator to a half-metal under substitutional doping combined with the colossal figure of merit opens up great potential in the emerging field of spin-caloritronics.

  7. The realization of half-metal and spin-semiconductor for metal adatoms on arsenene

    Science.gov (United States)

    Li, Geng; Zhao, Yinchang; Zeng, Shuming; Ni, Jun

    2016-12-01

    First-principles calculations have been performed to study the adsorption of 15 different metal adatoms on silicenelike arsenene. The adsorption energies, geometries, density of states, dipole moments, work functions, net magnetic moments and Bader charges transferred from adatoms to arsenene sheet are calculated. All of the 15 metal adatoms on arsenene have binding energies larger than cohesive energies of the bulk metal, implying that stable adsorbates can be formed. As a result of the localized states originating from adatoms, the adsorption systems show a rich variety of electronic properties, such as metal, half-metal, semiconducting, and spin-semiconducting behaviors. The Co doped arsenene displays a half-metal property. The adsorption of Cu, Ag, and Au turns semiconducting arsenene into a narrow gap spin-semiconductor. These results indicate potential applications of functionalizations of silicenelike arsenene with metal adatoms, in particular for spintronics and dilute magnetic semiconductor materials.

  8. Graphene-based half-metal and spin-semiconductor for spintronic applications

    Science.gov (United States)

    Qi, Jingshan; Chen, Xiaofang; Hu, Kaige; Feng, Ji

    2016-03-01

    In this letter we propose a strategy to make graphene become a half-metal or spin-semiconductor by combining the magnetic proximity effects and sublattice symmetry breaking in graphone/graphene and graphone/graphene/BN heterostructures. Exchange interactions lift the spin degeneracy and sublattice symmetry breaking opens a band gap in graphene. More interestingly, the gap opening depends on the spin direction and the competition between the sublattice asymmetry and exchange field determines the system is a half-metal or a spin-semiconductor. By first-principles calculations and a low-energy effective model analysis, we elucidate the underlying physical mechanism of spin-dependent gap opening and spin degeneracy splitting. This offers an alternative practical platform for graphene-based spintronics.

  9. Structural properties of the quaternary Heusler alloy Co{sub 2}Cr{sub 1-x}Fe{sub x}Al

    Energy Technology Data Exchange (ETDEWEB)

    Wurmehl, Sabine [Institut fuer Anorganische Chemie und Analytische Chemie, Johannes Gutenberg-Universitaet, D-55099 Mainz (Germany); Alves, Maria C Martins [Instituto de Quimica, Universidade Federal do Rio Grande do Sul, Porto Alegre 91501-970 (Brazil); Morais, Jonder [Instituto de Fisica, Universidade Federal do Rio Grande do Sul, Porto Alegre 91501-970 (Brazil); Ksenofontov, Vadim [Institut fuer Anorganische Chemie und Analytische Chemie, Johannes Gutenberg-Universitaet, D-55099 Mainz (Germany); Teixeira, Sergio R [Instituto de Fisica, Universidade Federal do Rio Grande do Sul, Porto Alegre 91501-970 (Brazil); Machado, Giovanna [Instituto de Fisica, Universidade Federal do Rio Grande do Sul, Porto Alegre 91501-970 (Brazil); Fecher, Gerhard H [Institut fuer Anorganische Chemie und Analytische Chemie, Johannes Gutenberg-Universitaet, D-55099 Mainz (Germany); Felser, Claudia [Institut fuer Anorganische Chemie und Analytische Chemie, Johannes Gutenberg-Universitaet, D-55099 Mainz (Germany)

    2007-03-21

    The quarternary substitutional series Co{sub 2}Cr{sub 1-x}Fe{sub x}Al was investigated by means of surface and bulk sensitive techniques in order to exploit its structural and compositional properties. Both bulk and powder samples of the alloy series were investigated to obtain specific information about this material. The long range order was determined by means of x-ray diffraction and neutron diffraction, while the site specific (short range) order was proved by extended x-ray absorption fine structure spectroscopy. The magnetic structure was investigated by Moessbauer spectroscopy in transmission and scattering modes in order to compare and separate powder and bulk properties. The chemical composition was analysed by means of x-ray photo emission spectroscopy combined with Auger electron spectroscopy depth profiling. The results from these methods are compared to get an insight into the differences between surface and bulk properties and the appearance of disorder in such alloys. The material shows an extremely high sensitivity to oxygen. In particular, powder materials show a high amount of oxygen contamination. Therefore, an additional oxide-mediated tunnel magneto-resistance may always contribute to measurements of magneto-resistive effects because the oxide layers will provide natural tunnelling barriers. In addition, the results suggest that thin films have to be produced under ultra-high vacuum conditions.

  10. Half metallicity in bare BC{sub 2}N nanoribbons with zigzag edges

    Energy Technology Data Exchange (ETDEWEB)

    Li, Hong, E-mail: lihong@ncut.edu.cn [College of Mechanical and Material Engineering, North China University of Technology, Beijing 100144 (China); Xiao, Xiang; Tie, Jun [College of Mechanical and Material Engineering, North China University of Technology, Beijing 100144 (China); Lu, Jing [State Key Laboratory of Mesoscopic Physics and Department of Physics, Peking University, Beijing 100871 (China)

    2017-06-09

    We study the electronic and magnetic properties of bare zigzag BC{sub 2}N nanoribbons (ZBC{sub 2}NNRs) by using first principles calculations. The ZBC{sub 2}NNRs which we studied are assigned to four edge types, and we carefully examine the size effect and edge magnetic coupling orders. We find that the N edge and the C edge adjacent to N atoms have a ferromagnetic coupling, while the B edge and the C edge adjacent to B atoms have an anti-ferromagnetic coupling. These novel properties arise from the unsaturated edge with specific edge determined magnetic moment distribution. All the investigated ribbons exhibit magnetic ground states with room-temperature accessible half-metallic character, irrespective of the ribbon width. Our results suggest that ZBC{sub 2}NNRs can have potential applications in spintronics. - Highlights: • DFT study on bare zigzag BC{sub 2}N nanoribbons (ZBC{sub 2}NNRs). • All the studied bare ZBC{sub 2}NNRs are half-metals at room temperature. • The half-metal characters come from specific spin couplings on the edge atoms. • We predict bare ZBC{sub 2}NNRs as practical candidate for spintronics.

  11. First-principles and Monte Carlo studies of C-doped Ni45Co5Mn37In13 Heusler alloys

    Directory of Open Access Journals (Sweden)

    Sokolovskiy Vladimir

    2015-01-01

    Full Text Available In this work, we report the study of the effect of carbon on electronic and magnetic properties of the Ni45Co5Mn37In13 alloy. Two compounds with addition of 5 at.% C for Mn and In with ferro- and ferrimagnetic spin configurations have been discussed in the framework of first-principles and Monte Carlo calculations. In order to calculate the magnetic exchange parameters, magnetic moments, and electronic density of states curves we have used the SPR-KKR package. We have shown that the addition of carbon leads to enhancement of antiferromagnetic exchange interactions between Mn atoms in martensite of both compounds. The temperature dependences of magnetizations as well as Curie temperatures of austenite and martensite have been obtained.

  12. Recent Advances in Nanostructured Thermoelectric Half-Heusler Compounds

    Directory of Open Access Journals (Sweden)

    Terry M. Tritt

    2012-11-01

    Full Text Available Half-Heusler (HH alloys have attracted considerable interest as promising thermoelectric (TE materials in the temperature range around 700 K and above, which is close to the temperature range of most industrial waste heat sources. The past few years have seen nanostructuing play an important role in significantly enhancing the TE performance of several HH alloys. In this article, we briefly review the recent progress and advances in these HH nanocomposites. We begin by presenting the structure of HH alloys and the different strategies that have been utilized for improving the TE properties of HH alloys. Next, we review the details of HH nanocomposites as obtained by different techniques. Finally, the review closes by highlighting several promising strategies for further research directions in these very promising TE materials.

  13. A first-principles approach to half-Heusler thermoelectrics: Accelerated prediction and understanding of material properties

    Directory of Open Access Journals (Sweden)

    Alexander Page

    2016-06-01

    Full Text Available Half-Heusler alloys are an exciting class of thermoelectric materials that have shown great improvements in the thermoelectric figure of merit, ZT, during the past 15 years. Many of the key discoveries in half-Heusler alloys have been brought forth by fundamental understandings gained from first-principles investigations. Several methods in particular have recently been used to great effect. Density functional theory provides a framework in which band structure predictions, phase diagrams enabled by cluster expansion methods, and the phase stability of unknown compounds can be calculated. Recent theoretical work, which has led to significant discoveries, has proven half-Heusler alloys to be a versatile and promising class of thermoelectric materials.

  14. Gd impurities effect on Co2CrSi alloy: first-principle calculations

    Indian Academy of Sciences (India)

    2018-02-02

    Feb 2, 2018 ... Abstract. First-principle calculations have been performed to study Gd impurities doping effect on the physical properties of the Heusler half-metallic ferromagnet Co2CrSi using the density functional theory in the local spin density approximation with an additional Hubbard correlation term for the rare-earth ...

  15. Low-moment ferrimagnetic phase of the Heusler compound Cr{sub 2}CoAl

    Energy Technology Data Exchange (ETDEWEB)

    Jamer, Michelle E., E-mail: jamermic@gmail.com [Department of Physics, Northeastern University, Boston, MA 02115 (United States); Marshall, Luke G. [Department of Chemical Engineering, Northeastern University, Boston, MA 02115 (United States); Sterbinsky, George E. [Photon Sciences Directorate, Brookhaven National Laboratory, Upton, NY 11973 (United States); Lewis, Laura H. [Department of Chemical Engineering, Northeastern University, Boston, MA 02115 (United States); Heiman, Don [Department of Physics, Northeastern University, Boston, MA 02115 (United States)

    2015-11-15

    Synthesizing half-metallic fully compensated ferrimagnets that form in the inverse Heusler phase could lead to superior spintronic devices. These materials would have high spin polarization at room temperature with very little fringing magnetic fields. Previous theoretical studies indicated that Cr{sub 2}CoAl should form in a stable inverse Heusler lattice due to its low activation energy. Here, stoichiometric Cr{sub 2}CoAl samples were arc-melted and annealed at varying temperatures, followed by studies of their structural and magnetic properties. High-resolution synchrotron X-ray diffraction revealed a chemically ordered Heusler phase in addition to CoAl and Cr phases. Soft X-ray magnetic circular dichroism revealed that the Cr and Co magnetic moments are antiferromagnetically oriented leading to the observed low magnetic moment in Cr{sub 2}CoAl. - Highlights: • Ordered Cr{sub 2}CoAl was synthesized via arc-melting stoichiometric constituents and annealing at various temperatures. • SQUID magnetometry revealed a low-moment ferromagnetic phase with a large Curie temperature (T{sub c} = 750 K). • X-ray magnetic circular dichroism measurements determined that the Cr and Co atomic moments are antiferromagnetically coupled. • Future spintronic devices could benefit from this compound's large Curie temperature and low magnetic moment.

  16. The Effect of Cobalt-Sublattice Disorder on Spin Polarisation in Co2FexMn1−xSi Heusler Alloys

    Directory of Open Access Journals (Sweden)

    Philip J. Hasnip

    2014-02-01

    Full Text Available In this work we present a theoretical study of the effect of disorder on spin polarisation at the Fermi level, and the disorder formation energies for Co2FexMn1−xSi (CFMS alloys. The electronic calculations are based on density functional theory with a Hubbard U term. Chemical disorders studied consist of swapping Co with Fe/Mn and Co with Si; in all cases we found these are detrimental for spin polarisation, i.e., the spin polarisation not only decreases in magnitude, but also can change sign depending on the particular disorder. Formation energy calculation shows that Co–Si disorder has higher energies of formation in CFMS compared to Co2MnSi and Co2FeSi, with maximum values occurring for x in the range 0.5–0.75. Cross-sectional structural studies of reference Co2MnSi, Co2Fe0.5Mn0.5Si, and Co2FeSi by Z-contrast scanning transmission electron microscopy are in qualitative agreement with total energy calculations of the disordered structures.

  17. Critical behavior near the ferromagnetic-paramagnetic transformation in the austenite phase of Ni43Mn46Sn8X3 (X = In and Cr) Heusler alloys

    Science.gov (United States)

    Nan, W. Z.; Thanh, Tran Dang; Nam, G.; You, T. S.; Piao, H. G.; Pan, L. Q.; Yu, S. C.

    2017-12-01

    In this work, we present a detailed study on the magnetic property and critical behavior in the austenitic phase of Ni43Mn46Sn8X3 alloys with X = Cr and In, which were prepared by an arc-melting method in an argon ambience. The M(T) curve of the Cr sample (X = Cr) exhibits a single magnetic phase transition at the Curie temperature of the ferromagnetic (FM) austenitic phase with TAC = 303 K. In contrast, the In sample (X = In) exhibits multiple magnetic phase transitions, including a magnetic phase transition from a FM state to weakly magnetic state at TMC = 165 K of the martensitic phase, a martensitic transition from the weakly magnetic to the FM austenite phase at TM-A = 259 K, and a magnetic phase transition from the FM to paramagnetic (PM) at TAC = 297 K of the austenite phase. Based on the Landau theory and M(H) data measured at different temperatures, we pointed that the FM-PM phase transitions around TAC in both samples were the second-order phase transition. Our results suggest an existence of the long-range FM interactions in the austenite phase. A small deviation from the mean-field theory of the critical exponents has been also observed pointing out an existence of the inhomogeneous magnetism that could be associated with the presence of the anti-FM interactions in these samples. Besides, their effective exponents βeff(ε) and γeff(ε) have been also calculated.

  18. Magnetic microstructure of candidates for epitaxial dual Heusler magnetic tunnel junctions

    Energy Technology Data Exchange (ETDEWEB)

    Kaiser, A. [Forschungszentrum Juelich, Institut fuer Festkoerperforschung IFF-9 and JARA-FIT, 52425 Juelich (Germany)], E-mail: a.kaiser@fz-juelich.de; Banerjee, D. [Forschungszentrum Juelich, Institut fuer Festkoerperforschung IFF-9 and JARA-FIT, 52425 Juelich (Germany); Rata, A.D. [Leibniz-Institut fuer Festkoerper- und Werkstoffforschung, Dresden (Germany); Wiemann, C.; Cramm, S.; Schneider, C.M. [Forschungszentrum Juelich, Institut fuer Festkoerperforschung IFF-9 and JARA-FIT, 52425 Juelich (Germany)

    2009-05-15

    Heusler alloys are considered as interesting ferromagnetic electrode materials for magnetic tunnel junctions, because of their high spin polarization. We, therefore, investigated the micromagnetic properties in a prototypical thin film system comprising two different Heusler phases Co{sub 2}MnSi (CMS) and Co{sub 2}FeSi (CFS) separated by a MgO barrier. The magnetic microstructure was investigated by X-ray photoemission electron microscopy (XPEEM). We find a strong influence of the Heusler phase formation process on the magnetic domain patterns. SiO{sub 2}/V/CMS/MgO/CFS and SiO{sub 2}/V/CFS/MgO/CMS trilayer structures exhibit a strikingly different magnetic behavior, which is due to pinhole coupling through the MgO barrier and a strong thickness dependence of the magnetic ordering in Co{sub 2}MnSi.

  19. Enhanced half-metallicity in the zigzag graphene nanoribbons by adsorption of the zigzag hydrogen fluoride molecular chains

    Directory of Open Access Journals (Sweden)

    Xue Gong

    2014-06-01

    Full Text Available A comprehensive theoretical study of the half-metallicity in the zigzag graphene nanoribbons (ZGNRs by adsorption of the zigzag hydrogen fluoride chains was presented. The ZGNR by adsorption of the hydrogen fluoride chains could be half-metallic when a critical length of the hydrogen fluoride chain is achieved on the ZGNR at low temperature. It was found that the strong dipole moments of the hydrogen fluoride chains act as the constant electric field. Our results suggest a huge possibility in spintronics device applications for achieving half-metallicity in the ZGNRs without the excessively high external electric fields.

  20. Anomalous conductance oscillations and half-metallicity in atomic Ag-O chains

    DEFF Research Database (Denmark)

    Strange, Mikkel; Thygesen, Kristian Sommer; Sethna, James P

    2008-01-01

    Using spin density functional theory, we study the electronic and magnetic properties of atomically thin, suspended chains containing silver and oxygen atoms in an alternating sequence. Chains longer than 4 atoms develop a half-metallic ground state implying fully spin-polarized charge carriers....... The conductances of the chains exhibit weak even-odd oscillations around an anomalously low value of 0.1G(0) (G(0) = 2e(2)/h) which coincide with the averaged experimental conductance in the long chain limit. The unusual conductance properties are explained in terms of a resonating-chain model, which takes...

  1. Study of half-metallic ferromagnetism and elastic properties of Cd{sub 1-x}Cr{sub x}Z (Z=S, Se)

    Energy Technology Data Exchange (ETDEWEB)

    Rani, Anita [Guru Nanak College for Girls, Sri Muktsar Sahib, Punjab (India); Kumar, Ranjan [Panjab University Chandigarh, Department of Physics, Chandigarh (India)

    2016-12-15

    We have studied the structural, electronic and magnetic properties of Cd{sub 1-x}Cr{sub x}S and Cd{sub 1-x}Cr{sub x}Se diluted magnetic semiconductors in zinc blende (B3) phase at x = 0.25, 0.125 and 0.0625. The calculations have been performed using DFT (density functional theory) as implemented in SIESTA code using LDA (local density approximation) as exchange-correlation (XC) potential. Study of band structures and DOS (density of states) shows HMF (half-metallic ferromagnetic) nature of Cd{sub 1-x}Cr{sub x}S and Cd{sub 1-x}Cr{sub x}Se alloys. The calculated values of s-d exchange constant Nα and p-d exchange constant Nβ show the magnetic behavior of these compounds. Moreover, both DMSs retain their half-metallic nature at 0.25, 0.125 and 0.0625 concentrations with 100% spin polarization at Fermi level (E{sub F}). Total magnetic moment of these compounds is due to 3d states of Cr atom and also existence of small induced magnetic moment on other non-magnetic atoms as well. HM robustness is also calculated as a function of lattice constants. (orig.)

  2. Half-Metallic Properties of Single-Walled Polymeric Manganese Phthalocyanine Nanotubes

    Science.gov (United States)

    Jiang, Hongbin; Bai, Meilin; Wei, Peng; Sun, Lili; Shen, Ziyong; Hou, Shimin

    2012-01-01

    We present a theoretical study of the electronic and magnetic properties of single-walled manganese phthalocyanine (MnPc) nanotubes which can be thought of as rolled-up ribbons of the two-dimensional (2D) polymeric MnPc sheet. Our density functional theory calculations show that all of the MnPc nanotubes investigated here are half-metals with 100% spin polarization around the Fermi level. Following the increase of the tube diameter, the number of spin-down energy bands of MnPc nanotubes is always increased while the spin-up band gap of MnPc nanotubes approaches that of the 2D MnPc sheet in an oscillatory manner. Because the half-metallic character of MnPc nanotubes is deeply rooted in the distribution of electrons in the energy bands dominated by the Mn 3d atomic orbitals, adsorption of CO molecules on the Mn ions leads to a redistribution of electrons in the Mn 3d orbitals and thus can tune precisely the spin state and electronic transport properties of MnPc nanotubes, demonstrating promising applications of MnPc nanotubes in future molecular spintronics and single-molecule sensors. PMID:23012498

  3. First principles study of Fe in diamond: A diamond-based half metallic dilute magnetic semiconductor

    Science.gov (United States)

    Benecha, E. M.; Lombardi, E. B.

    2013-12-01

    Half-metallic ferromagnetic ordering in semiconductors, essential in the emerging field of spintronics for injection and transport of highly spin polarised currents, has up to now been considered mainly in III-V and II-VI materials. However, low Curie temperatures have limited implementation in room temperature device applications. We report ab initio Density Functional Theory calculations on the properties of Fe in diamond, considering the effects of lattice site, charge state, and Fermi level position. We show that the lattice sites and induced magnetic moments of Fe in diamond depend strongly on the Fermi level position and type of diamond co-doping, with Fe being energetically most favorable at the substitutional site in p-type and intrinsic diamond, while it is most stable at a divacancy site in n-type diamond. Fe induces spin polarized bands in the band gap, with strong hybridization between Fe-3d and C-2s,2p bands. We further consider Fe-Fe spin interactions in diamond and show that substitutional Fe+1 in p-type diamond exhibits a half-metallic character, with a magnetic moment of 1.0 μB per Fe atom and a large ferromagnetic stabilization energy of 33 meV, an order of magnitude larger than in other semiconductors, with correspondingly high Curie temperatures. These results, combined with diamond's unique properties, demonstrate that Fe doped p-type diamond is likely to be a highly suitable candidate material for spintronics applications.

  4. Observation of large low-field magnetoresistance in spinel cobaltite: A new half-metal

    KAUST Repository

    Li, Peng

    2015-12-10

    Low-field magnetoresistance is an effective and energy-saving way to use half-metallic materials in magnetic reading heads and magnetic random access memory. Common spin-polarized materials with low field magnetoresistance effect are perovskite-type manganese, cobalt, and molybdenum oxides. In this study, we report a new type of spinel cobaltite materials, self-assembled nanocrystalline NiCo2O4, which shows large low field magnetoresistance as large as –19.1% at 0.5 T and –50% at 9 T (2 K). The large low field magnetoresistance is attributed to the fast magnetization rotation of the core nanocrystals. The surface spin-glass is responsible for the observed weak saturation of magnetoresistance under high fields. Our calculation demonstrates that the half-metallicity of NiCo2O4 comes from the hopping eg electrons within the tetrahedral Co-atoms and the octahedral Ni-atoms. The discovery of large low-field magnetoresistance in simple spinel oxide NiCo2O4, a non-perovskite oxide, leads to an extended family of low-field magnetoresistance materials. (© 2016 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim)

  5. Half-Metallic Properties of Single-Walled Polymeric Manganese Phthalocyanine Nanotubes

    Directory of Open Access Journals (Sweden)

    Hongbin Jiang

    2012-06-01

    Full Text Available We present a theoretical study of the electronic and magnetic properties of single-walled manganese phthalocyanine (MnPc nanotubes which can be thought of as rolled-up ribbons of the two-dimensional (2D polymeric MnPc sheet. Our density functional theory calculations show that all of the MnPc nanotubes investigated here are half-metals with 100% spin polarization around the Fermi level. Following the increase of the tube diameter, the number of spin-down energy bands of MnPc nanotubes is always increased while the spin-up band gap of MnPc nanotubes approaches that of the 2D MnPc sheet in an oscillatory manner. Because the half-metallic character of MnPc nanotubes is deeply rooted in the distribution of electrons in the energy bands dominated by the Mn 3d atomic orbitals, adsorption of CO molecules on the Mn ions leads to a redistribution of electrons in the Mn 3d orbitals and thus can tune precisely the spin state and electronic transport properties of MnPc nanotubes, demonstrating promising applications of MnPc nanotubes in future molecular spintronics and single-molecule sensors.

  6. Half-metallic ferromagnetic properties of Cr- and V-doped AlP semiconductors

    Energy Technology Data Exchange (ETDEWEB)

    Boutaleb, M., E-mail: miloudb20@gmail.com [Modelling and Simulation in Materials Science Laboratory, Physics Department, Djillali Liabes University of Sidi Bel-Abbes, 22000 Sidi Bel-Abbes (Algeria); Doumi, B. [Faculty of Sciences, Department of Physics, Dr. Tahar Moulay University of Saida, 20000 Saida (Algeria); Tadjer, A. [Modelling and Simulation in Materials Science Laboratory, Physics Department, Djillali Liabes University of Sidi Bel-Abbes, 22000 Sidi Bel-Abbes (Algeria); Sayede, A. [Unité de Catalyse et Chimie du Solide (UCCS), UMR CNRS 8181, Faculté des Sciences, Université d’Artois, Rue Jean Souvraz, SP 18, 62307 Lens (France)

    2016-01-01

    Using the full-potential linearized augmented plane-wave (FP-LAPW) calculations with generalized gradient approximation functional (GGA), we investigated the structural, electronic and magnetic properties of the family compounds AlP as ternary diluted semiconductors (DMS)s Al{sub 1−x}(TM=Cr,V){sub x}P with concentration of 0.25 and 0.125 in zinc blende phase (B3). The interaction of 3d orbital of transition metal with the 3p states of the four phosphorus atoms who occupy the summits of the tetrahedron resulting from SP3 hybridization, stabilize more the phenomena of magnetization by the effect of Zener's p–d exchange. The analyses of electronic and magnetic properties using the total and partial density of state and bands structure show that Al{sub 1−x}Cr{sub x}P and Al{sub 1−x}V{sub x}P are spin-polarized with a half-metallic band gap. We seem that these materials will be among the good candidates for spintronic applications. - Highlights: • Two doping concentrations of 0.25 and 0.125 with Al1-x(TM=Cr,V)xP are realizing. • Total and Partial -DOS calculations show the half-metallic ferromagnetic behavior. • Our compounds seem to be good materials for spintronic application.

  7. Half-metallic and magnetic properties in nonmagnetic element embedded graphitic carbon nitride sheets.

    Science.gov (United States)

    Meng, Bo; Xiao, Wen-zhi; Wang, Ling-ling; Yue, Li; Zhang, Song; Zhang, Hong-yun

    2015-09-14

    We have investigated the structures, electronic structures and magnetic properties of the triazine-based g-C3N4 (gt-C3N4) monolayer doped with B, Al, and Cu atoms based on density functional theory using ab initio calculations. The B atom prefers to be situated at the center of the triazine ring, whereas the Al and Cu atoms tend to be located above the center of the triazine ring. The doping at the interstitial sites results in nonplanar structures which are thermodynamically stable. Each dopant atom induces a total magnetic moment of 1.0 μB which mainly arises from the pz orbitals because the n-type doping injects unpaired electrons into anti-π orbitals. The results obtained from the GGA-PBE and HSE06 schemes show that all the doped systems exhibit half-metallic behaviors. B- and Al-doped systems are at a ferromagnetic ground state, while the Cu-doped case is at an anti-ferromagnetic ground state. The long-range half-metallic ferromagnetic order is attributed to the p-p interactions. In particular, the estimated Curie temperature implies that the systems doped with B are potential candidates for spintronics applications in future.

  8. A review of the electronic and magnetic properties of tetrahedrally bonded half-metallic ferromagnets

    Science.gov (United States)

    Mavropoulos, Ph; Galanakis, I.

    2007-08-01

    The emergence of the field of spintronics has brought half-metallic ferromagnets to the centre of scientific research. A lot of interest was focused on newly created transition-metal pnictides (such as CrAs) and chalcogenides (such as CrTe) in the metastable zinc-blende lattice structure. These compounds were found to have the advantage of high Curie temperatures in addition to their structural similarity to semiconductors. Significant theoretical activity has been devoted to the study of the electronic and magnetic properties of these compounds in an effort to achieve a better control of their experimental behaviour in realistic applications. This paper is devoted to an overview of the studies of these compounds, with emphasis on theoretical results, covering their bulk properties (electronic structure, magnetism, stability of the zinc-blende phase, stability of ferromagnetism) as well as low-dimensional structures (surfaces, interfaces, nanodots and transition-metal delta-doped semiconductors) and phenomena that can possibly destroy the half-metallic property, like structural distortions or defects.

  9. Emergence of ferrimagnetic half-metallicity in two-dimensional MXene Mo3N2F2

    Science.gov (United States)

    Li, Sheng-shi; Hu, Shu-jun; Ji, Wei-xiao; Li, Ping; Zhang, Kun; Zhang, Chang-wen; Yan, Shi-shen

    2017-11-01

    Ferrimagnetic half-metal is more promising in spintronic devices than its ferromagnetic counterpart due to its lower stray fields and favorable robustness of magnetism. In comparison to the three-dimensional counterpart, the realization on two-dimensional ferrimagnetic half-metal remains blank up to date. Here, based on first-principles calculations and Monte Carlo simulations, we predict a ferrimagnetic half-metallicity in two-dimensional MXene Mo3N2F2 with a Curie temperature of 237 K and a considerable magnetic anisotropy energy. The ferrimagnetic coupling is mainly from the interactions of itinerant d electron between different Mo layers, and thus endows a 100% spin-polarization at the Fermi level with a sizable half-metallic gap of 0.47 eV. Such ferrimagnetic half-metallicity is also robust against external strains. Additionally, diverse magnetic and electronic characters can be controlled, depending on a differently terminated Mo3N2F2 surface. These findings provide an ideal platform to design spintronic devices related to two-dimensional ferrimagnetic half-metals.

  10. Shell-ferromagnetism in Ni-Mn-based Heuslers in view of ductile Ni-Mn-Al

    Directory of Open Access Journals (Sweden)

    A. Çakır

    2017-05-01

    Full Text Available The present work deals with magnetic and structural phase instabilities in Ni-Mn-based Heusler alloys especially Ni-Mn-Al. The temper-annealed Ni50Mn45Al5 Heusler alloy decomposes into the full stoichiometric Ni2MnAl and NiMn phases. The decomposed stoichiometric Heusler forms precipitates in an anti-ferromagnetic NiMn matrix and exhibits shell-ferromagnetic properties when the temper-annealing is performed under magnetic field. The shell-ferromagnetism results from the magnetic proximity effect and is observed as vertically shifted magnetization loops. The presence of this property in Ni50Mn45Al5 adds the possibility of having a ductile material while preserving the shell-ferromagnetic properties.

  11. First-principles study of new quaternary Heusler compounds without 3d transition metal elements: ZrRhHfZ (Z = Al, Ga, In)

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Xiaotian [School of Material Sciences and Engineering, Hebei University of Technology, Tianjin 300130 (China); Institute for Superconducting & Electronic Materials (ISEM), University of Wollongong, Wollongong 2500 (Australia); Cheng, Zhenxiang, E-mail: cheng@uow.edu.au [Institute for Superconducting & Electronic Materials (ISEM), University of Wollongong, Wollongong 2500 (Australia); Guo, Ruikang [School of Material Sciences and Engineering, Hebei University of Technology, Tianjin 300130 (China); Wang, Jianli [Institute for Superconducting & Electronic Materials (ISEM), University of Wollongong, Wollongong 2500 (Australia); Rozale, Habib [Condensed Matter and Sustainable Development Laboratory, Physics Department, University of Sidi-Bel-Abbès, 22000 Sidi-Bel-Abbès (Algeria); Wang, Liying [Department of Physics, Tianjin University, Tianjin 300350 (China); Yu, Zheyin [Institute for Superconducting & Electronic Materials (ISEM), University of Wollongong, Wollongong 2500 (Australia); Liu, Guodong, E-mail: gdliu1978@126.com [School of Material Sciences and Engineering, Hebei University of Technology, Tianjin 300130 (China)

    2017-06-01

    Plane-wave pseudo-potential methods based on density functional theory are employed to investigate the electronic structures, and the magnetic and half-metallic properties of the newly designed quaternary Heusler compounds ZrRhHfZ (Z = Al, Ga, In) without 3d transition metal elements. The calculated results show that ZrRhHfZ (Z = Al, Ga, In) compounds are half-metallic, with 100% spin polarization around the Fermi level. The structural stability of these compounds has been tested from the aspects of their cohesion energy and formation. The spin-flip/half-metallic gaps of ZrRhHfZ (Z = Al, Ga, In) compounds are quite large, with values of 0.2548 eV, 0.3483 eV, and 0.2866 eV, respectively. These compounds show Slater-Pauling behavior, and the total spin magnetic moment per unit cell (M{sub t}) scales with the total number of valence electrons (Z{sub t}) following the rule: M{sub t} = Z{sub t} - 18. The magnetization of ZrRhHfZ (Z = Al, Ga, In) compounds mainly comes from the 4d electrons of the Zr atoms and the 5d electrons of the Hf atoms. Furthermore, the effects of uniform strain and tetragonal deformation on the half metallicity has been investigated in detail, which is important for practical application. Finally, we reveal that the half-metallicity can be maintained when the Coulomb interactions are considered. - Highlights: • New quaternary compounds without 3d transition metal elements have been designed. • The electronic structures and magnetism of the ZrRhHfZ compounds have been studied. • The effect of strain on the half-metallic behavior has been tested. • The effect of the Coulomb interactions on the half-metallicity has been investigated.

  12. Half-metallic ferromagnetism in Cr-doped semiconducting Ge-chalcogenide: Density functional approach

    Energy Technology Data Exchange (ETDEWEB)

    Saini, Hardev S., E-mail: hardevdft@gmail.com [Department of Physics, National Institute of Technology, Kurukshetra-136119, Haryana (India); Singh, Mukhtiyar; Thakur, Jyoti; Kashyap, Manish K. [Department of Physics, Kurukshetra University, Kurukshetra-136119, Haryana (India)

    2014-04-24

    A supercell approach has been used to calculate the electronic and magnetic properties of Cr-doped Ge chalcogenide, Ge{sub 1−x}Cr{sub x}Te (x = 0.25 and 0.125). The calculations have been performed using full potential Linear Augmented Plane Wave (FPLAPW) method within generalized gradient approximation (GGA) as exchange-correlation (XC) potential. The calculated results show that the doping of Cr induces the 100% spin polarization at Fermi level (EF) and showed the robust half metallic ferromagnetism in this compound. Thus, the compound at both dopant concentrations behave as dilute magnetic semiconductor (DMS) showing metallic property in majority and semiconducting for minority spin channels which is best suited for spintronic applications. The total magnetic moments of this compound are mainly due to Cr-d states present at E{sup F} with negligible contribution from electronic states of other atoms.

  13. Atomically Thin Transition-Metal Dinitrides: High-Temperature Ferromagnetism and Half-Metallicity.

    Science.gov (United States)

    Wu, Fang; Huang, Chengxi; Wu, Haiping; Lee, Changhoon; Deng, Kaiming; Kan, Erjun; Jena, Puru

    2015-12-09

    High-temperature ferromagnetic two-dimensional (2D) materials with flat surfaces have been a long-sought goal due to their potential in spintronics applications. Through comprehensive first-principles calculations, we show that the recently synthesized MoN2 monolayer is such a material; it is ferromagnetic with a Curie temperature of nearly 420 K, which is higher than that of any flat 2D magnetic materials studied to date. This novel property, made possible by the electron-deficient nitrogen ions, render transition-metal dinitrides monolayers with unique electronic properties which can be switched from the ferromagnetic metals in MoN2, ZrN2, and TcN2 to half-metallic ones in YN2. Transition-metal dinitrides monolayers may, therefore, serve as good candidates for spintronics devices.

  14. A Phenomenological Model For The Spin Stiffness Of A Half-metallic Ferromagnet

    Science.gov (United States)

    Chura, Raul; Bedell, Kevin

    By using the Fermi Liquid Theory for Spin Polarized Systems, more specifically, by using the linearized form of Landau Silin Kinetic Equation, and after considering an appropriate approximation, we have obtained the dispersion relationships describing the collective modes for the spin waves in a Half Metallic Ferromagnetic (HMF) material. Our results predict the existence of a gapless mode for the spin dynamics of a HMF, in agreement with experiment. In addition, our calculations allowed us to get a phenomenological formula for the spin stiffness of HMF materials, which being entirely in terms of band theory and Landau interaction parameters, allowed us to test that formula for those HMF materials for which we were able to find, in the available literature, the required data. For these materials our model is consistent with experiment. Work supported by Grant Number CANON-CU-005-2013 at UNSAAC, Cusco, Peru.

  15. One-dimensional half-metallic interfaces of two-dimensional honeycomb insulators

    Science.gov (United States)

    Bristowe, N. C.; Stengel, Massimiliano; Littlewood, P. B.; Artacho, Emilio; Pruneda, J. M.

    2013-10-01

    We study zigzag interfaces between insulating compounds that are isostructural to graphene, specifically II-VI, III-V, and IV-IV two-dimensional honeycomb insulators. We show that these one-dimensional interfaces are polar, with a net density of excess charge that can be simply determined by using the ideal (integer) formal valence charges, regardless of the predominant covalent character of the bonding in these materials. We justify this finding on fundamental physical grounds by analyzing the topology of the formal polarization lattice in the parent bulk materials. First-principles calculations elucidate an electronic compensation mechanism not dissimilar to oxide interfaces, which is triggered by a Zener-like charge transfer between interfaces of opposite polarity. In particular, we predict the emergence of one-dimensional electron and hole gases, which in some cases are ferromagnetic half metallic.

  16. Room temperature ferromagnetism and half metallicity in nickel doped ZnS: Experimental and DFT studies

    Energy Technology Data Exchange (ETDEWEB)

    Akhtar, Muhammad Saeed [School of Materials, The University of Manchester, Oxford Road, Manchester M13 9PL (United Kingdom); Centre of Excellence in Solid State Physics, University of the Punjab, Lahore 54590 (Pakistan); Malik, Mohammad Azad, E-mail: Azad.malik@manchester.ac.uk [School of Materials, The University of Manchester, Oxford Road, Manchester M13 9PL (United Kingdom); Riaz, Saira; Naseem, Shahzad [Centre of Excellence in Solid State Physics, University of the Punjab, Lahore 54590 (Pakistan)

    2015-06-15

    The nickel doped nanocrystalline ZnS thin films were deposited onto glass substrates by chemical bath deposition (CBD). Also ZnS:Ni nanoparticles were synthesized by CBD/co-precipitation method. Powder X-ray diffraction (p-XRD) studies demonstrate that both thin films and nanoparticles correspond to sphalerite (cubic) phase of ZnS with slight shift towards higher 2θ values due to incorporation of nickel in the ZnS lattice. The crystallite sizes estimated by Scherrer equation were 4 and 2.6 nm for ZnNiS thin films and nanoparticles, respectively. Scanning Electron Microscopy (SEM) images reveal that the morphology of thin films is based on quasi-spherical particles with nano scale dimensions. Energy Dispersive X-ray (EDX) spectroscopy confirms that the as-deposited thin films have a stoichiometry consistent with the nickel doped ZnS. Full-potential linearized augmented plane wave (FP-L/APW) method based on spin-polarized density functional theory (DFT) was employed to investigate the electronic and magnetic properties of ZnNiS for the doping concentration. Exchange-correlation functional was studied using generalized gradient approximation (GGA + U) method. Electronic band structures and density of states (DOS) demonstrate 100% spin polarization (half metallicity) with ferromagnetic exchange interactions. Superconducting quantum interference device (SQUID) analysis confirms the theoretical observation of ferromagnetism in nickel doped ZnS. These ZnS based half metallic ferromagnets seem to have virtuous applications in future spintronic devices. - Highlights: • ZnS.Ni thin films and nanoparticles were deposited onto glass substrates by CBD. • p-XRD correspond to sphalerite (cubic) phase of ZnS with slight shift in peaks. • DFT was employed to investigate the properties of ZnS.Ni. • DOS demonstrate 100% spin polarization with ferromagnetic exchange interactions. • SQUID analysis confirms the theoretical observations of nickel doped ZnS.

  17. Half metallicity in Sr{sub 2}CrOsO{sub 6} via Na doping

    Energy Technology Data Exchange (ETDEWEB)

    Zu, Ningning [State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022 (China); Wang, Jing [Key Laboratory of Applied Chemistry, Yanshan University, Qinhuangdao 066004 (China); Wang, Ying, E-mail: ywang_2012@ciac.ac.cn [State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022 (China); Wu, Zhijian, E-mail: zjwu@ciac.ac.cn [State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022 (China)

    2015-07-05

    Highlights: • Na-doped Sr{sub 2}CrOsO{sub 6} is investigated by using the density functional theory. • Both NaSr{sub 5}Cr{sub 3}Os{sub 3}O{sub 18} and NaSrCrOsO{sub 6} are half metals. • The Curie temperature of NaSr{sub 5}Cr{sub 3}Os{sub 3}O{sub 18} and NaSrCrOsO{sub 6} is higher than room temperature. - Abstract: The insulating Sr{sub 2}CrOsO{sub 6} has the highest Curie temperature of 725 K among the double perovskites so far. In this study, by doping with Na, NaSr{sub 5}Cr{sub 3}Os{sub 3}O{sub 18} and NaSrCrOsO{sub 6} are investigated by using the density functional theory. The calculated results indicated that the hole generated by Na goes to Os 5d t{sub 2g} orbitals. This makes one of the insulating spin channels in Sr{sub 2}CrOsO{sub 6} to be metallic in the Na-doped compounds. Thus, they become half metals. The estimated magnetic ordering temperature is 579 K for NaSr{sub 5}Cr{sub 3}Os{sub 3}O{sub 18} and 615 K for NaSrCrOsO{sub 6}, which are higher than the room temperature. Therefore, we expect that the Na-doped Sr{sub 2}CrOsO{sub 6} would be promising candidates as spintronic material.

  18. Band structure of Heusler compounds studied by photoemission and tunneling spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Arbelo Jorge, Elena

    2011-07-01

    Heusler compounds are key materials for spintronic applications. They have attracted a lot of interest due to their half-metallic properties predicted by band structure calculations. The aim of this work is to evaluate experimentally the validity of the predictions of half metallicity by band structure calculations for two specific Heusler compounds, Co{sub 2}FeAl{sub 0.3}Si{sub 0.7} and Co{sub 2}MnGa. Two different spectroscopy methods for the analysis of the electronic properties were used: Angular Resolved Ultraviolet Photoemission Spectroscopy (ARUPS) and Tunneling Spectroscopy. Heusler compounds are prepared as thin films by RF-sputtering in an ultra high vacuum system. For the characterization of the samples, bulk and surface crystallographic and magnetic properties of Co{sub 2}FeAl{sub 0.3}Si{sub 0.7} and Co{sub 2}MnGa are studied. X-ray and electron diffraction reveal a bulk and surface crossover between two different types of sublattice order (from B2 to L2{sub 1}) with increasing annealing temperature. X-ray magnetic circular dichroism results show that the magnetic properties in the surface and bulk are identical, although the magnetic moments obtained are 5 % below from the theoretically predicted. By ARUPS evidence for the validity of the predicted total bulk density of states (DOS) was demonstrated for both Heusler compounds. Additional ARUPS intensity contributions close to the Fermi energy indicates the presence of a specific surface DOS. Moreover, it is demonstrated that the crystallographic order, controlled by annealing, plays an important role on broadening effects of DOS features. Improving order resulted in better defined ARUPS features. Tunneling magnetoresistance measurements of Co{sub 2}FeAl{sub 0.3}Si{sub 0.7} and Co{sub 2}MnGa based MTJ's result in a Co{sub 2}FeAl{sub 0.3}Si{sub 0.7} spin polarization of 44 %, which is the highest experimentally obtained value for this compound, although it is lower than the 100 % predicted. For Co

  19. Structural characterization of Heusler compounds using NMR

    Energy Technology Data Exchange (ETDEWEB)

    Wurmehl, Sabine; Fecher, Gerhard; Balke, Benjamin; Ksenofontov, Vadim; Jung, Verena; Felser, Claudia [Johannes Gutenberg - Universitaet, 55099 Mainz (Germany); Wojcik, Marek [Institute of Physics, Polish Academy of Sciences, 02-668 Warszawa (Poland)

    2007-07-01

    The L2{sub 1} ordered Heusler alloys Co{sub 2}Mn{sub 1-x}Fe{sub x}Si with 0{<=}x{<=}1 attracted much scientific interest, as they are predicted to show high spin polarisation at the Fermi-energy. Therefore Co{sub 2}Mn{sub 1-x}Fe{sub x}Si samples were investigated using spin echo nuclear magnetic resonance (NMR) measurements. This method provides a tool to measure the hyperfine fields. The hyperfine fields represent a very sensitive local probe to order-disorder phenomena. The NMR measurements of polycrystalline Co{sub 2}FeSi samples exhibit a two-peak spectrum with an additional shoulder. This additional signals are attributed to second-order quadrupole splitting, a so called asymmetric line broadening and might be caused by tension within the structure (strain). This effect occurs even in highly ordered systems. Thus previous structural results are corroborated, demonstrating even locally a very high degree of order in Co{sub 2}FeSi. The NMR spectra of the series Co{sub 2}Mn{sub 1-x}Fe{sub x}Si (0.1{<=}x{<=}0.9) exhibit multiplet structures. These might be explained by quadrupole splitting and statistical distribution of Mn and Fe atoms on the Mn site. In summary, the high degree of order in Co{sub 2}Mn{sub 1-x}Fe{sub x}Si is shown.

  20. Half-metallicity and giant magneto-optical Kerr effect in N-doped NaTaO3

    KAUST Repository

    Saeed, Yasir

    2012-09-01

    We use density functional theory and the modified Becke-Johnson (mBJ) approach to analyze the electronic and magneto-optical properties of N-doped NaTaO 3. The mBJ results show a half-metallic nature of NaTaO 2N, in contrast to the generalized gradient approximation. We find a giant polar Kerr rotation of 2.16°at 725 nm wave length (visible region), much higher than in other half-metallic perovskites and the prototypical half-metal PtMnSb. We explain the physical origin of this unexpected property. © 2012 Elsevier B.V. All rights reserved.

  1. Electric-Field-Driven Dual Vacancies Evolution in Ultrathin Nanosheets Realizing Reversible Semiconductor to Half-Metal Transition.

    Science.gov (United States)

    Lyu, Mengjie; Liu, Youwen; Zhi, Yuduo; Xiao, Chong; Gu, Bingchuan; Hua, Xuemin; Fan, Shaojuan; Lin, Yue; Bai, Wei; Tong, Wei; Zou, Youming; Pan, Bicai; Ye, Bangjiao; Xie, Yi

    2015-12-02

    Fabricating a flexible room-temperature ferromagnetic resistive-switching random access memory (RRAM) device is of fundamental importance to integrate nonvolatile memory and spintronics both in theory and practice for modern information technology and has the potential to bring about revolutionary new foldable information-storage devices. Here, we show that a relatively low operating voltage (+1.4 V/-1.5 V, the corresponding electric field is around 20,000 V/cm) drives the dual vacancies evolution in ultrathin SnO2 nanosheets at room temperature, which causes the reversible transition between semiconductor and half-metal, accompanyied by an abrupt conductivity change up to 10(3) times, exhibiting room-temperature ferromagnetism in two resistance states. Positron annihilation spectroscopy and electron spin resonance results show that the Sn/O dual vacancies in the ultrathin SnO2 nanosheets evolve to isolated Sn vacancy under electric field, accounting for the switching behavior of SnO2 ultrathin nanosheets; on the other hand, the different defect types correspond to different conduction natures, realizing the transition between semiconductor and half-metal. Our result represents a crucial step to create new a information-storage device realizing the reversible transition between semiconductor and half-metal with flexibility and room-temperature ferromagnetism at low energy consumption. The as-obtained half-metal in the low-resistance state broadens the application of the device in spintronics and the semiconductor to half-metal transition on the basis of defects evolution and also opens up a new avenue for exploring random access memory mechanisms and finding new half-metals for spintronics.

  2. Emergence of half metallicity in Cr-doped GaP dilute magnetic semiconductor compound within solubility limit

    Energy Technology Data Exchange (ETDEWEB)

    Saini, Hardev S.; Singh, Mukhtiyar [Department of Physics, Kurukshetra University, Kurukshetra, 136119 Haryana (India); Reshak, Ali H. [School of Complex Systems, FFWP - South Bohemia University, Nove Hrady 37333 (Czech Republic); School of Material Engineering, University Malaysia Perlis, P.O. Box 77, d/a Pejabat Pos Besar, 01007 Kangar, Perlis (Malaysia); Kashyap, Manish K., E-mail: manishdft@gmail.com [Department of Physics, Kurukshetra University, Kurukshetra, 136119 Haryana (India)

    2012-09-25

    Highlights: Black-Right-Pointing-Pointer This compound is true half metallic ferromagnet for all studied Cr concentrations. Black-Right-Pointing-Pointer The half metallicity is preserved up to lowest doping concentration, x = 0.03. Black-Right-Pointing-Pointer The HM gap increases with reduction in doping concentration from 0.25 to 0.03. Black-Right-Pointing-Pointer p-d hybridization induces ferromagnetism and half metallicity in the compound. Black-Right-Pointing-Pointer Double exchange mechanism is responsible for the stabilization of ferromagnetism. - Abstract: The electronic and magnetic properties of Ga{sub 1-x}Cr{sub x}P dilute magnetic semiconductor (DMS) compound for dopant concentration, x = 0.25, 0.125, 0.06 and 0.03 have been investigated using WIEN2k implementation of full potential linearized augmented plane wave (FPLAPW) method in order to seek out the possibility of new dilute magnetic semiconductor (DMS) compound within generalized gradient approximation (GGA) as exchange-correlation (XC) potential. The calculated results show that the Cr doping in GaP induces the ferromagnetism and originates a half metallic (HM) gap at Fermi level (E{sub F}) in minority spin channel (MIC) for all concentrations. The half metallicity is originated by the hybridization of Cr-d states with P-p states. Moreover, the half metallicity remains intact for all Cr-concentration. We also observed that the HM gap increases with the reduction in doping concentration from 0.25 to 0.03. The total magnetic moment of this compound is mainly due to Cr-d states present at E{sub F}. A small induced magnetic moment on other non magnetic atoms (Ga and P) for all doping concentrations is a consequence of p-d hybridization between Cr-d and P-p states.

  3. Optical and electronic structure studies of half metallic in Sr2CoWO6 double perovskite

    Science.gov (United States)

    Mandal, Golak; Jha, Dhiraj; Himanshu, A. K.; Mukherjee, P.; Das, N. K.; Singh, B. K.; Kumar, Uday; Sinha, T. P.

    2017-05-01

    The density function theory (DFT) under the generalised gradient approximation has been used to investigate the electronic structure of the double perovskite half metallic Sr2CoWO6 synthesied by the solid state reaction technique. The band gap of the system was measured from the Uv-Vis spectra and compared with the theoretically calculated values. Our results states that Sr2CoWO6 material behaves as insulators for the spin-up orientation and spindown orientation as found for the half metallic systems.

  4. The Two-Dimensional MnO2/Graphene Interface: Half-metallicity and Quantum Anomalous Hall State

    KAUST Repository

    Gan, Liyong

    2015-10-07

    We explore the electronic properties of the MnO2/graphene interface by first-principles calculations, showing that MnO2 becomes half-metallic. MnO2 in the MnO2/graphene/MnO2 system provides time-reversal and inversion symmetry breaking. Spin splitting by proximity occurs at the Dirac points and a topologically nontrivial band gap is opened, enabling a quantum anomalous Hall state. The half-metallicity, spin splitting, and size of the band gap depend on the interfacial interaction, which can be tuned by strain engineering.

  5. Virtual half-metallicity at the CoS2/FeS2 interface induced by strain

    KAUST Repository

    Nazir, Safdar

    2013-01-01

    Spin polarized ab initio calculations based on density functional theory are performed to investigate the electronic and magnetic properties of the interface between the ferromagnetic metal CoS2 and the nonmagnetic semiconductor FeS2. Relaxation of the interface structure is taken into account by atomic force minimization. We find that both Co and Fe are close to half-metallicity at the interface. Tensile strain is shown to strongly enhance the spin polarization so that a virtually half-metallic interface can be achieved, for comparably moderate strain. © 2012 The Royal Society of Chemistry.

  6. Local Structural Analysis of Half-Metallic Ferromagnet CrO2

    Science.gov (United States)

    Kodama, Katsuaki; Ikeda, Kazutaka; Isobe, Masahiko; Takeda, Hikaru; Itoh, Masayuki; Ueda, Yutaka; Shamoto, Shin-ichi; Otomo, Toshiya

    2016-09-01

    We have performed powder neutron diffraction on the half-metallic ferromagnet CrO2 which has a rutile-type crystal structure with a tetragonal unit cell. Although the powder diffraction pattern can be fitted by the reported crystal structure including a single Cr site, the atomic pair distribution function (PDF) can be fitted by the structural model with an orthorhombic unit cell including two kinds of inequivalent Cr sites. The difference between the valences of the two inequivalent Cr sites, δ of Cr+4±δ, estimated from the local structural parameters is about 0.06. The shapes of the two CrO6 octahedra are slightly different, suggesting the short-range orbital ordering of the Cr 3d orbitals. The lattice distortion and the improvement of the fitting to the PDF obtained using the locally distorted structure model are apparent in the region below about 10 Å, suggesting that the domain size or correlation length of the locally distorted structure is about 10 Å, roughly corresponding to the size of two unit cells.

  7. Comment on “Structural, elastic, electronic, magnetic and optical properties of RbSrX (C, SI, Ge) half-Heusler compounds”

    Energy Technology Data Exchange (ETDEWEB)

    Jalilian, Jaafar, E-mail: jaafarjalilian@gmail.com [Young Researchers and Elite Club, Kermanshah Branch, Islamic Azad University, Kermanshah (Iran, Islamic Republic of); Motiepour, Pouria [Electrical Engineering Department, Technical and Vocational University, Kermanshs (Iran, Islamic Republic of)

    2015-12-15

    In a recent article by Ahmad et al. (2015) [1] structural, elastic, electronic, magnetic and optical properties of RbSrX (C, Si, Ge) half-Heusler compounds have been studied by the first principles calculations. After studying this article, we found that there are some physical and computational mistakes in electronic and optical properties sections. In investigating optical properties, they did not consider intraband transitions contribution in complex dielectric function term, while this term has significant effect on optical spectra for half-metallic materials. - Highlights: • The spin up channel is more occupied than the spin down channel. • The intraband transition has remarkable effects on optical properties of half-metallic materials. • The intraband transitions increase reflectance in low energy ranges.

  8. Heusler compounds as ternary intermetallic nanoparticles: Co{sub 2}FeGa

    Energy Technology Data Exchange (ETDEWEB)

    Basit, Lubna; Wang Changhai; Jenkins, Catherine A; Balke, Benjamin; Ksenofontov, Vadim; Fecher, Gerhard H; Felser, Claudia [Johannes Gutenberg - Universitaet, Institut fuer analytische und anorganische Chemie, 55099 Mainz (Germany); Mugnaioli, Enrico; Kolb, Ute [Johannes Gutenberg - Universitaet, Institut fuer Physikalische Chemie, Elektronenmikroskopie-Zentrum Mainz (EMZM), 55099 Mainz (Germany); Nepijko, Sergej A; Schoenhense, Gerd [Johannes Gutenberg - Universitaet, Institut fuer Physik, 55099 Mainz (Germany); Klimenkov, Michael, E-mail: felser@uni-mainz.d [Institut fuer Materialforschung I, Forschungszentrum Karlsruhe GmbH, 76021 Karlsruhe (Germany)

    2009-04-21

    This work describes the preparation of ternary nanoparticles based on the Heusler compound Co{sub 2}FeGa. Nanoparticles with sizes of about 20 nm were synthesized by reducing a methanol impregnated mixture of CoCl{sub 2} {center_dot} 6H{sub 2}O, Fe(NO{sub 3}){sub 3} {center_dot} 9H{sub 2}O and Ga(NO{sub 3}){sub 3} {center_dot} xH{sub 2}O after loading on fumed silica. The dried samples were heated under pure H{sub 2} gas at 900 {sup 0}C. The obtained nanoparticles-embedded in silica-were investigated by means of x-ray diffraction (XRD), transmission electron microscopy, temperature dependent magnetometry and Moessbauer spectroscopy. All methods clearly revealed the Heusler-type L2{sub 1} structure of the nanoparticles. In particular, anomalous XRD data demonstrate the correct composition in addition to the occurrence of the L2{sub 1} structure. The magnetic moment of the particles is about 5{mu}{sub B} at low temperature in good agreement with the value of bulk material. This suggests that the half-metallic properties are conserved even in particles on the 10 nm scale.

  9. Transition-metal doping of semiconducting chalcopyrites: half-metallicity and magnetism

    Science.gov (United States)

    Sarkisov, Sergey Y.; Picozzi, Silvia

    2007-01-01

    An extensive ab initio investigation of the electronic and magnetic structure of transition-metal-doped chalcopyrites is reported, focusing on Cr, Mn and Fe in CuAlS2, AgGaS2, ZnGeP2 and CdGeAs2. Our results show that the electronic properties, in terms of defect-induced density of states, largely depend on the specific combination of host, transition-metal dopant and substituted cation. In particular, for AgGaS2 doped with Cr, Mn and Fe in both cationic sites, we show that the transition metal substituting silver gives rise to strongly localized orbitals in proximity to the Fermi level, whereas generally a much higher hybridization occurs when the transition metal substitutes for Ga. On the other hand, if we fix the dopant, namely Cr, and introduce it into different hosts, Cr-doped CuAlS2 and AgGaS2 show more localized defect-induced states, whereas in more covalently bonded hosts, such as ZnGeP2 and CdGeAs2, a stronger hybridization between Cr d states and the host valence band occurs. Our findings have important consequences on the exchange interaction range, that, along with the exchange interaction strength, must be taken into account in a careful materials design aiming at optimizing the ferromagnetic properties. Finally, exploiting a simple model to predict magnetic moments in diluted magnetic semiconductors, we achieve half-metallic antiferromagnetism in chalcopyrites by co-doping CuAlS2 with Mn and V; indeed, we obtain a 100% spin-polarized density of states, with a mixed impurity band due to both Mn and V d states, ferrimagnetically coupled in the ground state.

  10. Electronic structure, magnetism and disorder in the Heusler compound Co{sub 2}TiSn

    Energy Technology Data Exchange (ETDEWEB)

    Kandpal, Hem Chandra [Institut fuer Anorganische Chemie und Analytische Chemie, Johannes Gutenberg-Universitaet, Staudinger Weg 9, 55099 Mainz (Germany); Ksenofontov, Vadim [Institut fuer Anorganische Chemie und Analytische Chemie, Johannes Gutenberg-Universitaet, Staudinger Weg 9, 55099 Mainz (Germany); Wojcik, Marek [Institute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, 02-668 Warsaw (Poland); Seshadri, Ram [Materials Department and Materials Research Laboratory, University of California, Santa Barbara, CA 93106 (United States); Felser, Claudia [Institut fuer Anorganische Chemie und Analytische Chemie, Johannes Gutenberg-Universitaet, Staudinger Weg 9, 55099 Mainz (Germany)

    2007-03-21

    Polycrystalline samples of the Heusler compound Co{sub 2}TiSn have been prepared and studied using bulk techniques (x-ray diffraction and magnetization) as well as local probes ({sup 119}Sn Moessbauer spectroscopy and {sup 59}Co nuclear magnetic resonance spectroscopy) in order to determine how disorder affects the half-metallic behaviour and also to establish the joint use of Moessbauer and NMR spectroscopies as a quantitative probe of local atom ordering in these compounds. Additionally, density functional electronic structure calculations on ordered and partially disordered Co{sub 2}TiSn compounds have been carried out at a number of different levels of theory in order to simultaneously understand how the particular choice of DFT scheme as well as disorder affects the computed magnetization. Our studies suggest that a sample which seems well ordered by x-ray diffraction and magnetization measurements can possess up to 10% of antisite (Co/Ti) disordering. Computations similarly suggest that even 12.5% antisite Co/Ti disorder does not destroy the half-metallic character of this material. However, the use of an appropriate level of non-local DFT is crucial.

  11. Electronic structure, magnetism, and disorder in the Heusler compound Co{sub 2}TiSn

    Energy Technology Data Exchange (ETDEWEB)

    Kandpal, Hem C.; Ksenofontov, Vadim; Felser, Claudia [Institut fuer Anorganische Chemie und Analytische Chemie, Johannes Gutenberg-Universitaet, Staudinger Weg 9, 55099 Mainz (Germany); Wojcik, Marek [Institute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, 02-668 Warszawa (Poland); Seshadri, Ram [Department and Materials Research Laboratory, University of California, Santa Barbara, CA (United States)

    2007-07-01

    Polycrystalline samples of the Heusler compound Co{sub 2}TiSn have been prepared and studied using bulk techniques (X-ray diffraction and magnetization) as well as local probes ({sup 119}Sn Moessbauer spectroscopy and {sup 59}Co nuclear magnetic resonance spectroscopy) in order to determine how disorder affects half-metallic behavior and also, to establish the joint use of Moessbauer and NMR spectroscopies as a quantitative probe of local atom ordering in these compounds. Additionally, density functional electronic structure calculations on ordered and partially disordered Co{sub 2}TiSn compounds have been carried out at a number of different levels of theory in order to simultaneously understand how the particular choice of DFT scheme as well as disorder affect the computed magnetization. Our studies suggest that a sample which seems well-ordered by X-ray diffraction and magnetization measurements can possess up to 10% of antisite (Co/Ti) disordering. Computations similarly suggest that even 12.5% antisite Co/Ti disorder does not destroy the half-metallic character of this material.

  12. Crystal Structure of New Heusler Compounds

    OpenAIRE

    Graf, Tanja; Casper, Frederick; Winterlik, Jürgen; Balke, Benjamin; Fecher, Gerhard H.; Felser, Claudia

    2009-01-01

    Abstract Heusler compounds are promising materials in many fields of contemporary research. The spectrum of their possible applications ranges from magnetic and magneto-mechanical materials over semiconductors and thermoelectrics to superconductors. An important feature of the Heusler compounds is the possibility of controlling the valence electron concentration by partial substitution of elements. On the other hand, the properties also depend on the degree of ordering of the the c...

  13. First-principles calculated spin-gapless semiconducting behavior in quaternary VCoHfGa and CrFeHfGa Heusler compounds

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Xiude; Wu, Xiaolin [Institute of Theoretical Physics, Zunyi Normal College, Zunyi 563002 (China); Wu, Bo, E-mail: fqwubo@zync.edu.cn [Institute of Theoretical Physics, Zunyi Normal College, Zunyi 563002 (China); School of Marine Science and Technology, Northwestern Polytechnical University, Xian 710072 (China); Feng, Yu [School of Physical Science and Technology, Southwest University, Chongqing 400715 (China); Li, Ping [Institute for Clean Energy & Advanced Materials (ICAEM), Southwest University, Chongqing 400715 (China); Huang, Haishen [Institute of Theoretical Physics, Zunyi Normal College, Zunyi 563002 (China)

    2016-07-15

    Highlights: • Structural, electronic and magnetic properties of quaternary Heusler alloy [VCo,CrFe]HfGa were detected theoretically. • The quaternary Heusler alloy [VCo,CrFe]HfGa are (or are nearly) spin gapless semiconductors at the lowest energy state. • The ferromagnetic coupling plays an important role in magnetism. - Abstract: By using generalized gradient approximation (GGA) scheme within the density functional theory (DFT), the structural, electronic and magnetic properties of LiMgPdSn-type quaternary Heusler alloy CrFeHfGa and VCoHfGa were detected compressively. The results reveal that the two alloys are (or are nearly) potential spin gapless semiconductors with a magnetic moment of 3 μ{sub B} per primitive cell and the minority-spin gap of 0.8 eV and 0.6 eV at Fermi level (ε{sub F}) during the rate of lattice change of about −5%, respectively. We deduce that the ferromagnetic coupling among transitional metals plays an important role in magnetism of Heusler alloy [CrFe,VCo]HfGa.

  14. First-principles calculations of a half-metallic ferromagnet zinc blende Zn{sub 1−x}V{sub x}Te

    Energy Technology Data Exchange (ETDEWEB)

    El Amine Monir, M.; Baltache, H. [Laboratoire de Physique Quantique de la Modélisation Mathématique (LPQ3M), Université de Mascara, 29000 (Algeria); Khenata, R., E-mail: khenata_rabah@yahoo.fr [Laboratoire de Physique Quantique de la Modélisation Mathématique (LPQ3M), Université de Mascara, 29000 (Algeria); Murtaza, G. [Materials Modeling Laboratory, Department of Physics, Islamia College University, Peshawar (Pakistan); Azam, Sikander [New Technologies-Research Center, University of West Bohemia, Univerzitni 8, 306 14 Pilsen (Czech Republic); Bouhemadou, A. [Laboratory for Developing New Materials and their Characterization, Department of Physics, Faculty of Science, University Setif 1, 19000 Setif (Algeria); Al-Douri, Y. [Institute of Nano Electronic Engineering, University Malaysia Perlis, 01000 Kangar, Perlis (Malaysia); Bin Omran, S. [Department of Physics and Astronomy, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451 (Saudi Arabia); Ali, Roshan [Materials Modeling Lab, Department of Physics, Post Graduate Jahanzeb College, Swat (Pakistan)

    2015-03-15

    First-principles calculations have been used to study the structural, elastic, electronic, magnetic and thermal properties of zinc blende Zn{sub 1−x}V{sub x}Te for x=0, 0.25, 0.50, 0.75 and 1 using the full-potential linearized augmented plane wave method (FP-LAPW) based on spin-polarized density functional theory (DFT). The electronic exchange-correlation potential is approached using the spin generalized gradient approximation (spin-GGA). The structural properties of the Zn{sub 1−x}V{sub x}Te alloys (x=0, 0.25, 0.50, 0.75 and 1) are given for the lattice constants and the bulk moduli and their pressure derivatives. The elastic constants C{sub 11}, C{sub 12} and C{sub 44} are calculated using numerical first-principles calculations implemented in the WIEN2k package. An analysis of the band structures and the densities of states reveals that Zn{sub 0.50}V{sub 0.50}Te and Zn{sub 0.75}V{sub 0.25}Te exhibit a half-metallic character, while Zn{sub 0.25}V{sub 0.75}Te is nearly half-metallic. The band structure calculations are used to estimate the spin-polarized splitting energies Δ{sub x}(d) and Δ{sub x}(pd) produced by the V(3d)-doped and s(p)–d exchange constants N{sub 0α} (conduction band) and N{sub 0β} (valence band). The p–d hybridization reduces the magnetic moment of V from its atomic charge value of 3µ{sub B} and creates small local magnetic moments on the nonmagnetic Zn and Te sites. Finally, we present the thermal effect on the macroscopic properties of these alloys, such as the thermal expansion coefficient, heat capacity and Debye temperature, based on the quasi-harmonic Debye model. - Highlights: • Some physical properties of Vanadium doped ZnTe have been investigated. • Structural parameters for the parent compounds compare well with the available data. • The elastic and thermal properties are studied for the first time.

  15. Electronic and magnetic properties of Co{sub 2}Fe(Ga{sub 1−x}Si{sub x}) and Co{sub 2}Fe(Al{sub 1−y}Si{sub y}) Heusler alloys with high Curie temperature

    Energy Technology Data Exchange (ETDEWEB)

    Zhu, Xingfeng, E-mail: zxf_physics@163.com; Dai, Yafei; Luo, Chenglin

    2016-01-15

    We investigate the electronic and magnetic properties of Co{sub 2}Fe(Ga{sub 1−x}Si{sub x}) and Co{sub 2}Fe(Al{sub 1−y}Si{sub y}) alloys using first-principles density functional theory based method. With increasing concentration of Si, lattice constant decreases linearly whereas bulk modulus and total magnetic moment increase. Electronic structure calculations show that the minority DOS exhibits a gap around Fermi level confirming the half-metallic character of the material for all the concentrations studied and the Fermi level can be shifted within the energy gap by changing the Si concentration. The Heisenberg exchange coupling parameters obtained from our calculations predict strong ferromagnetic coupling and high Curie temperatures, which is in accord with the experimental results. - Highlights: • Lattice constant decreases linearly whereas bulk modulus increases. • Total magnetic moment reveals a linear dependence of the Si concentration. • The Fermi level can be shifted within the energy gap by changing the Si concentration. • The Heisenberg exchange coupling parameters predict strong ferromagnetic coupling and high Curie temperatures.

  16. Breakdown of half-metallic ferromagnetism in zinc-blende II-V compounds: First-principles calculations

    Science.gov (United States)

    Li, Yun; Yu, Jaejun

    2008-10-01

    We investigated the electronic and magnetic properties of a series of zinc-blend II-V compounds by carrying out density-functional theory calculations including spin-orbit couplings. Contrary to the case of CaN and CaP, the half-metallic characteristics of the II-V compounds such as CaBi were found to be destroyed. Our analysis of the valence-band structures of CaAs, CaSb, and CaBi revealed a critical role of the spin-orbit coupling interactions on the exchange-split band structure, thereby leading to breakdown of the half-metallic ferromagnetism for the systems with heavier group V elements in the zinc-blend II-V compounds.

  17. Influence of thickness-dependent structural evolution on ultrafast magnetization dynamics in C o2F e0.4M n0.6Si Heusler alloy thin films

    Science.gov (United States)

    Pan, Santanu; Mondal, Sucheta; Seki, Takeshi; Takanashi, Koki; Barman, Anjan

    2016-11-01

    We experimentally investigate thickness (t )-dependent evolution of structural and magnetic properties in C o2F e0.4M n0.6Si (CFMS) thin films and correlate them with ultrafast demagnetization time (τd) and relaxation time (τ1) as well as the Gilbert damping coefficient (α ). Structural ordering and magnetic parameters, including α , exhibit a nonmonotonic variation with increasing t . A remarkably low value of α of 0.009 is obtained for the CFMS film with t =20 nm without any buffer layers, which helps to avoid possible diffusion of the buffer layer into CFMS. Highest saturation magnetization, lowest coercivity, and the α value imply CFMS film with t =20 nm is most suitable for integrated spintronics devices, viz. low-current switched spin transfer torque, and magnetic tunnel junction with a high tunnel magnetoresistance ratio at room temperature. Despite the presence of strain, a lower degree of chemical ordering in the low-t regime, and increased defect density in the high-t regime, we obtained a reasonably low value of damping. In addition to the intrinsic fourfold magnetocrystalline anisotropy, an induced uniaxial anisotropy is found, which also varies nonmonotonically with t . Finally, unique band structure controlled demagnetization and fast relaxation in half-metallic CFMS is correlated to α .

  18. Compensated Ferrimagnetism in the Zero-Moment Heusler Alloy Mn3Al

    Energy Technology Data Exchange (ETDEWEB)

    Jamer, Michelle E.; Wang, Yung Jui; Stephen, Gregory M.; McDonald, Ian J.; Grutter, Alexander J.; Sterbinsky, George E.; Arena, Dario A.; Borchers, Julie A.; Kirby, Brian J.; Lewis, Laura H.; Barbiellini, Bernardo; Bansil, Arun; Heiman, Don

    2017-06-01

    While antiferromagnets have been proposed as components to limit stray magnetic fields, their inability to be spin polarized inhibits their use in spintronic devices. Compensated ferrimagnets are a unique solution to this dilemma since they have zero net moment, but their nonsymmetric density of states allows the achievement of high spin polarization. Density-functional theory predicts Mn3Al in the D0(3) structure to be fully compensated and retain half-metallicity at room temperature. In this work, 50-nm Mn3Al thin films are synthesized using molecular beam epitaxy and annealed at various temperatures in order to investigate their magnetic properties. Magnetometry measurements confirm the high Curie temperature of 605 K. Polarized-neutron reflectometry (PNR) indicates a low net magnetic moment, along with depth profiles of the structure and magnetization. From the PNR data, a saturation moment of 0.11 +/- 0.04 mu B/f.u. is extracted, confirming the nominal zero moment present in these thin films.

  19. Electronic structure and band alignments of ZnTe/CrTe(0 0 1), CdSe ...

    Indian Academy of Sciences (India)

    2011-08-02

    Heusler NiMnSb and PtMnSb alloys, several half-metallic ferro- magnets such as rutile CrO2 [2], double perovskite Sr2FeMoO6 [3], spinel Fe3O4 [4], pyrite-type CoS2 [5,6] and Heusler alloys [7] have been theoretically predicted ...

  20. Comparing magnetostructural transitions in Ni{sub 50}Mn{sub 18.75}Cu{sub 6.25}Ga{sub 25} and Ni{sub 49.80}Mn{sub 34.66}In{sub 15.54} Heusler alloys

    Energy Technology Data Exchange (ETDEWEB)

    Dubenko, Igor [Department of Physics, Southern Illinois University, Carbondale, IL 62901 (United States); Granovsky, Alexander [Faculty of Physics, Lomonosov Moscow State University, Moscow 119991 (Russian Federation); Lahderanta, Erkki [Lappeenranta University of Technology, 53851 (Finland); Kashirin, Maxim; Makagonov, Vladimir [Voronezh State Technical University, Voronezh 394026 (Russian Federation); Aryal, Anil; Quetz, Abdiel; Pandey, Sudip [Department of Physics, Southern Illinois University, Carbondale, IL 62901 (United States); Rodionov, Igor [Faculty of Physics, Lomonosov Moscow State University, Moscow 119991 (Russian Federation); Samanta, Tapas; Stadler, Shane [Department of Physics & Astronomy, Louisiana State University, Baton Rouge, LA 70803 (United States); Mazumdar, Dipanjan, E-mail: dmazumdar@siu.edu [Department of Physics, Southern Illinois University, Carbondale, IL 62901 (United States); Ali, Naushad [Department of Physics, Southern Illinois University, Carbondale, IL 62901 (United States)

    2016-03-01

    The crystal structure, magnetic and transport properties, including resistivity and thermopower, of Ni{sub 50}Mn{sub 18.75}Cu{sub 6.25}Ga{sub 25} and Ni{sub 49.80}Mn{sub 34.66}In{sub 15.54} Heusler alloys were studied in the (10–400) K temperature interval. We show that their physical properties are remarkably different, thereby pointing to different origin of their magnetostructural transition (MST). A Seebeck coefficient (S) was found to pass minimum of about −20 µV/K in respect of temperature for both compounds. It was shown that MST observed for both compounds results in jump-like changes in S for Ga-based compound and jump in resistivity of about 20 and 200 µΩ cm for Ga and In –based compounds, respectively. The combined analyzes of the present results with that from literature show that the density of states at the Fermi level does not change strongly at the MST in the case of Ni–Mn–In alloys as compared to that of Ni–Mn–Ga. - Graphical abstract: Temperature dependencies of resistivity for Ni{sub 50}Mn{sub 18.75}Cu{sub 6.25}Ga{sub 25} and Ni{sub 49.80}Mn{sub 34.66}In{sub 15.54} obtained on heating (open symbols) and cooling (closed symbols). Arrows indicate the temperature of direct (T{sub M}) and inverse (T{sub A}) martensitic transitions and ferromagnetic ordering of the austenitic (T{sub C}) and martensitic (T{sub CM}) phases. The T{sub CM}=T{sub A}/T{sub M} in the case of Ga-based alloy. - Highlights: • Magnetostructural transitions (MST) in two compounds with same parent material. • The figure exemplifies how sensitive MST properties are to the density of states. • Proper understanding is required for utilizing these multifunctional materials.

  1. Magnetic interactions in martensitic Ni-Mn based Heusler systems

    Energy Technology Data Exchange (ETDEWEB)

    Aksoy, Seda

    2010-04-22

    In this work, magnetic, magnetocaloric and structural properties are investigated in Ni-Mn-based martensitic Heusler alloys with the aim to tailor these properties as well as to understand in detail the magnetic interactions in the various crystallographic states of these alloys. We choose Ni{sub 50}Mn{sub 34}In{sub 16} as a prototype which undergoes a martensitic transformation and exhibits field-induced strain and the inverse magnetocaloric effect. Using the structural phase diagram of martensitic Ni-Mn-based Heusler alloys, we substitute gallium and tin for indium to carry these effects systematically closer to room temperature by shifting the martensitic transformation. A magneto-calorimeter is designed and built to measure adiabatically the magnetocaloric effect in these alloys. The temperature dependence of strain under an external magnetic field is studied in Ni{sub 50}Mn{sub 50-x}Z{sub x} (Z: Ga, Sn, In and Sb) and Ni{sub 50}Mn{sub 34}In{sub 16-x}Z{sub x} (Z: Ga and Sn). An argument based on the effect of the applied magnetic field on martensite nucleation is adopted to extract information on the direction of the magnetization easy axis in the martensitic unit cell in Heusler alloys. Parallel to these studies, the structure in the presence of an external field is also studied by powder neutron diffraction. It is demonstrated that martensite nucleation is influenced by cooling the sample under a magnetic field such that the austenite phase is arrested within the martensitic state. The magnetic interactions in Ni{sub 50}Mn{sub 37}Sn{sub 13} and Ni{sub 50}Mn{sub 40}Sb{sub 10} are characterized by using neutron polarization analysis. Below the martensitic transformation temperature, M{sub s}, an antiferromagnetically correlated state is found. Ferromagnetic resonance experiments are carried out on Ni{sub 50}Mn{sub 37}Sn{sub 13} and Ni{sub 50}Mn{sub 34}In{sub 16} to gain more detailed information on the nature of the magnetic interactions. The experimental

  2. Generating magnetic response and half-metallicity in GaP via dilute Ti-doping for spintronic applications

    Energy Technology Data Exchange (ETDEWEB)

    Saini, Hardev S. [Department of Physics, Panjab University, Chandigarh 160014 (India); Kashyap, Manish K., E-mail: manishdft@gmail.com [Department of Physics, Kurukshetra University, Kurukshetra 136119, Haryana (India); Kumar, Manoj [Department of Physics, Panjab University, Chandigarh 160014 (India); Kendriya Vidyalya No. 1, Kanchrapara, 743193 West Bengal (India); Thakur, Jyoti [Department of Physics, Kurukshetra University, Kurukshetra 136119, Haryana (India); Singh, Mukhtiyar [Department of Physics, Dyanand Postgraduate College, Hisar, 125001 Haryana (India); Reshak, Ali H. [New Technologies – Research Centre, University of West Bohemia, Univerzitni 8, 306 14 Pilsen (Czech Republic); Center of Excellence Geopolymer and Green Technology, School of Material Engineering, University Malaysia Perlis, 01007 Kangar, Perlis (Malaysia); Saini, G.S.S. [Department of Physics, Panjab University, Chandigarh 160014 (India)

    2015-11-15

    Existence of band gap in one spin channel and metallic character in other leads to interesting magnetic and optical properties of any material. These materials are capable to generate fully spin polarized current and are responsible for maximizing the efficiency of spintronic devices. The present work explores the electronic and magnetic properties of Ti-doped GaP compound with dopant concentrations; x = 0.02, 0.03 and 0.06 in order to search new Diluted Magnetic Semiconductor (DMS) compounds as spintronic materials using full potential linearized augmented plane wave plus local orbitals (FPLAPW + lo) method. The generalized gradient approximation (GGA) is used to decide exact exchange-correlation (XC) potentials. The calculated results showed that the total magnetic moment of ∼1.00 μ{sub B} gets induced after Ti-doping in GaP at all dopant concentrations, irrespective of any magnetic element present. Further, this doping also generates half-metallicity in GaP with a half-metallic (HM) gap at Fermi level (E{sub F}) in minority spin channel. The half metallicity is originated by the hybridization of Ti-d states with P–p states. This induced magnetism appeared in the systems is the result of exchange interactions between host (GaP) and Ti-atom. - Highlights: • Dilute doping of Ti in Gap is addressed to produce authenticate theoretical data. • Ti-doping generates band gap at Fermi level in minority spin channel. • Magnetism appeared is the result of exchange interactions between host (GaP) and Ti. • Magnetic moment remains constant within studied dopant concentrations.

  3. Gate-voltage control of equal-spin Andreev reflection in half-metal/semiconductor/superconductor junctions

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Xiuqiang, E-mail: xianqiangzhe@126.com [National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing 210093 (China); Meng, Hao, E-mail: menghao1982@shu.edu.cn [School of Physics and Telecommunication Engineering, Shanxi University of Technology, Hanzhong 723001 (China)

    2016-04-22

    With the Blonder–Tinkham–Klapwijk (BTK) approach, we investigate conductance spectrum in Ferromagnet/Semiconductor/Superconductor (FM/Sm/SC) double tunnel junctions where strong Rashba spin–orbit interaction (RSOI) is taken into account in semiconductors. For the half-metal limit, we find that the in-gap conductance becomes finite except at zero voltage when inserting a ferromagnetic insulator (FI) at the Sm/SC interface, which means that the appearance of a long-range triplet states in the half-metal. This is because of the emergence of the unconventional equal-spin Andreev reflection (ESAR). When the FI locates at the FM/Sm interface, however, we find the vanishing in-gap conductance due to the absence of the ESAR. Moreover, the non-zero in-gap conductance shows a nonmonotonic dependence on RSOI which can be controlled by applying an external gate voltage. Our results can be used to generate and manipulate the long-range spin triplet correlation in the nascent field of superconducting spintronics. - Highlights: • We study the equal-spin Andreev reflection in half-metal/semiconductor/superconductor (HM/Sm/SC) junctions. • The equal-spin Andreev reflection appearance when inserting a ferromagnetic insulator at the Sm/SC interface. • The finite in-gap conductance is attributed to the emergence of the equal-spin Andreev reflection. • The finite in-gap conductance shows a nonmonotonic dependence on Rashba spin–orbit interaction. • The finite in-gap conductance can be controlled by applying an external gate voltage.

  4. Electronic structure and physical properties of Heusler compounds for thermoelectric and spintronic applications

    Energy Technology Data Exchange (ETDEWEB)

    Ouardi, Siham

    2012-03-19

    This thesis focuses on synthesis as well as investigations of the electronic structure and properties of Heusler compounds for spintronic and thermoelectric applications. The first part reports on the electronic and crystal structure as well as the mechanical, magnetic, and transport properties of the polycrystalline Heusler compound Co{sub 2}MnGe. The crystalline structure was examined in detail by extended X-ray absorption fine structure spectroscopy and anomalous X-ray diffraction. The low-temperature magnetic moment agrees well with the Slater-Pauling rule and indicates a half-metallic ferromagnetic state of the compound, as is predicted by ab-initio calculations. Transport measurements and hard X-ray photoelectron spectroscopy (HAXPES) were performed to explain the electronic structure of the compound. A major part of the thesis deals with a systematical investigation of Heusler compounds for thermoelectric applications. This thesis focuses on the search for new p-type Heusler compounds with high thermoelectric efficiency. The substitutional series NiTi{sub 1-x}M{sub x}Sn (where M=Sc, V and 0Heusler compound. The pure compounds showed n-type behavior, while under Sc substitution the system switched to p-type behavior. A maximum Seebeck coefficient of +230 {mu}V/K (350 K) was obtained for NiTi{sub 0.26}Sc{sub 0.04}Zr{sub 0.35}Hf{sub 0.35}Sn. HAXPES valence band measurement show massive in gap states for the parent compounds NiTiSn, CoTiSb and NiTi{sub 0.3}Zr{sub 0.35}Hf{sub 0.35}Sn. This proves that the electronic states close to the Fermi energy play a key role for the behavior of the transport properties. Furthermore, the electronic structure of the gapless Heusler compounds PtYSb, PtLaBi and PtLuSb were investigated by bulk

  5. Martensitic transition, inverse magnetocaloric effect and shape memory characteristics in Mn{sub 48−x}Cu{sub x}Ni{sub 42}Sn{sub 10} Heusler alloys

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Changqin [Department of Physics, Shanghai University, Shanghai 200444 (China); Li, Zhe [Reasearch center for magnetic materials and devices & Key Laboratory for Advanced Functional and Low Dimensional Materials of Yunnan Higher Education Institute, Qujing Normal University, Qujing 655011 (China); Zhang, Yuanlei [Department of Physics, Shanghai University, Shanghai 200444 (China); Reasearch center for magnetic materials and devices & Key Laboratory for Advanced Functional and Low Dimensional Materials of Yunnan Higher Education Institute, Qujing Normal University, Qujing 655011 (China); Liu, Yang; Sun, Junkun; Huang, Yinsheng; Kang, Baojuan [Department of Physics, Shanghai University, Shanghai 200444 (China); Xu, Kun [Reasearch center for magnetic materials and devices & Key Laboratory for Advanced Functional and Low Dimensional Materials of Yunnan Higher Education Institute, Qujing Normal University, Qujing 655011 (China); Deng, Dongmei [Department of Physics, Shanghai University, Shanghai 200444 (China); Jing, Chao, E-mail: cjing@staff.shu.edu.cn [Department of Physics, Shanghai University, Shanghai 200444 (China)

    2017-03-01

    In this paper, we have systematically prepared a serials of polycrystalline Mn{sub 48−x}Cu{sub x}Ni{sub 42}Sn{sub 10} alloys (x=0, 1, 3, 5, 6, 8, 10 and 12) and investigated the influence of the Cu doping on martensitic transition (MT) as well as magnetic properties. Experimental results indicate that the MT temperature and the martensite Curie temperature (T{sub c}{sup M}) shift to high temperature with increasing the substitution of Cu (from Mn rich alloy to Ni rich alloy), while the austenite Curie temperature (T{sub c}{sup A}) is almost unchanged. It was found that the structures undergo L2{sub 1} and 4O with the increasing of Cu concentration near room temperature. Therefore, the magnetostructural transition can be tuned by appropriate Cu doping in these alloys. Moreover, we mainly studied the multiple functional properties for inverse magnetocaloric effect and shape memory characteristics associated with the martensitic transition. A large positive isothermal entropy change of Mn{sub 48}Ni{sub 42}Sn{sub 10} was obtained, and the maximum transition entropy change achieves about 48 J/kg K as x=8. In addition, a considerable temperature-induced spontaneous strain with the value of 0.16% was obtained for Mn{sub 48}Ni{sub 42}Sn{sub 10} alloys.

  6. Intrinsic Dirac half-metal and quantum anomalous Hall phase in a hexagonal metal-oxide lattice

    Science.gov (United States)

    Zhang, Shou-juan; Zhang, Chang-wen; Zhang, Shu-feng; Ji, Wei-xiao; Li, Ping; Wang, Pei-ji; Li, Sheng-shi; Yan, Shi-shen

    2017-11-01

    The quantum anomalous Hall (QAH) effect has attracted extensive attention due to time-reversal symmetry broken by a staggered magnetic flux emerging from ferromagnetic ordering and spin-orbit coupling. However, the experimental observations of the QAH effect are still challenging due to its small nontrivial bulk gap. Here, based on density functional theory and Berry curvature calculations, we propose the realization of intrinsic QAH effect in two-dimensional hexagonal metal-oxide lattice, N b2O3 , which is characterized by the nonzero Chern number (C =1 ) and chiral edge states. Spin-polarized calculations indicate that it exhibits a Dirac half-metal feature with temperature as large as TC=392 K using spin-wave theory. When the spin-orbit coupling is switched on, N b2O3 becomes a QAH insulator. Notably, the nontrivial topology is robust against biaxial strain with its band gap reaching up to Eg=75 meV , which is far beyond room temperature. A tight-binding model is further constructed to understand the origin of nontrivially electronic properties. Our findings on the Dirac half-metal and room-temperature QAH effect in the N b2O3 lattice can serve as an ideal platform for developing future topotronics devices.

  7. Atomically Thin B doped g-C3N4 Nanosheets: High-Temperature Ferromagnetism and calculated Half-Metallicity.

    Science.gov (United States)

    Gao, Daqiang; Liu, Yonggang; Liu, Peitao; Si, Mingsu; Xue, Desheng

    2016-10-20

    Since the graphitic carbon nitride (g-C4N3), which can be seen as C-doped graphitic-C3N4 (g-C3N4), was reported to display ferromagnetic ground state and intrinsic half-metallicity (Du et al., PRL,108,197207,2012), it has attracted numerous research interest to tune the electronic structure and magnetic properties of g-C3N4 due to their potential applications in spintronic devices. In this paper, we reported the experimentally achieving of high temperature ferromagnetism in metal-free ultrathin g-C3N4 nanosheets by introducing of B atoms. Further, first-principles calculation results revealed that the current flow in such a system was fully spin-polarized and the magnetic moment was mainly attributed to the p orbital of N atoms in B doped g-C3N4 monolayer, giving the theoretic evidence of the ferromagnetism and half-metallicity. Our finding provided a new perspective for B doped g-C3N4 spintronic devices in future.

  8. Biphasic thermoelectric materials derived from the half-Heusler/full-Heusler system Ti-Ni-Sn

    Science.gov (United States)

    Douglas, Jason Everett

    Among the possible avenues for increasing the efficiency of global energy usage, thermoelectrics are an exciting, solid-state option. Thermoelectric materials, which convert an internal temperature gradient into a voltage and vice versa, have found applications in refrigeration as well as power generation from waste heat. TiNiSn, a semiconductor of the half-Heusler (hH) crystal structure, is of particular interest due to its very favorable electronic transport properties, conductivity (sigma) and Seebeck coefficient ( S), at relevant temperature regimes (between 600 K and 900 K). Unfortunately, its overall efficiency is hampered by a comparatively high thermal conductivity (kappa). In the design of thermoelectric materials, a number of approaches have been taken to increase the thermoelectric figure of merit, ZT = ( S2sigma/kappa)T, where T is temperature. In this work we examine how microstructure can be used to alter these thermoelectric propertiesin a biphasic Ti-Ni-Sn materials containing full-Heusler (fH) TiNi2Sn embedded within hH thermoelectric TiNiSn. We explored a wide range of Ni compositions in TiNi1+xSn--from stoichiometric TiNiSn to high Heusler volume fraction, TiNi1.25Sn--materials prepared by levitation induction melting followed by annealing. Phase distributions and microstructure were characterized using synchrotron x-ray diffraction and optical and electron microscopy. In a sample of the nominal composition TiNi1.15Sn, a significant decrease in thermal conductivity (about 30%) is observed for the biphasic material despite the metallic second-phase particles existing at the micrometer scale; a 50% increase in the electrical conductivity is also measured. These result in a maximum figure of merit, ZT, of 0.44 at 800 K, which is 25% greater than is observed for the x = 0 sample. Density functional theory calculations using hybrid functionals were performed to determine band alignments between the half- and full-Heusler compounds, as well as

  9. Effective Zeeman splitting in bent lateral heterojunctions of graphene and hexagonal boron nitride: A new mechanism towards half-metallicity

    Science.gov (United States)

    Yue, Ling; Seifert, Gotthard; Chang, Kai; Zhang, Dong-Bo

    2017-11-01

    Low-dimensional half-metallic (HM) systems are invaluable for future spintronics. Yet a definitive experimental demonstration of HM characteristic in two-dimensional (2D) materials remains elusive. Here, we reveal that in recently synthesized graphene/hexagonal boron nitride (G /h BN ) lateral heterojunctions, pronounced HM can be achieved by applying an in-plane bending. We demonstrate with generalized Bloch theorem that bending has strong influence on interfacial spin states, mimicking the Zeeman effect, which consequently leads to the desired HM phase with a sizable HM gap and excellent magnetic stability. Given recent experimental advances in fabrication of G /h BN heterostructures, this strain-driven HM phase may be practically accessible. The generalized Bloch theorem coupled with self-consistent charge density-functional tight binding is useful to model 2D structures under fundamental deformations, thus may boost the study of strain tunable electronic property of low-dimensional materials with inhomogeneous strain patterns.

  10. Fabrication and characterization of nanostructured Fe3S4, an isostructural compound of half-metallic Fe3O4

    KAUST Repository

    Li, Peng

    2015-06-10

    High-purity, well-crystallized spinel Fe3S4 nanoplatelets were synthesized by the hydrothermal method, and the saturation magnetic moment of Fe3S4 was measured at 1.83 μB/f.u. The temperature-dependent resistivity of Fe3S4 was metallic-like for T < 180 K: room-temperature resistivity was measured at 7.711 × 103  μΩ cm. The anomalous Hall conductivity of Fe3S4 decreased with increasing longitudinal conductivity, in sharp contrast with the accepted theory of the anomalous Hall effect in a dirty-metal regime. Furthermore, negligible spin-dependent magnetoresistance was observed. Band structure calculations confirmed our experimental observations that Fe3S4 is a metal and not a half metal as expected.

  11. Half-metallic ferromagnetism in Mn-doped zigzag AlN nanoribbon from first-principles

    Energy Technology Data Exchange (ETDEWEB)

    Aghili, S., E-mail: sara.aghili.physics@gmail.com [Physics Department, Faculty of Science, Islamic Azad University Central Tehran Branch (Iran, Islamic Republic of); Beiranvand, R. [Physics Department, Faculty of Science, Ayatollah Boroujerdi University (Iran, Islamic Republic of); Elahi, S.M.; Abolhasani, M.R. [Physics Department, Faculty of Science, Islamic Azad University Central Tehran Branch (Iran, Islamic Republic of)

    2016-12-15

    Based on first-principles calculations, we investigate the effect of Mn impurity on the electronic and magnetic properties of H-terminated zigzag AlN nanoribbons (ZAlNNRs), using the band structure results obtained through the full potential linearized augmented plane wave method within the density functional theory. The calculated results show that the H-terminated ZAlNNR is semiconducting and non magnetic material with a direct band gap of about 2.78 eV. Density of state analyses shows that the top of the valence band is mainly contributed by N atoms, while just beside the conduction band the whole DOS is mainly contributed by Al atoms. The main result is a transition from non-magnetic semiconducting character to half-metallic features upon doping. The Mn-doped ZAlNNR shows complete (100%) spin polarization at the Fermi level and the charge transport is totally originated from Manganese spin up electrons in the nanoribbon. These results propose potential application for the development of AlN nanoribbon-based in magneto-electronic devices. - Highlights: • We show that ZAlNNR is semiconducting and nonmagnetic material with an indirect band gap of about 2.78 eV. • ZAlNNRs with Mn doping, display strong spin-polarization close to the Fermi level which will result in spin-anisotropic transport. • ZAlNNRs with Mn doping, display strong spin-polarization close to the Fermi level which will result in spin-anisotropic transport.The spin-resolved band structures show half-metallic character in Mn-doped ZAlNNR. • The calculated total magnetic moment is about 4.00µB which the main contribution, 2.92 µB, comes from the Mn impurity.

  12. Giant and reversible room-temperature elastocaloric effect in a single-crystalline Ni-Fe-Ga magnetic shape memory alloy

    National Research Council Canada - National Science Library

    Li, Yang; Zhao, Dewei; Liu, Jian

    2016-01-01

    Good mechanical properties and large adiabatic temperature change render Heusler-type Ni2FeGa-based magnetic shape memory alloys as a promising candidate material for solid-state mechanical cooling...

  13. Density functional study of d0 half-metallic ferromagnetism in a bulk and (001) nano-surface of KP compound

    Science.gov (United States)

    Kazemi, Marjan; Amiri, Peiman; Salehi, Hamdollah

    2017-08-01

    According to many applications of half-metals in the spintronics devices, we investigate half-metallic properties of KP compound in rock-salt (RS), zinc-blende (ZB), cesium chloride (CsCl) and wurtzite (WZ) structural phases by using density functional theory. Results indicate that KP compound is half-metal in RS, ZB and WZ structures, while in CsCl structure, due to small lattice constant and failure of Stoner criterion, KP compound doesn't have any magnetic properties. Half-metallic gap values obtained are 0.47, 0.95 and 0.91 eV for RS, ZB, WZ structures, respectively. Although KP compound in CsCl structure is more stable than RS structure energetically, but from dynamical point of view only RS structure is stable and other structures are unstable. Calculations corresponding to (001) surface of RS structure demonstrate the conservation of bulk half-metallic properties in this crystallographic direction. So nano-layers of KP compound in RS structure might be an appropriate candidate for application in near future spintronics devices.

  14. Influence of defects and disorder on anomalous Hall effect and spin Seebeck effect on permalloy and Heusler compounds

    Energy Technology Data Exchange (ETDEWEB)

    Vilanova Vidal, Enrique

    2012-09-19

    In this work Heusler thin films have been prepared and their transport properties have been studied. Of particularly interest is the anomalous Hall effect (AHE). The effect is a long known but still not fully understood transport effect. Most theory papers focus on the influence of one particular contribution to the AHE. Actual measured experimental data, however, often are not in accordance with idealized assumptions. This thesis discusses the data analysis for materials with low residual resistivity ratios. As prototypical materials, half metallic Heusler compounds are studied. Here, the influence of defects and disorder is apparent in a material with a complex topology of the Fermi surface. Using films with different degrees of disorder, the different scattering mechanisms can be separated. For Co{sub 2}FeSi{sub 0.6}Al{sub 0.4} and Co{sub 2}FeGa{sub 0.5}Ge{sub 0.5}, the AHE induced by B2-type disorder and temperature-dependent scattering is positive, while DO{sub 3}-type disorder and possible intrinsic contributions possess a negative sign. For these compounds, magneto-optical Kerr effects (MOKE) are investigated. First order contributions as a function of intrinsic and extrinsic parameters are qualitatively analyzed. The relation between the crystalline ordering and the second order contributions to the MOKE signal is studied. In addition, sets of the Heusler compound Co{sub 2}MnAl thin films were grown on MgO(100) and Si(100) substrates by radio frequency magnetron sputtering. Composition, magnetic and transport properties were studied systematically for samples deposited at different conditions. In particular, the anomalous Hall effect resistivity presents an extraordinarily temperature independent behavior in a moderate magnetic field range from 0 to 0.6 T. The off-diagonal transport at temperatures up to 300 C was analyzed. The data show the suitability of the material for Hall sensors working well above room temperature. Recently, the spin Seebeck effect

  15. Large adiabatic temperature change in magnetoelastic transition in Ni{sub 50}Mn{sub 35}Cr{sub 2}Sn{sub 13} Heusler alloy of granular nanostructure

    Energy Technology Data Exchange (ETDEWEB)

    Prakash, H. R.; Sharma, S. K.; Ram, S., E-mail: prakashhr73@gmail.com [Materials Science Centre, Indian Institute of Technology, Kharagpur-721302 (India); Chatterjee, S. [High Magnetic Field Lab, UGC-DAE Consortium of Scientific Research, Kolkata-700098 (India)

    2016-05-06

    The Ni-Mn-Sn alloys are a pioneering series of magnetocaloric materials of a huge heat-energy exchanger in the martensite transition. A small additive of nearly 2 at% Cr effectively tunes the valence electron density of 8.090 electrons per atom and a large change in the entropy ΔS{sub M←A} = 4.428 J/kg-K (ΔS{sub M→A} = 3.695 J/kg-K in the recycle) at the martensite ← austenite phase transition as it is useful for the magnetic refrigeration and other cooling devices. The Cr additive tempers the tetragonality with the aspect ratio c/a = 0.903 of the martensite phase and exhibits an adiabatic temperature change of 10 K. At room temperature, a hysteresis loop exhibits 48.91 emu/g saturation magnetization and 82.1 Oe coercivity.

  16. Uniformly wetting deposition of Co atoms on MoS(2) monolayer: a promising two-dimensional robust half-metallic ferromagnet.

    Science.gov (United States)

    Chen, Qian; Ouyang, Yixin; Yuan, Shijun; Li, Runze; Wang, Jinlan

    2014-10-08

    Synthesis of two-dimensional (2D) metal chalcogenide based half-metallic nanosheets is in high demand for modern electronics and spintronics applications. Herein, we predict from first-principles calculations that the 2D heterostructure Co/MoS2, consisting of a monolayer of Co atoms deposited on a single MoS2 sheet, possesses robust ferromagnetic and half-metallic features and exhibits 100% spin-filter efficiency within a broad bias range. Its ferromagnetic and half-metallic nature persists even when overlaid with a graphene sheet. Because of the relatively strong surface binding energy and low clustering ratio of Co atoms on the MoS2 surface, we predict that the heterostructure is synthesizable via wetting deposition of Co on MoS2 by electron-beam evaporation technique. Our work strongly suggests Co/MoS2 as a compelling and feasible candidate for highly effective information and high-density memory devices.

  17. Engineered Heusler Ferrimagnets with a Large Perpendicular Magnetic Anisotropy

    Directory of Open Access Journals (Sweden)

    Reza Ranjbar

    2015-09-01

    Full Text Available Synthetic perpendicular magnetic anisotropy (PMA ferrimagnets consisting of 30-nm-thick D022-MnGa and Co2MnSi (CMS cubic Heusler alloys with different thicknesses of 1, 3, 5, 10 and 20 nm, buffered and capped with a Cr film, are successfully grown epitaxially on MgO substrate. Two series samples with and without post annealing at 400 °C are fabricated. The (002 peak of the cubic L21 structure of CMS films on the MnGa layer is observed, even for the 3-nm-thick CMS film for both un-annealed and annealed samples. The smaller remnant magnetization and larger switching field values of CMS (1–20 nm/MnGa (30 nm bilayers compared with 30-nm-thick MnGa indicates antiferromagnetic (AFM interfacial exchange coupling (Jex between MnGa and CMS films for both un-annealed and annealed samples. The critical thickness of the CMS film for observing PMA with AFM coupling in the CMS/MnGa bilayer is less than 10 nm, which is relatively large compared to previous studies.

  18. Planar heterostructures of single-layer transition metal dichalcogenides: Composite structures, Schottky junctions, tunneling barriers, and half metals

    Science.gov (United States)

    Aras, Mehmet; Kılıç, ćetin; Ciraci, S.

    2017-02-01

    Planar composite structures formed from the stripes of transition metal dichalcogenides joined commensurately along their zigzag or armchair edges can attain different states in a two-dimensional (2D), single-layer, such as a half metal, 2D or one-dimensional (1D) nonmagnetic metal and semiconductor. Widening of stripes induces metal-insulator transition through the confinements of electronic states to adjacent stripes, that results in the metal-semiconductor junction with a well-defined band lineup. Linear bending of the band edges of the semiconductor to form a Schottky barrier at the boundary between the metal and semiconductor is revealed. Unexpectedly, strictly 1D metallic states develop in a 2D system along the boundaries between stripes, which pins the Fermi level. Through the δ doping of a narrow metallic stripe one attains a nanowire in the 2D semiconducting sheet or narrow band semiconductor. A diverse combination of constituent stripes in either periodically repeating or finite-size heterostructures can acquire critical fundamental features and offer device capacities, such as Schottky junctions, nanocapacitors, resonant tunneling double barriers, and spin valves. These predictions are obtained from first-principles calculations performed in the framework of density functional theory.

  19. Realizing semiconductor-half-metal transition in zigzag graphene nanoribbons supported on hybrid fluorographene-graphane nanoribbons.

    Science.gov (United States)

    Tang, Shaobin; Cao, Xinrui

    2014-11-14

    Hydrogenation and fluorination provide promising applications for tuning the properties of graphene-based nanomaterials. Using first-principles calculations, we investigate the electronic and magnetic properties of zigzag graphene nanoribbons (ZGNRs) supported on hydrogenated and fluorinated ZGNRs. Our results indicate that the support of zigzag graphane nanoribbon with its full width has less impact on the electronic and magnetic properties of ZGNRs, whereas the ZGNRs supported on fluorographene nanoribbons can be tuned to metal with almost degenerated ferro- and anti-ferromagnetic states due to the intrinsic polarization of substrate. The ZGNRs supported on zigzag hybrid fluorographene-graphane nanoribbons are spin-polarized half-semiconductors with distinct band gaps for spin-up and spin-down channels. Interestingly, in the absence of an external electric field, the spin-polarized band gaps of supported ZGNRs can be well modulated in the opposite direction by changing the ratio of fluorination to hydrogenation concentration in hybrid substrates. Furthermore, the ZGNRs supported on hybrid nanoribbons exhibit the half-semiconducting to half-metallic behavior transition as the interlayer spacing is gradually reduced, which is realized more easily for the hybrid support with a relatively wide fluorographene moiety compared to its narrow counterpart. Present results provide a novel way for designing substrate-supported graphene spintronic devices.

  20. FP-LMTO investigation of the structural, electronic and agneticproperties of Heusler compounds Ru2CrZ (Ge, Sn, Si

    Directory of Open Access Journals (Sweden)

    Elchikh M.

    2013-03-01

    Full Text Available The electronic structure of the antiferomagnetic full Heusler alloys Ru2CrZ (Ge, Sn, Si have been studied by first principal calculations using Full-Potential linearized Muffin Tin Orbital (FP-LMTO method based on the generalized Gradient Approximation (GGA. It was shown that obtained equilibrium lattice parameters agree well with available experimental data. The influence of Z-elements on the electronic structure and magnetic properties of these compounds is analysed.

  1. Rare earth-based quaternary Heusler compounds MCoVZ (M = Lu, Y; Z = Si, Ge with tunable band characteristics for potential spintronic applications

    Directory of Open Access Journals (Sweden)

    Xiaotian Wang

    2017-11-01

    Full Text Available Magnetic Heusler compounds (MHCs have recently attracted great attention since these types of material provide novel functionalities in spintronic and magneto-electronic devices. Among the MHCs, some compounds have been predicted to be spin-filter semiconductors [also called magnetic semiconductors (MSs], spin-gapless semiconductors (SGSs or half-metals (HMs. In this work, by means of first-principles calculations, it is demonstrated that rare earth-based equiatomic quaternary Heusler (EQH compounds with the formula MCoVZ (M = Lu, Y; Z = Si, Ge are new spin-filter semiconductors with total magnetic moments of 3 µB. Furthermore, under uniform strain, there are physical transitions from spin-filter semiconductor (MS → SGS → HM for EQH compounds with the formula LuCoVZ, and from HM → SGS → MS → SGS → HM for EQH compounds with the formula YCoVZ. Remarkably, for YCoVZ EQH compounds there are not only diverse physical transitions, but also different types of spin-gapless feature that can be observed with changing lattice constants. The structural stability of these four EQH compounds is also examined from the points of view of formation energy, cohesive energy and mechanical behaviour. This work is likely to inspire consideration of rare earth-based EQH compounds for application in future spintronic and magneto-electronic devices.

  2. Shell-ferromagnetism in a Ni-Mn-In off-stoichiometric Heusler studied by ferromagnetic resonance

    Directory of Open Access Journals (Sweden)

    Franziska Scheibel

    2017-05-01

    Full Text Available Next to the multifunctional properties of Ni-Mn-based Heusler alloys new functionalities related to shell-ferromagnetism are emerging. To understand in more detail the properties of shell-ferromagnetism we examine a decomposed Ni50.0Mn45.1In4.9 off-stoichiometric compound using magnetic resonance techniques which provides details on magnetic interactions. We find that the ferromagnetic resonance profile of the shell-ferromagnetic state is symmetric for positive and negative fields and is independent of the direction of the field-sweep except for the hysteresis observed at small fields.

  3. Prediction of composition for stable half-Heusler phases from electronic-band-structure analyses

    Energy Technology Data Exchange (ETDEWEB)

    Offernes, L. [Department of Chemistry, University of Oslo, P.O. Box 1033, Blindern, N-0315 Oslo (Norway)], E-mail: Laila.offernes@kjemi.uio.no; Ravindran, P.; Seim, C.W.; Kjekshus, A. [Department of Chemistry, University of Oslo, P.O. Box 1033, Blindern, N-0315 Oslo (Norway)

    2008-06-30

    This report describes a procedure to predict the frequently occurring non-stoichiometry of the half-Heusler XYZ alloys (viz. deviations from the equiatomic 1:1:1 composition and the usually accompanied narrow homogeneity regions) from ab initio calculated electronic-band-structure characteristics. The essential feature of this approach is to utilize the valence electron content (VEC) and the calculated electronic band structure to expose factors that according to rigid-band considerations should determine the possible deviations from 1:1:1 stoichiometry and direction of the stable solid-solution regions. These means have been used to predict the direction of equilibrium solid-solution regions for a number of ternary phase diagrams that comprise half-Heusler phases and the predictions have been tested with experimental data from literature and presently synthesized and microprobe analysed samples of NiTiSn, PtTiSn, CoTiSb, PtMnSb, NiMnSb, and CoMnSb. The predictions are made based on maximum band filling of bonding states identified through the crystal-orbital-Hamilton population (COHP) analysis and density-of-states (DOS) integration.

  4. Joining of Half-Heusler and Bismuth Tellurides for Segmented Thermoelectric Generators

    DEFF Research Database (Denmark)

    Ngan, Pham Hoang; Han, Li; Christensen, Dennis Valbjørn

    2018-01-01

    -Heusler alloys p-type Hf0.5Zr0.5CoSn0.2Sb0.8 and n-type Ti0.6Hf0.4NiSn. A two-step process was introduced to join the half-Heusler to the bismuth tellurides to form a segmented structure which was then characterized for its thermoelectric and structural properties. The output power generation was characterized......Segmented generators where the p- or n-type legs are formed by joining materials in series enables each material to operate in their most efficient temperature range. Here, we have fabricated and characterized segmented thermoelectric p- and n-type legs based on bismuth tellurides and half...... under various hot side temperatures up to 873 K with the cold side fixed at 323 K. The stability of the joints was also investigated under heat treatment and thermal cycling. Under working temperatures from 323 K to 873 K, the obtained p-type segmented legs could deliver a power density of 0.3 W cm−2...

  5. Optimized thermoelectric performance of the n-type half-Heusler material TiNiSn by substitution and addition of Mn

    Directory of Open Access Journals (Sweden)

    Enkhtaivan Lkhagvasuren

    2017-04-01

    Full Text Available Alloys based on the half-Heusler compound TiNiSn with the addition of Mn or with a substitution of Ti by Mn are investigated as high-temperature thermoelectric materials. In both materials an intrinsic phase separation is observed, similar to TiNiSn where Ti has been partially substituted by Hf, with increasing Mn concentration the phase separation drastically reduces the lattice thermal conductivity while the power factor is increased. The thermoelectric performance of the n-type conducting alloy can be optimized both by substitution of Ti by Mn as well as the addition of Mn.

  6. High mobility half-metallicity in the (LaMnO3)2/(SrTiO3)8 superlattice

    Science.gov (United States)

    Cossu, F.; Singh, N.; Schwingenschlögl, U.

    2013-01-01

    First principles calculations have been performed to investigate the LaMnO3/SrTiO3 superlattice. Structural relaxation within the generalized gradient approximation results in no significant tiltings or rotations of oxygen octahedra, but in distinct distortions in the SrTiO3 region. Taking into account the onsite Coulomb interaction, we find that the Mn spins order ferromagnetically, in contrast to the antiferromagnetic state of bulk LaMnO3. Most importantly, the interface strain combined with charge transfer across the interface induces half-metallicity within the MnO2 layers. The superlattice is particulary interesting for spintronics applications because the half-metallic states are characterized by an extraordinary high mobility.

  7. A first principles study of half-metallic ferromagnetism in In{sub 1-x}Ti{sub x}P (x = 0.06) diluted magnetic semiconductor

    Energy Technology Data Exchange (ETDEWEB)

    Saini, Hardev S., E-mail: hardevdft@gmail.com; Saini, G. S. S. [Department of Physics, Panjab University, Chandigarh-160014, Chandigarh (India); Singh, Mukhtiyar [Department of Physics, Dyanand Postgraduate College, Hisar-125001 (Haryana) (India); Thakur, Jyoti; Kashyap, Manish K. [Department of Physics, Kurukshetra University, Kurukshetra-136119, Haryana (India)

    2016-05-23

    A first principles approach has been used to calculate the electronic and magnetic properties of In{sub 1-x}Ti{sub x}P (x = 0.06) diluted magnetic semiconductor (DMS) compound. The calculations have been carried out using the highly precise all electron full potential Linear Augmented Plane Wave (FPLAPW) method within generalized gradient approximation (GGA) as exchange-correlation (XC) potentials. The estimated results show that the Ti-doping generate robust half metallic ferromagnetism with the 100% spin polarization at Fermi level (E{sub F}) in InP. Due to this peculiar property, the resultant compound behaves as true half-metallic ferromagnet which is best suited for spintronic applications. The total magnetic moments of this compound are mainly due to Ti-d states present at E{sub F} with almost negligible contribution from other atoms.

  8. A first principles study of half-metallic ferromagnetism in In1-xTixP (x = 0.06) diluted magnetic semiconductor

    Science.gov (United States)

    Saini, Hardev S.; Singh, Mukhtiyar; Thakur, Jyoti; Saini, G. S. S.; Kashyap, Manish K.

    2016-05-01

    A first principles approach has been used to calculate the electronic and magnetic properties of In1-xTixP (x = 0.06) diluted magnetic semiconductor (DMS) compound. The calculations have been carried out using the highly precise all electron full potential Linear Augmented Plane Wave (FPLAPW) method within generalized gradient approximation (GGA) as exchange-correlation (XC) potentials. The estimated results show that the Ti-doping generate robust half metallic ferromagnetism with the 100% spin polarization at Fermi level (EF) in InP. Due to this peculiar property, the resultant compound behaves as true half-metallic ferromagnet which is best suited for spintronic applications. The total magnetic moments of this compound are mainly due to Ti-d states present at EF with almost negligible contribution from other atoms.

  9. Half-metallicity of graphene nanoribbons and related systems: a new quantum mechanical El Dorado for nanotechnologies... or a hype for materials scientists?

    Science.gov (United States)

    Deleuze, Michael S; Huzak, Matija; Hajgató, Balázs

    2013-07-01

    In this work we discuss in some computational and analytical details the issue of half-metallicity in zig-zag graphene nanoribbons and nanoislands of finite width, i.e. the coexistence of metallic nature for electrons with one spin orientation and insulating nature for the electrons of opposite spin, which has been recently predicted from so-called first-principle calculations employing Density Functional Theory. It is mathematically demonstrated and computationally verified that, within the framework of non-relativistic and time-independent quantum mechanics, like the size-extensive spin-contamination to which it relates, half-metallicity is nothing else than a methodological artefact, due to a too approximate treatment of electron correlation in the electronic ground state.

  10. High mobility half-metallicity in the (LaMnO3)2/(SrTiO3)8 superlattice

    KAUST Repository

    Cossu, Fabrizio

    2013-01-28

    First principles calculations have been performed to investigate the LaMnO3/SrTiO3 superlattice. Structural relaxation within the generalized gradient approximation results in no significant tiltings or rotations of oxygen octahedra, but in distinct distortions in the SrTiO3 region. Taking into account the onsite Coulomb interaction, we find that the Mn spins order ferromagnetically, in contrast to the antiferromagnetic state of bulk LaMnO3. Most importantly, the interface strain combined with charge transfer across the interface induces half-metallicity within the MnO2 layers. The superlattice is particulary interesting for spintronics applications because the half-metallic states are characterized by an extraordinary high mobility.

  11. Longitudinal spin Seebeck effect in a half-metallic L a0.7S r0.3Mn O3 film

    Science.gov (United States)

    Wu, B. W.; Luo, G. Y.; Lin, J. G.; Huang, S. Y.

    2017-08-01

    The longitudinal spin Seebeck effect (LSSE) with a vertical temperature gradient is one of the most important mechanisms to generate pure spin current. Previous studies of the LSSE excited spin current focus mainly on the magnetic insulators, a little on ferromagnetic metals, and rarely on ferromagnetic half metals. In this work, we demonstrate a significant spin current injected from the highly spin polarized ferromagnetic half metal L a0.7S r0.3Mn O3 by the LSSE. The sign of the thermal voltage can be reversed by using the spin current detector Cr with a large negative spin Hall angle. The ratio of the inverse spin Hall voltage to the total thermal signal in L a0.7S r0.3Mn O3 is much larger than that in ferromagnetic metals, such as permalloy and CoFeB. The nontrivial temperature-dependent voltage suggests that the thermal transport in L a0.7S r0.3Mn O3 is carried by magnons. This study provides insight into the mechanism of thermally excited spin current in ferromagnetic half metals and recommends the highly spin polarized L a0.7S r0.3Mn O3 as a promising candidate for metal-based spin caloritronics devices.

  12. Corrosion protection of zirconium surface based on Heusler alloy

    Czech Academy of Sciences Publication Activity Database

    Horáková, Kateřina; Cichoň, Stanislav; Lančok, Ján; Kratochvílová, Irena; Fekete, Ladislav; Sajdl, P.; Krausová, A.; Macák, J.; Cháb, Vladimír

    2017-01-01

    Roč. 89, č. 4 (2017), s. 553-563 ISSN 0033-4545 R&D Projects: GA MŠk LO1409; GA ČR(CZ) GA16-03085S; GA ČR GJ17-19910Y; GA ČR(CZ) GA15-05095S Institutional support: RVO:68378271 ; RVO:67985858 Keywords : electrochemistry * silicon * spectroscopy * SSC-2016 * surface chemistry * wate * zirconium Subject RIV: JI - Composite Materials Impact factor: 2.626, year: 2016

  13. Hybrid Spintronic Structures With Magnetic Oxides and Heusler Alloys

    DEFF Research Database (Denmark)

    Xu, Y. B.; Hassan, S. S. A.; Wong, P. K. J.

    2008-01-01

    As(100) and the unit cell of the Fe3O4 was found to be rotated by 45 degrees to match the gallium arsenide GaAs. The films were found to have a bulk-like moment down to 3-4 nm and a low coercivity indicating a high-quality magnetic interface. The magnetization hysteresis loops of the ultrathin films...

  14. Half-metallicity in a BiFeO3/La2/3Sr1/3MnO3 superlattice: A first-principles study

    KAUST Repository

    Jiwuer, Jilili

    2013-06-01

    We present first-principles results for the electronic, magnetic, and optical properties of the heterostructure as obtained by spin-polarized calculations using density functional theory. The electronic states of the heterostructure are compared to those of the bulk compounds. Structural relaxation turns out to have only a minor impact on the chemical bonding, even though the oxygen octahedra in develop some distortions due to the interface strain. While a small charge transfer affects the heterointerfaces, our results demonstrate that the half-metallic character of is fully maintained. © EPLA, 2013.

  15. Prediction of half-metallic properties in TlCrS{sub 2} and TlCrSe{sub 2} based on density functional theory

    Energy Technology Data Exchange (ETDEWEB)

    Hashimzade, F.M.; Huseinova, D.A. [Institute of Physics, National Academy of Sciences of Azerbaijan, AZ 1143 Baku (Azerbaijan); Jahangirli, Z.A. [Institute of Physics, National Academy of Sciences of Azerbaijan, AZ 1143 Baku (Azerbaijan); Institute of Radiation Problems, National Academy of Sciences of Azerbaijan, AZ 1143 Baku (Azerbaijan); Mehdiyev, B.H., E-mail: bachschi@yahoo.de [Institute of Physics, National Academy of Sciences of Azerbaijan, AZ 1143 Baku (Azerbaijan)

    2017-08-01

    Highlights: • Half-metallic properties of TlCrS2, TlCrSe2 and hypothetical TlCrSSe have been investigated by first-principles all-electron full-potential linearized augmented plane wave plus local orbital (FP-LAPW+lo) method based on density functional theory (DFT). • Total magnetic moment keeps its integer value on a relatively wide range of changes in volume (−10% ÷ 10%) for TlCrS2 and TlCrSSe, while total magnetic moment TlCrSe2 decreases with increasing volume, approaching to integer value 3 μB. • The states at the Fermi level in the case of spin-up channel consist of a hybridization of p-states of the atom S(Se) with d-states of Cr. - Abstract: Half-metallic properties of TlCrS{sub 2}, TlCrSe{sub 2} and hypothetical TlCrSSe have been investigated by first-principles all-electron full-potential linearized augmented plane wave plus local orbital (FP-LAPW+lo) method based on density functional theory (DFT). The results of calculations show that TlCrS{sub 2} and TlCrSSe are half-metals with energy gap (E{sub g}) ∼0.12 eV for spin-down channel. Strong hybridization of p-state of chalchogen and d-state of Cr leads to bonding and antibonding states and subsequently to the appearance of a gap in spin-down channel of TlCrS{sub 2} and TlCrSSe. In the case of TlCrSe{sub 2}, there is a partial hybridization and p-state is partially present in the DOS at Fermi level making this compound nearly half-metallic. The present calculations revealed that total magnetic moment keeps its integer value on a relatively wide range of changes in volume (−10% ÷ 10%) for TlCrS{sub 2} and TlCrSSe, while total magnetic moment of TlCrSe{sub 2} decreases with increasing volume approaching to integer value 3 μB.

  16. Half metallic ferromagnetism in tri-layered perovskites Sr{sub 4}T{sub 3}O{sub 10}(T = Co, Rh)

    Energy Technology Data Exchange (ETDEWEB)

    Ghimire, Madhav Prasad, E-mail: ghimire.mpg@gmail.com [Faculty of Science, Nepal Academy of Science and Technology, P. O. Box 3323, Khumaltar, Lalitpur (Nepal); International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science, Tsukuba 305-0044 (Japan); Thapa, R. K.; Sandeep [Department of Physics, Mizoram University, Aizawl 796-004 (India); Rai, D. P. [Department of Physics, Pachhunga University College, Aizawl 796-001 (India); Sinha, T. P. [Department of Physics, Bose Institute, Kolkata 700-009 (India); Hu, Xiao [International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science, Tsukuba 305-0044 (Japan)

    2015-02-14

    First-principles density functional theory (DFT) is used to investigate the electronic and magnetic properties of Sr{sub 4}Rh{sub 3}O{sub 10}, a member of the Ruddlesden-Popper series. Based on the DFT calculations taking into account the co-operative effect of Coulomb interaction (U) and spin-orbit couplings (SOC), Sr{sub 4}Rh{sub 3}O{sub 10} is found to be a half metallic ferromagnet (HMF) with total magnetic moment μ{sub tot} = 12 μ{sub B} per unit cell. The material has almost 100% spin-polarization at the Fermi level despite of sizable SOC. Replacement of Rh atom by the isovalent Co atom is considered. Upon full-replacement of Co, a low-spin to intermediate spin transition happens resulting in a HMF state with the total magnetic moment three-time larger (i.e., μ{sub tot} = 36 μ{sub B} per unit cell), compared to Sr{sub 4}Rh{sub 3}O{sub 10}. We propose Sr{sub 4}Rh{sub 3}O{sub 10} and Sr{sub 4}Co{sub 3}O{sub 10} as candidates of half metals.

  17. First-Principle Predictions of Electronic Properties and Half-Metallic Ferromagnetism in Vanadium-Doped Rock-Salt SrO

    Science.gov (United States)

    Berber, Mohamed; Doumi, Bendouma; Mokaddem, Allel; Mogulkoc, Yesim; Sayede, Adlane; Tadjer, Abdelkader

    2018-01-01

    We have used first-principle methods of density functional theory within the full potential linearized augmented plane wave scheme to investigate the electronic and magnetic properties of cubic rock-salt, SrO, doped with vanadium (V) impurity as Sr1- x V x O at various concentrations, x = 0.25, 0.5, and 0.75. We have found that the ferromagnetic state arrangement of Sr1- x V x O is more stable compared to the anti-ferromagnetic state configuration. The electronic structures have a half-metallic (HM) ferromagnetic (F) behavior for Sr0.75V0.25O and Sr0.5V0.5O. This feature results from the metallic and semiconducting natures of majority-spin and minority-spin bands, respectively. The HMF gap decreases with the increasing concentration of vanadium atoms due to the broadening of 3 d (V) levels in the gap, and hence the Sr0.25V0.75O becomes metallic ferromagnetic. The Sr0.75V0.25O revealed a large HM gap with spin polarization of 100%. The Sr1- x V x O compound at low concentrations seems a better candidate to explore the half-metallicity for practical spintronics applications.

  18. Dilute Magnetic Semiconductor and Half-Metal Behaviors in 3 d Transition-Metal Doped Black and Blue Phosphorenes: A First-Principles Study

    Science.gov (United States)

    Yu, Weiyang; Zhu, Zhili; Niu, Chun-Yao; Li, Chong; Cho, Jun-Hyung; Jia, Yu

    2016-02-01

    We present first-principles density-functional calculations for the structural, electronic, and magnetic properties of substitutional 3 d transition metal (TM) impurities in two-dimensional black and blue phosphorenes. We find that the magnetic properties of such substitutional impurities can be understood in terms of a simple model based on the Hund's rule. The TM-doped black phosphorenes with Ti, V, Cr, Mn, Fe, and Ni impurities show dilute magnetic semiconductor (DMS) properties while those with Sc and Co impurities show nonmagnetic properties. On the other hand, the TM-doped blue phosphorenes with V, Cr, Mn, and Fe impurities show DMS properties, with Ni impurity showing half-metal properties, whereas Sc- and Co-doped systems show nonmagnetic properties. We identify two different regimes depending on the occupation of the hybridized electronic states of TM and phosphorous atoms: (i) bonding states are completely empty or filled for Sc- and Co-doped black and blue phosphorenes, leading to nonmagnetic; (ii) non-bonding d states are partially occupied for Ti-, V-, Cr-, Mn-, Fe- and Ni-doped black and blue phosphorenes, giving rise to large and localized spin moments. These results provide a new route for the potential applications of dilute magnetic semiconductor and half-metal in spintronic devices by employing black and blue phosphorenes. PACS numbers: 73.22.-f, 75.50.Pp, 75.75. + a

  19. First-Principle Predictions of Electronic Properties and Half-Metallic Ferromagnetism in Vanadium-Doped Rock-Salt SrO

    Science.gov (United States)

    Berber, Mohamed; Doumi, Bendouma; Mokaddem, Allel; Mogulkoc, Yesim; Sayede, Adlane; Tadjer, Abdelkader

    2017-09-01

    We have used first-principle methods of density functional theory within the full potential linearized augmented plane wave scheme to investigate the electronic and magnetic properties of cubic rock-salt, SrO, doped with vanadium (V) impurity as Sr1-x V x O at various concentrations, x = 0.25, 0.5, and 0.75. We have found that the ferromagnetic state arrangement of Sr1-x V x O is more stable compared to the anti-ferromagnetic state configuration. The electronic structures have a half-metallic (HM) ferromagnetic (F) behavior for Sr0.75V0.25O and Sr0.5V0.5O. This feature results from the metallic and semiconducting natures of majority-spin and minority-spin bands, respectively. The HMF gap decreases with the increasing concentration of vanadium atoms due to the broadening of 3d (V) levels in the gap, and hence the Sr0.25V0.75O becomes metallic ferromagnetic. The Sr0.75V0.25O revealed a large HM gap with spin polarization of 100%. The Sr1-x V x O compound at low concentrations seems a better candidate to explore the half-metallicity for practical spintronics applications.

  20. Half-Metallic Ferromagnetism and Surface Functionalization-Induced Metal-Insulator Transition in Graphene-like Two-Dimensional Cr2C Crystals.

    Science.gov (United States)

    Si, Chen; Zhou, Jian; Sun, Zhimei

    2015-08-12

    Graphene-like two-dimensional materials have garnered tremendous interest as emerging device materials for nanoelectronics due to their remarkable properties. However, their applications in spintronics have been limited by the lack of intrinsic magnetism. Here, using hybrid density functional theory, we predict ferromagnetic behavior in a graphene-like two-dimensional Cr2C crystal that belongs to the MXenes family. The ferromagnetism, arising from the itinerant Cr d electrons, introduces intrinsic half-metallicity in Cr2C MXene, with the half-metallic gap as large as 2.85 eV. We also demonstrate a ferromagnetic-antiferromagnetic transition accompanied by a metal to insulator transition in Cr2C, caused by surface functionalization with F, OH, H, or Cl groups. Moreover, the energy gap of the antiferromagnetic insulating state is controllable by changing the type of functional groups. We further point out that the localization of Cr d electrons induced by the surface functionalization is responsible for the ferromagnetic-antiferromagnetic and metal to insulator transitions. Our results highlight a new promising material with tunable magnetic and electronic properties toward nanoscale spintronics and electronics applications.

  1. Joining of Half-Heusler and Bismuth Tellurides for Segmented Thermoelectric Generators

    Science.gov (United States)

    Ngan, Pham Hoang; Han, Li; Christensen, Dennis Valbjørn

    2018-01-01

    Segmented generators where the p- or n-type legs are formed by joining materials in series enables each material to operate in their most efficient temperature range. Here, we have fabricated and characterized segmented thermoelectric p- and n-type legs based on bismuth tellurides and half-Heusler alloys p-type Hf0.5Zr0.5CoSn0.2Sb0.8 and n-type Ti0.6Hf0.4NiSn. A two-step process was introduced to join the half-Heusler to the bismuth tellurides to form a segmented structure which was then characterized for its thermoelectric and structural properties. The output power generation was characterized under various hot side temperatures up to 873 K with the cold side fixed at 323 K. The stability of the joints was also investigated under heat treatment and thermal cycling. Under working temperatures from 323 K to 873 K, the obtained p-type segmented legs could deliver a power density of 0.3 W cm-2 and maximum voltage of 115 mV. With the same condition, the power density and the maximum voltage generated by n-type segmented leg were 0.25 W cm-2 and 102 mV. The area-specific contact resistances of the p- and n-type legs were 50 μΩ cm2 and 35 μΩ cm2, respectively. The output performance of each leg was ˜ 95% after 6 cycles from 323 K to 873 K.

  2. Magnetic properties and temperature-dependent half-metallicity of Co2Mn(Ga(1-x)Z(x)) (Z=Si, Ge, Sn) from first-principles calculation.

    Science.gov (United States)

    Luo, Hu-Bin; Hu, Qing-Miao; Li, Chun-Mei; Johansson, Börje; Vitos, Levente; Yang, Rui

    2013-04-17

    Using the first-principles exact muffin-tin orbitals method in combination with the coherent potential approximation, we investigated the magnetic properties, exchange interactions, and temperature-dependent half-metallicity of the Co2Mn(Ga1-xZx) (Z=Si, Ge, Sn) alloys. The total magnetic moment follows perfectly a previously proposed Slater-Pauling relation, i.e., μ0 = Nt - 24, with Nt being the number of valence electrons. The Co-Mn and Co1-Co2 (inter-sublattice) interactions are dominated by direct exchange, whereas the Co1-Co1 (intra-sublattice) interaction is characterized by superexchange. The Mn-Mn exchange interaction in Co2MnGa is of long-ranged RKKY-type. However, the Mn-Mn exchange interactions in Co2MnZ are relatively localized and can be attributed to superexchange. The Co-Mn, Co1-Co2 and Co1-Co1 total exchange interactions increase with x, whereas the Mn-Mn total exchange interactions show convex behavior. The calculated Curie temperature (TC) increases with x. The ability of Z to enhance TC follows the sequence of Si > Ge > Sn, in agreement with the experimental findings. The temperature dependence of the spin polarization at the Fermi level [P(T)] is investigated based on the disordered local moment model. P(T) drops abruptly at temperatures much lower than TC. At temperatures higher than 200 K, the composition with higher TC generally corresponds to larger P(T).

  3. First-principles investigation of competing magnetic interactions in (Mn ,Fe )Ru2Sn Heusler solid solutions

    Science.gov (United States)

    Decolvenaere, Elizabeth; Gordon, Michael; Seshadri, Ram; Van der Ven, Anton

    2017-10-01

    Many Heusler compounds possess magnetic properties well suited for applications as spintronic materials. The pseudobinary Mn0.5Fe0.5Ru2Sn , formed as a solid solution of two full Heuslers, has recently been shown to exhibit exchange hardening suggestive of two magnetic phases, despite existing as a single chemical phase. We have performed a first-principles study of the chemical and magnetic degrees of freedom in the Mn1 -xFexRu2Sn pseudobinary to determine the origin of the unique magnetic behavior responsible for exchange hardening within a single phase. We find a transition from antiferromagnetic (AFM) to ferromagnetic (FM) behavior upon replacement of Mn with Fe, consistent with experimental results. The lowest energy orderings in Mn1 -xFexRu2Sn consist of chemically and magnetically uniform (111) planes, with Fe-rich regions preferring FM ordering and Mn-rich regions preferring AFM ordering, independent of the overall composition. Analysis of the electronic structure suggests that the magnetic behavior of this alloy arises from a competition between AFM-favoring Sn-mediated superexchange and FM-favoring RKKY exchange mediated by spin-polarized conduction electrons. Changes in valency upon replacement of Mn with Fe shifts the balance from superexchange-dominated interactions to RKKY-dominated interactions.

  4. Spin-phonon coupling in rod-shaped half-metallic CrO sub 2 ultrafine particles: a magnetic Raman scattering study

    CERN Document Server

    Yu, T; Sun, W X; Lin, J Y; Ding, J

    2003-01-01

    Half-metallic CrO sub 2 powder compact with rod-shaped nanoparticles was studied by micro-Raman scattering in the presence of an external magnetic field at room temperature (300 K). In the low-field region (H <= 250 mT), the frequency and intensity of the E sub g mode, an internal phonon mode of CrO sub 2 , increase dramatically with increase in the magnetic field, while the corresponding linewidth decreases. The above parameters become constant when the CrO sub 2 powder enters the saturation state at higher magnetic field. The pronounced anomalies of the Raman phonon parameters under a low magnetic field are attributed to the spin-phonon coupling enhanced by the magnetic ordering, which is induced by the external magnetic field. (letter to the editor)

  5. Spin-polarized structural, elastic, electronic and magnetic properties of half-metallic ferromagnetism in V-doped ZnSe

    Energy Technology Data Exchange (ETDEWEB)

    Monir, M. El Amine.; Baltache, H. [Laboratoire de Physique Quantique de la Matière et de la Modélisation Mathématique (LPQ3M), Faculté des Sciences, Université de Mascara, Mascara 29000 (Algeria); Murtaza, G., E-mail: murtaza@icp.edu.pk [Materials Modeling Lab, Department of Physics, Islamia College University, Peshawar (Pakistan); Khenata, R., E-mail: khenata_rabah@yahoo.fr [Laboratoire de Physique Quantique de la Matière et de la Modélisation Mathématique (LPQ3M), Faculté des Sciences, Université de Mascara, Mascara 29000 (Algeria); Ahmed, Waleed K. [ERU, Faculty of Engineering, United Arab Emirates University, Al Ain (United Arab Emirates); Bouhemadou, A. [Laboratory for Developing New Materials and their Characterization, Department of Physics, Faculty of Science, University of Setif, 19000 Setif (Algeria); Omran, S. Bin [Department of Physics and Astronomy, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451 (Saudi Arabia); Seddik, T. [Laboratoire de Physique Quantique de la Matière et de la Modélisation Mathématique (LPQ3M), Faculté des Sciences, Université de Mascara, Mascara 29000 (Algeria)

    2015-01-15

    Based on first principles spin-polarized density functional theory, the structural, elastic electronic and magnetic properties of Zn{sub 1−x}V{sub x}Se (for x=0.25, 0.50, 0.75) in zinc blende structure have been studied. The investigation was done using the full-potential augmented plane wave method as implemented in WIEN2k code. The exchange-correlation potential was treated with the generalized gradient approximation PBE-GGA for the structural and elastic properties. Moreover, the PBE-GGA+U approximation (where U is the Hubbard correlation terms) is employed to treat the “d” electrons properly. A comparative study between the band structures, electronic structures, total and partial densities of states and local moments calculated within both GGA and GGA+U schemes is presented. The analysis of spin-polarized band structure and density of states shows the half-metallic ferromagnetic character and are also used to determine s(p)-d exchange constants N{sub 0}α (conduction band ) and N{sub 0}β (valence band) due to Se(4p)–V(3d) hybridization. It has been clearly evidence that the magnetic moment of V is reduced from its free space change value of 3 µ{sub B} and the minor atomic magnetic moment on Zn and Se are generated. - Highlights: • Half metallicity origins by doping V in ZnSe. • PBE-GGA+U approximation is employed to treat the “d” electrons properly. • s(p)-d Exchange constants N{sub 0}α (conduction band ) and N{sub 0}β (valence band) are due to Se(4p)-V(3d) hybridization.

  6. Ferromagnetism and half metallicity induced by oxygen vacancies in the double perovskite BaSrNiWO{sub 6}: DFT study

    Energy Technology Data Exchange (ETDEWEB)

    Aharbil, Y. [Laboratoire de Chimie Physique des Matériaux LCPM, Faculté des Sciences Ben M' Sik, Casablanca (Morocco); Labrim, H. [Unité Science de la Matière/DERS/Centre National de l’Energie, des Sciences et des Techniques Nucléaires (CNESTEN), Rabat (Morocco); Benmokhtar, S.; Haddouch, M. Ait [Laboratoire de Chimie Physique des Matériaux LCPM, Faculté des Sciences Ben M' Sik, Casablanca (Morocco); Bahmad, L., E-mail: bahmad@fsr.ac.ma [Mohammed V University in Rabat, Laboratoire de Magnétisme et Physique des Hautes Energies L.M.P.H.E. URAC-12, B.P. 1014, Rabat (Morocco); Belhaj, A. [LIRST, Département de Physique, Faculté Poly-disciplinaire, Université Sultan Moulay Slimane, Béni Mellal (Morocco); Ez-Zahraouy, H.; Benyoussef, A. [Mohammed V University in Rabat, Laboratoire de Magnétisme et Physique des Hautes Energies L.M.P.H.E. URAC-12, B.P. 1014, Rabat (Morocco)

    2016-11-01

    Using the spin polarized density functional theory (DFT) and exploring the Plane-Wave Self-Consistent Field (PWscf) code implemented in Quantum-ESPRESSO package, we investigate the effect of the Oxygen vacancies (V{sub O}) and the Oxygen interstitial (O{sub i}) on the double perovskite BaSrNiWO{sub 6}. This deals with the magnetic ordering and the electronic structure in such a pure sample exhibiting the insulating anti-ferromagnetic (AFM) state. This study shows that the presence of oxygen deficient defects converts the insulating to half metal with ferromagnetic or anti-ferromagnetic states. The magnetic ordering in BaSrNiWO{sub 6−δ} depends on the position of the Oxygen vacancy in the unit cell. However, it has been shown that the Oxygen interstitial preserves the anti-ferromagnetic propriety. We have computed the formation energies of different positions of the Oxygen vacancy (V{sub O}) and the Oxygen interstitial (O{sub i}) in the BaSrNiWO{sub 6} compound. We showed that the formation of V{sub O} is easier and vice versa for the O{sub i} formation. The obtained results reveal(V{sub O}) and the Oxygen interstitial (O{sub i}) that the anti-ferromagnetic can be converted to ferromagnetic in the double perovskite BaSrNiWO{sub 6} induced by Oxygen vacancies V{sub O}. - Highlights: • We have studied the ferromagnetism and Half Metallicity in Double Perovskite BaSrNiWO{sub 6}. • We have applied the Ab-inito calculations using the DFT approach. • We showed the effects induced by Oxygen Vacancies and Oxygen interstitial. • We found that the magnetic ordering in BaSrNiWO{sub 6−δ} depends on the position of the Oxygen vacancy in the unit cell.

  7. Influence of disorder and interfaces on electronic and magnetic properties of Heusler systems; Einfluss von Unordnung und Grenzflaechen auf elektronische und magnetische Eigenschaften von Heusler-Systemen

    Energy Technology Data Exchange (ETDEWEB)

    Krumme, Bernhard

    2012-07-17

    A Moessbauer-spectroscopic investigation of Fe{sub 3} films on GaAs(100) and MgO(100) revealed a disordered growth mode of Fe{sub 3}Si on GaAs(100), which is caused by an interdiffusion of Ga/As atoms. Implementing a 3 nm thick MgO tunnelbarrier on the GaAs suface inhibits the interdiffusion and enables an epitaxial film growth of Fe{sub 3}Si. By comparing experimental X-ray absorption measurements with DFT calculations we are able to resolve the contribution of the different Fe sublattices to the XAS and XMCD signal. Taking into account atomic disorder arising from Ga/As atoms within DFT calculation yields a small reduction of the spin polarization of Fe{sub 3}Si, indicating that the system Fe{sub 3}Si/GaAs(100) still is an interesting candidate for spintronic applications. For the Heusler compounds Co{sub 2}MnSi and Co{sub 2}FeSi the influence of the 3d transition metals Mn/Fe on the hybridization was determined by X-ray absorption and DFT calculations. A depth-selective study of the electronic structure of Mn in Co{sub 2}MnSi at the vicinity to a MgO tunnelbarrier indicates an increased number of unoccupied d states referring a MnSi terminated interface. The electronic structure of Si-rich Co{sub 2}FeSi depends on the external magnetic field. This points to magnetostrictive effects in this compound. Furthermore, the Heusler compound Ni{sub 51.6}Mn{sub 32.9}Sn{sub 15.5} was studied in this work. The compound is a shape memory alloy exhibiting a large inverse magnetocaloric effect. In this work the focus was put on the element-specific magnetic properties of Ni and Mn. For Mn a strong increase of the ratio of orbital to spin magnetic moment m{sub l}/m{sub S} was observed. In the austenite phase this ratio accounts for 5 %, whereas in the martensite this value becomes 13.5 %. For Ni m{sub l}/m{sub S} is almost constant at 28 %. applying a magnetic field of 3 T in the martensite phase leads to a reduction of m{sub l}/m{sub S} for both elements, indicating a field

  8. Study of the half-metallic materials double perovskites Sr{sub 2}ZnBO{sub 6} (B=Tc, Re, Ru, Os, Co, Pd, and Au) via first-principle calculations

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Y.P. [Department of Physics, National Taiwan Normal University, Taipei 116, Taiwan (China); Fuh, H.R. [Graduate Institute of Applied Physics, National Taiwan University, Taipei 106, Taiwan (China); Wang, Y.K., E-mail: kant@ntnu.edu.tw [Center for General Education and Department of Physics, National Taiwan Normal University, Taipei 106, Taiwan (China)

    2013-09-15

    Based on the density functional theory calculations, the structural optimization, magnetic stable phase, and electronic structure of the double perovskites Sr{sub 2}ZnBO{sub 6} (B=Tc, Re, Ru, Os, Co, Pd, and Au) were investigated with full structural optimization by using the generalized gradient approximation (GGA) and by adding the correlation effect (GGA+U). The results indicate that all compounds can be stable half-metallic ferromagnetic materials in the GGA(+U) scheme with a spin splitting e{sub g} band of the B ion, which causes half-metallicity at the Fermi level except Sr{sub 2}ZnCoO{sub 6} becomes a conductor in GGA+U scheme. We suggest that the double exchange interaction dominates the half metallicity and magnetism in these materials. - Highlights: • Finding the possible half-metallic materials. • Examining the materials by structure optimization. • The strong correlation effect was considered. • Finding the most stable magnetic phase. • Sr{sub 2}ZnBO{sub 6} (B=Tc, Re, Ru, Os, Co, Pd and Au) could be the candidate of half-metallic materials.

  9. Perovskite- and Heusler based materials for thermoelectric converters

    Science.gov (United States)

    Weidenkaff, Anke

    2015-03-01

    The broad application of thermoelectric converters in future energy technologies requires the development of active, stable, low cost and sustainable materials. Semiconductors based on perovskite and heusler structures show substantial potential for thermoelectric energy conversion processes. Their good performance can be explained based on their suitable band structure, adjusted charge carrier density, mass and mobility, limited phonon transport, electron filtering possibilities, strongly correlated electronic systems, etc. These properties are widely tuneable by following theoretical concepts and a deep composition-structure-property understanding to change the composition, structure and size of the crystallites in innovative scalable synthesis procedures. Improved thermoelectric materials are developed, synthesised and tested in diverse high temperature applications to improve the efficiency and energy density of the thermoelectric conversion process. The lecture will provide a summary on the field of advanced perovskite-type ceramics and Heusler compounds gaining importance for a large number of future energy technologies.

  10. Ferromagnetic half-metallic characteristic in bulk Ni 0.5M 0.5O (M=Cu, Zn and Cd): A GGAU study

    KAUST Repository

    Mi, Wenbo

    2012-07-01

    Ferromagnetic half metallicity with a high spin polarization of 100% was predicted in the bulk Ni 0.5Cu 0.5O using density-functional theory method. The band gap of majority spin is 3.45 eV for Ni 0.5Cu 0.5O. The density of states of minority spin at the Fermi level are mainly from Cu 3d and O 2p in the Ni 0.5Cu 0.5O. The magnetic moments are from Ni 3d states. Ni 0.5Zn 0.5O and Ni 0.5Cd 0.5O systems are ferromagnetic insulators, but the magnetic moment of Ni 2 ions is enhanced by the Zn and Cd incorporation. Therefore, Ni 0.5Cu 0.5O is the potential candidate for spintronics devices because of the predicted high spin polarization. © 2012 Elsevier Ltd. All rights reserved.

  11. Fabrication and characterization of nanostructured Fe{sub 3}S{sub 4}, an isostructural compound of half-metallic Fe{sub 3}O{sub 4}

    Energy Technology Data Exchange (ETDEWEB)

    Li, Peng [Division of Physical Science and Engineering, King Abdullah University of Science and Technology (KAUST), Thuwal 23955 (Saudi Arabia); Tianjin Key Laboratory of Low Dimensional Materials Physics and Preparing Technology, Faculty of Science, Institute of Advanced Materials Physics, Tianjin University, Tianjin 300072 (China); Xia, Chuan; Zhang, Qiang; Alshareef, Husam N.; Zhang, Xi-xiang, E-mail: xixiang.zhang@kaust.edu.sa [Division of Physical Science and Engineering, King Abdullah University of Science and Technology (KAUST), Thuwal 23955 (Saudi Arabia); Guo, Zaibing [Advanced Nanofabrication, Imaging and Characterization Core Lab, King Abdullah University of Science and Technology, Thuwal-239955 (Saudi Arabia); Cui, Wenyao; Bai, Haili [Tianjin Key Laboratory of Low Dimensional Materials Physics and Preparing Technology, Faculty of Science, Institute of Advanced Materials Physics, Tianjin University, Tianjin 300072 (China)

    2015-06-14

    High-purity, well-crystallized spinel Fe{sub 3}S{sub 4} nanoplatelets were synthesized by the hydrothermal method, and the saturation magnetic moment of Fe{sub 3}S{sub 4} was measured at 1.83 μ{sub B}/f.u. The temperature-dependent resistivity of Fe{sub 3}S{sub 4} was metallic-like for T < 180 K: room-temperature resistivity was measured at 7.711 × 10{sup 3 }μΩ cm. The anomalous Hall conductivity of Fe{sub 3}S{sub 4} decreased with increasing longitudinal conductivity, in sharp contrast with the accepted theory of the anomalous Hall effect in a dirty-metal regime. Furthermore, negligible spin-dependent magnetoresistance was observed. Band structure calculations confirmed our experimental observations that Fe{sub 3}S{sub 4} is a metal and not a half metal as expected.

  12. Quantum anomalous Hall phase and half-metallic phase in ferromagnetic (111) bilayers of 4 d and 5 d transition metal perovskites

    Science.gov (United States)

    Chandra, Hirak Kumar; Guo, Guang-Yu

    2017-04-01

    Extraordinary electronic phases can form in artificial oxide heterostructures, which will provide a fertile ground for new physics and also give rise to novel device functions. Based on a systematic first-principles density functional theory study of the magnetic and electronic properties of the (111) superlattices (ABO3) 2/(AB'O3)10 of 4 d and 5 d transition metal perovskite (B = Ru, Rh, Ag, Re, Os, Ir, Au; AB'O3=LaAlO3 , SrTiO3) , we demonstrate that due to quantum confinement, bilayers (LaBO3)2 (B = Ru, Re, Os) and (SrBO3)2 (B = Rh, Os, Ir) are ferromagnetic with ordering temperatures up to room temperature. In particular, bilayer (LaOsO3)2 is an exotic spin-polarized quantum anomalous Hall insulator, while the other ferromagnetic bilayers are metallic with large Hall conductances comparable to the conductance quantum. Furthermore, bilayers (LaRuO3)2 and (SrRhO3)2 are half metallic, while the bilayer (SrIrO3)2 exhibits a peculiar colossal magnetic anisotropy. Our findings thus show that 4 d and 5 d metal perovskite (111) bilayers are a class of quasi-two-dimensional materials for exploring exotic quantum phases and also for advanced applications such as low-power nanoelectronics and oxide spintronics.

  13. Spin distribution and electronic structure of the ferromagnetic half-metal [Mn(bipy)(N{sub 3}){sub 2}]: Ab initio study

    Energy Technology Data Exchange (ETDEWEB)

    Li, Y.L. [Department of Physics, Huazhong University of Science and Technology, Wuhan 430074 (China)]. E-mail: liyanli128@163.com; Yao, K.L. [Department of Physics, Huazhong University of Science and Technology, Wuhan 430074 (China) and International Center of Materials Physics, Chinese Academy of Science, Shenyang 110015 (China) and CCAST (World Lab), P.O. Box 8730, Beijing 10080 (China)]. E-mail: klyao@hust.edu.cn; Liu, Z.L. [Department of Physics, Huazhong University of Science and Technology, Wuhan 430074 (China)

    2007-05-31

    Ab initio calculations have been performed to study the electronic structure and the alternating ferromagnetic-antiferromagnetic interactions of the manganese(II)-azido one-dimensional compound: [Mn(bipy)(N{sub 3}){sub 2}] (bipy=2,2'-bipyridine). The density of states, the total energy and the spin magnetic moment were calculated. The calculations predict that the compound [Mn(bipy)(N{sub 3}){sub 2}] is a ferromagnetic half-metal and the spin magnetic moment is 4.000{mu} {sub B} per molecule. At the same time, it has a metallic antiferromagnetic metastable state. Based on the spin distribution obtained from ab initio calculations, we found that the spin populations are strongly positive on the Mn{sup 2+} ions. For the end-on (EO) azido groups, the magnetic moments are mainly distributed on the two terminal N1 and N3 atoms, weakly positive on the central N2 atoms. While for the end-to-end (EE) azido groups, the magnetic moments of the terminal N6 atoms are larger and that of the other terminal N4 atoms are smaller. The analysis of the spin populations shows that the ferromagnetic coupling through the azido groups is resulted from a spin delocalization mechanism together with the spin polarization effect. The results of our calculation are in good agreement with the experiment.

  14. Half-metallic properties, single-spin negative differential resistance, and large single-spin Seebeck effects induced by chemical doping in zigzag-edged graphene nanoribbons.

    Science.gov (United States)

    Yang, Xi-Feng; Zhou, Wen-Qian; Hong, Xue-Kun; Liu, Yu-Shen; Wang, Xue-Feng; Feng, Jin-Fu

    2015-01-14

    Ab initio calculations combining density-functional theory and nonequilibrium Green's function are performed to investigate the effects of either single B atom or single N atom dopant in zigzag-edged graphene nanoribbons (ZGNRs) with the ferromagnetic state on the spin-dependent transport properties and thermospin performances. A spin-up (spin-down) localized state near the Fermi level can be induced by these dopants, resulting in a half-metallic property with 100% negative (positive) spin polarization at the Fermi level due to the destructive quantum interference effects. In addition, the highly spin-polarized electric current in the low bias-voltage regime and single-spin negative differential resistance in the high bias-voltage regime are also observed in these doped ZGNRs. Moreover, the large spin-up (spin-down) Seebeck coefficient and the very weak spin-down (spin-up) Seebeck effect of the B(N)-doped ZGNRs near the Fermi level are simultaneously achieved, indicating that the spin Seebeck effect is comparable to the corresponding charge Seebeck effect.

  15. Reactively sputtered MgAl2O4 barrier layers for Heusler tunnel junctions

    Science.gov (United States)

    Inagaki, K.; Fukatani, N.; Mari, K.; Fujita, H.; Miyawaki, T.; Ueda, K.; Asano, H.

    2013-08-01

    Epitaxial MgAl2O4 thin films were deposited on a lattice-matched Heusler alloy, Fe2CrSi, by reactive magnetron sputtering of an MgAl2 target in an Ar+O2 atmosphere. Epitaxial Fe2CrSi/MgAl2O4 junctions were obtained by inserting an ultrathin MgAl2 interlayer, which worked as a protective layer for oxidization at the surface of the Fe2CrSi. The growth of MgAl2O4 was found to be very sensitive to the MgAl2 thickness and the oxygen partial pressure during the deposition of MgAl2O4. Both epitaxial growth and characteristics of the efficient tunneling barrier were obtained in an Fe2CrSi/MgAl2O4 (3 nm)/CoFe tunneling device for MgAl2O4 thin films grown by reactive sputtering. The present epitaxial MgAl2O4 barrier deposited by reactive sputtering is expected to realize high performance spintronic devices.

  16. Spin-filter and spin-gapless semiconductors: The case of Heusler compounds

    Energy Technology Data Exchange (ETDEWEB)

    Galanakis, I. [Department of Materials Science, School of Natural Sciences, University of Paras, GR-26504 Patra (Greece); Özdoğan, K. [Department of Physics, Yildiz Technical University, 34210 Istanbul (Turkey); Şaşıoğlu, E. [Peter Grünberg Institut and Institute for Advanced Simulation, Forschungszentrum Jülich and JARA, 52425 Jülich, Germany and Department of Physics, Fatih University, 34500, Büyükçekmece, Istanbul (Turkey)

    2016-05-15

    We review our recent first-principles results on the inverse Heusler compounds and the ordered quaternary (also known as LiMgPdSn-type) Heusler compounds. Among these two subfamilies of the full-Heusler compounds, several have been shown to be magnetic semiconductors. Such material can find versatile applications, e.g. as spin-filter materials in magnetic tunnel junctions. Finally, a special case are the spin-gapless semiconductors, where the energy gap at the Fermi level for the one spin-direction is almost vanishing, offering novel functionalities in spintronic/magnetoelectronic devices.

  17. Half-metallic properties of CoS2, doped CoN0.25S1.75 and CoP0.25S1.75

    Science.gov (United States)

    Zhao, Jin-Yang; Zhang, Jian-Min

    2017-08-01

    We use first-principles calculations to investigate the half-metallicity of pure \\text{Co}{{\\text{S}}2} , doped \\text{Co}{{\\text{N}}0.25}{{\\text{S}}1.75} and \\text{Co}{{\\text{P}}0.25}{{\\text{S}}1.75} systems. The results show that the conduction bands minimum (CBM) of pure \\text{Co}{{\\text{S}}2} is mainly contributed by the low intensity state of S \\text{pp}{σ\\ast} in the spin-down channel. The S \\text{pp}{σ\\ast} state extends below the Fermi level (E F) and destroys the half-metallicity of \\text{Co}{{\\text{S}}2} , rather than Co-{{e}\\text{g\\downarrow}} states proposed previously. Replacing sulfur (S) with nitrogen (N) reduces the bandwidth of the S (N) \\text{pp}{σ\\ast} bands and destroys the continuous S \\text{pp}{σ\\ast} network, as a result the bottom of the S \\text{pp}{σ\\ast} band shifts upward above the bottom of the Co-{{e}\\text{g\\downarrow}} band and makes the \\text{Co}{{\\text{N}}0.25}{{\\text{S}}1.75} a perfect half metal ferromagnet (HMF) and a promising candidate for spintronic devices.

  18. Crystallographic Characterization on Polycrystalline Ni-Mn-Ga Alloys with Strong Preferred Orientation

    Directory of Open Access Journals (Sweden)

    Zongbin Li

    2017-04-01

    Full Text Available Heusler type Ni-Mn-Ga ferromagnetic shape memory alloys can demonstrate excellent magnetic shape memory effect in single crystals. However, such effect in polycrystalline alloys is greatly weakened due to the random distribution of crystallographic orientation. Microstructure optimization and texture control are of great significance and challenge to improve the functional behaviors of polycrystalline alloys. In this paper, we summarize our recent progress on the microstructure control in polycrystalline Ni-Mn-Ga alloys in the form of bulk alloys, melt-spun ribbons and thin films, based on the detailed crystallographic characterizations through neutron diffraction, X-ray diffraction and electron backscatter diffraction. The presented results are expected to offer some guidelines for the microstructure modification and functional performance control of ferromagnetic shape memory alloys.

  19. Modeling of half-Heusler compound NiMnSb within tight-binding approximation

    Science.gov (United States)

    Sugiyanto, Majidi, M. A.; Nanto, D.

    2017-07-01

    Heusler compounds are families of magnetic materials with general stoichiometry of either X2YZ (full-Heusler compound) or XYZ (half-Heusler compound), with X and Y being transition metal elements, and Z a main-group element. Their various potentials for technology development make them be still relevant as a subject of both experimental and theoretical studies. Half-Heusler compounds are generally crystallized in the C1b-type structure. The magnetic moments of such materials may be predicted using Slater-Pauling rule, giving m = (Nvalence electrons - 18)µB per formula unit. However, this simple counting rule does not always work for all compounds in this group. This motivates us to perform a theoretical study to investigate the mechanism of magnetic moment formation microscopically. As a case study, we focus on NiMnSb, a particular half-Heusler compound, for which comparison between existing experimental results and theoretical predictions of its magnetic moment has not yet been quite convincing. We model the system by constructing a tight-binding-based Hamiltonian, incorporating Hubbard repulsive as well as spin-spin interactions for the electrons occupying the d-orbitals. We solve the model using Green's function approach, and treat the interaction terms within the mean-field approximation. At this stage, we aim to formulate the computational algorithm for the overall calculation process. Our final goal is to compute the total magnetic moment per unit cell of this system and compare it with available experimental data.

  20. Size effects on magnetic actuation in Ni-Mn-Ga shape-memory alloys.

    Science.gov (United States)

    Dunand, David C; Müllner, Peter

    2011-01-11

    The off-stoichiometric Ni(2)MnGa Heusler alloy is a magnetic shape-memory alloy capable of reversible magnetic-field-induced strains (MFIS). These are generated by twin boundaries moving under the influence of an internal stress produced by a magnetic field through the magnetocrystalline anisotropy. While MFIS are very large (up to 10%) for monocrystalline Ni-Mn-Ga, they are near zero (textiles, foams and composites). Various strategies are proposed to accentuate this geometric effect which enables large MFIS in polycrystalline Ni-Mn-Ga by matching grain and sample sizes.

  1. Structural and magnetic properties of Fe2CoGa Heusler nanoparticles

    Science.gov (United States)

    Wang, Changhai; Casper, Frederick; Gasi, Teuta; Ksenofontov, Vadim; Balke, Benjamin; Fecher, Gerhard H.; Felser, Claudia; Hwu, Yeu-Kuang; Lee, Jeu-Jau

    2012-07-01

    Fe2CoGa Heusler nanoparticles are synthesized by a chemical method. The structure and magnetic properties of Fe2CoGa Heusler nanoparticles are investigated by x-ray diffraction, extended x-ray absorption fine structure and Mössbauer spectroscopy. The crystal structure of Fe2CoGa nanoparticles is described by the X-type structure (prototype: Li2AgSb). Magnetic measurements reveal the presence of small Fe2CoGa nanoparticles and lower magnetic moments compared with the theoretically predicted values.

  2. Variation of half metallicity and magnetism of Cd{sub 1−x}Cr{sub x}Z (Z=S, Se and Te) DMS compounds on reducing dilute limit

    Energy Technology Data Exchange (ETDEWEB)

    Saini, Hardev S.; Singh, Mukhtiyar [Department of Physics, Kurukshetra University, Kurukshetra 136119, Haryana (India); Reshak, Ali H. [School of Complex systems, FFPW, CENAKVA, University of South Bohemia in CB, Nove Hrady 37333 (Czech Republic); School of Material Engineering, Malaysia University of Perlis, P.O. Box 77, d/a Pejabat Pos Besar, 01007 Kangar, Perlis (Malaysia); Kashyap, Manish K., E-mail: manishdft@gmail.com [Department of Physics, Kurukshetra University, Kurukshetra 136119, Haryana (India)

    2013-04-15

    The electronic and magnetic properties of Cr-doped Cd-Chalcogenides, Cd{sub 1−x}Cr{sub x}Z (Z=S, Se and Te) for dopant concentration, x=0.25 and 0.125 are presented in order to search new Dilute Magnetic Semiconductor (DMS) compounds suitable for spintronic applications. The calculations have been performed using full potential Linear Augmented Plane Wave (FPLAPW) method within generalized gradient approximation (GGA) as exchange–correlation (XC) potential. The calculated results show that the doping of Cr atom induces ferromagnetism in these compounds. Moreover, all DMS compounds retain half metallicity at both dopant concentrations with 100% spin polarization at Fermi level (E{sub F}). The total magnetic moments of these compounds are mainly due to Cr-d states present at E{sub F} where as there exist small induced magnetic moments on other non-magnetic atoms as well. -- Highlights: ► The half metallicity is preserved at lower doping concentration, x=0.125. ► The HM gap increases with reduction in doping concentration from 0.25 to 0.125. ► Induced ferromagnetism is explained by p–d hybridization between Cr-d and Z-p states. ► Double exchange mechanism is responsible for observed ferromagnetism in present DMS.

  3. Extrinsic doping of the half-Heusler compounds.

    Science.gov (United States)

    Stern, Robin; Dongre, Bonny; Madsen, Georg K H

    2016-08-19

    Controlling the p- and n-type doping is a key tool to improve the power-factor of thermoelectric materials. In the present work we provide a detailed understanding of the defect thermochemistry in half-Heusler compounds. We calculate the formation energies of intrinsic and extrinsic defects in state of the art n-type TiNiSn and p-type TiCoSb thermoelectric materials. It is shown how the incorporation of online repositories can reduce the workload in these calculations. In TiNiSn we find that Ni- and Ti-interstitial defects play a crucial role in the carrier concentration of TiNiSn. Furthermore, we find that extrinsic doping with Sb can substantially enhance the carrier concentration, in agreement with experiment. In case of TiCoSb, we find ScTi, FeCo and SnSb being possible p-type dopants. While experimental work has mainly focussed on Sn-doping of the Sb site, the present result underlines the possibility to p-dope TiCoSb on all lattice sites.

  4. Emergence of thermoelectricity in Half Heusler topological semimetals with strain

    Energy Technology Data Exchange (ETDEWEB)

    Kaur, Kulwinder, E-mail: kulwinderphysics@gmail.com [Department of Physics, Panjab University, Chandigarh 160014 (India); Dhiman, Shobhna [Department of Applied Sciences, PEC University of Technology, Chandigarh 160012 (India); Kumar, Ranjan [Department of Physics, Panjab University, Chandigarh 160014 (India)

    2017-01-30

    The band structure and thermoelectric properties of Half Heusler topological materials XPtBi (X = Sc,Y, Lu) have been investigated using density functional theory and semi-classical Boltzmann equations. At 5% strain, the band gap opens in all the materials but maximum band opens in LuPtBi and acts as thermoelectric materials. We have calculated the Seebeck coefficient, electrical conductivity, electronic thermal conductivity and lattice thermal conductivity of these materials. Thermoelectric properties at high temperature and lattice thermal conductivity of these materials are studied first time in this work. The thermoelectric performance of LuPtBi is high because of low lattice thermal conductivity as compared to ScPtBi and YPtBi. - Highlights: • LuPtBi is good thermoelectric material as compared to ScPtBi and YPtBi. • These materials open band gap at 5% strain. • Thermoelectric properties and lattice thermal conductivity of these materials are studied first time in this report. • These materials serve as thermoelectric materials at 5% strain.

  5. Recent progress in half-Heusler thermoelectric materials

    Energy Technology Data Exchange (ETDEWEB)

    Huang, Lihong; Zhang, Qinyong; Yuan, Bo; Lai, Xiang [Center for Advanced Materials and Energy, Xihua University, Chengdu, Sichuan 610039 (China); Yan, Xiao, E-mail: yanxiao@mail.xhu.edu.cn [Center for Advanced Materials and Energy, Xihua University, Chengdu, Sichuan 610039 (China); Ren, Zhifeng [Department of Physics and TcSUH, University of Houston, Houston, TX 77204 (United States)

    2016-04-15

    Highlights: • Summarize the recent progress and advances in HH thermoelectric materials. • Preparing nanocomposites could reduce thermal conductivity. • Introducing enhance phonon scattering could further reduce the thermal conductivity. • Forming ternary systems to reducing the cost effectively. • The new class of HHs presents another opportunity to further optimize the HH system. - Abstract: Half-Heusler (HH) thermoelectric (TE) materials have been attracting extensive research interest over the last two decades, owing to their thermal stability, mechanical strength, and moderate ZT. This material system are potential candidates for medium to high temperature applications, which is close to the temperature range of most industrial waste heat sources. In this mini-review article, we briefly summarize the recent progress and advances in HH thermoelectric materials. Some effectively available approaches, such as HH nanocomposites to reduce thermal conductivity, using larger atomic mass and size differences to enhance phonon scattering to further reduce the thermal conductivity, forming ternary systems following the cost effective approach. In addition, new thermoelectric HH members are also discussed in this article, which points out that many new HH compounds may be possible for TE applications.

  6. Weak itinerant ferromagnetism in Heusler-type Fe2VAl0.95

    NARCIS (Netherlands)

    Sato, K.; Naka, T.; Taguchi, M.; Nakane, T.; Ishikawa, F.; Yamada, Y.; Takaesu, Y.; Nakama, T.; de Visser, A.; Matsushita, A.

    2010-01-01

    We report measurements of the magnetic, transport, and thermal properties of the Heusler-type compound Fe2VAl0.95. We show that while stoichiometric Fe2VAl is a nonmagnetic semimetal a 5% substitution on the Al site with the 3d elements Fe and V atoms leads to a ferromagnetic ground state with a

  7. Microstructure and mechanical properties of zirconium doped NiAl/Cr(Mo) hypoeutectic alloy prepared by injection casting

    Science.gov (United States)

    Sheng, L. Y.; Du, B. N.; Guo, J. T.

    2017-01-01

    NiAl based materials has been considered as most potential candidate of turbine blade, due to its excellent high-temperature properties. However the bad room-temperature properties handicap its application. In the present paper, the zirconium doped NiAl/Cr(Mo) hypoeutectic alloy is fabricated by conventional casting and injection casting technology to improve its room-temperature properties. The microstructure and compressive properties at different temperatures of the conventionally-cast and injection-cast were investigated. The results exhibit that the conventionally-cast alloy comprises coarse primary NiAl phase and eutectic cell, which is dotted with irregular Ni2AlZr Heusler phase. Compared with the conventionally-cast alloy, the injection-cast alloy possesses refined the primary NiAl, eutectic cell and eutectic lamella. In addition, the Ni2AlZr Heusler phase become smaller and distribute uniformly. Moreover, the injection casting decrease the area fraction of primary NiAl phase at the cell interior or cell boundaries. The compressive ductility and yield strength of the injection-cast alloy at room temperature increase by about 100% and 35% over those of conventionally-cast alloy, which should be ascribed to the microstructure optimization.

  8. Enhancement of thermoelectric properties in the Nb–Co–Sn half-Heusler/Heusler system through spontaneous inclusion of a coherent second phase

    Energy Technology Data Exchange (ETDEWEB)

    Buffon, Malinda L. C., E-mail: mandibuffon@mrl.ucsb.edu; Verma, Nisha; Lamontagne, Leo; Pollock, Tresa M. [Materials Department, University of California, Santa Barbara, California 93106 (United States); Materials Research Laboratory, University of California, Santa Barbara, California 93106 (United States); Laurita, Geneva [Materials Research Laboratory, University of California, Santa Barbara, California 93106 (United States); Ghadbeigi, Leila; Sparks, Taylor D. [Materials Science and Engineering, University of Utah, Salt Lake City, Utah 84112 (United States); Lloyd, Demetrious L. [Materials Research Laboratory, University of California, Santa Barbara, California 93106 (United States); Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106 (United States); Seshadri, Ram [Materials Department, University of California, Santa Barbara, California 93106 (United States); Materials Research Laboratory, University of California, Santa Barbara, California 93106 (United States); Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106 (United States)

    2016-08-21

    Half-Heusler XYZ compounds with an 18 valence electron count are promising thermoelectric materials, being thermally and chemically stable, deriving from relatively earth-abundant components, and possessing appropriate electrical transport properties. The typical drawback with this family of compounds is their high thermal conductivity. A strategy for reducing thermal conductivity is through the inclusion of secondary phases designed to minimize negative impact on other properties. Here, we achieve this through the addition of excess Co to half-Heusler NbCoSn, which introduces precipitates of a semi-coherent NbCo{sub 2}Sn Heusler phase. A series of NbCo{sub 1+x}Sn materials are characterized here using X-ray and neutron diffraction studies and electron microscopy. Electrical and thermal transport measurements and electronic structure calculations are used to understand property evolution. We find that annealing has an important role to play in determining antisite ordering and properties. Antisite disorder in the as-prepared samples improves thermoelectric performance through the reduction of thermal conductivity, but annealing during the measurement degrades properties to resemble those of the annealed samples. Similar to the more widely studied TiNi{sub 1+x}Sn system, Co addition to the NbCoSn phase results in improved thermoelectric performance through a decrease in thermal conductivity which results in a 20% improvement in the thermoelectric figure of merit, zT.

  9. Structural and electronic properties of V- and Co-doped single-walled ZnONT(8,0): Transition from semiconducting to metallic and half-metallic states

    Science.gov (United States)

    Taghavi Mendi, R.; Majidiyan Sarmazdeh, M.; Elahi, S. M.; Abolhassani, M. R.; Boochani, A.; Zelati, A.

    2015-02-01

    In this paper, some structural and electronic properties of V- and Co-doped single-walled ZnO nanotube (8,0), such as cohesive energy, geometric structure, density of states and band structure were investigated using first principles calculations. Our results showed that, first, the pure SWZnONT(8,0) can be stable and second, doped SWZnONTs(8,0) by V and Co atoms are more stable than pure SWZnONT(8,0) and TM impurities distort the structure of nanotubes around the TM impurities. The electronic results showed that pure SWZnONT(8,0) have a direct band gap about 1.443 eV and it is semiconductor. While with substituting V and Co instead of Zn in nanotube, a transition occurs from semiconducting to metallic and half-metallic states which these doped nanotubes as well as their magnetic properties are qualified for using in spintronic devices.

  10. Directional solidification and elastocaloric effect in a Ni45Mn44Sn11 magnetic shape memory alloy

    Science.gov (United States)

    Sun, Wen; Liu, Jian; Zhao, Dewei; Zhang, Mingxiao

    2017-11-01

    In this work, the microstructural evolution, texture development and elastocaloric effect have been investigated in directionally solidified Heusler-type Ni45Mn44Sn11 alloys. A multi-phase structure is found in the as-grown sample, while only L21 phase exists after annealing. By employing the infrared thermography method, a significant average temperature change of  -7.5 K is observed in the annealed Ni45Mn44Sn11 alloy with a highly oriented [2 2 0] texture. Also, the formation of cracks and its influence on the mechanical stability and elastocaloric cooling behavior have been studied.

  11. Pressure dependence of magneto-structural properties of Co-doped off-stoichiometric Ni2MnGa alloys

    Directory of Open Access Journals (Sweden)

    Arnold Z.

    2013-01-01

    Full Text Available A strong effect of pressure on magnetization and paramagnetic moment of the Co-doped Mn-rich Ni50-xCoxMn25+yGa25-y (x = 5,7,9 and y = 5,6,7,8 Heusler alloys is presented and compared with very weak pressure sensitivity of magnetization of the stoichiometric Ni2MnGa alloy. The effects of both, the pressure and the magnetic field, on temperature of the structural martensitic transition in the alloys are discussed with a use of the Clausius-Clapeyron relations. An analysis of pressure and field effects provides a possibility to evaluate structural and magnetic parts of latent heat of the martensitic transitions in the studied alloys. The Curie temperature of martensite phase of the Co-rich alloys is not affected by pressure.

  12. Possible martensitic transformation in Heusler alloy Mn{sub 2}PdSn from first principles

    Energy Technology Data Exchange (ETDEWEB)

    Feng, L., E-mail: author.fenglin@tyut.edu.cn [Key Laboratory of Advanced Transducers and Intelligent Control System, Ministry of Education, Computational Condensed Matter Physics Laboratory, Department of Physics, Taiyuan University of Technology, Taiyuan 030024 (China); Feng, X. [Key Laboratory of Advanced Transducers and Intelligent Control System, Ministry of Education, Computational Condensed Matter Physics Laboratory, Department of Physics, Taiyuan University of Technology, Taiyuan 030024 (China); Liu, E.K.; Wang, W.H.; Wu, G.H. [Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Hu, J.F.; Zhang, W.X. [Key Laboratory of Advanced Transducers and Intelligent Control System, Ministry of Education, Computational Condensed Matter Physics Laboratory, Department of Physics, Taiyuan University of Technology, Taiyuan 030024 (China)

    2016-12-01

    The tetragonal distortion, electronic structure and magnetic property of Mn{sub 2}PdSn have been systematically investigated by first-principles calculations. The results indicate that the total energy of tetragonal martensitic phase is lower than cubic austenitic phase for Mn{sub 2}PdSn. The corresponding c/a ratio and energy difference are 1.23 and 41.62 meV/f.u., respectively. This suggests that there is a great possibility for martensitic transformation to occur in Mn{sub 2}PdSn with temperature decreasing. The electronic structure shows that there are sharp DOS peaks originating from p–d hybridization in the vicinity of Fermi level in the cubic phase. And these peaks disappear or become more flat in the martensitic phase. - Highlights: • The martensitic transformation is prone to occur with temperature decreasing in Mn{sub 2}PdSn. • Electronic structure and magnetic property of Mn{sub 2}PdSn are investigated. • Both the austenitic and martensitic phases of Mn{sub 2}PdSn are ferrimagnetic.

  13. Construction of a setup for Ultrafast Electron Diffraction : First experiments on bimetallic foils and Heusler alloys

    NARCIS (Netherlands)

    van Abswoude, Peter

    2016-01-01

    Tijdsopgeloste elektronendiffractie maakt het mogelijk om filmpjes te maken van atomaire bewegingen op een tijdsschaal van 100 femtosecondes – een femtoseconde is een duizendste van een miljoenste van een miljoenste van een seconde. Dit is precies de tijdsschaal waarop bindingen tussen atomen worden

  14. Pressure effects of the ferromagnetic Heusler alloy Rh{sub 2}NiGe

    Energy Technology Data Exchange (ETDEWEB)

    Adachi, Y. [Faculty of Engineering, Yamagata University, Yonezawa 992-8510 (Japan)]. E-mail: adachy@yz.yamagata-u.ac.jp; Morita, H. [Faculty of Engineering, Yamagata University, Yonezawa 992-8510 (Japan); Kanomata, T. [Faculty of Engineering, Tohoku Gakuin University, Tagajo 985-8537 (Japan); Yanagihashi, H. [Faculty of Engineering, Tohoku Gakuin University, Tagajo 985-8537 (Japan); Yoshida, H. [Institute for Materials Research, Tohoku University, Sendai 980-8577 (Japan); Kaneko, T. [Institute for Materials Research, Tohoku University, Sendai 980-8577 (Japan); Fukumoto, H. [Faculty of Science and Technology, Ryukoku University, Otsu 520-2123 (Japan); Nishihara, H. [Faculty of Science and Technology, Ryukoku University, Otsu 520-2123 (Japan); Yamada, M. [Institute for Solid State Physics, University of Tokyo, Kashiwa 277-8581 (Japan); Goto, T. [Institute for Solid State Physics, University of Tokyo, Kashiwa 277-8581 (Japan)

    2006-08-10

    Magnetic properties under pressure have been investigated on the weak itinerant electron ferromagnet Rh{sub 2}NiGe. The pressure derivative of the Curie temperature T {sub C} has been obtained from the results of the temperature dependence of the initial permeability under pressure up to 10 kbar. The value of dT {sub C}/dp is found to be -0.60 K/kbar. The pressure change of the spontaneous magnetization {sigma} {sub s} at 4.2 K for Rh{sub 2}NiGe has been determined by the subtraction method under pressure up to 10 kbar. The value of d{sigma} {sub s}/dp is found to be -0.014 emu/g kbar. The obtained results are analyzed using the spin fluctuation theory.

  15. Microstructural evolution and creep of Fe-Al-Ta alloys

    Energy Technology Data Exchange (ETDEWEB)

    Prokopcakova, Petra; Svec, Martin [Technical University of Liberec (Czech Republic). Dept. of Material Science; Palm, Martin [Max-Planck-Institut fuer Eisenforschung GmbH, Duesseldorf (Germany). Structure and Nano-/Micromechanics of Materials

    2016-05-15

    The microstructural evolution in Fe-Al-Ta alloys containing 23 - 31 at.% Al and 1.5 - 2.2 at.% Ta has been studied in the temperature range 650 - 750 C by annealing for 1, 10, 100 and 1 000 h. The experiments confirm that in this temperature range the precipitation of the stable hexagonal C14 Laves phase is preceded by formation of coherent, metastable L2{sub 1} Heusler phase precipitates within the Fe-Al matrix. However, precipitates of C14 are observed after much shorter annealing times than previously assumed. Creep strength increases substantially with increasing Al content of the alloys because the solid solubility for Ta in the Fe-Al matrix increases with increasing Al content and solid-solution hardening contributes substantially to the observed high creep strength. It may therefore be that the microstructural changes during creep have no noticeable effect on creep strength.

  16. Magnetic antiskyrmions above room temperature in tetragonal Heusler materials

    Science.gov (United States)

    Nayak, Ajaya K.; Kumar, Vivek; Ma, Tianping; Werner, Peter; Pippel, Eckhard; Sahoo, Roshnee; Damay, Franoise; Rößler, Ulrich K.; Felser, Claudia; Parkin, Stuart S. P.

    2017-08-01

    Magnetic skyrmions are topologically stable, vortex-like objects surrounded by chiral boundaries that separate a region of reversed magnetization from the surrounding magnetized material. They are closely related to nanoscopic chiral magnetic domain walls, which could be used as memory and logic elements for conventional and neuromorphic computing applications that go beyond Moore’s law. Of particular interest is ‘racetrack memory’, which is composed of vertical magnetic nanowires, each accommodating of the order of 100 domain walls, and that shows promise as a solid state, non-volatile memory with exceptional capacity and performance. Its performance is derived from the very high speeds (up to one kilometre per second) at which chiral domain walls can be moved with nanosecond current pulses in synthetic antiferromagnet racetracks. Because skyrmions are essentially composed of a pair of chiral domain walls closed in on themselves, but are, in principle, more stable to perturbations than the component domain walls themselves, they are attractive for use in spintronic applications, notably racetrack memory. Stabilization of skyrmions has generally been achieved in systems with broken inversion symmetry, in which the asymmetric Dzyaloshinskii-Moriya interaction modifies the uniform magnetic state to a swirling state. Depending on the crystal symmetry, two distinct types of skyrmions have been observed experimentally, namely, Bloch and Néel skyrmions. Here we present the experimental manifestation of another type of skyrmion—the magnetic antiskyrmion—in acentric tetragonal Heusler compounds with D2d crystal symmetry. Antiskyrmions are characterized by boundary walls that have alternating Bloch and Néel type as one traces around the boundary. A spiral magnetic ground-state, which propagates in the tetragonal basal plane, is transformed into an antiskyrmion lattice state under magnetic fields applied along the tetragonal axis over a wide range of temperatures

  17. Magnetic properties and electronic structure of the Heusler compounds Ru2-x Fex CrSi

    Science.gov (United States)

    Hiroi, Masahiko; Rokkaku, Tsugumi; Mizutani, Sou; Fujii, Sinpei; Ishida, Shoji

    2009-03-01

    We have been trying to find Heusler compounds with high spin polarization which are robust against chemical disorders, because it is considered that disorders often degrade high spin polarization. The Heusler compound Ru2-x Fe:cCrSi is shown to be such a material from first principles band structure calculations, and it is also shown that for the Ru-rich compound antiferromagnetic states are energetically preferable to the ferromagnetic state. Experimentally the Fe-rich compound is shown to be ferromagnetic, whereas for x <= 0.2 ferromagnetism is found to disappear and a cusp in the temperature dependence in magnetization is found, which appears to indicate an antiferromagnetic transition. These results seem to agree with the theory on the whole. The experimental results are examined in the light of calculated band structures.

  18. Shell-ferromagnetism of nano-Heuslers generated by segregation under magnetic field

    Science.gov (United States)

    Çakır, A.; Acet, M.; Farle, M.

    2016-01-01

    We report on a new functional property in an AF martensitic Heusler Ni50Mn45In5, which when annealed at high temperatures under a magnetic field, segregates and forms Ni50Mn25In25 Heusler precipitates embedded in a Ni50Mn50 matrix. The precipitates are paramagnetic whereas the matrix is antiferromagnetic. However, the spins at the interface with the Ni50Mn50 matrix align with the field during their nucleation and growth and become strongly pinned in the direction of the applied field during annealing, whereas the core spins become paramagnetic. This shell-ferromagnetism persists up to 600 K and is so strongly pinned that the remanent magnetization remains unchanged, even when the field is reversed or when the temperature is cycled between low temperatures and close to the annealing temperature. PMID:27412644

  19. Resolving the phase structure of nonstoichiometric Co2FeGa Heusler nanoparticles

    Science.gov (United States)

    Wang, Changhai; Casper, Frederick; Guo, Yanzhi; Gasi, Teuta; Ksenofontov, Vadim; Balke, Benjamin; Fecher, Gerhard H.; Felser, Claudia; Hwu, Yeu-Kuang; Lee, Jey-Jau

    2012-12-01

    Heusler nanocrystals, i.e., Heusler compounds with dimensions in nanometer range are promising materials for next-generation spin-related devices. Recently, we have developed a chemical approach to prepare L21 ordered Heusler nanoparticles and characterized their size-related structure and magnetic properties. In this work, effect of precursor composition is investigated in terms of their importance in controlling the phase structure of Co2FeGa nanoparticles. The formation of the L21 ordered Co2FeGa phase is evidenced by combining X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS) spectroscopy and Mössbauer spectroscopy measurements. From XRD, precursor compositions of low Co and high Fe are associated with decreasing amounts and even disappearance of fcc Co and fcc Fe impurities. We also find that, even though the XRD data indicate only pure Co2FeGa phase in sample with excess Fe, EXAFS and Mössbauer spectroscopy data unambiguously reveal the co-existence of bcc Fe with Co2FeGa main phase.

  20. Noncollinear magnetism in Mn{sub 2}RhSn Heusler compound

    Energy Technology Data Exchange (ETDEWEB)

    Meshcheriakova, Olga

    2014-09-15

    Heusler compounds is a large class of materials, which exhibits diverse fundamental phenomena, together with the possibility of their specific tailoring for various engineering demands. Present work discusses the magnetic noncollinearity in the family of noncentrosymmetric ferrimagnetic Mn{sub 2}-based Heusler compounds. Based on the obtained experimental and theoretical results, Mn{sub 2}YZ Heusler family is suspected to provide promising candidates for the formation of the skyrmion lattice. The work is focused on Mn{sub 2}RhSn bulk polycrystalline sample, which serves as a prototype. It crystallizes in the tetragonal noncentrosymmetric structure (No. 119, I anti 4m2), which enables the anisotropic Dzyaloshinskii-Moriya (DM) exchange coupling. Additional short-range modulation, induced by the competing nearest and next-nearest interplanes Heisenberg exchange, is suppressed above the 80 K. This allows to develop the long-range modulations in the ideal ferrimagnetic structure within the ab crystallographic planes, and thus, favors to the occurrence of the skyrmion lattice within the temperature range of (80≤T≤ 270) K. The studies of Mn{sub 2}RhSn were expanded to the broad composition range and continued on thin film samples.

  1. Transport properties of high-performance all-Heusler Co2CrSi/Cu2CrAl/Co2CrSi giant magnetoresistance device

    Science.gov (United States)

    Bai, Z. Q.; Lu, Y. H.; Shen, L.; Ko, V.; Han, G. C.; Feng, Y. P.

    2012-05-01

    Transport properties of giant magnetoresistance (MR) junction consisting of trilayer Co2CrSi/Cu2CrAl/Co2CrSi Heusler alloys (L21) are studied using first-principles approach based on density functional theory and the non-equilibrium Green's function method. Highly conductive channels are found in almost the entire k-plane when the magnetizations of the electrodes are parallel, while they are completely blocked in the antiparallel configuration, which leads to a high magnetoresistance ratio (the pessimistic MR ratio is nearly 100%). Furthermore, the calculated I-V curve shows that the device behaves as a good spin valve with a considerable disparity in currents under the parallel and antiparallel magnetic configurations of the electrodes. The Co2CrSi/Cu2CrAl/Co2CrSi junction could be useful for high-performance all-metallic current-perpendicular-to-plane giant magnetoresistance reading head for the next generation high density magnetic storage.

  2. Superconducting properties of Zr1+xNi2-xGa and Zr1-xNi2+xGa Heusler compounds

    Directory of Open Access Journals (Sweden)

    Saad Alzahrani

    2017-05-01

    Full Text Available The superconducting properties of a series of Zr1+xNi2-xGa and Zr1-xNi2+xGa compounds have been investigated by x-ray diffraction, electrical resistivity, dc magnetization, and ac susceptibility measurements. While the parent compound, ZrNi2Ga, exhibited the cubic L21 Heusler structure, multiple non-cubic structures formed in the Zr and Ni rich doped materials. For x ≤ 0.3, all Zr1-xNi2+xGa compounds demonstrated superconducting behavior, but no superconductivity was observed in the Zr1+xNi2-xGa alloys for x > 0.2. The magnetization data revealed that all materials in both Zr1+xNi2-xGa and Zr1-xNi2+xGa series exhibited type-II superconductivity. With increasing doping concentration x, the paramagnetic ordering were enhanced in both systems while the superconducting properties were found to weaken. The observations are discussed considering the structural disorders in the systems.

  3. Theoretical investigations of Co{sub 2}Mn{sub 1-x}Cr{sub x}Sn and Co{sub 2}MnSn{sub 1-y}Si{sub y} pseudo-ternary alloys: First principles calculations

    Energy Technology Data Exchange (ETDEWEB)

    Charifi, Z., E-mail: charifizoulikha@gmail.com [Physics Department, Faculty of Science, University of M' sila, 28000 M' sila (Algeria); Hamad, B. [Physics Department, The University of Jordan, Amman 11942 (Jordan); Physics Department, University of Arkansas, 825 W. Dickson St., Fayetteville, AR 72701 (United States); Baaziz, H. [Physics Department, Faculty of Science, University of M' sila, 28000 M' sila (Algeria); Soyalp, F. [Yüzüncü Yıl University, Faculty of Education, Department of Physics, Van 65080 (Turkey)

    2015-11-01

    The electronic and magnetic properties of Co{sub 2}Mn{sub 1−x}Cr{sub x}Sn and Co{sub 2}MnSn{sub 1−y}Si{sub y} alloys are investigated using density functional theory (DFT) within a full-potential linearized augmented-plane-wave (FP-LAPW) method. Amongst the systems under investigation, Co{sub 2}MnSn{sub 1−y}Si{sub y} alloys show half metallicity with 100% spin polarization at the Fermi level, however Co{sub 2}Mn{sub 1−x}Cr{sub x}Sn are found to be pseudo-half metals with few minority states at the Fermi level and high spin polarization. The substitution of Si with Sn keeps the magnetic moment constant in Co{sub 2}MnSn{sub 1−y}Si{sub y} alloys, whereas the substitution of Mn with Cr decreases the magnetic moment and degrade the half-metallicity in Co{sub 2}Mn{sub 1−x}Cr{sub x}Sn alloys. The Curie temperature is calculated and it is found to be about 928 K for all Co{sub 2}MnSn{sub 1−y}Si{sub y} alloys, whereas it decreases linearly with x for Co{sub 2}Mn{sub 1−x}Cr{sub x}Sn alloys. The lattices constants, bulk modulii, energy gaps, polarization ratio and density of states are calculated and their variation versus x or y are discussed. - Highlights: • The band structure calculations show that Co{sub 2}MnSn{sub 1−y}Si{sub y} alloys are half-metallic ferromagnets. • The effect of substituting Sn by Si is a slight change in the position of the Fermi level and an increase in the band gap. • For Co{sub 2}Mn{sub 1−x}Cr{sub x}Sn alloys, the results suggest that there is a finite density of states in the minority-spin d band of manganese. • The Co{sub 2}Mn{sub 1−x}Cr{sub x}Sn compounds cannot be classified as half-metallic ferromagnets. • The substitution of Mn with Cr decreases the magnetic moment per formula unit from 5.0 to 4.0µ{sub B}.

  4. First-principles calculation on dilute magnetic alloys in zinc blend crystal structure

    Energy Technology Data Exchange (ETDEWEB)

    Ullah, Hamid, E-mail: hamidullah@yahoo.com [Department of Physics, Government Post Graduate Jahanzeb College, Saidu Sharif Swat (Pakistan); Inayat, Kalsoom [Department of Physics, Government Post Graduate Jahanzeb College, Saidu Sharif Swat (Pakistan); Khan, S.A; Mohammad, S. [Department of Physics, Materials Modeling Laboratory, Hazara University, Mansehra 21300 (Pakistan); Ali, A. [Department of Advanced Materials Science & Engineering, Hanseo University, Seosan-si, Chungnam-do 356-706 (Korea, Republic of); Alahmed, Z.A. [Department of Physics and Astronomy, King Saud University, Riyadh 11451 (Saudi Arabia); Reshak, A.H. [New Technologies-Research Center, University of West Bohemia, Univerzitni 8, 306 14 Pilsen (Czech Republic); Center of Excellence Geopolymer and Green Technology, School of Material Engineering, University Malaysia Perlis, 01007 Kangar, Perlis (Malaysia)

    2015-07-01

    Ab-initio calculations are performed to investigate the structural, electronic and magnetic properties of spin-polarized diluted magnetic alloys in zinc blende structure. The first-principles study is carried out on Mn doped III–V semiconductors. The calculated band structures, electronic properties and magnetic properties of Ga{sub 1−x}Mn{sub x}X (X=P, As) compounds reveal that Ga{sub 0.75}Mn{sub 0.25}P is half metallic turned to be metallic with increasing x to 0.5 and 0.75, whereas substitute P by As cause to maintain the half-metallicity nature in both of Ga{sub 0.75}Mn{sub 0.25}As and Ga{sub 0.5}Mn{sub 0.5}As and tune Ga{sub 0.25}Mn{sub 0.75}As to be metallic. Calculated total magnetic moments and the robustness of half-metallicity of Ga{sub 0.75}Mn{sub 0.25}P, Ga{sub 0.75}Mn{sub 0.25}As and Ga{sub 0.5}Mn{sub 0.5}As with respect to the variation in lattice parameters are also discussed. The predicted theoretical evidence shows that some Mn-doped III–V semiconductors can be effectively used in spintronic devices.

  5. VANADIUM ALLOYS

    Science.gov (United States)

    Smith, K.F.; Van Thyne, R.J.

    1959-05-12

    This patent deals with vanadium based ternary alloys useful as fuel element jackets. According to the invention the ternary vanadium alloys, prepared in an arc furnace, contain from 2.5 to 15% by weight titanium and from 0.5 to 10% by weight niobium. Characteristics of these alloys are good thermal conductivity, low neutron capture cross section, good corrosion resistance, good welding and fabricating properties, low expansion coefficient, and high strength.

  6. Elastic constants determined by nanoindentation for p-type thermoelectric half-Heusler

    Energy Technology Data Exchange (ETDEWEB)

    Gahlawat, S.; Wheeler, L.; White, K. W., E-mail: zren@uh.edu, E-mail: kwwhite@uh.edu [Department of Mechanical Engineering, University of Houston, Houston, Texas 77204 (United States); He, R.; Chen, S.; Ren, Z. F., E-mail: zren@uh.edu, E-mail: kwwhite@uh.edu [Department of Physics and TcSUH, University of Houston, Houston, Texas 77204 (United States)

    2014-08-28

    This paper presents a study of the elastic properties of the p-type thermoelectric half-Heusler material, Hf{sub 0.44}Zr{sub 0.44}Ti{sub 0.12}CoSb{sub 0.8}Sn{sub 0.2}, using nanoindentation. Large grain-sized polycrystalline specimens were fabricated for these measurements, providing sufficient indentation targets within single grains. Electron Backscatter Diffraction methods indexed the target grains for the correlation needed for our elastic analysis of individual single crystals for this cubic thermoelectric material. Elastic properties, including the Zener ratio and the Poisson ratio, obtained from the elasticity tensor are also reported.

  7. Growth and Electronic Structure of Heusler Compounds for Use in Electron Spin Based Devices

    Science.gov (United States)

    2015-06-01

    well, these were the people who kept me sane and let me think about something else for a change, like teaching me how to ski : Jason S., Evelyn, Alex S...Dissertation, 2014. [2] T. Graf, C. Felser, and S. S. Parkin. Simple rules for the understanding of Heusler compounds. Progress in Solid State Chemistry ...manganese. Journal of Physics and Chemistry of Solids, 32, 1971. doi:10.1016/S0022-3697(71)80180-4. [5] S. Sakurada and N. Shutoh. Effect of Ti

  8. Transport Properties of Heusler Compound Ru2-xFexCrSi under Pressure

    Science.gov (United States)

    Ito, Masakazu; Hisamatsu, Toru; Nakashima, Shingo; Shigeta, Iduru; Matsubayashi, Kazuyosi; Uwatoko, Yoshiya; Hiroi, Masahiko

    2011-01-01

    We investigated transport properties of the full-Heusler compound Ru2-xFexCrSi (x = 0.1), which is an insulator, under pressure P up to 8 GPa. The temperature dependence of electric resistance R(T) for Ru1.9Fe0.1CrSi is insensitive to pressure. R(T) is not described by the simple activation-type but -logT in the wide T and all P range we measured. This might be due to atomic disorder in the crystalline.

  9. 3{omega} measurements of half-Heusler thin films using a passive circuit

    Energy Technology Data Exchange (ETDEWEB)

    Mix, Christian; Jaeger, Tino; Jakob, Gerhard [Institut fuer Physik, Universitaet Mainz, Staudinger Weg 7, 55128 Mainz (Germany)

    2011-07-01

    One possibility to increase the thermoelectric Figure-of-Merit of thin films is to decrease the thermal conductivity, by replacing the thin film with a superlattice of the same thickness. This is one of the major challenges in ongoing research. For this purpose a 3{omega}-measurement system is built up to obtain the thermal conductivity of thin films. To nullify influences of active elements, a setup including a wheatstone bridge is used. Different aspects of the measurement system like the influence of thermal penetration depth and the energy losses by atmosphere are discussed. Additionally, first results on Half-Heusler thin films and superlattices are presented.

  10. Iron-based Heusler compounds Fe2YZ: Comparison with theoretical predictions of the crystal structure and magnetic properties

    Science.gov (United States)

    Gasi, T.; Ksenofontov, V.; Kiss, J.; Chadov, S.; Nayak, A. K.; Nicklas, M.; Winterlik, J.; Schwall, M.; Klaer, P.; Adler, P.; Felser, C.

    2013-02-01

    The present work reports on the new soft ferromagnetic Heusler phases Fe2NiGe, Fe2CuGa, and Fe2CuAl, which in previous theoretical studies have been predicted to exist in a tetragonal Heusler structure. Together with the known phases Fe2CoGe and Fe2NiGa these materials have been synthesized and characterized by powder x-ray diffraction, 57Fe Mössbauer spectroscopy, superconducting quantum interference device, and energy-dispersive x-ray measurements. In particular Mössbauer spectroscopy was used to monitor the degree of local atomic order/disorder and to estimate magnetic moments at the Fe sites from the hyperfine fields. It is shown that in contrast to the previous predictions all the materials except Fe2NiGa basically adopt the inverse cubic Heusler (X) structure with differing degrees of disorder. The experimental data are compared with results from ab initio electronic structure calculations on local-density approximation level incorporating the effects of atomic disorder by using the coherent potential approximation. A good agreement between calculated and experimental magnetic moments is found for the cubic inverse Heusler phases. Model calculations on various atomic configurations demonstrate that antisite disorder tends to enhance the stability of the X structure.

  11. The effect of a fourth element (Co, Cu, Fe, Pd) on the standard enthalpy of formation of the Heusler compound Ni{sub 2}MnSn

    Energy Technology Data Exchange (ETDEWEB)

    Yin, Ming, E-mail: myin1@hawk.iit.edu; Nash, Philip

    2016-05-15

    The standard enthalpies of formation of quaternary Heusler compounds (X, Ni){sub 2}MnSn (X = Co, Cu, Fe, Pd) were investigated experimentally using high temperature direct reaction calorimetry. Lattice parameters of these compounds were determined using X-ray diffraction analysis. Microstructures were identified using scanning electron microscopy and energy dispersive spectroscopy. The effect of an additional X element on the standard enthalpy of formation of the Heusler compound Ni{sub 2}MnSn is discussed. - Highlights: • Enthalpies of formation of (X,Ni){sub 2}YZ (X = Co, Cu, Fe, Pd) were measured by drop calorimeters. • Magnetic contribution to enthalpy of formation plays an important role. • Introducing a fourth element could stabilize an unstable Heusler structure. • Lattice parameters do not necessarily obey the Vegard's law. • It is possible to tailor properties of Heusler compounds with enough background information.

  12. On the Driving Forces of Magnetically Induced Martensitic Transformation in Directionally Solidified Polycrystalline Ni-Mn-In Meta-Magnetic Shape Memory Alloy with Structural Anisotropy

    Science.gov (United States)

    Hu, Qiaodan; Zhou, Zhenni; Yang, Liang; Huang, Yujin; Li, Jun; Li, Jianguo

    2017-11-01

    The magnetic anisotropy energy (MAE) in the ferromagnetic shape memory alloys (FSMAs) provides the driving forces to obtain large magnetic field induced strain (MFIS) by rearranging the martensitic variants. However, to date, no significant MAE was observed in the new class of Ni-Mn-Z ( Z = In, Sn, Sb) metamagnetic shape memory alloys (MSMAs). Here, we report a significant magnetic anisotropy in Ni48Mn35In17 Heusler alloy with a [110]A fiber texture prepared by the directional solidification. In this case, when the applied magnetic field is along the [110]A direction, a larger magnetization change is obtained compared with that of the randomly oriented samples, which increases the driving forces for the magnetically induced martensitic transformation (MIMT). In contrast, along the [110]A direction, the magnetocaloric effect (MCE) is enhanced by 60 pct, the MFIS is improved by 20 pct, and the critical field for the MFIS is reduced by 0.5 T. Such a peculiar magnetic behavior could be well explained by a proposed model on the viewpoint of the transformation of ferromagnetic austenite phase. Furthermore, considering the thermodynamics aspects, we demonstrate that two main magnetic energies of the Zeeman energy and the MAE in the MSMAs assist each other to promote the MIMT, instead of opposing each other in the FSMAs. This discovery of the strong magnetic anisotropy in highly textured polycrystals provides a feasible route to enhance the MIMT, and new insights to design and prepare the Ni-Mn-based Heusler alloys for practical applications.

  13. Synthesis and Thermoelectric Properties of Ni-Doped ZrCoSb Half-Heusler Compounds

    Directory of Open Access Journals (Sweden)

    Degang Zhao

    2018-01-01

    Full Text Available The Ni-doped ZrCo1−xNixSb half-Heusler compounds were prepared by arc-melting and spark plasma sintering technology. X-ray diffraction analysis results showed that all samples were crystallized in a half-Heusler phase. Thermoelectric properties of ZrCo1−xNixSb compounds were measured from room temperature to 850 K. The electrical conductivity and the absolute value of Seebeck coefficient increased with the Ni-doping content increasing due to the Ni substitution at Co. sites. The lattice thermal conductivity of ZrCo1−xNixSb samples was depressed dramatically because of the acoustic phonon scattering and point defect scattering. The figure of merit of ZrCo1−xNixSb compounds was improved due to the decreased thermal conductivity and improved power factor. The maximum ZT value of 0.24 was achieved for ZrCo0.92Ni0.08Sb sample at 850 K.

  14. NMR Evidence for the Topologically Nontrivial Nature in a Family of Half-Heusler Compounds

    KAUST Repository

    Zhang, Xiaoming

    2016-03-16

    Spin-orbit coupling (SOC) is expected to partly determine the topologically nontrivial electronic structure of heavy half-Heusler ternary compounds. However, to date, attempts to experimentally observe either the strength of SOC or how it modifies the bulk band structure have been unsuccessful. By using bulk-sensitive nuclear magnetic resonance (NMR) spectroscopy combined with first-principles calculations, we reveal that 209Bi NMR isotropic shifts scale with relativity in terms of the strength of SOC and average atomic numbers, indicating strong relativistic effects on NMR parameters. According to first-principles calculations, we further claim that nuclear magnetic shieldings from relativistic p1/2 states and paramagnetic contributions from low-lying unoccupied p3/2 states are both sensitive to the details of band structures tuned by relativity, which explains why the hidden relativistic effects on band structure can be revealed by 209Bi NMR isotropic shifts in topologically nontrivial half-Heusler compounds. Used in complement to surface-sensitive methods, such as angle resolved photon electron spectroscopy and scanning tunneling spectroscopy, NMR can provide valuable information on bulk electronic states.

  15. BRAZING ALLOYS

    Science.gov (United States)

    Donnelly, R.G.; Gilliland, R.G.; Slaughter, G.M.

    1962-02-20

    A brazing alloy is described which, in the molten state, is characterized by excellent wettability and flowability and is capable of forming a corrosion-resistant brazed joint. At least one component of said joint is graphite and the other component is a corrosion-resistant refractory metal. The brazing alloy consists essentially of 40 to 90 wt % of gold, 5 to 35 wt% of nickel, and 1 to 45 wt% of tantalum. (AEC)

  16. High energy high resolution photoemission from Heusler compounds in half tunnelling-junctions

    Energy Technology Data Exchange (ETDEWEB)

    Gloskovskii, Andrei; Balke, Benjamin; Ouardi, Siham; Fecher, Gerhard H.; Felser, Claudia [Institute of Inorganic and Analytical Chemistry, Johannes Gutenberg - University, Mainz (Germany); Yamamoto, Masafumi [Graduate School of Informatic Science and Technology, Hokkaido University, Sapporo (Japan)

    2008-07-01

    This work reports on high resolution photoelectron spectroscopy from the valence band of buried Co{sub 2}MnSi thin films excited by photons of about 5.9 keV energy. The measurements were performed on Co{sub 2}MnSi thin films covered by MgO(z)/AlO{sub x}(1 nm) with different thickness z from 2 nm to 20 nm of the MgO interlayer. The film structure corresponds to half a tunnelling magnetoresistive (TMR) junction. It is shown that the high energy spectra reveal the bulk electronic structure of the Heusler compound close to the Fermi energy even through the MgO layer. The high resolution measurements of the valence band close to the Fermi energy indicate a very large electron mean free path of the electrons through the MgO layer. The spectra of the buried thin films agree well with previous measurements from bulk samples.

  17. Integration of antiferromagnetic Heusler compound Ru2MnGe into spintronic devices

    Science.gov (United States)

    Balluff, Jan; Huminiuc, Teodor; Meinert, Markus; Hirohata, Atsufumi; Reiss, Günter

    2017-07-01

    We report on the integration of an antiferromagnetic Heusler compound acting as a pinning layer into magnetic tunneling junctions (MTJs). The antiferromagnet Ru2MnGe is used to pin the magnetization direction of a ferromagnetic Fe layer in MgO based thin film tunneling magnetoresistance stacks. The samples were prepared using magnetron co-sputtering. We investigate the structural properties by X-ray diffraction and reflection, as well as atomic force and high-resolution transmission electron microscopy. We find an excellent crystal growth quality with a low interface roughnesses of 1-3 Å, which is crucial for the preparation of working tunneling barriers. Using Fe as a ferromagnetic electrode material, we prepared magnetic tunneling junctions and measured the magnetoresistance. We find a sizeable maximum magnetoresistance value of 135%, which is comparable to other common Fe based MTJ systems.

  18. Properties of half-Heusler compounds TaIrGe by using first-principles calculations

    Energy Technology Data Exchange (ETDEWEB)

    Wei, JunHong [Henan Normal University, College of Physics and Information Engineering, Xinxiang, Henan (China); Henan Institute of Science and Technology, School of Mechanical and Electrical Engineering, Xinxiang, Henan (China); Wang, Guangtao [Henan Normal University, College of Physics and Information Engineering, Xinxiang, Henan (China)

    2017-05-15

    The electronic structures, optical and thermoelectric properties of ternary half-Heusler compound TaIrGe were investigated by using the first-principles and Boltzmann transport theory. Spin-orbit coupling (SOC) removed the degeneracy of VBM, and then decreased the Seebeck coefficients and power factor. From the compressive to tensile strain, the band gap gradually increases from 0.96 to 1.11 eV, accompanied by the absorption coefficient peak red-shift. The effective mass (m{sup *}{sub DOS}) of VBM and CBM gradually increases from the compressive to tensile strain, which enhances the Seebeck coefficient and power factor. Our results indicate that the electronic structures, optical and thermoelectric properties of TaIrGe can be effectively tuned by the strain and TaIrGe can be used as an important photoelectric and thermoelectric material in the future. (orig.)

  19. Magnetic and magnetocaloric properties of Ni50-xCuxMn39Sn11 alloys

    Science.gov (United States)

    Kaya, Melike; Dincer, Ilker

    2017-11-01

    The effect of Cu substitution on the martensitic transition and magnetocaloric properties of arc-melted Ni50-xCuxMn39Sn11 (x = 6 and 7) Heusler alloys are investigated by differential scanning calorimetry, X-ray powder diffraction, scanning electron microscopy and magnetic measurements. According to XRD patterns, while Ni44Cu6Mn39Sn11 alloy exhibit orthorhombic structure, Ni43Cu7Mn39Sn11 alloy crystallize cubic L21 structure at room temperature. The substitution of Cu for Ni leads to decreasing on the martensitic transition temperatures to lower values. The magnetic entropy changes calculated from M(T) curves, for avoiding hysteresis losses in the vicinity of the martensitic transition region, by using Maxwell relation. The maximum magnetic entropy change, ΔSM is found 11.0 J kg-1 K-1 for Ni43Cu7Mn39Sn11 alloy around the martensitic transition region, which is nearly twice as large as the Ni44Cu6Mn39Sn11 alloy under the magnetic field changing from 0 to 2 T.

  20. Electrical Resistance Alloys and Low-Expansion Alloys

    DEFF Research Database (Denmark)

    Kjer, Torben

    1996-01-01

    The article gives an overview of electrical resistance alloys and alloys with low thermal expansion. The electrical resistance alloys comprise resistance alloys, heating alloys and thermostat alloys. The low expansion alloys comprise alloys with very low expansion coefficients, alloys with very low...

  1. Large linear magnetoresistance and shubnikov-de hass oscillations in single crystals of YPdBi heusler topological insulators

    KAUST Repository

    Wang, Wenhong

    2013-07-12

    We report the observation of a large linear magnetoresistance (MR) and Shubnikov-de Hass (SdH) quantum oscillations in single crystals of YPdBi Heusler topological insulators. Owning to the successfully obtained the high-quality YPdBi single crystals, large non-saturating linear MR of as high as 350% at 5K and over 120% at 300K under a moderate magnetic field of 7T is observed. In addition to the large, field-linear MR, the samples exhibit pronounced SdH quantum oscillations at low temperature. Analysis of the SdH data manifests that the high-mobility bulk electron carriers dominate the magnetotransport and are responsible for the observed large linear MR in YPdBi crystals. These findings imply that the Heusler-based topological insulators have superiorities for investigating the novel quantum transport properties and developing the potential applications.

  2. Design of L2_1-type antiferromagnetic semiconducting full-Heusler compounds: A first principles DFT+GW study

    OpenAIRE

    Tas, M.; Sasioglu, E.; Friedrich, C.; Blugel, S.; Galanakis, I.

    2016-01-01

    Antiferromagnetic spintronics is an on-going growing field of research. Employing both standard density functional theory and the $GW$ approximation within the framework of the FLAPW method, we study the electronic and magnetic properties of seven potential antiferromagnetic semiconducting Heusler compounds with 18 (or 28 when Zn is present) valence electrons per unit cell. We show that in these compounds G-type antiferromagnetism is the ground state and that they are all either emiconductors...

  3. Orthodontic silver brazing alloys.

    Science.gov (United States)

    Brockhurst, P J; Pham, H L

    1989-10-01

    Orthodontic silver brazing alloys suffer from the presence of cadmium, excessive flow temperatures, and crevice corrosion on stainless steel. Seven alloys were examined. Two alloys contained cadmium. The lowest flow temperature observed was 629 degrees C for a cadmium alloy and 651 degrees C for two cadmium free alloys. Three alloys had corrosion resistance superior to the other solders. Addition of low melting temperature elements gallium and indium reduced flow temperature in some cases but produced brittleness in the brazing alloy.

  4. Magnetic properties and magnetocaloric effect in Ni–Mn–Sn alloys

    Energy Technology Data Exchange (ETDEWEB)

    Dan, N.H., E-mail: dannh@ims.vast.ac.vn [Institute of Materials Science, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet, Cau Giay, Hanoi (Viet Nam); Duc, N.H.; Yen, N.H.; Thanh, P.T. [Institute of Materials Science, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet, Cau Giay, Hanoi (Viet Nam); Bau, L.V.; An, N.M. [Hong Duc University, 565 Quang Trung, Dong Ve, Thanh Hoa (Viet Nam); Anh, D.T.K.; Bang, N.A.; Mai, N.T. [Faculty of Physics, VNU University of Science, 334 Nguyen Trai, Hanoi (Viet Nam); Anh, P.K. [Vietnam Academy of Military Science, 322 Le Trong Tan, Thanh Xuan, Hanoi (Viet Nam); Thanh, T.D. [Institute of Materials Science, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet, Cau Giay, Hanoi (Viet Nam); Department of Physics, Chungbuk National University, Cheongju 361-763 (Korea, Republic of); Phan, T.L. [Department of Physics, Chungbuk National University, Cheongju 361-763 (Korea, Republic of); Yu, S.C., E-mail: scyu@chungbuk.ac.kr [Department of Physics, Chungbuk National University, Cheongju 361-763 (Korea, Republic of)

    2015-01-15

    Magnetic and magnetocaloric properties in Ni{sub 50}Mn{sub 50−x}Sn{sub x} alloys with wide range of the Sn-concentration (x=0–40) were investigated. The alloys were prepared by arc-melting and subsequently annealing at 850 °C for 4 h. The X-ray diffraction analyses manifest the formation of the crystalline phases (Ni{sub 2}MnSn, NiMn, Ni{sub 3}Sn{sub 2}, Mn{sub 3}Sn, and MnSn{sub 2}) in the alloys with various compositions and fabrication conditions. With increasing x, the saturation magnetization first increases from near zero (at x=10) to above 40 emu/g (at x=20) and then decreases to below 10 emu/g (at x=40) for both the as-melted and annealed cases. The martensitic–austenitic transition was observed in the alloys with a narrow range of x (13–15). The magnetic transitions in the alloy can be controlled by changing Sn-concentration. The alloy reveals both the positive and negative entropy changes with quite large magnitude (∆S{sub m}>1 J/kg K with ∆H=12 kOe) with appropriate compositions and annealing conditions. - Highlights: • Crystalline phases and magnetic properties in Ni{sub 50}Mn{sub 50−x}Sn{sub x} alloys (x=0–40). • Simultaneous transitions of structural and magnetic phases. • Coexistence of positive and negative giant magnetocaloric effect in Heusler alloys. • Tuning giant magnetocaloric effect in room temperature region.

  5. Influence of growth temperature on phase and intermixing in Ni 2MnIn Heusler films on InAs(0 0 1)

    Science.gov (United States)

    Zolotaryov, A.; Volland, A.; Heyn, Ch.; Novikov, D.; Stryganyuk, G.; Kornowski, A.; Vossmeyer, T.; Albrecht, O.; Coric, E.; Hansen, W.

    2009-04-01

    This paper reports on the influence of deposition temperature on structure and morphology of uncapped Ni 2MnIn Heusler films grown by molecular beam epitaxy on InAs(0 0 1). Deposition temperatures between 80 and 360 °C and layer thicknesses between 20 and 100 nm have been used. Our studies reveal that during growth beyond 80 °C an intermixing layer arises at the Heusler/substrate interface that is formed by diffusion of arsenic from the substrate. The intermixing process, which is found to take place via interstitial sites, becomes increasingly severe with increasing growth temperature. Furthermore, we find that the films grown at 80 °C are polycrystalline with crystallites in the B2 phase. At 250 °C the films are found to be single-crystalline and pseudomorphically strained in the B2 phase. The desired L2 1 phase and single-crystalline Heusler films are observed at a growth temperature of 300 °C. Interestingly, Heusler films in L2 1 phase are found to have a (1 1 0) surface orientation in contrast to the InAs(0 0 1) substrate crystal. At temperatures higher than 300 °C, strong intermixing and a morphological degradation of the L2 1 Heusler films is observed.

  6. The investigation of electronic, magnetic, mechanical, and lattice dynamical properties of PdMX (M  =  Cr, Fe and X  =  Si and Ge) ferromagnetic half-Heusler metallics: an ab initio study

    Science.gov (United States)

    Erkisi, Aytac; Surucu, Gokhan

    2017-06-01

    PdMX (M  =  Cr, Fe and X  =  Si, Ge) half-Heusler alloys, have been investigated in cubic C1 b crystal structure which conforms to F\\bar{4}3m space group by using local spin density approximation (LSDA) within the density functional theory (DFT). Firstly, for all materials, the most stable structural phase, which is type-II phase, has been determined. Then, all materials have been considered in ferromagnetic (FM), paramagnetic (PM) and antiferromagnetic (AFM) orders in the most stable type-II structure. The estimated Curie temperatures by using energy differences between FM and PM phases in mean field approximation have been found to be noticeably higher than the room temperature. After the determination of the most stable magnetic phase, their full structural, mechanical, electronic, and lattice dynamical properties have been studied in the most stable magnetic and structural phase. The calculated electronic band structure and total electronic density of states (DOS) have showed that there is no band gap revealing metallic behavior. The estimated elastic constants and calculated phonon dispersion curves have confirmed the stability of FM phase, both mechanically and dynamically.

  7. Technical Operations Support III (TOPS III). Task Order 0061: Fundamental Theory Based Assessment of Thermoelectric Merit Factor for Heusler Alloys

    Science.gov (United States)

    2010-10-01

    can yet be commercialized. Moreover, these materials are not very practical due to scarcity of the elements, toxicity and decomposition-evaporation...are not very practical due to scarcity of the elements, toxicity and decomposition-evaporation problems at elevated temperatures [1]. Today, there...Maximum zT: 0.8 at over 1000K Atoms: 12 Lanthanum Aluminium Silicide (LaAlSi) Experimental Structure: cubic [a b c]: 5.94 Bandgap: (-) DFT(GGA) Energy

  8. Tunnel magnetoresistance in epitaxially grown magnetic tunnel junctions using Heusler alloy electrode and MgO barrier

    Energy Technology Data Exchange (ETDEWEB)

    Tsunegi, S.; Sakuraba, Y.; Oogane, M.; Telling, N. D.; Shelford, L. R.; Arenholz, E.; van der Laan, G.; Hicken, R. J.; Takanashi, K.; Ando, Y.

    2009-07-01

    Epitaxially grown magnetic tunnel junctions (MTJs) with a stacking structure of Co{sub 2}MnSi/MgO/CoFe were fabricated. Their tunnel magnetoresistance (TMR) effects were investigated. The TMR ratio and tunnelling conductance characteristics of MTJs were considerably different between those with an MgO barrier prepared using sputtering (SP-MTJ) and those prepared using EB evaporation (EB-MTJ). The EB-MTJ exhibited a very large TMR ratio of 217% at room temperature and 753% at 2 K. The bias voltage dependence of the tunnelling conductance in the parallel magnetic configuration for the EB-MTJ suggests that the observed large TMR ratio at RT results from the coherent tunnelling process through the crystalline MgO barrier. The tunnelling conductance in the anti-parallel magnetic configuration suggests that the large temperature dependence of the TMR ratio results from the inelastic spin-flip tunnelling process.

  9. Tunnel magnetoresistance effect and interface study in magnetic tunnel junctions using epitaxial Fe2CrSi Heusler alloy electrode

    Science.gov (United States)

    Wang, Yu-Pu; Han, Gu-Chang; Lu, Hui; Qiu, Jinjun; Yap, Qi-Jia; Ji, Rong; Teo, Kie-Leong

    2013-07-01

    We report the studies of magnetic tunnel junctions (MTJs) using epitaxially grown Fe2CrSi (FCS) as a bottom electrode. A tunnel magnetoresistance (TMR) ratio of 2.5% was obtained for MTJ at room temperature. The low TMR ratio is attributed to the oxidation of FCS at the interface with MgO barrier. With the insertion of 0.3 nm Mg layer between the FCS and MgO barrier layers, the TMR ratio increases to 8.1%. X-ray Photoelectron Spectroscopy results show that the FCS film is most likely terminated at Fe and Si atomic layers, which is found to be bonded to oxygen at the interface, while Cr remains at metallic state. Post-annealing effect shows that TMR first increases with annealing temperature (Ta) due to improvement in crystalline structure of MgO and top electrode and then decreases due to oxidation of the bottom electrode. The TMR finally disappears due to the depinning of top electrode induced by Mn diffusion at high Ta.

  10. A First Principle Calculation of Full-Heusler Alloy Co2TiAl: LSDA+U Method

    OpenAIRE

    Rai, D. P.; Thapa, R.K.

    2012-01-01

    We performed the structure optimization of Co2TiAl based on the generalized gradient approximation (GGA) and linearized augmented plane wave (LAPW) method. The calculation of electronic structure was based on the full-potential linear augmented plane wave (FP-LAPW) method and local spin density approximation exchange correlation LSDA+U. We also studied the impact of the Hubbard potential or onsite Coulomb repulsion (U) on electronic structure; the values are varied within reasonable limits to...

  11. Spin injection from epitaxial Heusler alloy thin films into InGaAs/GaAs quantum wells

    DEFF Research Database (Denmark)

    Damsgaard, Christian Danvad

    2006-01-01

    to typically 0.02-0.1 Ωmm2 for Fe and Co contacts but two orders of magnitude higher for the Co2MnGa contacts. Point contact Andreev reflection measurements on an off-stoichiometric thin film (Co2.4Mn1.6Ga) show a spin polarization of P ≈ 50 %. Furthermore spin injection into a InGaAs/GaAs quantum well have...

  12. Band structure and thermoelectric properties of half-Heusler semiconductors from many-body perturbation theory

    Science.gov (United States)

    Zahedifar, Maedeh; Kratzer, Peter

    2018-01-01

    Various ab initio approaches to the band structure of A NiSn and A CoSb half-Heusler compounds (A = Ti, Zr, Hf) are compared and their consequences for the prediction of thermoelectric properties are explored. Density functional theory with the generalized-gradient approximation (GGA), as well as the hybrid density functional HSE06 and ab initio many-body perturbation theory in the form of the G W0 approach, are employed. The G W0 calculations confirm the trend of a smaller band gap (0.75 to 1.05 eV) in A NiSn compared to the A CoSb compounds (1.13 to 1.44 eV) already expected from the GGA calculations. While in A NiSn materials the G W0 band gap is 20% to 50% larger than in HSE06, the fundamental gap of A CoSb materials is smaller in G W0 compared to HSE06. This is because G W0 , similar to PBE, locates the valence band maximum at the L point of the Brillouin zone, whereas it is at the Γ point in the HSE06 calculations. The differences are attributed to the observation that the relative positions of the d levels of the transition metal atoms vary among the different methods. Using the calculated band structures and scattering rates taking into account the band effective masses at the extrema, the Seebeck coefficients, thermoelectric power factors, and figures of merit Z T are predicted for all six half-Heusler compounds. Comparable performance is predicted for the n -type A NiSn materials, whereas clear differences are found for the p -type A CoSb materials. Using the most reliable G W0 electronic structure, ZrCoSb is predicted to be the most efficient material with a power factor of up to 0.07 W/(K2 m) at a temperature of 600 K. We find strong variations among the different ab initio methods not only in the prediction of the maximum power factor and Z T value of a given material, but also in comparing different materials to each other, in particular in the p -type thermoelectric materials. Thus we conclude that the most elaborate, but also most costly G W0

  13. FP-LMTO investigation of the structural, electronic and magnetic properties of Heusler compounds Ru2CrZ(Ge, Sn, Si)

    Science.gov (United States)

    Bahlouli, S.; Aarizou, Z.; Elchikh, M.; Vergoten, G.

    2013-01-01

    We report structural and magnetic properties as well as band structures and density of states (DOS) of full Heusler Ru2CrSi, Ru2CrGe and Ru2CrSn. This was performed in the frame work of self-consistent first-principle calculations, using the Full-Potential Linearized Muffin Tin Orbital (FP-LMTO) method based on the Generalized Gradient Approximation (GGA), to investigate the structure and magnetic properties through the calculation of the electronic structure, equilibrium lattice constant and magnetic properties. Our results will show that our three Full-Heusler compounds are antiferromagnets.

  14. Magnetic vortex in epitaxially-grown Co{sub 2}(Fe,Mn)Si alloy

    Energy Technology Data Exchange (ETDEWEB)

    Yamamoto, T., E-mail: tyamamoto@imr.tohoku.ac.jp; Takanashi, K. [Institute for Materials Research, Tohoku University, Sendai 980-8577 (Japan); Seki, T. [Institute for Materials Research, Tohoku University, Sendai 980-8577 (Japan); PRESTO, Japan Science and Technology Agency, Saitama 322-0012 (Japan); Kotsugi, M. [Tokyo University of Science, Katsushika 125-8525 (Japan)

    2016-04-11

    We report magnetic vortex formation in epitaxially grown Co{sub 2}Fe{sub 0.4}Mn{sub 0.6}Si (CFMS) Heusler alloy discs that was confirmed using photoemission electron microscopy and the magneto-optical Kerr effect. The phase diagram of magnetic domain structures as functions of the disc thickness (t) and diameter (D) indicates that the magnetic vortex is stable in wide ranges of t and D even for the epitaxial CFMS. The annihilation field of vortex core depended not only on the disc aspect ratio but also on t. Numerical simulation suggests that this t dependence results from extrinsic pinning of a vortex core due to the epitaxial growth.

  15. High electron mobility and large magnetoresistance in the half-Heusler semimetal LuPtBi

    KAUST Repository

    Hou, Zhipeng

    2015-12-18

    Materials with high carrier mobility showing large magnetoresistance (MR) have recently received much attention because of potential applications in future high-performance magnetoelectric devices. Here, we report on an electron-hole-compensated half-Heusler semimetal LuPtBi that exhibits an extremely high electron mobility of up to 79000cm2/Vs with a nonsaturating positive MR as large as 3200% at 2 K. Remarkably, the mobility at 300 K is found to exceed 10500cm2/Vs, which is among the highest values reported in three-dimensional bulk materials thus far. The clean Shubnikov–de Haas quantum oscillation observed at low temperatures and the first-principles calculations together indicate that the high electron mobility is due to a rather small effective carrier mass caused by the distinctive band structure of the crystal. Our findings provide a different approach for finding large, high-mobility MR materials by designing an appropriate Fermi surface topology starting from simple electron-hole-compensated semimetals.

  16. Simulation of stress-modulated magnetization precession frequency in Heusler-based spin torque oscillator

    Energy Technology Data Exchange (ETDEWEB)

    Huang, Houbing, E-mail: hbhuang@ustb.edu.cn; Zhao, Congpeng; Ma, Xingqiao, E-mail: xqma@sas.ustb.edu.cn

    2017-03-15

    We investigated stress-modulated magnetization precession frequency in Heusler-based spin transfer torque oscillator by combining micromagnetic simulations with phase field microelasticity theory, by encapsulating the magnetic tunnel junction into multilayers structures. We proposed a novel method of using an external stress to control the magnetization precession in spin torque oscillator instead of an external magnetic field. The stress-modulated magnetization precession frequency can be linearly modulated by externally applied uniaxial in-plane stress, with a tunable range 4.4–7.0 GHz under the stress of 10 MPa. By comparison, the out-of-plane stress imposes negligible influence on the precession frequency due to the large out-of-plane demagnetization field. The results offer new inspiration to the design of spin torque oscillator devices that simultaneously process high frequency, narrow output band, and tunable over a wide range of frequencies via external stress. - Highlights: • We proposed stress-modulated magnetization precession in spin torque oscillator. • The magnetization precession frequency can be linearly modulated by in-plane stress. • The stress also can widen the magnetization frequency range 4.4–7.0 GHz. • The stress-modulated oscillation frequency can simplify STO devices.

  17. Structural and magnetic properties in Heusler-type ferromagnet/antiferromagnet bilayers

    Science.gov (United States)

    Fukatani, N.; Inagaki, K.; Miyawaki, T.; Ueda, K.; Asano, H.

    2013-05-01

    The structure and magnetic properties of Heusler ferromagnet/antiferromagnet (FM/AFM) bilayers were investigated. Structural characterization revealed that Fe2CrSi/Ru2MnGe bilayers were epitaxially grown with an L21 ordered structure when the Ru2MnGe growth temperature was 573 K. The magnetization curve indicates that exchange bias occurs in the Fe2CrSi/Ru2MnGe bilayers at 77 K. The appearance of an exchange-anisotropy field Hex depends on the growth of Ru2MnGe layer, indicating that the exchange bias originates from the epitaxial Fe2CrSi/Ru2MnGe interface. The exchange anisotropy energy Jk of the Fe2CrSi/Ru2MnGe and Co2MnGe/Ru2MnGe bilayer systems appears to follow a Heisenberg-like exchange coupling model. This suggests that the Cr and Mn interface atoms in the FM layers play significant roles in exchange coupling in the Fe2CrSi/Ru2MnGe and Co2MnGe/Ru2MnGe bilayer systems, respectively.

  18. A first-principles DFT+GW study of spin-filter and spin-gapless semiconducting Heusler compounds

    Science.gov (United States)

    Tas, M.; Şaşıoğlu, E.; Friedrich, C.; Galanakis, I.

    2017-11-01

    Among Heusler compounds, the ones being magnetic semiconductors (also known as spin-filter materials) are widely studied as they offer novel functionalities in spintronic and magnetoelectronic devices. The spin-gapless semiconductors are a special case. They possess a zero or almost-zero energy gap in one of the two spin channels. We employ the GW approximation to simulate the electronic band structure of these materials. Our results suggest that in most cases the use of GW self energy instead of the usual density functionals is important to accurately determine the electronic properties of magnetic semiconductors.

  19. Transport Properties of Heusler Compound Ru{sub 2-x}Fe{sub x}CrSi under Pressure

    Energy Technology Data Exchange (ETDEWEB)

    Ito, Masakazu; Hisamatsu, Toru; Nakashima, Shingo; Shigeta, Iduru; Hiroi, Masahiko [Graduate School of Science and Engineering, Kagoshima University, Korimoto 1-21-35, Kagoshima 890-0065 (Japan); Matsubayashi, Kazuyosi; Uwatoko, Yoshiya, E-mail: showa@sci.kagoshima-u.ac.jp [Institute for Solid State Physics, University of Tokyo, Kashiwanoha, Kashiwa, Chiba 277-8581 (Japan)

    2011-01-01

    We investigated transport properties of the full-Heusler compound Ru{sub 2-x}Fe{sub x}CrSi (x = 0.1), which is an insulator, under pressure P up to 8 GPa. The temperature dependence of electric resistance R(T) for Ru{sub 1.9}Fe{sub 0.1}CrSi is insensitive to pressure. R(T) is not described by the simple activation-type but -logT in the wide T and all P range we measured. This might be due to atomic disorder in the crystalline.

  20. The electronic, structural and magnetic properties of Heusler compounds ZrCrCoZ(Z=B, Al, Ga, In): A first-principles study

    Science.gov (United States)

    Guo, R. K.; Liu, G. D.; Lin, T. T.; Wang, W.; Wang, L. Y.; Dai, X. F.

    2018-02-01

    It is predicted that the ZrCrCoZ(Z=B, Al, Ga, In) compounds with LiMnPbSn-type structure are half-metallic ferrimagnets with a large half-metallic gap by the first-principles calculations. The half-metallicity of the ZrCrCoZ(Z=B, Al, Ga, In) compounds are quite robust to the axial and uniaxial strain. The total magnetic moments in per unit cell are 4 μB for the ZrCrCoZ(Z=B, Al, Ga, In) compounds and follow the Slater-Pauling rule, which can be attributed to the great spin-splitting. The calculated formation energies are negative for all the ZrCrCoZ(Z=B, Al, Ga, In) compounds, which indicates that those compounds are in the thermodynamic stability and the possibility of synthesis in experiment.

  1. Spin-transfer magnetization switching in ordered alloy-based nanopillar devices

    Energy Technology Data Exchange (ETDEWEB)

    Mitani, S [National Institute for Materials Science, Tsukuba 305-0047 (Japan)

    2011-09-28

    This paper reviews spin-transfer magnetization switching in ordered alloy-based nanopillar devices. L1{sub 0}-ordered FePt was used for one of the earliest demonstrations of spin-transfer switching in perpendicularly magnetized systems. The behaviour of magnetization switching deviates from the predictions based on a macro-spin model, suggesting incoherent magnetization switching in the system with a large perpendicular magnetic anisotropy. The effect of a 90{sup 0} spin injector on spin-transfer switching was also examined using L1{sub 0}-ordered FePt. Full-Heusler alloys are in another fascinating material class for spin-transfer switching because of their high-spin polarization of conduction electrons and possible small magnetization damping. A B2-ordered Co{sub 2}FeAl{sub 0.5}Si{sub 0.5}-based device showed a low intrinsic critical current density of 9.3 x 10{sup 6} A cm{sup -2} for spin-transfer switching as well as a relatively large current-perpendicular-to-plane giant-magnetoresistance (CPP-GMR) up to {approx}9%. The specific physical properties of ordered alloys may be useful for fundamental studies and applications in spin-transfer switching.

  2. Spin-transfer magnetization switching in ordered alloy-based nanopillar devices

    Science.gov (United States)

    Mitani, S.

    2011-09-01

    This paper reviews spin-transfer magnetization switching in ordered alloy-based nanopillar devices. L10-ordered FePt was used for one of the earliest demonstrations of spin-transfer switching in perpendicularly magnetized systems. The behaviour of magnetization switching deviates from the predictions based on a macro-spin model, suggesting incoherent magnetization switching in the system with a large perpendicular magnetic anisotropy. The effect of a 90° spin injector on spin-transfer switching was also examined using L10-ordered FePt. Full-Heusler alloys are in another fascinating material class for spin-transfer switching because of their high-spin polarization of conduction electrons and possible small magnetization damping. A B2-ordered Co2FeAl0.5Si0.5-based device showed a low intrinsic critical current density of 9.3 × 106 A cm-2 for spin-transfer switching as well as a relatively large current-perpendicular-to-plane giant-magnetoresistance (CPP-GMR) up to ~9%. The specific physical properties of ordered alloys may be useful for fundamental studies and applications in spin-transfer switching.

  3. A comparison of thermoelectric phenomena in diverse alloy systems

    Energy Technology Data Exchange (ETDEWEB)

    Cook, Bruce [Iowa State Univ., Ames, IA (United States)

    1999-01-01

    The study of thermoelectric phenomena in solids provides a wealth of opportunity for exploration of the complex interrelationships between structure, processing, and properties of materials. As thermoelectricity implies some type of coupled thermal and electrical behavior, it is expected that a basic understanding of transport behavior in materials is the goal of such a study. However, transport properties such as electrical resistivity and thermal diffusivity cannot be fully understood and interpreted without first developing an understanding of the material's preparation and its underlying structure. It is the objective of this dissertation to critically examine a number of diverse systems in order to develop a broad perspective on how structure-processing-property relationships differ from system to system, and to discover the common parameters upon which any good thermoelectric material is based. The alloy systems examined in this work include silicon-germanium, zinc oxide, complex intermetallic compounds such as the half-Heusler MNiSn, where M = Ti, Zr, or Hf, and rare earth chalcogenides.

  4. Insights into Ultrafast Demagnetization in Pseudogap Half-Metals

    National Research Council Canada - National Science Library

    Mann, Andreas; Walowski, Jakob; Münzenberg, Markus; Maat, Stefan; Carey, Matthew J; Childress, Jeffrey R; Mewes, Claudia; Ebke, Daniel; Drewello, Volker; Reiss, Günter; Thomas, Andy

    2012-01-01

    .... To gain new and relevant insights, we performed ultrafast optical pump-probe experiments to characterize the demagnetization processes of highly spin-polarized magnetic thin films on a femtosecond time scale...

  5. Temperature and pressure dependent structural and thermo-physical properties of quaternary CoVTiAl alloy

    Science.gov (United States)

    Yousuf, Saleem; Gupta, Dinesh C.

    2017-09-01

    Investigation of band structure and thermo-physical response of new quaternary CoVTiAl Heusler alloy within the frame work of density functional theory has been analyzed. 100% spin polarization with ferromagnetic stable ground state at the optimized lattice parameter of 6.01 Å is predicted for the compound. Slater-Pauling rule for the total magnetic moment of 3 μB and an indirect semiconducting behavior is also seen for the compound. In order to perfectly analyze the thermo-physical response, the lattice thermal conductivity and thermodynamic properties have been calculated. Thermal effects on some macroscopic properties of CoVTiAl are predicted using the quasi-harmonic Debye model, in which the lattice vibrations are taken into account. The variations of the lattice constant, volume expansion coefficient, heat capacities, and Debye temperature with pressure and temperature in the ranges of 0 GPa to 15 GPa and 0 K to 800 K have been obtained.

  6. Half-metallic and insulating natures in Ru-based ordered double perovskite oxides Ba{sub 2}X{sup III}Ru{sup V}O{sub 6} (X = V, Cr) induced by 3d-t{sub 2g}{sup n} orbital filling

    Energy Technology Data Exchange (ETDEWEB)

    Saad, H.-E.M. Musa, E-mail: musa.1964@gmail.com; Althoyaib, S.S.

    2017-04-01

    In this paper, we present results of a comprehensive systemic study of the crystal, electronic and magnetic structures on two members of Ru-based ordered double perovskite oxides Ba{sub 2}XRuO{sub 6} (X = V, Cr). For the corporate compound, the analysis of density of states (DOS) results suggests that the 3d-t{sub 2g} orbital filling plays a major role in governing the conduction mechanism in these systems. The DOS and magnetic results show that Ba{sub 2}XRuO{sub 6} exhibits half-metallic (HM) nature as X = V, where the electronic structure of Ba{sub 2}V{sup III}Ru{sup V}O{sub 6} with 3d-t{sub 2g}{sup 2} behaves like that of HM ferrimagnetic (FI), switches to compensate FI insulating behavior as X = Cr, with an extra electron filled 3d-t{sub 2g}{sup 3} in Ba{sub 2}Cr{sup III}Ru{sup V}O{sub 6}. We find, on consideration of electron correlation (LSDA+U) and spin-orbital coupling (SOC) effects that the electronic structure of Ba{sub 2}XRuO{sub 6} takes a HM nature, whereas it is completely transformed to insulating nature once an extra electron filled the 3d-t{sub 2g} orbitals in X = Cr case. Such tuning is accompanied by spin-state hopping of one electron from half-filled spin-state in Ru{sup V} (t{sub 2g}{sup 3} e{sub g}{sup 0}) to two and three occupied spin-state in V{sup III} (t{sub 2g}{sup 2} e{sub g}{sup 0}) and Cr{sup III} (t{sub 2g}{sup 3} e{sub g}{sup 0}), respectively. The charge distribution results show that this extra electron occupies chiefly the spin-down of conduction orbitals and plays a major role in determining the electronic and magnetic structures of Ba{sub 2}XRuO{sub 6} system. - Highlights: • Half-metallic and insulating natures are observed in Ba{sub 2}XRuO{sub 6} (X = V, Cr). • 3d-t{sub 2g}{sup n} orbitals filling plays a major role in governing the conduction mechanism. • LSDA+U method under density functional theory (DFT) is considered. • HM ferrimagnetic (FI) (X = V) switch to compensate FI insulating (X = Cr).

  7. Anti-site-induced diverse diluted magnetism in LiMgPdSb-type CoMnTiSi alloy

    Science.gov (United States)

    Lin, T. T.; Dai, X. F.; Guo, R. K.; Cheng, Z. X.; Wang, L. Y.; Wang, X. T.; Liu, G. D.

    2017-02-01

    The effect of three kinds of anti-site disorder to electronic structure and magnetic properties of the LiMgPdSb-type CoMnTiSi alloy are investigated. It was found the Mn-Ti anti-site disorder can induce the diluted magnetism in CoMnTiSi matrix. The magnetic structure has an oscillation between the ferromagnetic and antiferromagnetic states with the different degree of Mn-Ti anti-site disorder. Two novel characteristics: the diluted antiferromagnetic half-metallicity and the diluted zero-gap half-metallity are found in the different degree range of the Mn-Ti anti-site disorder. The Co-Mn and Co-Ti anti-site disorder have little effect on the magnetic properties. The width of energy gap and the intensity of DOS at the Fermi level can be adjusted by the degree of Co-Mn or Co-Ti anti-site disorder. The independent control to the carrier concentration and magnetization can be realized by introducing the different anti-site disorder.

  8. Rhenium alloying of tungsten heavy alloys

    Energy Technology Data Exchange (ETDEWEB)

    Bose, A.; Jerman, G.; German, R.M.

    1989-06-01

    Alloying experiments have been performed using rhenium additions to a classic 90 mass% tungsten heavy alloy. The mixed powder system was liquid phase sintered to full density at 1500/sup 0/C in 60 min. The rhenium modified alloys exhibited a smaller grain size, higher hardness, higher strength, and lower ductility than the unalloyed system. For an alloy with a composition of 84W-6Re-8Ni-2Fe, the sintered density was 17,4 Mg/m/sup 3/ with a yield strength of 815 MPa, tensile strength of 1180 MPa, and elongation to failure of 13%. This property combination results from the aggregate effects of grain size reduction and solid solution hardening due to rhenium. In the unalloyed system these properties require post-sintering swaging and aging; thus, alloying with rhenium is most attractive for applications where netshaping is desired, such as by powder injection molding. (orig.).

  9. Rhenium alloying of tungsten heavy alloys

    Energy Technology Data Exchange (ETDEWEB)

    German, R.M.; Bose, A.; Jerman, G.

    1989-01-01

    Alloying experiments were performed using rhenium additions to a classic 90 mass % tungsten heavy alloy. The mixed-powder system was liquid phase sintered to full density at 1500 C in 60 min The rhenium-modified alloys exhibited a smaller grain size, higher hardness, higher strength, and lower ductility than the unalloyed system. For an alloy with a composition of 84W-6Re-8Ni-2Fe, the sintered density was 17, 4 Mg/m{sup 3} with a yield strength of 815 MPa, tensile strength of 1180 MPa, and elongation to failure of 13%. This property combination results from the aggregate effects of grain size reduction and solid solution hardening due to rhenium. In the unalloyed system these properties require post-sintering swaging and aging; thus, alloying with rhenium is most attractive for applications where net shaping is desired, such as by powder injection molding.

  10. Nickel alloys development-Inconel alloys development

    Energy Technology Data Exchange (ETDEWEB)

    Park, Yong Soo; Uhm, Tae Sik; Kim, Taek Jun; Jeon, Yu Taek; Chang, Hyun Young [Yonsei University, Seoul (Korea, Republic of); Kim, Young Sik [Andong National University, Andon (Korea, Republic of)

    1996-07-01

    This report dealt with the evaluation of Alloy 600 and alloy 690 of steam= generator materials. The experimental alloys were divided into two groups. ; Seamless tubings made by different ingot, and Mo-modified alloys. Thermal treatment had no influenced on the anodic polarization resistance in some caustic solution, but improved stress corrosion resistance by CERT. The effect of SO{sub 4}{sup =} ions reduced markedly caustic SCC resistance. The corrosion mode by 70 days and 120 days C-ring tests revealed the intergranular corrosion instead of stress corrosion cracking. Mo addition on the corrosion resistance of Alloy 690M showed beneficial effect in neutral and acidic solutions, but a little effect in caustic solutions. However, the caustic stress corrosion resistance was improved by the addition of molybdenum. 27 refs., 84 figs., 5 tabs. (author)

  11. Magnetic hysterysis evolution of Ni-Al alloy with Fe and Mn substitution by vacuum arc melting to produce the room temperature magnetocaloric effect material

    Energy Technology Data Exchange (ETDEWEB)

    Notonegoro, Hamdan Akbar [PPS Materials Science, FMIPA-Universitas Indonesia, Depok 16424 (Indonesia); Mechanical Engineering Dept., FT-Universitas Sultan Ageng Tirtayasa, Cilegon 42435 (Indonesia); Kurniawan, Budhy; Manaf, Azwar, E-mail: azwar@sci.ui.ac.id [PPS Materials Science, FMIPA-Universitas Indonesia, Depok 16424 (Indonesia); Setiawan, Jan [Center for Nuclear Fuel Tecnology-Badan Tenaga Atom Nasional, Tangerang Selatan 15310 (Indonesia)

    2016-06-17

    The development of magnetocaloric effect (MCE) material is done in order to reduce the damage of the ozone layer caused by the chlorofluorocarbons (CFCs) emitted into the air. The research dealing with synthesis of magnetocaloric materials based of Ni-Al Heusler Alloy structure and by varying substitution some atoms of Ni with Fe and Al with Mn on Ni-Al Heusler Alloy structure to become Ni{sub 44}Fe{sub 6}Mn{sub 32}Al{sub 18}. Vacuum Arc Melting (VAM) equipment is used to form the alloys on vacuum condition and by flowing argon gas atmosphere and then followed by annealing process for 72 hours. X-Ray Diffraction (XRD) reveals that crystallite structure of material is observed. We define that Ni{sub 44}Fe{sub 6} as X{sub 2}, Mn{sub 25} as Y, and Al{sub 18}Mn{sub 7} as Z. Based on the XRD result, we observed that the general formula X{sub 2}YZ is not changed. The PERMAGRAF measurement revealed that there exists of magnetic hysterysis. The hysterysis show that the magnetic structures of the system undego evolution from diamagnetic to soft ferromagnetic material which all of the compound have the same crystallite structure. This evolution indicated that the change in the composition has led to changes the magnetic composition. Mn is the major element that gives strong magnetic properties to the sample. When Mn partially replaced position of Al, the sample became dominant to be influenced to improve their magnetic properties. In addition, substitution a part of Ni by Fe in the composition reveals a pinning of the domain walls in the sample.

  12. Design of L21-type antiferromagnetic semiconducting full-Heusler compounds: A first principles DFT + GW study

    Science.gov (United States)

    Tas, M.; Şaşıoǧlu, E.; Friedrich, C.; Blügel, S.; Galanakis, I.

    2017-02-01

    Antiferromagnetic spintronics is an on-going growing field of research. Employing both standard density functional theory and the GW approximation within the framework of the full-potential linearized augmented-plane-wave method, we study the electronic and magnetic properties of seven potential antiferromagnetic semiconducting Heusler compounds with 18 (or 28 when Zn is present) valence electrons per unit cell. We show that in these compounds G-type antiferromagnetism is the ground state and that they are all either semiconductors (Cr2ScP, Cr2TiZn, V2ScP, V2TiSi, and V3Al) or semimetals (Mn2MgZn and Mn2NaAl). The many-body corrections have a minimal effect on the electronic band structure with respect to the standard electronic structure calculations.

  13. Enhanced thermoelectric properties of n-type NbCoSn half-Heusler by improving phase purity

    Directory of Open Access Journals (Sweden)

    Ran He

    2016-10-01

    Full Text Available Here we report the thermoelectric properties of NbCoSn-based n-type half-Heuslers (HHs that were obtained through arc melting, ball milling, and hot pressing process. With 10% Sb substitution at the Sn site, we obtained enhanced n-type properties with a maximum power factor reaching ∼35 μW cm−1 K−2 and figure of merit (ZT value ∼0.6 in NbCoSn0.9Sb0.1. The ZT is doubled compared to the previous report. In addition, the specific power cost ($ W−1 is decreased by ∼68% comparing to HfNiSn-based n-type HH because of the elimination of Hf.

  14. Dirac cone and pseudogapped density of states in the topological half-Heusler compound YPtBi

    Science.gov (United States)

    Kronenberg, A.; Braun, J.; Minár, J.; Elmers, H.-J.; Kutnyakhov, D.; Zaporozhchenko, A. V.; Wallauer, R.; Chernov, S.; Medjanik, K.; Schönhense, G.; Kläui, M.; Chadov, S.; Ebert, H.; Jourdan, M.

    2016-10-01

    Topological insulators (TIs) are exciting materials, which exhibit unprecedented properties, such as helical spin-momentum locking, which leads to large torques for magnetic switching and highly efficient spin current detection. Here we explore the compound YPtBi, an example from the class of half-Heusler materials, for which the typical band inversion of topological insulators was predicted. We prepared this material as thin films by conventional cosputtering from elementary targets. By in situ time-of-flight momentum microscopy, a Dirac conelike surface state with a Dirac point ≃300 meV below the Fermi energy was observed, in agreement with electronic structure-photoemission calculations. Only little additional spectral weight due to other states was observed at EF, which corroborates the identification of the topologically protected surface state and is highly relevant for spintronics applications.

  15. Electronic structure and superconducting behaviour of LuPtBi half-Heusler compound: A first principle study

    Science.gov (United States)

    Shrivastava, Deepika; Sanyal, Sankar P.

    2018-01-01

    The electronic, phonon and superconducting properties of LuPtBi half-Heusler compound in MgAgAs-type cubic structure have been studied by using first principles density functional theory and linear response technique. Electronic and bonding properties have been analysed from electronic band structure, density of states, Fermi surfaces and charge density plot. Positive phonon frequencies confirm the stability of LuPtBi in cubic MgAgAs phase. Superconducting transition temperature (TC) is calculated using Eliashberg spectral function (α2F(ω)). For calculation of TC we have used screened Coulomb repulsion constant (μ*) as 0.15 and found TC = 1.1 K, which agree well with the experimental value (TC = 1.0 K). About 10% error in TC from its experimental value is observed for μ* = 0.15 which increases by 40% when the value of μ* = 0.13 (TC = 1.4 K).

  16. Bending strain-tunable magnetic anisotropy in Co2FeAl Heusler thin film on KaptonxAE

    Science.gov (United States)

    Gueye, M.; Wague, B. M.; Zighem, F.; Belmeguenai, M.; Gabor, M. S.; Petrisor, T.; Tiusan, C.; Mercone, S.; Faurie, D.

    2014-08-01

    Bending effect on the magnetic anisotropy in 20 nm Co2FeAl Heusler thin film grown on Kapton® has been studied by ferromagnetic resonance and glued on curved sample carrier with various radii. The results reported in this Letter show that the magnetic anisotropy is drastically changed in this system by bending the thin films. This effect is attributed to the interfacial strain transmission from the substrate to the film and to the magnetoelastic behavior of the Co2FeAl film. Moreover, two approaches to determine the in-plane magnetostriction coefficient of the film, leading to a value that is close to λCFA= 14 × 10-6, have been proposed.

  17. On the possibility of thermoelectricity in half Heusler XRuSb (X = V, Nb, Ta) materials: A first principles prospective

    Science.gov (United States)

    Kaur, Kulwinder; Kumar, Ranjan

    2017-11-01

    In this study, we explored the electronic and thermoelectric properties of three semiconducting half Heusler compounds XRuSb (X = V, Nb, Ta) using density functional theory and semi-classical Boltzmann transport theory. We calculated the Seebeck coefficient and the electrical, electronic, and lattice thermal conductivity with changes in the temperature. These materials were identified as good thermoelectric materials with narrow band gaps and flat electronic bands in the valence band. The Seebeck coefficient and electronic thermal conductivity increased with temperature. The electrical conductivity and lattice thermal conductivity decreased as the temperature increased. The calculations indicated that p-type doping had a higher power factor than n-type doping. The spin orbit coupling (SOC) effect on the thermoelectric properties was also considered. The relaxation time (τ) decreased as the temperature increased. The maximum value for the figure of merit was equal to 0.13, which was achieved by VRuSb.

  18. High strength alloys

    Energy Technology Data Exchange (ETDEWEB)

    Maziasz, Phillip James; Shingledecker, John Paul; Santella, Michael Leonard; Schneibel, Joachim Hugo; Sikka, Vinod Kumar; Vinegar, Harold J.; John, Randy Carl; Kim, Dong Sub

    2012-06-05

    High strength metal alloys are described herein. At least one composition of a metal alloy includes chromium, nickel, copper, manganese, silicon, niobium, tungsten and iron. System, methods, and heaters that include the high strength metal alloys are described herein. At least one heater system may include a canister at least partially made from material containing at least one of the metal alloys. At least one system for heating a subterranean formation may include a tublar that is at least partially made from a material containing at least one of the metal alloys.

  19. High strength alloys

    Energy Technology Data Exchange (ETDEWEB)

    Maziasz, Phillip James [Oak Ridge, TN; Shingledecker, John Paul [Knoxville, TN; Santella, Michael Leonard [Knoxville, TN; Schneibel, Joachim Hugo [Knoxville, TN; Sikka, Vinod Kumar [Oak Ridge, TN; Vinegar, Harold J [Bellaire, TX; John, Randy Carl [Houston, TX; Kim, Dong Sub [Sugar Land, TX

    2010-08-31

    High strength metal alloys are described herein. At least one composition of a metal alloy includes chromium, nickel, copper, manganese, silicon, niobium, tungsten and iron. System, methods, and heaters that include the high strength metal alloys are described herein. At least one heater system may include a canister at least partially made from material containing at least one of the metal alloys. At least one system for heating a subterranean formation may include a tubular that is at least partially made from a material containing at least one of the metal alloys.

  20. Magnetic properties and electronic structure of the Heusler compounds Ru{sub 2-x} Fe{sub x} CrSi

    Energy Technology Data Exchange (ETDEWEB)

    Hiroi, Masahiko; Rokkaku, Tsugumi; Mizutani, Sou; Fujii, Sinpei; Ishida, Shoji, E-mail: hiroi@sci.kagoshima-u.ac.j [Department of Physics, Faculty of Science, Kagoshima University, Kagoshima 890-0065 (Japan)

    2009-03-01

    We have been trying to find Heusler compounds with high spin polarization which are robust against chemical disorders, because it is considered that disorders often degrade high spin polarization. The Heusler compound Ru{sub 2-x} Fe{sub :c}CrSi is shown to be such a material from first principles band structure calculations, and it is also shown that for the Ru-rich compound antiferromagnetic states are energetically preferable to the ferromagnetic state. Experimentally the Fe-rich compound is shown to be ferromagnetic, whereas for x <= 0.2 ferromagnetism is found to disappear and a cusp in the temperature dependence in magnetization is found, which appears to indicate an antiferromagnetic transition. These results seem to agree with the theory on the whole. The experimental results are examined in the light of calculated band structures.

  1. Creep Resistant Zinc Alloy

    Energy Technology Data Exchange (ETDEWEB)

    Frank E. Goodwin

    2002-12-31

    This report covers the development of Hot Chamber Die Castable Zinc Alloys with High Creep Strengths. This project commenced in 2000, with the primary objective of developing a hot chamber zinc die-casting alloy, capable of satisfactory service at 140 C. The core objectives of the development program were to: (1) fill in missing alloy data areas and develop a more complete empirical model of the influence of alloy composition on creep strength and other selected properties, and (2) based on the results from this model, examine promising alloy composition areas, for further development and for meeting the property combination targets, with the view to designing an optimized alloy composition. The target properties identified by ILZRO for an improved creep resistant zinc die-casting alloy were identified as follows: (1) temperature capability of 1470 C; (2) creep stress of 31 MPa (4500 psi); (3) exposure time of 1000 hours; and (4) maximum creep elongation under these conditions of 1%. The project was broadly divided into three tasks: (1) Task 1--General and Modeling, covering Experimental design of a first batch of alloys, alloy preparation and characterization. (2) Task 2--Refinement and Optimization, covering Experimental design of a second batch of alloys. (3) Task 3--Creep Testing and Technology transfer, covering the finalization of testing and the transfer of technology to the Zinc industry should have at least one improved alloy result from this work.

  2. Biocompatibility of dental alloys

    Energy Technology Data Exchange (ETDEWEB)

    Braemer, W. [Heraeus Kulzer GmbH and Co. KG, Hanau (Germany)

    2001-10-01

    Modern dental alloys have been used for 50 years to produce prosthetic dental restorations. Generally, the crowns and frames of a prosthesis are prepared in dental alloys, and then veneered by feldspar ceramics or composites. In use, the alloys are exposed to the corrosive influence of saliva and bacteria. Metallic dental materials can be classified as precious and non-precious alloys. Precious alloys consist of gold, platinum, and small amounts of non-precious components such as copper, tin, or zinc. The non-precious alloys are based on either nickel or cobalt, alloyed with chrome, molybdenum, manganese, etc. Titanium is used as Grade 2 quality for dental purposes. As well as the dental casting alloys, high purity electroplated gold (99.8 wt.-%) is used in dental technology. This review discusses the corrosion behavior of metallic dental materials with saliva in ''in vitro'' tests and the influence of alloy components on bacteria (Lactobacillus casei and Streptococcus mutans). The test results show that alloys with high gold content, cobalt-based alloys, titanium, and electroplated gold are suitable for use as dental materials. (orig.)

  3. The local structure of Co{sub 2}FeZ (Z=Si,Al,Ga,Ge) Heusler compounds probed by {sup 59}Co NMR

    Energy Technology Data Exchange (ETDEWEB)

    Wurmehl, Sabine; Kohlhepp, Juergen T.; Swagten, Henk J.M.; Koopmans, Bert [Eindhoven University of Technology, Eindhoven (Netherlands); Wojcik, Marek [Polish Academy of Sciences, Warszawa (Poland); Blum, Christian G.F.; Balke, Benjamin; Fecher, Gerhard H.; Ksenofontov, Vadim; Felser, Claudia [Johannes Gutenberg - Universitaet, Mainz (Germany)

    2008-07-01

    A thorough structural characterisation is one of the key tools in understanding the properties of spin polarised materials as the Heusler compounds Co{sub 2}FeZ with Z=(Si,Al,Ge,Ga). Spin echo nuclear magnetic resonance (NMR) spectroscopy provides a tool to probe the local structure by measuring the resonance frequencies and to probe the local hyperfine fields including the unique possibility to resolve the occupation and hyperfine fields of the neighboring shells. Thus, NMR was used to study the local (magnetic) structure of Co{sub 2}FeZ (Z=Al,Si,Ga,Ge) Heusler compounds, revealing different types of multiplet resonance lines for different types of Z atoms. The observed splitting of the resonance lines originates from different local environments of the {sup 59}Co nuclei. Analysis of the spectra yields the corresponding resonance frequencies and hyperfine magnetic fields as well as the spacing between consecutive resonance lines which leads to macroscopic structural models for the investigated Co{sub 2}FeZ Heusler compounds with Z=(Si,Al,Ge,Ga).

  4. Characteristics of 5M modulated martensite in Ni-Mn-Ga magnetic shape memory alloys

    Directory of Open Access Journals (Sweden)

    A. Çakır

    2015-09-01

    Full Text Available The applicability of the magnetic shape memory effect in Ni-Mn-based martensitic Heusler alloys is closely related to the nature of the crystallographically modulated martensite phase in these materials. We study the properties of modulated phases as a function of temperature and composition in three magnetic shape memory alloys Ni49.8Mn25.0Ga25.2, Ni49.8Mn27.1Ga23.1 and Ni49.5Mn28.6Ga21.9. The effect of substituting Ga for Mn leads to an anisotropic expansion of the lattice, where the b-parameter of the 5M modulated structure increases and the a and c-parameters decrease with increasing Ga concentration. The modulation vector is found to be both temperature and composition dependent. The size of the modulation vector corresponds to an incommensurate structure for Ni49.8Mn25.0Ga25.2 at all temperatures. For the other samples the modulation is incommensurate at low temperatures but reaches a commensurate value of q ≈ 0.400 close to room temperature. The results show that commensurateness of the 5M modulated structure is a special case of incommensurate 5M at a particular temperature.

  5. Catalyst Alloys Processing

    Science.gov (United States)

    Tan, Xincai

    2014-10-01

    Catalysts are one of the key materials used for diamond formation at high pressures. Several such catalyst products have been developed and applied in China and around the world. The catalyst alloy most widely used in China is Ni70Mn25Co5 developed at Changsha Research Institute of Mining and Metallurgy. In this article, detailed techniques for manufacturing such a typical catalyst alloy will be reviewed. The characteristics of the alloy will be described. Detailed processing of the alloy will be presented, including remelting and casting, hot rolling, annealing, surface treatment, cold rolling, blanking, finishing, packaging, and waste treatment. An example use of the catalyst alloy will also be given. Industrial experience shows that for the catalyst alloy products, a vacuum induction remelt furnace can be used for remelting, a metal mold can be used for casting, hot and cold rolling can be used for forming, and acid pickling can be used for metal surface cleaning.

  6. Low activation ferritic alloys

    Science.gov (United States)

    Gelles, D.S.; Ghoniem, N.M.; Powell, R.W.

    1985-02-07

    Low activation ferritic alloys, specifically bainitic and martensitic stainless steels, are described for use in the production of structural components for nuclear fusion reactors. They are designed specifically to achieve low activation characteristics suitable for efficient waste disposal. The alloys essentially exclude molybdenum, nickel, nitrogen and niobium. Strength is achieved by substituting vanadium, tungsten, and/or tantalum in place of the usual molybdenum content in such alloys.

  7. Hard X-ray photoelectron spectroscopy of bulk and thin films of Heusler compounds

    Energy Technology Data Exchange (ETDEWEB)

    Kozina, Xeniya

    2012-03-26

    recently it has been widely applied for the characterization of surfaces using low energy photons, the bulk properties have stayed inaccessible. Therefore in this work this method was integrated to HAXPES to provide an access to exploration of magnetic phenomena in the buried layers of the complex multilayer structures. Chapter 8 contains the results of the MCDAD measurements employing hard x-rays for exploration of magnetic properties of the common CoFe-based band-ferromagnets as well as half-metallic ferromagnet Co{sub 2}FeAl-based MTJs. In as much as the magnetoresistive characteristics in spintronic devices are fully defined by the electron spins of ferromagnetic materials their direct measurements always attracted much attention but up to date have been limited by the surface sensitivity of the developed techniques. Chapter 9 presents the results on the successfully performed spin-resolved HAXPES experiment using a spin polarimeter of the SPLEED-type on a buried Co{sub 2}FeAl{sub 0.5}Si{sub 0.5} magnetic layer. The measurements prove that a spin polarization of about 50 % is retained during the transmission of the photoelectrons emitted from the Fe 2p{sub 3/2} state through a 3-nm-thick oxide capping layer.

  8. Effect of on-site Coulomb interaction on electronic and transport properties of 100% spin polarized CoMnVAs

    Science.gov (United States)

    Bhat, Tahir Mohiuddin; Gupta, Dinesh C.

    2017-08-01

    The structural, electronic, magnetic and transport properties of a new quaternary Heusler alloy CoMnVAs have been investigated by employing generalized gradient approximation (GGA), modified Becke-Johnson (mBJ) and GGA with Hubbard U correction (GGA + U). The alloy is energetically more stable in ferromagnetic Y1 type structure. Elastic parameters reveal high anisotropy and ductile nature of the material. CoMnVAs shows half-metallic ferromagnet character with 100% spin polarization at Fermi level with band gap of 0.55 eV in the minority spin state. The alloy also possesses high electrical conductivity and Seebeck coefficients with 15 μVK-1 at room temperature, achieving a figure of merit of 0.65 at high temperatures. The high degree of ductility, 100% spin polarization and large Seebeck coefficient, makes it an attractive candidate to be used in spin voltage generators and thermoelectric materials.

  9. Copper-tantalum alloy

    Science.gov (United States)

    Schmidt, Frederick A.; Verhoeven, John D.; Gibson, Edwin D.

    1986-07-15

    A tantalum-copper alloy can be made by preparing a consumable electrode consisting of an elongated copper billet containing at least two spaced apart tantalum rods extending longitudinally the length of the billet. The electrode is placed in a dc arc furnace and melted under conditions which co-melt the copper and tantalum to form the alloy.

  10. Ultrahigh temperature intermetallic alloys

    Energy Technology Data Exchange (ETDEWEB)

    Brady, M.P.; Zhu, J.H.; Liu, C.T.; Tortorelli, P.F.; Wright, J.L.; Carmichael, C.A.; Walker, L.R. [Oak Ridge National Lab., TN (United States). Metals and Ceramics Div.

    1997-12-01

    A new family of Cr-Cr{sub 2}X based alloys with fabricability, mechanical properties, and oxidation resistance superior to previously developed Cr-Cr{sub 2}Nb and Cr-Cr{sub 2}Zr based alloys has been identified. The new alloys can be arc-melted/cast without cracking, and exhibit excellent room temperature and high-temperature tensile strengths. Preliminary evaluation of oxidation behavior at 1100 C in air indicates that the new Cr-Cr{sub 2}X based alloys form an adherent chromia-based scale. Under similar conditions, Cr-Cr{sub 2}Nb and Cr-Cr{sub 2}Zr based alloys suffer from extensive scale spallation.

  11. ETUDE AB-INITIO DES PROPRIETES STRUCTURALES, MAGNETIQUES DES ALLIAGES SEMI-HEUSLER DE XTISB (X=CO, NI, FE

    Directory of Open Access Journals (Sweden)

    MILOUD IBRIR

    2015-06-01

    Full Text Available Les propriétés structurelles, électroniques et magnétiques de trois composés de semi-Heusler : CoTiSb, NiTiSb et FeTiSb ont été calculées par la méthode des ondes planes augmentées (FP-LAPW qui se base sur la théorie de la fonctionnelle de la densité (DFT en utilisant le code de Wien2K. Nous avons utilisé l'approximation du gradient généralisé (GGA(06 pour le terme du potentiel d'échange et de corrélation (XC. Les valeurs du paramètre de maille d’équilibre sont en accord avec les résultats expérimentaux disponibles. Les propriétés  électroniques montrent que CoTiSb est un semi-conducteur, NiTiSb est un métal et FeTiSb est un semi-métalferromagnétique.

  12. Thermoelectric performance and the role of anti-site disorder in the 24-electron Heusler TiFe2Sn

    Science.gov (United States)

    Buffon, Malinda L. C.; Laurita, Geneva; Lamontagne, Leo; Levin, Emily E.; Mooraj, Shahryar; Lloyd, Demetrious L.; White, Natalie; Pollock, Tresa M.; Seshadri, Ram

    2017-10-01

    Heusler compounds XY 2 Z with 24 valence electrons per formula unit are potential thermoelectric materials, given their thermal and chemical stability and their relatively earth-abundant constituent elements. We present results on the 24-electron compound TiFe2Sn here. First principles calculations on this compound suggest semiconducting behavior. A relatively flat conduction band that could be associated with a high Seebeck coefficient upon electron doping is found. A series of compounds have been prepared and characterized using a combination of synchrotron x-ray and neutron diffraction studies to understand the effects of site order/disorder phenomena and n-type doping. Samples fabricated by a three step processing approach were subjected to high temperature Seebeck and electrical resistivity measurements. Ti:Fe anti-site disorder is present in the stoichiometric compound and these defects are reduced when starting Ti-rich compositions are employed. Additionally, we investigate control of the Seebeck coefficient through the introduction of carriers through the substitution of Sb on the Sn site in these intrinsically p-type materials.

  13. Electronic and thermoelectric properties of nonmagnetic inverse Heusler semiconductors Sc2FeSi and Sc2FeGe

    Science.gov (United States)

    Li, Jie; Yang, Guang; Yang, Yanmin; Ma, Hongran; Zhang, Qiang; Zhang, Zhidong; Fang, Wei; Yin, Fuxing; Li, Jia

    2017-11-01

    The electronic and thermoelectric properties of two nonmagnetic Hg2CuTi-type or called inverse Heusler semiconductors Sc2FeSi and Sc2FeGe are predicted by using first principles calculations and Boltzmann transport theory. The band gaps of Sc2FeSi and Sc2FeGe are 0.54 eV and 0.60 eV, respectively. Their zero total magneticmoments both satisfy the Mt = Zt-18 while not the Mt = Zt-24 rule. The good thermoelectric properties are achieved under the condition of electron doping. At the room temperature 300 K, the peak value of Seebeck coefficient is -592.02 μVK-1 for Sc2FeSi, and -609.38 μVK-1 for Sc2FeGe by electron doping. The maximum power factor is 48.77(1014 μW cm-1 K-2 s-1) for Sc2FeSi and 47.11(1014 μW cm-1 K-2 s-1) for Sc2FeGe with electron doping concentration -2.29 × 1026 m-3 and -2.42 × 1026 m-3, respectively, which are close to the power factor of well-known thermoelectric material Bi2Te3, indicating their potential applying values for thermoelectric devices.