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Sample records for heusler alloy investigated

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

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    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.

  2. Magnetism of quaternary Heusler alloys

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    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.

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

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    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.

  4. 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.

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

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    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

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

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    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

  7. 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.

  8. 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.

  9. 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.

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

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    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.

  11. 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.

  12. 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...

  13. 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.

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

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    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

  15. 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.

  16. 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.

  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

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    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. 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. 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.

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

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    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.

  1. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

    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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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).

  11. 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}.

  12. 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.

  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. 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.

  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. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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....

  4. 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.

  5. 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.

  6. 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 .

  7. 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)

  8. 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.

  9. 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.

  10. 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.

  11. 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...

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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...

  16. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

    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.

  18. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

    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)

  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. 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.

  2. 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.

  3. 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.

  4. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

    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)

  6. 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.

  7. 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

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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...

  13. 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.

  14. 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.

  15. 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.

  16. 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

  17. 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...

  18. 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...

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

    Energy Technology Data Exchange (ETDEWEB)

    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.)

  1. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

    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.

  3. 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.

  4. 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.

  5. 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

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  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. 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.

  13. 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.

  14. 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.

  15. 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.

  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. 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. 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...

  20. 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.

  1. 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.

  2. 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

  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. 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.

  5. 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.

  6. 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.

  7. 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”.

  8. 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.

  9. 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%.

  10. 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

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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

  16. 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.

  17. 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.

  18. 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.

  19. 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

    Energy Technology Data Exchange (ETDEWEB)

    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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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}.

  7. 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.

  8. 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.

  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. 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.

  11. 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.

  12. 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.

  13. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

    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.

  15. 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.

  16. 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.

  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. 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.

  19. INVESTIGATION OF MAGNESIUM ALLOYS MACHINABILITY

    Directory of Open Access Journals (Sweden)

    Berat Barıs BULDUM

    2013-01-01

    Full Text Available Magnesium is the lightest structural metal. Magnesium alloys have a hexagonal lattice structure, which affects the fundamental properties of these alloys. Plastic deformation of the hexagonal lattice is more complicated than in cubic latticed metals like aluminum, copper and steel. Magnesium alloy developments have traditionally been driven by industry requirements for lightweight materials to operate under increasingly demanding conditions. Magnesium alloys have always been attractive to designers due to their low density, only two thirds that of aluminium and its alloys [1]. The element and its alloys take a big part of modern industry needs. Especially nowadays magnesium alloys are used in automotive and mechanical (trains and wagons manufacture, because of its lightness and other features. Magnesium and magnesium alloys are the easiest of all metals to machine, allowing machining operations at extremely high speed. All standard machining operations such as turning, drilling, milling, are commonly performed on magnesium parts.

  20. 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.

  1. INVESTIGATION OF MAGNESIUM ALLOYS MACHINABILITY

    OpenAIRE

    Berat Barıs BULDUM; Aydın SIK; Iskender OZKUL

    2013-01-01

    Magnesium is the lightest structural metal. Magnesium alloys have a hexagonal lattice structure, which affects the fundamental properties of these alloys. Plastic deformation of the hexagonal lattice is more complicated than in cubic latticed metals like aluminum, copper and steel. Magnesium alloy developments have traditionally been driven by industry requirements for lightweight materials to operate under increasingly demanding conditions. Magnesium alloys have always been attra...

  2. 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.

  3. 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.

  4. 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.

  5. 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

  6. 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.

  7. 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.

  8. 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).

  9. 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.

  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. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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%.

  20. 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...

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

    Energy Technology Data Exchange (ETDEWEB)

    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.

  2. 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.

  3. 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.

  4. 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

    Heusler alloy can be used to obtain information about the half-metallicity and the magnons as reported by Taira et al in this issue. An improvement of the tunnel magnetoresistance effect (TMR) at room temperature could be achieved by shifting the Fermi energy from the edges of the valence or the conduction band into the middle of the gap [12]. In the case of Co2FeSi0.5Al0.5 (CFAS), TMR values higher than 200% can be achieved [13]. The improvement of the interface seems to be important as has been shown by XMCD (x-ray magnetic circular dichroism) [14] and photoemission spectroscopy [15]. The interface magnetization is very often reduced [14]; however, the interface and the surface electron spin polarization can be improved by post annealing as reported by Wüstenberg et al in this issue. High energy photoemission spectroscopy is a new tool for investigating bulk properties of Heusler compounds [16]. In this issue we report on the investigation of a whole device structure by this technique due to the high escape depth inherent to this method in the contribution of Herbort et al. Dynamic correlations might be a reason for the formation of non-quasi-particles such as magnons in the gap [17], which destroy the half-metallicity and thus can be considered as another cause for the reduced TMR at room temperature. Thus correlations have to be taken into account. This is demonstrated for the Heusler compound Co2Mn1 - xFexSi as reported by Chadov et al in this issue. Magneto-optic methods are powerful instruments for investigating magnetic properties of Heusler compounds. The determination of the huge quadratic Kerr effect in the Co2FeSi Heusler compound is a good example [18]. In this issue Hamrle et al and Gaier et al report on the determination of the exchange constant by measuring the magnon dispersion properties using Brillouin light scattering spectroscopy. The magnon dispersion was calculated by Thoene et al. New developments in the field of spintronics go into the direction

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  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. Investigations on the optimization of phase and alloy compositions of Al-Cu-Si-Mg alloys

    Energy Technology Data Exchange (ETDEWEB)

    Eskin, D.G. (A.A. Baikov Inst. of Metallurgy, Russian Academy of Sciences, Moscow (Russia))

    1992-10-01

    The effect of the supersaturated solid solution composition on the phase composition of aging products in Al - (4 mass%) Cu-Si-Mg alloys has been investigated in a broad compositional range. The diagram of distribution of phase regions has been constructed for the Al-Cu (4 mass%)-Si-Mg alloys after aging at 170degC for 20 h. With cast and deformed alloys, it has been shown exemplarily that the best complex of mechanical properties is associated with alloy compositions ensuring the precipitation of [Theta]' and [beta]'' phases. The composition of cast Al - Si - Cu - Mg alloys has been optimized. (orig.).

  18. 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.

  19. 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

  20. 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.

  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. 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.

  3. 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.

  4. Investigation into the grinding of titanium alloys

    OpenAIRE

    Wang, S. H.

    2000-01-01

    Titanium alloys are used extensively in the aerospace industry due to their high specific strength and excellent corrosion resistance. However, their poor thermal conductivity and high chemical reactivity with tool materials make the machining difficult, especially when grinding. During grinding, the excessive heat generated at the wheel-work piece interface may result in poor surface finisil,1_, a transformed surface layer, excessive plastic deformation, thermallyinduced...

  5. EXAFS investigation on microstructure of La-based alloy deuteride

    CERN Document Server

    Chen Bo Fei; Xie Chao Mei; Chen Xi Ping; Liu Li Juan; Xie Ya Ning; Hu Tian Dou; Zhang Jing

    2002-01-01

    Extended X-ray absorption fine structure (EXAFS) spectra were measured to investigate the microstructure of La-based alloy deuteride. The radial structural functions of LaNi sub 4 sub . sub 2 sub 5 Al sub 0 sub . sub 7 sub 5 D sub x samples were obtained and the comparisons among different samples were performed. The results show that removal of deuterium is fast in La-Ni-Al hydrogen storage alloys under non-airtight condition

  6. 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...

  7. 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.

  8. Biphasic thermoelectric materials derived from the half-Heusler/full-Heusler system Ti-Ni-Sn

    Science.gov (United States)

    Douglas, Jason Everett

    comparative energies of formation. We discuss the effects of thermal treatment on the microstructure of biphasic materials comprising hH and fH phases, as well as on their associated thermal transport properties. The fH phase is observed to be semi-coherent with the hH majority phase. Microstructural analysis, both in 2-D and 3-D, shows that the fH solidifies first and the hH then nucleates on these fH dendrites as the melt becomes depleted of Ni. The various heat treatments generated microstructures containing second phase precipitates ranging from 10 nm to a few micrometers, reducing the connectivity of the percolated network observed previously. The materials were characterized with regard to morphology, size, shape and orientation relationship of the fH precipitates with the hH matrix. The precipitate size and morphology are very sensitive to Ni concentration in fH/hH phase. The thermal conductivity is found to drop by 50% as the precipitate size increases; however, this enhancement was not retained after high temperature exposure. In addition to the microstructural implications of TiNi 1+xSn alloying, the (crystal) structural implications of excess Ni in the TiNiSn hH compound were investigated next through a combination of synchrotron x-ray and neutron scattering studies, in conjunction with first principles density functional theory calculations on supercells. Despite the phase diagram suggesting that TiNiSn is a line compound with no solid solution, for small x in TiNi 1+xSn there is indeed an appearance--from careful analysis of the scattering--of some solubility, with the excess Ni occupying the interstitial tetrahedral site in the hH structure. The analysis performed here would point to the excess Ni not being statistically distributed, but rather occurring as coherent nanoclusters. First principles calculations of energetics, carried out using supercells, support a scenario of Ni interstitials clustering, rather than a statistical distribution. Finally, we also

  9. 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.

  10. 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.

  11. 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

  12. Thermal analytical investigations of the magnesium alloy AZ91

    Directory of Open Access Journals (Sweden)

    K.N. Braszczyńska - Malik

    2007-04-01

    Full Text Available The results of thermal derivative analysis (TDA, differential scanning calorimetric (DSC measurements and microstructure investigations of commercial AZ91 magnesium alloy are presented. The performed examinations allowed to determine the microstructure after solidification process and also precipitation process during continuous heating of supersaturated solid solution. The α-phase and α+γ semi-divorced eutectic were observed in as-cast material, whereas both discontinuous and continuous precipitates of γ phase were revealed after heating supersaturated AZ91 alloy.

  13. 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.

  14. 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.

  15. 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.

  16. Investigation of the Precipitation Behavior in Aluminum Based Alloys

    KAUST Repository

    Khushaim, Muna S.

    2015-11-30

    The transportation industries are constantly striving to achieve minimum weight to cut fuel consumption and improve overall performance. Different innovative design strategies have been placed and directed toward weight saving combined with good mechanical behavior. Among different materials, aluminum-based alloys play a key role in modern engineering and are widely used in construction components because of their light weight and superior mechanical properties. Introduction of different nano-structure features can improve the service and the physical properties of such alloys. For intelligent microstructure design in the complex Al-based alloy, it is important to gain a deep physical understanding of the correlation between the microstructure and macroscopic properties, and thus atom probe tomography with its exceptional capabilities of spatially resolution and quantitative chemical analyses is presented as a sophisticated analytical tool to elucidate the underlying process of precipitation phenomena in aluminum alloys. A complete study examining the influence of common industrial heat treatment on the precipitation kinetics and phase transformations of complex aluminum alloy is performed. The qualitative evaluation results of the precipitation kinetics and phase transformation as functions of the heat treatment conditions are translated to engineer a complex aluminum alloy. The study demonstrates the ability to construct a robust microstructure with an excellent hardness behavior by applying a low-energy-consumption, cost-effective method. The proposed strategy to engineer complex aluminum alloys is based on both mechanical strategy and intelligent microstructural design. An intelligent microstructural design requires an investigation of the different strengthen phases, such as T1 (Al2CuLi), θ′(Al2Cu), β′(Al3Zr) and δ′(Al3Li). Therefore, the early stage of phase decomposition is examined in different binary Al-Li and Al-Cu alloys together with different

  17. Investigation on a Roman copper alloy artefact from Pompeii (Italy).

    Science.gov (United States)

    Baraldi, Pietro; Baraldi, Cecilia; Ferrari, Giorgia; Foca, Giorgia; Marchetti, Andrea; Tassi, Lorenzo

    2006-01-01

    A selection of samples, obtained from a particular copper-alloy domestic artefact of Roman style from Pompeii, has been analysed by using different techniques (IR, Raman, SEM-EDX, FAAS), in order to investigate the chemical nature and composition of the metals utilised for such manufacturing pieces. The surface analysis of the bright red metallic microfragments conducted by different analytical techniques, emphasises the presence of pure unalloyed copper and confirms the absence of other metallic species on the upper layers. On the contrary, the mapping analysis of the section of the laminar metal of the investigated sample shows a consistent enrichment in tin content. Finally, destructive analysis by FAAS confirms that the artefact looks like a bronze metal alloy, with a medium Sn content of about 6.5%.

  18. 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.

  19. 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.

  20. Experimental Investigation of Ternary Alloys for Fusion Breeding Blankets

    Energy Technology Data Exchange (ETDEWEB)

    Choi, B. William [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Chiu, Ing L. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

    2015-10-26

    Future fusion power plants based on the deuterium-tritium (DT) fuel cycle will be required to breed the T fuel via neutron reactions with lithium, which will be incorporated in a breeding blanket that surrounds the fusion source. Recent work by LLNL proposed the used of liquid Li as the breeder in an inertial fusion energy (IFE) power plant. Subsequently, an LDRD was initiated to develop alternatives ternary alloy liquid metal breeders that have reduced chemical reactivity with water and air compared to pure Li. Part of the work plan was to experimentally investigate the phase diagrams of ternary alloys. Of particular interest was measurement of the melt temperature, which must be low enough to be compatible with the temperature limits of the steel used in the construction of the chamber and heat transfer system.

  1. 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.

  2. 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.)

  3. 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.

  4. Investigation of solidification dynamics of Zr-based alloys

    Energy Technology Data Exchange (ETDEWEB)

    Kobold, Raphael; Herlach, Dieter [Institut fuer Materialphysik im Weltraum, Deutsches Zentrum fuer Luft- und Raumfahrt, 51170 Koeln (Germany); Ruhr-Universitaet Bochum, 44780 Bochum (Germany)

    2013-07-01

    In contrast to experiments with most undercooled binary alloys the velocity of dendritic growth of a Cu50Zr50 alloy does not increase monotonically with undercooling but passes through a maximum and then decreases. To study this behaviour we investigate Zr-based alloys such as CuZr, NiZr and NiZrAl with Zirconium concentrations ranging from 36 to 64 at.% including eutectic and intermetallic phases. We use electrostatic levitation technique to melt and undercool samples with a diameter of 2-3 mm under ultra-high-vacuum conditions. Containerless processing is an effective tool for undercooling metallic melts far below their equilibrium melting temperatures since heterogeneous nucleation on container walls is completely avoided. During crystallisation of the undercooled melt the heat of crystallisation is released. The rapid increase of the temperature at the solid-liquid interface makes the solidification front visible. The velocities of the solidification front are recorded by using a high-speed camera with a maximum rate of 50.000 frames per second and are analyzed with a software for optical ray tracing. Furthermore, we try to model the growth velocity vs. the undercooling temperature and perform sample EBSD analysis with a scanning electron microscope.

  5. 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 ...

  6. 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.

  7. 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.

  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. 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

    Strong ferromagnetism has been detected in the semiconducting half-Heusler CoTiSb compound. The synthesis process was carried out by direct fusion of highly pure Co, Ti, and Sb in an evacuated quartz tube. The structural, micro structural and magnetic properties were investigated. The crystal structure was refined from X-ray powder diffraction data by the Rietveld method. Applying the search match program, three nano-crystalline phases of CoTiSb, Ti{sub 3}Sb and CoTi{sub 2} (50%, 33.3% and 16.7% respectively) were identified for the prepared system. The term “phase” is used to address the co-existence of different stable chemical composition for the same half-Heusler alloy. The scanning electron microscope SEM and the high resolution transmission electron microscope HR-TEM were applied to characterize the morphology, size, shape, crystallinity and lattice spacing. A mixture of ordered and disordered arrangement was detected. Well defined nano-crystalline structure with an average interatomic distance equals 0.333 nm and sharp diffraction spots were measured. Contrary to this, the HR-TEM and electron diffraction image shows distorted structured planes and smeared halo surrounded by weak rings. Thermo-magnetic measurements (M–T) have been measured between 640 °K and 920 °K. Clear magnetic phase transition is detected above 900 °K (T{sub c}), in addition to a second possible phase transition (T{sub FF}) around 740 °K. The latter is clarified by plotting ΔM/ΔT vs. T. To determine the type of the detected phase transitions, the field dependence of magnetization was measured at 300 °K and 740 °K. Arrot plots (M{sup 2}−H/M) confirm the ferromagnetic character at both temperatures. It may be reasonable to assume the T{sub FF} transition as an additional ferromagnetic contribution stemming from some sort of exchange interactions. A tentative magnetic phase diagram is given. Overall, the present results suggest that the prepared multiphases CoTiSb system does

  10. Yield surface investigation of alloys during model disk spin tests

    Directory of Open Access Journals (Sweden)

    E. P. Kuzmin

    2014-01-01

    Full Text Available Gas-turbine engines operate under heavy subsequently static loading conditions. Disks of gas-turbine engine are high loaded parts of irregular shape having intensive stress concentrators wherein a 3D stress strain state occurs. The loss of load-carrying capability or burst of disk can lead to severe accident or disaster. Therefore, development of methods to assess deformations and to predict burst is one of the most important problems.Strength assessment approaches are used at all levels of engine creation. In recent years due to actively developing numerical method, particularly FEA, it became possible to investigate load-carrying capability of irregular shape disks, to use 3D computing schemes including flow theory and different options of force and deformation failure criteria. In spite of a wide progress and practical use of strength assessment approaches, there is a lack of detailed research data on yield surface of disk alloys. The main purpose of this work is to validate the use of basis hypothesis of flow theory and investigate the yield surface of disk alloys during the disks spin test.The results of quasi-static numerical simulation of spin tests of model disk made from high-temperature forged alloy are presented. To determine stress-strain state of disk during loading finite element analysis is used. Simulation of elastic-plastic strain fields was carried out using incremental theory of plasticity with isotropic hardening. Hardening function was taken from the results of specimens tensile test. Specimens were cut from a sinkhead of model disk. The paper investigates the model sensitivity affected by V.Mises and Tresca yield criteria as well as the Hosford model. To identify the material model parameters the eddy current sensors were used in the experimental approach to measure rim radial displacements during the load-unload of spin test. The results of calculation made using different material models were compared with the

  11. 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.

  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. 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.

  14. Structural, thermal and magnetic investigations on immiscible Ag–Co nanocrystalline alloy with addition of Mn

    Energy Technology Data Exchange (ETDEWEB)

    Mondal, B.N., E-mail: bholanath_mondal@yahoo.co.in [Department of Central Scientific Services, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700 032 (India); Chabri, S. [Department of Metallurgy and Materials Engineering, Bengal Engineering and Science University, Shibpur, Howrah 711 103 (India); Sardar, G. [Department of Zoology, Baruipur College, South 24 Parganas 743610 (India); Nath, D.N. [Department of Physical Chemistry, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700 032 (India); Chattopadhyay, P.P. [Department of Metallurgy and Materials Engineering, Bengal Engineering and Science University, Shibpur, Howrah 711 103 (India)

    2016-08-15

    50Ag–50Co (at%) and 40Ag–40Co–20Mn (at%) alloys prepared by ball milling up to 50 h and subsequent isothermal annealing at the temperature range of 350–650 °C for 1 h has been investigated systematically. Mn promotes early formation of the nanostructures and solid solutions of the alloys by ball milling. In contrast, annealing at 350 °C of Ag–Co alloy resulted the dissolution of hcp Co. Annealing above 350 °C decomposes the metastable Ag–Co alloy into the polycrystalline and segregated Ag and fcc Co. Enthalpy of mixing of both the alloy has increased with increase in milling time. Both the nanocrystalline alloys prepared by ball milling and annealing have been revealed the ferromagnetic behavior. The most significant improvement of magnetic properties is yielded in as-milled Ag–Co–Mn alloy obtained after annealing at 550 °C for 1 h. - Highlights: • A complete solid solution of Ag–Co–Mn alloy obtained after 50 h of milling. • A complete solid solution of milled Ag–Co alloy forms annealed at 350 {sup °}C for 1 h. • Precipitation of fcc Co are observed after annealing above 350 °C. • Enthalpy of mixing of the alloys increased with increase in milling time. • The superior magnetic properties achieved of Ag–Co–Mn alloy annealed at 550 °C.

  15. 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.

  16. 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.

  17. Gallium alloy films investigated for use as boundary lubricants

    Science.gov (United States)

    1966-01-01

    Gallium alloyed with other low melting point metals has excellent lubricant properties of fluidity and low vapor pressure for high temperature or vacuum environments. The addition of other soft metals reduces the corrosivity and formation of undesirable alloys normally found with gallium.

  18. 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.

  19. 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

  20. Mossbauer investigations of corrosion environment influence on Fe valence states in oxide films of zirconium alloys

    NARCIS (Netherlands)

    Filippov, V. P.; Petrov, V. I.; Shikanova, Yu. A.

    2006-01-01

    Mossbauer investigations about iron atom redistribution in oxide films of zirconium alloys subjected to corrosion at 500 degrees C in pure oxygen and water pair have been analysed. The alloys were also subjected to autoclave conditions at a pressure of 10.0 MPa and autoclave conditions at 350

  1. 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.

  2. An Investigation on Metallic Ion Release from Four Dental Casting Alloys

    Directory of Open Access Journals (Sweden)

    F. Nejatidanesh

    2005-12-01

    Full Text Available Statement of Problem: Element release from dental casting alloys into the oral environment is of clinical concern and is considered to be a potential health problem to all patients.Purpose: The aim of this study was to investigate the metallic ion release of four base metal alloys.Materials and Methods: Two Ni-Cr (Minalux and Supercast and two Co-Cr alloys (Minalia and Wironit were examined. Nine specimens of each type were prepared in 13×11×1.4 mm dimensions and each of the four alloys (3 specimens per group were conditioned in artificial saliva at 37 c for one, three and seven days.The conditioning media were analyzed for element-release using Inductive CoupledPlasma Atomic Emission Spectrophotometer (ICPAES. Collected data were statistically analyzed using ANOVA and Duncan multiple range test (P< 0.05.Results: The greatest amount of element release was seen after seven days (134.9 ppb Supercast, 159.2 ppb Minalux, 197.2 ppb Minalia, and 230.2 ppb Wironit. There was a significant difference between the released elements from the alloys after the three conditioning times (p<0.001.Conclusion: Element release from the studied alloys is proportional to the conditioning time. The Ni-Cr alloys tested in this investigation were more resistant to corrosion as compared to the Co-Cr alloys in artificial saliva. Supercast had the highest corrosion resistance.

  3. 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.

  4. INVESTIGATION OF THE RECOVERY PROCESS AT PRODUCTION OF ALLOYED HIGHCARBON ALLOYS

    Directory of Open Access Journals (Sweden)

    A. G. Slutskij

    2006-01-01

    Full Text Available The thermodynamic calculations of the temperature of the disoxidation onset of a raw of alloying element by solid carbon are canned out. It is determined that using of additives on the basis of wastes allows to reduce the cost of castings due to replacement of expensive raw materials.

  5. Investigation on the optimized heat treatment procedure for laser fabricated IN718 alloy

    Science.gov (United States)

    Zhang, Yaocheng; Yang, Li; Chen, Tingyi; Zhang, Weihui; Huang, Xiwang; Dai, Jun

    2017-12-01

    The laser fabricated IN718 alloys were prepared by laser cladding system. The microstructure and microhardness of laser fabricated IN718 alloys were investigated after heat treatment. The microstructure and the elevated temperature mechanical properties of laser fabricated IN718 alloys were analyzed. The results showed that the microstructure of laser fabricated IN718 alloy consisted of austenitic matrix and dendritic Laves/γ eutectic. Most all Laves/γ eutectic was dissolved into austenitic matrix, and the complete recrystallization and the large grains occurred in the laser fabricated IN718 alloy after homogenization at 1080-1140 °C for 1 h, the dendritic Laves/γ eutectic was refined and the partial recrystallization occurred during the solid solution at 940-1000 °C for 1.5 h, the microhardness of the double aging (DA) alloys was about more than twice that of as-fabricated IN718 alloy. The recrystallized microstructure was obtained in the heat-treated laser fabricated IN718 alloy after 1100 °C/1 h air cooling (AC), 980 °C/1.5 h (AC), 700 °C/8 h furnace cooling (FC, 100 °C/h) to 600 °C/8 h (AC). The microhardness and the elevated temperature tensile strength were more than twice that of as-fabricated IN718 alloy due to a large concentration of γ″ phase precipitation to improve the transgranular strength and large grain to guarantee the grain boundary strength. The fracture morphologies of as-fabricated and heat-treated laser fabricated IN718 alloys were presented as the fiber dimples, the fracture mechanism of as-fabricated and heat-treated laser fabricated IN718 alloys was ductile fracture.

  6. Investigations of intermetallic alloy hydriding mechanisms. Annual progress report, May 1 1979-April 30, 1980

    Energy Technology Data Exchange (ETDEWEB)

    Livesay, B.R.; Larsen, J.W.

    1980-05-01

    Investigations are being conducted on mechanisms involved with the hydrogen-metal interactions which control the absorption and desorption processes in intermetallic compounds. The status of the following investigations is reported: modeling of hydride formation; microbalance investigations; microstructure investigations; flexure experiments; resistivity experiments; and nuclear backscattering measurements. These investigations concern fundamental hydrogen interaction mechanisms involved in storage alloys.

  7. 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.

  8. Investigation of the mechanism of mercury removal from a silver dental amalgam alloy

    Directory of Open Access Journals (Sweden)

    M. DJURDJEVIC

    2004-12-01

    Full Text Available An investigation of silver dental amalgam decomposition and the mercury removal mechanism was performed. The decomposition process was analysed during thermal treatment in the temperature interval from 400 °C to 850 °C and for times from 0.5 to 7.5 h. The chemical compositions of the silver dental amalgam alloy and the treated alloy were tested and microstructure analysis using optical and scanning electron microscopy was carried out. The phases were identified using energy disperse electron probe microanalysis. A mechanism for the mercury removal process from silver dental amalgam alloy is suggested.

  9. Experimental investigation of the efficiency of HTO reduction by Zr-Fe-Mn getter alloy

    Energy Technology Data Exchange (ETDEWEB)

    Ghezzi, F.; Shmayda, W.T.; Bonizzoni, G. [Istituto di Fisica del Plasma-CNR, Milano (Italy)

    1997-01-01

    Tritium gas handling involves the production of tritiated water, which is 10000 times more hazardous than tritium gas. If tritium emission to the environment must be minimized, the need to process tritiated water and recover the chemically bound tritium appears clear. Facilities for processing tritiated water produced in fission reactors are already available, while facilities for a deuterium-tritium fusion machine are under development. However, these facilities are intended for large-scale applications and are neither practical nor economical for small-scale applications. HTO vapor reduction to HT over a hot metal getter other than uranium offers a simple, safe, and economical solution. A high alloy capacity and conversion rate combined with a low tritium residual inventory in the exhausted alloy make this method attractive. An experimental investigation of the efficiency of reducing HTO by a Zr-Fe-Mn alloy is presented. The results, obtained by three independent diagnostics (stripper set, ionization chambers, and mass spectrometry), show that for gas residence times > 1 s and alloy temperature > 400{degree}C, a conversion efficiency exceeding 90% is achievable. Specific conversion rates > 0.1 {mu}mol/s.g{sup -1} are observed during te alloy usage, while a capacity of the alloy, measured as an oxygen-to-alloy mole ratio, > 2.6 has been measured. 50 refs., 21 figs., 5 tabs.

  10. An investigation of wear behaviors of different Monel alloys produced by powder metallurgy

    Energy Technology Data Exchange (ETDEWEB)

    Esgin, U.; Özyürek, D. [Karabük University, Technology Faculty, Department of Manufacturing Engineering / Karabuk (Turkey); Kaya, H., E-mail: hasan.kaya@kocaeli.edu.tr [Kocaeli University, Asim Kocabiyik Vocational School of Higher Education, Department of Machine / Kocaeli (Turkey)

    2016-04-21

    In the present study, wear behaviors of Monel 400, Monel 404, Monel R-405 and Monel K-500 alloys produced by Powder Metallurgy (P/M) method were investigated. These compounds prepared from elemental powders were cold-pressed (600 MPa) and then, sintered at 1150°C for 2 hours and cooled down to the room temperature in furnace environment. Monel alloys produced by the P/M method were characterized through scanning electron microscope (SEM+EDS), X-ray diffraction (XRD), hardness and density measurements. In wear tests, standard pin-on-disk type device was used. Specimens produced within four different Monel Alloys were tested under 1ms{sup −1} sliding speed, under three different loads (20N, 30N and 40N) and five different sliding distances (400-2000 m). The results show that Monel Alloys have γ matrix and that Al{sub 0,9}Ni{sub 4,22} intermetallic phase was formed in the structure. Also, the highest hardness value was measured with the Monel K-500 alloy. In wear tests, the maximum weight loss according to the sliding distance, was observed in Monel 400 and Monel 404 alloys while the minimum weight loss was achieved by the Monel K-500 alloy.

  11. 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.

  12. Textured Al2024 alloy surface for super-hydrophobicity investigation

    Science.gov (United States)

    Chen, Lijuan; Chen, Miao; Zhou, Huidi; Chen, Jianmin

    2008-01-01

    To mimic the lotus leaf structure, micro- and nanometer honeycomb-like porous hierarchical microstructures were constructed on the Al2024 alloy surface in which the average diameter of micro-pores was ca. 10 μm while those of nano-pores varied from 200 to 300 nm. Super-hydrophobicity was achieved with a water contact angle of 158° and the sliding angle of 4° by modifying the textured surface with HFTHTMS (HFTHTMS = (heptadecafluoro-1,1,2,2-tetrahydrodecyl) trimethoxysilane).

  13. Corrosion resistance investigation of vanadium alloys in liquid lithium

    Science.gov (United States)

    Borovitskaya, I. V.; Lyublinskiy, I. E.; Bondarenko, G. G.; Paramonova, V. V.; Korshunov, S. N.; Mansurova, A. N.; Lyakhovitskiy, M. M.; Zharkov, M. Yu.

    2016-12-01

    A major concern in using vanadium alloys for first wall/blanket systems in fusion reactors is their activity with regard to nonmetallic impurities in the coolants. This paper presents the results of studying the corrosion resistance in high-purity liquid lithium (with the nitrogen and carbon content of less than 10-3 wt %) of vanadium and vanadium alloys (V-1.86Ga, V-3.4Ga-0.62Si, V-4.81Ti-4.82Cr) both in the initial state and preliminarily irradiated with Ar+ ions with energy of 20 keV to a dose of 1022 m-2 at an irradiation temperature of 400°C. The degree of corrosion was estimated by measuring the changes in the weight and microhardness. Corrosion tests were carried out under static isothermal conditions at a temperature of 600°C for 400 h. The identity of corrosion mechanisms of materials both irradiated with Ar ions and not irradiated, which consisted in an insignificant penetration of nitrogen into the materials and a substantial escape of oxygen from the materials, causing the formation of a zone with a reduced microhardness near the surface, was established. The influence of the corrosive action of lithium on the surface morphology of the materials under study was found, resulting in the manifestation of grain boundaries and slip lines on the sample surface, the latter being most clearly observed in the case of preliminary irradiation with Ar ions.

  14. First principle investigations of the structural, electronic and magnetic properties of predicted new zirconium based full-Heusler compounds, Zr{sub 2}MnZ (Z=Al, Ga and In)

    Energy Technology Data Exchange (ETDEWEB)

    Birsan, A., E-mail: anca_birsan@infim.ro [National Institute of Materials Physics, 105 bis Atomistilor Street, PO Box MG-7, 077125 Magurele-Ilfov (Romania); University of Bucharest, Faculty of Physics, 105 Atomistilor Street, PO Box MG-11, 077125, Magurele-Ilfov (Romania); Kuncser, V. [National Institute of Materials Physics, 105 bis Atomistilor Street, PO Box MG-7, 077125 Magurele-Ilfov (Romania)

    2016-05-15

    The crystal structure, electronic and magnetic properties of predicted new full-Heusler compounds Zr{sub 2}MnZ (Z=Al, Ga, In) were studied within the density functional theory (DFT) framework. These materials exhibit unique properties that connect the spin gapless semiconducting character with the completely compensated ferrimagnetism. Magnetically ordered Zr{sub 2}MnZ (Z=Al, Ga, In) compounds crystallize in inverse Heusler structure are stable against decomposition and have zero magnetic moment per formula unit, in agreement with Slater–Pauling rule. The Zr{sub 2}MnAl compound presents semiconducting properties with an energy band gap of 0.41 eV in the majority spin channel and a zero band gap in the minority spin channel. By substituting completely the Al in Zr{sub 2}MnAl via Ga and In elements, semiconducting pseudo band gaps are formed in the majority spin channels due to different neighborhoods around the manganese atoms, which decreases the energy of Mn triple degenerated anti-bonding states. - Highlights: • Zr{sub 2}MnZ (Z=Al, Ga, In) compounds exhibit zero magnetic moments per formula unit, in the ground state. • Zr{sub 2}MnAl exhibits spin gapless semiconducting properties. • Zr{sub 2}MnZ (Z=Ga, In) presents semiconducting pseudo band gaps, around Fermi level.

  15. Shape memory alloys applied to improve rotor-bearing system dynamics - an experimental investigation

    DEFF Research Database (Denmark)

    Enemark, Søren; Santos, Ilmar; Savi, Marcelo A.

    2015-01-01

    hysteretic stress-strain relations which may be utilized for damping purposes. These ideas are tested in this study on a dedicated test-rig, consisting of a rigid shaft and disc held vertically by passive magnetic bearings, where the damping is low. The bearing housings is flexibly supported by shape memory......tor-bearing systems have critical speeds and to pass through them is an ongoing challenge in the field of mechanical engineering. The incorporation of shape memory alloys in rotating systems has an increasing importance to improve system performance and to avoid potential damaging situations when...... passing through critical speeds. In this work, the feasibility of applying shape memory alloys to a rotating system is experimentally investigated. Shape memory alloys can change their stiffness with temperature variations and thus they may change system dynamics. Shape memory alloys also exhibit...

  16. Investigation of Microstructure in Solid State Welded Al-Cu-Li alloy

    Directory of Open Access Journals (Sweden)

    No Kookil

    2016-01-01

    Full Text Available Al-Li alloys have been extensively used in aerospace vehicle structure since the presence of lithium increases the modulus and reduce the density of the alloy. Especially the third generation Al-Cu-Li alloy shows enhanced fracture toughness at cryogenic temperatures so that the alloy has been used on the fuel tank of space launchers, like Super Lightweight External Tank of the Space Shuttle. Since the commercial size of the plate cannot accommodate the large tank size of the launcher, joining several pieces is required. However, lithium is highly reactive and its compounds can decompose with heat from conventional fusion welding and form different types of gases which result in formation of defects. In this study, the microstructure change is investigated after solid state welding process to join the Al-Cu-Li sheets with optical and transmission electron microscopic analysis of precipitates.

  17. Investigation of Wear Resistant of Low-Alloyed and Chromium Cast Steel

    Directory of Open Access Journals (Sweden)

    A. Studnicki

    2012-04-01

    Full Text Available Results of investigations of wear resistant of two species of cast steel were introduced in the article (low-alloyed and chromium cast steel on the background of the standard material which was low alloy wear resistant steel about the trade name CREUSABRO ®8000. The investigations were executed with two methods: abrasive wears in the stream of loose particles (the stream of quartz sand and abrasive wears particles fixed (abrasive paper with the silicon carbide. Comparing the results of investigations in the experiments was based about the counted wear index which characterizes the wears of the studied material in the relation to the standard material.

  18. Corrosion resistance investigation of vanadium alloys in liquid lithium

    Energy Technology Data Exchange (ETDEWEB)

    Borovitskaya, I. V., E-mail: symp@imet.ac.ru [Russian Academy of Sciences, Baikov Institute of Metallurgy and Materials Science (Russian Federation); Lyublinskiy, I. E. [JSC Red Star (Russian Federation); Bondarenko, G. G. [National Research University Higher School of Economics (Russian Federation); Paramonova, V. V. [Russian Academy of Sciences, Baikov Institute of Metallurgy and Materials Science (Russian Federation); Korshunov, S. N.; Mansurova, A. N. [National Research Center Kurchatov Institute (Russian Federation); Lyakhovitskiy, M. M. [Russian Academy of Sciences, Baikov Institute of Metallurgy and Materials Science (Russian Federation); Zharkov, M. Yu. [JSC Red Star (Russian Federation)

    2016-12-15

    A major concern in using vanadium alloys for first wall/blanket systems in fusion reactors is their activity with regard to nonmetallic impurities in the coolants. This paper presents the results of studying the corrosion resistance in high-purity liquid lithium (with the nitrogen and carbon content of less than 10{sup –3} wt %) of vanadium and vanadium alloys (V–1.86Ga, V–3.4Ga–0.62Si, V–4.81Ti–4.82Cr) both in the initial state and preliminarily irradiated with Ar+ ions with energy of 20 keV to a dose of 10{sup 22} m{sup –2} at an irradiation temperature of ~400°C. The degree of corrosion was estimated by measuring the changes in the weight and microhardness. Corrosion tests were carried out under static isothermal conditions at a temperature of 600°C for 400 h. The identity of corrosion mechanisms of materials both irradiated with Ar ions and not irradiated, which consisted in an insignificant penetration of nitrogen into the materials and a substantial escape of oxygen from the materials, causing the formation of a zone with a reduced microhardness near the surface, was established. The influence of the corrosive action of lithium on the surface morphology of the materials under study was found, resulting in the manifestation of grain boundaries and slip lines on the sample surface, the latter being most clearly observed in the case of preliminary irradiation with Ar ions.

  19. 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...

  20. Investigation of ordering phenomenon in Me–Pt (Me=Fe,Ni liquid alloys

    Directory of Open Access Journals (Sweden)

    Yisau Adelaja Odusote

    2008-01-01

    Full Text Available The phase diagrams of Fe–Pt and Ni–Pt liquid alloy systems show the existence of FePt and NiPt intermetallic compounds, respectively, in their solid intermediate states, and the associative tendency between unlike atoms in these liquid alloys has been analysed using the self-association model. The concentration dependences of mixing properties such as the free energy of mixing, GM; the concentration fluctuations, Scc(0, in the long-wavelength limits; the chemical short-range order (CSRO parameter, α1; as well as the chemical diffusion, enthalpy and entropy of the mixing of Fe–Pt and Ni–Pt liquid alloys have been investigated to determine the nature of ordering in the liquid alloys. The results show that heterocoordination occurs in the alloys at all concentrations. The effect of CSRO on Scc(0, chemical diffusion, D, and the order parameter, α1, has been considered. The ordering phenomenon in the liquid alloys is also related to the effect of the atomic size mismatch volume on Scc(0.

  1. Investigation of microstructure in hot-pressed Nb–23Ti–15Al alloy

    Energy Technology Data Exchange (ETDEWEB)

    Shi, Zhiwu; Wei, Hua; Zhang, Hongyu; Wu, Duoli; Jin, Tao; Sun, Xiaofeng; Zheng, Qi, E-mail: qzheng@imr.ac.cn

    2015-07-05

    Highlights: • The Ti(O, C), a new strengthening phase, is found in Nb–Ti–Al alloys. • Ti(O, C) has a face-centered cubic structure and a lattice parameter of 4.27 Å. • Two different morphologies of Ti(O, C) are observed. • β and δ phases exhibit as large irregular blocks and equiaxed particles. • Ordering of β phase is observed in hot-pressed Nb–Ti–Al alloy. - Abstract: Microstructure of hot-pressed Nb–23Ti–15Al alloy has been systematically investigated, with emphasis on the characterization of Ti(O, C) phase. The microstructure and composition of Nb–23Ti–15Al alloy were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM) and electron probe microanalysis (EPMA). The results indicate the presence of β, δ and Ti(O, C) phases in the alloy. The β phase exhibits as large irregular blocks, while the δ phase presents as small equiaxed particles linked together around β blocks. Ordering of β phase is shown by related selected area electronic diffraction (SAED) patterns and dark-field micrograph. The Ti(O, C), a solid-solution of TiO or TiC, is characterized for the first time in Nb–Ti–Al alloy. The Ti(O, C) has a face-centered cubic (FCC) structure and a moderate lattice parameter between that of TiO and TiC. Two different morphologies of Ti(O, C) are observed in the alloy: large cobblestone-like aggregated particles and small dispersive particles. The formation of Ti(O, C) phase can potentially increase high-temperature strength of Nb–Ti–Al alloy.

  2. 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.

  3. Phase equilibria investigation and alloys characterization in Sn-In-Ag system

    Directory of Open Access Journals (Sweden)

    Milosavljević Aleksandra R.

    2008-01-01

    Full Text Available Lead-free soldering has become very popular in the world recently, especially in electronics, because of high ecological demands in industry. Some of lead-free solder alloys are already used in electronic industry, but despite that investigations are still going in order to find suitable replacement for Pb-Sn standard solder. In this paper phase equilibria and characterization of Sn-In-Ag alloys in section In:Ag = 7:3 are investigated. The results of phase diagram calculation are obtained by ThermoCalc software, and characteristic temperatures by DSC method. The results of XRD analysis, optical microscopy, microhardness and electrical conductivity are also presented. These results are given in order to contribute the knowledge about lead-free solders, especially Sn-In-Ag solder alloys, which are potential candidates for replacement standard lead solders.

  4. Investigations of binary and ternary phase change alloys for future memory applications

    Energy Technology Data Exchange (ETDEWEB)

    Rausch, Pascal

    2012-09-13

    The understanding of phase change materials is of great importance because it enables us to predict properties and tailor alloys which might be even better suitable to tackle challenges of future memory applications. Within this thesis two topics have been approached: on the one hand the understanding of the alloy In{sub 3}Sb{sub 1}Te{sub 2} and on the other hand the so called resistivity drift of amorphous Ge-Sn-Te phase change materials. The main topic covers an in depth discussion of the ternary alloy In{sub 3}Sb{sub 1}Te{sub 2}. At first glance, this alloy does not fit into the established concepts of phase alloys: e.g. the existence of resonant bonding in the crystalline phase is not obvious and the number of p-electrons is very low compared to other phase change alloys. Furthermore amorphous phase change alloys with high indium content are usually not discussed in literature, an exception being the recent work by Spreafico et al. on InGeTe{sub 2}. For the first time a complete description of In{sub 3}Sb{sub 1}Te{sub 2} alloy is given in this work for the crystalline phase, amorphous phase and crystallization process. In addition comparisons are drawn to typical phase change materials like Ge{sub 2}Sb{sub 2}Te{sub 5}/GeTe or prototype systems like AgInTe{sub 2} and InTe. The second topic of this thesis deals with the issue of resistivity drift, i.e. the increase of resistivity of amorphous phase change alloys with aging. This drift effect greatly hampers the introduction of multilevel phase change memory devices into the market. Recently a systematic decrease of drift coefficient with stoichiometry has been observed in our group going from GeTe over Ge{sub 3}Sn{sub 1}Te{sub 4} to Ge{sub 2}Sn{sub 2}Te{sub 4}. These alloys are investigated with respect to constraint theory.

  5. 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.

  6. 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.

  7. Design changes of device to investigation of alloys linear contraction and shrinkage stresses

    Directory of Open Access Journals (Sweden)

    J. Mutwil

    2009-07-01

    Full Text Available Some design changes in device elaborated by author to examination of linear contraction and shrinkage stresses progress of metals and alloys during– and after solidification have been described. The introduced changes have been focused on design of closing of shrinkage test rod mould. The introduced changes have been allowed to simplify a mounting procedure of thermocouples measuring a temperature of the shrinkage rod casting (in 6 points. Exemplary investigation results of linear contraction and shrinkage stresses development in Al-Si13.5% alloy have been presented.

  8. Three-dimensional investigation of recrystallization nucleation in a particle-containing Al alloy

    DEFF Research Database (Denmark)

    Zhang, Yonghao; Juul Jensen, Dorte; Zhang, Yubin

    2012-01-01

    The effects of an inhomogeneous distribution of second-phase particles on nucleation of recrystallization in a particle-containing aluminum alloy are investigated by 3-D serial sectioning. Clusters and bands of big intermetallic particles are the dominating nucleation sites, but other sites...

  9. First-principles investigations of the Ni3Sn alloy at steam reforming conditions

    DEFF Research Database (Denmark)

    Saadi, Souheil; Hinnemann, Berit; Helveg, Stig

    2009-01-01

    The structure and surface composition of a Ni3Sn alloy at conditions relevant for the steam reforming reaction was investigated using density functional theory calculations. Both the flat Ni3Sn [1 0 (1) over bar 0] surface and a surface with steps in the closed packed direction [1 0 (1) over bar 0...

  10. An investigation into the effects of hydrogen on the fracture and deformation of Alloy X-750

    Energy Technology Data Exchange (ETDEWEB)

    Symons, Douglas M. [Carnegie Mellon Univ., Pittsburgh, PA (United States). Dept. of Materials Science and Engineering

    1994-11-01

    this study investigated the effect of hydrogen on the fracture of a nickel-base superalloy, Alloy X-750 in the solution treated and aged (HTH) condition. The effect of hydrogen was examined through tensile testing and fracture toughness testing incorporating observations from scanning electron microscopy and light microscopy.

  11. An investigation of shape memory alloys as actuating elements in aerospace morphing applications

    DEFF Research Database (Denmark)

    Karagiannis, Dimitrios; Stamatelos, Dimtrios; Kappatos, Vasileios

    2017-01-01

    Two innovative actuating concepts for aerospace morphing applications, based on Shape Memory Alloys (SMAs), are proposed. The first concept investigates a composite plate incorporating embedded SMA wires. A Nonlinear Auto Regressive with eXogenous excitation (NARX) model is proposed for controlling...

  12. Investigation of Martensite Formation in Fe Based Alloys During Heating From Boiling Nitrogen Temperature

    DEFF Research Database (Denmark)

    Villa, Matteo; Christiansen, Thomas L.; Hansen, Mikkel F.

    2015-01-01

    he austenite-to-martensite transformation at temperatures below room temperature was investigated in situ by magnetometry in Fe-N, Fe-Cr-C and Fe-Cr-Ni based alloys. After quenching to room temperature, samples were immersed in boiling nitrogen and martensite formation was followed during...

  13. 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.

  14. Experimental Investigation on Laser Impact Welding of Fe-Based Amorphous Alloys to Crystalline Copper

    Science.gov (United States)

    Wang, Xiao; Luo, Yapeng; Huang, Tao; Liu, Huixia

    2017-01-01

    Recently, amorphous alloys have attracted many researchers’ attention for amorphous structures and excellent properties. However, the welding of amorphous alloys to traditional metals in the microscale is not easy to realize in the process with amorphous structures unchanged, which restrains the application in industry. In this paper, a new method of welding Fe-based amorphous alloys (GB1K101) to crystalline copper by laser impact welding (LIW) is investigated. A series of experiments was conducted under different laser energies, during which Fe-based amorphous alloys and crystalline copper were welded successfully by LIW. In addition, the microstructure and mechanical properties of welding joints were observed and measured, respectively. The results showed that the surface wave and springback were observed on the flyer plate after LIW. The welding interface was straight or wavy due to different plastic deformation under different laser energies. The welding interface was directly bonded tightly without visible defects. No visible element diffusion and intermetallic phases were found in the welding interface. The Fe-based amorphous alloys retained amorphous structures after LIW under the laser energy of 835 mJ. The nanoindentation hardness across the welding interface showed an increase on both sides of the welding interface. The results of the lap shearing test showed that the fracture position was on the side of copper coil. PMID:28772886

  15. An experimental investigation of fatigue damage in aluminum 2024-T3 alloys

    Science.gov (United States)

    Ferguson, Milton W.

    1993-01-01

    Aluminum alloys are finding increasing use in the aerospace and automobile industries due to their attractive low density-high modulus and low density-high strength characteristics. Unfortunately, cyclic stress-strain deformation alters the microstructure of the material. These structural changes can lead to fatigue damage and ultimately service failure. Therefore, in order to assess the integrity of the alloy, a correlation between fatigue damage and a measurable microstructural property is needed. Aluminum 2024-T3, a commonly used commercial alloy, contains many grains (individual crystals) of various orientations. The sizes and orientations of these grains are known to affect the strength, hardness, and magnetic permeability of polycrystalline alloys and metals; therefore, perhaps a relationship between a grain property and the fatigue state can be established. Tension-compression cycling in aluminum alloys can also induce changes in their dislocation densities. These changes can be studied from measurements of the electrical resistivities of the materials. Consequently, the goals of this investigation were: to study the grain orientation of aluminum 2024-T3 and to seek a correlation between the grain orientation and the fatigue state of the material; and to measure the electrical resistivities of fatigued samples of aluminum 2024-T3 and to interpret the findings.

  16. Experimental Investigation of Size Effects on the Thermal Conductivity of Silicon-Germanium Alloy Thin Films

    Science.gov (United States)

    Cheaito, Ramez; Duda, John C.; Beechem, Thomas E.; Hattar, Khalid; Ihlefeld, Jon F.; Medlin, Douglas L.; Rodriguez, Mark A.; Campion, Michael J.; Piekos, Edward S.; Hopkins, Patrick E.

    2012-11-01

    We experimentally investigate the role of size effects and boundary scattering on the thermal conductivity of silicon-germanium alloys. The thermal conductivities of a series of epitaxially grown Si1-xGex thin films with varying thicknesses and compositions were measured with time-domain thermoreflectance. The resulting conductivities are found to be 3 to 5 times less than bulk values and vary strongly with film thickness. By examining these measured thermal conductivities in the context of a previously established model, it is shown that long wavelength phonons, known to be the dominant heat carriers in alloy films, are strongly scattered by the film boundaries, thereby inducing the observed reductions in heat transport. These results are then generalized to silicon-germanium systems of various thicknesses and compositions; we find that the thermal conductivities of Si1-xGex superlattices are ultimately limited by finite size effects and sample size rather than periodicity or alloying. This demonstrates the strong influence of sample size in alloyed nanosystems. Therefore, if a comparison is to be made between the thermal conductivities of superlattices and alloys, the total sample thicknesses of each must be considered.

  17. Experimental Investigation on Laser Impact Welding of Fe-Based Amorphous Alloys to Crystalline Copper.

    Science.gov (United States)

    Wang, Xiao; Luo, Yapeng; Huang, Tao; Liu, Huixia

    2017-05-12

    Recently, amorphous alloys have attracted many researchers' attention for amorphous structures and excellent properties. However, the welding of amorphous alloys to traditional metals in the microscale is not easy to realize in the process with amorphous structures unchanged, which restrains the application in industry. In this paper, a new method of welding Fe-based amorphous alloys (GB1K101) to crystalline copper by laser impact welding (LIW) is investigated. A series of experiments was conducted under different laser energies, during which Fe-based amorphous alloys and crystalline copper were welded successfully by LIW. In addition, the microstructure and mechanical properties of welding joints were observed and measured, respectively. The results showed that the surface wave and springback were observed on the flyer plate after LIW. The welding interface was straight or wavy due to different plastic deformation under different laser energies. The welding interface was directly bonded tightly without visible defects. No visible element diffusion and intermetallic phases were found in the welding interface. The Fe-based amorphous alloys retained amorphous structures after LIW under the laser energy of 835 mJ. The nanoindentation hardness across the welding interface showed an increase on both sides of the welding interface. The results of the lap shearing test showed that the fracture position was on the side of copper coil.

  18. Investigation of TiNi shape memory alloy for thermosensitive wire drive

    Directory of Open Access Journals (Sweden)

    Ostropiko Eugene

    2015-01-01

    Full Text Available TiNi shape memory alloys are nowadays widely used in engineering and medicine. The unique capabilities of this material are particularly apparent in applications for space technology. One of the actual present problems is the design of thermosensitive devices for space applications. In this work, we investigated a TiNi alloy as a working element material for the thermosensitive wire drive as an actuator. An optimum thermomechanical treatment of NiTi alloys was selected based on the analysis of functional and mechanical properties. It consists of a multi-cycle implementation of transformation plasticity under 220 MPa constant stress and a shape memory effect in the free state.

  19. 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).

  20. Micro/nano-scale investigation on tin alloys and tin dioxide nanowires

    Science.gov (United States)

    Sun, Yong

    Tin (Sn) and its alloys have been at people's service since 3000 BC when bronze (alloy of tin and copper) was produced in large scale. They have unique properties and find applications in various engineering fields. Correspondingly, there is abundant information waiting to be clarified surrounding these Sn-related materials. As the key element used for solder alloys, the properties of Sn alloys have been of great interest to the electronic packaging community. At the same time, the intriguing phenomenon of spontaneous Sn whisker growth from Sn / Sn-alloy thin films have bothered, yet also inspired materials scientists for over 60 years. The most commonly seen Sn-containing compound, SnO 2, is in high demand as well due to its exceptional electronic and chemical properties. In addition, nanostructures of SnO2 are intensively studied for their potential applications as solid-state sensors, transparent conducting materials, lithium-ion batteries, high-efficiency solar cell and recently, supercapacitors. The objective of this proposed research is to explore the amazing properties of Sn and Sn-alloys from several different perspectives. Firstly, ever since the banish of lead in solder alloys, lead-free alloys such as Sn-Ag-Cu (SAC) has been put under the spotlight. We intend to use our expertise in nanomechanics to give an in-depth and thorough investigation on a popular SAC387 alloy. The mechanical properties of each phase and the local deformation mechanisms have been considered. Secondly, the Sn whisker growth phenomenon is to be re-visited. With the aid of digital image correlation (DIC) techniques, it was found that magnitude of the strain gradient plays an important role in whisker growth. Moreover, DIC helps to visualize the dynamic growth process in which the alteration of strain field has been identified to cause growth of subsequent whiskers. Last but not least, the performance of SnO2 nanowires is to be evaluated in several aspects including mechanical

  1. Experimental Investigation and FE Analysis on Constitutive Relationship of High Strength Aluminum Alloy under Cyclic Loading

    OpenAIRE

    Yuanqing Wang; Zhongxing Wang

    2016-01-01

    Experiments of 17 high strength aluminum alloy (7A04) specimens were conducted to investigate the constitutive relationship under cyclic loading. The monotonic behavior and hysteretic behavior were focused on and the fracture surface was observed by scanning electron microscope (SEM) to investigate the microfailure modes. Based on Ramberg-Osgood model, stress-strain skeleton curves under cyclic loading were fitted. Parameters of combined hardening model including isotropic hardening and kinem...

  2. Experimental Investigation on the Joining of Aluminum Alloy Sheets Using Improved Clinching Process.

    Science.gov (United States)

    Chen, Chao; Zhao, Shengdun; Han, Xiaolan; Zhao, Xuzhe; Ishida, Tohru

    2017-08-01

    Aluminum alloy sheets have been widely used to build the thin-walled structures by mechanical clinching technology in recent years. However, there is an exterior protrusion located on the lower sheet and a pit on the upper sheet, which may restrict the application of the clinching technology in visible areas. In the present study, an improved clinched joint used to join aluminum alloy sheets was investigated by experimental method. The improved clinching process used for joining aluminum alloy evolves through four phases: (a) localized deformation; (b) drawing; (c) backward extrusion; and (d) mechanical interlock forming. A flat surface can be produced using the improved clinching process. Shearing strength, tensile strength, material flow, main geometrical parameters, and failure mode of the improved clinched joint were investigated. The sheet material was compressed to flow radially and upward using a punch, which generated a mechanical interlock by producing severe localized plastic deformation. The neck thickness and interlock of the improved clinched joint were increased by increasing the forming force, which also contributed to increase the strength of the clinched joint. The improved clinched joint can get high shearing strength and tensile strength. Three main failure modes were observed in the failure process, which were neck fracture mode, button separation mode, and mixed failure mode. The improved clinched joint has better joining quality to join aluminum alloy sheets on the thin-walled structures.

  3. Experimental Investigation on the Joining of Aluminum Alloy Sheets Using Improved Clinching Process

    Directory of Open Access Journals (Sweden)

    Chao Chen

    2017-08-01

    Full Text Available Aluminum alloy sheets have been widely used to build the thin-walled structures by mechanical clinching technology in recent years. However, there is an exterior protrusion located on the lower sheet and a pit on the upper sheet, which may restrict the application of the clinching technology in visible areas. In the present study, an improved clinched joint used to join aluminum alloy sheets was investigated by experimental method. The improved clinching process used for joining aluminum alloy evolves through four phases: (a localized deformation; (b drawing; (c backward extrusion; and (d mechanical interlock forming. A flat surface can be produced using the improved clinching process. Shearing strength, tensile strength, material flow, main geometrical parameters, and failure mode of the improved clinched joint were investigated. The sheet material was compressed to flow radially and upward using a punch, which generated a mechanical interlock by producing severe localized plastic deformation. The neck thickness and interlock of the improved clinched joint were increased by increasing the forming force, which also contributed to increase the strength of the clinched joint. The improved clinched joint can get high shearing strength and tensile strength. Three main failure modes were observed in the failure process, which were neck fracture mode, button separation mode, and mixed failure mode. The improved clinched joint has better joining quality to join aluminum alloy sheets on the thin-walled structures.

  4. Microgalvanic Corrosion Behavior of Cu-Ag Active Braze Alloys Investigated with SKPFM

    Directory of Open Access Journals (Sweden)

    Armen Kvryan

    2016-04-01

    Full Text Available The nature of microgalvanic couple driven corrosion of brazed joints was investigated. 316L stainless steel samples were joined using Cu-Ag-Ti and Cu-Ag-In-Ti braze alloys. Phase and elemental composition across each braze and parent metal interface was characterized and scanning Kelvin probe force microscopy (SKPFM was used to map the Volta potential differences. Co-localization of SKPFM with Energy Dispersive Spectroscopy (EDS measurements enabled spatially resolved correlation of potential differences with composition and subsequent galvanic corrosion behavior. Following exposure to the aggressive solution, corrosion damage morphology was characterized to determine the mode of attack and likely initiation areas. When exposed to 0.6 M NaCl, corrosion occurred at the braze-316L interface preceded by preferential dissolution of the Cu-rich phase within the braze alloy. Braze corrosion was driven by galvanic couples between the braze alloys and stainless steel as well as between different phases within the braze microstructure. Microgalvanic corrosion between phases of the braze alloys was investigated via SKPFM to determine how corrosion of the brazed joints developed.

  5. 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.

  6. 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.

  7. Organic alloy systems suitable for the investigation of regular binary and ternary eutectic growth

    Science.gov (United States)

    Sturz, L.; Witusiewicz, V. T.; Hecht, U.; Rex, S.

    2004-09-01

    Transparent organic alloys showing a plastic crystal phase were investigated experimentally using differential scanning calorimetry and directional solidification with respect to find a suitable model system for regular ternary eutectic growth. The temperature, enthalpy and entropy of phase transitions have been determined for a number of pure substances. A distinction of substances with and without plastic crystal phases was made from their entropy of melting. Binary phase diagrams were determined for selected plastic crystal alloys with the aim to identify eutectic reactions. Examples for lamellar and rod-like eutectic solidification microstructures in binary systems are given. The system (D)Camphor-Neopentylglycol-Succinonitrile is identified as a system that exhibits, among others, univariant and a nonvariant eutectic reaction. The ternary eutectic alloy close to the nonvariant eutectic composition solidifies with a partially faceted solid-liquid interface. However, by adding a small amount of Amino-Methyl-Propanediol (AMPD), the temperature of the nonvariant eutectic reaction and of the solid state transformation from plastic to crystalline state are shifted such, that regular eutectic growth with three distinct nonfaceted phases is observed in univariant eutectic reaction for the first time. The ternary phase diagram and examples for eutectic microstructures in the ternary and the quaternary eutectic alloy are given.

  8. Multi-scale Investigation on Microstructure, Mechanical Properties, and Deformation Mechanisms in Mg Alloys

    Science.gov (United States)

    Zhang, Dalong

    Mg and its alloys are promising candidates for light-weight structural applications, e.g., aircraft, automobile, electronic, etc. However, the inherent hexagonal close packed crystal structure makes the deformation of Mg anisotropic, namely deformation only occurs predominantly by dislocation slip in the close-packed (0001) plane (i.e., basal plane), or by deformation twinning in {101¯2} planes. Both basal slip and twinning cause the crystal to re-orient. Consequently, polycrystalline Mg alloys that have undergone thermomechanical processing usually contain strong texture, i.e., preferred crystallographic orientation in grains. The texture in turn leads to anisotropic deformation in wrought Mg alloys. For example, in extruded Mg alloys, the compressive yield strength is usually much lower than the tensile yield strength (so-called yield asymmetry and strength differential). It is the anisotropy that hinders the broader application of Mg alloys. Recent modeling studies on Mg predict that certain alloying elements, particularly rare-earth elements (e.g., Y, Ce, Nd, Gd, etc.), could alter the active deformation modes and enhance homogeneous deformation and overall mechanical properties in Mg. Therefore, the objective of this dissertation research is to investigate experimentally the effects of alloying element Y in reducing the intrinsic and extrinsic anisotropy, modifying texture, and enhancing the overall strength and ductility for Mg. In addition, the research also uncovered some unexpected "side effects" of Y and these phenomena were studied and explained from a fundamental perspective. The methodology used in this work is described as follows. Ultrafine grained Mg 2.5 at.% Y alloy (UFG Mg-2.5Y) was prepared by powder metallurgy method, including gas atomization for producing Mg-2.5Y powder, degassing and hot isostatic pressing (HIP), and hot extrusion. Both the as-HIPed and the as-extruded materials were characterized by electron back-scattered diffraction (EBSD

  9. 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.

  10. 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.

  11. Investigation of solidification behavior of the Sn-rich ternary Sn–Bi–Zn alloys

    Directory of Open Access Journals (Sweden)

    S Mladenović

    2017-03-01

    Full Text Available Solidification properties and microstructure of six as-cast Sn–Bi–Zn alloys with 80 at.% of Sn and variable contents of Bi and Zn were experimentally investigated using the scanning electron microscopy (SEM with energy-dispersive X-ray spectroscopy (EDS and differential scanning calorimetry (DSC. The experimentally obtained results were compared with predicted phase equilibria according to the calculation of phase diagram (CALPHAD method and by the Scheil solidification simulation.

  12. Investigation of localization effect in GaN-rich InGaN alloys and ...

    Indian Academy of Sciences (India)

    Abstract. The temperature-dependent PL properties of GaN-rich InxGa1−xN alloys is investigated and S-shaped temperature dependence is observed in all InGaN samples. It is found that the origin of localization effect in samples. A and B are different from that in sample C. For samples A and B, In content fluctuations ...

  13. A Metallurgical Investigation of the Direct Energy Deposition Surface Repair of Ferrous Alloys

    Science.gov (United States)

    Marya, Manuel; Singh, Virendra; Hascoet, Jean-Yves; Marya, Surendar

    2018-01-01

    Among additive manufacturing (AM) processes, the direct energy deposition (DED) by laser is explored to establish its applicability for the repair of ferrous alloys such as UNS G41400 low-alloy steel, UNS S41000 martensitic stainless steel, UNS S17400 precipitation-strengthened martensitic stainless steel, and UNS S32750 super-duplex stainless steel. Unlike plating, thermal spray, and conventional cladding weld, DED laser powder deposition offers potential advantages, e.g., thin deposits, limited dilutions, narrow heat-affected zones (HAZ), potentially improved surface properties. In this investigation, all AM deposits were completed with an IREPA CLAD™ system using a powder feed of UNS N06625, an alloy largely selected for its outstanding corrosion resistance. This investigation first addresses topological aspects of AM deposits (including visual imperfections) before focusing on changes in microstructure, microhardness, chemical composition across AM deposits and base materials. It has been established that dense, uniform, hard ( 300 HVN), crack-free UNS N06625-compliant AM deposits of fine dendritic microstructures are reliably produced. However, except for the UNS S32750 steel, a significant martensitic hardening was observed in the HAZs of UNS G41400 ( 650 HVN), UNS S41000 ( 500 HVN), and UNS S17400 ( 370 HVN). In summary, this investigation demonstrates that the DED laser repair of ferrous parts with UNS N06625 may restore damaged surfaces, but it also calls for cautions and complementary investigations for alloys experiencing a high HAZ hardening, for which industry standard recommendations are exceeded and lead to an increased risk of delayed cracking in corrosive environments.

  14. Liquid oxygen LOX compatibility evaluations of aluminum lithium (Al-Li) alloys: Investigation of the Alcoa 2090 and MMC weldalite 049 alloys

    Science.gov (United States)

    Diwan, Ravinder M.

    1989-01-01

    The behavior of liquid oxygen (LOX) compatibility of aluminum lithium (Al-Li) alloys is investigated. Alloy systems of Alcoa 2090, vintages 1 to 3, and of Martin Marietta Corporation (MMC) Weldalite 049 were evaluated for their behavior related to the LOX compatibility employing liquid oxygen impact test conditions under ambient pressures and up to 1000 psi. The developments of these aluminum lithium alloys are of critical and significant interest because of their lower densities and higher specific strengths and improved mechanical properties at cryogenic temperatures. Of the different LOX impact tests carried out at the Marshall Space Flight Center (MSFC), it is seen that in certain test conditions at higher pressures, not all Al-Li alloys are LOX compatible. In case of any reactivity, it appears that lithium makes the material more sensitive at grain boundaries due to microstructural inhomogeneities and associated precipitate free zones (PFZ). The objectives were to identify and rationalize the microstructural mechanisms that could be relaxed to LOX compatibility behavior of the alloy system in consideration. The LOX compatibility behavior of Al-Li 2090 and Weldalite 049 is analyzed in detail using microstructural characterization techniques with light optical metallography, scanning electron microscopy (SEM), electron microprobe analysis, and surface studies using secondary ion mass spectrometry (SIMS), electron spectroscopy in chemical analysis (ESCA) and Auger electron spectroscopy (AES). Differences in the behavior of these aluminum lithium alloys are assessed and related to their chemistry, heat treatment conditions, and microstructural effects.

  15. Experimental investigation of laser peening on Ti17 titanium alloy for rotor blade applications

    Energy Technology Data Exchange (ETDEWEB)

    Hongchao, Qiao, E-mail: hcqiao@sia.cn

    2015-10-01

    Highlights: • Laser peening on Ti17 titanium alloys is investigated. • Roughness and residual stress value were grown on laser energy and impact times. • Hardened layer depth increases significantly with laser peening impact times. • Laser peening is effectively in lower fatigue stress level. • Laser peening makes the microstructures evolution. - Abstract: Laser peening is an innovative surface treatment technique, and can significantly improve the mechanical performance of metallic components. To investigate the fatigue life of Ti17 titanium alloy by laser peening, laser peening experiment was undertaken using Nd:YAG laser system with the pulse-width of 15 ns and max pulse-energy of 7 J. Firstly, the mechanical properties and microstructure with different laser peening parameters were investigated, which were measured and observed by Vickers indenter, X-ray diffraction, scanning electron microscope and transmission electron microscope. Micro-hardness and compressive residual stress distribution was remarkably improved. High-density dislocations and fine-grains were observed in the surface layer. Then, several stress levels were chosen to be applied on the tension and compression fatigue specimens. The fatigue life and fracture mechanism of the specimens without- and with-laser peened were compared, and the strengthening mechanism was indicated by analyzing the effects on the microstructure and residual stress evolution. The results demonstrate that laser peening could effectively improve the fatigue life of Ti17 titanium alloy.

  16. Investigations on the Hot Stamping of AW-7921-T4 Alloy Sheet

    Directory of Open Access Journals (Sweden)

    M. Kumar

    2017-01-01

    Full Text Available AW-7xxx alloys have been nowadays considered for greater light weighting potential in automotive industry due to its higher strength compared to AW-5xxx and AW-6xxx alloys. However, due to their lower formability the forming processes are still in development. This paper investigates one such forming process called hot stamping. The investigation started by carrying out hot tensile testing of an AW-7xxx alloy, that is, AW-7921 at temperatures between 350°C and 475°C, to measure the strength and formability. Formability was found to improve with increasing temperature and was sensitive to the strain rate. Dynamic recovery is considered as usual reason for the formability improvement. However, examining the precipitation states of the as-received condition and after hot stamping using differential scanning calorimetry (DSC, the dissolution of precipitates was also believed to contribute to this increase in formability. Following solution heat treatment there was no precipitation during cooling across the cooling rates investigated (5–10°C/s. Samples taken from parts hot stamped at 10 and 20 mm s−1 had similar yield strengths. A 3-step paint baking heat treatment yielded a higher postpaint baking strength than a single step treatment.

  17. Microstructural Investigation and Phase Relationships of Fe-Al-Hf Alloys

    Science.gov (United States)

    Yildirim, Mehmet; Akdeniz, M. Vedat; Mekhrabov, Amdulla O.

    2014-07-01

    The effect of Hf addition on microstructures, phase relationships, microhardness, and magnetic properties of Fe50Al50- n Hf n alloys for n = 1, 3, 5, 7, and 9 at. pct has been investigated. At all investigated compositions, the ternary intermetallic HfFe6Al6 τ 1 phase forms due to the limited solid solubility of Hf in FeAl phase and tends to develop a eutectic phase mixture with the Fe-Al-based phase. The Hf concentration of the eutectic composition is found to be 7 at. pct from the microstructural examinations and the eutectic phase transition temperature is determined as 1521 K (1248 °C) independent of Hf amount by differential scanning calorimetry measurements. Furthermore, the enthalpies and activation energies (based on Kissinger and Ozawa methods) of eutectic phase transitions are reported. The minimum activation energy is calculated for the fully eutectic composition. Moreover, variation of the microhardness of Fe-Al-based alloys as a function of the Hf content is investigated, and its dependence on the thermal history of the alloys is explained.

  18. 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 .

  19. Piezostrain tuning non-volatile 90° magnetic easy axis rotation in Co2FeAl Heusler alloy film grown on Pb(Mg1/3Nb2/3)O3-PbTiO3 heterostructures

    Science.gov (United States)

    Zhou, Cai; Wang, Fenglong; Dunzhu, Gesang; Yao, Jinli; Jiang, Changjun

    2016-11-01

    Non-volatile electric field-based control of magnetic anisotropy in Co2FeAl/ Pb(Mg1/3Nb2/3)O3-PbTiO3 (CFA/PMN-PT) heterostructures is investigated at room temperature. The remnant magnetization response under different electric fields shows a asymmetric butterfly-like behavior; specifically, this behavior is consistent with the asymmetric butterfly-like piezostrain versus applied electric field curve. Thus electric field-induced non-volatile 90° magnetic easy axis rotation can be attributed to the piezostrain effect. Further, the result measured by rotating-angle ferromagnetic resonance demonstrates piezostrain-mediated non-volatile 90° magnetic easy axis rotation at the initial state and the two remnant polarization states after application of the poling fields of 10 and  -10 kV cm-1 turned off. The angular dependence of magnetic damping also indicates a 90° phase shift at the above mentioned three different states. Additionally, the piezostrain-mediated non-volatile stable magnetization reversal in the two directions of easy and hard magnetization axes are observed under positive and negative pulsed electric fields, which can be used to improve the performance of low-loss multiple-state memory devices.

  20. 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.

  1. Investigation of Flat Clinching Process Combined with Material Forming Technology for Aluminum Alloy.

    Science.gov (United States)

    Chen, Chao; Zhao, Shengdun; Han, Xiaolan; Wang, Yongfei; Zhao, Xuzhe

    2017-12-15

    In recent years, the use of aluminum alloy has tended to increase for building lightweight automobiles to reduce their automotive weight, which is helpful to save energy and protect the environment. In order to join aluminum alloy, a flat-clinching process combined with material forming technology was investigated to join aluminum alloy sheets using an experimental and a numerical method. Al1060 was chosen as the material of the sheet, and DEFORM-2D software was used to build the numerical model. After the numerical model was validated by the experimental results, the influences of punch diameter and holder force on the materials deforming behavior of the clinched joint were analyzed using the numerical model. Then, the material flow, joining ability, and joining quality were investigated to assess the clinched joint. The results showed that an increase in punch diameter could give rise to an increase in neck thickness and interlocking length, while an increase in blank holder force induced a decrease in interlocking length and an increase in neck thickness. The joining quality could be increased by increasing the forming force. It can be concluded that a clinched joint has better joining quality for joining light-weight sheets onto automotive structures.

  2. Experimental Investigation and FE Analysis on Constitutive Relationship of High Strength Aluminum Alloy under Cyclic Loading

    Directory of Open Access Journals (Sweden)

    Yuanqing Wang

    2016-01-01

    Full Text Available Experiments of 17 high strength aluminum alloy (7A04 specimens were conducted to investigate the constitutive relationship under cyclic loading. The monotonic behavior and hysteretic behavior were focused on and the fracture surface was observed by scanning electron microscope (SEM to investigate the microfailure modes. Based on Ramberg-Osgood model, stress-strain skeleton curves under cyclic loading were fitted. Parameters of combined hardening model including isotropic hardening and kinematic hardening were calibrated from test data according to Chaboche model. The cyclic tests were simulated in finite element software ABAQUS. The test results show that 7A04 aluminum alloy has obvious nonlinearity and ultra-high strength which is over 600 MPa, however, with relatively poor ductility. In the cyclic loading tests, 7A04 aluminum alloy showed cyclic hardening behavior and when the compressive strain was larger than 1%, the stiffness degradation and strength degradation occurred. The simulated curves derived by FE model fitted well with experimental curves which indicates that the parameters of this combined model can be used in accurate calculation of 7A04 high strength aluminum structures under cyclic loading.

  3. Investigation the effect of modification with nanopowders on crystallization process and microstructure of some alloys

    Science.gov (United States)

    Kuzmanov, P. M.; Popov, S. I.; Yovkov, L. V.; Dimitrova, R. N.; Cherepanov, A. N.; Manolov, V. K.

    2017-10-01

    Modified with nano-powders (NP), AlSi7Mg aluminum alloy, P265GH steel and GG25 gray cast iron, have been investigated. Thermal and metallographic analyses have been made. For modified AlSi7Mg alloy, reduction of overcooling and duration of crystallization at the initial crystallization and their increase at eutectic crystallization have been found. For cast iron GG25, reduction of overcooling at crystallization was established and for P265GH steel, overcooling was not recorded, only a change in the slope of the temperature dependence. The thermal effects obtained in the crystallization correspond to the refinement of micro- and macrostructures. A mathematical model for crystallization of samples for thermal analysis has been developed and solved.

  4. Investigations on rechargeable lithium alloys on the basis of Al-Ni and Al-Mn alloys

    Energy Technology Data Exchange (ETDEWEB)

    Hauke, I. (Dresden Univ. of Technology, Inst. of Physical Chemistry and Electrochemistry, Dresden (Germany)); Machill, S. (Dresden Univ. of Technology, Inst. of Physical Chemistry and Electrochemistry, Dresden (Germany)); Rahner, D. (Dresden Univ. of Technology, Inst. of Physical Chemistry and Electrochemistry, Dresden (Germany)); Wiesener, K. (Dresden Univ. of Technology, Inst. of Physical Chemistry and Electrochemistry, Dresden (Germany))

    1993-04-15

    Different Al-Ni and Al-Mn alloying substrates have been tested by cyclic voltammetry and a.c. impedance measurements in 1 M LiClO[sub 4]/propylene carbonate (PC) at room temperature. Small portions of the second metal influence the current efficiency of lithium deposition and dissolution as well as the 'steady-state' process in the measured cyclic voltammograms. The impedance spectra of the different alloys are influenced by the metal and its concentration. (orig.)

  5. Investigation on local ductility of 6xxx-aluminium sheet alloys

    Science.gov (United States)

    Henn, P.; Liewald, M.; Sindel, M.

    2017-09-01

    Within the scope of this paper influence of localization of loading conditions on the ductility of two different 6xxx-aluminium sheet alloys is investigated. In order to improve the prediction of sheet material crash performance, material parameters based on uniaxial tensile and notched tensile tests are determined with varying consolidation areas. Especially evaluation methods based on the localized necking behaviour in tensile tests are investigated. The potential of local ductility characterisation is validated with results of Edge-Compression Tests (ECT) which applies load conditions that occur in actual crash events.

  6. Investigation on mechanical behaviour of ECAPed 2A12 aluminium alloy

    Directory of Open Access Journals (Sweden)

    Wang Cun-xian

    2015-01-01

    Full Text Available In the present work, the uniaxial compressive behavior of aluminum alloy processed by equal channel angular pressing (ECAP for 1–8 passes are investigated experimentally under both quasi-static and dynamic loading conditions via an electronic universal testing machine with a maximum load capacity of 10KN and the split Hopkinson pressure bar (SHPB. The strain hardening rate as well as strain rate sensitivity the ECAPed with different passes have been determined and compared with annealed coarse grained counterpart. The experimental results show a continuously increase of both flow stress and strain rate sensitivity for the aluminum alloy subjected to ECAP process as the pressing pass number increasing. It is proposed that the reduction in grain size plays an important role in the enhancement of flow stress and strain rate sensitivity. However, the strain hardening rate of the ECAPed materials decreases remarkably. Meanwhile, compressive experiments at elevated temperatures indicate the temperature sensitivity of the material increases as the grain size is refined into fine grain regime. Based on thermal activation theory, it is proposed that the enhanced temperature and strain rate sensitivity of ECAPed aluminum alloy can be related to the reduction in activation volume due to grain refinement.

  7. Corrosion investigation of multilayered ceramics and experimental nickel alloys in SCWO process environments

    Energy Technology Data Exchange (ETDEWEB)

    Garcia, K.M.; Mizia, R.

    1995-02-01

    A corrosion investigation was done at MODAR, Inc., using a supercritical water oxidation (SCWO) vessel reactor. Several types of multilayered ceramic rings and experimental nickel alloy coupons were exposed to a chlorinated cutting oil TrimSol, in the SCWO process. A corrosion casing was designed and mounted in the vessel reactor with precautions to minimize chances of degrading the integrity of the pressure vessel. Fifteen of the ceramic coated rings were stacked vertically in the casing at one time for each test. There was a total of 36 rings. The rings were in groupings of three rings that formed five sections. Each section saw a different SCWO environment, ranging from 650 to 300{degrees}C. The metal coupons were mounted on horizontal threaded holders welded to a vertical rod attached to the casing cover in order to hang down the middle of the casing. The experimental nickel alloys performed better than the baseline nickel alloys. A titania multilayered ceramic system sprayed onto a titanium ring remained intact after 120-180 hours of exposure. This is the longest time any coating system has withstood such an environment without significant loss.

  8. 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

  9. 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...

  10. Investigation on Formation Mechanism of Irregular Shape Porosity in Hypoeutectic Aluminum Alloy by X-Ray Real Time Observation

    Science.gov (United States)

    Liao, Hengcheng; Zhao, Lei; Wu, Yuna; Fan, Ran; Wang, Qigui; Pan, Ye

    2012-08-01

    The formation mechanism of irregular shape porosity in hypoeutectic aluminum silicon alloy (A356) was investigated by X-ray real time observation on porosity evolution during solidification and re-melting. Porosity in the hypoeutectic aluminum A356 alloy with high hydrogen content (>0.3 mL/100 g Al) first forms in the liquid as small spherical gas bubbles, then expands along with the pressure drop in the mushy zone due to shrinkage and lack of feeding, and finally deforms into irregular morphology by the impingement of aluminum dendrite network. Degassing is a key to eliminate porosity in aluminum alloy castings.

  11. Investigations of quaternary interdiffusion in a constituent system of high entropy alloys

    Energy Technology Data Exchange (ETDEWEB)

    Kulkarni, Kaustubh; Chauhan, Gyanendra Pratap Singh [Department of Materials Science and Engineering, Indian Institute of Technology Kanpur, U.P. 208016 (India)

    2015-09-15

    Interdiffusion was investigated at 1000°C in a quaternary Fe-Ni-Co-Cr system, which is an essential constituent of many high-entropy alloys. The relative values of main and cross interdiffusion coefficients determined from concentrations and interdiffusion fluxes developed in a single diffusion couple indicate that significant diffusional interactions exist in this system. Thermodynamic interactions between the binary constituents were analyzed based on the activity coefficient relations and it is shown that the observed diffusional interactions of a component with others are consistent with relative thermodynamic interactions between them.

  12. Application of the Positron Annihilation Spectroscopy for Chromium Effect Investigation in Binary Fe-Cr Alloys

    Energy Technology Data Exchange (ETDEWEB)

    Sojak, S.; Krsjak, V.; Slugen, V.; Stancek, S.; Petriska, M.; Vitazek, K.; Stacho, M. [Department of Nuclear Physics and Technology, Faculty of Electrical Engineering and Information Technology, Slovak University of Technology, Ilkovicova 3, 812 19 Bratislava (Slovakia)

    2008-07-01

    Positron annihilation spectroscopy (PAS) is one of the non-destructive techniques applied with advantage for evaluation of the radiation treated materials microstructure. In this work, the PAS was used for study of different Fe-Cr alloys implanted by ions of helium. Investigation was focused on the chromium effect and the radiation defects resistance. In particular, the vacancy type defects (mono-vacancies, vacancy clusters) have been studied. The results show that the specific content of chromium has important influence on the size and distribution of induced defects. (authors)

  13. 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.

  14. Computational Investigation of Hardness Evolution During Friction-Stir Welding of AA5083 and AA2139 Aluminum Alloys

    Science.gov (United States)

    2011-01-01

    M.J. Starink, Precipitates and Intermetallic Phases in 972Precipitation Hardening Al-Cu-Mg-(Li) Based Alloys, Int. Mater. Rev., 9732005, 50, p 193...REPORT Computational Investigation of Hardness Evolution During Friction-Stir Welding of AA5083 and AA2139 Aluminum Alloys 14. ABSTRACT 16. SECURITY...CLASSIFICATION OF: A fully coupled thermo-mechanical finite-element analysis of the friction-stir welding (FSW) process developed in our previous work

  15. An electrochemical investigation of the corrosion behavior of Al-Si-Cu hypereutectic alloys in alcoholic environments

    OpenAIRE

    TRALDI, S.M.; ROSSI, J.L.; Costa, I.

    2003-01-01

    Al-Si-Cu hypereutetic alloys produced by spray forming are mostly used in the automotive industry, especially for cylinder liners. They have the advantage of low weight associated with low coefficient of thermal expansion and excellent mechanical properties - mainly wear resistance at high temperatures. The corrosion resistance of these alloys in fuels, particularly alcoholic media, however is not yet known. In this investigation, electrochemical impedance spectroscopy (EIS) and potentiodynam...

  16. 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.

  17. 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 0investigated theoretically and experimentally with respect to electronic structure and transport properties. The results show the possibility to create n-type and p-type thermoelectrics within one Heusler 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

  18. Investigation on some factors affecting crack formation in high resistance aluminum alloys

    Directory of Open Access Journals (Sweden)

    A. Brotzu

    2017-10-01

    Full Text Available Aluminum alloys having good mechanical properties are Al-ZnMg alloys (7xxx and Al-Cu-Li alloys (Weldalite. These alloys may be subjected to stress corrosion cracking. In order to overcome this problem the Al 7050 alloy has been developed and it is widely used for aerospace applications. Despite that, some components made of this alloy cracked during the manufacturing process including machining and chemical anodization. In a previous work cracked Al 7050 components have been analyzed in order to identify possible causes of crack formation. In this work the susceptibility of this alloy to intergranular corrosion has been analysed and compared with that of other high resistance aluminum alloys

  19. 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.

  20. Chemical analysis of the elements in UZrNb alloy at CDTN: preliminary investigation

    Energy Technology Data Exchange (ETDEWEB)

    Ferraz, Wilmar Barbosa; Palmieri, Helena Eugenia L.; Reis, Sergio Carneiro dos; Santos, Ana Maria Matildes dos; Souza, Adalberto Leles de, E-mail: ferrazw@cdtn.br, E-mail: help@cdtn.br, E-mail: reissc@cdtn.br, E-mail: amms@cdtn.br, E-mail: adalbertoleles@yahoo.com.br [Centro de Desenvolvimento da Tecnologia Nuclear (CDTN/CNEN-MG), Belo Horizonte, MG (Brazil)

    2012-07-01

    The complete determination of major, minor, and impurity element contents in nuclear fuel is essential for quality assurance in the production of nuclear fuels. The control over all the stages of the development of nuclear fuel involves a combination of different analytical methods such as spectrometric methods. The goal of our investigation is to develop and evaluate procedures for the determination of main elements and carbon impurity present in some uranium alloys. In this paper the element contents in U2.5Zr7.5Nb, U3Zr9Nb alloys and U6Nb, in weight percent, were investigated by means of scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDS), inductively coupled plasma mass spectrometry (ICP-MS), wavelength dispersive fluorescence spectrometry (XRF/WDS) and energy-dispersive X-ray spectroscopy (EDX). The total carbon was determined using a carbon analyzer in which the sample is oxidized to carbon dioxide (IR absorption). It was observed a satisfactory correlation between the results obtained by employed methods. (author)

  1. Investigation into the stress corrosion cracking properties of AA2099, an aluminum-lithium-copper alloy

    Science.gov (United States)

    Padgett, Barbara Nicole

    Recently developed Al-Li-Cu alloys show great potential for implementation in the aerospace industry because of the attractive mix of good mechanical properties and low density. AA2099 is an Al-Li-Cu alloy with the following composition Al-2.69wt%Cu-1.8wt%Li-0.6wt%Zn-0.3wt%Mg-0.3wt%Mn-0.08wt%Zr. The environmental assisted cracking and localized corrosion behavior of the AA2099 was investigated in this thesis. The consequences of uncontrolled grain boundary precipitation via friction stir welding on the stress corrosion cracking (SCC) behavior of AA2099 was investigated first. Using constant extension rate testing, intergranular corrosion immersion experiments, and potentiodynamic scans, the heat-affected zone on the trailing edge of the weld (HTS) was determined to be most susceptible of the weld zones. The observed SCC behavior for the HTS was linked to the dissolution of an active phase (Al2CuLi, T1) populating the grain boundary. It should be stated that the SCC properties of AA2099 in the as-received condition were determined to be good. Focus was then given to the electrochemical behavior of precipitate phases that may occupy grain and sub-grain boundaries in AA2099. The grain boundary micro-chemistry and micro-electrochemistry have been alluded to within the literature as having significant influence on the SCC behavior of Al-Li-Cu alloys. Major precipitates found in this alloy system are T1 (Al 2CuLi), T2 (Al7.5Cu4Li), T B (Al6CuLi3), and theta (Al2 Cu). These phases were produced in bulk form so that the electrochemical nature of each phase could be characterized. It was determined T1 was most active electrochemically and theta was least. When present on grain boundaries in the alloy, electrochemical behavior of the individual precipitates aligned with the observed corrosion behavior of the alloy (e.g. TB was accompanied by general pitting corrosion and T 1 was accompanied by intergranular corrosion attack). In addition to the electrochemical behavior of

  2. 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.

  3. 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.

  4. Thermodynamic and solidification modeling coupled with experimental investigation of the multicomponent aluminum alloys

    Science.gov (United States)

    Yan, Xinyan

    2001-07-01

    .19wt%Mg quaternary alloys, have been experimentally investigated using directional solidification and electron probe microanalysis (EPMA). Calculated results from this model are in accord with the experimental data. Finally, the micromodel and the 12-component Al thermodynamic database were used to predict the microsegregation and microstructure in two commercial alloys (10-component W319 and 11-component 7050). Predicted results are in very good agreement with the experimental data. The verified aluminum database and micromodel can be used with confidence in the aluminum industry.

  5. 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.

  6. Investigate The Effect Of Welding Parameters On Mechanical Properties During The Welding Of Al-6061 Alloy

    Directory of Open Access Journals (Sweden)

    Rajendra Prasad

    2017-10-01

    Full Text Available Friction welding is a solid state welding technique which is being used in recent times to weld similar as well as dissimilar metals for getting defect free weld. Many combinations like low carbon to stainless steel austenitic to ferrite stainless steel aluminium to copper and titanium to aluminium or steel have been tried out by various solid state welding processes with quite good results. In the present work the 3 level full factorial design has been employed to investigate the effect of welding parameters on tensile strength toughness and heat generation during the welding of Al-6061 alloy. Mathematical relationships between friction welding parameters and mechanical properties like heat generation tensile strength and toughness have also been developed. An attempt has also been made to examine the fracture surfaces of test specimens using SEM. It has been found that welding speed is the most significant parameter thats affect the heat generation tensile strength and toughness. it has been found that tensile strength and toughness during welding increases with increased in welding speed while tensile strength and toughness initially increased as the welding time increases after that it decreased with increase in welding time. The difference in weight of alloying elements can be clearly seen by analyzing spectrum of elements.

  7. Density functional investigations of methanol dehydrogenation on Pd-Zn surface alloy.

    Science.gov (United States)

    Huang, Yucheng; Chen, Zhao-Xu

    2010-07-06

    Methanol dehydrogenation on Pd(111) and various Pd-Zn surface alloy films supported on Pd(111) have been investigated using density functional method in combination with periodic slab models. Calculations show that compared to Pd(111) the interaction between CH(3)O and the films is enhanced, whereas that for CH(2)O and CHO is weakened. Zn in top layer facilitates the CH(3)O stability. At variance, the subsurface Zn reduces the interaction of CH(2)O and CHO with the substrate significantly. Addition of Zn promotes the O-H breaking of CH(3)OH and the dehydrogenation of CHO but hinders the dehydrogenation of CH(3)O and CH(2)O. Comparison shows that the third-layer Zn atoms have essentially no effect on the reactions. Our calculations demonstrate that the experimentally observed 360 K desorption peak cannot be originated from CH(2)O adsorbed at flat Pd-Zn alloy surfaces, and it is very likely that CH(2)O combines preferentially with some species before decomposing into CHO during methanol steam reforming if CH(2)O is an intermediate. Finally, we show that the newly proposed relationship between the energy of the initial states and transition states exhibits better correlation than the classical BEP relation.

  8. INVESTIGATING OF ECO- AND ENERGY-EFFICIENT LUBRICATION STRATEGIES FOR THE DRILLING OF LIGHT METAL ALLOYS

    Directory of Open Access Journals (Sweden)

    N.F. Treurnicht

    2012-01-01

    Full Text Available

    ENGLISH ABSTRACT: Energy use will be one of the main drivers for the achievement of more eco-efficient drilling processes in the automotive industry. Industry awareness of the environmental impact of used cutting emulsions, and the negative effect on worker health, has increased sharply. This has led to innovative lubrication methods such as through-spindle minimal quantity lubrication (MQL for drilling aluminium-silicon alloys. In this work the performance of MQL at different cutting speeds and feed rates has been investigated using infrared temperature measurements. The results indicate that MQL is a feasible eco-efficient alternative to conventional flood cooling when drilling aluminium-silicon alloys.

    AFRIKAANSE OPSOMMING: Energiebenutting maak een van die hoofdryfvere uit om eko-doeltreffendheid te behaal in boorprosesse in die motornywerheid. Nywerheidsbewustheid van die omgewingsimpak van gebruikte sny-vloeistowwe, en die negatiewe effek daarvan op werkergesondheid, het skerp toegeneem. Hierdie bewustheid het aanleiding gegee tot die ontwikkeling van smeringsmetodes soos deur-spil minimale hoeveelheid smering (Engels: Minimal Quantity Lubrication, MQL vir die boor van aluminium-silikon legerings. In hierdie werk word die prestasie van MQL ondersoek teen verskillende snyspoed- en voertempo-kondisies deur middel van infra-rooi temperatuurmeting. Die resultate dui daarop dat MQL ’n lewensvatbare eko-vriendelike alternatief tot konvensionele vloedverkoeling is, wanneer aluminium-silikon legerings geboor word.

  9. Investigation of cracking and erratic behavior of the uranium-titanium alloy

    Energy Technology Data Exchange (ETDEWEB)

    Bird, E.L.

    1993-07-07

    The uranium-0.8 wt % titanium (U-0.8 Ti) alloy is often used in weapon applications where high strength and fairly good ductility are necessary. Components are immersion quenched in water from the gamma phase to produce a martensitic structure that is amenable to aging. Undesirable conditions occur when a component occasionally cracks during the quenching process, and when tensile specimens fail prematurely during mechanical testing. These two failures prompted an investigative analysis and a series of studies to determine the causes of the cracking and erratic behavior observed in this alloy. Quench-related failures whereby components that cracked either during or immediately after the heat treatment/quenching operation were sectioned for metallographic examination of the microstructure to examine the degree of phase transformation. Examination of premature tensile specimen failures by scanning electron microscopy and x-ray imaging of fracture surfaces revealed pockets of inclusions at the crack origins. In addition, tests were conducted to evaluate the detrimental effects of internal hydrogen on ductility and crack initiation in this allay.

  10. Investigating the Acid Failure of Aluminium Alloy in 2 M Hydrochloric Acid Using Vernonia amygdalina

    Directory of Open Access Journals (Sweden)

    Olugbenga A. Omotosho

    2012-04-01

    Full Text Available The acid failure of aluminium alloy in 2 M hydrochloric acid solution in the presence of Vernonia amygdalina extract was investigated using gasometric technique. Aluminium alloy coupons of dimension 4 cm by 1 cm were immersed in test solutions of free acid and also those containing extract volumes of 2, 3, 4 and 5 cm3 at ambient temperature for 30 minutes. The volumes of hydrogen gas evolved as a result of the rate of reaction were recorded and analyzed. Analysis revealed that maximum inhibitor efficiency which corresponds to the lowest corrosion rate was obtained at optimum inhibitor volumes of 5 cm3, with reduction in the corrosion rate observed to follow in order of increasing extract volumes. Adsorption study revealed that Temkin isotherm best described the metal surface interaction with the extract phytochemicals, with 12 minutes becoming the best exposure time for the phytochemicals to adsorb to the metal surface at all volumes. Statistical modelling of the corrosion rate yielded an important relationship suitable for estimating corrosion rate values once volumes of the extract is known. Microstructural studies, showed an indirect relationship between crack growth rates and extract volumes, while consistency of the irregular intermetallic phases increases with increasing extract volumes.

  11. Investigation of the Deformation Mechanism of a near β Titanium Alloy through Isothermal Compression

    Directory of Open Access Journals (Sweden)

    Jie Wu

    2017-11-01

    Full Text Available This study investigated the hot deformation behavior of Ti-4Al-1Sn-2Zr-5Mo-8V-2.5Cr alloy through isothermal compression tests at temperatures from 780 to 930 °C with strain rates ranging from 0.001 to 1 s−1. The flow stress decreases with a decreased strain rate and an increased temperature. A constitutive equation was established for this alloy and the dependence of activation energy on temperature and strain rate is discussed. We further proposed a processing map using the dynamic materials model. On the processing map various domains of flow stability and flow instability can be identified. The deformation mechanisms associated with flow stability regions are mainly dynamic recrystallization (DRX and dynamic recovery (DRV. The flow instability is manifested in the form of the band of flow localizations. The optimum processing conditions are suggested such that the temperature range is from 780 to 880 °C and the strain rate ranges from 0.001 to 0.01 s−1.

  12. Energy investigations on the mechanical properties of magnesium alloyed by X = C, B, N, O and vacancy

    KAUST Repository

    Wu, Xiaozhi

    2013-10-25

    The generalized stacking fault (GSF) energies and surface energies of magnesium and its alloys with alloying atoms X = C, B, N, O and vacancy have been investigated using the first-principles methods. It is found that the predominant reducing effects of the alloying atoms and vacancy on the stacking fault energy are resulted from the position of them in the 1st layer near the slip plane. The stacking fault energies are nearly the same as the pure magnesium while the alloying atoms and vacancy are placed in the 2nd, 3rd, 4th, 5th and 6th layers. It has been shown that O strongly reduces the GSF energy of Mg. The alloying atoms C, B and N increase the surface energy, but O and vacancy reduce the surface energy of Mg. The ductilities of Mg and Mg alloys have been discussed based on the Rice criterion by using the ratio between surface energy and unstable stacking fault energy. © 2013 Higher Education Press and Springer-Verlag Berlin Heidelberg.

  13. Investigation of thermal, mechanical and magnetic behaviors of the Cu-11%Al alloy with Ag and Mn additions

    Energy Technology Data Exchange (ETDEWEB)

    Silva, R.A.G., E-mail: galdino.ricardo@gmail.com [Departamento de Ciencias Exatas e da Terra-UNIFESP, Diadema-SP (Brazil); Paganotti, A.; Gama, S. [Departamento de Ciencias Exatas e da Terra-UNIFESP, Diadema-SP (Brazil); Adorno, A.T.; Carvalho, T.M.; Santos, C.M.A. [Instituto de Quimica - UNESP, Araraquara-SP (Brazil)

    2013-01-15

    The investigation of thermal, mechanical and magnetic behaviors of the Cu-11%Al, Cu-11%Al-3%Ag, Cu-11%Al-10%Mn and Cu-11%Al-10%Mn-3%Ag alloys was made using microhardness measurements, differential scanning calorimetry, X-ray diffractometry, scanning electron microscopy, energy dispersion X-ray spectroscopy and magnetic moment change with applied field measurement. The results indicated that the Mn addition changes the phase stability range, the microhardness values and makes undetectable the eutectoid reaction in annealed Cu-11%Al and Cu-11%Al-3%Ag alloys while the presence of Ag does not modify the phase transformation sequence neither microhardness values of the annealed Cu-11%Al and Cu-11%Al-10%Mn alloys, but it increases the magnetic moment of this latter at about 2.7 times and decreases the rates of eutectoid and peritectoid reactions of the former. - Highlights: Black-Right-Pointing-Pointer The microstructure of Cu-Al alloy is modified in the Ag presence. Black-Right-Pointing-Pointer ({alpha} + {gamma}) phase is stabilized down to room temperature when Ag is added to Cu-Al alloy. Black-Right-Pointing-Pointer Ag-rich phase modifies the magnetic characteristics of Cu-Al-Mn alloy.

  14. Investigations on tunneling and kissing bond defects in FSW joints for dissimilar aluminum alloys

    Energy Technology Data Exchange (ETDEWEB)

    Khan, Noor Zaman, E-mail: noor_0315@yahoo.com [Department of Mechanical Engineering, Jamia Millia Islamia (A Central University), New Delhi (India); Siddiquee, Arshad Noor; Khan, Zahid A. [Department of Mechanical Engineering, Jamia Millia Islamia (A Central University), New Delhi (India); Shihab, Suha K. [Department of Mechanical Engineering, Engineering College, Diyala University, Diyala (Iraq)

    2015-11-05

    In this paper an attempt has been made to investigate the effect of two Friction Stir Welding (FSW) parameters i.e. tool pin offset and tool plunge depth on the formation of defects such as tunnel (tunneling defect) and kissing bond (KB) during welding of dissimilar aluminum alloys. 4.75 mm thick plates of AA5083-H116 and AA6063-T6 were welded using a novel work-fixture developed in-house which, apart from clamping the plated also imparted continuous variation of offset on both side of the faying line. The tunneling defect was modeled as a function of offset and plunge depth. The welds were characterised using optical microscopy (OM), scanning electron microscopy (SEM) and mechanical testing. The causes of such defects have been analyzed and discussed and recommendations have been made to prevent their occurrence. The findings of the study have revealed that the tunneling defects are formed at all offset (including zero offset) values towards stronger material (advancing side). And the cross-section of the tunnel varied with the amount of offset. Further, KBs are formed at the interface for all pin offset values except 0.5 mm towards weaker material and high plunge depth resulting in the poor mechanical properties. - Highlights: • Two dissimilar aluminum alloys are welded using FSW. • Formation of kissing bond and tunneling defects are investigated. • Defects are formed at pin offsets towards stronger material and also without offset. • The size of tunnel reduces significantly by increasing the plunge depth. • Tool pin offset towards weaker material prevent tunneling defects.

  15. Investigation of fatigue crack growth rate of Al 5484 ultrafine grained alloy after ECAP process

    Energy Technology Data Exchange (ETDEWEB)

    Brynk, Tomasz; Rasinski, Marcin; Pakiela, Zbigniew; Kurzydlowski, Krzysztof J. [Faculty of Materials Science and Engineering, Warsaw University of Technology (Poland); Olejnik, Lech [Faculty of Production Engineering, Warsaw University of Technology (Poland)

    2010-05-15

    During the last decade equal-channel angular pressing (ECAP) has emerged as a widely used fabrication route of ultrafine-grained (UFG) metals and alloys. Enhanced mechanical properties of UFG materials produced by severe plastic deformation, with a grain size smaller than 1 {mu}m, have been reported in a large number of publications. However, the higher strength does not imply higher resistance to fatigue both high- and low-cyclic. In fact, due to reduced plasticity, higher fatigue crack propagation rates are reported for UFG materials, particularly in low-amplitude range. The aim of this work was to investigate fatigue crack propagation in samples of Al 5483 alloy subjected to ECAP treatment. Because of small dimensions of the coupons processed by ECAP, non-standard, mini-samples were used in a crack propagation tests. Two test procedures were used to estimate stress intensity factor (K). The first was based on optical measurements of crack length from images recorded during the test. The second method was based on digital image correlation (DIC), which was used to determine K value directly from displacement field near the crack tip. Comparison of these two methods is made and the relationship between the intensity of ECAP process (measured in terms of the number of ECAP passes) and fatigue crack propagation rates proposed. In addition to fatigue resistance, the results of tensile tests carried out with mini-samples are presented. Applicability of such samples in the investigations of the mechanical properties of UFG materials is discussed. (Abstract Copyright [2010], Wiley Periodicals, Inc.)

  16. Adsorbate induced surface alloy formation investigated by near ambient pressure X-ray photoelectron spectroscopy

    DEFF Research Database (Denmark)

    Nierhoff, Anders Ulrik Fregerslev; Conradsen, Christian Nagstrup; McCarthy, David Norman

    2014-01-01

    Formation of meta-stable surface-alloys can be used as a way to tune the binding strength of reaction intermediates and could therefore be used as improved catalyst materials for heterogeneous catalysis. Understanding the role of adsorbates on such alloy surfaces can provide new insights for engi......Formation of meta-stable surface-alloys can be used as a way to tune the binding strength of reaction intermediates and could therefore be used as improved catalyst materials for heterogeneous catalysis. Understanding the role of adsorbates on such alloy surfaces can provide new insights...

  17. Ab initio investigation of the surface properties of austenitic Fe-Ni-Cr alloys in aqueous environments

    Energy Technology Data Exchange (ETDEWEB)

    Rák, Zs., E-mail: zrak@ncsu.edu; Brenner, D.W.

    2017-04-30

    Highlights: • The trend in the surface energies of austenitic stainless steels is: (111) < (100) < (110). • On the (111) orientation Ni segregates to the surface and Cr segregates into the bulk. • The surface stability of the alloys in contact with water decrease with temperature and pH. - Abstract: The surface energetics of two austenitic stainless steel alloys (Type 304 and 316) and three Ni-based alloys (Alloy 600, 690, and 800) are investigated using theoretical methods within the density functional theory. The relative stability of the low index surfaces display the same trend for all alloys; the most closely packed orientation and the most stable is the (111), followed by the (100) and the (110) surfaces. Calculations on the (111) surfaces using various surface chemical and magnetic configurations reveal that Ni has the tendency to segregate toward the surface and Cr has the tendency to segregate toward the bulk. The magnetic frustration present on the (111) surfaces plays an important role in the observed segregation tendencies of Ni and Cr. The stability of the (111) surfaces in contact with aqueous solution are evaluated as a function of temperature, pH, and concentration of aqueous species. The results indicate that the surface stability of the alloys decrease with temperature and pH, and increase slightly with concentration. Under conditions characteristic to an operating pressurized water reactor, the Ni-based alloy series appears to be of better quality than the stainless steel series with respect to corrosion resistance and release of aqueous species when in contact with aqueous solutions.

  18. Numerical investigations of the electroslag remelting process for alloy 718; Numerische Untersuchungen des Elektroschlacke-Umschmelzprozesses fuer Alloy 718

    Energy Technology Data Exchange (ETDEWEB)

    Giesselmann, Nils

    2014-07-01

    literature sources. Interdendritic fluid flow simulations on a micro scale were performed based on the lattice Boltzmann method to determine the permeability perpendicular to the dendrites. The simulated permeability agrees very well with the calibrated permeability obtained from the remelting simulation. Besides using this permeability to validate the calibrated value, knowledge of the interdendritic permeability is required in Boettger's freckle criterion. The influence of the copper mold's base plate cooling on the process has also been investigated. It was found that its effect on the pool decreases quickly as the ingot grows. The influenced region gets even smaller as the melting rate is increased. Furthermore the electrode's energy balance has been reviewed. It was concluded analytically and numerically that for a specific alloy the ratio between melting rate and electrode diameter is crucial to predicting a possible rise of the melting rate before entering the hot topping stage.

  19. Mechanical Behaviour Investigation Of Aluminium Alloy Tailor Welded Blank Developed By Using Friction Stir Welding Technique

    Science.gov (United States)

    Dwi Anggono, Agus; Sugito, Bibit; Hariyanto, Agus; Subroto; Sarjito

    2017-10-01

    The objective on the research was to investigate the mechanical properties and microstructure of tailor welded blank (TWB) made from AA6061-T6 and AA1100 using friction stir welding (FSW) process. Due to the dissimilar mechanical properties of the two aluminium alloys, microhardness test was conducted to measure the hardness distribution across the weld nugget. The mixing of two distinct materials was influenced by tool rotation speed. Therefore, microstructure analysis was carried out to investigate the grain size and shape. The grain size of AA6061-T6 has increased in the heat affected zone (HAZ) while for AA1100 has decreased. In the weld nugget, it has found a hook defects in the dissimilar aluminium joining. By using monotonic tensile load, the different weld line direction was observed with the expansion in tool rotation. The joints failure were consistently on the area of AA1100 series. Furthermore, two specimens were investigated, one through the dissimilar aluminium and the other through similiar material. Inspection of the weld nugget hardness was shown that nonhomogen material intermixing during the stiring process as confirmed by microhardness measurement.

  20. 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.

  1. Investigation of the Wear and Hardness Behaviour of Aluminium Alloy Coated Using the Powder Flame Spraying Method

    Directory of Open Access Journals (Sweden)

    Nurullah KIRATLI

    2009-03-01

    Full Text Available In this study, the wear behavior of aluminum alloy AL 5754 ( Etial 53 coated with powders of 10Al-Cu alloy (RotoTec® 19850 and 15Cr7Fe-Ni alloy (RotoTec® 19985 using powder flame spraying method has been investigated. To avoid thermal expansions between substrate and coating materials, Ni-Al RotoTec® 51000 was used as binding material. The wear test was performed on a pin-on-disc test apparatus. As an abrasive material, a SiC, 800 sandpaper was used. The wear tests of coated materials were carried out at room temperature and at 1.0m/s sliding speed with 0.35 and 0.70MPa pressures. To characterize coated specimens, they have been examined with optical microscope. As a result, it is found that the both coating materials have improved wear resistance.

  2. Investigation of texture, microstructure, and mechanical properties of a magnesium-lanthanum alloy after thermo-mechanical processing

    Energy Technology Data Exchange (ETDEWEB)

    Elfiad, Djazia; Bourezg, Yousf Islem; Bradai, Djamel [USTHB, Algiers (Algeria). Faculty of Physics; Azzeddine, Hiba [USTHB, Algiers (Algeria). Faculty of Physics; M' sila Univ. (Algeria). Dept. of Physics

    2016-04-15

    The texture, microstructure, and mechanical properties of Mg-1.33La (wt.%) alloy after hot rolling and cold plane strain compression were investigated by using X-ray diffraction, optical microscopy, and micro-hardness measurements. This thermo-mechanical processing resulted in a relative weakening of the texture that was mainly a basal type. The microstructures after hot rolling and cold plane strain compression revealed the presence of a second phase (Mg{sub 17}La{sub 2}), mostly at grain boundaries. Twins were profuse, and their morphologies were quite different after hot rolling and cold plane strain compression. The Mg-1.33La (wt.%) alloy exhibited good room temperature formability and an increase in strength. The alloy's hardness increased with increasing deformation strain. Such properties were explained by the effect of both the Mg{sub 17}La{sub 2} phase precipitation and the sample's texture.

  3. Molecular dynamics investigation of the thermal conductivity of ternary silicon–germanium–tin alloys

    Science.gov (United States)

    Lee, Yongjin; Hwang, Gyeong S.

    2017-12-01

    A further reduction of the thermal conductivity (κ) of silicon-germanium (SiGe) alloys is indispensable for their use as thermoelectric materials. Thus far, heteroatom-doped and nanostructured SiGe systems have been mainly synthesized and tested. This work presents a possibility of reducing the κ of SiGe by alloying with tin (Sn). Our molecular dynamics simulations predict that the κ of ternary SiGeSn alloys can be 40% lower than those of binary SiGe and GeSn alloys due mainly to increased mass disorder scattering of phonons. Our findings provide insight into the mechanism of κ suppression in multielement alloys and guidance on how to design them for thermoelectric applications.

  4. Investigation of austenitic alloys for advanced heat recovery and hot gas cleanup systems

    Energy Technology Data Exchange (ETDEWEB)

    Swindeman, R.W.; Ren, W. [Oak Ridge National Lab., TN (United States)

    1995-08-01

    Alloys for design and construction of structural components needed to contain process streams and provide internal structures in advanced heat recovery and hot gas cleanup systems were examined. Emphasis was placed on high-strength, corrosion-resistant alloys for service at temperatures above 1000 {degrees}F (540{degrees}C). Data were collected that related to fabrication, joining, corrosion protection, and failure criteria. Alloys systems include modified type 310 and 20Cr-25Ni-Nb steels and sulfidation-resistance alloys HR120 and HR160. Types of testing include creep, stress-rupture, creep crack growth, fatigue, and post-exposure short-time tensile. Because of the interest in relatively inexpensive alloys for high temperature service, a modified type 310 stainless steel was developed with a target strength of twice that for standard type 310 stainless steel.

  5. Investigation of austenitic alloys for advanced heat recovery and hot gas cleanup systems

    Energy Technology Data Exchange (ETDEWEB)

    Swindeman, R.W.; Ren, W. [Oak Ridge National Lab., TN (United States)

    1996-08-01

    Materials properties were collected for the design and construction of structural components for use in advanced heat recovery and hot gas cleanup systems. Alloys systems included 9Cr-1Mo-V steel, modified 316 stainless steel, modified type 310 stainless steel, modified 20Cr-25Ni-Nb stainless steel, modified alloy 800, and two sulfidation resistant alloys: HR160 and HR120. Experimental work was undertaken to expand the databases for potentially useful alloys. Types of testing included creep, stress-rupture, creep-crack growth, fatigue, and post-exposure short-time tensile tests. Because of the interest in relatively inexpensive alloys for service at 700{degrees}C and higher, research emphasis was placed on a modified type 310 stainless steel and a modified 20Cr-25Ni-Nb stainless steel. Both steels were found to have useful strength to 925{degrees}C with good weldability and ductility.

  6. Report on investigations and studies on development of materials for hydrogen absorbing alloys; Suiso kyuzo gokin no zairyo no kaihatsu ni kansuru chosa kenkyu hokokokusho

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    1984-03-01

    This paper describes investigations and studies on hydrogen absorbing alloy materials and the technologies to utilize them. In the investigations and studies, literatures were collected and put into order, questionnaire surveys were performed and analyzed, lecture meetings and panel discussions were held, and the discussion results were summarized. In the present status of developing hydrogen absorbing alloys, the current status of and problems in developing such hydrogen absorbing alloys as Ti-based, Mg-based, and rare earth-based alloys were put into order. Discussions were given on prospects of possibilities of developing new alloys, making them amorphous, and putting them into mass production. In the current status of developing the utilizing technologies, such technologies as hydrogen storage systems and heat pumps were put into order and discussed. With regard to problems in hydrogen absorbing alloys, discussions were given on alloy weight, pulverization, activation, heat conductivity, and alloy costs. In discussing the safety, discussions were given on the safety and compliance with related laws and regulations relative to hydrogen transportation using a great amount of hydrogen absorbing alloys, their storage, and heat storage systems. In addition, questionnaire surveys were carried out with an objective to identify the status of developing hydrogen absorbing alloys and needs from the industries. (NEDO)

  7. Characterization investigations during mechanical alloying and sintering of Ni-W solid solution alloys dispersed with WC and Y{sub 2}O{sub 3} particles

    Energy Technology Data Exchange (ETDEWEB)

    Genc, Aziz, E-mail: agenc@itu.edu.t [Particulate Materials Laboratories, Department of Metallurgical and Materials Engineering, Istanbul Technical University, Maslak, 34469 Istanbul (Turkey); Luetfi Ovecoglu, M. [Particulate Materials Laboratories, Department of Metallurgical and Materials Engineering, Istanbul Technical University, Maslak, 34469 Istanbul (Turkey)

    2010-10-15

    Research highlights: {yields} Characterization investigations on the Ni-W solid solution alloys fabricated via mechanical alloying and the evolution of the properties of the powders with increasing MA durations. {yields} Reinforcement of the selected Ni-W powders with WC and Y{sub 2}O{sub 3} particles and further MA together for 12 h. {yields} There is no reported literature on the development and characterization of Ni-W solid solution alloys matrix composites fabricated via MA. {yields} Sintering of the developed composites and the characterization investigations of the sintered samples. {yields} Identification of new 'pomegranate-like' structures in the bulk of the samples. - Abstract: Blended elemental Ni-30 wt.% W powders were mechanically alloyed (MA'd) for 1 h, 3 h, 6 h, 12 h, 24 h, 36 h and 48 h in a Spex mixer/mill at room temperature in order to investigate the effects of MA duration on the solubility of W in Ni and the grain size, hardness and particle size. Microstructural and phase characterizations of the MA'd powders were carried out using X-ray diffractometer (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). On the basis of achieved saturation on the solid solubility, hardness and particle size, the Ni-30 wt.% W powders MA'd for 48 h were chosen as the matrix which was reinforced with different amounts of WC and/or with 1 wt.% Y{sub 2}O{sub 3} particles. The reinforced powders were further MA'd for 12 h. The MA'd powders were sintered at 1300 {sup o}C for 1 h under Ar and H{sub 2} gas flowing conditions. Microstructural characterizations of the sintered samples were conducted via XRD and SEM. Sintered densities were measured by using the Archimedes' method. Vickers microhardness tests were performed on both MA'd powders and the sintered samples. Sliding wear experiments were done in order to investigate wear behaviors of the sintered samples.

  8. Thermodynamic investigation of the effect of alkali metal impuries on the processing of aluminum and magnesium alloys

    Science.gov (United States)

    Zhang, Shengjun

    2006-12-01

    Aluminum and magnesium alloys are widely used in the automobile and aerospace industries as structural materials due to their light weight, high specific strength and good formability. However, they suffer from the poor hot rolling characteristics due to undesired impurities like calcium, potassium, lithium and sodium. They increase the hydrogen solubility in the melt and promote the formation of porosity in aluminum castings. During fabrication of aluminum alloys, they cause the hot-shortness and embrittlement due to cracking. They also led to "blue haze" corrosion which promotes the discoloration of aluminum under humid condition. The removal of these elements increases overall melt loss of aluminum alloys when aluminum products are remelted and recast. Na is one of the common impurities in the Al and Mg alloys. In industry, primary Al is produced by the Hall-Heroult process, through the electrolysis of the mixture of molten alumina and cryolite (Al2O3+Na 3AlF6), the latter being added to lower the melting point. Therefore, Al inevitably contains some Na (>0.002%) without further treatment. The Na content in Al is influenced by the thermodynamics and kinetics of the electrolysis. Similarly, in the electrolytic production and subsequent processing of Mg, Mg is commonly in contact with molten salt mixtures of NaCl and MgCl 2. Consequently, 2--20 wt. ppm Na is often found in Mg alloys. Besides originating from the industrial production process, Na can be introduced in laboratory experiments from alumina crucibles by the reaction between the molten Al-Mg alloys and the Na2O impurity in the alumina crucible. The trace element K plays a similar role in Al alloys although it is seldom discussed. No systematic theoretic research has been carried out to investigate the behavior of these impurities during the processing of aluminum alloys. The thermodynamic description of the Al-Ca-K-Li-Mg-Na system is needed to understand the effects of Ca, K, Li and Na on phase stability

  9. Dendritic solidification and thermal expansion of refractory Nb-Zr alloys investigated by electrostatic levitation

    Energy Technology Data Exchange (ETDEWEB)

    Yang, S.J.; Hu, L.; Wang, L.; Wei, B. [Northwestern Polytechnical University, Department of Applied Physics, Xi' an (China)

    2017-05-15

    The dendritic growth and thermal expansion of isomorphous refractory Nb-5%Zr, Nb-10%Zr, and Nb-15%Zr alloys were studied by electrostatic levitation technique. The obtained maximum undercoolings for the three alloys were 534 (0.2T{sub L}), 498 (0.19T{sub L}), and 483 K (0.18T{sub L}), respectively. Within these undercooling ranges, the dendritic growth velocities of the three alloys all exhibited power laws, and achieved 38.5, 34.0, and 27.1 m s{sup -1} at each maximum undercooling. The microstructures were characterized by coarse dendrites at small undercooling, while they transformed into refined dendrites under large undercooling condition. In addition, the measured thermal expansion coefficients of solid Nb-Zr alloys increased linearly with temperature. The values at liquid state were more than double of those at solid state, which also displayed linear dependence on temperature. (orig.)

  10. The precipitation process in Mg-Ca-(Zn) alloys investigated by positron annihilation spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Ortega, Yanicet [Departamento de Fisica, Universidad Carlos III de Madrid, 28911 Leganes (Spain); Departamento de Fisica de Materiales, Facultad de Ciencias Fisicas, Universidad Complutense de Madrid, 28040 Madrid (Spain)], E-mail: yanicet@fis.ucm.es; Monge, Miguel Angel; Pareja, Ramiro [Departamento de Fisica, Universidad Carlos III de Madrid, 28911 Leganes (Spain)

    2008-09-08

    Coincidence doppler broadening (CDB) spectroscopy has been applied to study the precipitation process induced by aging in Mg-1.0 wt.% Ca and Mg-1.0 wt.% Ca-1.0 wt.% Zn alloys. In addition positron lifetime experiments and microhardness measurements have been performed. A peak centered at {approx}11.5 x 10{sup -3}m{sub 0}c is found in the CDB ratio spectra of the alloys aged at 473 K. It is attributed to annihilations with the core electrons of Ca. The results indicate the formation of a particle dispersion that hardens the alloys. This dispersion is correlated with the appearance of the peak attributed to Ca atoms. Zn atoms in the Mg matrix inhibit the formation of quenched-in vacancies bound to Ca atoms in the aged ternary alloy producing the dispersion refinement.

  11. Investigation of austenitic alloys for advanced heat recovery and hot-gas cleanup systems

    Energy Technology Data Exchange (ETDEWEB)

    Swindeman, R.W. [Oak Ridge National Lab., TN (United States)

    1997-12-01

    Materials properties were collected for the design and construction of structural components for use in advanced heat recovery and hot gas cleanup systems. Alloys systems included 9Cr-1Mo-V steel, modified 316 stainless steel, modified type 310 stainless steel, modified 20Cr-25Ni-Nb stainless steel, and modified alloy 800. Experimental work was undertaken to expand the databases for potentially useful alloys. Types of testing included creep, stress-rupture, creep-crack growth, fatigue, and post-exposure short-time tensile tests. Because of the interest in relatively inexpensive alloys for service at 700 C and higher, research emphasis was placed on a modified type 310 stainless steel and a modified 20Cr-25Ni-Nb stainless steel. Both steels were found to have useful strength to 925 C with good weldability and ductility.

  12. Experimental investigation of cavitation fracture at very high strain rates in superplastic aluminium alloy matrix composites

    Energy Technology Data Exchange (ETDEWEB)

    Higashi, Kenji (Dept. of Mechanical Systems Engineering, Coll. of Engineering, Univ. of Osaka (Japan)); Mabuchi, Mamoru (National Industrial Research, Inst. of Nagoya (Japan))

    1994-03-31

    The level and rate of cavitation with superplastic strain were investigated for a powder metallurgically processed 20 vol.% Si[sub 3]N[sub 4p]-6061 composite (where the subscript p denotes particulate) and a mechanically alloyed 15 vol.% SiC[sub p]-IN9021 composite, in which large superplastic elongations of more than 500% were found at very high strain rates of 2 s[sup -1] and 5 s[sup -1] respectively. Cavities initiated at the poles of particulate reinforcements and parallel to the applied stress direction within initial small strains, and their subsequent growth and coalescence invariably leads to premature failure. Also, cavity growth seems to be plasticity controlled. It is concluded that cavitation in superplastically deformed Si[sub 3]N[sub 4p]-6061 and SiC[sub p]-IN9021 composites is very low, owing to the accommodation process to relieve the stress constraints from interfacial sliding by the presence of the liquid phase at interfaces at optimum superplastic temperatures. (orig.)

  13. Investigations of linear contraction and shrinkage stresses development in hypereutectic al-si binary alloys

    Directory of Open Access Journals (Sweden)

    J. Mutwil

    2009-07-01

    Full Text Available Shrinkage phenomena during solidification and cooling of hypereutectic aluminium-silicon alloys (AlSi18, AlSi21 have been examined. A vertical shrinkage rod casting with circular cross-section (constant or fixed: tapered has been used as a test sample. Two type of experiments have been conducted: 1 on development of the test sample linear dimension changes (linear expansion/contraction, 2 on development of shrinkage stresses in the test sample. By the linear contraction experiments the linear dimension changes of the test sample and the metal test mould as well a temperature in six points of the test sample have been registered. By shrinkage stresses examination a shrinkage tension force and linear dimension changes of the test sample as well a temperature in three points of the test sample have been registered. Registered time dependences of the test bar and the test mould linear dimension changes have shown, that so-called pre-shrinkage extension has been mainly by mould thermal extension caused. The investigation results have shown that both: the linear contraction as well as the shrinkage stresses development are evident dependent on metal temperature in a warmest region the sample (thermal centre.

  14. Investigation of Corrosion Behaviour of Aluminium Alloy Subjected to Laser Shock Peening without a Protective Coating

    Directory of Open Access Journals (Sweden)

    U. Trdan

    2015-01-01

    Full Text Available The effect of shock waves and strain hardening of laser shock peening without protective coating (LSPwC on alloy AA 6082-T651 was investigated. Analysis of residual stresses confirmed high compression in the near surface layer due to the ultrahigh plastic strains and strain rates induced by multiple laser shock waves. Corrosion tests in a chloride environment were carried out to determine resistance to localised attack, which was also verified on SEM/EDS. OCP transients confirmed an improved condition, that is, a more positive and stable potential after LSPwC treatment. Moreover, polarisation resistance of the LSPwC treated specimen was by a factor of 25 higher compared to the untreated specimen. Analysis of voltammograms confirmed an improved enhanced region of passivity and significantly smaller anodic current density of the LSPwC specimen compared to the untreated one. Through SEM, reduction of pitting attack at the LSPwC specimen surface was confirmed, despite its increased roughness.

  15. Investigation on microstructural evolution and hardening mechanism in dilute Zr–Nb binary alloys

    Energy Technology Data Exchange (ETDEWEB)

    Yang, H.L., E-mail: yanghuilong@tokai.t.u-tokyo.ac.jp [Department of Nuclear Engineering, Graduate School of Engineering, The University of Tokyo, 2-22 Shirakata Shirane, Tokai, Ibaraki 319-1188 (Japan); Matsukawa, Y. [Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Sendai 980-8577 (Japan); Kano, S. [Department of Nuclear Engineering, Graduate School of Engineering, The University of Tokyo, 2-22 Shirakata Shirane, Tokai, Ibaraki 319-1188 (Japan); Duan, Z.G. [Graduate School of Engineering, Tohoku University, 2-1-1 Katahira, Sendai 980-8577 (Japan); Murakami, K. [Department of Nuclear Engineering, Graduate School of Engineering, The University of Tokyo, 2-22 Shirakata Shirane, Tokai, Ibaraki 319-1188 (Japan); Abe, H. [Department of Nuclear Engineering, Graduate School of Engineering, The University of Tokyo, 2-22 Shirakata Shirane, Tokai, Ibaraki 319-1188 (Japan); Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Sendai 980-8577 (Japan)

    2016-12-01

    In this study, the microstructural changes induced by doping of Nb in Zr were investigated by the combined utilization of electron backscatter diffraction and electron transmission microscopy techniques, followed by the correlated hardening mechanism being elucidated based on the obtained microstructural parameters. Microstructural characterization results revealed that microstructural changes caused by doping of Nb in Zr were mainly embodied via two aspects: reducing the matrix α-Zr grain size and increasing the amount of β-Nb particles. β-phase stabilizing effect, dragging effect and pinning effect introduced and enhanced by Nb addition, worked together to significantly reduce the grain size in Zr–Nb alloys. β-Nb particles were firstly observed in Zr0.5Nb specimen with the fairly low number density of ∼2.0 × 10{sup 18}/m{sup 3}, then this value explosively increased to ∼3.3 × 10{sup 20}/m{sup 3} for Zr2Nb specimen. In addition, hardness was increased with an increase in the Nb content. The hardening contributions from solid solution hardening, grain boundary hardening and precipitation hardening were quantitatively estimated as per the obtained microstructural parameters. Results inferred that solid solution hardening contributed the majority when the Nb atoms were solid dissolved (≤0.5 wt%), whereas the precipitation hardening surpassed any other factors when the β-Nb particles were steadily precipitated (≥1 wt%).

  16. 'FOURCRACK' - An investigation of the creep performance of advanced high alloy steel welds

    Energy Technology Data Exchange (ETDEWEB)

    Allen, D.J. [E.On-Uk, Materials and Welding Section, Power Technology, Ratcliffe on Soar, Nottingham NG11 0EE (United Kingdom)]. E-mail: David.Allen@eon-uk.com; Harvey, B. [Mitsui Babcock (United Kingdom); Brett, S.J. [RWE npower (United Kingdom)

    2007-01-15

    Creep failure by 'Type IV' cracking in the weld heat-affected zone (HAZ) is likely to be the life-limiting failure mechanism in high-alloy steel components for advanced power plant. A UK collaborative project, 'FOURCRACK', has therefore been carried out to investigate and compare the cross-weld creep rupture performance of several casts of the advanced steels E911, P92, and P122, and the established steel P91. The experimental matrix included both stress and temperature variations while minimising the testing required to characterise the comparative performance of different welded materials. The results clarify the interplay between weld metal and HAZ failure mechanisms, the relationships between parent material and cross-weld creep strength, and the relative merits of the alternative steels. Finally, problems which arise in the assessment of cross-weld creep test data are discussed, and recommendations put forward to address the risks of biased assessment when failure can take place in different locations within the weldment.

  17. Investigation of the martensitic transformation of (Cu-Zn-Ni) shape memory alloys

    Science.gov (United States)

    Naat, N. A.; Mohammed, M. A.

    2017-02-01

    (Cu-Zn-Ni) shape memory alloy with different percent have been prepared by using high frequency induction furnace under argon atmosphere. All of the specimens obtained from this alloys were heated in furnace for (15 minutes at 865°C) for homogenization and quenched in iced-water. Comparisons has been made with data obtained via differential scanning calorimetry (DSC) and energy-dispersive X-ray spectroscopy (EDS). The metallographic analyses were carried out by using optical microscopy (OM).

  18. EXPERIMENTAL INVESTIGATION ON ELECTRICAL DISCHARGE MACHINING OF TITANIUM ALLOY USING COPPER, BRASS AND ALUMINUM ELECTRODES

    Directory of Open Access Journals (Sweden)

    S. DHANABALAN

    2015-01-01

    Full Text Available In the present study, an evaluation has been done on Material Removal Rate (MRR, Surface Roughness (SR and Electrode Wear Rate (EWR during Electrical Discharge Machining (EDM of titanium alloy using copper, brass and aluminum electrodes. Analyzing previous work in this field, it is found that electrode wear and material removal rate increases with an increase current. It is also found that the electrode wear ratio increases with an increase in current. The higher wear ratio is found during machining of titanium alloy using a brass electrode. An attempt has been made to correlate the thermal conductivity and melting point of electrode with the MRR and electrode wear. The MRR is found to be high while machining titanium alloy using brass electrode. During machining of titanium alloy using copper electrodes, a comparatively smaller quantity of heat is absorbed by the work material due to low thermal conductivity. Due to the above reason, the MRR becomes very low. Duringmachining of titanium alloy using aluminium electrodes, the material removal rate and electrode wear rate are only average value while machining of titanium alloy using brass and copper electrodes.

  19. A comprehensive investigation of the strengthening effects of dislocations, texture and low and high angle grain boundaries in ultrafine grained AA6063 aluminum alloy

    NARCIS (Netherlands)

    Najafi, S.; Eivani, A. R.; Samaee, M.; Jafarian, H. R.; Zhou, J.

    2018-01-01

    The effect of equal channel angular pressing (ECAP) on the microstructure and mechanical properties of AA6063 aluminum alloy was investigated. For this purpose, samples of AA6063 aluminum alloy were deformed up to 10 passes using ECAP and the evolution of microstructure, texture and dislocation

  20. 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.

  1. Experimental investigations of visco-plastic properties of the aluminium and tungsten alloys used in KE projectiles

    Directory of Open Access Journals (Sweden)

    Magier M.

    2012-08-01

    Full Text Available The main aim of studies on dynamic behaviour of construction materials at high strain rates is to determine the variation of mechanical properties (strength, plasticity in function of the strain rate and temperature. On the basis of results of dynamic tests on the properties of constructional materials the constitutive models are formulated to create numerical codes applied to solve constructional problems with computer simulation methods. In the case of military applications connected with the phenomena of gunshot and terminal ballistics it’s particularly important to develop a model of strength and armour penetration with KE projectile founded on reliable results of dynamic experiments and constituting the base for further analyses and optimization of projectile designs in order to achieve required penetration depth. Static and dynamic results of strength investigations of the EN AW-7012 aluminium alloy (sabot and tungsten alloy (penetrator are discussed in this paper. Static testing was carried out with the INSTRON testing machine. Dynamic tests have been conducted using the split Hopkinson pressure bars technique at strain rates up to 1,2 ⋅ 104s−1 (for aluminium alloy and 6 ⋅ 103s−1 (for tungsten alloy.

  2. 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.

  3. Experimental and Theoretical Investigation of Three Alloy 690 Mockup Components: Base Metal and Welding Induced Changes

    Directory of Open Access Journals (Sweden)

    Rickard R. Shen

    2014-01-01

    Full Text Available The stress corrosion cracking (SCC resistance of cold deformed thermally treated (TT Alloy 690 has been questioned in recent years. As a step towards understanding its relevancy for weld deformed Alloy 690 in operating plants, Alloy 690 base metal and heat affected zone (HAZ microstructures of three mockup components have been studied. All mockups were manufactured using commercial heats and welding procedures in order to attain results relevant to the materials in the field. Thermodynamic calculations were performed to add confidence in phase identification as well as understanding of the evolution of the microstructure with temperature. Ti(C,N banding was found in all materials. Bands with few large Ti(C,N precipitates had negligible effect on the microstructure, whereas bands consisting of numerous small precipitates were associated with locally finer grains and coarser M23C6 grain boundary carbides. The Ti(C,N remained unaffected in the HAZ while the M23C6 carbides were fully dissolved close to the fusion line. Cold deformed solution annealed Alloy 690 is believed to be a better representation of this region than cold deformed TT Alloy 690.

  4. In situ synchrotron radiation diffraction investigation of the compression behaviour at 350 °C of ZK40 alloys with addition of CaO and Y

    Energy Technology Data Exchange (ETDEWEB)

    Buzolin, R.H. [Institute of Materials Research, Helmholtz-Zentrum Geesthacht, Max-Planck-Strasse 1, D 21502 Geesthacht (Germany); Department of Material Engineering, University of São Paulo, Av. Jão Dagnone, 1100 Jd. Sta Angelina, 13563-120 São Carlos (Brazil); Mendis, C.L., E-mail: chamini.mendis@hzg.de [Institute of Materials Research, Helmholtz-Zentrum Geesthacht, Max-Planck-Strasse 1, D 21502 Geesthacht (Germany); Tolnai, D.; Stark, A.; Schell, N. [Institute of Materials Research, Helmholtz-Zentrum Geesthacht, Max-Planck-Strasse 1, D 21502 Geesthacht (Germany); Pinto, H. [Department of Material Engineering, University of São Paulo, Av. Jão Dagnone, 1100 Jd. Sta Angelina, 13563-120 São Carlos (Brazil); Kainer, K.U.; Hort, N. [Institute of Materials Research, Helmholtz-Zentrum Geesthacht, Max-Planck-Strasse 1, D 21502 Geesthacht (Germany)

    2016-05-10

    The evolution of the microstructure during compression is investigated with in situ synchrotron radiation diffraction in as-cast ZK40, ZK40-2CaO and ZK40-1Y Mg alloys. The specimens were compressed at 350 °C with a strain rate of 10{sup −3} s{sup −1} until 30% deformation. The Y containing alloy showed the highest 0.2% proof strength in compression of 35 MPa at 350 °C which is double that of the ZK40 alloy, while the CaO added alloy shows a moderate increment at 23 MPa. The Y containing alloy shows some work hardening, while the CaO modified and the ZK40 alloys do not show work hardening after yield. Synchrotron radiation diffraction timelines show that continuous and discontinuous dynamic recrystallization occurs during deformation of the ZK40 alloy while a small amount of dynamic recrystallization was observed in the ZK40-1Y alloy. However, dynamic recrystallization was not present in the ZK40-2CaO alloy. SEM-EBSD analysis conducted on the deformed samples shows a significantly high volume fraction of twins in the Y and CaO containing alloys which was absent in the ZK40 alloy. The modified deformation behaviours observed in the CaO and Y containing alloys were attributed to the presence of intermetallic particles found at the grain boundaries and to the role of Ca and Y in stabilising twinning.

  5. Investigation of welding crack in micro laser welded NiTiNb shape memory alloy and Ti6Al4V alloy dissimilar metals joints

    Science.gov (United States)

    Yuhua, Chen; Yuqing, Mao; Weiwei, Lu; Peng, He

    2017-06-01

    Dissimilar metals of NiTiNb shape memory alloy and Ti6Al4V alloy with a same thickness of 0.2 mm were joined by micro laser welding. The effect of laser power on crack sensitivity of the weld was investigated. The results show that full penetrated welds are obtained when the laser power of 7.2 W is used, many cracks are observed in the weld. With increasing the laser power to 12 W, the number of all cracks and cracking width first increase and then decrease. By XRD analysis, three different kinds of Ti2Ni, NbNi3 and AlNbTi2 intermetallic compounds are found in the weld. According to the formation enthalpy and binary phase diagram, brittle Ti2Ni phase with more contents is existed in the weld due to final solidification, and which is the main reason of crack formation along with large stress concentration. Moreover, the welding cracks like the weld center longitudinal solidification cracks, weld metal toe transversal liquid cracks, heat-affected-zone hot cracks and crater cracks are classified in the laser welded joints. A brittle cleavage fracture with cleavage planes and river patterns in the joints is presented from the fracture surface.

  6. 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.

  7. The Investigation of a Shape Memory Alloy Micro-Damper for MEMS Applications

    Directory of Open Access Journals (Sweden)

    Chongdu Cho

    2007-09-01

    Full Text Available Some shape memory alloys like NiTi show noticeable high damping property inpseudoelastic range. Due to its unique characteristics, a NiTi alloy is commonly used forpassive damping applications, in which the energy may be dissipated by the conversion frommechanical to thermal energy. This study presents a shape memory alloy based micro-damper, which exploits the pseudoelasticity of NiTi wires for energy dissipation. Themechanical model and functional principle of the micro-damper are explained in detail.Moreover, the mechanical behavior of NiTi wires subjected to various temperatures, strainrates and strain amplitudes is observed. Resulting from those experimental results, thedamping properties of the micro-damper involving secant stiffness, energy dissipation andloss factor are analyzed. The result indicates the proposed NiTi based micro-damper exhibitsgood energy dissipation ability, compared with conventional materials damper.

  8. In situ TEM investigation of microstructural behavior of superplastic Al–Mg–Sc alloy

    Energy Technology Data Exchange (ETDEWEB)

    Dám, Karel, E-mail: damk@vscht.cz [Department of Metals and Corrosion Engineering, Institute of Chemical Technology, Prague, Technická 5, 166 28 Prague 6 (Czech Republic); Institute of Physics of the ASCR, Na Slovance 2, 182 21 Prague 8 (Czech Republic); Lejček, Pavel, E-mail: lejcekp@fzu.cz [Institute of Physics of the ASCR, Na Slovance 2, 182 21 Prague 8 (Czech Republic); Michalcová, Alena [Department of Metals and Corrosion Engineering, Institute of Chemical Technology, Prague, Technická 5, 166 28 Prague 6 (Czech Republic)

    2013-02-15

    Dynamic changes in microstructure of the superplastic ultrafine-grained Al–3Mg–0.2Sc (wt.%) alloy refined by equal-channel angular pressing (ECAP). were observed by in situ transmission electron microscopy at temperatures up to 300 °C (annealing and tensile deformation) in order to simulate the initial stages of superplastic testing. It was found that the microstructure changes significantly during the preheating before the superplastic deformation, which was accompanied by decreased microhardness. During the deformation at 300 °C, high dislocation activity as well as motion of low-angle grain boundaries was observed while high-angle grain boundaries did not move due to the presence of scandium in the alloy. - Highlights: ► We performed in situ TEM annealing and straining on superplastic Al–Mg–Sc alloy. ► We simulated the conditions of early stages of superplastic testing. ► Significant changes in microstructure occur during preheating before deformation.

  9. The Investigation of a Shape Memory Alloy Micro-Damper for MEMS Applications.

    Science.gov (United States)

    Pan, Qiang; Cho, Chongdu

    2007-09-11

    Some shape memory alloys like NiTi show noticeable high damping property inpseudoelastic range. Due to its unique characteristics, a NiTi alloy is commonly used forpassive damping applications, in which the energy may be dissipated by the conversion frommechanical to thermal energy. This study presents a shape memory alloy based micro-damper, which exploits the pseudoelasticity of NiTi wires for energy dissipation. Themechanical model and functional principle of the micro-damper are explained in detail.Moreover, the mechanical behavior of NiTi wires subjected to various temperatures, strainrates and strain amplitudes is observed. Resulting from those experimental results, thedamping properties of the micro-damper involving secant stiffness, energy dissipation andloss factor are analyzed. The result indicates the proposed NiTi based micro-damper exhibitsgood energy dissipation ability, compared with conventional materials damper.

  10. Development of advanced high strength tantalum base alloys. Part 1: Screening investigation

    Science.gov (United States)

    Buckman, R. W., Jr.

    1971-01-01

    Five experimental tantalum alloy compositions containing 13-18% W+Re+Hf solid solution solute additions with dispersed phase strengthening achieved by carbon or nitrogen additions were prepared as 1.4 inch diameter ingot processed to 3/8 inch diameter rod and evaluated. Elevated temperature tensile and creep strength increased monotonically with increasing solute content. Room temperature elongation decreased for 20% to less than 2% as the solute content was increased above 16%. Phase identification indicated that the precipitating phase in the carbide containing alloys was Ta2C.

  11. 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.

  12. 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.

  13. Phase-field investigation on the non-equilibrium interface dynamics of rapid alloy solidification

    Energy Technology Data Exchange (ETDEWEB)

    Choi, Jeong [Iowa State Univ., Ames, IA (United States)

    2011-01-01

    spacings. This oscillatory dynamics including instantaneous jump of interface velocities are consistent with a previous phenomenological model by and a numerical investigation, which may cause the formation of banded structures. Additionally, the selection of the steady state growth dynamics in the highly undercooled melt is demonstrated. The transition of the growth morphology, interface velocity selection, and solute trapping phenomenon with increasing melt supersaturations was described by the phase-field simulation. The tip selection for the dendritic growth was consistent with Ivantsov's function, and the non-equilibrium chemical partitioning behavior shows good qualitative agreement with the Aziz's solute trapping model even though the model parameter(VD) remains as an arbitrary constant. This work is able to show the possibility of comprehensive description of rapid alloy growth over the entire time-dependent non-equilibrium phenomenon.

  14. 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.

  15. 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.)

  16. An investigation of the loss of ductility in hydrogen charged beta-Ti alloys

    Science.gov (United States)

    Robertson, Ian M.

    1995-01-01

    The high strength, low density, and good corrosion resistance of Ti-based alloys make them candidate materials for a number of applications in the aerospace industry. A major limitation in the use of these alloys in the advanced hypersonic flight vehicle program is their susceptibility to hydrogen embrittlement. This study focuses on the hydrogen sensitivity of TIMETAL 21S beta-Ti alloy. The material received was in the form of grip-ends of failed tensile test samples which had been exposed to different charging conditions (combinations of hydrogen pressure and temperature). The samples received, the charging conditions, and their fracture mode are discussed. It can be seen that the fracture behavior changes from ductile to brittle with increasing hydrogen content, but the transition in behavior occurs for a small increase in hydrogen concentration. The aim of this program was to assess the microstructural differences between the ductile and brittle alloys to ascertain the embrittlement mechanism. A range of tools which included x-ray diffraction, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used.

  17. Neutron diffraction investigation of liquid alkali metal-gallium alloys. Giant cluster formation?

    NARCIS (Netherlands)

    Alvarez, M; Lomba, E; Verkerk, P; van der Aart, SA; Bionducci, M; Mirebeau, [No Value; van der Lugt, W

    Neutron diffraction experiments were performed on the liquid alloys NaGa, NaGa3, KGa3 and CsGa3. The structure factors of KGa3 and CsGa3 display prepeaks at small wavenumbers (0.64 and 0.61 (A) over circle -1, respectively). This may indicate the existence of extremely large aggregates of atoms in

  18. Physical simulation method for the investigation of weld seam formation during the extrusion of aluminum alloys

    NARCIS (Netherlands)

    Fang, G; Zhou, J.

    2017-01-01

    Extrusion through the porthole die is a predominant forming process used in the production of hollow aluminum alloy profiles across the aluminum extrusion industry. Longitudinal weld seams formed during the process may negatively influence the quality of extruded profiles. It is therefore of

  19. First-principles investigation of phase stability in the Mg-Sc binary alloy

    Science.gov (United States)

    Natarajan, Anirudh Raju; Van der Ven, Anton

    2017-06-01

    The recent discovery of shape memory behavior in Mg-Sc alloys has opened the door to the possibility of lightweight shape memory alloys. Very little is known, however, about martensitic phase transformations or about equilibrium phase stability in this alloy system. Here we report on a first-principles statistical mechanics study of zero Kelvin and finite temperature phase stability of hcp, bcc, and fcc based phases in the Mg-Sc binary. Our calculations reveal a rich array of phase transitions among the different low-temperature ordered and high-temperature disordered phases. Ground state orderings on hcp, bcc, and fcc belong to families of hierarchical structures containing rods of scandium atoms assembled in layers that repeat periodically. Both fcc and bcc are found to undergo a series of second-order phase transformations with increasing temperature until they completely disorder. A high degree of degeneracy is predicted at low and high temperatures among hcp, bcc, and fcc, a property that is likely to play an important role in the shape memory effects observed in this alloy.

  20. {open_quotes}Exchange-spring{close_quotes} Nd-Fe-B alloys: Investigations into reversal mechanisms and their temperature dependence

    Energy Technology Data Exchange (ETDEWEB)

    Lewis, L.H.; Welch, D.O. [Brookhaven National Labs., Upton, NY (United States); Panchanathan, V. [Magnequench International, (MQI), Inc., Anderson, IN (United States)

    1996-10-01

    In order to investigate factors affecting coercivity a series of two-phase Nd{sub 2}Fe{sub 14}B-based nanocomposite alloys with different excess iron concentrations were produced by melt-spinning methods. The constituent grain size was estimated by diffraction methods to be in the range of 150 {Angstrom} - 500 {Angstrom}, and room-temperature demagnetization curves verify that the alloys studied exhibit a modest remanence enhancement. Isothermal remanence magnetization (IRM) and dc-demagnetization (DCD) measurements performed at temperatures in the range 275 K {le} T {le} 350 K illustrate that the coercivity and irreversible magnetization develops in a bimodal, incoherent manner from a demagnetized state but upon demagnetization from a saturated state the system evinces collective, exchange-coupled behavior as illustrated by the reversible magnetization M{sub rev}. The temperature dependencies and values of the irreversible susceptibility X{sub irr} (DCD) suggest that a moderating phase with a magnetic anisotropy intermediate to the two constituent main phases may be present in the alloys.

  1. 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

  2. The magnetic properties of Ce/Pd surface alloys investigated using DFT

    KAUST Repository

    Shuttleworth, I.G.

    2014-06-01

    The surface alloys that form between Ce and Pd(1 1 1), Pd(1 0 0) and both unreconstructed and missing-row type Pd(1 1 0) at low Ce coverage ( θCe=19ML) have shown permanent magnetism that is mediated in part by an RKKY-like delocalized Ce 6s-Pd 5s interaction. The Pd 4d states are significantly affected by alloying and their behavior cannot be explained by a purely spin-dependent Hamiltonian. Experimental observations of changes to the Pd 4d states are explained and the implications of Ce/Pd magnetism in reforming catalysis are discussed. © 2014 Elsevier B.V. All rights reserved.

  3. Investigation of Adhesive Resistance of Aluminum Alloy by Sandblasting and Electrochemical Machining

    Directory of Open Access Journals (Sweden)

    Jianbing Meng

    2017-03-01

    Full Text Available A novel method for fabricating an adhesive resistance surface is presented. Sandblasting and electrochemical machining were introduced to prepare micro-nano structures on the sample surface. Then, the prepared sample was immersed in a tridecafluoroctyltriethoxysilane ethanol solvent. The surface of the aluminum alloy sample roughened and covered with low-surface-energy chemical groups was examined by scanning electron microscope (SEM and atomic force microscope (AFM. Surface wettability and adhesive resistance of the treated sample were characterized by water contact angles, area fraction, sliding angle and solid surface energy. Furthermore, the effects of some process parameters, such as sand size, current density, electrochemical machining time, and electrolyte concentration, on the contact angle, area fraction, sliding angle and the solid surface-energy of the modified sample surfaces were provided. The results show that the combination of binary micro-structures and surface modification of tridecafluoroctyltriethoxysilane plays a role to improve adhesive resistance of the aluminum alloy surface.

  4. Structure and Properties Investigation of MCMgAl12Zn1 Magnesium Alloy

    Directory of Open Access Journals (Sweden)

    Dobrzański L.A.

    2013-03-01

    Full Text Available This work presents an influence of cooling rate on crystallization process, structure and mechanical properties of MCMgAl12Zn1 cast magnesium alloy. The experiments were performed using the novel Universal Metallurgical Simulator and Analyzer Platform. The apparatus enabled recording the temperature during refrigerate magnesium alloy with three different cooling rates, i.e. 0.6, 1.2 and 2.4°C/s and calculate a first derivative. Based on first derivative results, nucleation temperature, beginning of nucleation of eutectic and solidus temperature were described. It was fund that the formation temperatures of various thermal parameters, mechanical properties (hardness and ultimate compressive strength and grain size are shifting with an increasing cooling rate.

  5. Development of advanced high strength tantalum base alloys. Part 2: Scale-up investigation

    Science.gov (United States)

    Ammon, R. L.; Buckman, R. W., Jr.

    1970-01-01

    Three experimental tantalum alloy compositions containing 14-16% W, 1% Re, 0.7% Hf, 0.025% C or 0.015% C and 0.015% N were prepared as two inch diameter ingots by consumable electrode vacuum arc melting. The as-cast ingots were processed by extrusion and swaging to one inch and 0.4 inch diameter rod and evaluated. Excellent high temperature forging behavior was exhibited by all three compositions. Creep strength at 2000 F to 2400 F was enhanced by higher tungsten additions as well as substitution of nitrogen for carbon. Weldability of all three compositions was determined to be adequate. Room temperature ductility was retained in the advanced tantalum alloy compositions as well as a notched/unnotched strength ratio of 1.4 for a notched bar having a K sub t = 2.9.

  6. Structure and Properties Investigation of MCMgAl12Zn1 Magnesium Alloy

    Directory of Open Access Journals (Sweden)

    L.A. Dobrzański

    2013-01-01

    Full Text Available This work presents an influence of cooling rate on crystallization process, structure and mechanical properties of MCMgAl12Zn1 castmagnesium alloy. The experiments were performed using the novel Universal Metallurgical Simulator and Analyzer Platform. Theapparatus enabled recording the temperature during refrigerate magnesium alloy with three different cooling rates, i.e. 0.6, 1.2 and 2.4C/s and calculate a first derivative. Based on first derivative results, nucleation temperature, beginning of nucleation of eutectic and solidus temperature were described. It was fund that the formation temperatures of various thermal parameters, mechanical properties (hardness and ultimate compressive strength and grain size are shifting with an increasing cooling rate.

  7. Investigation of Stress Corrosion Cracking in Magnesium Alloys by Quantitative Fractography Methods

    Directory of Open Access Journals (Sweden)

    Sozańska M.

    2017-06-01

    Full Text Available The article shows that the use of quantitative fracture description may lead to significant progress in research on the phenomenon of stress corrosion cracking of the WE43 magnesium alloy. Tests were carried out on samples in air, and after hydrogenation in 0.1 M Na2SO4 with cathodic polarization. Fracture surfaces were analyzed after different variants of the Slow Strain Rate Test. It was demonstrated that the parameters for quantitative evaluation of fracture surface microcracks can be closely linked with the susceptibility of the WE43 magnesium alloy operating under complex state of the mechanical load in corrosive environments. The final result of the study was the determination of the quantitative relationship between Slow Strain Rate Test parameters, the mechanical properties, and the parameters of the quantitative evaluation of fracture surface (microcracks.

  8. An Investigation of the Mechanical Properties of a Weldment of 7% Nickel Alloy Steels

    Directory of Open Access Journals (Sweden)

    Jeong Yeol Park

    2016-11-01

    Full Text Available During the last decade, the demand for natural gas has steadily increased for the prevention of environmental pollution. For this reason, many liquefied natural gas (LNG carriers have been manufactured. Since one of the most important issues in the design of LNG carriers is to guarantee structural safety, the use of low-temperature materials is increasing. Among commonly employed low-temperature materials, nickel steel has many benefits such as good strength and outstanding corrosion resistance. Accordingly, nickel steels are one of the most commonly used low-temperature steels for LNG storage tanks. However, the study of fracture toughness with various welding consumables of 7% nickel alloy steel is insufficient for ensuring the structural safety of LNG storage tanks. Therefore, the aim of this study was to evaluate fracture toughness of several different weldments for 7% nickel alloy steels. The weldment of 7% nickel alloy steel was fabricated by tungsten inert gas (TIG, flux cored arc welding (FCAW, and gas metal arc welding (GMAW. In order to assess the material performance of the weldments at low temperature, fracture toughness such as crack tip opening displacement (CTOD and the absorbed impact energy of weldments were compared with those of 9% nickel steel weldments.

  9. Experimental investigation of laser peening on TiAl alloy microstructure and properties

    Directory of Open Access Journals (Sweden)

    Qiao Hongchao

    2015-04-01

    Full Text Available In order to study the effect of laser peening on microstructures and properties of TiAl alloy, TiAl alloy samples were treated by Nd:YAG laser system with the wavelength of 1064 nm, pulse-width of 18 ns, and pulse-energy of 0–10 J. Surface micro-hardness, roughness, and microstructural characteristics were tested with micro-hardness tester, roughness tester and scanning electron microscope. Residual stress and pole figures were tested with X-ray diffraction and its high-temperature stability was analyzed. The experimental results show that surface micro-hardness increases by up to 30%, roughness increases to 0.37 μm, compressive residual stress increases to 337 MPa, and local texture and typical lamellar microstructure are generated. Residual stress, micro-hardness, and (002 pole figures tests are conducted, compressive residual stress value drops from 337 MPa to 260 MPa, hardness value drops from 377 HV0.2 to 343 HV0.2, and the (002 poles shift back to the center slightly. Laser peening improves microstructure and properties of TiAl alloy significantly.

  10. Fabrication and magnetic investigations of highly uniform CoNiGa alloy nanowires

    Science.gov (United States)

    Li, Wen-Jing; Khan, U.; Irfan, Muhammad; Javed, K.; Liu, P.; Ban, S. L.; Han, X. F.

    2017-06-01

    CoNiGa ternary alloy nanowire arrays were successfully fabricated by simple DC electrodeposition into the anodized aluminum oxide (AAO) templates. A systematic study of the potential and components of the electrolyte were conducted to obtain different components of CoNiGa nanowires. The largest Ga content in the prepared alloy nanowires was about 17%, while for Co and Ni contents which can be controlled in a wide range by adjusting the composition and pH value of the electrolyte appropriately. X-ray diffraction analysis confirmed that the as-grown CoNiGa nanowire arrays were polycrystal with fcc phase of Co where Co atoms partially substituted by Ni and Ga. Magnetization curves of samples with different composition were measured at room temperature as well as low temperature. The results showed that the components of the alloy nanowires have a great impact on its magnetic properties. For Co55Ni28Ga17 nanowires, the magnetization reversal mode changes from curling mode to coherent rotation as the angle increases, and the temperature dependence of coercivity can be well described by the thermal activation effect.

  11. 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.

  12. 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

  13. 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).

  14. First principles investigation of the activity of thin film Pt, Pd and Au surface alloys for oxygen reduction

    DEFF Research Database (Denmark)

    Tripkovic, Vladimir; Hansen, Heine Anton; Rossmeisl, Jan

    2015-01-01

    Further advances in fuel cell technologies are hampered by kinetic limitations associated with the sluggish cathodic oxygen reduction reaction. We have investigated a range of different formulations of binary and ternary Pt, Pd and Au thin films as electrocatalysts for oxygen reduction. The most...... driving force for surface segregation, diffusion to defects or surface self-assembling. On the basis of stability and activity analysis we conclude that the near surface alloy of Pd in Pt and some PdAu binary and PtPdAu ternary thin films with a controlled amount of Au are the best catalysts for oxygen...

  15. Investigating deformation processes in AM60 magnesium alloy using the acoustic emission technique

    Energy Technology Data Exchange (ETDEWEB)

    Mathis, K. [Department of Metal Physics, Charles University, Ke Karlovu 5, 121 16 Prague 2 (Czech Republic); Chmelik, F. [Department of Metal Physics, Charles University, Ke Karlovu 5, 121 16 Prague 2 (Czech Republic)]. E-mail: chmelik@met.mff.cuni.cz; Janecek, M. [Department of Metal Physics, Charles University, Ke Karlovu 5, 121 16 Prague 2 (Czech Republic); Hadzima, B. [Department of Materials Engineering, University of Zilina, Vel' ky diel, 010 26 Zilina (Slovakia); Trojanova, Z. [Department of Metal Physics, Charles University, Ke Karlovu 5, 121 16 Prague 2 (Czech Republic); Lukac, P. [Department of Metal Physics, Charles University, Ke Karlovu 5, 121 16 Prague 2 (Czech Republic)

    2006-12-15

    Microstructure changes in an AM60 magnesium alloy were monitored using the acoustic emission (AE) technique during tensile tests in the temperature range from 20 to 300 deg. C. The correlation of the AE signal and the deformation processes is discussed. It is shown, using transmission electron and light microscopy, that the character of the AE response is associated with various modes of mechanical twinning at lower temperatures, whereas at higher temperatures also the influence of non-basal dislocations on the AE response must be taken into account.

  16. Photoluminescence Investigations of InGaAsN Alloys Lattice-Matched to GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Jones, E.D.; Modine, N.R.; Allerman, A.A.; Fritz, I.J.; Kurtz, S.R.; Wright, A.F.; Tozer, S.T.; Wei, Xing

    1999-06-01

    InGaAsN is a semiconductor alloy system with the property that the inclusion of only 2% nitrogen reduces the bandgap by more than 30%. In this paper, we have measured the conduction-band mass measurements by three different techniques for 2% nitrogen in InGaAsN lattice matched to GaAs. Additionally, we also report pressure dependent measurements of the conduction-band mass between ambient and 40 kbar. Based on our results, we suggest that the observed changes in masses are a result of {Lambda}-X mixing.

  17. [Experimental investigation of quantitatively analysing trace Mo in complex metallic alloys by laser induced breakdown spectroscopy].

    Science.gov (United States)

    Wang, Zhen-Nan; Li, Ying; Zhang, Qing-Yu; Lu, Yuan; Zheng, Rong-Er

    2011-06-01

    The quantitative analysis using laser induced breakdown spectroscopy (LIBS), lack of appropriate interior label element, is described and applied to trace element molybdenum (Mo) detection in complex metallic alloys. A Q-switched Nd : YAG laser operating at 532 nm was utilized to generate plasma and the emission was recorded by a grating spectrometer equipped with CCD, boxcar and PMT. The three peak heights of Mo I , 550.649, 553.305 and 557.045 nm, changing with Mo mass fraction in metallic alloys were measured to produce calibration curves respectively, and double blind method was used to analyse a test sample. Based on Mo I 550.649 nm line, the Mo mass fraction in the test sample was determined to be 2.229% with relative error of 5.57% in comparison with the given value of 2.111%. On using Mo I 557.045 nm line, the relative error was found to be doubled due to the overlap with Fe emission lines. While taking the total height of three atomic lines into account in analysis, the resulted error dropped to 7.58%, even better than the average of predicted concentrations based on the above three lines. The obtained results demonstrate that satisfactory precision could be obtained under a consistent experiment condition with the above scheme, even without appropriate interior label element. The methods of maintaining stable laser ablation efficiency on sample are also discussed.

  18. Investigation of precipitate refinement in Mg alloys by an analytical composite failure model

    Energy Technology Data Exchange (ETDEWEB)

    Tabei, Ali; Li, Dongsheng; Lavender, Curt A.; Garmestani, Hamid

    2015-10-01

    An analytical model is developed to simulate precipitate refinement in second phase strengthened magnesium alloys. The model is developed based on determination of the stress fields inside elliptical precipitates embedded in a rate dependent inelastic matrix. The stress fields are utilized to determine the failure mode that governs the refinement behavior. Using an AZ31 Mg alloy as an example, the effects the applied load, aspect ratio and orientation of the particle is studied on the macroscopic failure of a single α-Mg17Al12 precipitate. Additionally, a temperature dependent version of the corresponding constitutive law is used to incorporate the effects of temperature. In plane strain compression, an extensional failure mode always fragments the precipitates. The critical strain rate at which the precipitates start to fail strongly depends on the orientation of the precipitate with respect to loading direction. The results show that the higher the aspect ratio is, the easier the precipitate fractures. Precipitate shape is another factor influencing the failure response. In contrast to elliptical precipitates with high aspect ratio, spherical precipitates are strongly resistant to sectioning. In pure shear loading, in addition to the extensional mode of precipitate failure, a shearing mode may get activated depending on orientation and aspect ratio of the precipitate. The effect of temperature in relation to strain rate was also verified for plane strain compression and pure shear loading cases.

  19. Investigation of the as-solidified microstructure of an Al–Mg–Si–Cu alloy

    Energy Technology Data Exchange (ETDEWEB)

    Li, Kai; Song, Min [State Key Laboratory of Powder Metallurgy, Central South University, Changsha 410083 (China); Du, Yong, E-mail: yongducalphad@gmail.com [State Key Laboratory of Powder Metallurgy, Central South University, Changsha 410083 (China); Tang, Ying [State Key Laboratory of Powder Metallurgy, Central South University, Changsha 410083 (China); Dong, Hongbiao [Department of Engineering, University of Leicester, Leicester LE1 7RH (United Kingdom); Ni, Song [State Key Laboratory of Powder Metallurgy, Central South University, Changsha 410083 (China)

    2014-07-25

    Highlights: • AlMgSiCu-Q particles preferentially grow along the solidification direction. • A new orientation relationship between Q particles and α-Al matrix was found. • The solidified microstructure was simulated based on Scheil–Gulliver model. • The effect of solidification on solution and aging processes were analyzed. - Abstract: The as-solidified microstructure of an Al–Mg–Si–Cu alloy was characterized by scanning electron microscopy and transmission electron microscopy. Quaternary Q particles were found to elongate preferentially along the solidification direction of the cylindrical cast ingot, whilst a small number of Si leaf-like particles aggregate mainly along the grain boundaries. The volume fractions of the Q and Si particles are quantitatively measured from electron microscopy images and thermodynamically simulated based on the Scheil–Gulliver solidification model. The results from experimental measurement agree well with those from simulation. The Q particles, which have dendrite-like internal structure and are uniformly distributed within the α-Al grains with a different orientation from that found in the aged alloys, are fast-dissolving and aid the formation of uniform aged microstructures. The aggregation of the Si particles along the grain boundaries in the as-solidified microstructure results in Si-rich boundaries even after a solution treatment, and causes the re-emergence of Si particles in the over-aged microstructure. This phenomenon helps to reduce the width of the precipitate-free zones.

  20. Investigation of austenitic alloys for advanced heat recovery and hot gas cleanup systems

    Energy Technology Data Exchange (ETDEWEB)

    Swindeman, R.W.; Ren, W.

    1996-06-01

    The objective of the research is to provide databases and design criteria to assist in the selection of optimum alloys for construction of components needed to contain process streams in advanced heat recovery and hot-gas cleanup systems. Typical components include: steam line piping and superheater tubing for low emission boilers (600 to 700{degrees}C), heat exchanger tubing for advanced steam cycles and topping cycle systems (650 to 800{degrees}C), foil materials for recuperators, on advanced turbine systems (700 to 750{degrees}C), and tubesheets for barrier filters, liners for piping, cyclones, and blowback system tubing for hot-gas cleanup systems (850 to 1000{degrees}C). The materials being examined fall into several classes, depending on which of the advanced heat recovery concepts is of concern. These classes include martensitic steels for service to 650{degrees}C, lean stainless steels and modified 25Cr-30Ni steels for service to 700{degrees}C, modified 25Cr-20Ni steels for service to 900{degrees}C, and high Ni-Cr-Fe or Ni-Cr-Co-Fe alloys for service to 1000{degrees}C.

  1. Investigation of Material Performance Degradation for High-Strength Aluminum Alloy Using Acoustic Emission Method

    Directory of Open Access Journals (Sweden)

    Yibo Ai

    2015-02-01

    Full Text Available Structural materials damages are always in the form of micro-defects or cracks. Traditional or conventional methods such as micro and macro examination, tensile, bend, impact and hardness tests can be used to detect the micro damage or defects. However, these tests are destructive in nature and not in real-time, thus a non-destructive and real-time monitoring and characterization of the material damage is needed. This study is focused on the application of a non-destructive and real-time acoustic emission (AE method to study material performance degradation of a high-strength aluminum alloy of high-speed train gearbox shell. By applying data relative analysis and interpretation of AE signals, the characteristic parameters of materials performance were achieved and the failure criteria of the characteristic parameters for the material tensile damage process were established. The results show that the AE method and signal analysis can be used to accomplish the non-destructive and real-time detection of the material performance degradation process of the high-strength aluminum alloy. This technique can be extended to other engineering materials.

  2. INVESTIGATION OF DIFFUSED-ALLOYED WASTE OF STEEL AND CAST-IRON GRIT FOR PRODUCTION OF PROTECTIVE COATS

    OpenAIRE

    E. E. Panteleenko; V. G. Shcherbakov

    2009-01-01

    The article is dedicated to solving of actual problem on creation of inexpensive alloying materials in the form of composite powders of the steel and cast iron grit waste by means of their diffusion alloying by boron.

  3. INVESTIGATION OF DIFFUSED-ALLOYED WASTE OF STEEL AND CAST-IRON GRIT FOR PRODUCTION OF PROTECTIVE COATS

    Directory of Open Access Journals (Sweden)

    E. E. Panteleenko

    2009-01-01

    Full Text Available The article is dedicated to solving of actual problem on creation of inexpensive alloying materials in the form of composite powders of the steel and cast iron grit waste by means of their diffusion alloying by boron.

  4. Experimental and Computational Investigation of High Entropy Alloys for Elevated-Temperature Applications

    Energy Technology Data Exchange (ETDEWEB)

    Liaw, Peter [Univ. of Tennessee, Knoxville, TN (United States); Zhang, Fan [CompuTherm LLC, Madison, WI (United States); Zhang, Chuan [CompuTherm LLC, Madison, WI (United States); Wang, Gongyao [Univ. of Tennessee, Knoxville, TN (United States); Xie, Xie [Univ. of Tennessee, Knoxville, TN (United States); Diao, Haoyan [Univ. of Tennessee, Knoxville, TN (United States); Kuo, Chih-Hsiang [Univ. of Tennessee, Knoxville, TN (United States); An, Zhinan [Univ. of Tennessee, Knoxville, TN (United States); Hemphill, Michael [Univ. of Tennessee, Knoxville, TN (United States)

    2016-07-30

    To create and design novel structural materials with enhanced creep-resistance, fundamental studies have been conducted on high-entropy alloys (HEAs), using (1) thermodynamic calculations, (2) mechanical tests, (3) neutron diffraction, (4) characterization techniques, and (5) crystal-plasticity finite-element modeling (CPFEM), to explore future candidates for next-generation power plants. All the constituent binary and ternary systems of the Al-Cr-Cu-Fe-Mn-Ni and Al-Co-Cr-Fe-Ni systems were thermodynamically modeled within the whole composition range. Comparisons between the calculated phase diagrams and literature data are in good agreement. Seven types of HEAs were fabricated from Al-Cr-Cu-Fe-Mn-Ni and Al-Co-Cr-Fe-Ni systems. The AlxCrCuFeMnNi HEAs have disordered [face-centered cubic (FCC) + body-centered cubic (BCC)] crystal structures, not FCC or BCC single structure. Excessive alloying of the Al element results in the change of both microstructural and mechanical properties in AlxCoCrFeNi HEAs. There are mainly three structural features in AlxCoCrFeNi: (1) the morphology, (2) the volume fractions of the constitute phases, and (3) existing temperatures of all six phases. After homogenization, the Al0.3CoCrFeNi material is a pure FCC solid solution. After aging at 700 °C for 500 hours, the optimal microstructure combinations, the FCC matrix, needle-like B2 phase within grains, and granular σ phase along grain boundary, is achieved for Al0.3CoCrFeNi. The cold-rolling process is utilized to reduce the grain size of Al0.1CoCrFeNi and Al0.3CoCrFeNi. The chemical elemental partitioning of FCC, BCC, B2, and σphases at different temperatures, before and after mechanical tests, in Al-Cr-Cu-Fe-Mn-Ni and Al-Co-Cr-Fe-Ni systems are quantitatively characterized by both synchrotron X-ray diffraction, neutron diffraction with levitation, scanning electron microscopy (SEM), advanced atom probe

  5. An electrochemical investigation of the corrosion behavior of Al-Si-Cu hypereutectic alloys in alcoholic environments

    Directory of Open Access Journals (Sweden)

    Traldi, S. M.

    2003-12-01

    Full Text Available Al-Si-Cu hypereutetic alloys produced by spray forming are mostly used in the automotive industry, especially for cylinder liners. They have the advantage of low weight associated with low coefficient of thermal expansion and excellent mechanical properties - mainly wear resistance at high temperatures. The corrosion resistance of these alloys in fuels, particularly alcoholic media, however is not yet known. In this investigation, electrochemical impedance spectroscopy (EIS and potentiodynamic polarisation have been used to evaluate the corrosion resistance of a hypereutectic Al-Si-Cu alloy in alcoholic environments. The EIS tests were carried out in pure ethanol, and ethanol with small additions (1 mM of acid and chloride, to investigate the effect of these contaminants on corrosion resistance. The corrosion resistance of a grey cast iron has also been evaluated in pure ethanol for comparison. The Al-Si-Cu alloy showed high corrosion resistance in pure ethanol, far superior to that of grey cast iron in the same medium.

    Aleaciones hipereutécticas producidas por conformación por spray son muy empleadas en la industria automovilística, especialmente en los revestimientos de los cilindros. Tienen la ventaja de añadir menos peso con bajo coeficiente de expansión térmica y excelentes propiedades mecánicas, sobre todo resistencia al desgaste en altas temperaturas. Todavía, la resistencia a la corrosión de estas aleaciones en combustibles no es conocida. En este estudio fueron utilizadas las técnicas de espectroscopia de impedancia electroquímica y polarización potenciodinámica, para evaluar la resistencia a la corrosión de una aleación hipereutéctica Al-Si-Cu en medio alcohólico. Las pruebas fueron conducidas en etanol puro y etanol con pequeñas adiciones (1 mM de ácido y cloruro, con la finalidad de investigar el efecto de estos contaminantes en la resistencia a la corrosión. Hierro fundido gris, también fue

  6. Investigation of creep rupture properties in air and He environments of alloy 617 at 800 °C

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Woo-Gon, E-mail: wgkim@kaeri.re.k [Korea Atomic Energy Research Institute, 989-111 Daedeok-daero, Yuseong-gu, Daejeon 305-353 (Korea, Republic of); Ekaputra, I.M.W.; Park, Jae-Young [Pukyong National University, Busan 608-739 (Korea, Republic of); Kim, Min-Hwan; Kim, Yong-Wan [Korea Atomic Energy Research Institute, 989-111 Daedeok-daero, Yuseong-gu, Daejeon 305-353 (Korea, Republic of)

    2016-09-15

    Creep rupture properties for Alloy 617 were investigated by a series of creep tests under different applied stresses in air and He environments at 800 °C. The creep rupture time in air and He environments exhibited almost similar life in a short rupture time. However, when the creep rupture time reaches above 3000 h, the creep life in the He environment reduced compared with those of the air environment. The creep strain rate in the He environment was a little faster than that in the air environment above 3000 h. The reduction of creep life in the He environment was due to the difference of various microstructure features such as the carbide depleted zone, oxidation structures, surface cracking, voids below the surface, and voids in the matrix in air and He environments. Alloy 617 followed Norton’s power law and the Monkman–Grant relationship well. As the stress decreased, the creep ductility decreased slightly. The thickness of the outer and internal oxide layers presented the trend of a parabolic increase with an increase in creep rupture time in both the air and He environments. The thickness in the He environment was found to be thicker than in the air environment, although pure helium gas of 99.999% was used in the present investigation. The differences in the oxide-layer thickness caused detrimental effects on the creep resistance, even in a low oxygen-containing He agent.

  7. Structural and vibrational investigations on Ge{sub 34}Sb{sub 66} solid solutions produced by mechanical alloying

    Energy Technology Data Exchange (ETDEWEB)

    Rebelo, Q.H.F.; Cotta, E.A. [Departamento de Física, Universidade Federal do Amazonas, 69077-000 Manaus, Amazonas (Brazil); Souza, S.M. de, E-mail: s.michielon@gmail.com [Departamento de Física, Universidade Federal do Amazonas, 69077-000 Manaus, Amazonas (Brazil); Trichês, D.M. [Departamento de Física, Universidade Federal do Amazonas, 69077-000 Manaus, Amazonas (Brazil); Machado, K.D. [Departamento de Física, Centro Politécnico, Universidade Federal do Paraná, 81531-990 Curitiba, Paraná (Brazil); Lima, J.C. de; Grandi, T.A. [Departamento de Física, Centro de Ciências Exatas, Universidade Federal de Santa Catarina, 88040-900 Florianópolis, Santa Catarina (Brazil); Poffo, C.M. [Departamento de Eng. Mecânica, Centro de Ciências Tecnológicas, Universidade Federal de Santa Catarina, 88040-900 Florianópolis, Santa Catarina (Brazil); Manzato, L. [Instituto Federal de Educação, Ciência e Tecnologia do Amazonas, 69075-351 Manaus, Amazonas (Brazil)

    2013-10-25

    Highlights: •A Ge{sub 34}Sb{sub 66} solid solution was prepared by mechanical alloying. •X-ray diffraction results indicate complete dissolution of Ge on the Sb matrix. •Raman measurements indicate the presence of nanocrystalline Ge dispersed in the matrix. -- Abstract: A nanostructured solid solution Ge{sub 34}Sb{sub 66} was produced from Ge and Sb by mechanical alloying and its structural and vibrational properties were investigated by X-ray diffraction (XRD) and micro-Raman spectroscopy. The Rietveld refinement of the XRD measurements allowed the investigation of the evolution of the solid solution with the milling time. The Bragg peaks of the Sb solvent phase showed a strongly reflection-indices-dependent line broadening due to the spatial variation of the Sb/Ge ratio. The asymmetric broadening in the deformed peaks was analyzed considering the Stephens model. Volume fractions of crystalline and interfacial components of the milled powder were estimated from the XRD patterns. Although XRD measurements indicated the formation of a solid solution, Raman measurements revealed the presence of nanocrystalline Ge, and its crystallite size was estimated from the Raman analysis.

  8. 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.

  9. Cross-Sectional Investigations of Oxide Scale Nanocrystalline FeCr Alloys after High-Temperature Oxidation Test at 900°C

    Science.gov (United States)

    Saryanto, H.; Sebayang, D.; Untoro, P.

    2017-05-01

    The cross-sectional examinations of oxide films formed by oxidation on the surface of FeCr alloys with various crystallite sizes were observed and investigated. X-ray diffraction (XRD) analysis was used to characterize the oxide scale morphology and to identify the phases and oxidation products. Furthermore, Scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDS) have been used to study the cross-sectional oxides produced by specimens after oxidation process. The cross-sectional investigation shows that the oxide scale formed on the surface of FeCr alloys consisted roughly of Cr2O3 with a small amount of FeO mixture. The outward diffusivity of Chromium to form Cr2O3 protective layers vary significantly occurrences on the surface of FeCr alloy with smallest crystallite size (38.51 nm), the scale had an enriched Cr content which improves the adherence of the oxide scale to the substrate, in another word, it increases the oxidation resistance. While the oxide scale formed on the surface of FeCr alloy with largest crystallite sizes (76.60 nm) had an enriched Fe content which reduces the resistance to oxidation, and adherence to the substrate. The thickness of oxide scale formed on nanocrystalline FeCr alloy with smallest crystallite sizes was found around 8 μm thick, which three-time thinner than FeCr alloy with largest crystallite sizes.

  10. Phase Identification of Nanometric Precipitates in Al-Si-Cu Aluminum Alloy by Hr-Stem Investigations

    Directory of Open Access Journals (Sweden)

    Pawlyta M.

    2016-09-01

    Full Text Available Aluminium recycling is cost-effective and beneficial for the environment. It is expected that this trend will continue in the future, and even will steadily increase. The consequence of the use of recycled materials is variable and difficult to predict chemical composition. This causes a significant reduction in the production process, since the properties of produced alloy are determined by the microstructure and the presence of precipitates of other phases. For this reason, the type and order of formation of precipitates were systematically investigated in recent decades. These studies involved, however, only the main systems (Al-Cu, Al-Mg-Si, Al-Cu-Mg, Al-Mg-Si-Cu, while more complex systems were not analysed. Even trace amounts of additional elements can significantly affect the alloy microstructure and composition of precipitates formed. This fact is particularly important in the case of new technologies such as laser surface treatment. As a result of extremely high temperature and temperature changes after the laser remelting large amount of precipitates are observed. Precipitates are nanometric in size and have different morphology and chemical composition. A full understanding of the processes that occur during the laser remelting requires their precise but also time effectively phase identification, which due to the diversity and nanometric size, is a major research challenge. This work presents the methodology of identification of nanometer phase precipitates in the alloy AlSi9Cu, based on the simultaneous TEM imaging and chemical composition analysis using the dispersion spectroscopy using the characteristic X-ray. Verification is performed by comparing the simulation unit cell of the identified phase with the experimental high-resolution image.

  11. Investigation of Surface Treatments to Improve the Friction and Wear of Titanium Alloys for Diesel Engine Components

    Energy Technology Data Exchange (ETDEWEB)

    Blau, Peter J. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Cooley, Kevin M. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Kirkham, Melanie J. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Bansal, Dinesh G. [Oak Ridge Associated Universities, TN (United States)

    2012-09-20

    This final report summarizes experimental and analytical work performed under an agreement between the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Office of Transportation Technologies, and UT-Battelle LLC. The project was directed by Jerry Gibbs, of the U.S. Department of Energy’s Propulsion Materials Program, with management by D. P. Stinton and J. A. Haynes of ORNL. Participants included Peter J. Blau (Principal Investigator), Kevin M. Cooley (senior technician), Melanie J. Kirkham (materials scientist) of the Materials Science and Technology Division or ORNL, and Dinesh G. Bansal, a post doctoral fellow employed by Oak Ridge Associated Universities (ORAU) and who, at the time of this writing, is an engineer with Cummins, Inc. This report covers a three-year effort that involved two stages. In the first stage, and after a review of the literature and discussions with surface treatment experts, a series of candidate alloys and surface treatments for titanium alloy (Ti-6Al-4V) was selected for initial screening. After pre-screening using an ASTM standard test method, the more promising surface treatments were tested in Phase 2 using a variable loading apparatus that was designed and built to simulate the changing load patterns in a typical connecting rod bearing. Information on load profiles from the literature was supplemented with the help of T.C. Chen and Howard Savage of Cummins, Inc. Considering the dynamic and evolving nature of materials technology, this report presents a snapshot of commercial and experimental bearing surface technologies for titanium alloys that were available during the period of this work. Undoubtedly, further improvements in surface engineering methods for titanium will evolve.

  12. Creep-Fatigue Damage Investigation and Modeling of Alloy 617 at High Temperatures

    Science.gov (United States)

    Tahir, Fraaz

    The Very High Temperature Reactor (VHTR) is one of six conceptual designs proposed for Generation IV nuclear reactors. Alloy 617, a solid solution strengthened Ni-base superalloy, is currently the primary candidate material for the tubing of the Intermediate Heat Exchanger (IHX) in the VHTR design. Steady-state operation of the nuclear power plant at elevated temperatures leads to creep deformation, whereas loading transients including startup and shutdown generate fatigue. A detailed understanding of the creep-fatigue interaction in Alloy 617 is necessary before it can be considered as a material for nuclear construction in ASME Boiler and Pressure Vessel Code. Current design codes for components undergoing creep-fatigue interaction at elevated temperatures require creep-fatigue testing data covering the entire range from fatigue-dominant to creep-dominant loading. Classical strain-controlled tests, which produce stress relaxation during the hold period, show a saturation in cycle life with increasing hold periods due to the rapid stress-relaxation of Alloy 617 at high temperatures. Therefore, applying longer hold time in these tests cannot generate creep-dominated failure. In this study, uniaxial isothermal creep-fatigue tests with non-traditional loading waveforms were designed and performed at 850 and 950°C, with an objective of generating test data in the creep-dominant regime. The new loading waveforms are hybrid strain-controlled and force-controlled testing which avoid stress relaxation during the creep hold. The experimental data showed varying proportions of creep and fatigue damage, and provided evidence for the inadequacy of the widely-used time fraction rule for estimating creep damage under creep-fatigue conditions. Micro-scale damage features in failed test specimens, such as fatigue cracks and creep voids, were quantified using a Scanning Electron Microscope (SEM) to find a correlation between creep and fatigue damage. Quantitative statistical

  13. Element specific investigation of ultrathin Co2MnGa/GaAs heterostructures

    DEFF Research Database (Denmark)

    Claydon, Jill S.; Hassan, Sameh; Damsgaard, Christian Danvad

    2007-01-01

    We have used x-ray magnetic circular dichroism to study the element specific magnetic properties of ultrathin films of the Heusler alloy Co2MnGa at room temperature. Nine films were grown by molecular beam epitaxy on GaAs substrates and engineered to vary in stoichiometry as Co1.86Mn0.99Ga1, Co1....

  14. Thermomechanical Effects during Direct Chill and Electromagnetic Casting of Aluminum Alloys Part I : Experimental Investigation

    Science.gov (United States)

    Drezet, J.-M.; Plata, M.

    The deformation and the temperature field evolution within direct chill (DC) and electromagnetic (EM) cast aluminum ingots have been measured in-situ using a simple experimental set-up. The deformation of the cross section of the cold ingots has also been characterized as a function of the casting speed, alloy composition and inoculation condition. The pull-in of the lateral rolling faces has been found to occur in two sequences for DC cast ingots whereas that associated with EMC was continuous. The pull-in was maximum at the center of these faces (about 7-9 %) and strongly depended upon the casting speed. The present results constitute a basis for the validation of the model presented in part II.

  15. Amorphous palladium-silicon alloys for the oxidation of formic acid and formaldehyde. A voltammetric investigation

    Directory of Open Access Journals (Sweden)

    Correia A.N.

    1999-01-01

    Full Text Available The electrocatalytic oxidation of formic acid and formaldehyde on Pd and on amorphous Pd(Si was studied by cyclic voltammetry and the results compared with the literature for similar systems. The oxidation of HCOOH on Pd occurs through direct catalytic dehydrogenation via (:C(OH2ads while on Pd(Si this intermediate does not appear to be formed. This is a consequence of the presence of inert Si on the surface that diminishes the probability of adjacent free sites. At high HCOOH concentrations, that intermediate undergoes dehydration on the Pd surface and COads oxidation peak is observed. For HCHO, the oxidation mechanism on both electrode materials appears similar to that previously proposed for Pt. However, the oxides formed on the amorphous Pd(Si alloy are more reactive than those on Pd thus affecting the overall kinetics of the process for both organic molecules, a fact revealed by the increase in anodic currents observed in the voltammograms.

  16. Investigation of laser metal deposited Alloy 718 onto an EN 1.4401 stainless steel substrate

    Science.gov (United States)

    Segerstark, Andreas; Andersson, Joel; Svensson, Lars-Erik

    2017-12-01

    This paper focuses on how process parameters affect the deposition of Alloy 718 onto an EN 1.4401 stainless steel substrate in terms of secondary phase formation, dilution and hardness. A columnar solidification structure with elongated grains growing in the direction normal to the substrate was observed for all parameters. In the interdendritic regions, phases with a high content of Niobium were identified. Scanning Electron Microscopy imaging and Energy Dispersive Spectroscopy measurements revealed these phases to most likely be Laves phase and Nb-carbides. Temperature measurements indicated no significant aging in the deposits. Considerable enrichment of iron was found in the initially deposited layers due to dilution from the substrate. The increased content of iron seemed to aid in forming constituents rich in niobium which, in turn, influenced the hardness. The highest mean hardness was noted in the sample with the lowest area fraction of Nb-rich constituents.

  17. Experimental investigation on local mechanical response of superelastic NiTi shape memory alloy

    Science.gov (United States)

    Xiao, Yao; Zeng, Pan; Lei, Liping

    2016-01-01

    In this paper, primary attention is paid to the local mechanical response of NiTi shape memory alloy (SMA) under uniaxial tension. With the help of in situ digital image correlation, sets of experiments are conducted to measure the local strain field at various thermomechanical conditions. Two types of mechanical responses of NiTi SMA are identified. The residual strain localization phenomena are observed, which can be attributed to the localized phase transformation (PT) and we affirm that most of the irreversibility is accumulated simultaneously during PT. It is found that temperature and PT play important roles in inducing delocalization of the reverse transformation. We conclude that forward transformation has more influence on the transition of mechanical response in NiTi SMA than reverse transformation in terms of the critical transition temperature for inducing delocalized reverse transformation.

  18. Steam assisted oxide growth on aluminium alloys using oxidative chemistries: Part I Microstructural investigation

    DEFF Research Database (Denmark)

    Din, Rameez Ud; Piotrowska, Kamila; Gudla, Visweswara Chakravarthy

    2015-01-01

    The surface treatment of aluminium alloys under steam containing KMnO4 and HNO3resulted in the formation of an oxide layer having a thickness of up to 825 nm. The use of KMnO4 and HNO3 in the steam resulted in incorporation of the respective chemical species into the oxide layer. Steam treatment...... with solution containing HNO3 caused dissolution of Cu and Si from the intermetallic particles in the aluminium substrate. The growth rate of oxide layer was observed to be a function of MnO4−and NO3−ions present in the aqueous solution. The NO3−ions exhibit higher affinity towards the intermetallic particles...

  19. Preliminary investigation of fabrication composite structures by using shape memory alloys

    Science.gov (United States)

    Klein, W.; Dudek, O.

    2017-09-01

    The paper shows method of smart forming composite structures and fundamentals of propose fabrication technology. The presented method is based on innovative 3D printing technics with SMA (Shape Memory Alloy) fibres application. The SMA fibres layout cause an eccentric axial load after thermal activation. The result of this process is composite structures deflection in a predictable direction. The technology demonstrator sample was fabricated as well as numerical simulations were performed in aim of proof of concept. The identification process was developed to determine the layout of SMA fibres. The simulations were performed in MATLAB and ANSYS environment, where the genetic algorithm was used to identify geometrical parameters. The MAC (Modal Assurance Criterion) criterion was used to compare nodal solution with the predefined shape pattern. The simulation results shows possibilities of forming composite structures on the example of deflected beam.

  20. Investigation of photocatalytic activity of titanium dioxide coating deposited on aluminium alloy substrate by plasma technique

    DEFF Research Database (Denmark)

    Daviðsdóttir, Svava; Soyama, Juliano; Dirscherl, Kai

    2011-01-01

    . The photocatalytic process is initiated by UV-light in TiO2 which creates electron-/hole pairs in the conduction band (CB) and valence band (VB) of TiO2, respectively. The electron/hole pairs generated have sufficient energy to cause reduction and oxidation on its surface providing the self-cleaning effect....... Literature consists of large number of publications on titanium dioxide coating for self-cleaning applications, with glass as the main substrate. Only little work is available on TiO2 coating of metallic alloys used for engineering applications. Engineering materials, such as light-weight aluminium and steel...... of the coating strongly influences the photocatalytic properties. In general, the photocatalytic activity increased with thickness. Quantification of images scanned with Atomic Force Microscope (AFM) revealed that there is a linear relationship between the thickness of the coating and the average cell size...

  1. Experiment investigation of laser shock peening on TC6 titanium alloy to improve high cycle fatigue performance

    Energy Technology Data Exchange (ETDEWEB)

    Nie, Xiangfan, E-mail: skingkgd@163.com; He, Weifeng; Zhou, Liucheng; Li, Qipeng; Wang, Xuede

    2014-01-31

    Laser shock peening (LSP) is an innovative surface treatment technique, and can significantly improve the fatigue performance of metallic components. In this paper, the objective of this work was to improve the fatigue resistance of TC6 titanium alloy by laser shock peening. Firstly, the effects on the microstructure and mechanical properties with different LSP impacts were investigated, which were observed and measured by X-ray diffraction (XRD), transmission electron microscope (TEM), residual stress tester and microhardness tester. Specially, nanostructure was detected in the laser-peened surface layer with multiple LSP impacts. Whereafter, a better parameter was chosen to be applied on the standard vibration fatigue specimens. Via the high-cycle vibration fatigue tests, the high cycle fatigue limits of the specimens without and with LSP were obtained and compared. The fatigue results demonstrate that LSP can effectively improve the fatigue limit of TC6 titanium alloy. The strengthening mechanism was indicated by analyzing the effects on the microstructure and mechanical properties comprehensively.

  2. Experimental investigation of Ti–6Al–4V titanium alloy and 304L stainless steel friction welded with copper interlayer

    Directory of Open Access Journals (Sweden)

    R. Kumar

    2015-03-01

    Full Text Available The basic principle of friction welding is intermetallic bonding at the stage of super plasticity attained with self-generating heat due to friction and finishing at upset pressure. Now the dissimilar metal joints are especially popular in defense, aerospace, automobile, bio-medical, refinery and nuclear engineerings. In friction welding, some special alloys with dual phase are not joined successfully due to poor bonding strength. The alloy surfaces after bonding also have metallurgical changes in the line of interfacing. The reported research work in this area is scanty. Although the sound weld zone of direct bonding between Ti–6Al–4V and SS304L was obtained though many trials, the joint was not successful. In this paper, the friction welding characteristics between Ti–6Al–4V and SS304L into which pure oxygen free copper (OFC was introduced as interlayer were investigated. Box–Behnken design was used to minimize the number of experiments to be performed. The weld joint was analyzed for its mechanical strength. The highest tensile strength between Ti–6Al–4V and SS304L between which pure copper was used as insert metal was acquired. Micro-structural analysis and elemental analysis were carried out by EDS, and the formation of intermetallic compound at the interface was identified by XRD analysis.

  3. Investigations on Laser Beam Welding of Different Dissimilar Joints of Steel and Aluminum Alloys for Automotive Lightweight Construction

    Science.gov (United States)

    Seffer, Oliver; Pfeifer, Ronny; Springer, André; Kaierle, Stefan

    Due to the enormous potential of weight saving, and the consequential reduction of pollutant emissions, the use of hybrid components made of steel and aluminum alloys is increasing steadily, especially concerning automotive lightweight construction. However, thermal joining of steel and aluminum is still being researched, due to a limited solubility of the binary system of iron and aluminum causing the formation of hard and brittle intermetallic phases, which decrease the strength and the formability of the dissimilar seam. The presented results show the investigation of laser beam welding for joining different dissimilar hybrid components of the steel materials HX220LAD+Z100, 22MnB5+AS150 and 1.4301, as well as the aluminum alloy AA6016-T4 as a lap joint. Among other things, the influences of the energy per unit length, the material grade, the sheet thickness t, the weld type (lap weld, fillet weld) and the arrangement of the base materials in a lap joint (aluminum-sided irradiation, steel-sided irradiation) on the achievable strengths are analyzed. The characterization of the dissimilar joints includes tensile shear tests and metallographic analyses, depending on the energy per unit length.

  4. Experimental and numerical investigation on under-water friction stir welding of armour grade AA2519-T87 aluminium alloy

    Directory of Open Access Journals (Sweden)

    S. Sree Sabari

    2016-08-01

    Full Text Available Friction stir welding (FSW is a promising welding process that can join age hardenable aluminium alloys with high joint efficiency. However, the thermal cycles experienced by the material to be joined during FSW resulted in the deterioration of mechanical properties due to the coarsening and dissolution of strengthening precipitates in the thermo-mechanical affected zone (TMAZ and heat affected zone (HAZ. Under water friction stir welding (UWFSW is a variant of FSW process which can maintain low heat input as well as constant heat input along the weld line. The heat conduction and dissipation during UWFSW controls the width of TMAZ and HAZ and also improves the joint properties. In this investigation, an attempt has been made to evaluate the mechanical properties and microstructural characteristics of AA2519-T87 aluminium alloy joints made by FSW and UWFSW processes. Finite element analysis has been used to estimate the temperature distribution and width of TMAZ region in both the joints and the results have been compared with experimental results and subsequently correlated with mechanical properties.

  5. Investigation of nano Pt and Pt-based alloys electrocatalysts for direct methanol fuel cells and their properties

    Directory of Open Access Journals (Sweden)

    Chunguang Suo

    2014-03-01

    Full Text Available The electrocatalysts used in micro direct methanol fuel cell (μDMFC, such as Pt/C and Pt alloy/C, prepared by liquid-phase NaBH4 reduction method have been investigated. XC-72 (Cobalt corp. Company, U.S.A is chosen as the activated carrier for the electrocatalysts to keep the catalysts powder in the range of several nanometers. The XRD, SEM, EDX analyses indicated that the catalysts had small particle size in several nanometers, in excellent dispersed phase and the molar ratio of the precious metals was found to be optimal. The performances of the DMFCs using cathodic catalyst with Pt percentage of 30wt% and different anodic catalysts (Pt-Ru, Pt-Ru-Mo were tested. The polarization curves and power density curves of the cells were measured to determine the optimal alloy composition and condition for the electrocatalysts. The results showed that the micro direct methanol fuel cell with 30wt% Pt/C as the cathodic catalyst and n(Pt:n(Ru:n(Mo = 3:2:2 PtRuMo/C as the anodic catalyst at room temperature using 2.0mol/L methanol solution has the best performances.

  6. Experimental and numerical investigations of hybrid laser arc welding of aluminum alloys in the thick T-joint configuration

    Science.gov (United States)

    Mazar Atabaki, M.; Nikodinovski, M.; Chenier, P.; Ma, J.; Liu, W.; Kovacevic, R.

    2014-07-01

    In the present investigation, a numerical finite element model was developed to simulate the hybrid laser arc welding of different aluminum alloys, namely 5××× to 6××× series. The numerical simulation has been considered two double-ellipsoidal heat sources for the gas metal arc welding and laser welding. The offset distance of the metal arc welding and laser showed a significant effect on the molten pool geometry, the heat distribution and penetration depth during the welding process. It was confirmed that when the offset distance is within the critical distance the laser and arc share the molten pool and specific amount of penetration and dilution can be achieved. The models and experiments show that the off-distance between the two heat sources and shoulder width have considerable influence on the penetration depth and appearance of the weld beads. The experiments also indicate that the laser power, arc voltage and type of the filler metal can effectively determine the final properties of the bonds, specifically the bead appearance and microhardness of the joints. The experiments verified the numerical simulation as the thermocouples assist to comprehend the amount of heat distribution on the T-joint coupons. The role of the welding parameters on the mechanism of the hybrid laser welding of the aluminum alloys was also discussed.

  7. Investigation on the corrosion behaviour and microstructure of 2024-T3 Al alloy treated via plasma electrolytic oxidation

    Energy Technology Data Exchange (ETDEWEB)

    Fadaee, Hossein; Javidi, Mehdi, E-mail: mjavidi@yahoo.com

    2014-08-01

    Highlights: • Plasma electrolytic oxidation used to improve corrosion resistance of 2024-T3 alloy. • A conventional DC source with low applied voltage was considered for PEO. • Use of glycerin was effective in enhancement of corrosion resistance. • The surface morphology indicated coatings have a dense structure without cracking. • Degradation of coatings with immersion time was investigated. - Abstract: Plasma electrolytic oxidation treatment was performed on 2024-T3 aluminium alloy in a simple and inexpensive electrolyte. It was found that treatment time of 30 min resulted in the most noble corrosion potential and lowest corrosion current density. The surface and cross-sectional morphology indicated that the coating has a dense structure without any cracking. Furthermore, the result of X-ray diffraction analysis indicated that the coating was formed mainly from α-Al{sub 2}O{sub 3}, γ-Al{sub 2}O{sub 3}, Al{sub 3.21}Si{sub 0.47} and small amounts of amorphous phases. The presence of glycerine in the electrolyte composition resulted in not only stabilising the solution but also improving the corrosion resistance.

  8. Further Investigation Into the Use of Laser Surface Preparation of Ti-6Al-4V Alloy for Adhesive Bonding

    Science.gov (United States)

    Palmieri, Frank L.; Crow, Allison; Zetterberg, Anna; Hopkins, John; Wohl, Christopher J.; Connell, John W.; Belcher, Tony; Blohowiak, Kay Y.

    2014-01-01

    Adhesive bonding offers many advantages over mechanical fastening, but requires robust materials and processing methodologies before it can be incorporated in primary structures for aerospace applications. Surface preparation is widely recognized as one of the key steps to producing robust and predictable bonds. This report documents an ongoing investigation of a surface preparation technique based on Nd:YAG laser ablation as a replacement for the chemical etch and/or abrasive processes currently applied to Ti-6Al-4V alloys. Laser ablation imparts both topographical and chemical changes to a surface that can lead to increased bond durability. A laser based process provides an alternative to chemical-immersion, manual abrasion, and grit blast process steps which are expensive, hazardous, environmentally unfriendly, and less precise. In addition, laser ablation is amenable to process automation, which can improve reproducibility to meet quality standards for surface preparation. An update on work involving adhesive property testing, surface characterization, surface stability, and the effect of laser surface treatment on fatigue behavior is presented. Based on the tests conducted, laser surface treatment is a viable replacement for the immersion chemical surface treatment processes. Testing also showed that the fatigue behavior of the Ti-6Al-4V alloy is comparable for surfaces treated with either laser ablation or chemical surface treatment.

  9. Effects of Microalloying on the Microstructures and Mechanical Properties of Directionally Solidified Ni-33(at.%)Al-31Cr-3Mo Eutectic Alloys Investigated

    Science.gov (United States)

    Whittenberger, J. Daniel; Raj, Sai V.; Locci, Ivan E.; Salem, Jonathan A.

    2002-01-01

    Despite nickel aluminide (NiAl) alloys' attractive combination of oxidation and thermophysical properties, their development as replacements for superalloy airfoils in gas turbine engines has been largely limited by difficulties in developing alloys with an optimum combination of elevated-temperature creep resistance and room-temperature fracture toughness. Alternatively, research has focused on developing directionally solidified NiAl-based in situ eutectic composites composed of NiAl and (Cr,Mo) phases in order to obtain a desirable combination of properties a systematic investigation was undertaken at the NASA Glenn Research Center to examine the effects of small additions of 11 alloying elements (Co, Cu, Fe, Hf, Mn, Nb, Re, Si, Ta, Ti, and Zr) in amounts varying from 0.25 to 1.0 at.% on the elevated-temperature strength and room-temperature fracture toughness of directionally solidified Ni-33Al-31Cr-3Mo eutectic alloy. The alloys were grown at 12.7 mm/hr, where the unalloyed eutectic base alloy exhibited a planar eutectic microstructure. The different microstructures that formed because of these fifth-element additions are included in the table. The additions of these elements even in small amounts resulted in the formation of cellular microstructures, and in some cases, dendrites and third phases were observed. Most of these elemental additions did not improve either the elevated-temperature strength or the room-temperature fracture toughness over that of the base alloy. However, small improvements in the compression strength were observed between 1200 and 1400 K when 0.5 at.% Hf and 0.25 at.% Ti were added to the base alloy. The results of this study suggest that the microalloying of Ni-33Al-31Cr-3Mo will not significantly improve either its elevatedtemperature strength or its room-temperature fracture toughness. Thus, any improvements in these properties must be acquired by changing the processing conditions.

  10. 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.

  11. Investigation of Carboxylic Acid-Neodymium Conversion Films on Magnesium Alloy

    Science.gov (United States)

    Cui, Xiufang; Liu, Zhe; Lin, Lili; Jin, Guo; Wang, Haidou; Xu, Binshi

    2015-01-01

    The new carboxylic acid-neodymium anhydrous conversion films were successfully prepared and applied on the AZ91D magnesium alloy surface by taking absolute ethyl alcohol as solvent and four kinds of soluble carboxylic acid as activators. The corrosion resistance of the coating was measured by potentiodynamic polarization test in 3.5 wt.% NaCl solution in pH 7.0. The morphology, structure, and constituents of the coating were observed by scanning electron microscope, energy dispersivespectrum, x-ray photoelectron spectrum, and Fourier infrared spectrometer. Results show that corrosion resistance properties of samples coated with four different anhydrous conversion films were improved obviously. The corrosion potential increased, corrosion current density decreased, and polarization resistance increased. Among these four kinds of conversion films the one added with phytic exhibits the best corrosion resistant property. The mechanism of anhydrous-neodymium conversion film formation is also analyzed in this paper. It reveals that the gadolinium conversion coating is mainly composed of stable Nd2O3, MgO, Mg(OH)2, and carboxylate of Nd. And that the sample surface is rich in organic functional groups.

  12. Macrosegregation in horizontal direct chill casting of ternary Al alloys: Investigation of solid motion

    Science.gov (United States)

    Vušanović, I.; Krane, M. J. M.

    2012-01-01

    Macrosegregation in direct chill casting processes is controlled by fluid flow due to the thermosolutal natural and forced convection, shrinkage, and transport of unattached solid grains. Because grain refinement is usually used in aluminum direct chill casting, some effort must be made to model free-floating solid grains, and their attachment to a rigid mushy zone. Criteria for attachment vary, but many are based on using a critical solid packing fraction, which is treated as uniform and constant throughout the domain. In the case of horizontal casting (HDC), gravity acts perpendicularly to the casting direction, and the assumption of a uniform packing fraction cannot be applied because the solid particles attach to some surfaces by settling and others by being swept into the rigid solid from below. In this simulation of HDC casting of an Al-Cu-Mg alloy, the rigid and unattached solid is tracked separately, and a rule set is developed to determine the attachment of free-floating solid. Comparison between cases with and without unattached solid movement shows qualitatively different results, particularly in bottom part of slab. Non-uniform packing fractions cause very different segregation patterns in the lower half of the ingot compared to the cases with no solid movement, less segregation near centerline compared to uniform packing fraction cases, and positive segregation near the place where inlet jet impinges on the mushy zone.

  13. Investigation of material removal in inner-jet electrochemical grinding of GH4169 alloy.

    Science.gov (United States)

    Li, Hansong; Niu, Shen; Zhang, Qingliang; Fu, Shuxing; Qu, Ningsong

    2017-06-14

    Electrochemical grinding (ECG) is a low-cost and highly efficient process for application to difficult-to-machine materials. In this process, the electrolyte supply mode directly affects machining stability and efficiency. This paper proposes a flow channel structure for an abrasive tool to be used for inner-jet ECG of GH4169 alloy. The tool is based on a dead-end tube with electrolyte outlet holes located in the sidewall. The diameter and number of outlet holes are determined through numerical simulation with the aim of achieving uniform electrolyte flow in the inter-electrode gap. Experiments show that the maximum feed rate and material removal rate are both improved by increasing the diamond grain size, applied voltage, electrolyte temperature and pressure. For a machining depth of 3 mm in a single pass, a feed rate of 2.4 mm min(-1) is achieved experimentally. At this feed rate and machining depth, a sample is produced along a feed path under computer numerical control, with the feed direction changing four times. Inner-jet ECG with the proposed abrasive tool shows good efficiency and flexibility for processing hard-to-cut metals with a large removal depth.

  14. Minimum Entropy Generation Theorem Investigation and Optimization of Metal Hydride Alloy Hydrogen Storage

    Directory of Open Access Journals (Sweden)

    Chi-Chang Wang

    2014-05-01

    Full Text Available The main purpose of this paper is to carry out numerical simulation of the hydrogen storage on exothermic reaction of metal hydride LaNi5 alloy container. In addition to accelerating the reaction speed of the internal metal hydride by internal control tube water-cooled mode, analyze via the application of second law of thermodynamics the principle of entropy generation. Use COMSOL Mutilphysics 4.3 a to engage in finite element method value simulation on two-dimensional axisymmetric model. Also on the premise that the internal control tube parameters the radius ri, the flow rate U meet the metal hydride saturation time, observe the reaction process of two parameters on the tank, entropy distribution and the results of the accumulated entropy. And try to find the internal tube parameter values of the minimum entropy, whose purpose is to be able to identify the reaction process and the reaction results of internal tank’s optimum energy conservation.

  15. Experimental Investigation and Finite Element Analysis on Fatigue Behavior of Aluminum Alloy 7050 Single-Lap Joints

    Science.gov (United States)

    Zhou, Bing; Cui, Hao; Liu, Haibo; Li, Yang; Liu, Gaofeng; Li, Shujun; Zhang, Shangzhou

    2018-01-01

    The fatigue behavior of single-lap four-riveted aluminum alloy 7050 joints was investigated by using high-frequency fatigue test and scanning electron microscope (SEM). Stress distributions obtained by finite element (FE) analysis help explain the fatigue performance. The fatigue test results showed that the fatigue lives of the joints depend on cold expansion and applied cyclic loads. FE analysis and fractography indicated that the improved fatigue lives can be attributed to the reduction in maximum stress and evolution of fatigue damage at the critical location. The beneficial effects of strengthening techniques result in tearing ridges or lamellar structure on fracture surface, decrease in fatigue striations spacing, delay of fatigue crack initiation, crack deflection in fatigue crack propagation and plasticity-induced crack closure.

  16. Investigation of the fatigue crack propagation behaviour in the Al alloy/Hybrid MMC Bi-layer material

    Science.gov (United States)

    Iqbal, AKM Asif; Arai, Yoshio

    2017-09-01

    In this study, the fatigue crack propagation behaviour in the Al alloy-hybrid MMC bi-material system has been investigated. Three-point bending fatigue test is carried out on the Shimadzu servopulser machine. The plastic replica technique is used to observe the crack growth during cyclic loading. The crack growth rate is analyzed at different stress intensity factor range, ΔK. The experimental results showed that the crack growth decelerates in the MMC layer side and maximum crack retardation occurs on the boundary of the bi-material system. Near the boundary of the bi-material, the crack tip becomes curved, which reduces the crack growth rate in the vicinity of the boundary of the bi-material even at higher ΔK. The particle-matrix interfacial debonding, as well as particle fracture, is observed in the hybrid MMC layer during fatigue loading.

  17. Investigation on the Effect of Cooling Rate on Hot Tearing Susceptibility of Al2024 Alloy Using Thermal Analysis

    Science.gov (United States)

    Shabestari, S. G.; Ghoncheh, M. H.

    2015-12-01

    Effect of different cooling rates and Al-5Ti-1B grain refiner on hot tearing susceptibility of Al2024 alloy were studied using thermal analysis. Influence of cooling rates on microsegregation, and the amount of gas and shrinkage porosities was investigated. The cooling rates used in the present study range from 0.4 to 17.5 K s-1. To evaluate the hot tearing susceptibility, Clyne and Davies' criterion is used. To calculate solid fraction during solidification, solid fraction vs time is plotted based on Newtonian technique via thermal analysis. The results show that the hot tearing susceptibility reduces initially by increasing the cooling rate and then increases at higher cooling rates. Hot tearing susceptibility is decreased by grain refinement. Solidification characteristics of Al2024 e.g., microsegregation, gas, and shrinkage porosities are decreased by increasing cooling rate.

  18. INVESTIGATION OF THE INFLUENCE OF ALLOYING ELEMENTS IN HARD-ALLOY MIXTURES ON WEAR RESISTANCE OF THE INSTRUMENT AT DRAWING OF HIGH-CARBON W IRE

    Directory of Open Access Journals (Sweden)

    D. V. Gontarj

    2004-01-01

    Full Text Available Using of new alloys allowed to stabilize the diameter of drawn wire in control limits, to reduce the volume of yellow metal in average by 30%, to increase the quality of its surface till one force, and also to reduce the processibility by 20 %.

  19. Transport measurements in superconductor/Heusler bilayers

    Energy Technology Data Exchange (ETDEWEB)

    Imort, Inga-Mareen; Fabretti, Savio; Thomas, Patrick; Reiss, Guenter; Thomas, Andy [Fakultaet fuer Physik, Universitaet Bielefeld, Bielefeld (Germany)

    2012-07-01

    Superconductivity and ferromagnetism are two contrary phenomena due to their electronic properties. The investigation of superconductor (S)/ferromagnet (F) heterostructures has attracted a lot of scientific interest since they allow studying the interplay between superconductivity and ferromagnetism. Additionally, applications seem possible such as F/S/F spin valves and S/F/S π-junctions. Using transport- and magnetotransport-measurements, we investigate the behavior of the superconducting transition temperature T{sub c} in NbTi/Co{sub 2}FeSi bilayers as a function of different layer thicknesses and for varying magnetic moments of the Co{sub 2}FeSi layers. Using rf-magnetron sputtering, NbTi/Co{sub 2}FeSi bilayers were grown on single-crystalline MgO(001) substrates and in-situ annealed at different temperatures. The layered character of our samples has been tested by X-ray diffraction (XRD) scans. The electronic and magnetic transport measurements have been performed between 3 and 300 K with the magnetic field up to 4 T oriented in the film plane. The dependence of T{sub c} on the NbTi- and Co{sub 2}FeSi-layer thickness enables an estimation of the interface transparency of the NbTi/Co{sub 2}FeSi barrier in the framework of recent theoretical models.

  20. In situ transmission electron microscopy investigation of quasicrystal-crystal transformations in Mg–Zn–Y alloys

    Energy Technology Data Exchange (ETDEWEB)

    Liu, J.F.; Yang, Z.Q., E-mail: yangzq34@yahoo.com; Ye, H.Q.

    2015-02-05

    Highlights: • Quasicrystal-to-crystal transformation sequence in Mg–Zn–Y alloys was determined. • H phase Zn{sub 3}MgY and W phase Zn{sub 3}Mg{sub 3}Y{sub 2} nucleated on icosahedral quasicrystal Zn{sub 6}Mg{sub 3}Y. • Growth of both H and W phase is controlled by diffusion. • The close relationship between building units plays a key role in the transformation. - Abstract: Evolution of icosahedral quasicrystals (IQC) in Mg–Zn–Y alloys during annealing was investigated by in situ transmission electron microscopy (TEM), in combination with differential thermal analysis and X-ray diffraction. In bulk samples, the IQC phase transformed to face-centered cubic phase W and hexagonal phase H at 720 K and 727 K, respectively. In TEM samples, IQC started to transform to W at 673 K and H at 688 K during heating, and H transformed to W at 623 K on cooling. Quantitative analysis of the in situ transformation process reveals that growth of both H and W is controlled by diffusion, agreeing with the Avrami’s model. The transformed products have specific orientation relationships with the parent phases: 3-fold{sub IQC}//[0 0 0 1]{sub H}//[1 1 1]{sub W} and 2-fold{sub IQC}//112{sup ¯}0]{sub H}//[01{sup ¯}1]{sub W}. The specific orientation relationships are attributed to close structural correlation among icosahedron, distorted icosahedron and cuboctahedron in IQC, H and W phases. The close structure relationship among IQC, H and W phases on the unit-cell level plays an important role in the phase transformations.

  1. Investigation on Long-term Creep Rupture Properties and Microstructure Stability of Fe-Ni based Alloy Ni-23Cr-7W at 700°C

    DEFF Research Database (Denmark)

    Tokairin, Tsuyoshi; Dahl, Kristian Vinter; Danielsen, Hilmar Kjartansson

    2013-01-01

    Long-term creep rupture properties and microstructural stability of Fe–Ni based alloy Ni–23Cr–7W (HR6W, ASME Code Case 2684) were experimentally investigated. Crept specimens at 700 °C for durations up to 37,667 h were chosen, the microstructure evolution during creep was characterized. Besides...... for the main strengthening precipitate, Laves phase. The alloy was proven to have good microstructural stability without observable coarsening of strengthening precipitates during long-term creep up to around 37,667 h. It was also verified that the growth kinetics of Laves phase can be well described...

  2. Investigation on the microstructure, mechanical property and corrosion behavior of the selective laser melted CoCrW alloy for dental application.

    Science.gov (United States)

    Lu, Yanjin; Wu, Songquan; Gan, Yiliang; Li, Junlei; Zhao, Chaoqian; Zhuo, Dongxian; Lin, Jinxin

    2015-04-01

    In this study, an experimental investigation on fabricating Ni-free CoCrW alloys by selective laser melting (SLM) for dental application was conducted in terms of microstructure, hardness, mechanical property, electrochemical behavior, and metal release; and line and island scanning strategy were applied to determine whether these strategies are able to obtain expected CoCrW parts. The XRD revealed that the γ-phase and ε-phase coexisted in the as-SLM CoCrW alloys; The OM and SEM images showed that the microstructure of CoCrW alloys appeared square-like pattern with the fine cellular dendrites at the borders; tensile test suggested that the difference of mechanical properties of line- and island-formed specimens was very small; whilst the outcomes from the electrochemical and metal release tests indicated that the island-formed alloys showed slightly better corrosion resistance than line-formed ones in PBS and Hanks solutions. Considering that the mechanical properties and corrosion resistance of line-formed and island-formed specimens meet the standards of ISO 22674:2006 and EN ISO 10271, CoCrW dental alloys can be successfully fabricated by line and island scanning strategies in the SLM process. Copyright © 2015 Elsevier B.V. All rights reserved.

  3. Pacific Northwest National Laboratory Investigation of the Stress Corrosion Cracking in Nickel-Base Alloys, Volume 2

    Energy Technology Data Exchange (ETDEWEB)

    Bruemmer, Stephen M.; Toloczko, Mychailo B.; Olszta, Matthew J.

    2012-03-01

    The objective of this program is to evaluate the primary water stress corrosion cracking (PWSCC) susceptibility of high chromium alloy 690 and its weld metals, establish quantitative measurements of crack-growth rates and determine relationships among cracking susceptibility, environmental conditions and metallurgical characteristics. Stress-corrosion, crack-growth rates have been determined for 12 alloy 690 specimens, 11 alloy 152/52/52M weld metal specimens, 4 alloy 52M/182 overlay specimens and 2 alloy 52M/82 inlay specimens in simulated PWR primary water environments. The alloy 690 test materials included three different heats of extruded control-rod-drive mechanism (CRDM) tubing with variations in the initial material condition and degree of cold work for one heat. Two cold-rolled (CR) alloy 690 plate heats were also obtained and evaluated enabling comparisons to the CR CRDM materials. Weld metal, overlay and inlay specimens were machined from industry mock ups to provide plant-representative materials for testing. Specimens have been tested for one alloy 152 weld, two alloy 52 welds and three alloy 52M welds. The overlay and inlay specimens were prepared to propagate stress-corrosion cracks from the alloy 182 or 82 material into the more resistant alloy 52M. In all cases, crack extension was monitored in situ by direct current potential drop (DCPD) with length resolution of about +1 µm making it possible to measure extremely low growth rates approaching 5x10-10 mm/s. Most SCC tests were performed at 325-360°C with hydrogen concentrations from 11-29 cc/kg; however, environmental conditions were modified during a few experiments to evaluate the influence of temperature, water chemistry or electrochemical potential on propagation rates. In addition, low-temperature (~50°C) cracking behavior was examined for selected alloy 690 and weld metal specimens. Extensive characterizations have been performed on material microstructures and stress-corrosion cracks by

  4. 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.

  5. 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.

  6. Experimental investigation of the behaviour of tungsten and molybdenum alloys at high strain-rate and temperature

    Directory of Open Access Journals (Sweden)

    Scapin Martina

    2015-01-01

    Full Text Available The introduction in recent years of new, extremely energetic particle accelerators such as the Large Hadron Collider (LHC gives impulse to the development and testing of refractory metals and alloys based on molybdenum and tungsten to be used as structural materials. In this perspective, in this work the experimental results of a tests campaign on Inermet®  IT180 and pure Molybdenum (sintered by two different producers are presented. The investigation of the mechanical behaviour was performed in tension varying the strain-rates, the temperatures and both of them. Overall six orders of magnitude in strain-rate (between 10−3 and 103 s−1 were covered, starting from quasi-static up to high dynamic loading conditions. The high strain-rate tests were performed using a direct Hopkinson Bar setup. Both in quasi-static and high strain-rate conditions, the heating of the specimens was obtained with an induction coil system, controlled in feedback loop, based on measurements from thermocouples directly welded on the specimen. The temperature range varied between 25 and 1000°C. The experimental data were, finally, used to extract the parameters of the Zerilli-Armstrong model used to reproduce the mechanical behaviour of the investigated materials.

  7. Investigation of Portevin-Le Chatelier effect in 5456 Al-based alloy using digital image correlation

    Science.gov (United States)

    Cheng, Teng; Xu, Xiaohai; Cai, Yulong; Fu, Shihua; Gao, Yue; Su, Yong; Zhang, Yong; Zhang, Qingchuan

    2015-02-01

    A variety of experimental methods have been proposed for Portevin-Le Chatelier (PLC) effect. They mainly focused on the in-plane deformation. In order to achieve the high-accuracy measurement, three-dimensional digital image correlation (3D-DIC) was employed in this work to investigate the PLC effect in 5456 Al-based alloy. The temporal and spatial evolutions of deformation in the full field of specimen surface were observed. The large deformation of localized necking was determined experimentally. The distributions of out-of-plane displacement over the loading procedure were also obtained. Furthermore, a comparison of measurement accuracy between two-dimensional digital image correlation (2D-DIC) and 3D-DIC was also performed. Due to the theoretical restriction, the measurement accuracy of 2D-DIC decreases with the increase of deformation. A maximum discrepancy of about 20% with 3D-DIC was observed in this work. Therefore, 3D-DIC is actually more essential for the high-accuracy investigation of PLC effect.

  8. 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.

  9. Demixion in simple liquid metals alloys comparative investigation of non local and local pseudopotentials: example of LiNa

    Energy Technology Data Exchange (ETDEWEB)

    Takhloukh, A; Grosdidier, B; Hellal, S [Laboratoire de Physique des Milieux Denses, Universite de Metz, Institut de Physique -electronique et de chimie 1 BdArago, 57078 Metz cedex 3 (France); Regnaut, C [Laboratoire de Physique des Liquides et des Milieux Complexes, Universite de Paris 12, Faculte des Sciences et Technologie, 61 Av. du General de Gaulle, 94 010 Creteil cedex (France)], E-mail: regnaut@univ-parisl2.fr

    2008-02-15

    Using perturbation theory and classical molecular dynamics simulations, we study the static structure and demixing behaviour of the liquid LiNa alloy from the pseudopotential approach and different classes of models. We find that the norm conserving pseudopotential does not lead to demixing while various local models, with few adjustable parameters correctly predict the structure and spinodal unstability in the alloy. Transferability of the pseudopotential to the alloy is improved if the parameters are fitted to some bulk or structural properties of the pure metal. We find that demixion can be predicted when the structure factors of the pure liquid Li and Na are reasonably reproduced from such pseudopotentials.

  10. Investigation of the effect of aluminum on the phase composition of Ti-Al-Nb-Mo gamma alloys

    Science.gov (United States)

    Terlikbaeva, A. Zh.; Alimzhanova, A. M.; Shayakhmetova, R. A.; Smagulov, D. U.; Osipov, P. A.

    2017-11-01

    A quantitative analysis of the influence of aluminum concentration on the phase composition of TNM-type Ti-Al-Nb-Mo γ-alloys has been carried out using the Thermo-Calc software and experimental methods. Isothermal and polythermal sections of the corresponding phase diagram have been calculated; the critical temperatures of phase transformations in the alloys of the system, and the chemical compositions of phases formed in them (β, α, α2, γ) have been determined. The influence of the annealing temperature on the microstructure and phase composition of the alloys containing 43 and 40% Al has been studied.

  11. Investigation of secondary dendrite arm coarsening of Al-Cu-Si alloy

    Energy Technology Data Exchange (ETDEWEB)

    Ronto, V.; Roosz, A. [Miskolc Univ. (Hungary). Dept. of Phys. Metall.

    2000-07-01

    Changing of dendritic structure was investigated during isothermal coarsening. A simple equation, {lambda}{sub 2}{sup m}-{lambda}{sub 2.0}{sup m} = K . (t-t{sub 0}), describes the isothermal coarsening. In this equation {lambda}{sub 2.0} was determined by interrupted solidification than m and K were calculated by Csebisev approximation method. The average coarsening parameter was calculated by the method of Tensi and Fuchs and was compared with our results. (orig.)

  12. Experimental investigation of hardness of FSW and TIG joints of Aluminium alloys of AA7075 and AA6061

    Directory of Open Access Journals (Sweden)

    Chetan Patil

    2016-07-01

    Full Text Available This paper reports hardness testing conducted on welded butt joints by FSW and TIG welding process on similar and dissimilar aluminium alloys. FSW joints were produced for similar alloys of AA7075T651 and dissimilar alloys of AA7075T651- AA6061T6. The Friction stir welds of AA7075 & AA6061 aluminium alloy were produced at different tool rotational speeds of 650,700, 800, 900, 1000 and transverse speed of 30, 35, 40 mm/min. TIG welding was conducted along the rolling direction of similar and dissimilar aluminium plates. The Brinell hardness testing techniques were employed to conduct the tests; these tests were conducted on the welds to ascertain the joint integrity before characterization to have an idea of the quality of the welds

  13. Experimental investigation of the behaviour of tungsten and molybdenum alloys at high strain-rate and temperature

    CERN Document Server

    Scapin, Martina; Carra, Federico; Peroni, Lorenzo

    2015-01-01

    The introduction in recent years of new, extremely energetic particle accelerators such as the Large Hadron Collider (LHC) gives impulse to the development and testing of refractory metals and alloys based on molybdenum and tungsten to be used as structural materials. In this perspective, in this work the experimental results of a tests campaign on Inermet® IT180 and pure Molybdenum (sintered by two different producers) are presented. The investigation of the mechanical behaviour was performed in tension varying the strain-rates, the temperatures and both of them. Overall six orders of magnitude in strain-rate (between 10−3 and 103 s−1) were covered, starting from quasi-static up to high dynamic loading conditions. The high strain-rate tests were performed using a direct Hopkinson Bar setup. Both in quasi-static and high strain-rate conditions, the heating of the specimens was obtained with an induction coil system, controlled in feedback loop, based on measurements from thermocouples directly welded on...

  14. Effect of the melt superheat on equiaxed solidification of Al-20 wt% Cu alloy investigated by in situ synchrotron radiography

    Science.gov (United States)

    Luo, Shifeng; Yang, Guangyu; Xiao, Lei; Huang, Wanxia; Yuan, Qingxi; Jie, Wanqi

    2017-10-01

    Effect of the melt superheat on equiaxed solidification of Al-20 wt% Cu alloy was investigated by in-situ synchrotron radiography at Beijing Synchrotron Radiation Facility. For comparison, the corresponding DSC analysis was also conducted. It was found that the grain size decreased with increasing the melt superheat. The relationship between the final mean grain size and the melt superheat can be expressed as: d = 4919.3 × ΔT-0.33 . During solidification, the mean grain size increased sharply in the first 70 s, then reached the final grain size gradually. Furthermore, with increasing the melt superheat, the mean nucleation rate increased, which can be attributed to the fact that increasing the melt superheat led to an increase in nucleation undercooling, and the growth rate and the duration of free growth stage decreased. As the melt superheat increased from 100 °C to 160 °C, the mean nucleation rate increased by 78.2% while the mean growth rate only decreased by 19.3%, which indicated that the high mean nucleation rate and the consequent low mean growth rate may be the real reasons for grain refinement. The increased nucleation density caused earlier growth deceleration due to solutal impingement effects.

  15. RETRACTED ARTICLE: Investigation on heterogeneous nucleation of MgAl2O4 in Al-Mg alloys

    Science.gov (United States)

    Haghayeghi, R.; Kapranos, P.

    2015-05-01

    This work investigates the mechanisms of grain refinement of Al-Mg alloys through ultrasonic treatment and varying Mg content. MgAl2O4 particles display an equiaxed and faceted morphology with {111} planes and when exposed to {111} of α-Al, can act as heterogeneous and potent nuclei for aluminium. Intensive vibrations by ultrasonic treatment lead to significant grain refinement through effective dispersion of MgAl2O4 particles. The equiaxed and faceted morphology of MgAl2O4 along with a well-defined cube-on-cube orientation relationship (1bar 11)[110] MgAl2O4//(1bar 11)[110] α-Al, provide improved refinement. Furthermore, multiplication of solidification sites by the ultrasonic pulses enhances heterogeneous nucleation. The resulting improved grain refinement relates in all probability to the increased nucleation sites, due to grain multiplications and wetting of impurities, the lowering of surface tension due to the segregation of magnesium to the surface of liquid aluminium, the appropriate growth restriction factor and the low lattice mismatch coupled with strong dispersion of oxides.The filtration test confirms these particles as potent refiners.

  16. An Investigation of Oxide Coating Synthesized on an Aluminum Alloy by Plasma Electrolytic Oxidation in Molten Salt

    Directory of Open Access Journals (Sweden)

    Alexander Sobolev

    2017-08-01

    Full Text Available Plasma electrolytic oxidation (PEO is a surface treatment process for obtaining oxide coatings with a high performance on valve metals. PEO is mostly performed in an aqueous solution electrolyte that limits the size of treated parts due to the fact that the system is heated. Therefore, the coating of large surfaces cannot be synthesized in an aqueous electrolyte. In the current work, an alternative approach of PEO treatment, whereby an aluminum 1050 alloy in nitrate molten salt at a temperature of 280 °C is applied, was investigated. The microstructure, phase and chemical compositions, and micro-hardness were examined using X-ray diffraction (XRD, scanning electron microscopy (SEM, energy-dispersive X-ray spectroscopy (EDS, and micro-hardness tests. The obtained results show that formed coating contains from two sub-layers: one is the outer sub-layer of the α-Al2O3 phase and the second is its inner sub-layer. It was found that the formed coating was free of any contaminants originating from the electrolyte and had no cracks or pores, which are usually present in coatings formed by PEO treatment in an aqueous solution electrolyte.

  17. Rapid Prototyping for In Vitro Knee Rig Investigations of Prosthetized Knee Biomechanics: Comparison with Cobalt-Chromium Alloy Implant Material

    Directory of Open Access Journals (Sweden)

    Christian Schröder

    2015-01-01

    Full Text Available Retropatellar complications after total knee arthroplasty (TKA such as anterior knee pain and subluxations might be related to altered patellofemoral biomechanics, in particular to trochlear design and femorotibial joint positioning. A method was developed to test femorotibial and patellofemoral joint modifications separately with 3D-rapid prototyped components for in vitro tests, but material differences may further influence results. This pilot study aims at validating the use of prostheses made of photopolymerized rapid prototype material (RPM by measuring the sliding friction with a ring-on-disc setup as well as knee kinematics and retropatellar pressure on a knee rig. Cobalt-chromium alloy (standard prosthesis material, SPM prostheses served as validation standard. Friction coefficients between these materials and polytetrafluoroethylene (PTFE were additionally tested as this latter material is commonly used to protect pressure sensors in experiments. No statistical differences were found between friction coefficients of both materials to PTFE. UHMWPE shows higher friction coefficient at low axial loads for RPM, a difference that disappears at higher load. No measurable statistical differences were found in knee kinematics and retropatellar pressure distribution. This suggests that using polymer prototypes may be a valid alternative to original components for in vitro TKA studies and future investigations on knee biomechanics.

  18. Investigation of electrochemical synthesis of ferrate, Part I: Electrochemical behavior of iron and its several alloys in concentrated alkaline solutions

    Directory of Open Access Journals (Sweden)

    Čekerevac Milan I.

    2009-01-01

    Full Text Available In recent years, considerable attention has been paid to various applications of Fe(VI due to its unique properties such as oxidizing power, selective reactivity, stability of the salt, and non-toxic decomposition by-products of ferric ion. In environmental remediation processes, Fe(VI has been proposed as green oxidant, coagulant, disinfectant, and antifoulant. Therefore, it is considered as a promising multi-purpose water treatment chemical. Fe(VI has also potential applications in electrochemical energy source, as 'green cathode'. The effectiveness of ferrate as a powerful oxidant in the entire pH range, and its use in environmental applications for the removal of wide range of contaminants has been well documented by several researchers. There is scientific evidence that ferrate can effectively remove arsenic, algae, viruses, pharmaceutical waste, and other toxic heavy metals. Although Fe(VI was first discovered in early eighteen century, detailed studies on physical and chemical properties of Fe(VI had to wait until efficient synthetic and analytical methods of Fe(VI were developed by Schreyer et al. in the 1950s. Actually, there have been developed three ways for the preparation of Fe(VI compounds : the wet oxidation of Fe(II and Fe(III compounds, the dry oxidation of the same, and the electrochemistry method, mainly based on the trans passive oxidation of iron. High purity ferrates Fe(VI can be generated when electrode of the pure iron metal or its alloys are anodized in concentrated alkaline solution. It is known that the efficiency of electrochemical process of Fe(VI production depends on many factors such as current density, composition of anode material, types of electrolyte etc. In this paper, the electrochemical synthesis of ferrate(VI solution by the anodic dissolution of iron and its alloys in concentrated water solution of NaOH and KOH is investigated. The process of transpassive dissolution of iron to ferrate(VI was studied by

  19. Investigation of microstructural and mechanical properties of cell walls of closed-cell aluminium alloy foams

    Energy Technology Data Exchange (ETDEWEB)

    Islam, M.A.; Kader, M.A.; Hazell, P.J.; Brown, A.D. [School of Engineering and Information Technology, UNSW Canberra, ACT 2610 (Australia); Saadatfar, M. [Department of Applied Mathematics, Australian National University, Canberra ACT 0200 (Australia); Quadir, M.Z [Electron Microscope Unit, Mark Wainwright Analytical Centre (MWAC), The University of New South Wales, Sydney, NSW 2052 (Australia); Microscopy and Microanalysis Facility (MMF), John de Laeter Centre (JdLC), Curtin University, WA 6102 (Australia); Escobedo, J.P., E-mail: J.Escobedo-Diaz@adfa.edu.au [School of Engineering and Information Technology, UNSW Canberra, ACT 2610 (Australia)

    2016-06-01

    This study investigates the influence of microstructure on the strength properties of individual cell walls of closed-cell stabilized aluminium foams (SAFs). Optical microscopy (OM), micro-computed X-ray tomography (µ-CT), electron backscattering diffraction (EBSD), and energy dispersive X-ray spectroscopy (EDS) analyses were conducted to examine the microstructural properties of SAF cell walls. Novel micro-tensile tests were performed to investigate the strength properties of individual cell walls. Microstructural analysis of the SAF cell walls revealed that the material consists of eutectic Al-Si and dendritic a-Al with an inhomogeneous distribution of intermetallic particles and micro-pores (void defects). These microstructural features affected the micro-mechanism fracture behaviour and tensile strength of the specimens. Laser-based extensometer and digital image correlation (DIC) analyses were employed to observe the strain fields of individual tensile specimens. The tensile failure mode of these materials has been evaluated using microstructural analysis of post-mortem specimens, revealing a brittle cleavage fracture of the cell wall materials. The micro-porosities and intermetallic particles reduced the strength under tensile loading, limiting the elongation to fracture on average to ~3.2% and an average ultimate tensile strength to ~192 MPa. Finally, interactions between crack propagation and obstructing intermetallic compounds during the tensile deformation have been elucidated.

  20. Numerical Investigation of Residual Stress in Thick Titanium Alloy Plate Joined with Electron Beam Welding

    Science.gov (United States)

    Liu, Chuan; Wu, Bing; Zhang, Jian Xun

    2010-10-01

    A finite-element (FE) simulation process integrating three dimensional (3D) with two-dimensional (2D) models is introduced to investigate the residual stress of a thick plate with 50-mm thickness welded by an electron beam. A combined heat source is developed by superimposing a conical volume heat source and a uniform surface heat source to simulate the temperature field of the 2D model with a fine mesh, and then the optimal heat source parameters are employed by the elongated heat source for the 3D simulation without trial simulations. The welding residual stress also is investigated with emphasis on the through-thickness stress for the thick plate. Results show that the agreement between simulation and experiment is good with a reasonable degree of accuracy in respect to the residual stress on the top surface and the weld profile. The through-thickness residual stress of the thick plate induced by electron beam welding is distinctly different from that of the arc welding presented in the references.

  1. Investigation of performance degradation of SOFC using chromium-containing alloy interconnects

    DEFF Research Database (Denmark)

    Beeaff, D.R.; Dinesen, A.; Hendriksen, Peter Vang

    2007-01-01

    The long-term aging of a stack element (fuel cell, current collectors, and interconnect materials) was studied. A pair of tests were made in which one sample contained an interconnect, a high-temperature stainless steel (Crofer 22 APU), treated with an LSMC coating applied to the cathode......O filler. Longterm degradation of each sample was determined using a current density of 250 mA.cm(-2) using humidified hydrogen as the fuel and air as the oxygen source. Additionally, the stack element was cycled and an investigation into the effect of cathode atmosphere was undertaken to elucidate......-side interconnect plate and the other sample containing a similar fuel cell but no steel interconnect. The interconnect-bearing sample was evaluated for thermochemical compatibility of cell components, including interconnect materials, under conditions typical of and/or expected during the lifetime of an installed...

  2. 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.

  3. 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.

  4. An investigation of the properties of conventional and severe shot peened low alloy steel

    Science.gov (United States)

    Quang Trung, Pham; Butler, David Lee; Win Khun, Nay

    2017-07-01

    The effects of the conventional shot peening and severe shot peening process on the mechanical and tribological properties of shot peened AISI 4340 high strength steel were systematically investigated. Compared with the conventional shot peened sample, the ultrafine grain surface layer with a depth of about 20 µm generated by the severe shot peening process can enhance the hardness and wear resistance of the treated material. However, deeper dimples generated by the high media velocity in the severe shot peening process resulted in a higher surface roughness, which is considered as a side effect of this method reducing the fatigue life of the material. Applying a smaller shot size with an appropriate intensity can be used to peen the severe shot peened samples to not only reduce the surface roughness and friction coefficient but also improve the wear resistance for these samples. This work was presented in the shot peening section during ‘The 30th International Conference on Surface Modification Technologies, 2016, Milan, Italy’ (SMT30, ID 61, entitled ‘Comparison of the effects of conventional shot peening and severe shot peening processes on the mechanical and tribological properties of shot peened AISI 4340’) and the authors were encouraged to submit a manuscript to the Materials Research Express journal after adding some nessesary information.

  5. Theoretical Investigation of the Thermodynamic Properties of η'-(Cu, Co)6Sn5 Alloys

    Science.gov (United States)

    Wu, Heng; Zhang, Xuechao; Zheng, Bing; Zhao, Xiuchen; Liu, Ying; Li, Hong; Cheng, Jingwei

    2018-02-01

    We perform theoretical investigations on the structures of η'-Cu6Sn5-based intermetallic compounds (IMCs) with different Co doping concentration (0-12.2 wt.%) based on density functional theory (DFT). The variations of the structural, elastic and thermodynamic properties of (Cu, Co)6Sn5 IMCs with pressure (0-18 GPa) and temperature (0-500 K) are obtained with the application of quasi-harmonic Debye model for the non-equilibrium Gibbs free energy. It is found that the volume of (Cu, Co)6Sn5 shrinks with Co concentration increasing in the range of imposed pressure and temperature. At the same time, the bulk modulus of Cu4Co2Sn5 is the largest among those of Cu6Sn5, Cu5Co1Sn5 and Cu4Co2Sn5. By calculating the Debye temperature of Cu6Sn5, we find that it is higher than that of Cu5Co1Sn5 and Cu4Co2Sn5 when the pressure is higher than 2 GPa. Meanwhile, heat capacities of all three Cu6Sn5, Cu5Co1Sn5, and Cu4Co2Sn5 converge to a near-constant value at about 1090 J/mol K in the range of the imposed pressures.

  6. Theoretical Investigation of the Thermodynamic Properties of η'-(Cu, Co)6Sn5 Alloys

    Science.gov (United States)

    Wu, Heng; Zhang, Xuechao; Zheng, Bing; Zhao, Xiuchen; Liu, Ying; Li, Hong; Cheng, Jingwei

    2017-11-01

    We perform theoretical investigations on the structures of η'-Cu6Sn5-based intermetallic compounds (IMCs) with different Co doping concentration (0-12.2 wt.%) based on density functional theory (DFT). The variations of the structural, elastic and thermodynamic properties of (Cu, Co)6Sn5 IMCs with pressure (0-18 GPa) and temperature (0-500 K) are obtained with the application of quasi-harmonic Debye model for the non-equilibrium Gibbs free energy. It is found that the volume of (Cu, Co)6Sn5 shrinks with Co concentration increasing in the range of imposed pressure and temperature. At the same time, the bulk modulus of Cu4Co2Sn5 is the largest among those of Cu6Sn5, Cu5Co1Sn5 and Cu4Co2Sn5. By calculating the Debye temperature of Cu6Sn5, we find that it is higher than that of Cu5Co1Sn5 and Cu4Co2Sn5 when the pressure is higher than 2 GPa. Meanwhile, heat capacities of all three Cu6Sn5, Cu5Co1Sn5, and Cu4Co2Sn5 converge to a near-constant value at about 1090 J/mol K in the range of the imposed pressures.

  7. The Effect of Sb Addition on Sn-Based Alloys for High-Temperature Lead-Free Solders: an Investigation of the Ag-Sb-Sn System

    Science.gov (United States)

    Li, D.; Delsante, S.; Watson, A.; Borzone, G.

    2012-01-01

    Today there is renewed interest in alloys belonging to the Sb-Sn-X (X = Cu, Ag, Bi) ternary systems and their phase equilibria, phase transformations, and thermodynamic properties because of their possible use as high-temperature lead-free solders in the electronics industry. The integral mixing enthalpy of Ag-Sb-Sn liquid alloys has been measured along five different sections (Ag0.25Sn0.75, Ag0.50Sn0.50, Sb0.30Sn0.70, Sb0.50Sn0.50, and Sb0.70Sn0.30) at 530°C, 600°C, and 630°C, using a high-temperature Calvet calorimeter by dropping pure elements (Ag or Sb) in the binary alloy liquid bath. The ternary extrapolation models of Muggianu and Toop were used to calculate the integral enthalpy of mixing and to compare measured and extrapolated values. Selected ternary alloys have been prepared for thermal investigation by using a differential scanning calorimeter at different heating/cooling rates in order to clarify the temperature of the invariant reactions and the crystallization path.

  8. Investigation of the Influence of Cr on the Microstructure and Properties of Ti6Al4VxCr Alloys with a Combinatorial Approach

    Science.gov (United States)

    Wu, D.; Liu, L. B.; Zhang, L. G.; Zeng, L. J.; Shi, X.

    2017-09-01

    A combinatorial approach has been applied to investigate the influence of Cr on the microstructure and properties of Ti6Al4VxCr alloys. A diffusion couple was manufactured with Ti6Al4V and Ti6Al4V20Cr alloys and annealed at 1000 °C for 600 h to obtain a wide range of compositions. It was heated to 1050 °C (above β transus) for 6 h, quenched to room temperature and subsequently aged at 600 °C for 6 h to achieve the typical α + β two-phase microstructures. Combining electron probe microanalysis, scanning electron microscope and nanoindentation, the relationships between the composition and microstructure as well as hardness of the diffusion couple were determined. By calculating the volume fractions using Thermo-Calc, it was found that after aging the Ti6Al4V6Cr sample contained a reasonable ( 57 vol%) content of fine α phase and showed peak hardness among the Ti6Al4VxCr alloys. HAADF-STEM and XRD revealed that after solution treatment above the β transus temperature and quenching, the metastable α″ lamellar formed in the Ti6Al4V6Cr alloy. Subsequent isothermal aging of the α″ lamellar became coarse acting as precursors/preferential nucleation sites for the stable α phase.

  9. Investigations of the Electronic Properties and Surface Structures of Aluminium-Rich Quasicrystalline Alloys

    Energy Technology Data Exchange (ETDEWEB)

    Barrow, Jason A. [Iowa State Univ., Ames, IA (United States)

    2003-01-01

    The work presented in this dissertation has investigated three distinct areas of interest in the field of quasicrystals: bulk structure, transport properties, and electronic structure. First, they have described the results of a study which explored the fundamental interactions between the atomic species of the icosahedral Al-Pd-Mn quasicrystal. The goal of this work was to determine whether the pseudo-MacKay or Bergman type clusters have a special stability or are merely a geometric coincidence. This was carried out by using laser vaporization to produce gas-phase metal clusters, which were analyzed using time-of-flight mass spectrometry. Both the kinetic and thermodynamic stabilities of the clusters were probed. The data indicated no special stability for either pseudo-MacKay or Bergman type clusters as isolated units. This, however, is not proof that these clusters are simply a geometric coincidence. It is possible that such clusters only have stability in the framework of the bulk matrix and do not exist as isolated units. Next, they have reported their investigations of the bulk thermal transport properties of a decagonal Al-Ni-Co two dimensional quasicrystal in the temperature range 373K-873K. The properties of a sample oriented along the periodic axis and another oriented along the aperiodic axis were measured. A high degree of anisotropy was observed between the aperiodic and periodic directions. Additionally, the properties were measured for a sample miscut to an orientation 45° off-axis. The properties of the miscu