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Sample records for ferromagnetic compound pd2tisn

  1. Half-metallic ferromagnetism in the CsSe compound by density functional theory

    Energy Technology Data Exchange (ETDEWEB)

    Karaca, Mustafa; Kervan, Selçuk; Kervan, Nazmiye, E-mail: nkervan@gazi.edu.tr

    2015-08-05

    Graphical abstract: The ferromagnetic ground state of the CsSe compound is the most stable with CsCl-type structure with a total magnetic moment of 1 μ{sub B}/f.u. although this compound does not include transition metal atoms. The CsSe compound is half-metallic ferromagnet with a half-metallic band gap of 3.75 eV. The half-metallicity is also found to be robust with respect to the lattice distortion in the CsCl-type structure. The Curie temperature is estimated to be 390 K in the mean field approximation (MFA). - Highlights: • The CsSe compound is the most stable with CsCl-type structure. • The half-metallic band gap is about 3.5 eV for all types of structure. • The total magnetic moment is of 1 μ{sub B}/f.u. • The Curie temperature is estimated to be 390 K. - Abstract: The full-potential linearized augmented plane wave (FPLAPW) method based on the density functional theory is used to investigate the structural, magnetic and half-metallic properties of the CsSe compound in the CsCl-type, NaCl-type, ZnS-type, NiAs-type and wurtzite structures. The results show that the ferromagnetic ground state of the CsSe compound is the most stable with CsCl-type structure with a total magnetic moment of 1 μ{sub B}/f.u. although this compound does not include transition metal atoms. The CsSe compound is half-metallic ferromagnet for all types of structure. The half-metallic band gap is about 3.5 eV for all types of structure. The Curie temperature is estimated to be 390 K in the mean field approximation (MFA)

  2. Unusual signatures of the ferromagnetic transition in the heavy Fermion compound UMn$_2$Al$_{20}$

    OpenAIRE

    Wang, C H; Lawrence, J. M.; Bauer, E.D.; Kothapalli, K.; Gardner, J S; Ronning, F.; Gofryk, K.; Thompson, J.D.; Nakotte, H.; Trouw, F.

    2010-01-01

    Magnetic susceptibility results for single crystals of the new cubic compounds UT$_2$Al$_{20}$ (T=Mn, V, and Mo) are reported. Magnetization, specific heat, resistivity, and neutron diffraction results for a single crystal and neutron diffraction and inelastic spectra for a powder sample are reported for UMn$_2$Al$_{20}$. For T = V and Mo, temperature independent Pauli paramagnetism is observed. For UMn$_2$Al$_{20}$, a ferromagnetic transition is observed in the magnetic susceptibility at $T_...

  3. Ferromagnetism in orthorhombic RAgAl3 (R = Ce and Pr) compounds

    Science.gov (United States)

    Nallamuthu, S.; Dzubinska, Andrea; Reiffers, Marian; Fernandez, Jesus Rodriguez; Nagalakshmi, R.

    2017-09-01

    We present a detailed study on magnetic, thermodynamic and transport properties of polycrystalline RAgAl3(R = Ce and Pr) compounds. Both compounds crystallize in orthorhombic structure, which is distorted from the tetragonal BaAl4 structure with the space group Cmcm. Heat capacity measurement indicates the bulk magnetic ordering of the compounds. CeAgAl3 and PrAgAl3 order ferromagnetically at TC=3.8 K and 5.8 K, respectively as it was confirmed from magnetic measurements. CeAgAl3 exhibits heavy fermion behaviour. The Schottky behaviour in heat capacity data was observed in both compounds. The crystalline electric field (CEF) analysis of the magnetic parts of heat capacity of CeAgAl3 and PrAgAl3 yielded to a CEF level scheme with three doublets and nine singlets and with an overall splitting of 51 K and 180 K, respectively. Fit yielded a magnetic doublet state for CeAgAl3, whereas for PrAgAl3 a pseudo-doublet ground-state with an energy difference of 15 K has been obtained. The resistivity measurements display a low temperature drop at the magnetic ordering temperature of the compounds. Negative magnetoresistance (MR) due to the ferromagnetic ordering has been observed for both Ce and Pr compounds.

  4. Weak ferromagnetic component on the bulk ZnFe{sub 2}O{sub 4} compound

    Energy Technology Data Exchange (ETDEWEB)

    Jesus, C.B.R. [Departamento de Física, Campus prof. Aluísio de Campos, UFS, 49100-000 São Cristóvão, SE (Brazil); Mendonça, E.C. [Departamento de Física, Campus prof. Alberto Carvalho, UFS, 49500-000 Itabaiana, SE (Brazil); Silva, L.S. [Departamento de Física, Campus prof. Aluísio de Campos, UFS, 49100-000 São Cristóvão, SE (Brazil); Folly, W.S.D.; Meneses, C.T. [Departamento de Física, Campus prof. Alberto Carvalho, UFS, 49500-000 Itabaiana, SE (Brazil); Duque, J.G.S., E-mail: gerivaldoduque@gmail.com [Departamento de Física, Campus prof. Alberto Carvalho, UFS, 49500-000 Itabaiana, SE (Brazil)

    2014-01-15

    Magnetization data on the bulk ZnFe{sub 2}O{sub 4} antiferromagnetic compound (T{sub N}≈10 K) obtained via solid state reaction at different synthesis temperatures show one weak ferromagnetic component at room temperature. We have related it with the cationic disorder effect present on spinel structure of our bulk samples which comes from the magnetic interaction between iron ions sit on both octahedral and tetrahedral sites. The magnetization measurements show to all samples a clear peak around 10 K consistent with the antiferromagnetic phase transition. On the other hand, after extracted the paramagnetic component, the hysteresis loops measured at room temperature display one weak ferromagnetic component. Once the T-dependence of magnetization does not fit to a Curie–Weiss law to temperatures well above the magnetic transition we have used a combination of the Curie–Weiss law (paramagnetic spins) and a typical temperature dependence of M{sub 0}, M{sub 0}(T)=M{sub 0}(0)[1−(T/T{sub C}){sup 2}]{sup 0.5} (ordered ferromagnetic spins). We note an increase of the M{sub 0}(0) as function of the synthesis temperature. This reinforce our supposition of a cationic disorder effect driving the system to present two kinds of magnetic interactions between iron ions on A and B sites. - Highlights: • Study of the cationic disorder at bulk ZnFe{sub 2}O{sub 4} compound. • Structural and magnetization characterization. • The observation of two magnetic phases.

  5. Ferromagnetism in the Kondo-lattice compound CePd2P2.

    Science.gov (United States)

    Tran, Vinh Hung; Bukowski, Zbigniew

    2014-06-25

    We report physical properties of CePd2P2 crystallizing in the tetragonal ThCr2Si2-type structure (space group I4/mmm). Dc-magnetic susceptibility, magnetization, specific heat, electrical resistivity and magnetoresistance measurements establish a ferromagnetic ordering below the Curie temperature TC = 28.4 ± 0.2 K. Critical analysis of isothermal and isofield magnetization yields critical exponents of β = 0.405 ± 0.005, γ = 1.11 ± 0.05 and δ = 3.74 ± 0.04. The ordered state is characterized by saturation moment Ms ∼ 0.98μB and magnon energy gap Δ/kB ∼25–35 K. The studied properties reflect a competing influence of the Kondo and crystalline electric field (CEF) interactions. The strength of the Kondo effect is assigned by a low-temperature Kondo scale TK ∼19 ± 10 K and a high-temperature Kondo scale TK ~ H 117 } 10 K. A model of the inelastic scattering of the conduction electrons with an exchanged CEF energy ΔCEF was applied to the magnetic resistivity. An average value ΔCEF = 260 ± 30 K is consistent in the relationships with TK and TK H. We argue that the CePd2P2 compound appears to be a new ferromagnetic Kondo-lattice among the Ce-based intermetallics.

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

    Science.gov (United States)

    Sedeek, K.; 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, Ti3Sb and CoTi2 (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 (Tc), in addition to a second possible phase transition (TFF) 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 (M2-H/M) confirm the ferromagnetic character at both temperatures. It may be reasonable to assume the TFF 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 not obey the 18 valence electron/unit cell

  7. Ferromagnetism and chirality in two-dimensional cyanide-bridged bimetallic compounds.

    Science.gov (United States)

    Coronado, Eugenio; Gómez-García, Carlos J; Nuez, Alicia; Romero, Francisco M; Rusanov, Eduard; Stoeckli-Evans, Helen

    2002-09-09

    The combination of hexacyanoferrate(III) anions, [Fe(CN)(6)](3)(-), with nickel(II) complexes derived from the chiral ligand trans-cyclohexane-1,2-diamine (trans-chxn) affords the enantiopure layered compounds [Ni(trans-(1S,2S)-chxn)(2)](3)[Fe(CN)(6)](2).2H(2)O (1) and [Ni(trans-(1R,2R)-chxn)(2)](3)[Fe(CN)(6)](2).2H(2)O (2). These chiral systems behave as ferromagnets (T(c) = 13.8 K) with a relatively high coercive field (H(c) = 0.17 T) at 2 K. They also exhibit an unusual magnetic behavior at low temperatures that has been attributed to the dynamics of the magnetic domains in the ordered phase.

  8. Ferromagnetism and crystal electric field in the cerium compound CeRh3B2

    Science.gov (United States)

    Givord, F.; Boucherle, J.-X.; Galéra, R.-M.; Fillion, G.; Lejay, P.

    2007-09-01

    The magnetic behavior of CeRh3B2 is very unusual: it orders ferromagnetically with an exceptionally high Curie temperature TC around 115 K, but with a small saturation moment of about 0.4 μB/fu. The thermal variations of magnetization and susceptibility have been measured on a single crystal for fields applied along the easy and hard magnetization directions, with, in the latter case, special care taken to avoid rotation of the sample. The results are compared to calculations based on the crystalline electric field formalism. Due to its large value, one has to take into account the admixture of the two J multiplets of the Ce3+ ion as it is usually used for samarium compounds but not for cerium ones. These calculations actually show the important role of the excited J' = 7/2 multiplet on the 4f spin moment, leading to an enhancement of the exchange, i.e. the Curie temperature, and to a decrease of the moment. An extra polarization, as previously found from the study of magnetization density maps, is confirmed and discussed.

  9. The co-existence of superconductivity and ferromagnetism in actinide compounds

    Energy Technology Data Exchange (ETDEWEB)

    Huxley, Andrew [SPSMS-DRFMC, CEA Grenoble 38054 (France); Ressouche, Eric [SPSMS-DRFMC, CEA Grenoble 38054 (France); Grenier, Beatrice [SPSMS-DRFMC, CEA Grenoble 38054 (France); Aoki, Dai [SPSMS-DRFMC, CEA Grenoble 38054 (France); Flouquet, Jacques [SPSMS-DRFMC, CEA Grenoble 38054 (France); Pfleiderer, Christian [Physikalisches Institut, Universitaet Karlsruhe (Germany)

    2003-07-23

    Recently superconductivity has been observed in two different 5f-electron ferromagnets, UGe{sub 2} and URhGe, well below their Curie temperatures. While superconductivity could be generic to all clean ferromagnets an alternative possibility is that it occurs in these materials, which were after all carefully selected for study, due to some special features related to the participation of strongly correlated 5f electrons in the ferromagnetism. 5f electrons potentially give rise to strong anisotropies, strong spin-orbit interactions and also a strong energy dependence of the electronic density of states. Here we focus on UGe{sub 2}, and review several of the properties of the ferromagnetic state that could be a consequence of such features and discuss whether they promote superconductivity.

  10. The co-existence of superconductivity and ferromagnetism in actinide compounds

    Science.gov (United States)

    Huxley, Andrew; Ressouche, Eric; Grenier, Beatrice; Aoki, Dai; Flouquet, Jacques; Pfleiderer, Christian

    2003-07-01

    Recently superconductivity has been observed in two different 5f-electron ferromagnets, UGe2 and URhGe, well below their Curie temperatures. While superconductivity could be generic to all clean ferromagnets an alternative possibility is that it occurs in these materials, which were after all carefully selected for study, due to some special features related to the participation of strongly correlated 5f electrons in the ferromagnetism. 5f electrons potentially give rise to strong anisotropies, strong spin-orbit interactions and also a strong energy dependence of the electronic density of states. Here we focus on UGe2, and review several of the properties of the ferromagnetic state that could be a consequence of such features and discuss whether they promote superconductivity.

  11. Positive magnetoresistance and large magnetostriction at first-order antiferro ferromagnetic phase transitions in RMn2Si2 compounds

    Science.gov (United States)

    Gerasimov, E. G.; Mushnikov, N. V.; Koyama, K.; Kanomata, T.; Watanabe, K.

    2008-11-01

    The magnetostriction and magnetoresistance associated with the field-induced and spontaneous first-order antiferro-ferromagnetic (AF-F) phase transitions have been studied for quasi-single-crystalline samples of La0.25Sm0.75Mn2Si2, La0.25Y0.75Mn2Si2 and La0.27Y0.73Mn2Si2 compounds with natural layered ThCr2Si2-type structure. It was found that both the spontaneous and field-induced AF-F transitions are accompanied by a large volume magnetostriction ΔV/V≈2 × 10-3 and anisotropic linear changes of the lattice parameters Δa/a≈1.6 × 10-3, Δc/c≈-0.75 × 10-3. The field-induced AF-F magnetic phase transition has been observed in magnetic fields applied both along the c-axis and in the basal plane, and the magnetostriction value is virtually independent of the direction of applied field. It has been found also that the magnetoresistance is positive in these compounds (the value of the electrical resistance in the ferromagnetic state is higher than that in the antiferromagnetic state) for the fields applied both along the c-axis and in the basal plane. The value of the magnetoresistance observed along the c-axis is 30 times as high as that in the basal plane. The obtained results indicate that the electronic band structure changes are likely responsible for the AF-F magnetic phase transitions observed in the RMn2X2 compounds.

  12. Influence of Tb on easy magnetization direction and magnetostriction of ferromagnetic Laves phase GdFe2 compounds

    Science.gov (United States)

    Murtaza, Adil; Yang, Sen; Zhou, Chao; Song, Xiaoping

    2016-09-01

    The crystal structure, magnetization, and spontaneous magnetostriction of ferromagnetic Laves phase GdFe2 compound have been investigated. High resolution synchrotron x-ray diffraction (XRD) analysis shows that GdFe2 has a lower cubic symmetry with easy magnetization direction (EMD) along [100] below Curie temperature TC. The replacement of Gd with a small amount of Tb changes the EMD to [111]. The Curie temperature decreases while the field dependence of the saturation magnetization (Ms) measured in temperature range 5-300 K varies with increasing Tb concentration. Coercivity Hc increases with increasing Tb concentration and decays exponentially as temperature increases. The anisotropy in GdFe2 is so weak that some of the rare-earth substitution plays an important role in determining the easy direction of magnetization in GdFe2. The calculated magnetostrictive constant λ100 shows a small value of 37×10-6. This value agrees well with experimental data 30×10-6. Under a relatively small magnetic field, GdFe2 exhibits a V-shaped positive magnetostriction curve. When the field is further increased, the crystal exhibits a negative magnetostriction curve. This phenomenon has been discussed in term of magnetic domain switching. Furthermore, magnetostriction increases with increasing Tb concentration. Our work leads to a simple and unified mesoscopic explanation for magnetostriction in ferromagnets. It may also provide insight for developing novel functional materials. Project supported by the National Basic Research Program of China (Grant No. 2012CB619401).

  13. Single-crystalline study of the ferromagnetic kondo compound UCu{sub 0.9}Sb{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Bukowski, Z. [W. Trzebiatowski Institute of Low Temperature and Structure Research, Polish Academy of Sciences, P.O. Box 1410, 50-950 WrocIaw (Poland); Troc, R. [W. Trzebiatowski Institute of Low Temperature and Structure Research, Polish Academy of Sciences, P.O. Box 1410, 50-950 WrocIaw (Poland); Stepien-Damm, J. [W. Trzebiatowski Institute of Low Temperature and Structure Research, Polish Academy of Sciences, P.O. Box 1410, 50-950 WrocIaw (Poland); SuIkowski, C. [W. Trzebiatowski Institute of Low Temperature and Structure Research, Polish Academy of Sciences, P.O. Box 1410, 50-950 WrocIaw (Poland); Tran, V.H. [W. Trzebiatowski Institute of Low Temperature and Structure Research, Polish Academy of Sciences, P.O. Box 1410, 50-950 WrocIaw (Poland)]. E-mail: V.H.Tran@int.pan.wroc.pl

    2005-11-10

    Single crystals of UCu{sub 0.9}Sb{sub 2} have been grown using the self-flux method and studied by means of X-ray diffraction, magnetic and electrical transport measurements. This compound crystallizes in a tetragonal structure of the HfCuSi{sub 2}-type (space group P4/nmm) and orders ferromagnetically below T {sub C} = 113 K with the easy-magnetization direction along the c-axis exhibiting a large magnetocrystalline anisotropy in both the ordered and paramagnetic states. The electrical resistivity, magnetoresistivity and thermoelectric power data are also given. A Kondo-like behaviour of the resistivity in the paramagnetic state is reported.

  14. Ferromagnetism in half-metallic quaternary FeVTiAl Heusler compound

    Science.gov (United States)

    Bhat, Tahir Mohiuddin; Bhat, Idris Hamid; Yousuf, Saleem; Gupta, Dinesh C.

    2016-05-01

    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 µB/f.u. is in agreement with the Slater-Pauling rule for full Heusler alloys.

  15. Onset of itinerant ferromagnetism associated with semiconductor-metal transition in TiNb1-CoSn half Heusler solid solution compounds

    Indian Academy of Sciences (India)

    M A Kouacou; A A Koua; J T Zoueu; K Konan; J Pierre

    2008-07-01

    In this paper, the magnetic and transport properties of the TiNb1−CoSn solid solution compounds with half Heusler cubic MgAgAs-type structure have been studied. This work shows the onset of ferromagnetism associated with a semiconductor to metal transition. The transition occurs directly from ferromagnetic metal to semiconducting state as it is the case in the TiCoNi1−Sn series studied previously. A weak quantity of Ti in NbCoSn is sufficient to allow the appearance of ferromagnetic order and metallic state. The variations of the Curie temperature as a function of saturation and effective paramagnetic moments are related to the itinerant ferromagnetism model. A comparison is made with the TiCoSnSb1− series (also studied previously), where the transition from TiCoSn ferromagnetic metal to non-magnetic semiconductor TiCoSb occurs through an intermediate metallic Pauli-like state.

  16. Ferromagnetic exchange anisotropy from antiferromagnetic superexchange in the mixed 3d-5d transition-metal compound Sr3CuIrO6.

    Science.gov (United States)

    Yin, Wei-Guo; Liu, X; Tsvelik, A M; Dean, M P M; Upton, M H; Kim, Jungho; Casa, D; Said, A; Gog, T; Qi, T F; Cao, G; Hill, J P

    2013-08-02

    We report a combined experimental and theoretical study of the unusual ferromagnetism in the one-dimensional copper-iridium oxide Sr(3)CuIrO(6). Utilizing Ir L(3) edge resonant inelastic x-ray scattering, we reveal a large gap magnetic excitation spectrum. We find that it is caused by an unusual exchange anisotropy generating mechanism, namely, strong ferromagnetic anisotropy arising from antiferromagnetic superexchange, driven by the alternating strong and weak spin-orbit coupling on the 5d Ir and 3d Cu magnetic ions, respectively. From symmetry consideration, this novel mechanism is generally present in systems with edge-sharing Cu(2+)O(4) plaquettes and Ir(4+)O(6) octahedra. Our results point to unusual magnetic behavior to be expected in mixed 3d-5d transition-metal compounds via exchange pathways that are absent in pure 3d or 5d compounds.

  17. Circular Dichroism in the 3d and 4d Core Photoabsorption for Ferromagnetic Ce Compounds —Interplay of Hybridization, Spin Orbit Interaction and Crystal Field—

    Science.gov (United States)

    Jo, Takeo; Imada, Shin

    1990-04-01

    The Ce 3d- and 4d-core photoabsorption spectra (3d XAS and 4d XAS) of ferromagnetic mixed valent Ce compounds are calculated on the basis of the impurity Anderson model. The model takes into account the Coulomb interaction producing multiplet structures, the spin-orbit interaction, the crystal field effect and the molecular field acting on the 4f spin. The calculation shows a strong circular dichroism even for the Ce magnetic moment of ˜0.5 μB. The dichroism is furthermore shown to be a powerful method to measure the spin and orbital contributions to the 4f moment. On the basis of the calculation, the 4f magnetic state of the ferromagnet CeRh3B2 is discussed.

  18. Ground state properties and thermoelectric behavior of Ru2VZ (Z=Si, ge, sn) half-metallic ferromagnetic full-Heusler compounds

    Science.gov (United States)

    Yalcin, Battal Gazi

    2016-06-01

    The ground state properties namely structural, mechanical, electronic and magnetic properties and thermoelectric behavior of Ru2VZ (Z=Si, Ge and Sn) half-metallic ferromagnetic full-Heusler compounds are systematically investigated. These compounds are ferromagnetic and crystallize in the Heusler type L21 structure (prototype: Cu2MnAl, Fm-3m 225). This result is confirmed for Ru2VSi and Ru2VSn by experimental work reported by Yin and Nash using high temperature direct reaction calorimetry. The studied materials are half-metallic ferromagnets with a narrow direct band gap in the minority spin channel that amounts to 31 meV, 66 meV and 14 meV for Ru2VSi, Ru2VGe, and Ru2VSn, respectively. The total spin magnetic moment (Mtot) of the considered compounds satisfies a Slater-Pauling type rule for localized magnetic moment systems (Mtot=(NV-24)μB), where NV=25 is the number of valence electrons in the primitive cell. The Curie temperature within the random phase approximation (RPA) is found to be 23 K, 126 K and 447 K for Ru2VSi, Ru2VGe and Ru2VSn, respectively. Semi-classical Boltzmann transport theories have been used to obtain thermoelectric constants, such as Seebeck coefficient (S), electrical (σ/τ) and thermal conductivity (κ/τ), power factor (PF) and the Pauli magnetic susceptibility (χ). ZTMAX values of 0.016 (350 K), 0.033 (380 K) and 0.063 (315 K) are achieved for Ru2VSi, Ru2VGe and Ru2VSn, respectively. It is expected that the obtained results might be a trigger in future experimentally interest in this type of full-Heusler compounds.

  19. Positive magnetoresistance and large magnetostriction at first-order antiferro-ferromagnetic phase transitions in RMn{sub 2}Si{sub 2} compounds

    Energy Technology Data Exchange (ETDEWEB)

    Gerasimov, E G; Mushnikov, N V [Institute of Metals Physics, Ural Division of the Russian Academy of Science, Sofia Kovalevskaya Street, 18, 620041 Ekaterinburg (Russian Federation); Koyama, K; Watanabe, K [High Field Laboratory for Superconducting Materials HFLSM, Institute for Materials Research, Tohoku University, Sendai 980-8577 (Japan); Kanomata, T [Department of Applied Physics, Faculty of Engineering, Tohoku Gakuin University, Tagajo, Miyagi 985 (Japan)], E-mail: gerasimov@imp.uran.ru

    2008-11-05

    The magnetostriction and magnetoresistance associated with the field-induced and spontaneous first-order antiferro-ferromagnetic (AF-F) phase transitions have been studied for quasi-single-crystalline samples of La{sub 0.25}Sm{sub 0.75}Mn{sub 2}Si{sub 2}, La{sub 0.25}Y{sub 0.75}Mn{sub 2}Si{sub 2} and La{sub 0.27}Y{sub 0.73}Mn{sub 2}Si{sub 2} compounds with natural layered ThCr{sub 2}Si{sub 2}-type structure. It was found that both the spontaneous and field-induced AF-F transitions are accompanied by a large volume magnetostriction {delta}V/V{approx}2 x 10{sup -3} and anisotropic linear changes of the lattice parameters {delta}a/a{approx}1.6 x 10{sup -3}, {delta}c/c{approx}-0.75 x 10{sup -3}. The field-induced AF-F magnetic phase transition has been observed in magnetic fields applied both along the c-axis and in the basal plane, and the magnetostriction value is virtually independent of the direction of applied field. It has been found also that the magnetoresistance is positive in these compounds (the value of the electrical resistance in the ferromagnetic state is higher than that in the antiferromagnetic state) for the fields applied both along the c-axis and in the basal plane. The value of the magnetoresistance observed along the c-axis is 30 times as high as that in the basal plane. The obtained results indicate that the electronic band structure changes are likely responsible for the AF-F magnetic phase transitions observed in the RMn{sub 2}X{sub 2} compounds.

  20. Magnetic excitations in the S =1/2 antiferromagnetic-ferromagnetic chain compound BaCu2V2O8 at zero and finite temperature

    Science.gov (United States)

    Klyushina, E. S.; Tiegel, A. C.; Fauseweh, B.; Islam, A. T. M. N.; Park, J. T.; Klemke, B.; Honecker, A.; Uhrig, G. S.; Manmana, S. R.; Lake, B.

    2016-06-01

    Unlike most quantum systems which rapidly become incoherent as temperature is raised, strong correlations persist at elevated temperatures in S =1/2 dimer magnets, as revealed by the unusual asymmetric line shape of their excitations at finite temperatures. Here, we quantitatively explore and parametrize the strongly correlated magnetic excitations at finite temperatures using high-resolution inelastic neutron scattering of the model compound BaCu2V2O8 which we show to be an alternating antiferromagnetic-ferromagnetic spin -1/2 chain. Comparison to state of the art computational techniques shows excellent agreement over a wide temperature range. Our findings hence demonstrate the possibility to quantitatively predict coherent behavior at elevated temperatures in quantum magnets.

  1. Prediction of half-metallic ferromagnetism (HMF) in hypothetical Heusler compound Co{sub 2}VSb using modified Becke Johnson (mBJ) potential

    Energy Technology Data Exchange (ETDEWEB)

    Rai, D.P., E-mail: dibyaprakashrai@gmail.com [Beijing Computational Science Research Center, Heqing Rd. 3, Beijing 100084 (China); Maibam, J. [Department of Physics, Manipur University, Canchipur 795003 (India); Sharma, B.I. [Department of Physics, Assam University, Silchar 788 011 (India); Shankar, A.; Sandeep,; Thapa, R.K. [Department of Physics, Mizoram University, Aizawl 796004 (India); Ke, San Huang [Beijing Computational Science Research Center, Heqing Rd. 3, Beijing 100084 (China); Key Laboratory of Advanced Microstructure Materials, MOE, Dept. of Physics, Tongji University, 1239 Siping Rd. Shanghai 200092 (China)

    2014-03-15

    Highlights: • Half-metallic ferromagnetism were studied using GGA, LSDA+U and mBJ. • The calculated magnetic moment of 4.00 μ{sub B} (LSDA+U and mBJ). • mBJ is more effective to band gap calculation as compare to others. -- Abstract: In search of half-metallic ferromagnetism, we have studied the electronic and magnetic properties of Co{sub 2}VSb by using the different tools like GGA, LSDA+U and mBJ potential based on density functional theory (DFT). The compound Co{sub 2}VSb is analogous to Co{sub 2}VAl, Co{sub 2}VSn and Co{sub 2}VGa , these compounds were studied theoretically and experimentally by Buschow and Engen. We expect the similar kind of properties from Co{sub 2}VSb as that of Co{sub 2}VAl, Co{sub 2}VSn and Co{sub 2}VGa. The mBJ potential is considered to be more effective as compared to LDA and GGA which gives higher value of band gap. The theoretical lattice constant obtained from volume optimization is 6.072 Å. The calculated value of energy gaps was found to be 0.20 eV, 1.00 eV and 1.30 eV for GGA, LSDA+U and mBJ respectively. Our results of band gap calculation predicts that mBJ overestimate the results of GGA, LSDA and LSDA+U.

  2. Weak Ferromagnetism and Multiple Metamagnetic Transitions in the Non-centrosymmetric Tetragonal Compound CePdSi3

    Science.gov (United States)

    Ueta, Daichi; Ikeda, Yoichi; Yoshizawa, Hideki

    2016-10-01

    We have succeeded in growing single crystalline samples of CePdSi3 with the BaNiSn3-type non-centrosymmetric structure. Specific heat, magnetic susceptibility, and magnetization measurements were carried out, which revealed three successive magnetic transitions at TI = 4.85(5) K, TII = 2.78(5) K, and TIII = 2.30(5) K at zero field. Below TII, a weak ferromagnetic component was observed, indicating a canted antiferromagnetic ground state in CePdSi3. The observed large magnetic anisotropy in CePdSi3 was explained in terms of a simple crystalline-electric-field model. From the magnetization measurements, we identified five (three) magnetic states in the H-T phase diagrams for the H || [100] ([001]) direction. Interestingly, only three magnetization steps were observed for H || [110], suggesting the existence of the in-plane magnetic anisotropy in CePdSi3. We discuss a possible nature of the complex magnetic properties of CePdSi3.

  3. High-Tc ferromagnetic semiconductor-like behavior and unusual electrical properties in compounds with a 2×2×2 superstructure of the half-Heusler phase.

    Science.gov (United States)

    Xiong, Ding-Bang; Okamoto, Norihiko L; Waki, Takeshi; Zhao, Yufeng; Kishida, Kyosuke; Inui, Haruyuki

    2012-02-27

    Heusler phases, including the full- and half-Heusler families, represent an outstanding class of multifunctional materials on account of their great tunability in compositions, valence electron counts (VEC), and properties. Here we demonstrate a systematic design of a series of new compounds with a 2×2×2 superstructure of the half-Heusler unit cell in X-Y-Z (X=Fe, Ru, Co, Rh, Ir; Y=Zn, Mn; Z=Sn, Sb) systems. Their structures were solved by using both powder and single-crystal X-ray diffraction, and also directly observed by using high-angle annular dark-field imaging in a scanning transmission electron microscope (HAADF-STEM). The VEC values of these new compounds span a wide and continuous range comparable to those for the full- and half-Heusler families, thereby implying tunability in compositions and physical properties in the superstructure. In fact, we observed abnormal electrical properties and a ferromagnetic semiconductor-like behavior with a high and tunable Curie temperature in these superstructures. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  4. Ferromagnetic superconductors

    Science.gov (United States)

    Huxley, Andrew D.

    2015-07-01

    The co-existence of superconductivity and ferromagnetism is of potential interest for spintronics and high magnetic field applications as well as a fascinating fundamental state of matter. The recent focus of research is on a family of ferromagnetic superconductors that are superconducting well below their Curie temperature, the first example of which was discovered in 2000. Although there is a 'standard' theoretical model for how magnetic pairing might bring about such a state, why it has only been seen in a few materials that at first sight appear to be very closely related has yet to be fully explained. This review covers the current state of knowledge of the magnetic and superconducting properties of these materials with emphasis on how they conform and differ from the behaviour expected from the 'standard' model and from each other.

  5. Ferromagnetic superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Huxley, Andrew D.

    2015-07-15

    Highlights: • Review of ferromagnetic superconductors. • Covers UGe{sub 2}, URhGe and UCoGe and briefly other materials. • The focus is on experimental data and the pairing mechanism. - Abstract: The co-existence of superconductivity and ferromagnetism is of potential interest for spintronics and high magnetic field applications as well as a fascinating fundamental state of matter. The recent focus of research is on a family of ferromagnetic superconductors that are superconducting well below their Curie temperature, the first example of which was discovered in 2000. Although there is a ‘standard’ theoretical model for how magnetic pairing might bring about such a state, why it has only been seen in a few materials that at first sight appear to be very closely related has yet to be fully explained. This review covers the current state of knowledge of the magnetic and superconducting properties of these materials with emphasis on how they conform and differ from the behaviour expected from the ‘standard’ model and from each other.

  6. Ferromagnetism in metallocene-doped fullerenes

    CERN Document Server

    Mihailovic, D

    2003-01-01

    Ferromagnetism in fullerene-based systems doped with metallocenes is reviewed. These compounds form a ferromagnetic state by spin-coupling between pi electrons on fullerene units, while the metallocene molecules do not contribute to the spin ordering. One of these compounds has the highest critical temperature (19 K) for this class of compound. The magnetic properties of these materials are very strongly dependent on the crystallization conditions. Refs. 19 (author)

  7. Anomalous Hall Effect in a Kagome Ferromagnet

    Science.gov (United States)

    Ye, Linda; Wicker, Christina; Suzuki, Takehito; Checkelsky, Joseph; Joseph Checkelsky Team

    The ferromagnetic kagome lattice is theoretically known to possess topological band structures. We have synthesized large single crystals of a kagome ferromagnet Fe3Sn2 which orders ferromagnetically well above room temperature. We have studied the electrical and magnetic properties of these crystals over a broad temperature and magnetic field range. Both the scaling relation of anomalous Hall effect and anisotropic magnetic susceptibility show that the ferromagnetism of Fe3Sn2 is unconventional. We discuss these results in the context of magnetism in kagome systems and relevance to the predicted topological properties in this class of compounds. This research is supported by DMR-1231319.

  8. Raman evidence for presence of high-temperature ferromagnetic clusters in magnetodielectric compound Ba-doped La2NiMnO6

    Science.gov (United States)

    Barbosa, D. A. B.; Paschoal, C. W. A.

    2017-10-01

    Magnetodielectric ferromagnetic semiconductors are key materials because of their applications in spintronic devices; they can be used to control the magnetic properties by applying electric fields. La2NiMnO6 emerged as an important magnetodielectric ferromagnetic semiconductor because of its high Curie temperature near room temperature. Recently Ba doped was successfully used to improve magnetic properties in La2NiMnO6, originating partially ordered systems with different ordering degrees but presenting same Tc = 280 K. However, the influence of Ba doping on the temperature dependent vibrational properties of the system was not investigated. To investigate the Ba doping influence on temperature dependent phonon spectra in La2NiMnO6, we used Raman Spectroscopy to probe the symmetric stretching mode behavior in the range from 10 to 600 K. Remarkable softenings were detected in the phonon behavior due to spin phonon coupling, at several different temperatures, much above Tc. The FWHM dependence with temperature rules out magnetostriction effects. The phonon softenings are the largest reported so far for the RE2NiMnO6 systems and also indicate that Ba doping induces ordering in the Ni/Mn sites. The temperature discordance in characteristic softening onset of the spin phonon coupling are related to ferromagnetic short range clusters due the presence of Ni3 +, Mn3 + oxidation states.

  9. Photoluminescence and Raman studies for the confirmation of oxygen vacancies to induce ferromagnetism in Fe doped Mn:ZnO compound

    Energy Technology Data Exchange (ETDEWEB)

    Das, J., E-mail: jayashree304@gmail.com [Department of Physics, Silicon Institute of Technology, Bhubaneswar 751024, Odisha (India); Department of Physics, College of Science, Engineering and Technology, University of South Africa, Johannesburg 1710 (South Africa); Mishra, D.K. [Department of Physics, College of Science, Engineering and Technology, University of South Africa, Johannesburg 1710 (South Africa); Department of Physics, Institute of Technical Education and Research, Siksha ‘O’ Anusandhan University, Khandagiri Square, Bhubaneswar 751030, Odisha (India); Srinivasu, V.V. [Department of Physics, College of Science, Engineering and Technology, University of South Africa, Johannesburg 1710 (South Africa); Sahu, D.R. [Amity Institute of Nanotechnology, Amity University, Noida (India); Roul, B.K. [Institute of Materials Science, Planetarium Building, Acharya Vihar, Bhubaneswar, Odisha (India)

    2015-05-15

    With a motivation to compare the magnetic property, we synthesised undoped, transition metal (TM) Mn doped and (Mn:Fe) co-doped ZnO ceramics in the compositions ZnO, Zn{sub 0.98}Mn{sub 0.02}O and Zn{sub 0.96}(Mn{sub 0.02}Fe{sub 0.02})O. Systematic investigations on the structural, microstructural, defect structure and magnetic properties of the samples were performed. Low temperature as well as room temperature ferromagnetism has been observed for all our samples, however, enhanced magnetisation at room temperature has been noticed when ZnO is co-doped with Fe along with Mn. Particularly the sample with the composition Zn{sub 0.96}Mn{sub 0.02}Fe{sub 0.02}O showed a magnetisation value more than double of the sample with composition Zn{sub 0.98}Mn{sub 0.02}O, indicating long range strong interaction between the magnetic impurities leading to higher ferromagnetic ordering. Raman and PL studies reveal presence of higher defects in form of oxygen vacancy clusters created in the sample due to Fe co doping. PL study also reveals enhanced luminescence efficiency in the co doped sample. Temperature dependent magnetisation study of this sample shows the spin freezing temperature around 39 K indicating the presence of small impurity phase of Mn{sub 2−x}Zn{sub x}O{sub 3} type. Electron Spin Resonance signal obtained supports ferromagnetic state in the co doped sample. Enhancement of magnetisation is attributed to interactions mediated by magnetic impurities through large number of oxygen vacancies created by Fe{sup 3+} ions forming bound magnetic polarons (BMP) and facilitating long range ferromagnetic ordering in the co- doped system. - Highlights: • Comparison of magnetic property of ZnO, Zn{sub 0.98}Mn {sub 0.02}O and Zn{sub 0.96}(Mn{sub 0.02}Fe{sub 0.02})O. • Observation of enhanced magnetisation at room temperature in (Mn,Fe) doped ZnO. • Raman and PL studies reveal presence of higher oxygen vacancy clusters. • Electron Spin Resonance signal supports

  10. Anionogenic ferromagnets

    NARCIS (Netherlands)

    Attema, JJ; de Wijs, GA; Blake, GR; de Groot, RA; Wijs, Gilles A. de

    2005-01-01

    Magnetism in molecules and solids is understood to originate from atoms in that part of the periodic table where a particular value of the angular momentum appears first (i.e., the 2p, 3d, and 4f series). In contrast to the many magnetic compounds containing transition metal or lanthanide atoms, fer

  11. The structure, Raman spectroscopy and evidence of ferromagnetic transition in CuCr{sub 1−x}M{sub x}O{sub 2} (M=Mn and Rh) compounds

    Energy Technology Data Exchange (ETDEWEB)

    Elkhouni, T., E-mail: elkhouni@yahoo.fr [Laboratoire des Sciences des Matériaux et d’Environnement, Université de Sfax, Faculté des Sciences de Sfax, BP 802, 3018 Sfax (Tunisia); Amami, M. [Laboratoire des Sciences des Matériaux et d’Environnement, Université de Sfax, Faculté des Sciences de Sfax, BP 802, 3018 Sfax (Tunisia); Unité de Recherche de Chimie des Matériaux, ISSBAT, Université Tunis ElManar, 9, Avenue Dr. Zouhaier Safi, 1006 Tunis (Tunisia); Colin, C.V.; Strobel, P. [Institut Néel, CNRS et Université Joseph Fourier, BP 166, 38042 Grenoble Cedex 9 (France); Ben Salah, A. [Laboratoire des Sciences des Matériaux et d’Environnement, Université de Sfax, Faculté des Sciences de Sfax, BP 802, 3018 Sfax (Tunisia)

    2014-04-15

    The CuCr{sub 1−x}M{sub x}O{sub 2} (M=Mn, Rh) polycrystalline powders were synthesized by the direct solid state reaction of Cu{sub 2}O and M{sub 2}O{sub 3} (M=trivalent cation or mixer of trivalent cation for transition metal). The magnetic susceptibility was measured in the temperature range of 0–300 K. It was found that the magnetic susceptibility (χ) increases rapidly with the doping of Cr{sup 3+} by Mn{sup 3+} and Rh{sup 3+} ions with existence of paramagnetic substance at low temperature. With the substitution of magnetic Mn{sup 3+} and Rh{sup 3+} for Cr{sup 3+} (S=3/2), the antiferromagnetic (AF) transition becomes broader and the transition temperature increases. However, at low temperature, the magnetic data for CuCr{sub 1−x}M{sub x}O{sub 2} (M=Mn, Rh) show evidence for weak ferromagnetic (FM) transition between 100 K and 130 K. Clear hysteresis loops indicate that FM order exists in both of them Mn or Rh-doped samples at 4 K. All samples behave like semiconductors. The ferromagnetism properties can be attributed to the double exchange interaction between the Mn{sup 3+} or Rh{sup 3+} and Cr{sup 3+} semiconductors compounds. - Highlights: • Mn replacement of the Cr in the magnetic frustrated CuCrO{sub 2}. • Mn{sup 3+}/Mn{sup 4+} generate anisotropic microstrains in the structure. • Mn substitutions lead to an increase of the susceptibilities magnetic. • The incorporation of Mn{sup 3+}/Mn{sup 4+} in CuCrO{sub 2} induced weak ferromagnetic interactions at low temperature.

  12. Asymmetric Ferromagnet-Superconductor-Ferromagnet Switch

    Energy Technology Data Exchange (ETDEWEB)

    Cadden-Zimansky, P.; Bazaliy, Ya.B.; Litvak, L.M.; Jiang, J.S.; Pearson, J.; Gu, J.Y.; You, Chun-Yeol; Beasley, M.R.; Bader, S.D.

    2011-11-04

    In layered ferromagnet-superconductor-ferromagnet F{sub 1} /S/F{sub 2} structures, the critical temperature T{sub c} of the superconductors depends on the magnetic orientation of the ferromagnetic layers F{sub 1} and F{sub 2} relative to each other. So far, the experimentally observed magnitude of change in T{sub c} for structures utilizing weak ferromagnets has been 2 orders of magnitude smaller than is expected from calculations. We theoretically show that such a discrepancy can result from the asymmetry of F/S boundaries, and we test this possibility by performing experiments on structures where F{sub 1} and F{sub 2} are independently varied. Our experimental results indicate that asymmetric boundaries are not the source of the discrepancy. If boundary asymmetry is causing the suppressed magnitude of T{sub c} changes, it may only be possible to detect in structures with thinner ferromagnetic layers.

  13. Electrically detected ferromagnetic resonance

    NARCIS (Netherlands)

    Goennenwein, S.T.B.; Schink, S.W.; Brandlmaier, A.; Boger, A.; Opel, M.; Gross, R.; Keizer, R.S.; Klapwijk, T.M.; Gupta, A.; Huebl, H.; Bihler, C.; Brandt, M.S.

    2007-01-01

    We study the magnetoresistance properties of thin ferromagnetic CrO2 and Fe3O4 films under microwave irradiation. Both the sheet resistance ρ and the Hall voltage VHall characteristically change when a ferromagnetic resonance (FMR) occurs in the film. The electrically detected ferromagnetic resonanc

  14. Syntheses, structures, and magnetic properties of three one-dimensional end-to-end azide/cyanate-bridged copper(II) compounds exhibiting ferromagnetic interaction: new type of solid state isomerism.

    Science.gov (United States)

    Sasmal, Sujit; Sarkar, Sohini; Aliaga-Alcalde, Núria; Mohanta, Sasankasekhar

    2011-06-20

    The work in this paper presents the syntheses, structures, and magnetic properties of three end-to-end (EE) azide/cyanate-bridged copper(II) compounds [Cu(II)L(1)(μ(1,3)-NCO)](n)·2nH(2)O (1), [Cu(II)L(1)(μ(1,3)-N(3))](n)·2nH(2)O (2), and [Cu(II)L(2)(μ(1,3)-N(3))](n) (3), where the ligands used to achieve these species, HL(1) and HL(2), are the tridentate Schiff base ligands obtained from [1 + 1] condensations of salicylaldehyde with 4-(2-aminoethyl)-morpholine and 3-methoxy salicylaldehyde with 1-(2-aminoethyl)-piperidine, respectively. Compounds 1 and 2 crystallize in the monoclinic P2(1)/c space group, while compound 3 crystallizes in the orthorhombic Pbca space group. The metal center in 1-3 is in all cases pentacoordinated. Three coordination positions of the metal center in 1, 2, or 3 are satisfied by the phenoxo oxygen atom, imine nitrogen atom, and morpholine (for 1 and 2) or piperidine (for 3) nitrogen atom of one deprotonated ligand, [L(1)](-) or [L(2)](-). The remaining two coordination positions are satisfied by two nitrogen atoms of two end-to-end bridging azide ligands for 2 and 3 and one nitrogen atom and one oxygen atom of two end-to-end bridging cyanate ligands for 1. The coordination geometry of the metal ion is distorted square pyramidal in which one EE azide/cyanate occupies the apical position. Variable-temperature (2-300 K) magnetic susceptibilities of 1-3 have been measured under magnetic fields of 0.05 (from 2 to 30 K) and 1.0 T (from 30 to 300 K). The simulation reveals a ferromagnetic interaction in all three compounds with J values of +0.19 ± 0.01, +0.79 ± 0.01, and +1.25 ± 0.007 cm(-1) for 1, 2, and 3, respectively. Compound 1 is the sole example of a ferromagnetically coupled EE cyanate-bridged 1-D copper(II) system. In addition, a rare example of supramolecular isomerism and a nice example of magnetic isomerism have been observed and most interestingly a new type of solid state isomerism has emerged as a result of the comparison

  15. The influence of atomic order on the magnetic and structural properties of the ferromagnetic shape memory compound Ni sub 2 MnGa

    CERN Document Server

    Kreissl, M; Stephens, T; Ziebeck, K R A

    2003-01-01

    The effect of atomic order on the martensitic phase transition and magnetic properties of stoichiometric Ni sub 2 MnGa has been investigated in a sample quenched from 1000 deg C. Magnetization, resistivity and x-ray diffraction measurements indicate that the structural phase transition occurs at approx 103 K, substantially lower than the value reported for samples quenched from 800 deg C and ordered in the Heusler L2 sub 1 structure. A small reduction in the ferromagnetic moment was also observed, although the Curie temperature remained largely unaffected. The electronic Sommerfeld coefficient obtained from heat capacity measurements is enhanced but smaller than that observed for the 800 deg C quenched sample. The results are consistent with band structure calculations and the electronic changes brought about by atomic disorder.

  16. The Physics of Ferromagnetism

    CERN Document Server

    Miyazaki, Terunobu

    2012-01-01

    This book covers both basic physics of ferromagnetism such as magnetic moment, exchange coupling, magnetic anisotropy and recent progress in advanced ferromagnetic materials. Special interests are focused on NdFeB permanent magnets and the materials studied in the field of spintronics. In the latter, development of tunnel magnetoresistance effect through so called giant magnetoresistance effect is explained.

  17. Magnetic Properties of Uranium Based Ferromagnetic Superconductors

    NARCIS (Netherlands)

    Sakarya, S.

    2007-01-01

    Ferromagnetism and superconductivity have long been thought to be mutually exclusive. Recently however it was found that the compounds UGe2, URhGe and UIr belong to a class of materials in which ferromagnetisme and superconductivity appear simultaneously. One characteristic property of these compoun

  18. Physics of ferromagnetism

    CERN Document Server

    Graham, C D

    2009-01-01

    This book is a textbook for graduate students and researchers who are interested in ferromagnetism. The emphasis is primarily on explanation of physical concepts rather than on a rigorous theoretical treatment.

  19. Itinerant Ferromagnetism and Superconductivity

    OpenAIRE

    Karchev, Naoum

    2004-01-01

    Superconductivity has again become a challenge following the discovery of unconventional superconductivity. Resistance-free currents have been observed in heavy-fermion materials, organic conductors and copper oxides. The discovery of superconductivity in a single crystal of $UGe_2$, $ZrZn_2$ and $URhGe$ revived the interest in the coexistence of superconductivity and ferromagnetism. The experiments indicate that: i)The superconductivity is confined to the ferromagnetic phase. ii)The ferromag...

  20. Ferromagnetism in single-valent manganites

    Energy Technology Data Exchange (ETDEWEB)

    Troyanchuk, I.O., E-mail: troyan@physics.by [Scientific-Practical Materials Research Centre NAS of Belarus, P. Brovki str. 19, 220072 Minsk (Belarus); Bushinsky, M.V. [Scientific-Practical Materials Research Centre NAS of Belarus, P. Brovki str. 19, 220072 Minsk (Belarus); Sikolenko, V. [Helmholtz-Zentrum Berlin, Hahn-Meitner-Platz 1, 14109 Berlin (Germany); Joint Institute for Nuclear Research, Joliot-Curie 6, 141980 Dubna (Russian Federation); Efimov, V. [Joint Institute for Nuclear Research, Joliot-Curie 6, 141980 Dubna (Russian Federation); Volkov, N.V. [Kirensky Institute of Physics, Akademgorodok 50, bld. 38, 660036 Krasnoyarsk (Russian Federation); Többens, D.M. [Helmholtz-Zentrum Berlin, Hahn-Meitner-Platz 1, 14109 Berlin (Germany); Ritter, C. [Institut Laue-Langevin, 6 rue Jules Horowitz, BP 156, 38042 Grenoble Cedex 9 (France); Raveau, B. [Laboratoire CRISMAT, UMR 6508 associée au CNRS, ISMRA et Universite de Caen 6, Boulevard du Marechal Juin, 14050 Caen Cedex (France)

    2015-01-15

    Highlights: • Structural and magnetization measurements have been performed on the La{sub 0.7}Sr{sub 0.3}Mn{sub 0.85}Nb{sub 0.15−x}Mg{sub x}O{sub 3} stoichiometric compounds. • Ferromagnetism in single-valent manganites can be understood in terms of the superexchange scenario assuming dominant role of covalency. • The Mn–O–Mn bond angle is the key factor for p–d orbital hybridization associated with covalency which leads to positive superexchange interactions between localized e{sub g} electrons and, hence, ferromagnetism. - Abstract: Structural and magnetization measurements have been performed on the La{sub 0.7}Sr{sub 0.3}Mn{sub 0.85}Nb{sub 0.15-x}{sup 5+}Mg{sub x}{sup 2+}O{sub 3} stoichiometric compounds. With rise of the Mg{sup 2+} content the formal oxidation state manganese increases from +3 (x=0) up to +3.55 (x=0.15). The compositions with 0⩽x≤0.08 undergo a structural transition from rhombohedral to orthorhombic symmetry below room temperature whereas x=0.1 and x=0.15 compounds are rhombohedral down to 2 K. The structural parameters evidence that the orthorhombic phase is not long-range orbitally ordered and that the structural transition is associated with a steric effect. The Mg-free compound is ferromagnetic with the Curie point of around 150 K and a magnetic moment of 3.1 μ{sub B}/Mn. The substitution of Nb{sup 5+} with Mg{sup 2+} leads to a gradual weakening of the ferromagnetic component while in the x=0.15 compound A-type antiferromagnetic short-range order is stabilized in spite of macroscopic R3{sup ¯}c symmetry. All the compositions show insulating behavior. It is suggested that ferromagnetism is originated from superexchange interactions via oxygen. Covalence enhances the positive part of the superexchange interactions whereas structural disorder induced by Nb{sup 5+} and Mg{sup 2+} ions leads to suppression of ferromagnetism.

  1. Spin dynamics and spin freezing at ferromagnetic quantum phase transitions

    Science.gov (United States)

    Schmakat, P.; Wagner, M.; Ritz, R.; Bauer, A.; Brando, M.; Deppe, M.; Duncan, W.; Duvinage, C.; Franz, C.; Geibel, C.; Grosche, F. M.; Hirschberger, M.; Hradil, K.; Meven, M.; Neubauer, A.; Schulz, M.; Senyshyn, A.; Süllow, S.; Pedersen, B.; Böni, P.; Pfleiderer, C.

    2015-07-01

    We report selected experimental results on the spin dynamics and spin freezing at ferromagnetic quantum phase transitions to illustrate some of the most prominent escape routes by which ferromagnetic quantum criticality is avoided in real materials. In the transition metal Heusler compound Fe2TiSn we observe evidence for incipient ferromagnetic quantum criticality. High pressure studies in MnSi reveal empirical evidence for a topological non-Fermi liquid state without quantum criticality. Single crystals of the hexagonal Laves phase compound Nb1- y Fe2+ y provide evidence of a ferromagnetic to spin density wave transition as a function of slight compositional changes. Last but not least, neutron depolarisation imaging in CePd1- x Rh x underscore evidence taken from the bulk properties of the formation of a Kondo cluster glass.

  2. Gating a ferromagnetic semiconductor

    Science.gov (United States)

    Bove, A.; Altomare, F.; Kundtz, N.; Chang, A. M.; Cho, Y. J.; Liu, X.; Furdyna, J.

    2007-03-01

    Ferromagnetic semiconductors have the potential of revolutionizing the way current electronic devices work: more so, because they are compatible with current fabrication lines and can easily be integrated with today's technology. Particular interest lies in III-V Diluted Magnetic Semiconductor (DMS), where the ferromagnetism is hole-mediated and the Curie temperature can therefore be tuned by changing the concentration of free carriers. In these systems, most of the effort is currently applied toward the fabrication of devices working at room-temperature: this implies high carrier density accompanied by low mobility and short mean free path. We will report our results for a ferromagnetic 2DHG system with low carrier density (˜3.4E12 cm-2) and mobility (˜ 1000 cm^2/(Vs)), and we will discuss the effects of local gating in light of possible applications to the fabrication of ferromagnetic quantum dots. T. Dietl et al., Phys. Rev. B 63, 195205 (2001). H. Ohno et al., Nature 408, 944 (2000)

  3. Magnetically controlled ferromagnetic swimmers

    Science.gov (United States)

    Hamilton, Joshua K.; Petrov, Peter G.; Winlove, C. Peter; Gilbert, Andrew D.; Bryan, Matthew T.; Ogrin, Feodor Y.

    2017-03-01

    Microscopic swimming devices hold promise for radically new applications in lab-on-a-chip and microfluidic technology, diagnostics and drug delivery etc. In this paper, we demonstrate the experimental verification of a new class of autonomous ferromagnetic swimming devices, actuated and controlled solely by an oscillating magnetic field. These devices are based on a pair of interacting ferromagnetic particles of different size and different anisotropic properties joined by an elastic link and actuated by an external time-dependent magnetic field. The net motion is generated through a combination of dipolar interparticle gradient forces, time-dependent torque and hydrodynamic coupling. We investigate the dynamic performance of a prototype (3.6 mm) of the ferromagnetic swimmer in fluids of different viscosity as a function of the external field parameters (frequency and amplitude) and demonstrate stable propulsion over a wide range of Reynolds numbers. We show that the direction of swimming has a dependence on both the frequency and amplitude of the applied external magnetic field, resulting in robust control over the speed and direction of propulsion. This paves the way to fabricating microscale devices for a variety of technological applications requiring reliable actuation and high degree of control.

  4. Precessing Ferromagnetic Needle Magnetometer.

    Science.gov (United States)

    Jackson Kimball, Derek F; Sushkov, Alexander O; Budker, Dmitry

    2016-05-13

    A ferromagnetic needle is predicted to precess about the magnetic field axis at a Larmor frequency Ω under conditions where its intrinsic spin dominates over its rotational angular momentum, Nℏ≫IΩ (I is the moment of inertia of the needle about the precession axis and N is the number of polarized spins in the needle). In this regime the needle behaves as a gyroscope with spin Nℏ maintained along the easy axis of the needle by the crystalline and shape anisotropy. A precessing ferromagnetic needle is a correlated system of N spins which can be used to measure magnetic fields for long times. In principle, by taking advantage of rapid averaging of quantum uncertainty, the sensitivity of a precessing needle magnetometer can far surpass that of magnetometers based on spin precession of atoms in the gas phase. Under conditions where noise from coupling to the environment is subdominant, the scaling with measurement time t of the quantum- and detection-limited magnetometric sensitivity is t^{-3/2}. The phenomenon of ferromagnetic needle precession may be of particular interest for precision measurements testing fundamental physics.

  5. Magnetically controlled ferromagnetic swimmers

    Science.gov (United States)

    Hamilton, Joshua K.; Petrov, Peter G.; Winlove, C. Peter; Gilbert, Andrew D.; Bryan, Matthew T.; Ogrin, Feodor Y.

    2017-01-01

    Microscopic swimming devices hold promise for radically new applications in lab-on-a-chip and microfluidic technology, diagnostics and drug delivery etc. In this paper, we demonstrate the experimental verification of a new class of autonomous ferromagnetic swimming devices, actuated and controlled solely by an oscillating magnetic field. These devices are based on a pair of interacting ferromagnetic particles of different size and different anisotropic properties joined by an elastic link and actuated by an external time-dependent magnetic field. The net motion is generated through a combination of dipolar interparticle gradient forces, time-dependent torque and hydrodynamic coupling. We investigate the dynamic performance of a prototype (3.6 mm) of the ferromagnetic swimmer in fluids of different viscosity as a function of the external field parameters (frequency and amplitude) and demonstrate stable propulsion over a wide range of Reynolds numbers. We show that the direction of swimming has a dependence on both the frequency and amplitude of the applied external magnetic field, resulting in robust control over the speed and direction of propulsion. This paves the way to fabricating microscale devices for a variety of technological applications requiring reliable actuation and high degree of control. PMID:28276490

  6. Frequency mixer having ferromagnetic film

    Energy Technology Data Exchange (ETDEWEB)

    Khitun, Alexander; Roshchin, Igor V.; Galatsis, Kosmas; Bao, Mingqiang; Wang, Kang L.

    2016-03-29

    A frequency conversion device, which may include a radiofrequency (RF) mixer device, includes a substrate and a ferromagnetic film disposed over a surface of the substrate. An insulator is disposed over the ferromagnetic film and at least one microstrip antenna is disposed over the insulator. The ferromagnetic film provides a non-linear response to the frequency conversion device. The frequency conversion device may be used for signal mixing and amplification. The frequency conversion device may also be used in data encryption applications.

  7. Soliton dynamics in planar ferromagnets and anti-ferromagnets

    Institute of Scientific and Technical Information of China (English)

    LINFang-hua; SHATAHJalal

    2003-01-01

    The aim of this paper is to present a rigorous mathematical proof of the dynamical laws for the topological solitons( magnetic vortices) in ferromagnets and anti-ferromagnets. It is achieved through the conservation laws for the topological vorticity and the weak convergence methods.

  8. Magnetic and magnetoresistive properties of half-metallic ferromagnetic and charge ordered modified ferromagnetic manganite nanoparticles

    Science.gov (United States)

    Das, Kalipada; Das, I.

    2017-03-01

    In our present study, we address in detail magnetic and magneto-transport properties of well known half metallic La0.67Sr0.33MnO3 (LSMO) and charge order suppressed ferromagnetic La0.48Ca0.52MnO3 (LCMO) nanoparticles. The average particle size for LSMO and LCMO is ˜20 nm and ˜25 nm, respectively. With respect to their magnetic properties, both compounds exhibit ferromagnetic behavior, whereas they markedly differ in their magneto-transport characteristics. The magnetoresistive properties of LSMO nanoparticles indicate low field magnetoresistance and tendency for saturation at higher field values. In addition to the sharp low field magnetoresistance, we have achieved significantly large magnetoresistance at higher values of external magnetic field for the ferromagnetic LCMO nanoparticles. To address such anomalous behavior in these two different classes of ferromagnetic materials, we introduce the re-entrant core-shell type structure formation in charge ordered nanoparticles (LCMO) when charge ordering is completely suppressed.

  9. Ferromagnet / superconductor oxide superlattices

    Science.gov (United States)

    Santamaria, Jacobo

    2006-03-01

    The growth of heterostructures combining oxide materials is a new strategy to design novel artificial multifunctional materials with interesting behaviors ruled by the interface. With the (re)discovery of colossal magnetoresistance (CMR) materials, there has been renewed interest in heterostructures involving oxide superconductors and CMR ferromagnets where ferromagnetism (F) and superconductivity (S) compete within nanometric distances from the interface. In F/S/F structures involving oxides, interfaces are especially complex and various factors like interface disorder and roughness, epitaxial strain, polarity mismatch etc., are responsible for depressed magnetic and superconducting properties at the interface over nanometer length scales. In this talk I will focus in F/S/F structures made of YBa2Cu3O7 (YBCO) and La0.7Ca0.3MnO3 (LCMO). The high degree of spin polarization of the LCMO conduction band, together with the d-wave superconductivity of the YBCO make this F/S system an adequate candidate for the search of novel spin dependent effects in transport. We show that superconductivity at the interface is depressed by various factors like charge transfer, spin injection or ferromagnetic superconducting proximity effect. I will present experiments to examine the characteristic distances of the various mechanisms of superconductivity depression. In particular, I will discuss that the critical temperature of the superconductor depends on the relative orientation of the magnetization of the F layers, giving rise to a new giant magnetoresistance effect which might be of interest for spintronic applications. Work done in collaboration with V. Peña^1, Z. Sefrioui^1, J. Garcia-Barriocanal^1, C. Visani^1, D. Arias^1, C. Leon^1 , N. Nemes^2, M. Garcia Hernandez^2, S. G. E. te Velthuis^3, A. Hoffmann^3, M. Varela^4, S. J. Pennycook^4. Work supported by MCYT MAT 2005-06024, CAM GR- MAT-0771/2004, UCM PR3/04-12399 Work at Argonne supported by the Department of Energy, Basic

  10. Half metallic ferromagnets.

    Science.gov (United States)

    Dowben, Peter

    2007-08-01

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

  11. PREFACE: Half Metallic Ferromagnets

    Science.gov (United States)

    Dowben, Peter

    2007-08-01

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

  12. Control of ferromagnetism in Fe-doped In{sub 2}O{sub 3} by carbothermal annealing

    Energy Technology Data Exchange (ETDEWEB)

    Yan Shiming [Key Laboratory for Magnetism and Magnetic Materials of Ministry of Education, Lanzhou University, Lanzhou 730000 (China); College of Science, Henan University of Technology, Zhengzhou 450001 (China); Ge Shihui, E-mail: gesh@lzu.edu.c [Key Laboratory for Magnetism and Magnetic Materials of Ministry of Education, Lanzhou University, Lanzhou 730000 (China); Qiao Wen; Zuo Yalu; Xu Feng; Xi Li [Key Laboratory for Magnetism and Magnetic Materials of Ministry of Education, Lanzhou University, Lanzhou 730000 (China)

    2011-02-15

    Fe-doped In{sub 2}O{sub 3} powders were prepared using the sol-gel method. Solubility of Fe ions in the In{sub 2}O{sub 3} host compound reached up to 50%. Lattice constant decreased linearly as Fe doping concentration increased, indicating that Fe ions were incorporated into the host lattice and occupied the In sites. Ferromagnetism could be obtained from the samples with carbothermal annealing. The dependence of ferromagnetism on the carbon dosage was observed. The greater the carbon dosage, the higher the concentration of oxygen vacancies (V{sub o}) created, and the more robust the ferromagnetism. - Research Highlights: Solubility of Fe ions in the In2O3 host compound reached up to 50%. Ferromagnetism can be induced by carbothermal annealing. Ferromagnetism is related to the content of oxygen vacancies. The dependence of ferromagnetism on the carbon dosage was observed.

  13. Optical Orientation in Ferromagnet/Semiconductor Hybrids

    OpenAIRE

    Korenev, V. L.

    2008-01-01

    The physics of optical pumping of semiconductor electrons in the ferromagnet/semiconductor hybrids is discussed. Optically oriented semiconductor electrons detect the magnetic state of the ferromagnetic film. In turn, the ferromagnetism of the hybrid can be controlled optically with the help of the semiconductor. Spin-spin interactions near the interface ferromagnet/semiconductor play crucial role in the optical readout and the manipulation of ferromagnetism.

  14. Conserved nonlocal dynamics and critical behavior of uranium ferromagnetic superconductors.

    Science.gov (United States)

    Singh, Rohit; Dutta, Kishore; Nandy, Malay K

    2017-01-01

    A recent theoretical study [Phys. Rev. Lett. 112, 037202 (2014)10.1103/PhysRevLett.112.037202] has revealed that systems such as uranium ferromagnetic superconductors obey conserved dynamics. To capture the critical behavior near the paramagnetic to ferromagnetic phase transition of these compounds, we study the conserved critical dynamics of a nonlocal Ginzburg-Landau model. A dynamic renormalization-group calculation at one-loop order yields the critical indices in the leading order of ε=d_{c}-d, where d_{c}=4-2ρ is the upper critical dimension, with ρ an exponent in the nonlocal interaction. The predicted static critical exponents are found to be comparable with the available experimentally observed critical exponents for strongly uniaxial uranium ferromagnetic superconductors. The corresponding dynamic exponent z and linewidth exponent w are found to be z=4-ρε/4+O(ε^{2}) and w=1+ρ+3ε/4+O(ε^{2}).

  15. Conserved nonlocal dynamics and critical behavior of uranium ferromagnetic superconductors

    Science.gov (United States)

    Singh, Rohit; Dutta, Kishore; Nandy, Malay K.

    2017-01-01

    A recent theoretical study [Phys. Rev. Lett. 112, 037202 (2014), 10.1103/PhysRevLett.112.037202] has revealed that systems such as uranium ferromagnetic superconductors obey conserved dynamics. To capture the critical behavior near the paramagnetic to ferromagnetic phase transition of these compounds, we study the conserved critical dynamics of a nonlocal Ginzburg-Landau model. A dynamic renormalization-group calculation at one-loop order yields the critical indices in the leading order of ɛ =dc-d , where dc=4 -2 ρ is the upper critical dimension, with ρ an exponent in the nonlocal interaction. The predicted static critical exponents are found to be comparable with the available experimentally observed critical exponents for strongly uniaxial uranium ferromagnetic superconductors. The corresponding dynamic exponent z and linewidth exponent w are found to be z =4 -ρ ɛ /4 +O (ɛ2) and w =1 +ρ +3 ɛ /4 +O (ɛ2) .

  16. Ferromagnetic Objects Magnetovision Detection System

    Directory of Open Access Journals (Sweden)

    Michał Nowicki

    2013-12-01

    Full Text Available This paper presents the application of a weak magnetic fields magnetovision scanning system for detection of dangerous ferromagnetic objects. A measurement system was developed and built to study the magnetic field vector distributions. The measurements of the Earth’s field distortions caused by various ferromagnetic objects were carried out. The ability for passive detection of hidden or buried dangerous objects and the determination of their location was demonstrated.

  17. Properties of twisted ferromagnetic filaments

    Energy Technology Data Exchange (ETDEWEB)

    Belovs, Mihails; Cebers, Andrejs [University of Latvia, Zellu 8, LV-1002 (Latvia)], E-mail: aceb@tesla.sal.lv

    2009-02-01

    The full set of equations for twisted ferromagnetic filaments is derived. The linear stability analysis of twisted ferromagnetic filament is carried out. Two different types of the buckling instability are found - monotonous and oscillatory. The first in the limit of large twist leads to the shape of filament reminding pearls on the string, the second to spontaneous rotation of the filament, which may constitute the working of chiral microengine.

  18. Non-ferromagnetic overburden casing

    Energy Technology Data Exchange (ETDEWEB)

    Vinegar, Harold J. (Bellaire, TX); Harris, Christopher Kelvin (Houston, TX); Mason, Stanley Leroy (Allen, TX)

    2010-09-14

    Systems, methods, and heaters for treating a subsurface formation are described herein. At least one system for electrically insulating an overburden portion of a heater wellbore is described. The system may include a heater wellbore located in a subsurface formation and an electrically insulating casing located in the overburden portion of the heater wellbore. The casing may include at least one non-ferromagnetic material such that ferromagnetic effects are inhibited in the casing.

  19. Ferromagnetism beyond Lieb's theorem

    Science.gov (United States)

    Costa, Natanael C.; Mendes-Santos, Tiago; Paiva, Thereza; Santos, Raimundo R. dos; Scalettar, Richard T.

    2016-10-01

    The noninteracting electronic structures of tight-binding models on bipartite lattices with unequal numbers of sites in the two sublattices have a number of unique features, including the presence of spatially localized eigenstates and flat bands. When a uniform on-site Hubbard interaction U is turned on, Lieb proved rigorously that at half-filling (ρ =1 ) the ground state has a nonzero spin. In this paper we consider a "CuO2 lattice" (also known as "Lieb lattice," or as a decorated square lattice), in which "d orbitals" occupy the vertices of the squares, while "p orbitals" lie halfway between two d orbitals; both d and p orbitals can accommodate only up to two electrons. We use exact determinant quantum Monte Carlo (DQMC) simulations to quantify the nature of magnetic order through the behavior of correlation functions and sublattice magnetizations in the different orbitals as a function of U and temperature; we have also calculated the projected density of states, and the compressibility. We study both the homogeneous (H) case, Ud=Up , originally considered by Lieb, and the inhomogeneous (IH) case, Ud≠Up . For the H case at half-filling, we found that the global magnetization rises sharply at weak coupling, and then stabilizes towards the strong-coupling (Heisenberg) value, as a result of the interplay between the ferromagnetism of like sites and the antiferromagnetism between unlike sites; we verified that the system is an insulator for all U . For the IH system at half-filling, we argue that the case Up≠Ud falls under Lieb's theorem, provided they are positive definite, so we used DQMC to probe the cases Up=0 ,Ud=U and Up=U ,Ud=0 . We found that the different environments of d and p sites lead to a ferromagnetic insulator when Ud=0 ; by contrast, Up=0 leads to to a metal without any magnetic ordering. In addition, we have also established that at density ρ =1 /3 , strong antiferromagnetic correlations set in, caused by the presence of one fermion on each

  20. Flocking ferromagnetic colloids

    Science.gov (United States)

    Kaiser, Andreas; Snezhko, Alexey; Aranson, Igor S.

    2017-01-01

    Assemblages of microscopic colloidal particles exhibit fascinating collective motion when energized by electric or magnetic fields. The behaviors range from coherent vortical motion to phase separation and dynamic self-assembly. Although colloidal systems are relatively simple, understanding their collective response, especially under out-of-equilibrium conditions, remains elusive. We report on the emergence of flocking and global rotation in the system of rolling ferromagnetic microparticles energized by a vertical alternating magnetic field. By combing experiments and discrete particle simulations, we have identified primary physical mechanisms, leading to the emergence of large-scale collective motion: spontaneous symmetry breaking of the clockwise/counterclockwise particle rotation, collisional alignment of particle velocities, and random particle reorientations due to shape imperfections. We have also shown that hydrodynamic interactions between the particles do not have a qualitative effect on the collective dynamics. Our findings shed light on the onset of spatial and temporal coherence in a large class of active systems, both synthetic (colloids, swarms of robots, and biopolymers) and living (suspensions of bacteria, cell colonies, and bird flocks). PMID:28246633

  1. Competition between ferromagnetic and antiferromagnetic interactions by Cr doping at Mn sites in antiperovskite Mn{sub 3−x}Cr{sub x}ZnN (0≤x≤0.5) compounds

    Energy Technology Data Exchange (ETDEWEB)

    Malik, Muhammad Imran; Sun, Ying; Wang, Lei; Deng, Sihao; Shi, Kewen; Hu, Pengwei; Lu, Huiqing; Wang, Cong, E-mail: congwang@buaa.edu.cn

    2016-05-01

    The Cr doping effect on the lattice and magnetic properties in Mn{sub 3−x}Cr{sub x}ZnN was reported in the antiferromagnetic intermetallic host material Mn{sub 3}ZnN. The lattice parameter decreases with the increase of the Cr concentration. Measurements of magnetization from 10 K to 350 K reveal that sharp antiferromagnetic (AFM)-to-paramagnetic (PM) transitions of the host material exist at 185 K (ZFC) and 177 K (FC). The peak is broadened clearly as the Cr doping was increased and when the Cr concentration exceeded 0.3, a significant ferromagnetic (FM) character was found to coexist with an AFM phase. At x=0.4 and 0.5, the M–H curves exhibit small magnetic hysteresis loop, indicating the dominant FM interactions in these samples. Also, a positive value of Weiss Temperature (Θ{sub W}) at x=0.5 in H/M–T plot suggests that the FM interaction is dominant when the Cr doping increases.

  2. Ferromagnetic materials. V. 5

    Energy Technology Data Exchange (ETDEWEB)

    Buschow, K.H.J.; Wohlfarth, E.P. (Philips Gloeilampenfabrieken NV, Eindhoven (Netherlands). Forschungslaboratorium) (eds.)

    1990-01-01

    The topics dealt with in this volume include the increased activity and investigations of the magnetism of magnetic superconductors and investigations of the magnetic properties of the hydrides, the understanding of first-order magnetic processes and of quadrupolar interactions in 4f systems and their role in magnetic ordering and magnetoelastic effects, the magnetism of strongly enhanced itinerant alloys and compounds and the magnetism of INVAR alloys. Three chapters are in INIS scope, entitled respectively: Quadrupolar interactions and magnetoelastic effects in rate earth intermetallic compounds; Magnetooptical spectroscopy of f-electron systems, magnetic superconductors. (author). refs.; figs.; tabs.

  3. Dynamical response of vibrating ferromagnets

    CERN Document Server

    Gaganidze, E; Ziese, M

    2000-01-01

    The resonance frequency of vibrating ferromagnetic reeds in a homogeneous magnetic field can be substantially modified by intrinsic and extrinsic field-related contributions. Searching for the physical reasons of the field-induced resonance frequency change and to study the influence of the spin glass state on it, we have measured the low-temperature magnetoelastic behavior and the dynamical response of vibrating amorphous and polycrystalline ferromagnetic ribbons. We show that the magnetoelastic properties depend strongly on the direction of the applied magnetic field. The influence of the re-entrant spin glass transition on these properties is discussed. We present clear experimental evidence that for applied fields perpendicular to the main area of the samples the behavior of ferromagnetic reeds is rather independent of the material composition and magnetic state, exhibiting a large decrease of the resonance frequency. This effect can be very well explained with a model based on the dynamical response of t...

  4. A new ferromagnetic superconductor: CsEuFe4As4

    Institute of Scientific and Technical Information of China (English)

    Yi Liu; Ya-Bin Liu; Qian Chen; Zhang-Tu Tang; Wen-He Jiao; Qian Tao; Zhu-An Xu

    2016-01-01

    Superconductivity (SC) and ferromagnetism (FM) are in general antagonistic,which makes their coexistence very rare.Following our recent discovery of robust coexistence of SC and FM in RbEuFe4As4 (Liu et al.in Phys Rev B 93:214503,2016),here we report another example of such a coexistence in its sister compound CsEuFe4As4,synthesized for the first time.The new material exhibits bulk SC at 35.2 K and Eu2+-spin ferromagnetic ordering at 15.5 K,demonstrating that it is a new robust ferromagnetic superconductor.

  5. Theory of disordered Heisenberg ferromagnets

    Science.gov (United States)

    Stubbs, R. M.

    1973-01-01

    A Green's function technique is used to calculate the magnetic properties of Heisenberg ferromagnets in which the exchange interactions deviate randomly in strength from the mean interaction. Systems of sc, bcc, and fcc topologies and of general spin values are treated. Disorder produces marked effects in the density of spin wave states, in the form of enhancement of the low-energy density and extension of the energy band to higher values. The spontaneous magnetization and the Curie temperature decrease with increasing disorder. The effects of disorder are shown to be more pronounced in the ferromagnetic than in the paramagnetic phase.

  6. Critical parameters near the ferromagnetic-paramagnetic phase transition in La0.67-xYxBa0.23Ca0.1MnO3 compounds (x=0.10 andx=0.15)

    Institute of Scientific and Technical Information of China (English)

    Mounira Abassi; N Dhahri; J Dhahri; K Taibi; EK Hlil

    2015-01-01

    The critical properties of the mixed manganite La0.67–xYxBa0.23Ca0.1MnO3 withx=0.10 andx=0.15 around the paramagnetic (PM)-ferromagnetic (FM) phase transition were investigated through various techniques. These involved modified Arrott plots, Kou-vel-Fisher method and Widom scaling relation. Magnetic data, analyzed in the critical region, using the above methods, yielded the critical exponents for (x=0.10) La0.57Y0.10Ba0.23Ca0.1MnO3 (β=0.312±0.002 andγ=1.147±0.003 atTC=299.23±0.05 K). Moreover, the estimated critical exponents of (x=0.15) La0.52Y0.15Ba0.23Ca0.1MnO3 wereβ=0.286±0.004 andγ=0.943±0.002 atTC=289.53±0.06 K. The critical exponents’ values were close to the theoretical values of 3D-Ising model and tricritical mean-field model. These results suggested that the present composition should be close to a tricritical point in the La0.67–xYxBa0.23Ca0.1MnO3 phase diagram. Express-ing the field dependence asΔSM∝Hn allowed us to establish a relationship between the exponentn and the critical exponents of the material and to propose a phenomenological universal curve for the field dependence ofΔSM.

  7. Thermoelectric Detection of Ferromagnetic Resonance of a Nanoscale Ferromagnet

    NARCIS (Netherlands)

    Bakker, F. L.; Flipse, J.; Slachter, A.; Wagenaar, D.; van Wees, B. J.

    2012-01-01

    We present thermoelectric measurements of the heat dissipated due to ferromagnetic resonance of a Permalloy strip. A microwave magnetic field, produced by an on-chip coplanar strip waveguide, is used to drive the magnetization precession. The generated heat is detected via Seebeck measurements on a

  8. Orbital magnetization in dilute ferromagnetic semiconductors

    Science.gov (United States)

    Śliwa, Cezary; Dietl, Tomasz

    2014-07-01

    The relationship between the modern and classical Landau's approach to carrier orbital magnetization is studied theoretically within the envelope function approximation, taking ferromagnetic (Ga,Mn)As as an example. It is shown that while the evaluation of hole magnetization within the modern theory does not require information on the band structure in a magnetic field, the number of basis wave functions must be much larger than in the Landau approach to achieve the same quantitative accuracy. A numerically efficient method is proposed, which takes advantages of these two theoretical schemes. The computed magnitude of orbital magnetization is in accord with experimental values obtained by x-ray magnetic circular dichroism in (III,Mn)V compounds. The direct effect of the magnetic field on the hole spectrum is studied too, and employed to interpret a dependence of the Coulomb blockade maxima on the magnetic field in a single electron transistor with a (Ga,Mn)As gate.

  9. UGe{sub 2}: a ferromagnetic superconductor

    Energy Technology Data Exchange (ETDEWEB)

    Flouquet, J.; Huxley, A.; Sheikin, I.; Kernavanois, N.; Braithwaite, D.; Ressouche, E. [Departement de Recherche Fondamentale sur la Matiere Condensee, SPSMS, CEA/Grenoble, 17 rue des Martyrs, 38054 Grenoble Cedex 9 (France); Watanabe, Shinji; Miyake, Kazumasa [Department of Physical Science, Osaka University, Toyonaka, Osaka (Japan)

    2001-03-01

    The discovery of superconductivity within the ferromagnetic phase of the heavy-fermion compound UGe{sub 2} provides a fresh perspective from which to search for new mechanisms of unconventional superconductivity. We review here our recent neutron scattering experiments, which in particular fail to find evidence for a charge density (or spin density) wave below a characteristic temperature T{sub X}. Nevertheless the existence of such a state qualitatively accounts for transport measurements, and is not inconsistent with band-structure calculations that suggest nesting might occur across a majority spin Fermi surface. Finally we describe an anomalous behavior of the upper critical field. This is analyzed within a strong coupling formalism in which the superconductivity is driven by fluctuations due to a proximity to the charge density wave transition. (author)

  10. Novel room temperature ferromagnetic semiconductors

    Energy Technology Data Exchange (ETDEWEB)

    Gupta, Amita

    2004-11-01

    Today's information world, bits of data are processed by semiconductor chips, and stored in the magnetic disk drives. But tomorrow's information technology may see magnetism (spin) and semiconductivity (charge) combined in one 'spintronic' device that exploits both charge and 'spin' to carry data (the best of two worlds). Spintronic devices such as spin valve transistors, spin light emitting diodes, non-volatile memory, logic devices, optical isolators and ultra-fast optical switches are some of the areas of interest for introducing the ferromagnetic properties at room temperature in a semiconductor to make it multifunctional. The potential advantages of such spintronic devices will be higher speed, greater efficiency, and better stability at a reduced power consumption. This Thesis contains two main topics: In-depth understanding of magnetism in Mn doped ZnO, and our search and identification of at least six new above room temperature ferromagnetic semiconductors. Both complex doped ZnO based new materials, as well as a number of nonoxides like phosphides, and sulfides suitably doped with Mn or Cu are shown to give rise to ferromagnetism above room temperature. Some of the highlights of this work are discovery of room temperature ferromagnetism in: (1) ZnO:Mn (paper in Nature Materials, Oct issue, 2003); (2) ZnO doped with Cu (containing no magnetic elements in it); (3) GaP doped with Cu (again containing no magnetic elements in it); (4) Enhancement of Magnetization by Cu co-doping in ZnO:Mn; (5) CdS doped with Mn, and a few others not reported in this thesis. We discuss in detail the first observation of ferromagnetism above room temperature in the form of powder, bulk pellets, in 2-3 mu-m thick transparent pulsed laser deposited films of the Mn (<4 at. percent) doped ZnO. High-resolution transmission electron microscopy (HRTEM) and electron energy loss spectroscopy (EELS) spectra recorded from 2 to 200nm areas showed homogeneous

  11. Novel room temperature ferromagnetic semiconductors

    Energy Technology Data Exchange (ETDEWEB)

    Gupta, Amita [KTH Royal Inst. of Technology, Stockholm (Sweden)

    2004-06-01

    Today's information world, bits of data are processed by semiconductor chips, and stored in the magnetic disk drives. But tomorrow's information technology may see magnetism (spin) and semiconductivity (charge) combined in one 'spintronic' device that exploits both charge and 'spin' to carry data (the best of two worlds). Spintronic devices such as spin valve transistors, spin light emitting diodes, non-volatile memory, logic devices, optical isolators and ultra-fast optical switches are some of the areas of interest for introducing the ferromagnetic properties at room temperature in a semiconductor to make it multifunctional. The potential advantages of such spintronic devices will be higher speed, greater efficiency, and better stability at a reduced power consumption. This Thesis contains two main topics: In-depth understanding of magnetism in Mn doped ZnO, and our search and identification of at least six new above room temperature ferromagnetic semiconductors. Both complex doped ZnO based new materials, as well as a number of nonoxides like phosphides, and sulfides suitably doped with Mn or Cu are shown to give rise to ferromagnetism above room temperature. Some of the highlights of this work are discovery of room temperature ferromagnetism in: (1) ZnO:Mn (paper in Nature Materials, Oct issue, 2003); (2) ZnO doped with Cu (containing no magnetic elements in it); (3) GaP doped with Cu (again containing no magnetic elements in it); (4) Enhancement of Magnetization by Cu co-doping in ZnO:Mn; (5) CdS doped with Mn, and a few others not reported in this thesis. We discuss in detail the first observation of ferromagnetism above room temperature in the form of powder, bulk pellets, in 2-3 mu-m thick transparent pulsed laser deposited films of the Mn (<4 at. percent) doped ZnO. High-resolution transmission electron microscopy (HRTEM) and electron energy loss spectroscopy (EELS) spectra recorded from 2 to 200nm areas showed homogeneous

  12. Spin Seebeck effect in a weak ferromagnet

    Science.gov (United States)

    Arboleda, Juan David; Arnache Olmos, Oscar; Aguirre, Myriam Haydee; Ramos, Rafael; Anadon, Alberto; Ibarra, Manuel Ricardo

    2016-06-01

    We report the observation of room temperature spin Seebeck effect (SSE) in a weak ferromagnetic normal spinel Zinc Ferrite (ZFO). Despite the weak ferromagnetic behavior, the measurements of the SSE in ZFO show a thermoelectric voltage response comparable with the reported values for other ferromagnetic materials. Our results suggest that SSE might possibly originate from the surface magnetization of the ZFO.

  13. On the theory of ferromagnetism

    NARCIS (Netherlands)

    Ruijgrok, Th.W.

    1962-01-01

    An attempt is made to specify the conditions under which Heisenberg's model of ferromagnetism is correct. It is found that in addition to the exchange term there are other terms in the hamiltonian, describing the effects of the band width and of polar states. The new hamiltonian, which has a simple

  14. Skyrmion Excitations in Planar Ferromagnets

    Institute of Scientific and Technical Information of China (English)

    WANG Ji-Biao; REN Ji-Rong; LI Ran

    2009-01-01

    By making use of the (φ)-mapping topological current theory and the decomposition of gauge potential theory, we investigate the (2+1)-dimensional skyrmion excitations in ferromagnets. We also discuss the branch processes of these skyrmions and the generation and annihilation of skyrmion-antiskyrmion pairs.

  15. Investigation of Room temperature Ferromagnetism in Mn doped Ge

    Science.gov (United States)

    Colakerol Arslan, Leyla; Toydemir, Burcu; Onel, Aykut Can; Ertas, Merve; Doganay, Hatice; Gebze Inst of Tech Collaboration; Research Center Julich Collaboration

    2014-03-01

    We present a systematic investigation of structural, magnetic and electronic properties of MnxGe1 -x single crystals. MnxGe1-x films were grown by sequential deposition of Ge and Mn by molecular-beam epitaxy at low substrate temperatures in order to avoid precipitation of ferromagnetic Ge-Mn intermetallic compounds. Reflected high energy electron diffraction and x-ray diffraction observations revealed that films are epitaxially grown on Si (001) substrates from the initial stage without any other phase formation. Magnetic measurements carried out using a physical property measurement system showed that all samples exhibited ferromagnetism at room temperature. Electron spin resonance indicates the presence of magnetically ordered localized spins of divalent Mn ions. X-ray absorption measurements at the Mn L-edge confirm significant substitutional doping of Mn into Ge-sites. The ferromagnetism was mainly induced by Mn substitution for Ge site, and indirect exchange interaction of these magnetic ions with the intrinsic charge carriers is the origin of ferromagnetism. The magnetic interactions were better understood by codoping with nonmagnetic impurities. This work was supported by Marie-Curie Reintegration Grant (PIRG08-GA-2010-276973).

  16. Josephson junctions with ferromagnetic interlayer

    Energy Technology Data Exchange (ETDEWEB)

    Wild, Georg Hermann

    2012-03-04

    We report on the fabrication of superconductor/insulator/ferromagnetic metal/superconductor (Nb/AlO{sub x}/Pd{sub 0.82}Ni{sub 0.18}/Nb) Josephson junctions (SIFS JJs) with high critical current densities, large normal resistance times area products, and high quality factors. For these junctions, a transition from 0- to {pi}-coupling is observed for a thickness d{sub F}=6 nm of the ferromagnetic Pd{sub 0.82}Ni{sub 0.18} interlayer. The magnetic field dependence of the critical current of the junctions demonstrates good spatial homogeneity of the tunneling barrier and ferromagnetic interlayer. Magnetic characterization shows that the Pd{sub 0.82}Ni{sub 0.18} has an out-of-plane anisotropy and large saturation magnetization indicating negligible dead layers at the interfaces. A careful analysis of Fiske modes up to about 400 GHz provides valuable information on the junction quality factor and the relevant damping mechanisms. Whereas losses due to quasiparticle tunneling dominate at low frequencies, at high frequencies the damping is explained by the finite surface resistance of the junction electrodes. High quality factors of up to 30 around 200 GHz have been achieved. They allow to study the junction dynamics, in particular the switching probability from the zero-voltage into the voltage state with and without microwave irradiation. The experiments with microwave irradiation are well explained within semi-classical models and numerical simulations. In contrast, at mK temperature the switching dynamics without applied microwaves clearly shows secondary quantum effects. Here, we could observe for the first time macroscopic quantum tunneling in Josephson junctions with a ferromagnetic interlayer. This observation excludes fluctuations of the critical current as a consequence of an unstable magnetic domain structure of the ferromagnetic interlayer and affirms the suitability of SIFS Josephson junctions for quantum information processing.

  17. Superconducting magnetoresistance in ferromagnet/superconductor/ferromagnet trilayers.

    Science.gov (United States)

    Stamopoulos, D; Aristomenopoulou, E

    2015-01-01

    Magnetoresistance is a multifaceted effect reflecting the diverse transport mechanisms exhibited by different kinds of plain materials and hybrid nanostructures; among other, giant, colossal, and extraordinary magnetoresistance versions exist, with the notation indicative of the intensity. Here we report on the superconducting magnetoresistance observed in ferromagnet/superconductor/ferromagnet trilayers, namely Co/Nb/Co trilayers, subjected to a parallel external magnetic field equal to the coercive field. By manipulating the transverse stray dipolar fields that originate from the out-of-plane magnetic domains of the outer layers that develop at coercivity, we can suppress the supercurrent of the interlayer. We experimentally demonstrate a scaling of the magnetoresistance magnitude that we reproduce with a closed-form phenomenological formula that incorporates relevant macroscopic parameters and microscopic length scales of the superconducting and ferromagnetic structural units. The generic approach introduced here can be used to design novel cryogenic devices that completely switch the supercurrent 'on' and 'off', thus exhibiting the ultimate magnetoresistance magnitude 100% on a regular basis.

  18. Isotope shift of the ferromagnetic transition temperature in itinerant ferromagnets

    Science.gov (United States)

    Yanagisawa, Takashi; Hase, Izumi; Odagiri, Kosuke

    2017-02-01

    We present a theory of the isotope effect of the Curie temperature Tc in itinerant ferromagnets. The isotope effect in ferromagnets occurs via the electron-phonon vertex correction and the effective attractive interaction mediated by the electron-phonon interaction. The decrease of the Debye frequency increases the relative strength of the Coulomb interaction, which results in a positive isotope shift of Tc when the mass M of an atom increases. Following this picture, we evaluate the isotope effect of Tc by using the Stoner theory and a spin-fluctuation theory. When Tc is large enough as large as or more than 100 K, the isotope effect on Tc can be measurable. Recently, precise measurements on the oxygen isotope effect on Tc have been performed for itinerant ferromagnet SrRuO3 with Tc ∼ 160 K. A clear isotope effect has been observed with the positive shift of Tc ∼ 1 K by isotope substitution (16O →18O). This experimental result is consistent with our theory.

  19. Seal device for ferromagnetic containers

    Science.gov (United States)

    Meyer, Ross E.; Jason, Andrew J.

    1994-01-01

    A temporary seal or patch assembly prevents the escape of contents, e.g., fluids and the like, from within a container having a breach therethrough until the contents can be removed and/or a repair effected. A frame that supports a sealing bladder can be positioned over the breach and the frame is then attached to the container surface, which must be of a ferromagnet material, by using switchable permanent magnets. The permanent magnets are designed to have a first condition that is not attracted to the ferromagnetic surface and a second conditions whereby the magnets are attracted to the surface with sufficient force to support the seal assembly on the surface. Latching devices may be attached to the frame and engage the container surface with hardened pins to prevent the lateral movement of the seal assembly along the container surface from external forces such as fluid drag or gravity.

  20. Microwave metamaterials with ferromagnetic microwires

    Science.gov (United States)

    Panina, L. V.; Ipatov, M.; Zhukova, V.; Zhukov, A.; Gonzalez, J.

    2011-06-01

    This paper discusses a new type of wire media based on amorphous ferromagnetic microwires. The combination of two effects, namely, a strong dispersion of the effective permittivity in metallic wire composites (resonance or plasmonic type) and giant magnetoimpedance effect in wires, will result in unusual property that an effective dielectric response may strongly depend on the wire magnetization which can be changed with external stimuli: magnetic field, mechanical stress and temperature.

  1. Dynamical response of vibrating ferromagnets

    Science.gov (United States)

    Gaganidze, E.; Esquinazi, P.; Ziese, M.

    2000-02-01

    The resonance frequency of vibrating ferromagnetic reeds in a homogeneous magnetic field can be substantially modified by intrinsic and extrinsic field-related contributions. Searching for the physical reasons of the field-induced resonance frequency change and to study the influence of the spin glass state on it, we have measured the low-temperature magnetoelastic behavior and the dynamical response of vibrating amorphous and polycrystalline ferromagnetic ribbons. We show that the magnetoelastic properties depend strongly on the direction of the applied magnetic field. The influence of the re-entrant spin glass transition on these properties is discussed. We present clear experimental evidence that for applied fields perpendicular to the main area of the samples the behavior of ferromagnetic reeds is rather independent of the material composition and magnetic state, exhibiting a large decrease of the resonance frequency. This effect can be very well explained with a model based on the dynamical response of the reed and the magnetomechanical pole effect within a domain rotation model and is not related to magnetoelasticity.

  2. Superconductivity and ferromagnetism in nanomaterial NbSe2

    Science.gov (United States)

    Gill, Raminder

    2017-07-01

    Finding of superconductivity (SC) in ultra thin layer of Niobium diselenide (NbSe2) caught the attention of each condensed matter physicist in the era of nanotechnology. The coexistence of SC and magnetism have been a topic of interesting research in solid-state physics since the discovery of superconductivity. Ferromagnetism induced in any compound could destroy superconductivity by disturbing the cooper pairing of electrons of the atoms. The interplay between ferromagnetism (FM) and SC in nanomaterial NBSe2 impressed to study and to know the exact mechanism behind this coexistence which can lead to a very interesting research: superconductivity at room temperature. In this paper, I have theoretically studied the coexistence of SC and FM in NbSe2 and how this material could be useful in finding many high Tc nanomaterials.

  3. Giant ferromagnetic π -d interaction in a phthalocyanine molecule

    Science.gov (United States)

    Murakawa, H.; Kanda, A.; Ikeda, M.; Matsuda, M.; Hanasaki, N.

    2015-08-01

    We experimentally demonstrate that the ferromagnetic intramolecular π -d interaction works between an itinerant π -electron spin and a localized d -electron's magnetic moment in the iron-phthalocyanine (Pc) molecular compound. The evaluation of the hidden π -d coupling is achieved by preparing the isolated Fe(Pc )(CN ) 2 molecular solution with unpaired π - and d -electron spins, which is generated through the oxidization by iodine bromide (IBr). The monotonic increase of the magnetization with IBr addition and the saturation value of the Curie constant indicate the ferromagnetic π -d coupling. Furthermore, through the magnetization measurements of the single crystals of neutral π radical Fe(Pc )(CN ) 2.2 CHCl3 , we reveal that the on-site π -d interaction in Fe(Pc )(CN ) 2 is extremely large (Jπ d/kB>500 K ) among those in other molecular materials.

  4. Critical behaviour of coupled organic ferromagnet chains

    Institute of Scientific and Technical Information of China (English)

    Guo Ji-Yong; Chen Yu-Guang; Chen Hong

    2005-01-01

    The interchain coupling in a model, which is most relevant to organic ferromagnets, is studied by a kind of mean field theory. A full phase diagram is given for this model. It is shown that the interchain coupling dramatically affects the ferromagnetic order in the ground state. When the interchain coupling reaches a critical value, the high-spin ground state disappears and the system may transit from ferromagnetic phase into Kondo-singlet phase.

  5. On the Absence of Ferromagnetism in Typical 2D Ferromagnets

    Energy Technology Data Exchange (ETDEWEB)

    Biskup, Marek

    2010-04-06

    We consider the Ising systems in d dimensions with nearest-neighbor ferromagnetic interactions and long-range repulsive (antiferromagnetic) interactions that decay with power s of the distance. The physical context of such models is discussed; primarily this is d = 2 and s = 3 where, at long distances, genuine magnetic interactions between genuine magnetic dipoles are of this form.We prove that when the power of decay lies above d and does not exceed d + 1, then for all temperatures the spontaneous magnetization is zero. In contrast, we also show that for powers exceeding d + 1 (with d {ge} 2) magnetic order can occur.

  6. Coherent quantum trasport in ferromagnet-superconductor-ferromagnet graphene junctions

    Directory of Open Access Journals (Sweden)

    M Salehi

    2010-09-01

    Full Text Available In this paper, we investigate the coherent quantum transport in grapheme-based ferromagnet-superconductor-ferromagent junctions within the framework of BCS theory using DBdG quasiparticles equation .The coherency with the finite size of superconductor region has two characteristic features subgap electron transport and oscillations of differential conductance. we show that periodic vanishing of the Andreev reflection at the energies called geometrical resonances above the superconducting gap is a striking consequence of quasiparticles interference. We suggest to make devices that produce polarized spin-current with possible applications in spintronics.

  7. An extension to flat band ferromagnetism

    Science.gov (United States)

    Gulacsi, M.; Kovacs, G.; Gulacsi, Z.

    2014-11-01

    From flat band ferromagnetism, we learned that the lowest energy half-filled flat band gives always ferromagnetism if the localized Wannier states on the flat band satisfy the connectivity condition. If the connectivity conditions are not satisfied, ferromagnetism does not appear. We show that this is not always the case namely, we show that ferromagnetism due to flat bands can appear even if the connectivity condition does not hold due to a peculiar behavior of the band situated just above the flat band.

  8. Model for ballistic spin-transport in ferromagnet/two-dimensional electron gas/ferromagnet structures

    NARCIS (Netherlands)

    Schapers, T; Nitta, J; Heersche, HB; Takayanagi, H

    2002-01-01

    The spin dependent conductance of a ferromagnet/two-dimensional electron gas ferromagnet structure is theoretically examined in the ballistic transport regime. It is shown that the spin signal can be improved considerably by making use of the spin filtering effect of a barrier at the ferromagnet two

  9. Radioactive Probes on Ferromagnetic Surfaces

    CERN Multimedia

    2002-01-01

    On the (broad) basis of our studies of nonmagnetic radioactive probe atoms on magnetic surfaces and at interfaces, we propose to investigate the magnetic interaction of magnetic probe atoms with their immediate environment, in particular of rare earth (RE) elements positioned on and in ferromagnetic surfaces. The preparation and analysis of the structural properties of such samples will be performed in the UHV chamber HYDRA at the HMI/Berlin. For the investigations of the magnetic properties of RE atoms on surfaces Perturbed Angular Correlation (PAC) measurements and Mössbauer Spectroscopy (MS) in the UHV chamber ASPIC (Apparatus for Surface Physics and Interfaces at CERN) are proposed.

  10. Explanation of ferromagnetism origin in C-doped ZnO by first principle calculations

    Energy Technology Data Exchange (ETDEWEB)

    El Amiri, A., E-mail: aelamiri@casablanca.ma [Laboratoire de Physique Fondamentale et Appliquée (LPFA), Faculté des Sciences Ain Chock, Université Hassan II, B.P. 5366 Mâarif, Casablanca, Maroc (Morocco); Lassri, H. [Laboratoire de Physique des Matériaux, Micro-électronique, Automatique et Thermique (LPMMAT). Faculté des Sciences Ain Chock, Université Hassan II, B.P. 5366 Mâarif, Casablanca, Maroc (Morocco); Hlil, E.K. [Institut Néel, CNRS et Université Joseph Fourier, BP 166, 38042 Grenoble (France); Abid, M. [Laboratoire de Physique Fondamentale et Appliquée (LPFA), Faculté des Sciences Ain Chock, Université Hassan II, B.P. 5366 Mâarif, Casablanca, Maroc (Morocco)

    2015-01-15

    By ab-initio calculations, we systematically study possible source of ferromagnetism C-doped ZnO compound. The electronic structure and magnetic properties of C-doped ZnO with / without ZnO host and C defects were investigated using the Korringa–Kohn–Rostoker (KKR) method combined with coherent potential approximation (CPA). We show that Zn vacancy and presence of C defects (substitutional, interstitial or combination of both) induce the ferromagnetism in C-doped ZnO. From density of state (DOS) analysis, we show that p–p interaction between C atoms and/or C and O atoms is the mechanism of ferromagnetic coupling in C-doped ZnO. - Highlights: • We study the effect of ZnO host and C defects on ferromagnetism in C-doped ZnO. • Details of KKR method calculations performed to investigate both magnetic and electronic structures. • Magnetic moments, total and partial DOS for C-doped ZnO are well calculated and discussed. • Based on DOS calculations we interpret a origin of ferromagnetism in C-doped ZnO. • Mechanism of ferromagnetic coupling is well proposed.

  11. Structural changes concurrent with ferromagnetic transition

    Institute of Scientific and Technical Information of China (English)

    Yang Sen; Bao Hui-Xin; Zhou Chao; Wang Yu; Ren Xiao-Bing; Song Xiao-Ping; Yoshitaka Matsushita

    2013-01-01

    Ferromagnetic transition has generally been considered to involve only an ordering of magnetic moment with no change in the host crystal structure or symmetry,as evidenced by a wealth of crystal structure data from conventional X-ray diffractometry (XRD).However,the existence of magnetostriction in all known ferromagnetic systems indicates that the magnetic moment is coupled to the crystal lattice; hence there is a possibility that magnetic ordering may cause a change in crystal structure.With the development of high-resolution synchrotron XRD,more and more magnetic transitions have been found to be accompanied by simultaneous structural changes.In this article,we review our recent progress in understanding the structural change at a ferromagnetic transition,including synchrotron XRD evidence of structural changes at the ferromagnetic transition,a phenomenological theory of crystal structure changes accompanying ferromagnetic transitions,new insight into magnetic morphotropic phase boundaries (MPB) and so on.Two intriguing implications of non-centric symmetry in the ferromagnetic phase and the first-order nature of ferromagnetic transition are also discussed here.In short,this review is intended to give a self-consistent and logical account of structural change occurring simultaneously with a ferromagnetic transition,which may provide new insight for developing highly magneto-responsive materials.

  12. Spin relaxation in metallic ferromagnets

    Science.gov (United States)

    Berger, L.

    2011-02-01

    The Elliott theory of spin relaxation in metals and semiconductors is extended to metallic ferromagnets. Our treatment is based on the two-current model of Fert, Campbell, and Jaoul. The d→s electron-scattering process involved in spin relaxation is the inverse of the s→d process responsible for the anisotropic magnetoresistance (AMR). As a result, spin-relaxation rate 1/τsr and AMR Δρ are given by similar formulas, and are in a constant ratio if scattering is by solute atoms. Our treatment applies to nickel- and cobalt-based alloys which do not have spin-up 3d states at the Fermi level. This category includes many of the technologically important magnetic materials. And we show how to modify the theory to apply it to bcc iron-based alloys. We also treat the case of Permalloy Ni80Fe20 at finite temperature or in thin-film form, where several kinds of scatterers exist. Predicted values of 1/τsr and Δρ are plotted versus resistivity of the sample. These predictions are compared to values of 1/τsr and Δρ derived from ferromagnetic-resonance and AMR experiments in Permalloy.

  13. Spin-orbit ferromagnetic resonance

    Science.gov (United States)

    Ferguson, Andrew

    2013-03-01

    In conventional magnetic resonance techniques the magnitude and direction of the oscillatory magnetic field are (at least approximately) known. This oscillatory field is used to probe the properties of a spin ensemble. Here, I will describe experiments that do the inverse. I will discuss how we use a magnetic resonance technique to map out the current-induced effective magnetic fields in the ferromagnetic semiconductors (Ga,Mn)As and (Ga,Mn)(As,P). These current-induced fields have their origin in the spin-orbit interaction. Effective magnetic fields are observed with symmetries which resemble the Dresselhaus and Rashba spin-orbit interactions and which depend on the diagonal and off-diagonal strain respectively. Ferromagnetic semiconductor materials of different strains, annealing conditions and concentrations are studied and the results compared with theoretical calculations. Our original study measured the rectification voltage coming from the product of the oscillatory magnetoresistance, during magnetisation precession, and the alternating current. More recently we have developed an impedance matching technique which enables us to extract microwave voltages from these high resistance (10 k Ω) samples. In this way we measure the microwave voltage coming from the product of the oscillating magneto-resistance and a direct current. The direct current is observed to affect the magnetisation precession, indicating that anti-damping as well as field-like torques can originate from the spin-orbit interaction.

  14. Hydrogen in ferromagnetic semiconductors for planar spintronics

    Science.gov (United States)

    Farshchi, Rouin

    This dissertation documents the use of hydrogen for controlling electrical and magnetic properties of ferromagnetic semiconductors, particularly GaMnAs. With minimal structural perturbation, hydrogen forms complexes with Mn acceptors and renders them neutral, thereby substantially increasing electrical resistivity and removing ferromagnetism. A major finding presented herein is that laser annealing can be used to controllably dissociate the Mn-H complexes and restore ferromagnetism. Structural, electrical, and magnetic effects of the laser activation process are thoroughly explored through experiments and numerical modeling. Local laser activation with tightly-focused ultra-short laser pulses allows for high-resolution direct-writing of ferromagnetic patterns in semiconductors, introducing a new paradigm for device design. Prospects for laser formation of high-temperature phases in ferromagnetic semiconductors are investigated. Finally, several device concepts incorporating the laser activation process are discussed as building blocks towards planar all-semiconductor spintronics.

  15. Theory of ferromagnetic (III,Mn)V semiconductors

    Science.gov (United States)

    Jungwirth, T.; Sinova, Jairo; Mašek, J.; Kučera, J.; MacDonald, A. H.

    2006-07-01

    The body of research on (III,Mn)V diluted magnetic semiconductors (DMSs) initiated during the 1990s has concentrated on three major fronts: (i) the microscopic origins and fundamental physics of the ferromagnetism that occurs in these systems, (ii) the materials science of growth and defects, and (iii) the development of spintronic devices with new functionalities. This article reviews the current status of the field, concentrating on the first two, more mature research directions. From the fundamental point of view, (Ga,Mn)As and several other (III,Mn)V DMSs are now regarded as textbook examples of a rare class of robust ferromagnets with dilute magnetic moments coupled by delocalized charge carriers. Both local moments and itinerant holes are provided by Mn, which makes the systems particularly favorable for realizing this unusual ordered state. Advances in growth and postgrowth-treatment techniques have played a central role in the field, often pushing the limits of dilute Mn-moment densities and the uniformity and purity of materials far beyond those allowed by equilibrium thermodynamics. In (III,Mn)V compounds, material quality and magnetic properties are intimately connected. This review focuses on the theoretical understanding of the origins of ferromagnetism and basic structural, magnetic, magnetotransport, and magneto-optical characteristics of simple (III,Mn)V epilayers, with the main emphasis on (Ga,Mn)As. Conclusions are arrived at based on an extensive literature covering results of complementary ab initio and effective Hamiltonian computational techniques, and on comparisons between theory and experiment. The applicability of ferromagnetic semiconductors in microelectronic technologies requires increasing Curie temperatures from the current record of 173K in (Ga,Mn)As epilayers to above room temperature. The issue of whether or not this is a realistic expectation for (III,Mn)V DMSs is a central question in the field and motivates many of the analyses

  16. Fabrication and ferromagnetism of Si-SiGe/MnGe core-shell nanopillars

    Science.gov (United States)

    Wang, Liming; Liu, Tao; Wang, Shuguang; Zhong, Zhenyang; Jia, Quanjie; Jiang, Zuimin

    2016-10-01

    Si-Si0.5Ge0.5/Mn0.08Ge0.92 core-shell nanopillar samples were fabricated on ordered Si nanopillar patterned substrates by molecular beam epitaxy at low temperatures. The magnetic properties of the samples are found to depend heavily on the growth temperature of the MnGe layer. The sample grown at a moderate temperature of 300 °C has the highest Curie temperature of 240 K as well as the strongest ferromagnetic signals. On the basis of the microstructural results, the ferromagnetic properties of the samples are believed to come from the intrinsic Mn-doped amorphous or crystalline Ge ferromagnetic phase rather than any intermetallic ferromagnetic compounds of Mn and Ge. After being annealed at a temperature of 500 °C, all the samples exhibit the same Curie temperature of 220 K, which is in sharp contrast to the different Curie temperature for the as-grown samples, and the ferromagnetism for the annealed samples comes from Mn5GeSi2 compounds which are formed during the annealing.

  17. High temperature magnetism and microstructure of ferromagnetic alloy Si1-x Mn x

    Science.gov (United States)

    Aronzon, B. A.; Davydov, A. B.; Vasiliev, A. L.; Perov, N. S.; Novodvorsky, O. A.; Parshina, L. S.; Presniakov, M. Yu; Lahderanta, E.

    2017-02-01

    The results of a detailed study of magnetic properties and of the microstructure of SiMn films with a small deviation from stoichiometry are presented. The aim was to reveal the origin of the high temperature ferromagnetic ordering in such compounds. Unlike SiMn single crystals with the Curie temperature ~30 K, considered Si1-x Mn x compounds with x  =  0.5  +Δx and Δx in the range of 0.01-0.02 demonstrate a ferromagnetic state above room temperature. Such a ferromagnetic state can be explained by the existence of highly defective B20 SiMn nanocrystallites. These defects are Si vacancies, which are suggested to possess magnetic moments. The nanocrystallites interact with each other through paramagnons (magnetic fluctuations) inside a weakly magnetic manganese silicide matrix giving rise to a long range ferromagnetic percolation cluster. The studied structures with a higher value of Δx  ≈  0.05 contained three different magnetic phases: (a)—the low temperature ferromagnetic phase related to SiMn; (b)—the above mentioned high temperature phase with Curie temperature in the range of 200-300 K depending on the growth history and (c)—superparamagnetic phase formed by separated noninteracting SiMn nanocrystallites.

  18. Size dependence of Peltier cooling in ferromagnet/Au nanopillars

    Science.gov (United States)

    Bosu, Subrojati; Sakuraba, Yuya; Kubota, Takahide; Juarez-Acosta, Isaac; Sugiyama, Tomoko; Saito, Kesami; Olivares-Robles, Miguel A.; Takahashi, Saburo; Bauer, Gerrit E. W.; Takanashi, Koki

    2015-08-01

    We study Peltier cooling in current-perpendicular-to-plane multilayer nanopillars with diameters D varying from 60 to 430 nm and made from Au and various ferromagnets (FMs): Heusler compounds Co2MnSi and Co2FeSi (CFS) and conventional FM metals Fe and Co. We report an enhanced effective Peltier coefficient ΠCPP in resistance-current curves at small D (Peltier coefficient Πbulk (˜7 mV) and corresponds to a high cooling power of 43.6 MW/cm2.

  19. Half-metallic ferromagnetism induced by dynamic electron correlations in VAs

    NARCIS (Netherlands)

    Chioncel, L.; Mavropoulos, P.; Lezaic, M.; Bluegel, S.; Arrigoni, E.; Katsnelson, M.I.; Lichtenstein, A.I.

    2006-01-01

    The electronic structure of the VAs compound in the zinc-blende structure is investigated using a combined density-functional and dynamical mean-field theory approach. Contrary to predictions of a ferromagnetic semiconducting ground state obtained by density-functional calculations, dynamical

  20. Weak itinerant ferromagnetism in Heusler-type Fe2VAl0.95

    NARCIS (Netherlands)

    Sato, K.; Naka, T.; Taguchi, M.; Nakane, T.; Ishikawa, F.; Yamada, Y.; Takaesu, Y.; Nakama, T.; de Visser, A.; Matsushita, A.

    2010-01-01

    We report measurements of the magnetic, transport, and thermal properties of the Heusler-type compound Fe2VAl0.95. We show that while stoichiometric Fe2VAl is a nonmagnetic semimetal a 5% substitution on the Al site with the 3d elements Fe and V atoms leads to a ferromagnetic ground state with a

  1. Enhanced exchange in the itinerant ferromagnet UFe2

    DEFF Research Database (Denmark)

    Paolasini, L.; Lander, G.H.; Shapiro, S.M.

    1996-01-01

    Neutron inelastic-scattering experiments on the itinerant ferromagnet UFe2 have shown that the strong hybridization between the U 5 (f) under bar and Fe 3 (d) under bar electrons results in a number of major changes compared to the physics of the isostructural RFe(2) (R = Tb, Ho, and Er) compound...

  2. Nearly ferromagnetic Fermi-liquid behaviour in YFe2Zn20 and high-temperature ferromagnetism of GdFe2Zn20

    Science.gov (United States)

    Jia, S.; Bud'Ko, S. L.; Samolyuk, G. D.; Canfield, P. C.

    2007-05-01

    One of the historic goals of alchemy was to turn base elements into precious ones. Although the practice of alchemy has been superseded by chemistry and solid-state physics, the desire to dramatically change or tune the properties of a compound, preferably through small changes in stoichiometry or composition, remains. This desire becomes even more compelling for compounds that can be tuned to extremes in behaviour. Here, we report that the RT2Zn20 (R=rare earth and T=transition metal) family of compounds manifests exactly this type of versatility, even though they are more than 85% Zn. By tuning T, we find that YFe2Zn20 is closer to ferromagnetism than elemental Pd, the classic example of a nearly ferromagnetic Fermi liquid. By submerging Gd in this highly polarizable Fermi liquid, we tune the system to a remarkably high-temperature ferromagnetic (TC=86K) state for a compound with less than 5% Gd. Although this is not quite turning lead into gold, it is essentially tuning Zn to become a variety of model compounds.

  3. Vortex state in ferromagnetic nanoparticles

    Science.gov (United States)

    Betto, Davide; Coey, J. M. D.

    2014-05-01

    The evolution of the magnetic state of a soft ferromagnetic nanoparticle with its size is usually thought to be from superparamagnetic single domain to blocked single domain to a blocked multidomain structure. Néel pointed out that a vortex configuration produces practically no stray field at the cost of an increase in the exchange energy, of the order of RJS2lnR /c, where JS2 is the bond energy, R is the particle radius, and c is of the order of the exchange length. A vortex structure is energetically cheaper than single domain when the radius is greater than a certain value. The correct sequence should include a vortex configuration between the single domain and the multidomain states. The critical size is calculated for spherical particles of four important materials (nickel, magnetite, permalloy, and iron) both numerically and analytically. A vortex state is favored in materials with high magnetisation.

  4. Persistent currents in ferromagnetic condensates

    Science.gov (United States)

    Lamacraft, Austen

    2017-06-01

    Persistent currents in Bose condensates with a scalar order parameter are stabilized by the topology of the order parameter manifold. In condensates with multicomponent order parameters it is topologically possible for supercurrents to "unwind" without leaving the manifold. We study the energetics of this process in the case of ferromagnetic condensates using a long wavelength energy functional that includes both the superfluid and spin stiffnesses. Exploiting analogies to an elastic rod and rigid body motion, we show that the current carrying state in a 1D ring geometry transitions between a spin helix in the energy minima and a solitonlike configuration at the maxima. The relevance to recent experiments in ultracold atoms is briefly discussed.

  5. Magnetization of Coupled Ultrathin Ferromagnetic Films

    Institute of Scientific and Technical Information of China (English)

    WANG Huai-Yu; ZHOU Yun-Song; WANG Chong-Yu

    2002-01-01

    The magnetization of coupled ferromagnetic films is calculated by Green's function method. The coupling can either be ferromagnetic or antiferromagnetic. For the latter case, a concept of pseudo-spin is suggested to make calculation possible. A pseudo-spin is actually an anti-spin with its properties being analogue to other known anti particles such as a hole. The decreasing of Curie point as the coupling strength decays is computed. It is noted that with the same strength, antiferromagnetic coupling has higher Curie point than ferromagnetic coupling.

  6. Magnetic excitations in ferromagnetic phase of MnP

    Energy Technology Data Exchange (ETDEWEB)

    Yano, Shin-ichiro [Department of Physics and Mathematics, Aoyama Gakuin University, Sagamihara 229-8558 (Japan); Itoh, Shinichi, E-mail: shinichi.itoh@kek.jp [Neutron Science Division, Institute of Materials Structure Science, High Energy Accelerator Research Organization, Tsukuba 305-0801 (Japan); Yokoo, Tetsuya; Satoh, Setsuo [Neutron Science Division, Institute of Materials Structure Science, High Energy Accelerator Research Organization, Tsukuba 305-0801 (Japan); Kawana, Daichi [Condensed Matter Research Center, Institute of Materials Structure Science, High Energy Accelerator Research Organization, Tsukuba 305-0801 (Japan); Kousaka, Yusuke; Akimitsu, Jun [Department of Physics and Mathematics, Aoyama Gakuin University, Sagamihara 229-8558 (Japan); Endoh, Yasuo [Neutron Science Division, Institute of Materials Structure Science, High Energy Accelerator Research Organization, Tsukuba 305-0801 (Japan); Institute for Materials Research, Tohoku University, Sendai 980-8577 (Japan)

    2013-12-15

    Inelastic neutron scattering experiments were performed on an intermetallic compound, MnP. We used a newly developed High Resolution Chopper Spectrometer, HRC, for energy transfers E≤75meV, besides various triple axis spectrometers; LTAS for energy transfers E≤2meV, TOPAN for E≤7.5meV and TAS-1 for E≤35meV. Spin wave excitations were observed in the ferromagnetic phase of MnP in the entire Brillouin zone along the a{sup ⁎}- and b{sup ⁎}-axes. The zone boundary energies of spin waves were determined to be around 60 meV along the a{sup ⁎}-axis and around 75 meV along the b{sup ⁎}-axis, and the dispersion relations showed two branches for both axes. The observed dispersion relations of spin waves were well described by an isotropic Heisenberg interaction adding a single ion anisotropy with two sub-lattices. - Highlights: • Inelastic neutron scattering experiments were performed mainly using pulsed neutrons. • Spin waves were observed in the ferromagnetic phase of an intermetallic compound MnP. • The dispersion relations were determined entirely along the a{sup ⁎}- and b{sup ⁎}-axes. • We could describe the observed dispersion relations by a two sub-lattice model.

  7. Assembling non-ferromagnetic materials to ferromagnetic architectures using metal-semiconductor interfaces

    Science.gov (United States)

    Ma, Ji; Liu, Chunting; Chen, Kezheng

    2016-01-01

    In this work, a facile and versatile solution route was used to fabricate room-temperature ferromagnetic fish bone-like, pteridophyte-like, poplar flower-like, cotton-like Cu@Cu2O architectures and golfball-like Cu@ZnO architecture. The ferromagnetic origins in these architectures were found to be around metal-semiconductor interfaces and defects, and the root cause for their ferromagnetism lay in charge transfer processes from metal Cu to semiconductors Cu2O and ZnO. Owing to different metallization at their interfaces, these architectures exhibited different ferromagnetic behaviors, including coercivity, saturation magnetization as well as magnetic interactions. PMID:27680286

  8. High-temperature ferromagnetism in heavily Fe-doped ferromagnetic semiconductor (Ga,Fe)Sb

    Energy Technology Data Exchange (ETDEWEB)

    Tu, Nguyen Thanh [Department of Electrical Engineering and Information Systems, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-8656 (Japan); Department of Physics, Ho Chi Minh City University of Pedagogy, 280, An Duong Vuong Street, District 5, Ho Chi Minh City 748242 (Viet Nam); Hai, Pham Nam [Department of Electrical Engineering and Information Systems, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-8656 (Japan); Department of Physical Electronics, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro, Tokyo 152-0033 (Japan); Center for Spintronics Research Network (CSRN), The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan); Anh, Le Duc [Department of Electrical Engineering and Information Systems, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-8656 (Japan); Tanaka, Masaaki [Department of Electrical Engineering and Information Systems, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-8656 (Japan); Center for Spintronics Research Network (CSRN), The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan)

    2016-05-09

    We show high-temperature ferromagnetism in heavily Fe-doped ferromagnetic semiconductor (Ga{sub 1−x},Fe{sub x})Sb (x = 23% and 25%) thin films grown by low-temperature molecular beam epitaxy. Magnetic circular dichroism spectroscopy and anomalous Hall effect measurements indicate intrinsic ferromagnetism of these samples. The Curie temperature reaches 300 K and 340 K for x = 23% and 25%, respectively, which are the highest values reported so far in intrinsic III-V ferromagnetic semiconductors.

  9. Explanation of ferromagnetism origin in N-doped ZnO by first-principle calculations

    Indian Academy of Sciences (India)

    A El Amiri; H Lassri; E K Hlil; M Abid

    2016-02-01

    By $ab-initio$ calculations, the possible source of ferromagnetism in N-doped ZnO compound was systematically studied. The electronic structure and magnetic properties of N-doped ZnO with/without ZnO host and N defects were investigated using the Korringa–Kohn–Rostoker method combined with coherent potential approximation. It was shown that Zn vacancy and the presence of N defects (substitutional, interstitial or combination of both) induce the ferromagnetism in N-doped ZnO. From density of state analysis, it was shown that p–p interaction between 2p-elements (N,O) is the mechanism of ferromagnetic coupling in N-doped ZnO.

  10. Conserved momenta of a ferromagnetic soliton

    Energy Technology Data Exchange (ETDEWEB)

    Tchernyshyov, Oleg, E-mail: olegt@jhu.edu

    2015-12-15

    Linear and angular momenta of a soliton in a ferromagnet are commonly derived through the application of Noether’s theorem. We show that these quantities exhibit unphysical behavior: they depend on the choice of a gauge potential in the spin Lagrangian and can be made arbitrary. To resolve this problem, we exploit a similarity between the dynamics of a ferromagnetic soliton and that of a charged particle in a magnetic field. For the latter, canonical momentum is also gauge-dependent and thus unphysical; the physical momentum is the generator of magnetic translations, a symmetry combining physical translations with gauge transformations. We use this analogy to unambiguously define conserved momenta for ferromagnetic solitons. General considerations are illustrated on simple models of a domain wall in a ferromagnetic chain and of a vortex in a thin film.

  11. Modified Heisenberg Ferromagnet Model and Integrable Equation

    Institute of Scientific and Technical Information of China (English)

    2005-01-01

    We investigate some integrable modified Heisenberg ferromagnet models by using the prolongation structure theory. Through associating them with the motion of curve in Minkowski space, the corresponding coupled integrable equations are presented.

  12. Josephson tunnel junctions with ferromagnetic interlayer

    Energy Technology Data Exchange (ETDEWEB)

    Weides, M.P.

    2006-07-01

    Superconductivity and ferromagnetism are well-known physical properties of solid states that have been widely studied and long thought about as antagonistic phenomena due to difference in spin ordering. It turns out that the combination of both superconductor and ferromagnet leads to a very rich and interesting physics. One particular example, the phase oscillations of the superconducting order parameter inside the ferromagnet, will play a major role for the devices discussed in this work. In this thesis, I present Josephson junctions with a thin Al{sub 2}O{sub 3} tunnel barrier and a ferromagnetic interlayer, i.e. superconductor-insulator-ferromagnet-superconductor (SIFS) stacks. The fabrication of junctions was optimized regarding the insulation of electrodes and the homogeneity of the current transport. The junctions were either in the 0 or {pi} coupled ground state, depending on the thickness of the ferromagnetic layer and on temperature. The influence of ferromagnetic layer thickness on the transport properties and the coupling (0, {pi}) of SIFS tunnel junctions was studied. Furthermore, using a stepped ferromagnetic layer with well-chosen thicknesses, I obtained the so-called 0-{pi} Josephson junction. At a certain temperature this 0-{pi} junction can be made perfectly symmetric. In this case the ground state corresponds to a vortex of supercurrent creating a magnetic flux which is a fraction of the magnetic flux quantum {phi}{sub 0}. Such structures allow to study the physics of fractional vortices and to build various electronic circuits based on them. The SIFS junctions presented here have an exponentially vanishing damping at T {yields} 0. The SIFS technology developed within the framework of this work may be used to construct classical and quantum devices such as oscillators, memory cells and qubits. (orig.)

  13. First-principles calculations on the origin of ferromagnetism in transition-metal doped Ge

    Science.gov (United States)

    Shinya, Hikari; Fukushima, Tetsuya; Masago, Akira; Sato, Kazunori; Katayama-Yoshida, Hiroshi

    2017-09-01

    Many researchers have shown an interest in Ge-based dilute magnetic semiconductors (DMSs) due to potential advantages for semiconductor spintronics applications. There has been great discussion about mechanisms of experimentally observed ferromagnetism in (Ge,Fe) and (Ge,Mn). We investigate the electronic structures, structural stabilities, magnetic exchange coupling constants, and Curie temperature of Ge-based DMSs, and clarify origins of the ferromagnetism, on the basis of density functional theory calculations. In both the (Ge,Fe) and (Ge,Mn) cases, the inhomogeneous distribution of the magnetic impurities plays an important role to determine the magnetic states; however, physical mechanisms of the ferromagnetism in these two materials are completely different. By the spinodal nanodecomposition, the Fe impurities in Ge gather together with keeping the diamond structure, so that the number of the first-nearest-neighbor Fe pairs with strong ferromagnetic interaction increases. Therefore, the Curie temperature drastically increases with the progress of the annealing. Our cluster expansion method clearly reveals that the other ordered compounds with different crystal structures such as Ge3Mn5 and Ge8Mn11 are easily generated in the (Ge,Mn) system. The estimated Curie temperature of Ge3Mn5 is in agreement with the observed Curie temperature in experiments. It should be considered that the precipitation of the ferromagnetic Ge3Mn5 clusters is an origin of high Curie temperature in (Ge,Mn).

  14. Low-Temperature Properties of Quasi-One-Dimensional Molecule-Based Ferromagnets

    Science.gov (United States)

    Nakanishi, Takashi; Yamamoto, Shoji; Sakai, Tôru

    2001-05-01

    Quantum and thermal behaviors of low-dimensional mixed-spin systems are investigated with particular emphasis on the design of molecule-based ferromagnets. One can obtain a molecular ferromagnet by assembling molecular bricks so as to construct a low-dimensional system with a magnetic ground state and then coupling the chains or the layers again in a ferromagnetic fashion. Two of thus-constructed quasi-one-dimensional bimetallic compounds are qualitatively viewed within the spin-wave treatment, one of which successfully grows into a bulk magnet, while the other of which ends in a singlet ground state. Then, concentrating on the ferrimagnetic arrangement on a two-leg ladder which is well indicative of general coupled-chain ferrimagnets, we develop the spin-wave theory and fully reveal its low-energy structure. We inquire further into the ferromagnetic aspect of the ferrimagnetic ladder numerically calculating the sublattice magnetization and the magnetic susceptibility. There exists a moderate coupling strength between the chains in order to obtain the most ferromagnetic ferrimagnet.

  15. FMR Study of the Field Dependence of the Ferromagnetic Transition in an Organic Magnet

    Science.gov (United States)

    Kovalev, Alexey; Winter, Stephen; Hill, Stephen; Oakley, Richard

    2012-02-01

    Organic heterocyclic thia/selenazyl radicals have unique magnetic properties. First and foremost, in their crystalline form, they experience a transition to a ferromagnetic state at temperatures that are the highest for any material containing only non-metallic elements. Second, their low temperature uniaxial anisotropy field is the highest among purely organic ferromagnets [Winter et al., JACS 133, 8126 (2011)]. To investigate the effect of a magnetic field on the transition in the mixed Se-S compound (Tc= 12.5 K) at zero field, we employ ferromagnetic resonance (FMR) absorption as a measure of the anisotropy field for a single crystal. We also focus on the temperature and field dependence of the FMR linewidth. Our main finding is that the application of a field significantly broadens the ferromagnetic transition, with a noticeable FMR signal observed to as high as 2Tc in fields of a few tesla. Meanwhile, the FMR linewidth is relatively insensitive to frequency/field, though it becomes narrower upon decreasing the temperature and saturates below Tc. We will discuss the broadening of the ferromagnetic transition within the framework of scaling theory.

  16. Resonance frequency in ferromagnetic superlattices

    Energy Technology Data Exchange (ETDEWEB)

    Qiu Rongke; Huang Andong [School of Science, Shenyang University of Technology, Shenyang 110870 (China); Li Da; Zhang Zhidong, E-mail: rkqiu@163.com [Shenyang National Laboratory for Materials Science, Institute of Metal Research and International Centre for Materials Physics, Chinese Academy of Sciences, Shenyang 110016 (China)

    2011-10-19

    The resonance frequency in two-layer and three-layer ferromagnetic superlattices is studied, using the Callen's Green function method, the Tyablikov decoupling approximation and the Anderson-Callen decoupling approximation. The effects of interlayer exchange coupling, anisotropy, external magnetic field and temperature on the resonance frequency are investigated. It is found that the resonance frequencies increase with increasing external magnetic field. In a parameter region of the asymmetric system, each sublayer corresponds to its own resonance frequency. The anisotropy of a sublayer affects only the resonance frequency corresponding to this sublayer. The stronger the anisotropy, the higher is the resonance frequency. The interlayer exchange coupling affects only the resonance frequencies belonging to the sublayers connected by it. The stronger the interlayer exchange coupling, the higher are the resonance frequencies. All the resonance frequencies decrease as the reduced temperature increases. The results direct the method to enhance and adjust the resonance frequency of magnetic multilayered materials with a wide band.

  17. Richard L. Greene Dissertation Award in Experimental Condensed Matter or Materials Physics Talk: Ferromagnetic quantum criticality in YbNi4 P2

    Science.gov (United States)

    Steppke, Alexander

    In a number of strongly correlated electron systems quantum phase transitions can be observed by the suppression of antiferromagnetic order. In contrast the prototypical continuous quantum phase transition of a metallic ferromagnet is often preempted by a first-order transition or a superconducting state. We show that the Kondo lattice system YbNi4P2 exhibits a ferromagnetically ordered phase with a very low Curie temperature of 0.15K. The compound can be tuned to a ferromagnetic quantum critical point by substitution of phosphorus by arsenic. With thermodynamic studies of specific heat, ac susceptibility and thermal expansion we show strong evidence for the ferromagnetic order and the quantum criticality in the YbNi4(P 1-x As x)2 doping series and the existence of a ferromagnetic quantum critical point at zero applied field for small substitutions.

  18. Electronic structure of half-metallic ferromagnets and spinel ferromagnetic insulators

    Energy Technology Data Exchange (ETDEWEB)

    Szotek, Z [Daresbury Laboratory, Daresbury, Warrington WA4 4AD, Cheshire (United Kingdom); Temmerman, W M [Daresbury Laboratory, Daresbury, Warrington WA4 4AD, Cheshire (United Kingdom); Svane, A [Institute of Physics and Astronomy, University of Aarhus, DK-8000 Aarhus C (Denmark); Petit, L [Computer Science and Mathematics Division, and Center for Computational Sciences, Oak Ridge National Laboratory, Oak Ridge, TN 37831 (United States); Strange, P [School of Chemistry and Physics, Keele University, Staffordshire ST5 5BG (United Kingdom); Stocks, G M [Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, TN 37830 (United States); Koedderitzsch, D [Fachbereich Physik, Martin-Luther-Universitaet Halle-Wittenberg, Friedemann-Bach-Platz 6, D-06099 Halle (Germany); Hergert, W [Fachbereich Physik, Martin-Luther-Universitaet Halle-Wittenberg, Friedemann-Bach-Platz 6, D-06099 Halle (Germany); Winter, H [INFP, Forschungszentrum Karlsruhe GmbH, Postfach 3640, D-76021 Karlsruhe (Germany)

    2004-12-08

    We discuss an application of the self-interaction-corrected local spin density (SIC-LSD) approximation to study electronic structure of some half-metallic ferromagnets and ferromagnetic insulators of current interest in spintronics. Both d- and f-electron materials are considered, and we concentrate on the nominal valence and ground state properties of these systems.

  19. Current Induced Heat Generation in Ferromagnet-Quantum Dot-Ferromagnet System

    Directory of Open Access Journals (Sweden)

    Lili Zhao

    2015-06-01

    Full Text Available We study the heat generation in ferromagnet-quantum dot-ferromagnet system by the non-equilibrium Green’s functions method. Heat generation under the influence of ferromagnet leads is very different compared with a system with normal metal leads. The significant effects in heat generation are caused by the polarization angle θ associated with the orientation of polarized magnetic moment of electron in the ferromagnetic terminals. From the study of heat generation versus source drain bias (Q-eV curves, we find that the heat generation decreases as θ increases from 0 to 0.7π. The heat generation versus gate voltage (Q-eVg curves also display interesting behavior with increasing polarization angle θ. Meanwhile, heat generation is influenced by the relative angle θ of magnetic moment in the ferromagnetic leads. These results will provide theories to this quantum dot system as a new material of spintronics.

  20. Coexistence of charge and ferromagnetic order in fcc Fe.

    Science.gov (United States)

    Hsu, Pin-Jui; Kügel, Jens; Kemmer, Jeannette; Parisen Toldin, Francesco; Mauerer, Tobias; Vogt, Matthias; Assaad, Fakher; Bode, Matthias

    2016-03-14

    Phase coexistence phenomena have been intensively studied in strongly correlated materials where several ordered states simultaneously occur or compete. Material properties critically depend on external parameters and boundary conditions, where tiny changes result in qualitatively different ground states. However, up to date, phase coexistence phenomena have exclusively been reported for complex compounds composed of multiple elements. Here we show that charge- and magnetically ordered states coexist in double-layer Fe/Rh(001). Scanning tunnelling microscopy and spectroscopy measurements reveal periodic charge-order stripes below a temperature of 130 K. Close to liquid helium temperature, they are superimposed by ferromagnetic domains as observed by spin-polarized scanning tunnelling microscopy. Temperature-dependent measurements reveal a pronounced cross-talk between charge and spin order at the ferromagnetic ordering temperature about 70 K, which is successfully modelled within an effective Ginzburg-Landau ansatz including sixth-order terms. Our results show that subtle balance between structural modifications can lead to competing ordering phenomena.

  1. Phenomenological description of anisotropy effects in some ferromagnetic superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Shopova, Diana V., E-mail: sho@issp.bas.bg [TCCM Research Group, Institute of Solid State Physics, Bulgarian Academy of Sciences, BG-1784 Sofia (Bulgaria); Todorov, Michail D. [Department of Applied Mathematics and Computer Science, Technical University of Sofia, 1000 Sofia (Bulgaria)

    2015-07-03

    We study phenomenologically the role of anisotropy in ferromagnetic superconductors UGe{sub 2}, URhGe, and UCoGe for the description of their phase diagrams. We use the Ginzburg–Landau free energy in its uniform form as we will consider only spatially independent solutions. This is an expansion of previously derived results where the effect of Cooper-pair and crystal anisotropies is not taken into account. The three compounds are separately discussed with the special stress on UGe{sub 2}. The main effect comes from the strong uniaxial anisotropy of magnetization while the anisotropy of Cooper pairs and crystal anisotropy only slightly change the phase diagram in the vicinity of Curie temperature. The limitations of this approach are also discussed. - Highlights: • Anisotropic Landau energy for description of ferromagnetic superconductors is proposed. • Meissner phases are described with their existence and stability conditions. • The application of the model to UGe{sub 2} is discussed. • The limitations to apply the model for description of experimental data are explained.

  2. Peculiar properties of the ferromagnetic superconductor Eu(Fe0.91Rh0.09)2As2

    Science.gov (United States)

    Jiao, Wen-He; Liu, Yi; Tang, Zhang-Tu; Li, Yu-Ke; Xu, Xiao-Feng; Ren, Zhi; Xu, Zhu-An; Cao, Guang-Han

    2017-02-01

    Large single crystals of optimally doped Eu(Fe0.91Rh0.09)2As2 were grown by the self-flux method. Resistivity and magnetization measurements show that the compound undergoes a superconducting transition at 19.6 K, followed by a ferromagnetic ordering of the Eu2+ moments at 16.8 K. The upper critical fields at zero temperature are estimated to be 12.5 T and 15.1 T for fields along the ab plane and the c-axis, respectively. Moreover, anisotropy reversal of the upper critical field is observed near the magnetic ordering temperature, which may be related to the anisotropic magnetization of Eu ions and the demagnetization effect. Both ferromagnetic and superconducting features are displayed by the magnetic susceptibility and peculiar isothermal magnetization loop. Our combined results unambiguously demonstrate the coexistence of ferromagnetism and superconductivity in the title compound.

  3. Tunable magnon Weyl points in ferromagnetic pyrochlores

    CERN Document Server

    Mook, Alexander; Mertig, Ingrid

    2016-01-01

    The dispersion relations of magnons in ferromagnetic pyrochlores with Dzyaloshinskii-Moriya interaction is shown to possess Weyl points, i.\\,e., pairs of topological nontrivial crossings of two magnon branches with opposite topological charge. As a consequence of their topological nature, their projections onto a surface are connected by magnon arcs, thereby resembling closely Fermi arcs of electronic Weyl semimetals. On top of this, the positions of the Weyl points in reciprocal space can be tuned widely by an external magnetic field: rotated within the surface plane, the Weyl points and magnon arcs are rotated as well; tilting the magnetic field out-of-plane shifts the Weyl points toward the center $\\bar{\\Gamma}$ of the surface Brillouin zone. The theory is valid for the class of ferromagnetic pyrochlores, i.\\,e., three-dimensional extensions of topological magnon insulators on kagome lattices. In this Letter, we focus on the $(111)$ surface, identify candidates of established ferromagnetic pyrochlores whic...

  4. Ferromagnetism of polythiophene-capped Au nanoparticles

    Science.gov (United States)

    Suzuki, K.; Zhang, H.; Saito, K.; Garitaonandia, J. S.; Goikolea, E.; Insausti, M.

    2011-04-01

    The magnetic and electrical transport properties of regioregular poly(3-hexylthiophene)-capped Au nanoparticles (NPs) doped with iodine have been investigated to clarify the effectiveness of conductive polymer capping on the induction of ferromagnetism in Au. The room-temperature magnetization curve of the undoped polythiophene-capped Au NPs exhibits a clear hysteresis behavior with a coercive force of 160 Oe. The spontaneous magnetization normalized by the mass of Au is 2.0 × 10-2 emu/g. The spontaneous magnetization was found virtually unaffected by iodine doping, whereas the electrical conductivity is enhanced dramatically to ˜10 S/cm. Our results show that polythiophene capping could lead to spontaneous magnetic polarization in Au NPs, and the conductivity of the polymer capping does not affect the ferromagnetism of the Au nanoparticles, opening a possibility for further investigation into the magnetotransport behavior of ferromagnetic Au NPs.

  5. Rapidly solidified ferromagnetic shape memory alloys

    Science.gov (United States)

    Craciunescu, C. M.; Ercuta, A.; Mitelea, I.; Valeanu, M.; Teodorescu, V. S.; Lupu, N.; Chiriac, H.

    2008-05-01

    Ferromagnetic shape memory alloys have been manufactured by various techniques involving rapid solidification. Bulk alloys have been obtained by extracting the melted alloy in especially designed copper molds; glass coated wires have been obtained by drawing the melt from glass recipients followed by water cooling and ribbons have been fabricated by melt-spinning. Microstructural observations show particular solidification aspects of fractured areas, while ferromagnetic behavior has been detected in glass coated wires obtained by rapid solidification. The martensitic microstructure was observed on Co-Ni-Ga rapid solidified bulk alloys and Fe-Pd ribbons. The memory effect was detected using a Vibran system that allows the detection of the phase transition for the ribbons and by visual observation for other specimens. The conclusions of the observations are related to the comparison between the ferromagnetic behaviors of shape memory alloys solidified using different techniques.

  6. Simple and advanced ferromagnet/molecule spinterfaces

    Science.gov (United States)

    Gruber, M.; Ibrahim, F.; Djedhloul, F.; Barraud, C.; Garreau, G.; Boukari, S.; Isshiki, H.; Joly, L.; Urbain, E.; Peter, M.; Studniarek, M.; Da Costa, V.; Jabbar, H.; Bulou, H.; Davesne, V.; Halisdemir, U.; Chen, J.; Xenioti, D.; Arabski, J.; Bouzehouane, K.; Deranlot, C.; Fusil, S.; Otero, E.; Choueikani, F.; Chen, K.; Ohresser, P.; Bertran, F.; Le Fèvre, P.; Taleb-Ibrahimi, A.; Wulfhekel, W.; Hajjar-Garreau, S.; Wetzel, P.; Seneor, P.; Mattana, R.; Petroff, F.; Scheurer, F.; Weber, W.; Alouani, M.; Beaurepaire, E.; Bowen, M.

    2016-10-01

    Spin-polarized charge transfer between a ferromagnet and a molecule can promote molecular ferromagnetism 1, 2 and hybridized interfacial states3, 4. Observations of high spin-polarization of Fermi level states at room temperature5 designate such interfaces as a very promising candidate toward achieving a highly spin-polarized, nanoscale current source at room temperature, when compared to other solutions such as half-metallic systems and solid-state tunnelling over the past decades. We will discuss three aspects of this research. 1) Does the ferromagnet/molecule interface, also called an organic spinterface, exhibit this high spin-polarization as a generic feature? Spin-polarized photoemission experiments reveal that a high spin-polarization of electronics states at the Fermi level also exist at the simple interface between ferromagnetic cobalt and amorphous carbon6. Furthermore, this effect is general to an array of ferromagnetic and molecular candidates7. 2) Integrating molecules with intrinsic properties (e.g. spin crossover molecules) into a spinterface toward enhanced functionality requires lowering the charge transfer onto the molecule8 while magnetizing it1,2. We propose to achieve this by utilizing interlayer exchange coupling within a more advanced organic spinterface architecture. We present results at room temperature across the fcc Co(001)/Cu/manganese phthalocyanine (MnPc) system9. 3) Finally, we discuss how the Co/MnPc spinterface's ferromagnetism stabilizes antiferromagnetic ordering at room temperature onto subsequent molecules away from the spinterface, which in turn can exchange bias the Co layer at low temperature10. Consequences include tunnelling anisotropic magnetoresistance across a CoPc tunnel barrier11. This augurs new possibilities to transmit spin information across organic semiconductors using spin flip excitations12.

  7. Ferromagnetism in an Itinerant Electron Cluster

    Institute of Scientific and Technical Information of China (English)

    LIGang; TIANGuang-Shan

    2005-01-01

    In the present paper, we study the existence of metallic ferromagnetism in a cluster of nanometer scale,which is described by the Hubbard model defined on a complete graph. Therefore, the system is highly frustrated with respect to electron hopping. By solving the model exactly, we show that its ground state is fully spin-polarized at half-rilling, even if the Coulomb interaction is finite. This conclusion is in sharp contrast to the well-known result for the Hubbard model on a bipartite lattice. As a result, our exact solution strongly suggests that frustration may play an important role in causing metallic ferromagnetism.

  8. Ferromagnetism in an Itinerant Electron Cluster

    Institute of Scientific and Technical Information of China (English)

    LI Gang; TIAN Guang-Shan

    2005-01-01

    In the present paper, we study the existence of metallic ferromagnetism in a cluster of nanometer scale,which is described by the Hubbard model defined on a complete graph. Therefore, the system is highly frustrated with respect to electron hopping. By solving the model exactly, we show that its ground state is fully spin-polarized at half-filling, even if the Coulomb interaction is finite. This conclusion is in sharp contrast to the well-known result for the Hubbard model on a bipartite lattice. As a result, our exact solution strongly suggests that frustration may play an important role in causing metallic ferromagnetism.

  9. Cosmic Neutrino Background as a Ferromagnet

    CERN Document Server

    Arias, Paola; Lopez-Sarrion, Justo

    2013-01-01

    If cosmic background neutrinos interact very weakly with each other, through spin-spin interactions, then they may have experienced a phase transition, leading to a ferromagnetic ordering. The small magnetic field resulting from ferromagnetic ordering -- if present before galaxy formation -- could act as a primordial seed of the magnetic fields observed in several galaxies. Our findings suggest that the magnetization could occur in the right epoch, if the exchange gauge boson of neutrino-neutrino interaction is a massless boson beyond the Standard Model, with a coupling constant of $2.2\\times 10^{-13} \\left(\\frac{m_\

  10. Wellhead with non-ferromagnetic materials

    Energy Technology Data Exchange (ETDEWEB)

    Hinson, Richard A [Houston, TX; Vinegar, Harold J [Bellaire, TX

    2009-05-19

    Wellheads for coupling to a heater located in a wellbore in a subsurface formation are described herein. At least one wellhead may include a heater located in a wellbore in a subsurface formation; and a wellhead coupled to the heater. The wellhead may be configured to electrically couple the heater to one or more surface electrical components. The wellhead may include at least one non-ferromagnetic material such that ferromagnetic effects are inhibited in the wellhead. Systems and methods for using such wellheads for treating a subsurface formation are described herein.

  11. More on generalized Heisenberg ferromagnet models

    CERN Document Server

    Oh, P; Oh, Phillial; Park, Q Han

    1996-01-01

    We generalize the integrable Heisenberg ferromagnet model according to each Hermitian symmetric spaces and address various new aspects of the generalized model. Using the first order formalism of generalized spins which are defined on the coadjoint orbits of arbitrary groups, we construct a Lagrangian of the generalized model from which we obtain the Hamiltonian structure explicitly in the case of CP(N-1) orbit. The gauge equivalence between the generalized Heisenberg ferromagnet and the nonlinear Schr\\"{o}dinger models is given. Using the equivalence, we find infinitely many conserved integrals of both models.

  12. Three dimensional dynamics of ferromagnetic swimmer

    Energy Technology Data Exchange (ETDEWEB)

    Erglis, K.; Livanovics, R. [Department of Physics, University of Latvia, Zellu 8, Ri-bar ga LV-1002 (Latvia); Cebers, A., E-mail: aceb@tesla.sal.l [Department of Physics, University of Latvia, Zellu 8, Ri-bar ga LV-1002 (Latvia)

    2011-05-15

    It is shown that a flexible ferromagnetic filament self-propels perpendicularly to the AC magnetic field during a limited period of time due to the instability of the planar motion with respect to three dimensional perturbations. The transition from the oscillating U-like shapes to the oscillating S-like shapes is characterized by the calculated Wr number. - Research Highlights: A ferromagnetic filament self-propels perpendicularly to the AC field. During the self-propulsion cycle the filament moves both forward and backward. The self-propulsion stops due to the three dimensional instability. The mechanism of the self-propulsion is similar to that used by some microorganisms.

  13. Vortex dynamics in ferromagnetic/superconducting bilayers

    Energy Technology Data Exchange (ETDEWEB)

    Cieplak, M.Z.; Adamus, Z. [Polish Acad Sci, Inst Phys, PL-02668 Warsaw, (Poland); Konczykowski, M. [CEA, DSM, DRECAM, Lab Solides Irradies, Ecole Polytechnique, CNRS-UMR 7642, F-91128 Palaiseau (France); Zhu, L.Y.; Chien, C.L. [Johns Hopkins Univ, Dept Phys and Astron, Baltimore, MD 21218 (United States)

    2008-07-01

    The dependence of vortex dynamics on the geometry of magnetic domain pattern is studied in the superconducting/ferromagnetic bilayers, in which niobium is a superconductor, and Co/Pt multilayer with perpendicular magnetic anisotropy serves as a ferromagnetic layer. Magnetic domain patterns with different density of domains per surface area and different domain size, w, are obtained for Co/Pt with different thickness of Pt. The dense patterns of domains with the size comparable to the magnetic penetration depth (w {>=} {lambda}) produce large vortex pinning and smooth vortex penetration, while less dense patterns with larger domains (w {>=}{>=} {lambda}) enhance pinning less effectively and result in flux jumps during flux motion. (authors)

  14. Itinerant Ferromagnetism in Ultracold Fermi Gases

    DEFF Research Database (Denmark)

    Heiselberg, Henning

    2012-01-01

    Itinerant ferromagnetism in cold Fermi gases with repulsive interactions is studied applying the Jastrow-Slater approximation generalized to finite polarization and temperature. For two components at zero temperature a second order transition is found at akF ≃ 0.90 compatible with QMC. Thermodyna......Itinerant ferromagnetism in cold Fermi gases with repulsive interactions is studied applying the Jastrow-Slater approximation generalized to finite polarization and temperature. For two components at zero temperature a second order transition is found at akF ≃ 0.90 compatible with QMC...

  15. Fabrication of high quality ferromagnetic Josephson junctions

    Energy Technology Data Exchange (ETDEWEB)

    Weides, M. [Institute for Solid State Research, Research Centre Juelich, D-52425 Juelich (Germany) and CNI-Center of Nanoelectronic Systems for Information Technology, Research Centre Juelich, D-52425 Juelich (Germany)]. E-mail: m.weides@fz-juelich.de; Tillmann, K. [Institute for Solid State Research, Research Centre Juelich, D-52425 Juelich (Germany); Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons, Research Centre Juelich, D-52425 Juelich (Germany); Kohlstedt, H. [Institute for Solid State Research, Research Centre Juelich, D-52425 Juelich (Germany); CNI-Center of Nanoelectronic Systems for Information Technology, Research Centre Juelich, D-52425 Juelich (Germany); Department of Material Science and Engineering and Department of Physics, University of Berkeley, CA 94720 (United States)

    2006-05-15

    We present ferromagnetic Nb/Al{sub 2}O{sub 3}/Ni{sub 60}Cu{sub 40}/Nb Josephson junctions (SIFS) with an ultrathin Al{sub 2}O{sub 3} tunnel barrier. The junction fabrication was optimized regarding junction insulation and homogeneity of current transport. Using ion-beam-etching and anodic oxidation we defined and insulated the junction mesas. The additional 2 nm thin Cu-layer below the ferromagnetic NiCu (SINFS) lowered interface roughness and ensured very homogeneous current transport. A high yield of junctional devices with j {sub c} spreads less than 2% was obtained.

  16. Observation of weak ferromagnetism and the sizable magnetocaloric effect in Co2V2O7

    Science.gov (United States)

    Sannigrahi, J.; Giri, S.; Majumdar, S.

    2017-02-01

    The magnetic behavior of cobalt pyrovanadate compound Co2V2O7 with dichromate structure is reported. The compound undergoes long range magnetic ordering below TC=8 K and our study identifies the ground state to be a canted antiferromagnetic type with a weak ferromagnetic component. The transition at TC is found to be first-order in nature as evident from the presence of distinct thermal hysteresis in the temperature dependent magnetization data. Below TC, a significantly large value of magnetic relaxation is observed which is possibly due to the metastability associated with the first order phase transition. Interestingly, the sample exhibits a sizable magneto-caloric effect around TC (∼4.1 J kg-1. K-1 for 50 kOe of field change) which is reasonably high among antiferromagnetic transition metal oxides with weak ferromagnetism.

  17. Room Temperature Ferromagnetic, Anisotropic, Germanium Rich FeGe(001 Alloys

    Directory of Open Access Journals (Sweden)

    Cristian M. Teodorescu

    2013-02-01

    Full Text Available Ferromagnetic FexGe1−x with x = 2%–9% are obtained by Fe deposition onto Ge(001 at high temperatures (500 °C. Low energy electron diffraction (LEED investigation evidenced the preservation of the (1 × 1 surface structure of Ge(001 with Fe deposition. X-ray photoelectron spectroscopy (XPS at Ge 3d and Fe 2p core levels evidenced strong Fe diffusion into the Ge substrate and formation of Ge-rich compounds, from FeGe3 to approximately FeGe2, depending on the amount of Fe deposited. Room temperature magneto-optical Kerr effect (MOKE evidenced ferromagnetic ordering at room temperature, with about 0.1 Bohr magnetons per Fe atom, and also a clear uniaxial magnetic anisotropy with the in-plane  easy magnetization axis. This compound is a good candidate for promising applications in the field of semiconductor spintronics.

  18. Excitations and magnetization density distribution in the dilute ferromagnetic semiconductor Yb14MnSb11

    Science.gov (United States)

    Stone, M. B.; Garlea, V. O.; Gillon, B.; Cousson, A.; Christianson, A. D.; Lumsden, M. D.; Nagler, S. E.; Mandrus, D.; Sales, B. C.

    2017-01-01

    Yb14MnSb11 is a rare example of a Kondo lattice compound with ferromagnetic dominated RKKY interactions. As a ferromagnetic semiconductor with Tc≈53 K, it is also a potential compound for exploration of spintronic devices. Here we describe measurements which answer remaining questions regarding the energy scales of the exchange interactions, the valence, and the magnetization density distribution in this system. We find that the system consists of RKKY exchange coupled Mn2 + sites with nearest and next nearest exchange interactions dominating the magnetic spectrum with no significant magnetization density localized on other atomic sites. The extended spread of a negative magnetization around each of the Mn ions supports a Kondo screening cloud scenario for Yb14MnSb11 .

  19. Integrable Heisenberg Ferromagnet Equations with self-consistent potentials

    CERN Document Server

    Zhunussova, Zh Kh; Tungushbaeva, D I; Mamyrbekova, G K; Nugmanova, G N; Myrzakulov, R

    2013-01-01

    In this paper, we consider some integrable Heisenberg Ferromagnet Equations with self-consistent potentials. We study their Lax representations. In particular we give their equivalent counterparts which are nonlinear Schr\\"odinger type equations. We present the integrable reductions of the Heisenberg Ferromagnet Equations with self-consistent potentials. These integrable Heisenberg Ferromagnet Equations with self-consistent potentials describe nonlinear waves in ferromagnets with magnetic fields.

  20. Flexible ferromagnetic filaments and the interface with biology

    Energy Technology Data Exchange (ETDEWEB)

    Erglis, K.; Belovs, M. [University of Latvia, Zellu 8, Riga LV-1002 (Latvia); Cebers, A. [University of Latvia, Zellu 8, Riga LV-1002 (Latvia)], E-mail: aceb@tesla.sal.lv

    2009-04-15

    Flexible ferromagnetic filaments are studied both theoretically and experimentally. Two main deformation modes of the filament at magnetic field inversion are theoretically described and observed experimentally by using DNA-linked chains of ferromagnetic particles. Anomalous orientation of ferromagnetic filaments perpendicular to AC field with a frequency which is high enough is predicted and confirmed experimentally. By experimental studies of magnetotactic bacteria it is demonstrated how these properties of ferromagnetic filaments may be used to measure the flexibility of the chain of magnetosomes.

  1. Temperature limited heater utilizing non-ferromagnetic conductor

    Energy Technology Data Exchange (ETDEWEB)

    Vinegar,; Harold J. (Bellaire, TX), Harris; Kelvin, Christopher [Houston, TX

    2012-07-17

    A heater is described. The heater includes a ferromagnetic conductor and an electrical conductor electrically coupled to the ferromagnetic conductor. The ferromagnetic conductor is positioned relative to the electrical conductor such that an electromagnetic field produced by time-varying current flow in the ferromagnetic conductor confines a majority of the flow of the electrical current to the electrical conductor at temperatures below or near a selected temperature.

  2. Ferromagnetism in Laves-phase WFe2 nanoparticles

    Directory of Open Access Journals (Sweden)

    M. A. Koten

    2015-07-01

    Full Text Available While rare-earth based Laves phases are known to exhibit large magnetostriction, the magnetic properties of some binary Laves phases containing transition metals alone are not well known. This is because many of these compounds contain refractory elements that complicate melt processing due to high melting temperatures and extensive phase separation. Here, phase-pure WFe2 nanoclusters, with the hexagonal C14 Laves structure, were deposited via inert gas condensation, allowing for the first known measurement of ferromagnetism in this phase, with MS of 26.4 emu/g (346 emu/cm3 and a KU of 286 kerg/cm3, at 10 K, and a TC of 550 K.

  3. Ferromagnetism in Laves-phase WFe{sub 2} nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Koten, M. A.; Shield, J. E. [Department of Mechanical and Materials Engineering and Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln, Nebraska 68588-0526 (United States); Manchanda, P.; Balamurugan, B.; Skomski, R.; Sellmyer, D. J. [Department of Physics and Astronomy and Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln, Nebraska 68588-0299 (United States)

    2015-07-01

    While rare-earth based Laves phases are known to exhibit large magnetostriction, the magnetic properties of some binary Laves phases containing transition metals alone are not well known. This is because many of these compounds contain refractory elements that complicate melt processing due to high melting temperatures and extensive phase separation. Here, phase-pure WFe{sub 2} nanoclusters, with the hexagonal C14 Laves structure, were deposited via inert gas condensation, allowing for the first known measurement of ferromagnetism in this phase, with M{sub S} of 26.4 emu/g (346 emu/cm{sup 3}) and a K{sub U} of 286 kerg/cm{sup 3}, at 10 K, and a T{sub C} of 550 K.

  4. Intrinsic Ferromagnetism in Eu doped ZnO

    OpenAIRE

    Assadi, M. H. N.; Zhang,Y.B.; Ionescu, M.; Photongkam, P.; Li, S.

    2010-01-01

    We report room temperature ferromagnetism in as-implanted Eu doped ZnO (ZnO:Eu). To address the origin of ferromagnetism ab initio calculations of ZnO:Eu system are performed. Results show that the ferromagnetism is induced by ZnO point defects as Eu ions in perfect ZnO tend to align antiferromagnetically.

  5. Ferromagnets as pure spin current generators and detectors

    Energy Technology Data Exchange (ETDEWEB)

    Qu, Danru; Miao, Bingfeng; Chien, Chia -Ling; Huang, Ssu -Yen

    2015-09-08

    Provided is a spintronics device. The spintronics can include a ferromagnetic metal layer, a positive electrode disposed on a first surface portion of the ferromagnetic metal layer, and a negative electrode disposed on a second surface portion of the ferromagnetic metal.

  6. Ferromagnetic Order, Strong Magnetocrystalline Anisotropy, and Magnetocaloric Effect in the Layered Telluride Fe(3-δ)GeTe2.

    Science.gov (United States)

    Verchenko, Valeriy Yu; Tsirlin, Alexander A; Sobolev, Alexei V; Presniakov, Igor A; Shevelkov, Andrei V

    2015-09-08

    The ternary transition-metal compound Fe(3-δ)GeTe2 is formed for 0 magnetocaloric effect with the magnetic entropy change upon the ferromagnetic ordering transition, -ΔS ∼ 1.1 J·kg(-1)·K(-1) at 5 T, is found.

  7. Tunneling Conductance in Ferromagnetic Metal/Normal Metal/Spin-Singlet -Wave Ferromagnetic Superconductor Junctions

    Directory of Open Access Journals (Sweden)

    Hamidreza Emamipour

    2013-01-01

    Full Text Available In the framework of scattering theory, we study the tunneling conductance in a system including two junctions, ferromagnetic metal/normal metal/ferromagnetic superconductor, where ferromagnetic superconductor is in spin-singlet -wave pairing state. The non-magnetic normal metal is placed in the intermediate layer with the thickness ( which varies from 1 nm to 10000 nm. The interesting result which we have found is the existence of oscillations in conductance curves. The period of oscillations is independent of FS and FN exchange field while it depends on . The obtained results can serve as a useful tool to determine the kind of pairing symmetry in ferromagnetic superconductors.

  8. Static Theory for Planar Ferromagnets and Antiferromagnets

    Institute of Scientific and Technical Information of China (English)

    Feng Bo HANG; Fang Hua LIN

    2001-01-01

    Here we generalize the "BBH"-asymptotic analysis to a simplified mathematical model for the planar ferromagnets and antiferromagncts. To develop such a static theory is a necessary step for a rigorous mathematical justification of dynamical laws for the magnetic vortices formally derived in [1] and [2].

  9. Ferromagnetic hysteresis and the effective field

    NARCIS (Netherlands)

    Naus, H.W.L.

    2002-01-01

    The Jiles-Atherton model of the behavior of ferromagnetic materials determines the irreversible magnetization from the effective field by using a differential equation. This paper presents an exact, analytical solution to the equation, one displaying hysteresis. The inclusion of magnetomechanical co

  10. Neutron Depolarization in Submicron Ferromagnetic Materials

    NARCIS (Netherlands)

    Rekveldt, M.Th.

    1989-01-01

    The neutron depolarization technique is based on the loss of polarization of a polarized neutron beam after transmission through ferromagnetic substances. This loss, caused by Larmor precession in individual domains, determines the mean domain size, the mean square direction cosines of the domains a

  11. Silicon spintronics with ferromagnetic tunnel devices

    NARCIS (Netherlands)

    Jansen, R.; Dash, S. P.; Sharma, S.; Min, B. C.

    In silicon spintronics, the unique qualities of ferromagnetic materials are combined with those of silicon, aiming at creating an alternative, energy-efficient information technology in which digital data are represented by the orientation of the electron spin. Here we review the cornerstones of

  12. Integrable hierarchies of Heisenberg ferromagnet equation

    Science.gov (United States)

    Nugmanova, G.; Azimkhanova, A.

    2016-08-01

    In this paper we consider the coupled Kadomtsev-Petviashvili system. From compatibility conditions we obtain the form of matrix operators. After using a gauge transformation, obtained a new type of Lax representation for the hierarchy of Heisenberg ferromagnet equation, which is equivalent to the gauge coupled Kadomtsev-Petviashvili system.

  13. Measurment Of Residual Stress In Ferromagnetic Materials

    Science.gov (United States)

    Namkung, Min; Yost, William T.; Kushnick, Peter W.; Grainger, John L.

    1992-01-01

    Magnetoacoustic (MAC) and magnetoacoustic emission (MAE) techniques combined to provide complete characterization of residual stresses in ferromagnetic structural materials. Combination of MAC and MAE techniques makes it possible to characterize residual tension and compression without being limited by surface conditions and unavailability of calibration standards. Significant in field of characterization of materials as well as detection of fatigue failure.

  14. Angular and linear momentum of excited ferromagnets

    NARCIS (Netherlands)

    Yan, P.; Kamra, A.; Cao, Y.; Bauer, G.E.W.

    2013-01-01

    The angular momentum vector of a Heisenberg ferromagnet with isotropic exchange interaction is conserved, while under uniaxial crystalline anisotropy the projection of the total spin along the easy axis is a constant of motion. Using Noether's theorem, we prove that these conservation laws persist i

  15. Magnetization dissipation in ferromagnets from scattering theory

    NARCIS (Netherlands)

    Brataas, A.; Tserkovnyak, Y.; Bauer, G.E.W.

    2011-01-01

    The magnetization dynamics of ferromagnets is often formulated in terms of the Landau-Lifshitz-Gilbert (LLG) equation. The reactive part of this equation describes the response of the magnetization in terms of effective fields, whereas the dissipative part is parametrized by the Gilbert damping tens

  16. Effect of ferromagnetic nanoparticle on dyes biodegradation

    OpenAIRE

    Apostol, Laura; Pereira, Luciana; Pereira, Raquel; Alves, M.M.; Gavrilescu, M.

    2011-01-01

    In this study the biodecolourisation of two dyes, a xanthene dye, Erythrosine B (Ery B) and an azo dye, Reactive Red 51 (RR120), was investigated colourdecolourisationunder batch anaerobic conditions by using non - acclimated anaerobic granular sludge. The effect of ferromagnetic nanoparticle (FN) (as adsorbent or mediator) on dyes removal was experienced.

  17. Silicon spintronics with ferromagnetic tunnel devices

    NARCIS (Netherlands)

    Jansen, R.; Dash, S. P.; Sharma, S.; Min, B. C.

    2012-01-01

    In silicon spintronics, the unique qualities of ferromagnetic materials are combined with those of silicon, aiming at creating an alternative, energy-efficient information technology in which digital data are represented by the orientation of the electron spin. Here we review the cornerstones of sil

  18. Measurment Of Residual Stress In Ferromagnetic Materials

    Science.gov (United States)

    Namkung, Min; Yost, William T.; Kushnick, Peter W.; Grainger, John L.

    1992-01-01

    Magnetoacoustic (MAC) and magnetoacoustic emission (MAE) techniques combined to provide complete characterization of residual stresses in ferromagnetic structural materials. Combination of MAC and MAE techniques makes it possible to characterize residual tension and compression without being limited by surface conditions and unavailability of calibration standards. Significant in field of characterization of materials as well as detection of fatigue failure.

  19. Nanoengineering of an Si/MnGe quantum dot superlattice for high Curie-temperature ferromagnetism.

    Science.gov (United States)

    Nie, Tianxiao; Kou, Xufeng; Tang, Jianshi; Fan, Yabin; Lee, Shengwei; He, Qinglin; Chang, Li-Te; Murata, Koichi; Gen, Yin; Wang, Kang L

    2017-02-14

    The realization and application of spintronic devices would be dramatically advanced if room-temperature ferromagnetism could be integrated into semiconductor nanostructures, especially when compatible with mature silicon technology. Herein, we report the observation of such a system - an Si/MnGe superlattice with quantum dots well aligned in the vertical direction successfully grown by molecular beam epitaxy. Such a unique system could take full advantage of the type-II energy band structure of the Si/Ge heterostructure, which could trap the holes inside MnGe QDs, significantly enhancing the hole-mediated ferromagnetism. Magnetic measurements indeed found that the superlattice structure exhibited a Curie temperature of above 400 K. Furthermore, zero-field cooling and field cooling curves could confirm the absence of ferromagnetic compounds, such as Ge8Mn11 (Tc ∼ 270 K) and Ge3Mn5 (Tc ∼ 296 K) in our system. Magnetotransport measurement revealed a clear magnetoresistance transition from negative to positive and a pronounced anomalous Hall effect. Such a unique Si/MnGe superlattice sets a new stage for strengthening ferromagnetism due to the enhanced hole-mediation by quantum confinement, which can be exploited for realizing the room-temperature Ge-based spin field-effect transistors in the future.

  20. Coupled Lattice Polarization and Ferromagnetism in Multiferroic NiTiO 3 Thin Films

    Energy Technology Data Exchange (ETDEWEB)

    Varga, Tamas; Droubay, Timothy C.; Kovarik, Libor; Nandasiri, Manjula I. [Imaging; Shutthanandan, Vaithiyalingam; Hu, Dehong; Kim, Bumsoo [Materials; Department; Jeon, Seokwoo [Department; Hong, Seungbum [Materials; Department; Li, Yulan; Chambers, Scott A.

    2017-06-22

    Polarization-induced weak ferromagnetism (WFM) was demonstrated a few years back in LiNbO3-type compounds, MTiO3 (M = Fe, Mn, Ni). Although the coexistence of ferroelectric polarization and ferromagnetism has been demonstrated in this rare multiferroic family before, first in bulk FeTiO3, then in thin-film NiTiO3, the coupling of the two order parameters has not been confirmed Here, we report the stabilization of polar, ferromagnetic NiTiO3 by oxide epitaxy on a LiNbO3 substrate utilizing tensile strain and demonstrate the theoretically predicted coupling between its polarization and ferromagnetism by X-ray magnetic circular dichroism under applied fields. The experimentally observed direction of ferroic ordering in the film is supported by simulations using the phase-field approach. Our work validates symmetry-based criteria and first-principles calculations of the coexistence of ferroelectricity and WFM in MTiO3 transition metal titanates crystallizing in the LiNbO3 structure. It also demonstrates the applicability of epitaxial strain as a viable alternative to high-pressure crystal growth to stabilize metastable materials and a valuable tuning parameter to simultaneously control two ferroic order parameters to create a multiferroic. Multiferroic NiTiO3 has potential applications in spintronics where ferroic switching is used, such as new four-stage memories and electromagnetic switches.

  1. Room temperature ferromagnetism in Teflon due to carbon dangling bonds.

    Science.gov (United States)

    Ma, Y W; Lu, Y H; Yi, J B; Feng, Y P; Herng, T S; Liu, X; Gao, D Q; Xue, D S; Xue, J M; Ouyang, J Y; Ding, J

    2012-03-06

    The ferromagnetism in many carbon nanostructures is attributed to carbon dangling bonds or vacancies. This provides opportunities to develop new functional materials, such as molecular and polymeric ferromagnets and organic spintronic materials, without magnetic elements (for example, 3d and 4f metals). Here we report the observation of room temperature ferromagnetism in Teflon tape (polytetrafluoroethylene) subjected to simple mechanical stretching, cutting or heating. First-principles calculations indicate that the room temperature ferromagnetism originates from carbon dangling bonds and strong ferromagnetic coupling between them. Room temperature ferromagnetism has also been successfully realized in another polymer, polyethylene, through cutting and stretching. Our findings suggest that ferromagnetism due to networks of carbon dangling bonds can arise in polymers and carbon-based molecular materials.

  2. Electronic structure and magnetism in actinide compounds

    Energy Technology Data Exchange (ETDEWEB)

    Durakiewicz, T. [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States)]. E-mail: tomasz@lanl.gov; Joyce, J.J. [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Lander, G.H. [JRC, Institute of Transuranium Elements, Postfach 2340, 76125 Karlsruhe (Germany); Olson, C.G. [Ames Laboratory, Iowa State University, Ames, Iowa 5011 (United States); Butterfield, M.T. [Lawrence Livermoore National Laboratory, Livermoore, CA 94550 (United States); Guziewicz, E. [Institute of Physics, Polish Academy of Sciences, 02-668 Warsaw (Poland); Batista, C.D. [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Arko, A.J. [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Morales, L. [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Mattenberger, K. [Laboratorium fur Festkorperphysik, ETH, CH-8093, Zurich (Switzerland); Vogt, O. [Laboratorium fur Festkorperphysik, ETH, CH-8093, Zurich (Switzerland)

    2006-05-01

    A close relationship between electronic structure and magnetic properties is observed in actinide compounds. The exact nature of this relationship is under investigation. We present examples of a direct link between electronic structure and ordered magnetic moment and/or magnetization. Specifically, results obtained for cubic U, Np and Pu compounds and quasi-2D U compounds are be presented. In the case of cubic compounds, a direct relationship between binding energy of valence band features and magnetic moment will be discussed. A Stoner-like mechanism and simple mean-field explanation is proposed for ferromagnetic UTe.

  3. Ising Ferromagnet: Zero-Temperature Dynamic Evolution

    CERN Document Server

    Murilo-Castro de Oliveira, P; Sidoravicious, V; Stein, D L

    2006-01-01

    The dynamic evolution at zero temperature of a uniform Ising ferromagnet on a square lattice is followed by Monte Carlo computer simulations. The system always eventually reaches a final, absorbing state, which sometimes coincides with a ground state (all spins parallel), and sometimes does not (parallel stripes of spins up and down). We initiate here the numerical study of ``Chaotic Time Dependence'' (CTD) by seeing how much information about the final state is predictable from the randomly generated quenched initial state. CTD was originally proposed to explain how nonequilibrium spin glasses could manifest equilibrium pure state structure, but in simpler systems such as homogeneous ferromagnets it is closely related to long-term predictability and our results suggest that CTD might indeed occur in the infinite volume limit.

  4. Double negative metamaterials based on ferromagnetic microwires

    Science.gov (United States)

    Carbonell, Jorge; García-Miquel, Héctor; Sánchez-Dehesa, José

    2010-01-01

    Ferromagnetic microwires are investigated as fundamental components to generate metamaterials with double negative parameters. Electric and magnetic responses are, respectively, based on the finite conductivity and ferromagnetic resonance of the wires that in turn depend on their chemical composition. Tuning properties of samples are investigated in terms of the composition of the alloy and the applied magnetic field. The samples are measured and simulated in a waveguide environment for a large microwave frequency range. Numerical modeling supports the experimental results and helps to understand the physics involved in the transmission phenomena. Radius and conductivity of the wires are pointed out as the most critical parameters to generate a double negative response in terms of permittivity and permeability.

  5. Shot Noise in Ferromagnetic Superconductor Tunnel Junctions

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    In this paper, the superconducting order parameter and the energy spectrum of the Bogoliubov excitations are obtained from the Bogoliubov-de Gennes (BdG) equation for a ferromagnetic superconductor (FS). Taking into account the rough interface scattering effect, we calculate the shot noise and the differential conductance of the normal- metal insulator ferromagnetic superconductor junction. It is shown that the exchange energy Eh in FS can lead to splitting of the differential shot noise peaks and the conductance peaks. The energy difference between the two splitting peaks is equal to 2Eh. The rough interface scattering strength results in descent of conductance peaks and the shot noise-to-current ratio but increases the shot noise.

  6. Ferromagnetism and interlayer exchange coupling in thin metallic films

    Energy Technology Data Exchange (ETDEWEB)

    Kienert, Jochen

    2008-07-15

    This thesis is concerned with the ferromagnetic Kondo lattice (s-d,s-f) model for film geometry. The spin-fermion interaction of this model refers to substances in which localized spins interact with mobile charge carriers like in (dilute) magnetic semiconductors, manganites, or rare-earth compounds. The carrier-mediated, indirect interaction between the localized spins comprises the long-range, oscillatory RKKY exchange interaction in the weak-coupling case and the short-range doubleexchange interaction for strong spin-fermion coupling. Both limits are recovered in this work by mapping the problem onto an effective Heisenberg model. The influence of reduced translational symmetry on the effective exchange interaction and on the magnetic properties of the ferromagnetic Kondo lattice model is investigated. Curie temperatures are obtained for different parameter constellations. The consequences of charge transfer and of lattice relaxation on the magnetic stability at the surface are considered. Since the effective exchange integrals are closely related to the electronic structure in terms of the density of states and of the kinetic energy, the discussion is based on the modifications of these quantities in the dimensionally-reduced case. The important role of spin waves for thin film and surface magnetism is demonstrated. Interlayer exchange coupling represents a particularly interesting and important manifestation of the indirect interaction among localized magnetic moments. The coupling between monatomic layers in thin films is studied in the framework of an RKKY approach. It is decisively determined by the type of in-plane and perpendicular dispersion of the charge carriers and is strongly suppressed above a critical value of the Fermi energy. Finally, the temperature-dependent magnetic stability of thin interlayer-coupled films is addressed and the conditions for a temperature-driven magnetic reorientation transition are discussed. (orig.)

  7. Anisotropic magnetocapacitance in ferromagnetic-plate capacitors

    Science.gov (United States)

    Haigh, J. A.; Ciccarelli, C.; Betz, A. C.; Irvine, A.; Novák, V.; Jungwirth, T.; Wunderlich, J.

    2015-04-01

    The capacitance of a parallel-plate capacitor can depend on the applied magnetic field. Previous studies have identified capacitance changes induced via classical Lorentz force or spin-dependent Zeeman effects. Here we measure a magnetization direction-dependent capacitance in parallel-plate capacitors where one plate is a ferromagnetic semiconductor, gallium manganese arsenide. This anisotropic magnetocapacitance is due to the anisotropy in the density of states dependent on the magnetization through the strong spin-orbit interaction.

  8. Photoinduced itinerant ferromagnetism in copper octacyanomolybdates

    Science.gov (United States)

    Ohara, Jun; Yamamoto, Shoji

    2017-06-01

    We make a microscopic theory of the photoswitchable magnetism in copper octacyanomolybdates. By numerically solving a time-dependent Schrödinger equation based on the relevant extended Hubbard model, we reproduce magnetization by green-light irradiation and subsequent demagnetization by orange-light irradiation. At the onset of the ferromagnetism, the charge-transfer gap disappears. In an attempt to stimulate experimental investigations, we simulate time evolution of the angle-resolved photoemission spectroscopy and optical-conductivity spectra.

  9. Raman characterization of bulk ferromagnetic nanostructured graphite

    Energy Technology Data Exchange (ETDEWEB)

    Pardo, Helena, E-mail: hpardo@fq.edu.uy [Centro NanoMat, Polo Tecnologico de Pando, Facultad de Quimica, Universidad de la Republica, Cno. Aparicio Saravia s/n, 91000, Pando, Canelones (Uruguay); Crystallography, Solid State and Materials Laboratory (Cryssmat-Lab), DETEMA, Facultad de Quimica, Universidad de la Republica, Gral. Flores 2124, P.O. Box 1157, Montevideo (Uruguay); Divine Khan, Ngwashi [Mantfort University, Leicester (United Kingdom); Faccio, Ricardo [Centro NanoMat, Polo Tecnologico de Pando, Facultad de Quimica, Universidad de la Republica, Cno. Aparicio Saravia s/n, 91000, Pando, Canelones (Uruguay); Crystallography, Solid State and Materials Laboratory (Cryssmat-Lab), DETEMA, Facultad de Quimica, Universidad de la Republica, Gral. Flores 2124, P.O. Box 1157, Montevideo (Uruguay); Araujo-Moreira, F.M. [Grupo de Materiais e Dispositivos-CMDMC, Departamento de Fisica e Engenharia Fisica, UFSCar, Caixa Postal 676, 13565-905, Sao Carlos SP (Brazil); Fernandez-Werner, Luciana [Centro NanoMat, Polo Tecnologico de Pando, Facultad de Quimica, Universidad de la Republica, Cno. Aparicio Saravia s/n, 91000, Pando, Canelones (Uruguay); Crystallography, Solid State and Materials Laboratory (Cryssmat-Lab), DETEMA, Facultad de Quimica, Universidad de la Republica, Gral. Flores 2124, P.O. Box 1157, Montevideo (Uruguay)

    2012-08-15

    Raman spectroscopy was used to characterize bulk ferromagnetic graphite samples prepared by controlled oxidation of commercial pristine graphite powder. The G:D band intensity ratio, the shape and position of the 2D band and the presence of a band around 2950 cm{sup -1} showed a high degree of disorder in the modified graphite sample, with a significant presence of exposed edges of graphitic planes as well as a high degree of attached hydrogen atoms.

  10. Squeezing States of Magnons in a Ferromagnet

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    In this paper, we conduct an investigation into magnon self-squeezing states in a ferromagnet. In these states, the quantum fluctuations of the spin components can be lower than the zero-point quantum fluctuations of the coherent states. Through calculating the expectation values of spin fluctuations we gain the condition of achieving magnon self-squeezing. We introduce the mean-field theory for dealing with the nonlinear interaction term of Hamiltonian of magnon system.

  11. Ferromagnetic Resonance in Gd/Co Multilayers

    Institute of Scientific and Technical Information of China (English)

    A. V. Svalov; V. O. Vas'kovskiy; J. M. Barandiaran; G. V. Kurlyandskaya; L. Lezama; J. Gutiérrez; N. G. Bebenin; D. Schmool

    2001-01-01

    Magnetometric and ferromagnetic resonance (MFR) measurements have been performed on the polycrystalline multilayered structure, [Gd(7.5 nm)/Co(3nm)]20. The temperature dependence of magnetization of the sample suggests a compensation temperature Tcomp in the region of 240K, implying that the Co and Gd layers are antiferromagnetically aligned. The FMR curves are strongly temperature dependent, particularly in the vicinity of Tcomp.

  12. Dynamical magnetic effects in photoexcited ferromagnetic semiconductors

    Energy Technology Data Exchange (ETDEWEB)

    Chovan, J. [Institute of Electronic Structure and Laser, Foundation for Research and Technology-Hellas, P. O. Box 1527, 711 10 Heraklion (Greece); Kavousanaki, E.G. [Department of Physics, University of Crete, P. O. Box 2208, 710 03 Heraklion (Greece); Perakis, I.E. [Institute of Electronic Structure and Laser, Foundation for Research and Technology-Hellas, P. O. Box 1527, 711 10 Heraklion (Greece); Department of Physics, University of Crete, P. O. Box 2208, 710 03 Heraklion (Greece)

    2006-08-15

    We develop a theory of photoinduced dynamical magnetic effects in III-Mn-V ferromagnetic semiconductors valid in presence of strong carrier spin relaxation and dephasing. We treat relaxation by using the Lindblad semigroup method and calculate the nonlinear response numerically. We predict Mn-spin relaxation and precession towards the direction determined by nonlinear optical polarization. These effects occur during the pulse. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  13. On a Nonlocal Damping Model in Ferromagnetism

    Directory of Open Access Journals (Sweden)

    M. Moumni

    2015-01-01

    Full Text Available We consider a mathematical model describing nonlocal damping in magnetization dynamics. The model consists of a modified form of the Landau-Lifshitz-Gilbert (LLG equation for the evolution of the magnetization vector in a rigid ferromagnet. We give a global existence result and characterize the long time behaviour of the obtained solutions. The sensitivity of the model with respect to large and small nonlocal damping parameters is also discussed.

  14. Topological superconductivity induced by ferromagnetic metal chains

    Science.gov (United States)

    Li, Jian; Chen, Hua; Drozdov, Ilya K.; Yazdani, A.; Bernevig, B. Andrei; MacDonald, A. H.

    2014-12-01

    Recent experiments have provided evidence that one-dimensional (1D) topological superconductivity can be realized experimentally by placing transition-metal atoms that form a ferromagnetic chain on a superconducting substrate. We address some properties of this type of system by using a Slater-Koster tight-binding model to account for important features of the electronic structure of the transition-metal chains on the superconducting substrate. We predict that topological superconductivity is nearly universal when ferromagnetic transition-metal chains form straight lines on superconducting substrates and that it is possible for more complex chain structures. When the chain is weakly coupled to the substrate and is longer than superconducting coherence lengths, its proximity-induced superconducting gap is ˜Δ ESO/J where Δ is the s -wave pair potential on the chain, ESO is the spin-orbit splitting energy induced in the normal chain state bands by hybridization with the superconducting substrate, and J is the exchange splitting of the ferromagnetic chain d bands. Because of the topological character of the 1D superconducting state, Majorana end modes appear within the gaps of finite length chains. We find, in agreement with the experiment, that when the chain and substrate orbitals are strongly hybridized, Majorana end modes are substantially reduced in amplitude when separated from the chain end by less than the coherence length defined by the p -wave superconducting gap. We conclude that Pb is a particularly favorable substrate material for ferromagnetic chain topological superconductivity because it provides both strong s -wave pairing and strong Rashba spin-orbit coupling, but that there is an opportunity to optimize properties by varying the atomic composition and structure of the chain. Finally, we note that in the absence of disorder, a new chain magnetic symmetry, one that is also present in the crystalline topological insulators, can stabilize multiple

  15. Hierarchical Modeling of Ferromagnetic SMAs and Composites

    Science.gov (United States)

    2006-01-01

    Chapter 4. Processing of Particulate FSMA Composites ............................ 38 Chapter 5. Processing of FSMA Laminated Composites by Plasma ...shear of a ferromagnetic materia ,tf, and (e) reverse transformation shear stress, Tl. 1.414 1110 . . ...... . . . .... ....... 80 -1.411 414 X •:. ~40...useful comparison parameter. We measured the saturation magnetization(Ms) of Fe-TiNi particulate composites that we processed by using Spark Plasma

  16. Ferromagnetic nanoparticles suspensions in twisted nematic

    Science.gov (United States)

    Cîrtoaje, Cristina; Petrescu, Emil; Stan, Cristina; Creangă, Dorina

    2016-05-01

    Ferromagnetic nanoparticles insertions in nematic liquid crystals (NLC) in twisted configuration are studied and a theoretical model is proposed to explain the results. Experimental observation revealed that nanoparticles tend to overcrowd in long strings parallel to the rubbing direction of the alignment substrate of the LC cell. Their behavior under external field was studied and their interaction with their nematic host is described using elastic continuum theory.

  17. Simulation of coexisting ferromagnetic order and disorder of geometrically frustrated Co{sub 2}Cl(OH){sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Kitazaki, Tamotsu, E-mail: ad08001@bene.fit.ac.jp [Fukuoka Institute of Technology, Higashi-ku, Fukuoka 811-0295 (Japan); Koga, Yosuke; Kato, Tomohiko [Fukuoka Institute of Technology, Higashi-ku, Fukuoka 811-0295 (Japan)

    2011-10-15

    The ground state and phase transition of Co{sub 2}Cl(OH){sub 3} were investigated by Monte Carlo simulation. This compound is a magnet, with a pyrochlore structure distorted along one axis. The magnetic structure at low temperatures consists of coexisting ferromagnetism and random spin, according to experiments. However, the formation mechanism of the coexistence and the interaction between the spins were unclear. We assumed an anisotropic Ising model and examined the ground state by multicanonical Monte Carlo simulation. In a nearest neighbor model, the ground states were highly degenerated. Almost all of the states were spin glass states, but a few of the states were ferromagnetic. The latter magnetic states were ferromagnetic at triangular layers and two in-one out random state at Kagome layers. The latter states should be stabilized if weak ferromagnetic interactions exist between second nearest neighbor spins and correspond to the states reported by the experiments. This expectation was confirmed by simulation. - Highlights: > A peculiar coexisting state was interpreted by assuming an anisotropic Ising model. > In a nearest interaction model, the coexisting state is suppressed by spin glass. > The coexisting state is stabilized by weak ferromagnetic 2nd nearest interaction. > Temperature dependences of order parameters are consistent with the experiments.

  18. Tunable Magnon Weyl Points in Ferromagnetic Pyrochlores

    Science.gov (United States)

    Mook, Alexander; Henk, Jürgen; Mertig, Ingrid

    2016-10-01

    The dispersion relations of magnons in ferromagnetic pyrochlores with Dzyaloshinskii-Moriya interaction are shown to possess Weyl points, i. e., pairs of topologically nontrivial crossings of two magnon branches with opposite topological charge. As a consequence of their topological nature, their projections onto a surface are connected by magnon arcs, thereby resembling closely Fermi arcs of electronic Weyl semimetals. On top of this, the positions of the Weyl points in reciprocal space can be tuned widely by an external magnetic field: rotated within the surface plane, the Weyl points and magnon arcs are rotated as well; tilting the magnetic field out of plane shifts the Weyl points toward the center Γ ¯ of the surface Brillouin zone. The theory is valid for the class of ferromagnetic pyrochlores, i. e., three-dimensional extensions of topological magnon insulators on kagome lattices. In this Letter, we focus on the (111) surface, identify candidates of established ferromagnetic pyrochlores which apply to the considered spin model, and suggest experiments for the detection of the topological features.

  19. As diffusion in ferromagnetic {alpha}-Fe

    Energy Technology Data Exchange (ETDEWEB)

    Perez, R.A.; Dyment, F. [Comision Nacional de Energia Atomica (CNEA), Departamento de Materiales, Buenos Aires (Argentina); Consejo Nacional de Investigaciones Cientificas y Tecnicas (CONICET), Buenos Aires (Argentina); Torres, D.N. [Comision Nacional de Energia Atomica (CNEA), Departamento de Materiales, Buenos Aires (Argentina)

    2009-11-15

    Diffusion of As in {alpha}-Fe was studied. Diffusion couples were formed by ion implantation; measurements were made in the 673-1073 K temperature range using the heavy ion Rutherford backscattering (HIRBS) technique as the analysis tool. A curved Arrhenius plot was obtained, as a product of the ferromagnetism effect on diffusion; the previously developed model for diffusion of non-magnetic impurities in ferromagnetic Fe fits the data perfectly well. As diffusion is, on average, two orders of magnitude faster than self-diffusion given its smaller atomic radius (110 pm against 140 pm for Fe). Assuming a total increment in the activation energy due to the ferromagnetic alignment {alpha}Q=40 kJ mol{sup -1}, diffusion parameters for the paramagnetic region could be extrapolated, these being the pre-exponential factor D{sub 0} {sup p}=10{sup -5} m{sup 2}s{sup -1} and the activation energy Q{sup p}=197 kJ mol{sup -1}. (orig.)

  20. Robust ferromagnetism carried by antiferromagnetic domain walls

    Science.gov (United States)

    Hirose, Hishiro T.; Yamaura, Jun-Ichi; Hiroi, Zenji

    2017-02-01

    Ferroic materials, such as ferromagnetic or ferroelectric materials, have been utilized as recording media for memory devices. A recent trend for downsizing, however, requires an alternative, because ferroic orders tend to become unstable for miniaturization. The domain wall nanoelectronics is a new developing direction for next-generation devices, in which atomic domain walls, rather than conventional, large domains themselves, are the active elements. Here we show that atomically thin magnetic domain walls generated in the antiferromagnetic insulator Cd2Os2O7 carry unusual ferromagnetic moments perpendicular to the wall as well as electron conductivity: the ferromagnetic moments are easily polarized even by a tiny field of 1 mT at high temperature, while, once cooled down, they are surprisingly robust even in an inverse magnetic field of 7 T. Thus, the magnetic domain walls could serve as a new-type of microscopic, switchable and electrically readable magnetic medium which is potentially important for future applications in the domain wall nanoelectronics.

  1. Damage Detection by the Mode-Selectable Magnetostrictive Transducer for Cylindrical Ferromagnetic Waveguides

    Science.gov (United States)

    Kim, Youngkyu; Kim, Ikkyu; Kim, Yoon Young

    2004-02-01

    In recent years, ultrasonic inspection techniques adopting magnetostrictive effects have received much attention, because they are non-destructive and require no direct physical contact with target systems. By selecting the desired wave mode and thus rejecting the unwanted modes amongst propagating waves in cylindrical ferromagnetic waveguides, we can effectively detect various types of flaws. However, a bending wave mode selecting technique, in particular, has not been fully developed yet. The purpose of this work is to present a technique to select either bending or longitudinal waves alone from compound waves propagating in ferromagnetic cylindrical waveguide. To achieve this goal, a new bias magnet configuration suitable for bending mode selection is suggested. The experimental results verify the effectiveness of the proposed method.

  2. Prediction of a stable half-metal ferromagnetic BaCl solid

    Science.gov (United States)

    Greschner, Michael J.; Klug, Dennis D.; Yao, Yansun

    2016-03-01

    The modification of Ba in BaCl compounds from alkaline-metal to transition- and half-metal behavior is explored. High-pressure structural changes in BaCl are predicted using an ab initio structure search method. Dynamically stable bcc and R -3 m forms of BaCl are predicted at 15 and 10 GPa, respectively. The BaCl forms are more stable than elemental Ba plus BaC l2 above ˜10 GPa. Ba in stable BaCl adopts transition-metal properties via an s -d transition. At ambient pressure the fcc structure is ferromagnetic, and the bcc structure is half metallic and ferromagnetic. The transition-metal electronic structure found is sufficient to support superconductivity, with Tc as high as 3.4 K near ambient pressure.

  3. Photoemission study of the ferromagnetic Kondo system CeRh3B2

    Science.gov (United States)

    Fujimori, A.; Takahashi, T.; Okabe, A.; Kasaya, M.; Kasuya, T.

    1990-04-01

    We have studied the electronic structure of CeRh3B2, which has an anomalously high ferromagnetic ordering temperature, by photoemission and Auger-electron spectroscopy. The Ce 4f occupancy nf~=0.85 evaluated from the Ce 3d core-level photoemission spectrum indicates a moderately strong valence fluctuation in the Kondo regime. Rh d-derived valence-band photoemission spectra are found to be in good agreement with the results of band-structure calculations when a strong energy dependence of the hole lifetime is taken into account. This observation and the deviation of the Rh M4,5VV Auger spectrum from the self-convolution of the Rh d partial density of states provide evidence for electron correlation within the Rh d band of order of U=1-2 eV. We discuss a possible effect of the latter electron correlation on the ferromagnetic instability of this compound.

  4. 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.

  5. Electronic Structure Evolution across the Peierls Metal-Insulator Transition in a Correlated Ferromagnet

    Directory of Open Access Journals (Sweden)

    P. A. Bhobe

    2015-10-01

    Full Text Available Transition metal compounds often undergo spin-charge-orbital ordering due to strong electron-electron correlations. In contrast, low-dimensional materials can exhibit a Peierls transition arising from low-energy electron-phonon-coupling-induced structural instabilities. We study the electronic structure of the tunnel framework compound K_{2}Cr_{8}O_{16}, which exhibits a temperature-dependent (T-dependent paramagnetic-to-ferromagnetic-metal transition at T_{C}=180  K and transforms into a ferromagnetic insulator below T_{MI}=95  K. We observe clear T-dependent dynamic valence (charge fluctuations from above T_{C} to T_{MI}, which effectively get pinned to an average nominal valence of Cr^{+3.75} (Cr^{4+}∶Cr^{3+} states in a 3∶1 ratio in the ferromagnetic-insulating phase. High-resolution laser photoemission shows a T-dependent BCS-type energy gap, with 2G(0∼3.5(k_{B}T_{MI}∼35  meV. First-principles band-structure calculations, using the experimentally estimated on-site Coulomb energy of U∼4  eV, establish the necessity of strong correlations and finite structural distortions for driving the metal-insulator transition. In spite of the strong correlations, the nonintegral occupancy (2.25 d-electrons/Cr and the half-metallic ferromagnetism in the t_{2g} up-spin band favor a low-energy Peierls metal-insulator transition.

  6. Ferromagnetism appears in nitrogen implanted nanocrystalline diamond films

    Energy Technology Data Exchange (ETDEWEB)

    Remes, Zdenek [Institute of Physics ASCR v.v.i., Cukrovarnicka 10, 162 00 Prague 6 (Czech Republic); Sun, Shih-Jye, E-mail: sjs@nuk.edu.tw [Department of Applied Physics, National University of Kaohsiung, Kaohsiung 811, Taiwan (China); Varga, Marian [Department of Applied Physics, National University of Kaohsiung, Kaohsiung 811, Taiwan (China); Chou, Hsiung [Department of Physics, National Sun Yat-Sen University, Kaohsiung 804, Taiwan (China); Hsu, Hua-Shu [Department of Applied Physics, National Pingtung University of Education, Pingtung 900, Taiwan (China); Kromka, Alexander [Department of Applied Physics, National University of Kaohsiung, Kaohsiung 811, Taiwan (China); Horak, Pavel [Nuclear Physics Institute, 250 68 Rez (Czech Republic)

    2015-11-15

    The nanocrystalline diamond films turn to be ferromagnetic after implanting various nitrogen doses on them. Through this research, we confirm that the room-temperature ferromagnetism of the implanted samples is derived from the measurements of magnetic circular dichroism (MCD) and superconducting quantum interference device (SQUID). Samples with larger crystalline grains as well as higher implanted doses present more robust ferromagnetic signals at room temperature. Raman spectra indicate that the small grain-sized samples are much more disordered than the large grain-sized ones. We propose that a slightly large saturated ferromagnetism could be observed at low temperature, because the increased localization effects have a significant impact on more disordered structure. - Highlights: • Nitrogen implanted nanocrystalline diamond films exhibit ferromagnetism at room temperature. • Nitrogen implants made a Raman deviation from the typical nanocrystalline diamond films. • The ferromagnetism induced from the structure distortion is dominant at low temperature.

  7. Micromagnetic modeling of the shielding properties of nanoscale ferromagnetic layers

    Science.gov (United States)

    Iskandarova, I. M.; Knizhnik, A. A.; Popkov, A. F.; Potapkin, B. V.; Stainer, Q.; Lombard, L.; Mackay, K.

    2016-09-01

    Ferromagnetic shields are widely used to concentrate magnetic fields in a target region of space. Such shields are also used in spintronic nanodevices such as magnetic random access memory and magnetic logic devices. However, the shielding properties of nanostructured shields can differ considerably from those of macroscopic samples. In this work, we investigate the shielding properties of nanostructured NiFe layers around a current line using a finite element micromagnetic model. We find that thin ferromagnetic layers demonstrate saturation of magnetization under an external magnetic field, which reduces the shielding efficiency. Moreover, we show that the shielding properties of nanoscale ferromagnetic layers strongly depend on the uniformity of the layer thickness. Magnetic anisotropy in ultrathin ferromagnetic layers can also influence their shielding efficiency. In addition, we show that domain walls in nanoscale ferromagnetic shields can induce large increases and decreases in the generated magnetic field. Therefore, ferromagnetic shields for spintronic nanodevices require careful design and precise fabrication.

  8. Ferromagnetic exchange interaction between hard and soft ferromagnetic layers through ZnS semiconductor

    Energy Technology Data Exchange (ETDEWEB)

    Dinia, A. E-mail: aziz.dinia@ipcms.u-strasbg.fr; Colis, S.; Schmerber, G.; Ayoub, J.P

    2004-05-01

    We experimentally evidenced the presence of an indirect exchange coupling between hard and soft ferromagnetic electrodes through a ZnS barrier in magnetic tunnel junctions. For a 2 nm thick ZnS barrier, a negative shift of about -25 Oe is observed in asymmetric magnetization minor loop. This is attributed to a ferromagnetic interaction between the CoFe/Fe soft bilayer and the thick CoFe layer. The amplitude of the observed shift decreased as the thickness of the ZnS barrier increased, which agrees with theoretical models that the exchange interaction is mediated by spin polarized tunneling.

  9. New Spin-Wave Mode in Weak Ferromagnetic Fermi Liquids

    OpenAIRE

    Petkova, Penka I.

    1999-01-01

    We study a phenomenological model for weak ferromagnetic Fermi liquids and investigate the properties of the spin waves in the model. The Landau kinetic equation is used to derive, in addition to the known Goldstone mode, a new spin-wave mode -- the first Silin-like ferromagnetic mode. We discuss the role of the interaction parameter F^a_1 on the behavior of the Goldstone mode and the first Silin-like ferromagnetic mode.

  10. Quantum transport in ferromagnetic graphene: Role of Berry curvature

    Energy Technology Data Exchange (ETDEWEB)

    Chowdhury, Debashree; Basu, Banasri [Physics and Applied Mathematics Unit, Indian Statistical Institute, 203 Barrackpore Trunk Road, Kolkata 700 108 (India)

    2014-12-10

    The magnetic effects in ferromagnetic graphene basically depend on the principle of exchange interaction when ferromagntism is induced by depositing an insulator layer on graphene. Here we deal with the consequences of non-uniformity in the exchange coupling strength of the ferromagnetic graphene. We discuss how the in- homogeneity in the coordinate and momentum of the exchange vector field can provide interesting results in the conductivity analysis of the ferromagnetic graphene. Our analysis is based on the Kubo formalism of quantum transport.

  11. Phase transitions in pure and dilute thin ferromagnetic films

    Science.gov (United States)

    Korneta, W.; Pytel, Z.

    1983-10-01

    The mean-field model of a thin ferromagnetic film where the nearest-neighbor exchange coupling in surface layers can be different from that inside the film is considered. The phase diagram, equations for the second-order phase-transition lines, and the spontaneous magnetization profiles near the phase transitions are given. It is shown that there is no extra-ordinary transition in a thin film. If the thickness of the film tends to infinity the well-known results for the mean-field model of a semi-infinite ferromagnet are obtained. The generalization for disordered dilute thin ferromagnetic films and semi-infinite ferromagnets is also given.

  12. Room temperature ferromagnetism in ZnO prepared by microemulsion

    Directory of Open Access Journals (Sweden)

    Qingyu Xu

    2011-09-01

    Full Text Available Clear room temperature ferromagnetism has been observed in ZnO powders prepared by microemulsion. The O vacancy (VO clusters mediated by the VO with one electron (F center contributed to the ferromagnetism, while the isolated F centers contributed to the low temperature paramagnetism. Annealing in H2 incorporated interstitial H (Hi in ZnO, and removed the isolated F centers, leading to the suppression of the paramagnetism. The ferromagnetism has been considered to originate from the VO clusters mediated by the Hi, leading to the enhancement of the coercivity. The ferromagnetism disappeared after annealing in air due to the reduction of Hi.

  13. High-pressure synthesis of ferromagnetic Mn3Ge with the Cu3Au-type structure

    Science.gov (United States)

    Takizawa, H.; Yamashita, T.; Uheda, K.; Endo, T.

    2002-11-01

    A new intermetallic compound, Mn3Ge, has been synthesized by direct reaction of elemental components at 6.2 GPa and 1000°C for 30 min using a belt-type high-pressure apparatus. The compound crystallizes into a cubic structure with the space group Pm3m, namely the L12-type (Cu3Au-type) structure. The structure was refined by Rietveld analysis of the powder x-ray diffraction data and the lattice constant was determined as a = 0.380 19(3) nm. The compound shows metallic conductivity and ferromagnetism with a Curie temperature of 400 K.

  14. Quantitative study of the spin Hall magnetoresistance in ferromagnetic insulator/normal metal hybrids

    NARCIS (Netherlands)

    Althammer, M.; Meyer, S.; Nakayama, H.; Schreier, M.; Altmannshofer, S.; Weiler, M.; Huebl, H.; Gesprägs, S.; Opel, M.; Gross, R.; Meier, D.; Klewe, C.; Kuschel, T.; Schmalhorst, J.M.; Reiss, G.; Shen, L.; Gupta, A.; Chen, Y.T.; Bauer, G.E.W.; Saitoh, E.; Goennenwein, S.T.B.

    2013-01-01

    We experimentally investigate and quantitatively analyze the spin Hall magnetoresistance effect in ferromagnetic insulator/platinum and ferromagnetic insulator/nonferromagnetic metal/platinum hybrid structures. For the ferromagnetic insulator, we use either yttrium iron garnet, nickel ferrite, or ma

  15. Magnetic microstructure of nanocrystalline ferromagnets and nanocrystalline systems combining ferromagnetic and antiferromagnetic phases

    Energy Technology Data Exchange (ETDEWEB)

    Loeffler, J.; Wagner, W. [Paul Scherrer Inst. (PSI), Villigen (Switzerland); Kostorz, G. [Eidgenoessische Technische Hochschule, Zurich (Switzerland); Wiedenmann, A. [HMI Berlin (Germany)

    1997-09-01

    Magnetic small-angle neutron scattering measurements were performed on nanostructured ferromagnetic materials on the basis of Fe, Ni and Co, produced preferentially by the inert-gas condensation technique, with the aim to determine the magnetic microstructure of mesoscopic small-particle systems. (author) 1 fig., 3 refs.

  16. Room Temperature Ferromagnetic Mn:Ge(001

    Directory of Open Access Journals (Sweden)

    George Adrian Lungu

    2013-12-01

    Full Text Available We report the synthesis of a room temperature ferromagnetic Mn-Ge system obtained by simple deposition of manganese on Ge(001, heated at relatively high temperature (starting with 250 °C. The samples were characterized by low energy electron diffraction (LEED, scanning tunneling microscopy (STM, high resolution transmission electron microscopy (HRTEM, X-ray photoelectron spectroscopy (XPS, superconducting quantum interference device (SQUID, and magneto-optical Kerr effect (MOKE. Samples deposited at relatively elevated temperature (350 °C exhibited the formation of ~5–8 nm diameter Mn5Ge3 and Mn11Ge8 agglomerates by HRTEM, while XPS identified at least two Mn-containing phases: the agglomerates, together with a Ge-rich MnGe~2.5 phase, or manganese diluted into the Ge(001 crystal. LEED revealed the persistence of long range order after a relatively high amount of Mn (100 nm deposited on the single crystal substrate. STM probed the existence of dimer rows on the surface, slightly elongated as compared with Ge–Ge dimers on Ge(001. The films exhibited a clear ferromagnetism at room temperature, opening the possibility of forming a magnetic phase behind a nearly ideally terminated Ge surface, which could find applications in integration of magnetic functionalities on semiconductor bases. SQUID probed the co-existence of a superparamagnetic phase, with one phase which may be attributed to a diluted magnetic semiconductor. The hypothesis that the room temperature ferromagnetic phase might be the one with manganese diluted into the Ge crystal is formulated and discussed.

  17. Spin Transport in Ferromagnetic and Antiferromagnetic Textures

    KAUST Repository

    Akosa, Collins A.

    2016-12-07

    In this dissertation, we provide an accurate description of spin transport in magnetic textures and in particular, we investigate in detail, the nature of spin torque and magnetic damping in such systems. Indeed, as will be further discussed in this thesis, the current-driven velocity of magnetic textures is related to the ratio between the so-called non-adiabatic torque and magnetic damping. Uncovering the physics underlying these phenomena can lead to the optimal design of magnetic systems with improved efficiency. We identified three interesting classes of systems which have attracted enormous research interest (i) Magnetic textures in systems with broken inversion symmetry: We investigate the nature of magnetic damping in non-centrosymmetric ferromagnets. Based on phenomenological and microscopic derivations, we show that the magnetic damping becomes chiral, i.e. depends on the chirality of the magnetic texture. (ii) Ferromagnetic domain walls, skyrmions and vortices: We address the physics of spin transport in sharp disordered magnetic domain walls and vortex cores. We demonstrate that upon spin-independent scattering, the non-adiabatic torque can be significantly enhanced. Such an enhancement is large for vortex cores compared to transverse domain walls. We also show that the topological spin currents owing in these structures dramatically enhances the non-adiabaticity, an effect unique to non-trivial topological textures (iii) Antiferromagnetic skyrmions: We extend this study to antiferromagnetic skyrmions and show that such an enhanced topological torque also exist in these systems. Even more interestingly, while such a non-adiabatic torque inuences the undesirable transverse velocity of ferromagnetic skyrmions, in antiferromagnetic skyrmions, the topological non-adiabatic torque directly determines the longitudinal velocity. As a consequence, scaling down the antiferromagnetic skyrmion results in a much more efficient spin torque.

  18. Micromagnetic simulation of a ferromagnetic particle

    Directory of Open Access Journals (Sweden)

    Ntallis N.

    2014-01-01

    Full Text Available In this work, the magnetic behaviour of a ferromagnetic particle has been investigated by means of micromagnetic modelling, using the Finite Element Method. The simulations were performed on an ellipsoidal particle with uniaxial magnetocrystalline anisotropy by varying the anisotropy constant, the shape and dimensions of the particle. The results indicate the critical particle size for different reversal modes. Above a critical size the formation and motion of domain walls is clearly observed. The associated nucleation and coercive fields are estimated from the demagnetization curves.

  19. Spin transport in ferromagnetically contacted carbon nanotubes

    Energy Technology Data Exchange (ETDEWEB)

    Meyer, C.; Morgan, C.; Schneider, C.M. [Peter Gruenberg Institut, PGI-6, Forschungszentrum Juelich and JARA Juelich Aachen Research Alliance, 52425 Juelich (Germany)

    2011-11-15

    We present magnetoresistance (MR) measurements on carbon nanotubes (CNTs) with different ferromagnetic leads. A sample with permalloy (Ni{sub 80}Fe{sub 20}) contacts shows the expected tunneling-type MR effect. Measurements on devices with CoPd contacts show a larger change of resistance with magnetic field. However, only minor loops are observed, which is explained with domain wall pinning. This is supported by magnetic force microscopy (MFM) measurements, which reveal a complicated bubble and stripe domain pattern. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  20. Ferromagnetism in Electronic Models for Manganites

    OpenAIRE

    Riera, Jose; Hallberg, Karen; Dagotto, Elbio

    1996-01-01

    Ground state properties of the Kondo model for manganese oxides in one dimension are studied using numerical techniques. The large Hund coupling ($J_{H}$) limit is specially analyzed. A robust region of fully saturated ferromagnetism (FM) is identified at all densities. For open boundary conditions it is shown exactly that the ground state is FM at $J_{H} = \\infty$. Hole-spin phase separation competing with FM was also observed when a large exchange $J$ between the $Mn^{3+}$ ions is used. As ...

  1. Transport properties in ferromagnet UTeS

    Energy Technology Data Exchange (ETDEWEB)

    Ikeda, Shugo [Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195 (Japan)]. E-mail: ikeda.shugo@jaea.go.jp; Sakai, Hironori [Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195 (Japan); Matsuda, Tatsuma D. [Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195 (Japan); Aoki, Dai [Institute for Materials Research, Tohoku University, Oarai, Ibaraki 311-1313 (Japan); Homma, Yoshiya [Institute for Materials Research, Tohoku University, Oarai, Ibaraki 311-1313 (Japan); Yamamoto, Etsuji [Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195 (Japan); Nakamura, Akio [Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195 (Japan); Shiokawa, Yoshinobu [Institute for Materials Research, Tohoku University, Oarai, Ibaraki 311-1313 (Japan); Haga, Yoshinori [Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195 (Japan); Onuki, Yoshichika [Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195 (Japan); Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043 (Japan)

    2007-03-15

    The ferromagnet UTeS with the Curie temperature T{sub C}=87K has been studied by measuring the magnetoresistance and Hall resistivity. The Hall coefficient at 0.5T shows a large peak around T{sub C}, reflecting the extraordinary Hall effect. The present extraordinary Hall effect was, however, suppressed by applying a magnetic field of 5.5T. From the results of the electrical resistivity and Hall resistivity measurements, UTeS was found to be a semimetal.

  2. Spin Excitations in Dissipative Ferromagnetic Nanoshells

    Directory of Open Access Journals (Sweden)

    V.V. Kulish

    2016-10-01

    Full Text Available In the paper, dipole-exchange radial-angular spin excitations in a spherical ferromagnetic nanoshell are investigated. For such excitations, a differential equation for the magnetic potential is found, with account for the magnetic dipole-dipole interaction, the exchange interaction, the anisotropy effects and the dissipation. The equation is solved for the three cases – the case of a thin shell, the case of short waves and the case of radial excitations. For each of these cases, the dispersion relation and the spectrum of possible excitation frequencies are found.

  3. Ferromagnetic erbium studied by {mu}SR

    Energy Technology Data Exchange (ETDEWEB)

    Hartmann, O. [Uppsala Univ. (Sweden). Dept. of Theoretical Physics; Lidstroem, E. [Uppsala Univ. (Sweden). Dept. of Theoretical Physics; Ekstroem, M. [Uppsala Univ. (Sweden). Dept. of Theoretical Physics; Waeppling, R. [Uppsala Univ. (Sweden). Dept. of Theoretical Physics; Asch, L. [Technische Univ. Muenchen, Garching (Germany). Physik-Department; Kalvius, G.M. [Technische Univ. Muenchen, Garching (Germany). Physik-Department

    1997-04-01

    The ferromagnetic cone phase of erbium has been studied with {mu}SR. Two processing muon signals were observed with nearly equal intensities at T {approx} 15 K. At lower temperatures, one of the signals is gradually reduced and disappeared below 5 K. The two observed muon frequencies and their depolarisation behaviour show that the magnetic structure deduced from neutron and X-ray scattering must be modified and that a ``squaring up`` of the structure is likely to occur as the temperature is lowered. (orig.).

  4. Ferromagnetic erbium studied by {mu}SR

    Energy Technology Data Exchange (ETDEWEB)

    Hartmann, Ola; Lidstroem, Erik; Ekstroem, Mikael; Waeppling, Roger [Uppsala University, Department of Physics (Sweden); Asch, L.; Kalvius, G.M. [TU Muenich, Physics Department (Germany)

    1997-04-15

    The ferromagnetic cone phase of erbium has been studied with {mu}SR. Two precessing muon signals were observed with nearly equal intensities at T {approx} 15 K. At lower temperatures, one of the signals is gradually reduced and disappeared below 5 K. The two observed muon frequencies and their depolarisation behaviour show that the magnetic structure deduced from neutron and X-ray scattering must be modified and that a 'squaring up' of the structure is likely to occur as the temperature is lowered.

  5. Spin transport in half-metallic ferromagnets

    Science.gov (United States)

    Ohnuma, Y.; Matsuo, M.; Maekawa, S.

    2016-11-01

    We theoretically investigate spin transport in half-metallic ferromagnets at finite temperatures. The side-jump and skew-scattering contributions to spin Hall conductivity are derived using the Kubo formula. The electron-magnon interaction causes a finite density of states in the energy gap of the minority-spin band and induces spin Hall conductivity. We show that spin Hall conductivity is proportional to T3 /2, with T being temperature, and is sensitive to T . We propose that spin Hall conductivity may be a tool to study the minority-spin state.

  6. Carbon Nanotubes Filled with Ferromagnetic Materials

    Directory of Open Access Journals (Sweden)

    Albrecht Leonhardt

    2010-08-01

    Full Text Available Carbon nanotubes (CNT filled with ferromagnetic metals like iron, cobalt or nickel are new and very interesting nanostructured materials with a number of unique properties. In this paper we give an overview about different chemical vapor deposition (CVD methods for their synthesis and discuss the influence of selected growth parameters. In addition we evaluate possible growth mechanisms involved in their formation. Moreover we show their identified structural and magnetic properties. On the basis of these properties we present different application possibilities. Some selected examples reveal the high potential of these materials in the field of medicine and nanotechnology.

  7. Vanishing magnetic interactions in ferromagnetic thin films.

    Science.gov (United States)

    Dunn, J Hunter; Karis, O; Andersson, C; Arvanitis, D; Carr, R; Abrikosov, I A; Sanyal, B; Bergqvist, L; Eriksson, O

    2005-06-03

    We have used element-specific hysteresis measurements, based on the x-ray magnetic circular dichroism technique, to investigate magnetic trilayer structures composed of Fe and Ni layers. Within a critical regime we have discovered a class of structures in which the exchange interaction, the mechanism responsible for the macroscopic magnetism, can become vanishingly small. The experimental observations are supported by first principles theory and are explained as arising from a cancellation of several competing magnetic interactions. Hence, we have discovered a system with a novel exchange interaction between magnetic layers in direct contact that replaces the conventional exchange interaction in ferromagnets.

  8. Evidence of ferromagnetism in off-stoichiometric Fe{sub 2.5-x}V{sub 1+x}Al{sub 0.5} (X{sub 2}YZ) Heusler alloys

    Energy Technology Data Exchange (ETDEWEB)

    Paduani, C. [DF-UFSC, Florianopolis, CEP 88040-900, SC (Brazil)], E-mail: paduani@fisica.ufsc.br; Silveira, R.G. da; Santos, R.G.C. dos; Poettker, W.E. [DF-UFSC, Florianopolis, CEP 88040-900, SC (Brazil); Ardisson, J.D. [CDTN, Belo Horizonte, CEP 30123-970, MG (Brazil); Schaf, J. [IF-UFRGS, Porto Alegre, CEP 91501-970, RS (Brazil); Takeuchi, A.Y. [CBPF, Rio de Janeiro, CEP 22290-180 (Brazil); Yoshida, M.I. [DQ-ICEX-UFMG, Belo Horizonte, CEP 31270-901, MG (Brazil)

    2008-06-12

    In this work we study the structural and magnetic properties of Fe{sub 2.5-x}V{sub 1+x}Al{sub 0.5} alloys. These compounds exhibit a ferromagnetic behavior in the ordered L2{sub 1} phase (X{sub 2}YZ) at low temperature. The increase of the V concentration is detrimental to the onset of a long range ferromagnetic ordering in this system. The results indicate that the Fe atoms are carrying the largest magnetic moment. A re-entrant transition from a spin-glass to a ferromagnetic state was observed at low temperature.

  9. Ferromagnetism at room temperature in Co-doped KNbO{sub 3} bulk samples

    Energy Technology Data Exchange (ETDEWEB)

    Astudillo, A., E-mail: jaastudillo@unicauca.edu.co [Low Temperature Laboratory, Department of Physics, University of Cauca, Calle 5 No. 4-70, Popayán (Colombia); Izquierdo, J.L. [Universidad Nacional de Colombia, Campus Medellín, Departamento de Física, Laboratorio de Materiales Cerámicos y Vítreos, A.A. 568, Medellín (Colombia); Gómez, A. [Universidad Nacional de Colombia, Campus Medellín, Facultad de Minas, Laboratorio de Caracterización de Materiales, A.A. 568, Medellín (Colombia); Bolaños, G. [Low Temperature Laboratory, Department of Physics, University of Cauca, Calle 5 No. 4-70, Popayán (Colombia); Morán, O. [Universidad Nacional de Colombia, Campus Medellín, Departamento de Física, Laboratorio de Materiales Cerámicos y Vítreos, A.A. 568, Medellín (Colombia)

    2015-01-01

    In this work, polycrystalline KNb{sub 1−x}Co{sub x}O{sub 3} (x=0, 0.05 and 0.1) samples were synthesized through standard solid-state reaction, and their structural and magnetic properties were carefully studied. The X-ray powder diffraction (XRD) patterns show reflections of a pure orthorhombic structure (space group Bmm2) with lattice parameters being very close to those reported in the literature. The most important point here is that all the samples ended up being single-phase with no affectation by impurities or segregates. The XRD peaks of Co-doped samples are broadened and shifted to the right side as compared to those of the pristine compound (x=0) suggesting effective substitution of Nb by Co ions. The Co-doped samples exhibit ferromagnetic properties at room temperature, which contrasts starkly with the paramagnetic behavior exhibited by the undoped sample. Interactions between bound magnetic polarons are considered as a possible scenario to explain the appearance of the ferromagnetic signal in the Co-doped samples. - Highlights: • Polycrystalline KNb{sub 1−x}Co{sub x}O{sub 3} (x=0, 0.05 and 0.1) is synthesized by physical route. • XRD patterns show reflections of a pure orthorhombic structure. • No affectation by impurities or segregates is verified by XRD analysis. • The Co-doped samples exhibit ferromagnetic properties at room temperature.

  10. Spin-orbit torques in two-dimensional Rashba ferromagnets

    NARCIS (Netherlands)

    Qaiumzadeh, A.; Duine, R. A.|info:eu-repo/dai/nl/304830127; Titov, M.

    2015-01-01

    Magnetization dynamics in single-domain ferromagnets can be triggered by a charge current if the spin-orbit coupling is sufficiently strong. We apply functional Keldysh theory to investigate spin-orbit torques in metallic two-dimensional Rashba ferromagnets in the presence of spin-dependent

  11. General performance characteristics of an irreversible ferromagnetic Stirling refrigeration cycle

    NARCIS (Netherlands)

    Lin, G.; Bruck, E.H.; Tegus, O.; Zhang, L.

    2004-01-01

    A new magnetic-refrigeration-cycle model using ferromagnetic materials as a cyclic working substance is set up, in which finite-rate heat transfer, heat leak and regeneration time are taken into account. On the basis of the thermodynamic properties of a ferromagnetic material, the general performanc

  12. Spin dynamics of the ferromagnetic superconductor UGe 2

    Science.gov (United States)

    Raymond, S.; Huxley, A.

    2004-07-01

    Inelastic neutron scattering was used to study the low-energy magnetic excitations of the ferromagnetic superconductor UGe 2. The ferromagnetic fluctuations are of Ising nature with a non-conserved magnetization and have an intermediate behavior between localized and itinerant magnetism.

  13. Spin dynamics of the ferromagnetic superconductor UGe{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Raymond, S.; Huxley, A

    2004-07-15

    Inelastic neutron scattering was used to study the low-energy magnetic excitations of the ferromagnetic superconductor UGe{sub 2}. The ferromagnetic fluctuations are of Ising nature with a non-conserved magnetization and have an intermediate behavior between localized and itinerant magnetism.

  14. Phase transitions for continuous-spin Ising ferromagnets

    NARCIS (Netherlands)

    Beijeren, H. van; Sylvester, G.S.

    1978-01-01

    We study the comparison of continuous-spin ferromagnetic Ising models which differ only in their a priori single-spin weighting measures, and characterize the relationship of two even weighting measures ν′, ν on R such that the spin expectations of any ferromagnet with single-spin weighting measure

  15. Spin Heat Accumulation Induced by Tunneling from a Ferromagnet

    NARCIS (Netherlands)

    Vera-Marun, I.J.; Wees, B.J. van; Jansen, R.

    2014-01-01

    An electric current from a ferromagnet into a nonmagnetic material can induce a spin-dependent electron temperature. Here, it is shown that this spin heat accumulation, when created by tunneling from a ferromagnet, produces a non-negligible voltage signal that is comparable to that due to the coexis

  16. Magnetic excitons in singlet-ground-state ferromagnets

    DEFF Research Database (Denmark)

    Birgeneau, R.J.; Als-Nielsen, Jens Aage; Bucher, E.

    1971-01-01

    The authors report measurements of the dispersion of singlet-triplet magnetic excitons as a function of temperature in the singlet-ground-state ferromagnets fcc Pr and Pr3Tl. Well-defined excitons are observed in both the ferromagnetic and paramagnetic regions, but with energies which are nearly...

  17. Intertwined nematic orders in a frustrated ferromagnet

    Science.gov (United States)

    Iqbal, Yasir; Ghosh, Pratyay; Narayanan, Rajesh; Kumar, Brijesh; Reuther, Johannes; Thomale, Ronny

    2016-12-01

    We investigate the quantum phases of the frustrated spin-1/2 J1-J2-J3 Heisenberg model on the square lattice with ferromagnetic J1 and antiferromagnetic J2 and J3 interactions. Using the pseudofermion functional renormalization group technique, we find an intermediate paramagnetic phase located between classically ordered ferromagnetic, stripy antiferromagnetic, and incommensurate spiral phases. We observe that quantum fluctuations lead to significant shifts of the spiral pitch angles compared to the classical limit. By computing the response of the system with respect to various spin rotation and lattice symmetry-breaking perturbations, we identify a complex interplay between different nematic spin states in the paramagnetic phase. While retaining time-reversal invariance, these phases either break spin-rotation symmetry, lattice-rotation symmetry, or a combination of both. We therefore propose the J1-J2-J3 Heisenberg model on the square lattice as a paradigmatic example where different intimately connected types of nematic orders emerge in the same model.

  18. Anisotropy of a cubic ferromagnet at criticality

    Science.gov (United States)

    Kudlis, A.; Sokolov, A. I.

    2016-10-01

    Critical fluctuations change the effective anisotropy of cubic ferromagnet near the Curie point. If the crystal undergoes phase transition into orthorhombic phase and the initial anisotropy is not too strong, reduced anisotropy of nonlinear susceptibility acquires at Tc the universal value δ4*=2/v* 3 (u*+v*) where u* and v* are coordinates of the cubic fixed point on the flow diagram of renormalization group equations. In the paper, the critical value of the reduced anisotropy is estimated within the pseudo-ɛ expansion approach. The six-loop pseudo-ɛ expansions for u*, v*, and δ4* are derived for the arbitrary spin dimensionality n . For cubic crystals (n =3 ) higher-order coefficients of the pseudo-ɛ expansions obtained turn out to be so small that use of simple Padé approximants yields reliable numerical results. Padé resummation of the pseudo-ɛ series for u*, v*, and δ4* leads to the estimate δ4*=0.079 ±0.006 , indicating that detection of the anisotropic critical behavior of cubic ferromagnets in physical and computer experiments is certainly possible.

  19. Titanium nitride room-temperature ferromagnetic nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Morozov, Iu.G., E-mail: morozov@ism.ac.ru [Institute of Structural Macrokinetics and Materials Science, Russian Academy of Sciences, 8 Academician Osipyan Street, Chernogolovka, Moscow Region, 142432 (Russian Federation); Belousova, O.V. [Institute of Structural Macrokinetics and Materials Science, Russian Academy of Sciences, 8 Academician Osipyan Street, Chernogolovka, Moscow Region, 142432 (Russian Federation); Belyakov, O.A. [Ogarev Mordovia State University, Saransk, 68 Bol' shevistskaya Street, 430005 (Russian Federation); Parkin, I.P., E-mail: i.p.parkin@ucl.ac.uk [Department of Chemistry, Materials Chemistry Research Centre, University College London, 20 Gordon Street, London, WC1H 0AJ (United Kingdom); Sathasivam, S. [Department of Chemistry, Materials Chemistry Research Centre, University College London, 20 Gordon Street, London, WC1H 0AJ (United Kingdom); Kuznetcov, M.V., E-mail: maxim1968@mail.ru [All-Russian Research Institute on Problems of Civil Defense and Emergencies of Emergency Control Ministry of Russia (EMERCOM), 7 Davidkovskaya Street, Moscow, 121352 (Russian Federation)

    2016-08-05

    Cubic and near-spherical TiN nanoparticles ranging in average size from 20 to 125 nm were prepared by levitation-jet aerosol synthesis through condensation of titanium vapor in an inert gas flow with gaseous nitrogen injection. The nanoparticles were characterized by using scanning electron microscopy (SEM), X-ray diffraction (XRD), BET measurements, UV–Vis, FT-IR, Raman spectroscopy, XPS, and vibrating-sample magnetometry. Room-temperature ferromagnetism with maximum magnetization up to 2.5 emu/g was recorded for the nanoparticles. The results indicate that the observed ferromagnetic ordering was related to the defect Ti–N structures on the surface of nanoparticles. This suggestion is in good correlation with the measured spectroscopical data. - Highlights: • Levitation-jet aerosol synthesis of TiN nanoparticles (NPs). • SEM, XRD, BET, UV–vis, FT-IR, Raman, XPS and magnetic characterization of the NPs. • Correlation between optical and XPS measurements data and maximum magnetization of the NPs.

  20. Ferromagnetism and crystalline electric field effects in cubic UX2Zn20 (X=Co, Rh, Ir)

    Science.gov (United States)

    Bauer, E. D.; Thompson, J. D.; Sarrao, J. L.; Hundley, M. F.

    2007-03-01

    The physical properties of a new family of cubic UX2Zn20 (X=Co, Rh, Ir) heavy-fermion compounds are presented. Both UCo2Zn20 and URh2Zn20 show peaks in specific heat and magnetic susceptibility at ˜5-10 K suggesting the presence of crystalline electric field (CEF) effects in these materials, i.e., a localized 5f2 configuration of uranium. UIr2Zn20 exhibits a first-order ferromagnetic transition at Tc=2.1 K with a saturation moment μsat=0.4 μB at 2 K indicating itinerant ferromagnetism. All compounds in this series are heavy-fermion materials with enhanced electronic specific heat coefficients γ˜100-450 mJ/mol K2.

  1. High pressure studies on the ferromagnetic dense Kondo systems CeRh3B2 and UCu2Ge2

    Science.gov (United States)

    Cornelius, A. L.; Schilling, J. S.; Endstra, T.; Mydosh, J. A.

    1994-07-01

    The dependence of the Curie temperature of the anomalous ferromagnets UCu2Ge2 and CeRh3B2 on hydrostatic pressure to 11 GPa is determined using a diamond-anvil cell loaded with dense helium as pressure medium. A sensitive primary/secondary coil system allows the detection of the ferromagnetic transition in the ac susceptibility for tiny samples with less than 1 μ mass. The Curie temperatures of the above two compounds, Tc≊110 K and 118 K, both increase initially under pressure but pass through maxima at 8 GPa and 2 GPa, respectively, before falling rapidly at higher pressures. We take this as evidence that both compounds behave as dense Kondo system, where Tc depends on the exchange coupling J according to a magnetic phase diagram originally proposed by Doniach.

  2. Room-temperature ferromagnetism in cerium dioxide powders

    Energy Technology Data Exchange (ETDEWEB)

    Rakhmatullin, R. M., E-mail: rrakhmat@kpfu.ru; Pavlov, V. V.; Semashko, V. V.; Korableva, S. L. [Kazan Federal University, Institute of Physics (Russian Federation)

    2015-08-15

    Room-temperature ferromagnetism is detected in a CeO{sub 2} powder with a grain size of about 35 nm and a low (<0.1 at %) manganese and iron content. The ferromagnetism in a CeO{sub 2} sample with a submicron crystallite size and the same manganese and iron impurity content is lower than in the nanocrystalline sample by an order of magnitude. Apart from ferromagnetism, both samples exhibit EPR spectra of localized paramagnetic centers, the concentration of which is lower than 0.01 at %. A comparative analysis of these results shows that the F-center exchange (FCE) mechanism cannot cause ferromagnetism. This conclusion agrees with the charge-transfer ferromagnetism model proposed recently.

  3. Geometrical dependence of spin current absorption into a ferromagnetic nanodot

    Science.gov (United States)

    Nomura, Tatsuya; Ohnishi, Kohei; Kimura, Takashi

    2016-10-01

    We have investigated the absorption property of the diffusive pure spin current due to a ferromagnetic nanodot in a laterally configured ferromagnetic/nonmagnetic hybrid nanostructure. The spin absorption in a nano-pillar-based lateral-spin-valve structure was confirmed to increase with increasing the lateral dimension of the ferromagnetic dot. However, the absorption efficiency was smaller than that in a conventional lateral spin valve based on nanowire junctions because the large effective cross section of the two dimensional nonmagnetic film reduces the spin absorption selectivity. We also found that the absorption efficiency of the spin current is significantly enhanced by using a thick ferromagnetic nanodot. This can be understood by taking into account the spin absorption through the side surface of the ferromagnetic dot quantitatively.

  4. Magnetocaloric effect in Gd-based ferromagnet GdZn2

    Science.gov (United States)

    Matsumoto, Keisuke T.; Hiraoka, Koichi

    2017-02-01

    Magnetic properties and magnetocaloric effect of the Gd-based compound GdZn2 have been investigated. GdZn2 shows a ferromagnetic transition at TC = 85 K and spin-reorientation transition at TSR = 58 K. The maximum entropy change and relative cooling power (RCP) are estimated to be 11.5 J/K kg and 690 J/kg, respectively, for a magnetic field change of 7 T. The large value of RCP is suggested that GdZn2 is an attractive candidate for a low-temperature magnetic refrigerant.

  5. Joint effect of ferromagnetic and non-ferromagnetic cations for adjusting room temperature ferromagnetism of highly luminescent CuNiInS quaternary nanocrystals

    Science.gov (United States)

    Shen, Jin; Wang, Chunlei; Xu, Shuhong; Lv, Changgui; Zhang, Ruohu; Cui, Yiping

    2017-01-01

    In this work, highly luminescent quaternary CuNiInS nanocrystals (NCs) are put forward as a good prototype for investigating defect-induced room temperature ferromagnetism. A ferromagnetic Ni cation can preserve the strong luminescence of NCs without introducing intermediate energy levels in the center of the forbidden band. The strong luminescence of NCs is used as an indicator for monitoring the concentration of vacancy defects inside them, facilitating the investigation of the origin of room temperature ferromagnetism in CuNiInS NCs. Our results reveal that the patching of Cu vacancies ({{{{V}}}{{Cu}}}-) with Ni will result in bound magnetic polarons composed of both {{{{V}}}{{Cu}}}- and a substitution of Cu by Ni ({{{{Ni}}}{{Cu}}}+), giving rise to the room temperature ferromagnetism of CuNiInS NCs. Either the ferromagnetic Ni or the non-ferromagnetic Cu cation can tune the magnetism of CuNiInS NCs because of the change of bound magnetic polaron concentration at the altered concentration ratio of {{{{V}}}{{Cu}}}- and {{{{Ni}}}{{Cu}}}+.

  6. TUNNEL MAGNETORESISTANCE IN THE FERROMAGNETIC TUNNEL JUNCTION WITH FERROMAGNETIC LAYERS OF FINITE THICKNESS SUBJECTED TO AN ELECTRIC FIELD

    Institute of Scientific and Technical Information of China (English)

    1998-01-01

    Based on the two-band model, we investigate the tunnel magnetoresistance(TMR) in ferromagnet/insulator(semiconductor)/ferromagnet(FM/I(S)/FM) tunnel junction covered on both sides by nonmagnetic metal layers subjected to an electric field. Our results show that TMR oscillates with the thickness of ferromagnetic layers owing to the quantum-size effect and can reach very large value under suitable conditions, which may in general not be reached in FM/I(S)/FM with infinitely thick ferromagnetic layer. Although the electric field causes the change of the oscillation period, phase and amplitude of the TMR, a large TMR is still obtained in some situations with the electric field. Furthermore, the electric field does not change the feature that TMR varies monotonously with the change of magnetization angle of the middle ferromagnetic layer.

  7. FMR investigations of half-metallic ferromagnets

    Science.gov (United States)

    Rameev, B.; Yildiz, F.; Kazan, S.; Aktas, B.; Gupta, A.; Tagirov, L. R.; Rata, D.; Buergler, D.; Gruenberg, P.; Schneider, C. M.; Kämmerer, S.; Reiss, G.; Hütten, A.

    2006-05-01

    Thin films of various half-metallic ferromagnets, such as chromium dioxide (CrO2) and Heusler alloys (Co2Cr0.6Fe0.4Al, Co2MnSi) have been investigated by ferromagnetic resonance (FMR) technique. It is demonstrated that FMR is a very efficient method to study the nanoscale magnetic properties, in particular to probe the magnetic anisotropy and magnetic inhomogeneities of ferromagnetic thin films. Epitaxial CrO2 thin films of various thicknesses (25-535 nm) have been deposited on TiO2(100) substrates by chemical vapor deposition process. It is shown that the magnetic behavior of the CrO2 films results from a competition between the magnetocrystalline and strain anisotropies. For the ultrathin CrO2 film (25 nm) the magnetic easy axis switches from the c-direction to the b-direction of the rutile structure. Thin-film Co2Cr0.6Fe0.4Al samples (25 nm or 100 nm) have been grown by DC magnetron sputtering either on unbuffered SiO2(100) substrates or on the substrates capped by a 50 nm thick V buffer layer. The effects of the vanadium buffer layer and of the film thickness are revealed by FMR studies of the Co2Cr0.6Fe0.4Al samples. Well-resolved multiple spin-wave modes are observed in the unbuffered Co2Cr0.6Fe0.4Al sample with a thickness of 100 nm and the exchange stiffness constant has been estimated. Thin films of Co2MnSi (4-100 nm) have been grown by DC sputtering on silicon substrates on top of a 42 nm thick V seed layer and capped either by Al2O3 or by Co and V layers. A set of the 80 nm thick films has been annealed at different temperatures in the range of 425-550 °C. FMR studies of the Co2MnSi samples shows that at the fixed annealing temperature (450 °C) the highest magnetization is observed in the sample with a thickness of 61 nm, while the thicker samples (100 nm) reveal not only a lower magnetization but greater magnetic inhomogeneity as well. An annealing treatment at T ≥ 450 °C is essential to obtain higher magnetization as well as uniform magnetic

  8. Synthesis, structure, and magnetic properties of the fullerene-based ferromagnets Eu3C70 and Eu9C70.

    Science.gov (United States)

    Takenobu, Taishi; Chi, Dam H; Margadonna, Serena; Prassides, Kosmas; Kubozono, Yoshihiro; Fitch, Andrew N; Kato, Ken-Ichi; Iwasa, Yoshihiro

    2003-02-19

    Intercalation of C(70) with europium affords two kinds of magnetic compounds, a canted antiferromagnet Eu(x)C(70) (x approximately 3) and a ferromagnet Eu(x)C(70) (x approximately 9) with transition temperatures (T(C)) of 5 and 38 K, respectively. The Curie constants in the paramagnetic phase and the saturation moment in the ferromagnetic phase are both understood by the full moment of Eu(2+) for both systems. The structure of Eu(3)(-)(delta)C(70) (delta approximately 0.27) is pseudo-monoclinic, derived by a simple deformation of the parent face-centered cubic (fcc) structure. Eu(9)(-)(delta)C(70) (delta approximately 0.2) forms an fcc structure, in which cuboctahedral clustering of Eu(2+) ions is observed in the enhanced size octahedral holes. The observed T(C) of the Eu(9)(-)(delta)C(70) ferromagnet is comparable to or larger than those of simple binary Eu-based ferromagnets, such as Eu chalcogenides or carbides, despite the low atomic ratio of Eu in the chemical formulas. This can be understood by the short Eu(2+)-Eu(2+) distances and high coordination numbers permitted by the multiple occupation by Eu(2+) ions of the expanded octahedral interstitial sites in higher fullerene-based solids.

  9. Green's function study of a three-sublattice mixed-spin Heisenberg ferromagnetic and ferrimagnetic system

    Energy Technology Data Exchange (ETDEWEB)

    Mert, Gülistan, E-mail: gmert@selcuk.edu.tr

    2014-08-01

    The magnetic properties of a three-sublattice mixed-spin Heisenberg ferromagnetic and ferrimagnetic system are investigated with the help of the Green's function technique in order to clarify some characteristic magnetic behaviors of Prussian-blue compounds. Various types of magnetization curves are obtained, which exhibits one- and two-compensation temperatures. The first-order phase transitions from ferrimagnetic to ferromagnetic state have been observed. There are zero-temperature quantum fluctuations for the ferrimagnet at the absolute state while not for ferromagnet. Moreover, in the case of ferrimagnet, inverted magnetic hysteresis loop with negative coercivity is observed at a certain temperature range and the coercivity takes the value zero at the compensation point. - Highlights: • We investigate a three-sublattice Heisenberg ferromagnetic and ferrimagnetic system. • System exhibits one- and two-compensation temperatures. • One observes the first-order phase transitions. • Inverted hysteresis loop for ferrimagnet is obtained. • Coercive field for ferrimagnet reaches zero at compensation temperature.

  10. Magnetic evolution of itinerant ferromagnetism and interlayer antiferromagnetism in cerium doped LaCo2P2 crystals

    Science.gov (United States)

    Tian, Yong; Kong, Yixiu; Liu, Kai; Zhang, Anmin; He, Rui; Zhang, Qingming

    2017-05-01

    ThCr2Si2-type phosphide ACo2P2 (A=Eu, La, Pr, Nd, Ce) has the same structure as iron arsenides, but their magnetic behaviors are quite distinct. In this paper, we grew a series of La1-xCexCo2P2 single crystals (x=0.0 to1.0), made structural and magnetic characterizations. We found the introduction of cerium induces a rapid decrease of c-axis and a change from ferromagnetic to antiferromagnetic states. Compared to other trivalent doped compounds, the enhancement of ferromagnetism with doping is suppressed and the transition from ferromagnetism to antiferromagnetism appear earlier. By employing first-principles band-structure calculations, we identify the increase of Ce valence suppress the itinerant ferromagnetism and leading to formation of P-P bonding with the shortening of c-axis. The bonding effectively drives an increase of interlayer antiferromagnetic interaction, eventually leads to antiferromagnetic ordering of cobalt in high-doping region.

  11. Dynamic detection of spin accumulation in ferromagnet-semiconductor devices by ferromagnetic resonance (Conference Presentation)

    Science.gov (United States)

    Crowell, Paul A.; Liu, Changjiang; Patel, Sahil; Peterson, Tim; Geppert, Chad C.; Christie, Kevin; Stecklein, Gordon; Palmstrøm, Chris J.

    2016-10-01

    A distinguishing feature of spin accumulation in ferromagnet-semiconductor devices is its precession in a magnetic field. This is the basis for detection techniques such as the Hanle effect, but these approaches become ineffective as the spin lifetime in the semiconductor decreases. For this reason, no electrical Hanle measurement has been demonstrated in GaAs at room temperature. We show here that by forcing the magnetization in the ferromagnet to precess at resonance instead of relying only on the Larmor precession of the spin accumulation in the semiconductor, an electrically generated spin accumulation can be detected up to 300 K. The injection bias and temperature dependence of the measured spin signal agree with those obtained using traditional methods. We further show that this new approach enables a measurement of short spin lifetimes (techniques. The measurements were carried out on epitaxial Heusler alloy (Co2FeSi or Co2MnSi)/n-GaAs heterostructures. Lateral spin valve devices were fabricated by electron beam and photolithography. We compare measurements carried out by the new FMR-based technique with traditional non-local and three-terminal Hanle measurements. A full model appropriate for the measurements will be introduced, and a broader discussion in the context of spin pumping experimenments will be included in the talk. The new technique provides a simple and powerful means for detecting spin accumulation at high temperatures. Reference: C. Liu, S. J. Patel, T. A. Peterson, C. C. Geppert, K. D. Christie, C. J. Palmstrøm, and P. A. Crowell, "Dynamic detection of electron spin accumulation in ferromagnet-semiconductor devices by ferromagnetic resonance," Nature Communications 7, 10296 (2016). http://dx.doi.org/10.1038/ncomms10296

  12. Perfect GMR effect in gapped graphene-based ferromagnetic normal ferromagnetic junctions

    Institute of Scientific and Technical Information of China (English)

    Hossein Karbaschi; Gholam Reza Rashedi

    2015-01-01

    We investigate the quantum transport property in gapped graphene-based ferromagnetic/normal/ferromagnetic (FG/NG/FG) junctions by using the Dirac–Bogoliubov–de Gennes equation. The graphene is fabricated on SiC and BN substrates separately, so carriers in FG/NG/FG structures are considered as massive relativistic particles. Transmission prob-ability, charge, and spin conductances are studied as a function of exchange energy of ferromagnets (h), size of graphene gap, and thickness of normal graphene region (L) respectively. Using the experimental values of Fermi energy in the normal graphene part (EFN∼400 meV) and energy gap in graphene (260 meV for SiC and 50 meV for BN substrate), it is shown that this structure can be used for both spin-up and spin-down polarized current. The latter case has different behavior of gapped FG/NG/FG from that of gapless FG/NG/FG structures. Also perfect charge giant magnetoresistance is observed in a range of EFN−mv2F

  13. Magnetoresistive system with concentric ferromagnetic asymmetric nanorings

    Energy Technology Data Exchange (ETDEWEB)

    Avila, J. I., E-mail: javila@ulg.ac.be; Tumelero, M. A.; Pasa, A. A.; Viegas, A. D. C. [Laboratório de Filmes Finos e Superfícies (LFFS), Departamento de Física, Universidade Federal de Santa Catarina, CP 476 Florianópolis (Brazil)

    2015-03-14

    A structure consisting of two concentric asymmetric nanorings, each displaying vortex remanent states, is studied with micromagnetic calculations. By orienting in suitable directions, both the asymmetry of the rings and a uniform magnetic field, the vortices chiralities can be switched from parallel to antiparallel, obtaining in this way the analogue of the ferromagnetic and antiferromagnetic configurations found in bar magnets pairs. Conditions on the thickness of single rings to obtain vortex states, as well as formulas for their remanent magnetization are given. The concentric ring structure enables the creation of magnetoresistive systems comprising the qualities of magnetic nanorings, such as low stray fields and high stability. A possible application is as contacts in spin injection in semiconductors, and estimations obtained here of magnetoresistance change for a cylindrical spin injection based device show significant variations comparable to linear geometries.

  14. Possible room temperature ferromagnetism in silicon doped tellurium semiconductor

    Energy Technology Data Exchange (ETDEWEB)

    Mishra, P.K., E-mail: pkmishra@barc.gov.in [Technical Physics Division, Bhabha Atomic Research Centre, Mumbai 400085 (India); Babu, P.D., E-mail: pdbabu@csr.res.in [UGC-DAE Consortium for Scientific Research, Mumbai Centre, BARC, Mumbai 400085 (India); Ravikumar, G. [Technical Physics Division, Bhabha Atomic Research Centre, Mumbai 400085 (India); Mishra, R.; Roy, Mainak; Phapale, S. [Chemistry Division, Bhabha Atomic Research Centre, Mumbai 400085 (India); Sastry, P.U. [Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai 400085 (India)

    2015-08-05

    Highlights: • In this work we report the observation of ferromagnetism in a silicon doped tellurium sample at room temperature. • Isothermal magnetization hysteresis measurements shows ferromagnetism persists up to room temperature. • We ascribe the origin of ferromagnetism to possible modification of electronic band or generation of local magnetic moment by silicon doping into the parent tellurium lattice. • Potentially this could be a new type of room-temperature magnetic semiconductor that is not based on any oxide or nitride. - Abstract: We have found direct evidence of ferromagnetism in a silicon doped tellurium sample, a new type of magnetic semiconductor that is not based on any oxide or nitride. Room temperature ferromagnetism was very apparent from the magnetization hysteresis. Isothermal magnetization hysteresis loop and differences in ZFC and FC branches of magnetization shows that the ferromagnetic transition temperature is above room temperature. Observation of magnetization hysteresis only at low magnetic fields is indicative of smaller domain size. Average estimated magnetic moment μ per domain is 2.6 μ{sub B}. The origin of ferromagnetism could be ascribed to modification of electronic band or generation of local magnetic moment by silicon doping into the parent tellurium lattice.

  15. Interfacial Symmetry Control of Emergent Ferromagnetism at the Nanoscale.

    Science.gov (United States)

    Grutter, A J; Vailionis, A; Borchers, J A; Kirby, B J; Flint, C L; He, C; Arenholz, E; Suzuki, Y

    2016-09-14

    The emergence of complex new ground states at interfaces has been identified as one of the most promising routes to highly tunable nanoscale materials. Despite recent progress, isolating and controlling the underlying mechanisms behind these emergent properties remains among the most challenging materials physics problems to date. In particular, generating ferromagnetism localized at the interface of two nonferromagnetic materials is of fundamental and technological interest. Moreover, the ability to turn the ferromagnetism on and off would shed light on the origin of such emergent phenomena and is promising for spintronic applications. We demonstrate that ferromagnetism confined within one unit cell at the interface of CaRuO3 and CaMnO3 can be switched on and off by changing the symmetry of the oxygen octahedra connectivity at the boundary. Interfaces that are symmetry-matched across the boundary exhibit interfacial CaMnO3 ferromagnetism while the ferromagnetism at symmetry-mismatched interfaces is suppressed. We attribute the suppression of ferromagnetic order to a reduction in charge transfer at symmetry-mismatched interfaces, where frustrated bonding weakens the orbital overlap. Thus, interfacial symmetry is a new route to control emergent ferromagnetism in materials such as CaMnO3 that exhibit antiferromagnetism in bulk form.

  16. Coexistence of ferromagnetism and superconductivity in YBCO nanoparticles.

    Science.gov (United States)

    Zhu, Zhonghua; Gao, Daqiang; Dong, Chunhui; Yang, Guijin; Zhang, Jing; Zhang, Jinlin; Shi, Zhenhua; Gao, Hua; Luo, Honggang; Xue, Desheng

    2012-03-21

    Nanoparticles of superconducting YBa(2)Cu(3)O(7-δ) were synthesized via a citrate pyrolysis technique. Room temperature ferromagnetism was revealed in the samples by a vibrating sample magnetometer. Electron spin resonance spectra at selected temperatures indicated that there is a transition from the normal to the superconducting state at temperatures below 100 K. The M-T curves with various applied magnetic fields showed that the superconducting transition temperatures are 92 K and 55 K for the air-annealed and the post-annealed samples, respectively. Compared to the air-annealed sample, the saturation magnetization of the sample by reheating the air-annealed one in argon atmosphere is enhanced but its superconductivity is weakened, which implies that the ferromagnetism maybe originates from the surface oxygen defects. By superconducting quantum interference device measurements, we further confirmed the ferromagnetic behavior at high temperatures and interesting upturns in field cooling magnetization curves within the superconducting region are found. We attributed the upturn phenomena to the coexistence of ferromagnetism and superconductivity at low temperatures. Room temperature ferromagnetism of superconducting YBa(2)Cu(3)O(7-δ) nanoparticles has been observed in some previous related studies, but the issue of the coexistence of ferromagnetism and superconductivity within the superconducting region is still unclear. In the present work, it will be addressed in detail. The cooperation phenomena found in the spin-singlet superconductors will help us to understand the nature of superconductivity and ferromagnetism in more depth.

  17. UGe2: A ferromagnetic spin-triplet superconductor

    Science.gov (United States)

    Huxley, Andrew; Sheikin, Ilya; Ressouche, Eric; Kernavanois, Nolwenn; Braithwaite, Daniel; Calemczuk, Roberto; Flouquet, Jacques

    2001-04-01

    The identification of a spin-triplet superfluid phase in 3He naturally led to more general theoretical predictions that spin triplet superconductivity might occur near to a ferromagnetic instability in some metals. The recent discovery of superconductivity near a ferromagnetic quantum critical point in UGe2 now calls for these predictions to be reexamined experimentally. In this light it initially appears surprising that superconductivity in UGe2 has only been detected in the ferromagnetic phase and not also at pressures above the critical pressure for the suppression of ferromagnetism. In this paper we provide evidence that the superconductivity is indeed a bulk property. We also observe the evolution with pressure of the magnetic order by neutron scattering and find that the ferromagnetic component of the order is still present at a pressure and temperature where superconductivity is found. In resistivity measurements we identify an additional transition within the ferromagnetic state. The characteristic temperature of this transition, Tx, decreases with pressure and disappears at a pressure Px close to the pressure at which the superconductivity is strongest. Evidence is presented that this transition is also induced by a magnetic field at pressures just above Px. An observed unusual reentrant behavior of the superconductivity with field at a pressure of 13.5 kbar is then qualitatively explained. These results suggest that the transition at Px is intricately related to the appearance of superconductivity, which could explain why the superconductivity is apparently confined to the ferromagnetic phase.

  18. Spin-wave modes of ferromagnetic films

    Science.gov (United States)

    Arias, R. E.

    2016-10-01

    The spin-wave modes of ferromagnetic films have been studied for a long time experimentally as well as theoretically, either in the magnetostatic approximation or also considering the exchange interaction. A theoretical method is presented that allows one to determine with ease the exact frequency dispersion relations of dipole-exchange modes under general conditions: an obliquely applied magnetic field, and surface boundary conditions that allow for partial pinning, which may be of different origins. The method is a generalization of Green's theorem to the problem of solving the linear dynamics of ferromagnetic spin-wave modes. Convolution integral equations for the magnetization and the magnetostatic potential of the modes are derived on the surfaces of the film. For the translation-invariant film these become simple local algebraic equations at each in-plane wave vector. Eigenfrequencies result from imposing a 6 ×6 determinant to be null, and spin-wave modes follow everywhere through solving linear 6 ×6 inhomogeneous systems. An interpretation of the results is that the Green's functions represent six independent plane-wave solutions to the equations of motion, with six associated complex perpendicular wave vectors: volume modes correspond to the cases in which two of these are purely real at a given frequency. Furthermore, the convolution extinction equations enforce the boundary conditions: this is possible at specific eigenfrequencies for a given in-plane wave vector. Magnetostatic modes may also be obtained in detail. At low frequencies and for some obliquely applied magnetic fields, magnetostatic and dipole-exchange volume modes may have forward or backward character depending on the frequency range.

  19. Microwave permeability of metamaterials based on ferromagnetic composites

    Energy Technology Data Exchange (ETDEWEB)

    Adenot-Engelvin, Anne-Lise [CEA Le Ripault, BP 16 37260 Mounts (France)]. E-mail: anne-lise.adenot-engelvin@cea.fr; Dudek, Christophe [CEA Le Ripault, BP 16 37260 Mounts (France); LEMA, UMR 6157 CNSR, Universite de Tours, 37000 TOURS (France); Acher, Olivier [CEA Le Ripault, BP 16 37260 Mounts (France)

    2006-05-15

    In this paper, we focus on metamaterials based on ferromagnetic composite combined with an inductive pattern. CoFeSiB amorphous ferromagnetic glass-coated microwires and thin films are involved in the composite. The inductive pattern is a coiling of Copper wire with a varying number of loops. We derived the microwave permeability of the ferromagnetic material inside the inductive pattern through a Landau-Gilbert model of gyromagnetism. In agreement with experimental results, the engineering of resonance frequency of the sample is achieved through the number of loops of the coiling.

  20. Microwave permeability of metamaterials based on ferromagnetic composites

    Science.gov (United States)

    Adenot-Engelvin, Anne-Lise; Dudek, Christophe; Acher, Olivier

    2006-05-01

    In this paper, we focus on metamaterials based on ferromagnetic composite combined with an inductive pattern. CoFeSiB amorphous ferromagnetic glass-coated microwires and thin films are involved in the composite. The inductive pattern is a coiling of Copper wire with a varying number of loops. We derived the microwave permeability of the ferromagnetic material inside the inductive pattern through a Landau-Gilbert model of gyromagnetism. In agreement with experimental results, the engineering of resonance frequency of the sample is achieved through the number of loops of the coiling.

  1. Tunnel magnetoresis-tance(TMR) in ferromagnetic metalinsulator granular films

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    We review the recently discovered tunnel-type giant magnetoresistance (GMR) in ferromagnetic metal- insulator granular thin films, which is the magnetoresistance (MR) associated with the spin-dependent tunneling between two ferromagnetic metal particles. The theoretical and ex-perimental results including electrical resistivity, magnetore-sistance and their temperature dependence are described. Limitations to the applications of the ferromagnetic metal- insulator granular films are also discussed. Additionally, a brief survey of another two magnetic properties, high- fre-quency property and giant Hall effect (GHE) associated strongly with the granular structures is also presented.

  2. Andreev Tunneling Through a Ferromagnet/Quantum-Dot/Superconductor System

    Institute of Scientific and Technical Information of China (English)

    RAO Hong-Hu; ZHU Yu; LIN Tsung-Han

    2002-01-01

    We study Andreev tunneling through a ferromagnet/quantum-dot (QD)/superconductor system. By usingnonequilibrum Green function method, the averaged occupation of electrons in QD and the Andreev tunneling currentare studied. Comparing to the norma-metal/quantum-dot/superconductor, the system shows significant changes: (i)The averaged occupations of spin-up and spin-down electrons are not equal. (ii) With the increase of the polarizationof ferromagnetic lead, the Andreev reflection current decreases. (iii) However, even the ferromagnetic lead reaches fullpolarization, the averaged occupation of spin-down electrons is not zero. The physics of these changes is discussed.

  3. Ultrafast Control of Magnetism in Ferromagnetic Semiconductors via Photoexcited Transient Carriers

    Energy Technology Data Exchange (ETDEWEB)

    Cotoros, Ingrid A. [Univ. of California, Berkeley, CA (United States)

    2008-12-01

    The field of spintronics offers perspectives for seamless integration of coupled and inter-tunable electrical and magnetic properties in a single device. For integration of the spin degree of freedom with current electronic technology, new semiconductors are needed that show electrically-tunable magnetic properties at room temperature and above. Dilute magnetic semiconductors derived from III-V compounds, like GaMnAs and InMnAs, show coupled and tunable magnetic, transport, and optical properties, due to the fact that their ferromagnetism is hole-mediated. These unconventional materials are ideal systems for manipulating the magnetic order by changing the carrier polarization, population density, and energy band distribution of the complementary subsystem of holes. This is the main theme we cover in this thesis. In particular, we develop a unique setup by use of ultraviolet pump, near-infrared probe femtosecond laser pulses, that allows for magneto-optical Kerr effect (MOKE) spectroscopy experiments. We photo-excite transient carriers in our samples, and measure the induced transient magnetization dynamics. One set of experiments performed allowed us to observe for the first time enhancement of the ferromagnetic order in GaMnAs, on an ultrafast time scale of hundreds of picoseconds. The corresponding transient increase of Curie temperature (Tc, the temperature above which a ferromagnetic material loses its permanent magnetism) of about 1 K for our experimental conditions is a very promising result for potential spintronics applications, especially since it is seconded by observation of an ultrafast ferromagnetic to paramagnetic phase transition above Tc. In a different set of experiments, we "write" the magnetization in a particular orientation in the sample plane. Using an ultrafast scheme, we alter the distribution of holes in the system and detect signatures of the particular memory state in the subsequent magnetization dynamics, with unprecedented hundreds of

  4. Band gap tuning and room temperature ferromagnetism in Co doped Zinc stannate nanostructures

    Energy Technology Data Exchange (ETDEWEB)

    Sumithra, S., E-mail: ssmithra@gmail.com; Victor Jaya, N.

    2016-07-15

    The effect of Co doping on structural, optical and magnetic behavior of pure and Co doped Zinc stannate (ZTO) nanostructures was investigated. Pure and Co (1%, 3% & 5%) doped Zn{sub 2}SnO{sub 4} compounds were prepared through simple precipitation route. Formation of cubic inverse spinel structure and metal oxide vibrations of the samples were investigated using XRD and FTIR. Co doping influences the crystallite size producing micro strain in ZTO lattice. Poly dispersed rod like shape of the particles was examined by FESEM. Elemental composition of prepared samples was identified by EDAX analysis. Optical Absorption spectra shows significant red shift on increasing the dopant concentration which indicates the reduction in optical band gap. Visible luminescence observed from photoluminescence studies confirms the presence of oxygen vacancies and trap sites in the lattice. Magnetization analysis reveals the enhanced ferromagnetic behavior in all Co doped ZTO samples. The amplified ferromagnetic ordering in Co doped ZTO compounds has been explained in terms of defects serving as free spin polarized prophetic carriers.

  5. Possible mechanism for d0 ferromagnetism mediated by intrinsic defects

    KAUST Repository

    Zhang, Zhenkui

    2014-01-01

    We examine the effects of several intrinsic defects on the magnetic behavior of ZnS nanostructures using hybrid density functional theory to gain insights into d0 ferromagnetism. Previous studies have predicted that the magnetism is due to a coupling between partially filled defect states. By taking into account the electronic correlations, we find an additional splitting of the defect states in Zn vacancies and thus the possibility of gaining energy by preferential filling of hole states, establishing ferromagnetism between spin polarized S 3p holes. We demonstrate a crucial role of neutral S vacancies in promoting ferromagnetism between positively charged S vacancies. S dangling bonds on the nanoparticle surface also induce ferromagnetism. This journal is

  6. Emergent vortices at a ferromagnetic superconducting oxide interface

    Science.gov (United States)

    Petrović, A. P.; Paré, A.; Paudel, T. R.; Lee, K.; Holmes, S.; Barnes, C. H. W.; David, A.; Wu, T.; Tsymbal, E. Y.; Panagopoulos, C.

    2014-10-01

    Understanding the cohabitation arrangements of ferromagnetism and superconductivity at the LaAlO3/SrTiO3 interface remains an open challenge. Probing this coexistence with sub-Kelvin magnetotransport experiments, we demonstrate that a hysteretic in-plane magnetoresistance develops below the superconducting transition for ≤ft| {{H}//} \\right| \\lt 0.15 T, independently of the carrier density or oxygen annealing. This hysteresis is argued to arise from vortex depinning within a thin (\\lt 20 nm) superconducting layer, mediated by discrete ferromagnetic dipoles located solely above the layer. The pinning strength may be modified by varying the superconducting channel thickness via electric field-effect doping. No evidence is found for bulk magnetism or finite-momentum pairing, and we conclude that ferromagnetism is strictly confined to the interface, where it competes with superconductivity. Our work indicates that oxide interfaces are ideal candidate materials for the growth and analysis of nanoscale superconductor/ferromagnet hybrids.

  7. Highly thermal-stable ferromagnetism by a natural composite

    Science.gov (United States)

    Ma, Tianyu; Gou, Junming; Hu, Shanshan; Liu, Xiaolian; Wu, Chen; Ren, Shuai; Zhao, Hui; Xiao, Andong; Jiang, Chengbao; Ren, Xiaobing; Yan, Mi

    2017-01-01

    All ferromagnetic materials show deterioration of magnetism-related properties such as magnetization and magnetostriction with increasing temperature, as the result of gradual loss of magnetic order with approaching Curie temperature TC. However, technologically, it is highly desired to find a magnetic material that can resist such magnetism deterioration and maintain stable magnetism up to its TC, but this seems against the conventional wisdom about ferromagnetism. Here we show that a Fe-Ga alloy exhibits highly thermal-stable magnetization up to the vicinity of its TC, 880 K. Also, the magnetostriction shows nearly no deterioration over a very wide temperature range. Such unusual behaviour stems from dual-magnetic-phase nature of this alloy, in which a gradual structural-magnetic transformation occurs between two magnetic phases so that the magnetism deterioration is compensated by the growth of the ferromagnetic phase with larger magnetization. Our finding may help to develop highly thermal-stable ferromagnetic and magnetostrictive materials.

  8. Exchange bias training effect in coupled all ferromagnetic bilayer structures.

    Science.gov (United States)

    Binek, Ch; Polisetty, S; He, Xi; Berger, A

    2006-02-17

    Exchange coupled bilayers of soft and hard ferromagnetic thin films show remarkable analogies to conventional antiferromagnetic/ferromagnetic exchange bias heterostructures. Not only do all these ferromagnetic bilayers exhibit a tunable exchange bias effect, they also show a distinct training behavior upon cycling the soft layer through consecutive hysteresis loops. In contrast with conventional exchange bias systems, such all ferromagnetic bilayer structures allow the observation of training induced changes in the bias-setting hardmagnetic layer by means of simple magnetometry. Our experiments show unambiguously that the exchange bias training effect is driven by deviations from equilibrium in the pinning layer. A comparison of our experimental data with predictions from a theory based upon triggered relaxation phenomena shows excellent agreement.

  9. Reentrant ferromagnetism and its stability in magnetic semiconductors

    Science.gov (United States)

    Zutic, Igor; Erwin, Steven; Petukhov, Andre

    2007-03-01

    The magnetization of a ferromagnetic material normally decays monotonically with increasing temperature. Here we demonstrate theoretically the possibility of quite different behavior: reentrant ferromagnetism in semiconductors [1]. Reentrant magnetism can arise in semiconductors because as the temperature rises, the resulting higher concentration of thermally excited carriers can enhance the exchange coupling between magnetic impurities. This opens the possibility of materials exhibiting a transition from the low-temperature paramagnetic phase, in which carriers are frozen out, to a ferromagnetic phase at higher temperature. Thus, in the absence of other ferromagnetic mechanisms there will be two critical temperatures, Tc1 Zuti'c, A. Petukhov, S. C. Erwin, preprint. [2] I. Zuti'c, J. Fabian, S. C. Erwin, Phys. Rev. Lett. 97, 026602 (2006).

  10. Exchange bias effect in alloys and compounds.

    Science.gov (United States)

    Giri, S; Patra, M; Majumdar, S

    2011-02-23

    The phenomenology of exchange bias effects observed in structurally single-phase alloys and compounds but composed of a variety of coexisting magnetic phases such as ferromagnetic, antiferromagnetic, ferrimagnetic, spin-glass, cluster-glass and disordered magnetic states are reviewed. The investigations on exchange bias effects are discussed in diverse types of alloys and compounds where qualitative and quantitative aspects of magnetism are focused based on macroscopic experimental tools such as magnetization and magnetoresistance measurements. Here, we focus on improvement of fundamental issues of the exchange bias effects rather than on their technological importance.

  11. Observation of short range ferromagnetic interactions and magnetocaloric effect in cobalt substituted Gd5Si2Ge2.

    Science.gov (United States)

    Uthaman, Bhagya; Manju, P; Thomas, Senoy; Jaiswal Nagar, Deepshikha; Suresh, K G; Varma, Manoj Raama

    2017-05-17

    We report on the observation of double transition - a first order and a second order transition in Gd5Si2-xCoxGe2 with x = 0, 0.1, 0.2 and 0.4 with the appearance of short-range ferromagnetic correlations. The first order phase transition is due to a combined magnetostructural transition from monoclinic paramagnetic phase to orthorhombic ferromagnetic phase on cooling while the second order transition arises from an orthorhombic paramagnetic to ferromagnetic phase on cooling. Structural studies show that the substituted compounds crystallize in a combination of Gd5Si2Ge2 and Gd5Si4 phases. Low-temperature X-ray diffraction measurements confirm the complete transformation from monoclinic to orthorhombic phase. DC magnetization measurements reveal an anomalous low field magnetic behaviour indicating a Griffiths-like phase. This unusual behaviour is attributed to the local disorder within the crystallographic structure indicating the presence of short-range magnetic correlations and ferromagnetic clustering, which is stabilized and enhanced by competing intra-layer and inter-layer magnetic interactions. The magnetostructural transition results in entropy changes (-ΔSM) of 9 J kg(-1) K(-1) at 260 K for x = 0.1, 8.5 J kg(-1) K(-1) at 245 K for x = 0.2 and 4.2 J kg(-1) K(-1) at 210 K for x = 0.4 for a field change of 50 kOe. Co substitution induces compelling crystallographic and magnetoresponsive effects in the Gd-Si-Ge system, which could be useful for potential and smart applications such as solid-state magnetic refrigeration and sensitive magnetic switching from paramagnetic to ferromagnetic state. Universal curve analysis has been carried out on the substituted samples to study the order of the magnetic transition.

  12. Magnetic, phase transformation and magnetocaloric studies in ferromagnetic Ni55Mn20Ga25 Heusler alloy

    Science.gov (United States)

    Babita, I.; Gopalan, R.; Ram, S.

    2009-01-01

    The phase transformation and magnetic entropy change (ΔSM) in the Ni55Mn20Ga25 Heusler alloy has been studied. The temperature dependence of magnetization study shows the direct transition from ferromagnetic martensitic phase to paramagnetic austenitic phase occurred at 353 K. By compositional tuning the first order martensitic transformation (TM ~200 K for parent compound Ni2MnGa) and second order magnetic phase transition temperatures (TC ~375 K for parent compound Ni2MnGa) can be merged. This occurs for Ni55Mn20Ga25 alloy at 353 K. The magnetic entropy change, ΔSM-value of -7.0 Jkg-1K-1 has been obtained in a field change of 1.2 T. The origin of enhancement in ΔSM -value is attributed to the essential coincidence of TM and TC.

  13. Soft ferromagnetic properties of Ni44Fe6Mn32Al18 doped Co partially

    Science.gov (United States)

    Notonegoro, Hamdan Akbar; Kurniawan, Budhy; Kurniawan, Candra; Manaf, Azwar

    2017-01-01

    Research in finding suitable magnetocaloric material around room temperature made ferromagnetic (FM) (Ni-Mn)-based Heusler alloys receive considerable attention as a potential candidate for the magnetic refrigerator. This compound are associated with the shape-memory effect, magnetic superelasticity, and more others magneto-functional properties. The compounds were prepared by vacuum arc melter (VAM) under argon atmosphere which sintering and annealing process were running with quartz cube in vacuum condition. A small amount of coercivity value at σ = 0 in the hysteresis curve occurred whereas magnetization of the sample in various temperature does not reach saturation. The Currie temperature Tc of the sample was obtained at 358 K. Nevertheless, this is dubious value because at T = 300 K the curves had swooped down. Additional measurements necessary to taken as a comparison to verify this value.

  14. Theoretical models of ferromagnetic III-V semiconductors

    OpenAIRE

    Jungwirth, T.; Sinova, Jairo; Kučera, J.; MacDonald, A. H.

    2002-01-01

    Recent materials research has advanced the maximum ferromagnetic transition temperature in semiconductors containing magnetic elements toward room temperature. Reaching this goal would make information technology applications of these materials likely. In this article we briefly review the status of work over the past five years which has attempted to achieve a theoretical understanding of these complex magnetic systems. The basic microscopic origins of ferromagnetism in the (III,Mn)V compoun...

  15. Novel Majorana mode and magnetoresistance in ferromagnetic superconducting topological insulator

    OpenAIRE

    Goudarzi, Hadi; Khezerlou, Maryam; Asgarifar, Samin

    2017-01-01

    Among the potential applications of topological insulators, we investigate theoretically the effect of coexistence of proximity-induced ferromagnetism and superconductivity on the surface states of 3-dimensional topological insulator, where the superconducting electron-hole excitations can be significantly affected by the magnetization of ferromagnetic order. We find that, Majorana mode energy, as a verified feature of TI F/S structure, along the interface sensitively depends on the magnitude...

  16. Damped Topological Magnons in the Kagome-Lattice Ferromagnets

    Science.gov (United States)

    Chernyshev, A. L.; Maksimov, P. A.

    2016-10-01

    We demonstrate that interactions can substantially undermine the free-particle description of magnons in ferromagnets on geometrically frustrated lattices. The anharmonic coupling, facilitated by the Dzyaloshinskii-Moriya interaction, and a highly degenerate two-magnon continuum yield a strong, nonperturbative damping of the high-energy magnon modes. We provide a detailed account of the effect for the S =1 /2 ferromagnet on the kagome lattice and propose further experiments.

  17. Superconducting proximity effect in a mesoscopic ferromagnetic wire

    OpenAIRE

    Giroud, M.; Courtois, H.; Hasselbach, K.; Mailly, D.; Pannetier, B.

    1998-01-01

    We present an experimental study of the transport properties of a ferromagnetic metallic wire (Co) in metallic contact with a superconductor (Al). As the temperature is decreased below the Al superconducting transition, the Co resistance exhibits a significant dependence on both temperature and voltage. The differential resistance data show that the decay length for the proximity effect is much larger than we would simply expect from the exchange field of the ferromagnet.

  18. Magnetization Profiles of Ferromagnetic Ising Films in a Transverse Field

    Institute of Scientific and Technical Information of China (English)

    WANG Xiao-Guang; PAN Shao-Hua; YANG Guo-Zhen

    2000-01-01

    Within the framework of the mean field theory, we study the magnetization profiles of ferromagnetic Ising films in a transverse field. By the transfer matrix method, we first derive a general nonlinear equation for phase transition temperatures and then calculate the magnetization profiles of the system. The method proposed here can be applied to ferromagnetic films with arbitrary surface layer number, bulk layer number, exchange interaction constants and transverse fields.

  19. Strong Exchange Anisotropy in Heavy Atom Radical Ferromagnets

    Science.gov (United States)

    Winter, Stephen

    2012-02-01

    The discovery twenty years ago of ferromagnetic ordering in ``light atom'' p-block (N, O based) radicals appeared to provide a major conceptual advance, suggesting the possibility of a new era in non-metal molecular magnetism. However, the weak through-space magnetic exchange interactions present in these early radical-based ferromagnets afforded very low Curie temperatures TC (JACS 130, 8414-8425 (2008), JACS 133, 8126-8129 (2011).

  20. Odd triplet superconductivity in superconductor ferromagnet structures: a survey

    Energy Technology Data Exchange (ETDEWEB)

    Bergeret, F.S. [Universidad Autonoma de Madrid, Departamento de Fisica Teorica de la Materia Condensada C-V, Madrid (Spain); Volkov, A.F. [Ruhr-Universitaet Bochum, Theoretische Physik III, Bochum (Germany); Russian Academy of Sciences, Institute for Radioengineering and Electronics, Moscow (Russian Federation); Efetov, K.B. [Ruhr-Universitaet Bochum, Theoretische Physik III, Bochum (Germany); L.D. Landau Institute for Theoretical Physics RAS, Moscow (Russian Federation)

    2007-11-15

    We review the main features of odd triplet superconductivity in superconductor-ferromagnet (S/F) structures. We discuss the different types of superconducting condensate that can be experimentally observed and pay special attention to the triplet component induced in a ferromagnet which is in contact with a superconductor. The triplet component is an even function of the momentum and an odd function of the frequency and leads to novel phenomena. (orig.)

  1. Elimination of Ferromagnetic Particles Aggregation for Investigation by Electron Microscopy

    Directory of Open Access Journals (Sweden)

    О.S. Kuzema

    2011-01-01

    Full Text Available It has been described the device for sample preparation of highly dispersed ferromagnetic powders including micropowders for permanent magnets, magnetic carriers, machine and mechanism components’ wear products contained in lubricants for investigation of these materials by light and electron microscopy. The device eliminates the coalescence of ferromagnetic particles and improves reliability of the results of such objects investigation. The technique of such device application has been described and exemplified for various materials investigation.

  2. Evidence of weak ferromagnetism in chromium(III) oxide particles

    Energy Technology Data Exchange (ETDEWEB)

    Vazquez-Vazquez, Carlos E-mail: qfmatcvv@usc.es; Banobre-Lopez, Manuel; Lopez-Quintela, M.A.; Hueso, L.E.; Rivas, J

    2004-05-01

    The low temperature (4ferromagnetism is observed below 250 K. The magnetisation curves as a function of the applied field show coercive fields due to the canted antiferromagnetism of the particles. Around 55 K a maximum is observed in the zero-field-cooled curves; this maximum can be assumed as a blocking temperature, similarly to ultrafine ferromagnetic particles.

  3. Spin Orbit Torque in Ferromagnetic Semiconductors

    KAUST Repository

    Li, Hang

    2016-06-21

    Electrons not only have charges but also have spin. By utilizing the electron spin, the energy consumption of electronic devices can be reduced, their size can be scaled down and the efficiency of `read\\' and `write\\' in memory devices can be significantly improved. Hence, the manipulation of electron spin in electronic devices becomes more and more appealing for the advancement of microelectronics. In spin-based devices, the manipulation of ferromagnetic order parameter using electrical currents is a very useful means for current-driven operation. Nowadays, most of magnetic memory devices are based on the so-called spin transfer torque, which stems from the spin angular momentum transfer between a spin-polarized current and the magnetic order parameter. Recently, a novel spin torque effect, exploiting spin-orbit coupling in non-centrosymmetric magnets, has attracted a massive amount of attention. This thesis addresses the nature of spin-orbit coupled transport and torques in non-centrosymmetric magnetic semiconductors. We start with the theoretical study of spin orbit torque in three dimensional ferromagnetic GaMnAs. Using the Kubo formula, we calculate both the current-driven field-like torque and anti-damping-like torque. We compare the numerical results with the analytical expressions in the model case of a magnetic Rashba two-dimensional electron gas. Parametric dependencies of the different torque components and similarities to the analytical results of the Rashba two-dimensional electron gas in the weak disorder limit are described. Subsequently we study spin-orbit torques in two dimensional hexagonal crystals such as graphene, silicene, germanene and stanene. In the presence of staggered potential and exchange field, the valley degeneracy can be lifted and we obtain a valley-dependent Berry curvature, leading to a tunable antidamping torque by controlling the valley degree of freedom. This thesis then addresses the influence of the quantum spin Hall

  4. Damping and ferromagnetic resonance linewidth broadening in nanocrystalline soft ferromagnetic Fe-Co-Hf-N films

    Energy Technology Data Exchange (ETDEWEB)

    Seemann, K. [Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft, Institut fuer Material-forschung I, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen (Germany)], E-mail: klaus.seemann@imf.fzk.de; Leiste, H. [Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft, Institut fuer Material-forschung I, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen (Germany); Kovacs, A. [Institute of Scientific and Industrial Research, 8-1 Mihogaoka, Ibaraki, Osaka 5670047 (Japan)

    2008-07-15

    In order to describe high-frequency damping mechanisms of ferromagnetic films by means of the imaginary part of the frequency-dependant permeability, CMOS compatible ferromagnetic Fe{sub 36}Co{sub 44}Hf{sub 9}N{sub 11} films were deposited by reactive r.f. magnetron sputtering on oxidised 5x5 mm{sup 2}x380 {mu}m (1 0 0)-silicon substrates with a 6-in. Fe{sub 38}Co{sub 47}Hf{sub 15} target, as well as magnetic field annealing between 300 and 600 deg. C. An in-plane uniaxial anisotropy of around 4.5 mT as well as an excellent soft magnetic behaviour with a saturation polarisation of approximately 1.4 T could be observed after heat treatment at the above-mentioned temperatures, which drives these films to a high-frequency suitability. Ferromagnetic resonance frequencies of approximately up to 2.4 GHz could be obtained. The frequency-dependant permeability was measured with a broadband permeameter. Depending on the heat treatment, an increase of the full-width at half-maximum (FWHM) of the imaginary part of the frequency-dependant permeability is discussed in terms of two-magnon scattering, anisotropy-type competition and local resonance generation through predominant grain growth causing magnetisation and anisotropy inhomogeneities in the magnetic films. The grain size of the films was determined by (HRTEM) imaging and amounts from a few nanometres for films heat treated at 300 deg. C to more than 10 nm at 600 deg. C where the FWHM {delta}f{sub eff} and the Landau-Lifschitz-Gilbert equation damping parameter {alpha}{sub eff} increases with d{sub nm}{sup 2} and d{sub nm} (e.g. d{sub nm} is the grain diameter of the nonmagnetic Hf-N phase), respectively.

  5. A first principles study of half-metallic ferromagnetism in In1-xTixP (x = 0.06) diluted magnetic semiconductor

    Science.gov (United States)

    Saini, Hardev S.; Singh, Mukhtiyar; Thakur, Jyoti; Saini, G. S. S.; Kashyap, Manish K.

    2016-05-01

    A first principles approach has been used to calculate the electronic and magnetic properties of In1-xTixP (x = 0.06) diluted magnetic semiconductor (DMS) compound. The calculations have been carried out using the highly precise all electron full potential Linear Augmented Plane Wave (FPLAPW) method within generalized gradient approximation (GGA) as exchange-correlation (XC) potentials. The estimated results show that the Ti-doping generate robust half metallic ferromagnetism with the 100% spin polarization at Fermi level (EF) in InP. Due to this peculiar property, the resultant compound behaves as true half-metallic ferromagnet which is best suited for spintronic applications. The total magnetic moments of this compound are mainly due to Ti-d states present at EF with almost negligible contribution from other atoms.

  6. 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.

  7. The study of high Curie temperature ferromagnetism properties in Mn-doped SiC thin film

    Directory of Open Access Journals (Sweden)

    Chaoyang Kang

    2015-01-01

    Full Text Available Mn-doped 3C-SiC film has been prepared onto the Si (111 substrate by employing a molecular beam epitaxy method. The experimental analysis establishes that the prepared sample shows the ferromagnetic property with a relatively high Curie temperature (Tc of 355 K, which is an exciting phenomenon on account of the scarceness in the SiC-based diluted magnetic semiconductor. The analysis derived from the X-ray diffraction and absorption spectroscopy patterns indicates that Mn atoms should react with Si atoms and then form Mn4Si7 compounds. Combined with the theoretical simulation, it is speculated that a new alloy phase of Mn4Si7Cx maybe appear, which should be responsible for the exceptionally high Tc ferromagnetic behavior in the sample.

  8. Magnetic and structural characterization of the 2D XY-ferromagnet Rb2CrCl2I2 (abstract)

    Science.gov (United States)

    Visser, D.; Bramwell, S. T.; Kremer, R. K.

    1991-04-01

    Rb2CrCl2I2 crystallizes with a Jahn-Teller deformed K2NiF4 structure. This results in a ferromagnetic behavior for this compound. Rb2CrCl2I2 orders ferromagnetically at Tc=56.9(2) K. Magnetization and magnetic susceptibility measurements, using a vibrating sample magnetometer, Faraday balance, and SQUID magnetometer, on polycrystalline samples were used for the magnetic characterization. Rb2CrCl2I2 shows a Curie-Weiss behavior between 150 and 300 K. The intraplanar superexchange constant J/k=5.8 K. The intra- and interplanar anisotropy have been obtained from the magnetization curves at 4.2 K and are estimated at Hintra=0.16(2) T and Hinter=4.5(2) T.

  9. Native defect induced charge and ferromagnetic spin ordering and coexisting electronic phases in CoO epitaxial thin film

    Energy Technology Data Exchange (ETDEWEB)

    Negi, D. S., E-mail: devendranegi@jncasr.ac.in, E-mail: ranjan@jncasr.ac.in; Loukya, B.; Datta, R., E-mail: devendranegi@jncasr.ac.in, E-mail: ranjan@jncasr.ac.in [International Centre for Materials Science, Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore 560064 (India); Chemistry and Physics of Materials Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore 560064 (India)

    2015-12-07

    We report on the observation of Co vacancy (V{sub Co}) induced charge ordering and ferromagnetism in CoO epitaxial thin film. The ordering is associated with the coexistence of commensurate, incommensurate, and discommensurate electronic phases. Density functional theory calculation indicates the origin of ordering in Co atoms undergoing high spin to low spin transition immediately surrounding the V{sub Co(16.6 at. %)}. Electron magnetic chiral dichroism experiment confirms the ferromagnetic signal at uncompensated Co spins. Such a native defects induced coexistence of different electronic phases at room temperature in a simple compound CoO is unique and adds to the richness of the field with the possibility of practical device application.

  10. Low-temperature specific heat and magnetic properties of the filled skutterudite ferromagnet NdRu4As12

    Science.gov (United States)

    Rudenko, A.; Henkie, Z.; Cichorek, T.

    2016-09-01

    We present the low-temperature specific heat and magnetic properties of the filled skutterudite compound NdRu4As12 that exhibits a ferromagnetic transition at TC ≃ 2.3 K . Magnetic entropy considerations point at a quartet ground state of the Nd3+ ions. Deep in the ferromagnetic state, the heat capacity shows a Schottky anomaly that we ascribe to the Zeeman splitting in the presence of a molecular field. Comparison of the specific heats of NdRu4As12 and its Os-based homologue near their Curie temperatures supports our earlier observation suggesting an unusual lowering of the Th cubic point symmetry in the latter filled skutterudite.

  11. Ferromagnetic resonance of particulate magnetic recording tapes

    Science.gov (United States)

    Netzelmann, U.

    1990-08-01

    The room-temperature ferromagnetic resonance (FMR) spectra of γ-Fe2O3, CrO2, and barium ferrite particulate magnetic recording tapes have been measured at microwave frequencies of 9.35 and 35 GHz for various orientations of the static and high-frequency magnetic fields with respect to the tape. For CrO2 tapes, the influence of the width of the angular distribution of the particle orientations on the FMR spectra has been studied from the nearly isotropic case up to the highly oriented case. Hysteretic behavior for a CrO2 tape as well as the effect of tape calendering for a γ-Fe2O3 tape has been observed by FMR. Experimental results are found to be in reasonable agreement with results of theoretical calculations based on a model of an ellipsoidal single-domain particle with both shape and magnetocrystalline anisotropy. Magnetostatic interaction inside the magnetic film has been introduced by expressing the total magnetostatic energy as a combination of a part dependent on particle shape and a part dependent on the shape of the tape. As a result of a comparison of experimental data with calculated data from the model, the magnetocrystalline easy axis of the CrO2 particles is found to be parallel with the particle axis.

  12. Effective surface anisotropy in polycrystalline ferromagnetic nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Holanda, J.; Campos, C.L.A.V.; Franca, C.A.; Padrón-Hernández, E., E-mail: padron@df.ufpe.br

    2014-12-25

    Highlights: • Here we make a mixing of two models. A macroscopic and a microscopic model. • The principal idea in this paper is to write the free magnetic energy for a soft magnetic cylindrical nanowire and make the comparison with our previous models. • The model is tested to determine the effective constant in Ni nanowires. - Abstract: Here we express the effective surface anisotropy for soft ferromagnetic nanowires as the function of the micro-structural behaviors. Many papers about these systems determine the reversal modes for the magnetization to explain magnetic properties of the nanowires. Our previous works related morphological structure with magnetic properties. The principal idea in this paper is to write the free magnetic energy for a soft magnetic cylindrical nanowire and make the comparison with our previous models. In this way we include the macroscopic effective anisotropy due to the disordered atoms and ignoring other microstructure terms related in our previous works. From this idea and our last model to these systems, we made an association that permit to express the effective anisotropy in function of the principal morphological characteristics of nanowires. The model is tested to determine the numerical value of the mentioned constant in Ni nanowires obtained by electrodeposition in porous anodic aluminum oxide membranes using the Transmission Electron Microscopy.

  13. Single ferromagnetic layer magnetic random access memory

    Science.gov (United States)

    Xing, M.-J.; Jalil, M. B. A.; Ghee Tan, Seng; Jiang, Y.

    2013-08-01

    We propose a magnetic random access memory (MRAM) device in which both the writing and reading processes are realized within a single ferromagnetic (FM) layer. The FM layer is sandwiched between layers of heavy element and oxide to enhance the Rashba spin-orbit coupling (RSOC). When the in-plane FM moments are oriented at some intermediate angle to the current direction, the RSOC effect induces a spin accumulation in the FM layer, which in turn generates a Rashba spin torque field via the s-d exchange interaction. This field acts as the writing field of the memory device. The RSOC also induces a charge accumulation in the transverse direction via the inverse spin Hall effect (ISHE), which can be used to realize the memory read-out. The writing and read-out processes of the proposed memory are modeled numerically via the non-equilibrium Green's function technique. Besides the advantages of Rashba spin torque writing, i.e., no spin injection and symmetrical data-writing process, this single FM layer MRAM design does away with having a giant magnetoresistive or magnetic tunnel junction multilayer structure by utilizing the ISHE for the read-out process.

  14. Ferromagnetic properties of fcc Gd thin films

    Energy Technology Data Exchange (ETDEWEB)

    Bertelli, T. P., E-mail: tambauh@gmail.com; Passamani, E. C.; Larica, C.; Nascimento, V. P.; Takeuchi, A. Y. [Universidade Federal do Espírito Santo, Departamento de Física, Vitória/ES 29075-910 (Brazil); Pessoa, M. S. [Universidade Federal do Espírito Santo, Departamento de Ciências Naturais, São Mateus/ES 29932-540 (Brazil)

    2015-05-28

    Magnetic properties of sputtered Gd thin films grown on Si (100) substrates kept at two different temperatures were investigated using X-ray diffraction, ac magnetic susceptibility, and dc magnetization measurements. The obtained Gd thin films have a mixture of hcp and fcc structures, but with their fractions depending on the substrate temperature T{sub S} and film thickness x. Gd fcc samples were obtained when T{sub S} = 763 K and x = 10 nm, while the hcp structure was stabilized for lower T{sub S} (300 K) and thicker film (20 nm). The fcc structure is formed on the Ta buffer layer, while the hcp phase grows on the fcc Gd layer as a consequence of the lattice relaxation process. Spin reorientation phenomenon, commonly found in bulk Gd species, was also observed in the hcp Gd thin film. This phenomenon is assumed to cause the magnetization anomalous increase observed below 50 K in stressed Gd films. Magnetic properties of fcc Gd thin films are: Curie temperature above 300 K, saturation magnetization value of about 175 emu/cm{sup 3}, and coercive field of about 100 Oe at 300 K; features that allow us to classify Gd thin films, with fcc structure, as a soft ferromagnetic material.

  15. Laser-induced torques in metallic ferromagnets

    Science.gov (United States)

    Freimuth, Frank; Blügel, Stefan; Mokrousov, Yuriy

    2016-10-01

    We study laser-induced torques in bcc Fe, hcp Co, and L 10 FePt based on first-principles electronic structure calculations and the Keldysh nonequilibrium formalism. We find that the torques have two contributions, one from the inverse Faraday effect (IFE) and one from the optical spin-transfer torque (OSTT). Depending on the ferromagnet at hand and on the quasiparticle broadening the two contributions may be of similar magnitude, or one contribution may dominate over the other. Additionally, we determine the nonequilibrium spin polarization in order to investigate its relation to the torque. We find the torques and the perpendicular component of the nonequilibrium spin polarization to be odd in the helicity of the laser light, while the spin polarization that is induced parallel to the magnetization is helicity independent. The parallel component of the nonequilibrium spin polarization is orders of magnitude larger than the perpendicular component. In the case of hcp Co we find good agreement between the calculated laser-induced torque and a recent experiment.

  16. Stripe glasses in ferromagnetic thin films

    Science.gov (United States)

    Principi, Alessandro; Katsnelson, Mikhail I.

    2016-02-01

    Domain walls in magnetic multilayered systems can exhibit a very complex and fascinating behavior. For example, the magnetization of thin films of hard magnetic materials is in general perpendicular to the thin-film plane, thanks to the strong out-of-plane anisotropy, but its direction changes periodically, forming an alternating spin-up and spin-down stripe pattern. The latter is stabilized by the competition between the ferromagnetic coupling and dipole-dipole interactions, and disappears when a moderate in-plane magnetic field is applied. It has been suggested that such a behavior may be understood in terms of a self-induced stripe glassiness. In this paper we show that such a scenario is compatible with the experimental findings. The strong out-of-plane magnetic anisotropy of the film is found to be beneficial for the formation of both stripe-ordered and glassy phases. At zero magnetic field the system can form a glass only in a narrow interval of fairly large temperatures. An in-plane magnetic field, however, shifts the glass transition towards lower temperatures, therefore enabling it at or below room temperature. In good qualitative agreement with the experimental findings, we show that a moderate in-plane magnetic field of the order of 50 mT can lead to the formation of defects in the stripe pattern, which sets the onset of the glass transition.

  17. New ferromagnetic semiconductor double perovskites: La{sub 2}FeMO{sub 6} (M = Co, Rh, and Ir)

    Energy Technology Data Exchange (ETDEWEB)

    Fuh, Huei-Ru [Department of Physics, National Taiwan University, Taipei 106, Taiwan (China); Graduate Institute of Applied Physics, National Taiwan University, Taipei 106, Taiwan (China); Weng, Ke-Chuan [Department of Physics, National Taiwan University, Taipei 106, Taiwan (China); Liu, Yun-Ping [Department of Physics, National Taiwan Normal University, Taipei 116, Taiwan (China); Wang, Yin-Kuo [Center for General Education and Department of Physics, National Taiwan Normal University, Taipei 106, Taiwan (China)

    2015-02-15

    Highlights: • The La{sub 2}FeCoO{sub 6} is a potential candidate for ferromagnetic semiconductor. • The FM semiconductor originates from the exchange effect between Fe and Co. • We calculate the 406 combinations of possible La{sub 2}MM′O{sub 6} compounds here. - Abstract: Density functional theory with generalized gradient approximation (GGA) plus onsite Coulomb interaction (GGA + U) was used to calculate physical proprieties of new ferromagnetic semiconductor materials of the La{sub 2}FeMO{sub 6} (M = Co, Rh, and Ir). We calculate the 406 (C{sub 2}{sup 29}) La{sub 2}MM′O{sub 6} compounds which MM′ can be any pair taken from the 29 transition metal elements except La. La{sub 2}FeCoO{sub 6} is a potential candidate for ferromagnetic semiconductor. For the GGA + U scheme, La{sub 2}FeCo{sub 6} remains a stable FM semiconductor, whereas La{sub 2}FeRhO{sub 6} and La{sub 2}FeIrO{sub 6} are shown the FM and AFM states of which are degenerate with each other. The FM semiconductor gap remains in existence under tensile or compressive strain in La{sub 2}FeRhO{sub 6} and La{sub 2}FeIrO{sub 6}. The superexchange interaction in ferromagnetic La{sub 2}FeMO{sub 6} (M = Co, Rh, and Ir) is high spin (HS) Fe completely empty e{sub g} orbital hopping to the half-filled (LS) Co (Rh and Ir) empty e{sub g} orbital.

  18. Spin-dependent delay time in ferromagnet/insulator/ferromagnet heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Xie, ZhengWei; Zheng Shi, De; Lv, HouXiang [College of Physics and Electronic Engineering, Sichuan Normal University, Chengdu 610066, Sichuan (China)

    2014-07-07

    We study theoretically spin-dependent group delay and dwell time in ferromagnet/insulator/ferromagnet (FM/I/FM) heterostructure. The results indicate that, when the electrons with different spin orientations tunnel through the FM/I/FM junction, the spin-up process and the spin-down process are separated on the time scales. As the self-interference delay has the spin-dependent features, the variations of spin-dependent dwell-time and spin-dependent group-delay time with the structure parameters appear different features, especially, in low incident energy range. These different features show up as that the group delay times for the spin-up electrons are always longer than those for spin-down electrons when the barrier height or incident energy increase. In contrast, the dwell times for the spin-up electrons are longer (shorter) than those for spin-down electrons when the barrier heights (the incident energy) are under a certain value. When the barrier heights (the incident energy) exceed a certain value, the dwell times for the spin-up electrons turn out to be shorter (longer) than those for spin-down electrons. In addition, the group delay time and the dwell time for spin-up and down electrons also relies on the comparative direction of magnetization in two FM layers and tends to saturation with the thickness of the barrier.

  19. Ferromagnetic bond of Li10 cluster: An alternative approach in terms of effective ferromagnetic sites

    Science.gov (United States)

    Donoso, Roberto; Rössler, Jaime; Llano-Gil, Sandra; Fuentealba, Patricio; Cárdenas, Carlos

    2016-09-01

    In this work, a model to explain the unusual stability of atomic lithium clusters in their highest spin multiplicity is presented and used to describe the ferromagnetic bonding of high-spin Li10 and Li8 clusters. The model associates the (lack of-)fitness of Heisenberg Hamiltonian with the degree of (de-)localization of the valence electrons in the cluster. It is shown that a regular Heisenberg Hamiltonian with four coupling constants cannot fully explain the energy of the different spin states. However, a more simple model in which electrons are located not at the position of the nuclei but at the position of the attractors of the electron localization function succeeds in explaining the energy spectrum and, at the same time, explains the ferromagnetic bond found by Shaik using arguments of valence bond theory. In this way, two different points of view, one more often used in physics, the Heisenberg model, and the other in chemistry, valence bond, come to the same answer to explain those atypical bonds.

  20. Valley and spin resonant tunneling current in ferromagnetic/nonmagnetic/ferromagnetic silicene junction

    Directory of Open Access Journals (Sweden)

    Yaser Hajati

    2016-02-01

    Full Text Available We study the transport properties in a ferromagnetic/nonmagnetic/ferromagnetic (FNF silicene junction in which an electrostatic gate potential, U, is attached to the nonmagnetic region. We show that the electrostatic gate potential U is a useful probe to control the band structure, quasi-bound states in the nonmagnetic barrier as well as the transport properties of the FNF silicene junction. In particular, by introducing the electrostatic gate potential, both the spin and valley conductances of the junction show an oscillatory behavior. The amplitude and frequency of such oscillations can be controlled by U. As an important result, we found that by increasing U, the second characteristic of the Klein tunneling is satisfied as a result of the quasiparticles chirality which can penetrate through a potential barrier. Moreover, it is found that for special values of U, the junction shows a gap in the spin and valley-resolve conductance and the amplitude of this gap is only controlled by the on-site potential difference, Δz. Our findings of high controllability of the spin and valley transport in such a FNF silicene junction may improve the performance of nano-electronics and spintronics devices.

  1. Antiferromagnet-induced perpendicular magnetic anisotropy in ferromagnetic/antiferromagnetic/ferromagnetic trilayers

    Science.gov (United States)

    Wang, Bo-Yao; Lin, Po-Han; Tsai, Ming-Shian; Shih, Chun-Wei; Lee, Meng-Ju; Huang, Chun-Wei; Jih, Nae-Yeou; Wei, Der-Hsin

    2016-08-01

    This study demonstrates the effect of antiferromagnet-induced perpendicular magnetic anisotropy (PMA) on ferromagnetic/antiferromagnetic/ferromagnetic (FM/AFM/FM) trilayers and reveals its interplay with a long-range interlayer coupling between separated FM layers. In epitaxially grown 12 monolayer (ML) Ni/Co/Mn/5 ML Co/Cu(001) films, magnetic hysteresis loops and element-resolved magnetic domain imaging showed that the magnetization direction of the top layers of 12 ML Ni/Co films could be changed from the in-plane direction to the perpendicular direction, when the thickness of the Mn films (tMn) was greater than a critical value close to the thickness threshold associated with the onset of AFM ordering (tMn=3.5 ML). The top FM layers exhibited a significantly enhanced PMA when tMn increased further, and this enhancement can be attributed to a strengthened AFM ordering of the volume moments of the Mn films, as evidenced by the presence of induced domain frustration. By contrast, the long-range interlayer coupling presented clear effects only when tMn was at a lower coverage.

  2. Near room temperature ferromagnetism of copper phthalocyanine thin films

    Energy Technology Data Exchange (ETDEWEB)

    Wang, XueYan, E-mail: xueyanadeline@163.com; Zheng, JianBang; Chen, Lei; Qiao, Kai; Xu, JiaWei; Cao, ChongDe

    2015-11-30

    Highlights: • The α-CuPc films without and with light Ni-doping were characterized by X-ray photoelectron spectroscopy to confirm the absence of other ferromagnetic impurities. • The α-CuPc film exhibited ferromagnetic hysteresis with saturation magnetization of ∼6.77 emu/cm{sup 3} and coercivity of ∼96 Oe at 280 K, while that of the Ni-doped α-CuPc film are ∼0.69 emu/cm{sup 3} and ∼113 Oe, respectively. • Through the density functional theory calculations, the origin of the ferromagnetism arise from Cu 3d states and N 2s2p electronic spin polarization, as well as p–d exchange coupling interactions, and spin-unbalanced electronic structure of C 2p induced by the π–π interactions. - Abstract: We reported near room temperature ferromagnetism of α-CuPc films without and with light Ni-doping. Two samples were characterized by X-ray photoelectron spectroscopy (XPS) to confirm the absence of other ferromagnetic impurities. The α-CuPc film exhibited ferromagnetic hysteresis with saturation magnetization of ∼6.77 emu/cm{sup 3} and coercivity of ∼96 Oe at 280 K, while that of the Ni-doped α-CuPc film are ∼0.69 emu/cm{sup 3} and ∼113 Oe, respectively. Through the density functional theory (DFT) calculations, the origin of the ferromagnetism arise from Cu 3d states and N 2s2p electronic spin polarization, as well as p-d exchange coupling interactions, and spin-unbalanced electronic structure of C 2p induced by the π–π interactions.

  3. Magnetic phase diagram of Y1-xTbxMn6Sn6 compounds

    Science.gov (United States)

    Bykov, A. A.; Chetverikov, Yu. O.; Moskvin, E. V.; Pirogov, A. N.; Grigoriev, S. V.

    2017-02-01

    The Y1-xTbxMn6Sn6 compounds (x=0, 0.175, 0.2, 0.225, 0.25) were studied by small angle neutron scattering (SANS) and paramagnetic neutron spin echo. The YMn6Sn6 compound is found to be a helimagnet in the whole temperature range below TN=310 K. Close to TN an additional peak of a Lorenz shape was observed at Q=0. The peak is thought to have originated from the ferromagnetic fluctuations of the magnetic Mn moment in the ab-plane of the hexagonal crystal structure. Compounds, in which Y is replaced by Tb, change their magnetic order with the increase of temperature: from easy cone ferromagnetic phase at low T through the helicoidal phase to the ferromagnetic fluctuation close to TN. Temperature-concentration phase diagram of Y1-xTbxMn6Sn6 is built on the basis of the obtained data.

  4. Ferromagnetism and glassiness on the surface of topological insulators

    Science.gov (United States)

    Liu, Chun-Xiao; Roy, Bitan; Sau, Jay D.

    2016-12-01

    We investigate the nature of the ordering among magnetic adatoms, randomly deposited on the surface of topological insulators. Restricting ourselves to dilute impurity and weak coupling (between itinerant fermion and magnetic impurities) limit, we show that for arbitrary amount of chemical doping away from the apex of the surface Dirac cone the magnetic impurities tend to arrange themselves in a spin-density-wave pattern, with the periodicity approximately π /kF , where kF is the Fermi wave vector, when magnetic moment for impurity adatoms is isotropic. However, when magnetic moment possesses strong Ising or easy-axis anisotropy, pursuing both analytical and numerical approaches we show that the ground state is ferromagnetic for low to moderate chemical doping, despite the fragmentation of the system into multiple ferromagnetic islands. For high doping away from the Dirac point as well, the system appears to fragment into many ferromagnetic islands, but the magnetization in these islands is randomly distributed. Such magnetic ordering with net zero magnetization is referred to here as ferromagnetic spin glass, which is separated from the pure ferromagnet state by a first order phase transition. We generalize our analysis for cubic topological insulators (supporting three Dirac cones on a surface) and demonstrate that the nature of magnetic orderings and the transition between them remains qualitatively the same. We also discuss the possible relevance of our analysis to recent experiments.

  5. Indium oxide: A transparent, conducting ferromagnetic semiconductor for spintronic applications

    Science.gov (United States)

    Babu, S. Harinath; Kaleemulla, S.; Rao, N. Madhusudhana; Krishnamoorthi, C.

    2016-10-01

    The optical and electrical properties are the two important dimensions of Indium oxide and its derivatives (indium tin oxide) and were well studied to understand the origin of wide electronic band gap and high electrical conductivity at room temperature. In2O3 and its derivatives find many applications in electronic and optoelectronic domains based on the above properties. The recent discovery of ferromagnetism in In2O3 at room temperature become a third dimension and lead to intensive research on enhancement of ferromagnetic strength by various means such as dopants and synthesis protocols and extrinsic parameters. The research lead to enormous experimental data and theoretical models proliferation over the past one decade with diverse insights into the origin of ferromagnetism in In2O3 based dilute magnetic semiconductors. The experimental data and theoretical models of ferromagnetism in In2O3 has been thoroughly surveyed in the literature and compiled all the data and presented for easy of understanding in this review. We have identified best chemical composition, geometry and synthesis protocols for strongest ferromagnetic strength and suitable theoretical model of magnetism has been presented in this review.

  6. Strong ferromagnetic exchange interaction under ambient pressure in BaFe2S3

    Science.gov (United States)

    Wang, Meng; Jin, S. J.; Yi, Ming; Song, Yu; Jiang, H. C.; Zhang, W. L.; Sun, H. L.; Luo, H. Q.; Christianson, A. D.; Bourret-Courchesne, E.; Lee, D. H.; Yao, Dao-Xin; Birgeneau, R. J.

    2017-02-01

    Inelastic neutron scattering measurements have been performed to investigate the spin waves of the quasi-one-dimensional antiferromagnetic ladder compound BaFe2S3 , where a superconducting transition was observed under pressure [H. Takahashi et al., Nat. Mater. 14, 1008 (2015), 10.1038/nmat4351; T. Yamauchi et al., Phys. Rev. Lett. 115, 246402 (2015), 10.1103/PhysRevLett.115.246402]. By fitting the spherically averaged experimental data collected on a powder sample to a Heisenberg Hamiltonian, we find that the one-dimensional antiferromagnetic ladder exhibits a strong nearest-neighbor ferromagnetic exchange interaction (S JR=-71 ±4 meV) along the rung direction, an antiferromagnetic S JL=49 ±3 meV along the leg direction, and a ferromagnetic S J2=-15 ±2 meV along the diagonal direction. Our data demonstrate that the antiferromagnetic spin excitations are a common characteristic for the iron-based superconductors, while specific relative values for the exchange interactions do not appear to be unique for the parent states of the superconducting materials.

  7. Uniform annealing effect of electron irradiation on ferromagnetic GaMnAs thin films

    Science.gov (United States)

    Luo, Jia; Xiang, Gang; Gu, Gangxu; Zhang, Xi; Wang, Hailong; Zhao, Jianhua

    2017-01-01

    For more than a decade, researchers have been searching for means to improve the Curie temperature of ferromagnetic GaMnAs samples, among which post-growth annealing in furnace has been treated as the most important one. In this work, we demonstrate that the Curie temperature can be improved by electron irradiation for the first time. Different doses of electron irradiation (1 × 1014, 1 × 1015 and 1 × 1016 electrons/cm2) at 1.7 MeV were applied, the enhancement of magnetic and electrical properties of ferromagnetic GaMnAs films was experimentally confirmed by HR-XRD, SQUID and Magneto-transport measurements. Further SIMS characterizations and analyses reveal that electron irradiation causes bi-directional out-diffusion and redistribution of compensating Mn interstitials towards both the upper surface and the lower interface, a newly found uniform effect clearly different from that of conventional post-growth annealing. The technique of electron irradiation annealing may provide an alternative way to improve the properties of electronic and magnetic compounds such as GaMnAs films.

  8. Coexistence and interplay of superconductivity and ferromagnetism in URhGe

    Energy Technology Data Exchange (ETDEWEB)

    Levy, F [Departement de Physique de la Matiere Condensee, Universite de Geneve, quai Ernest-Ansermet 24, CH1211, Geneve 4 (Switzerland); Sheikin, I [GHMFL, CNRS BP166, 38042 Grenoble (France); Grenier, B [Universite Joseph Fourier and CEA, INAC/SPSMS/MDN, F-38054 Grenoble Cedex 9 (France); Marcenat, C [CEA, INAC, SPSMS, F-38054 Grenoble Cedex 9 (France); Huxley, A [Scottish Universities Physics Alliance, School of Physics, King' s Buildings, University of Edinburgh, Edinburgh EH9 3JZ (United Kingdom)], E-mail: florence.levy@physics.unige.ch

    2009-04-22

    As ferromagnetism and superconductivity are usually considered to be antagonistic, the discovery of their coexistence in UGe{sub 2}, URhGe, UIr and UCoGe has attracted a lot of interest. The mechanism to explain such a state has, however, not yet been fully elucidated. In these compounds superconductivity may be unconventional: Cooper pairs could be formed by electrons with parallel spins and magnetic fluctuations might be involved in the pairing mechanism. URhGe becomes ferromagnetic below a Curie temperature of 9.5 K, with a spontaneous moment aligned to the c-axis. For temperatures below 260 mK and fields lower than 2 T, superconductivity was first observed in 2001. Recently, we discovered a second pocket of superconductivity. This new pocket of superconductivity appears at higher fields applied close to the b-axis, enveloping a sudden magnetic moment rotation transition at H{sub R} = 12 T. Detailed studies of the field induced metamagnetic transition and superconductivity are presented. The possibility that magnetic fluctuations emerging from a quantum critical point provide the pairing mechanism for superconductivity is discussed.

  9. Coexistence and interplay of superconductivity and ferromagnetism in URhGe

    Science.gov (United States)

    Lévy, F.; Sheikin, I.; Grenier, B.; Marcenat, C.; Huxley, A.

    2009-04-01

    As ferromagnetism and superconductivity are usually considered to be antagonistic, the discovery of their coexistence in UGe2, URhGe, UIr and UCoGe has attracted a lot of interest. The mechanism to explain such a state has, however, not yet been fully elucidated. In these compounds superconductivity may be unconventional: Cooper pairs could be formed by electrons with parallel spins and magnetic fluctuations might be involved in the pairing mechanism. URhGe becomes ferromagnetic below a Curie temperature of 9.5 K, with a spontaneous moment aligned to the c-axis. For temperatures below 260 mK and fields lower than 2 T, superconductivity was first observed in 2001. Recently, we discovered a second pocket of superconductivity. This new pocket of superconductivity appears at higher fields applied close to the b-axis, enveloping a sudden magnetic moment rotation transition at HR = 12 T. Detailed studies of the field induced metamagnetic transition and superconductivity are presented. The possibility that magnetic fluctuations emerging from a quantum critical point provide the pairing mechanism for superconductivity is discussed.

  10. Order parameter symmetry in the superconducting ferromagnets UGe{sub 2} and URhGe

    Energy Technology Data Exchange (ETDEWEB)

    Huxley, A.; Mineev, V.; Grenier, B.; Ressouche, E.; Aoki, D.; Brison, J.P.; Flouquet, J

    2004-03-15

    In UGe{sub 2}, ZrZn{sub 2} and URhGe the co-existence of superconductivity and ferromagnetism appears to arise as a co-operative phenomena rather than as the overlap of two mutually competing orders. In all three compounds the magnetism is in intimate contact with the electronic degrees of freedom while the Curie temperatures are more than an order of magnitude higher than their critical temperatures for superconductivity. The most direct indication that the two orders are conjugate however is that the superconductivity and ferromagnetism are suppressed at the same critical pressure in both UGe{sub 2} and ZrZn{sub 2}. This has motivated the recent theoretical classification of the permitted superconducting order parameter symmetries for such states. In the following we will review the experimental evidence relevant to the identification of the actual symmetries. This is followed by a discussion of the possible states allowed theoretically. Finally we discuss briefly whether the magnetic order can indeed lead to an enhancement of the superconductivity.

  11. Order parameter symmetry in the superconducting ferromagnets UGe 2 and URhGe

    Science.gov (United States)

    Huxley, A.; Mineev, V.; Grenier, B.; Ressouche, E.; Aoki, D.; Brison, J. P.; Flouquet, J.

    2004-03-01

    In UGe 2, ZrZn 2 and URhGe the co-existence of superconductivity and ferromagnetism appears to arise as a co-operative phenomena rather than as the overlap of two mutually competing orders. In all three compounds the magnetism is in intimate contact with the electronic degrees of freedom while the Curie temperatures are more than an order of magnitude higher than their critical temperatures for superconductivity. The most direct indication that the two orders are conjugate however is that the superconductivity and ferromagnetism are suppressed at the same critical pressure in both UGe 2 and ZrZn 2. This has motivated the recent theoretical classification of the permitted superconducting order parameter symmetries for such states. In the following we will review the experimental evidence relevant to the identification of the actual symmetries. This is followed by a discussion of the possible states allowed theoretically. Finally we discuss briefly whether the magnetic order can indeed lead to an enhancement of the superconductivity.

  12. Coexistence and interplay of superconductivity and ferromagnetism in URhGe.

    Science.gov (United States)

    Lévy, F; Sheikin, I; Grenier, B; Marcenat, C; Huxley, A

    2009-04-22

    As ferromagnetism and superconductivity are usually considered to be antagonistic, the discovery of their coexistence in UGe(2), URhGe, UIr and UCoGe has attracted a lot of interest. The mechanism to explain such a state has, however, not yet been fully elucidated. In these compounds superconductivity may be unconventional: Cooper pairs could be formed by electrons with parallel spins and magnetic fluctuations might be involved in the pairing mechanism. URhGe becomes ferromagnetic below a Curie temperature of 9.5 K, with a spontaneous moment aligned to the c-axis. For temperatures below 260 mK and fields lower than 2 T, superconductivity was first observed in 2001. Recently, we discovered a second pocket of superconductivity. This new pocket of superconductivity appears at higher fields applied close to the b-axis, enveloping a sudden magnetic moment rotation transition at H(R) = 12 T. Detailed studies of the field induced metamagnetic transition and superconductivity are presented. The possibility that magnetic fluctuations emerging from a quantum critical point provide the pairing mechanism for superconductivity is discussed.

  13. Ferromagnetism in Transition Metal Doped GaN and Related Materials

    Science.gov (United States)

    Abernathy, Cammy

    2005-03-01

    There is high current interest in the development of dilute magnetic semiconductor (DMS) materials exhibiting ferromagnetic behavior for spin-based light-emitting diodes, sensors, and transistors. Such materials are formed through the introduction of transition metal (TM) ions, such as Mn and Cr, into semiconductor hosts. Unfortunately many DMS materials, such as GaMnAs, have a relatively low magnetic ordering temperature ( 170 K for GaMnAs), which severely limits their usefulness. In the past few years, several groups have reported achieving ferromagnetism at room temperature in wide bandgap materials, such as GaMnN. This property makes these materials attractive for use as ultra-low-power switching elements, where the bit state of the device is determined through control of electron spin. Furthermore, these materials may also allow for the integration of photonic (laser and light-emitting diodes), electronic (field-effect and bipolar transistors) and magnetic (information storage) devices on a single substrate, leading to a new class of electronic devices that offer multi-purpose functionality. However, to realize such devices, several challenges remain. One concern to date has been the relatively low thermal stability of the III-Mn-N compounds. Doping with Cr in place of Mn, however, appears to greatly enhance the ability of the material to retain its magnetic properties even after annealing at temperatures up to 700C, easing the road to practical device fabrication. In addition, the ability to achieve magnetic behavior in a semi-insulating barrier material such as AlCrN opens new device possibilities. The most evident application of ferromagnetic AlN is as a ferromagnetic tunnel barrier, similar to EuS, but unlike EuS should allow for operation at room temperature. Growth of tunnel devices using Al-TM-N as a barrier and Ga-TM-N as a spin injector will be discussed. This work is supported by the Army Research Office under ARO-DAAD19-01-0-0701 and NSF under ECS

  14. Ferromagnetic resonance response of electron-beam patterned arrays of ferromagnetic nanoparticles

    Science.gov (United States)

    Jung, Sukkoo; Watkins, Byron; Feller, Jeffrey; Ketterson, John; Chandrasekhar, Venkat

    2001-03-01

    We report on the fabrication and the dynamic magnetic properties of periodic permalloy dot arrays. Electron-beam lithography and e-gun evaporation have been used to make the arrays with the aspect ratio of 2 (dot diameter : 40 nm, height : 80 nm) and periods of 100 - 200 nm. The magnetic properties of the arrays and their interactions have been investigated by ferromagnetic resonance (FMR), magnetic force microscopy (MFM), and SQUID magnetometry. The measured FMR data show that the position and magnitude of resonant absorption peaks strongly depend on the angle between magnetic field and the lattice structure. The results of dot arrays with various kinds of structural parameters will be presented. Supported by Army Research Office, DAAD19-99-1-0334/P001

  15. Peculiar long-range supercurrent in superconductor-ferromagnet-superconductor junction containing a noncollinear magnetic domain in the ferromagnetic region

    Energy Technology Data Exchange (ETDEWEB)

    Meng, Hao, E-mail: menghao1982@shu.edu.cn [School of Physics and Telecommunication Engineering, Shaanxi University of Technology, Hanzhong 723001 (China); National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing 210093 (China); Wu, Xiuqiang [National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing 210093 (China); Ren, Yajie [School of Physics and Telecommunication Engineering, Shaanxi University of Technology, Hanzhong 723001 (China)

    2015-01-14

    We study the supercurrent in clean superconductor-ferromagnet-superconductor heterostructure containing a noncollinear magnetic domain in the ferromagnetic region. It is demonstrated that the magnetic domain can lead to a spin-flip scattering process, which reverses the spin orientations of the singlet Cooper pair and simultaneously changes the sign of the corresponding electronic momentum. If the ferromagnetic layers on both sides of magnetic domain have the same features, the long-range proximity effect will take place. That is because the singlet Cooper pair will create an exact phase-cancellation effect and gets an additional π phase shift as it passes through the entire ferromagnetic region. Then, the equal spin triplet pair only exists in the magnetic domain region and can not diffuse into the other two ferromagnetic layers. So, the supercurrent mostly arises from the singlet Cooper pairs, and the equal spin triplet pairs are not involved. This result can provide a approach for generating the long-range supercurrent.

  16. Ferromagnetic behavior and exchange bias effect in akaganeite nanorods

    Energy Technology Data Exchange (ETDEWEB)

    Tadic, Marin, E-mail: marint@vinca.rs [Condensed Matter Physics Laboratory, Vinca Institute of Nuclear Science, University of Belgrade, P.O. Box 522, 11001 Belgrade (Serbia); Milosevic, Irena; Motte, Laurence [Laboratoire CSPBAT, UMR 7244 CNRS Université Paris 13, 93017 Bobigny Cedex (France); Kralj, Slavko [Department for Materials Synthesis, Jožef Stefan Institute, Jamova 39, 1000 Ljubljana (Slovenia); Saboungi, Marie-Louise [CNRS, University of Orleans, F-45071 Orleans 2 (France); IMPMC, Sorbonne Univ-UPMC Univ Paris 06, UMR CNRS 7590, Museum National d' Histoire Naturelle, IRD UMR 206, 4 Place Jussieu, F-75005 Paris (France)

    2015-05-04

    We report ferromagnetic-like properties and exchange bias effect in akaganeite (β-FeOOH) nanorods. They exhibit a Néel temperature T{sub N} = 259 K and ferromagnetic-like hysteresis behavior both below and above T{sub N}. An exchange bias effect is observed below T{sub N} and represents an interesting behavior for akaganeite nanorods. These results are explained on the basis of a core-shell structure in which the core has bulk akaganeite magnetic properties (i.e., antiferromagnetic ordering) while the shell exhibits a disordered spin state. Thus, the nanorods show ferromagnetic properties and an exchange bias effect at the same time, increasing their potential for use in practical applications.

  17. Topological insulator in junction with ferromagnets: Quantum Hall effects

    Science.gov (United States)

    Chudnovskiy, A. L.; Kagalovsky, V.

    2015-06-01

    The ferromagnet-topological insulator-ferromagnet (FM-TI-FM) junction exhibits thermal and electrical quantum Hall effects. The generated Hall voltage and transverse temperature gradient can be controlled by the directions of magnetizations in the FM leads, which inspires the use of FM-TI-FM junctions as electrical and as heat switches in spintronic devices. Thermal and electrical Hall coefficients are calculated as functions of the magnetization directions in ferromagnets and the spin-relaxation time in TI. Both the Hall voltage and the transverse temperature gradient decrease but are not completely suppressed even at very short spin-relaxation times. The Hall coefficients turn out to be independent of the spin-relaxation time for symmetric configuration of FM leads.

  18. Mode-selectable ultrasonic transducer for cylindrical ferromagnetic waveguides

    Science.gov (United States)

    Kim, Youngkyu; Lee, Hocheol; Cho, Seung Hyun; Kim, Yoon Young

    2003-07-01

    Ultrasonic inspection techniques using magnetostrictive transducers have received much attention in recent years as non-contact, non-destructive means of inspecting ferromagnetic materials. By the selection of a desired mode and thus the rejection of the unwanted modes among propagating waves in a waveguide, different types of flaws existing in a cylindrical ferromagnetic waveguide can be effectively detected. However, desired mode selection methods have not been fully developed yet. The purpose of this research is to present a mangetostrictive sensor based technique for the selection of either the bending or longitudinal waves alone in a ferromagnetic waveguide. To achieve this goal, new bias magnet configurations, particularly for bending mode selection are suggested. Several experimental results are conducted to verify the effectiveness of the suggested magnetostrictive sensors.

  19. Ferromagnetic microwire composites from sensors to microwave applications

    CERN Document Server

    Peng, Hua-Xin; Phan, Manh-Huong

    2016-01-01

    Situated at the forefront of interdisciplinary research on ferromagnetic microwires and their multifunctional composites, this book starts with a comprehensive treatment of the processing, structure, properties and applications of magnetic microwires. Special emphasis is placed on the giant magnetoimpedance (GMI) effect, which forms the basis for developing high-performance magnetic sensors. After defining the key criteria for selecting microwires for various types of GMI sensors, the book illustrates how ferromagnetic microwires are employed as functional fillers to create a new class of composite materials with multiple functionalities for sensing and microwave applications. Readers are introduced to state-of-the-art fabrication methods, microwave tunable properties, microwave absorption and shielding behaviours, as well as the metamaterial characteristics of these newly developed ferromagnetic microwire composites. Lastly, potential engineering applications are proposed so as to highlight the most promisin...

  20. Large magnetostriction from morphotropic phase boundary in ferromagnets.

    Science.gov (United States)

    Yang, Sen; Bao, Huixin; Zhou, Chao; Wang, Yu; Ren, Xiaobing; Matsushita, Yoshitaka; Katsuya, Yoshio; Tanaka, Masahiko; Kobayashi, Keisuke; Song, Xiaoping; Gao, Jianrong

    2010-05-14

    For more than half of a century, morphotropic phase boundary (MPB) in ferroelectric materials has drawn constant interest because it can significantly enhance the piezoelectric properties. However, MPB has been studied merely in ferroelectric systems, not in another large class of ferroic systems, the ferromagnets. In this Letter, we report the existence of an MPB in a ferromagnetic system TbCo2-DyCo2. Such a magnetic MPB involves a first-order magnetoelastic transition, at which both magnetization direction and crystal structure change simultaneously. The MPB composition demonstrates a 3-6 times larger "figure of merit" of magnetostrictive response compared with that of the off-MPB compositions. The finding of MPB in ferromagnets may help to discover novel high-performance magnetostrictive and even magnetoelectric materials.

  1. Ferromagnetism in Mn-doped Sb(2)Te.

    Science.gov (United States)

    Luo, H; Gibson, Q; Krizan, J; Cava, R J

    2014-05-21

    We report that Sb2Te, a natural superlattice phase consisting of two elemental Sb2 layers interleaved with single Sb2Te3 layers, becomes ferromagnetic at low temperatures on doping with small percentages of Mn. Ferromagnetism appears for Mn concentrations as low as Sb1.98Mn0.02Te, where a ferromagnetic Tc of ~8.6 K is observed. Tc decreases with increasing Mn content in the stoichiometric materials but increases with increasing Te excess in materials of the type Sb1.93-yMn0.07Te1+y, starting at ~3 K at y = 0 and reaching a Tc of ~8.9 K at y = 0.06.

  2. Microscopic model for all optical switching in ferromagnets

    Science.gov (United States)

    Cornelissen, T. D.; Córdoba, R.; Koopmans, B.

    2016-04-01

    The microscopic mechanism behind the all optical switching (AOS) in ferromagnets has triggered intense scientific debate. Here, the microscopic three-temperature model is utilized to describe AOS in a perpendicularly magnetized ferromagnetic Co/Pt system. We demonstrate that AOS in such a ferromagnet can be explained with the Inverse Faraday Effect (IFE). The influence of the strength and lifetime of the IFE induced field pulse on the switching process are investigated. We found that because of strong spin-orbit coupling, the minimal lifetime of the IFE needed to obtain switching is of the order of 0.1 ps, which is shorter than previously assumed. Moreover, spatial images of the domain pattern after AOS in Co/Pt, as well as their dependence on applying an opposite magnetic field, are qualitatively reproduced.

  3. Nonlocal spin-transport measurement of superconductor-ferromagnet nanostructures

    Energy Technology Data Exchange (ETDEWEB)

    Kolenda, Stefan; Wolf, Michael J.; Huebler, Florian; Beckmann, Detlef [Institut fuer Nanotechnologie, Karlsruher Institut fuer Technologie (Germany)

    2015-07-01

    We present measurements of the nonlocal conductance of nanostructures with several ferromagnetic electrodes lying perpendicular on a superconducting wire. In these structures nonlocal conductance is mostly given by diffusion of quasiparticles, which are injected by one of the electrodes and detected by an other one. Applying a magnetic field induces a Zeeman splitting in the quasiparticles density of states, which suppresses the relaxation of injected spin imbalance, thus spin transport over distances of several micrometers is found. While in the previous experiments the magnetic field was aligned parallel to the ferromagnetic electrodes, we also show measurements applying the magnetic field noncollinear with the magnetization of the ferromagnetic electrodes. We compare our results to the previous case.

  4. Electron transport in a mesoscopic superconducting ferromagnetic hybrid conductor

    Energy Technology Data Exchange (ETDEWEB)

    Giroud, M.; Hasselbach, K.; Courtois, H.; Pannetier, B. [Centre de Recherche sur les Tres Basses Temperatures, CNRS, 38 - Grenoble (France); Mailly, D. [Laboratoire de Photonique et de Nanostructures, 91 - Marcoussis (France)

    2003-01-01

    We present electrical transport experiments performed on submicron hybrid devices made of a ferromagnetic conductor (Co) and a superconducting (Al) electrode. The sample was patterned in order to separate the contributions of the Co conductor and of the Co-Al interface. We observed a strong influence of the Al electrode superconductivity on the resistance of the Co conductor. This effect is large only when the interface is highly transparent. We characterized the dependence of the observed resistance decrease on temperature, bias current and magnetic field. As the differential resistance of the ferromagnet exhibits a non-trivial asymmetry, we claim that the magnetic domain structure plays an important role in the electron transport properties of superconducting / ferromagnetic conductors. (authors)

  5. Ballistic spin filtering across the ferromagnetic-semiconductor interface

    Directory of Open Access Journals (Sweden)

    Y.H. Li

    2012-03-01

    Full Text Available The ballistic spin-filter effect from a ferromagnetic metal into a semiconductor has theoretically been studied with an intention of detecting the spin polarizability of density of states in FM layer at a higher energy level. The physical model for the ballistic spin filtering across the interface between ferromagnetic metals and semiconductor superlattice is developed by exciting the spin polarized electrons into n-type AlAs/GaAs superlattice layer at a much higher energy level and then ballistically tunneling through the barrier into the ferromagnetic film. Since both the helicity-modulated and static photocurrent responses are experimentally measurable quantities, the physical quantity of interest, the relative asymmetry of spin-polarized tunneling conductance, could be extracted experimentally in a more straightforward way, as compared with previous models. The present physical model serves guidance for studying spin detection with advanced performance in the future.

  6. Optically oriented electron spin transmission across ferromagnet/semiconductor interfaces

    Science.gov (United States)

    Taniyama, T.; Suzuki, I.; Wada, E.; Shirahata, Y.; Naito, T.; Itoh, M.; Yamaguchi, M.

    2011-10-01

    Electron spin transmission across ferromagnetic metal/semiconductor interfaces with different ferromagnetic contacts, i.e., Fe and FeGa, is studied using optical spin orientation method. The bias dependence of spin dependent photocurrent, which is the difference between the photocurrents excited with left- and right- handed circularly polarized lights, is found to show a dip-like feature at -0.058 and 0.021 V for Fe and FeGa contacts, respectively. The origin of the bias dependence of the spin dependent photocurrent is discussed on the basis of the Breit-Wigner type resonant tunneling process via interface resonant states, comparing the results for the both contacts. The results also indicate that the control of interface states is crucial to achieve efficient spin filtering effect at the ferromagnet/semiconductor interfaces.

  7. Larmor diffraction in the ferromagnetic superconductor UGe{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Ritz, Robert; Pfleiderer, Christian [Physik Department E21, TU Muenchen, D-85748 Garching (Germany); Sokolov, Dmitry; Huxley, Andrew [School of Physics and Astronomy, Centre for Science at Extreme Conditions, University of Edinburgh, Edinburgh EH9 3JZ (United Kingdom); Keller, Thomas [MPI fuer Festkoerperforschung, Heisenbergstr. 1, D-70569 Stuttgart (Germany)

    2010-07-01

    Larmor Diffaction (LD) is a neutron resonance spin-echo technique which allows the study of the lattice constant as well the distribution of lattice constants. It was traditionally thought that neutron spin-echo measurements cannot be used in materials such as superconductors or ferromagnets, because they strongly depolarize a polarized neutron beam. In UGe{sub 2} we are able to demonstrate that this technique may be applied in ferromagnetic superconductors with a magnetic Ising anisotropy. UGe{sub 2} exhibits two ferromagnetic phases which are separated by a transition at temperature T{sub x}. With increasing hydrostatic pressure superconductivity emerges at the pressure for which T{sub x} is suppressed. Using LD we studied the temperature dependence of the lattice constant as well as the distribution of lattice constants for all three axis of UGe{sub 2} down to 0.5 K and at pressures up to 12 kbar.

  8. Quantum chemical analysis of binary and ternary ferromagnetic alloys; Quantenchemische Untersuchungen binaerer und ternaerer ferromagnetischer Legierungen

    Energy Technology Data Exchange (ETDEWEB)

    Jacobs, Yasemin Erika Charlotte

    2007-02-23

    . Finite temperature effects (Curie temperatures) are analysed using the mean-field description, and a surprisingly simple relationship between structural properties and the Curie temperature is found. The magnetic exchange parameters and also Curie temperatures decrease along the row Cu, Ni, Rh, Pd. The X-Mn interactions are limited by first neighbors while Mn-Mn interactions are quite long ranged. Non-spin-polarized COHP bonding analyses evidence antibonding metal-metal interactions as a prerequisite for becoming ferromagnetic, and these show up for the 3d-metal-Mn and also 4d-metal-Mn combinations but not for the wider Mn-Mn interactions. As an exception to this rule, the Cu2MnZ class of compounds evidences, on the opposite, large antibonding Mn-Mn interactions at the Fermi level. (orig.)

  9. Correspondence between neutron depolarization and higher order magnetic susceptibility to investigate ferromagnetic clusters in phase separated systems.

    Science.gov (United States)

    Manna, Kaustuv; Samal, D; Bera, A K; Elizabeth, Suja; Yusuf, S M; Kumar, P S Anil

    2014-01-08

    It is a tough task to distinguish a short-range ferromagnetically correlated cluster-glass phase from a canonical spin-glass-like phase in many magnetic oxide systems using conventional magnetometry measurements. As a case study, we investigate the magnetic ground state of La0.85Sr0.15CoO3, which is often debated based on phase separation issues. We report the results of two samples of La0.85Sr0.15CoO3 (S-1 and S-2) prepared under different conditions. Neutron depolarization, higher harmonic ac susceptibility and magnetic relaxation studies were carried out along with conventional magnetometry measurements to differentiate subtle changes at the microscopic level. There is no evidence of ferromagnetic correlation in the sample S-2 attributed to a spin-glass phase, and this is compounded by the lack of existence of a second order component of higher harmonic ac susceptibility and neutron depolarization. A magnetic relaxation experiment at different temperatures complements the spin glass characteristic in S-2. All these signal a sharp variance when we consider the cluster-glass-like phase (phase separated) in S-1, especially when prepared from an improper chemical synthesis process. This shows that the nonlinear ac susceptibility is a viable tool to detect ferromagnetic clusters such as those the neutron depolarization study can reveal.

  10. Comparison of ferromagnetism in n- and p-type magnetic semiconductor thin films of ZnCoO

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Y.H., E-mail: yuhua@phys.ncku.edu.t [Department of Physics, National Cheng Kung University, No. 1, Ta-Shuei Road, Tainan 70101, Taiwan (China); Lee, J.C.; Min, J.F. [Department of Physics, National Cheng Kung University, No. 1, Ta-Shuei Road, Tainan 70101, Taiwan (China); Su, C.W. [Department of Applied Physics, National Chiayi University, Chiayi 60004, Taiwan (China)

    2011-07-15

    Both n- and p-type diluted magnetic semiconductor ZnCoO are made by magnetron co-sputtering with, respectively, dopants of Al and dual dopants of Al and N. The two sputtering targets are compound ZnCoO with 5% weight of Co and pure metal Al. Sputtering gases for n- and p-type films are pure Ar and N{sub 2}, respectively. These films are magnetic at room temperature and possess free electron- and hole-concentration of 5.34x10{sup 20} and 5.27x10{sup 13} cm{sup -3}. Only the n-type film exhibits anomalous Hall-effect signals. Magnetic properties of these two types of films are compared and discussed based on measurements of microstructure and magneto-transport properties. - Research highlights: n-type ZnCoO:Al and p-type ZnCoO:(Al, N) films are made and are both ferromagnetic at room temperature. Signal of anomalous Hall-effect (AHE) is clearly observed only for n-type film but not for p-type film. Photoluminescence (PL) spectrum shows a peak attributed to shallow acceptor band of N. Ferromagnetic exchange coupling between magnetic ions in n-type film is through spin polarized free electrons. Ferromagnetism in p-type film is not attributed to the free hole-carriers mediation but to the overlap of BMP.

  11. Magnetotransport effects in lateral and vertical ferromagnetic semiconductor junctions

    OpenAIRE

    Rüster, Christian

    2005-01-01

    This work is an investigation of giant magnetoresistance (GMR), tunneling magnetoresistance (TMR) and tunneling anisotropic magnetoresistance (TAMR)effects in (Ga,Mn) based ferromagnetic semiconductor junctions. Detailed results are published in the following articles: [1] C. Rüster, T. Borzenko, C. Gould, G. Schmidt, L.W. Molenkamp, X. Liu, T.J.Wojtowicz, J.K. Furdyna, Z.G. Yu and M. Flatt´e, Very Large Magnetoresistance in Lateral Ferromagnetic (Ga,Mn)As Wires with Nanoconstrictions, Physic...

  12. Color Ferromagnetism and Quantum Hall states in Quark Matter

    CERN Document Server

    Iwazaki, A

    2003-01-01

    We discuss a possibility of the presence of a stable color ferromagnetic state in SU(2) gauge theory of quark matter; a color magnetic field is spontaneously generated due tothe gluon's dynamics. The state arises between the hadronic state and the color superconducting state when the density of quarks is varied. Although the state has been known to have unstable modes, we show that unstable modes form quantum Hall states, in which the instability disappears. Namely, the quark matter possesses a stable phase with the ferromagnetic state and the quantum Hall state of gluons.

  13. Magnetic excitations in the ferromagnetic superconductor UGe2 under pressure

    Science.gov (United States)

    Kepa, M. W.; Sokolov, D. A.; Böhm, M.; Huxley, A. D.

    2014-12-01

    Ferromagnetism and superconductivity coexist in UGe2 under pressures in the range of 10-16 kbar. Here, equal spin electrons are paired to give a spin triplet state but the pairing mechanism is still not verified experimentally. The work presented here attempts to verify whether the longitudinal magnetic fluctuations associated with a magnetic transition within the ferromagnetic state might be responsible for the electron pairing. We show that the energy scale of these fluctuations must be smaller than those associated with the second order phase transition at the Curie temperature. Furthermore, there is no significant change of the energy scale of the fluctuations at the Curie temperature as a function of pressure.

  14. Inverse Proximity Effect in Superconductor-ferromagnet Bilayer Structures

    Energy Technology Data Exchange (ETDEWEB)

    Xia, Jing

    2010-04-05

    Measurements of the polar Kerr effect using a zero-area-loop Sagnac magnetometer on Pb/Ni and Al/(Co-Pd) proximity-effect bilayers show unambiguous evidence for the 'inverse proximity effect,' in which the ferromagnet (F) induces a finite magnetization in the superconducting (S) layer. To avoid probing the magnetic effects in the ferromagnet, the superconducting layer was prepared much thicker than the light's optical penetration depth. The sign and size of the effect, as well as its temperature dependence agree with recent predictions by Bergeret et al.[1].

  15. Size and shape effects on Curie temperature of ferromagnetic nanoparticles

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    A simplified model was developed to describe the Curie temperature suppression of ferromagnetic nanoparticles. Based on a size and shape dependent model of cohesive energy, the critical temperature variations of ferromagnetic nanoparticles were deduced. It is predicted that the Curie temperature of nanoparticles depends on both size and shape conditions, among which the temperature suppression is strongly influenced by the particle size and the shape effect is comparably minor. The calculation values for freestanding nanoparticles are in good agreement with other theoretical model and the experimental results. The model is also potential for predictions for the nanoparticles embedded in different substrates.

  16. Nuclear ferromagnetism and superconductivity at negative nuclear temperatures

    CERN Document Server

    Dyugaev, A M; Vider, P

    2001-01-01

    The quantitative theory of effects of the ferromagnetism on the metal superconductivity is proposed with an account of the spin-spin electron-nuclear interaction. The nuclear ferromagnetism at the negative temperatures, when the nuclear magnetization is directed against the external magnetic field, does not suppress but rather facilitates the superconductivity. The critical magnetic field of the Be metals and TiH sub 2 sub . sub 0 sub 7 hydrate may by one order exceed the critical field of the nonmagnetic superconductor

  17. Magnetotunable left-handed FeSiB ferromagnetic microwires.

    Science.gov (United States)

    Labrador, Alberto; Gómez-Polo, Cristina; Pérez-Landazábal, José Ignacio; Zablotskii, Vitalii; Ederra, Iñigo; Gonzalo, Ramón; Badini-Confalonieri, Giovanni; Vázquez, Manuel

    2010-07-01

    The magnetotunable left-handed characteristics of Fe(77.5)Si(12.5)B(10) glass-coated ferromagnetic microwires are analyzed in array and single microwire configuration, employing a rectangular waveguide working in X band. While the negative permeability is ascribed to the natural ferromagnetic resonance (NFMR) of the highly and positive magnetostrictive microwire, the negative permittivity features of the medium are attributed to the interaction of the microwires with the metallic rectangular waveguide. The dependence of the NFMR frequency on the applied external magnetic field enables the design of magnetotunable left-handed systems with wide-frequency band.

  18. Ab initio calculations of half-metallic ferromagnetism in Cr-doped MgSe and MgTe semiconductors

    Energy Technology Data Exchange (ETDEWEB)

    Noor, N.A. [Department of Physics, University of the Punjab, Quaid-e-Azam Campus, 54590 Lahore (Pakistan); Alay-e-Abbas, S.M. [Department of Physics, University of Sargodha, Sargodha 40100 (Pakistan); Department of Physics, GC University Faisalabad, Allama Iqbal Road, Faisalabad 38000 (Pakistan); Sohaib, M.U. [Lahore Development Authority, 54590 Lahore (Pakistan); Ghulam Abbas, S.M. [Department of Chemistry, University of Agriculture, Faisalabad 38040 (Pakistan); Shaukat, A., E-mail: schaukat@gmail.com [Department of Physics, University of Sargodha, Sargodha 40100 (Pakistan)

    2015-01-15

    The full-potential linear-augmented-plane-waves plus local-orbitals (FP-LAPW+lo) method has been employed for investigation of half-metallic ferromagnetism in Cr-doped ordered zinc-blende MgSe and MgTe semiconductors. Calculations of exchange and correlation (XC) effects have been carried out using generalized gradient approximation (GGA) and orbital independent modified Becke–Johnson potential coupled with local (spin) density approximation (mBJLDA). The thermodynamic stability of the compounds and their preferred magnetic orders have been analyzed in terms of the heat of formation and minimum total energy difference in ferromagnetic (FM) and anti-ferromagnetic (AFM) ordering, respectively. Calculated electronic properties reveal that the Cr-doping induces ferromagnetism in MgSe and MgTe which gives rise to a half-metallic (HM) gap at Fermi level (E{sub F}). Further, the electronic band structure is discussed in terms of s (p)–d exchange constants that are consistent with typical magneto-optical experiment and the behavior of charge spin densities is presented for understanding the bonding nature. Our results demonstrate that the higher effective potential for the spin-down case is responsible for p–d exchange splitting. Total magnetic moment (mainly due to Cr-d states) of these compounds is 4µ{sub B}. Importantly, the electronic properties and HM gap obtained using mBJLDA show remarkable improvement as compared to the results obtained using standard GGA functional. - Highlights: • Spin effect theoretical study on Cr-doped MgSe and MgTe is performed. • Half-metallic ferromagnetism in Cr{sub x}Mg{sub 1−x}Se and Cr{sub x}Mg{sub 1−x}Te is established. • Results of WC-GGA and mBJLDA are compared for performance. • HM gaps for Cr{sub x}Mg{sub 1−x}Se and Cr{sub x}Mg{sub 1−x}Te show nonlinear variation with x. • Important values of exchange splitting/constants and moments are reported.

  19. Theoretical prediction of half metallic ferromagnetic full-Heusler alloys Cs2CrGe

    Science.gov (United States)

    Cherid, S.; Benstaali, W.; Abbad, A.; Bentata, S.; Lantri, T.; Abbar, B.

    2017-07-01

    The structural, electronic and elastic properties of full-Heusler alloys Cs2CrGe are examined in this study using FP-LAPW method based on density functional theory. Results of our calculations predict that the Hg2CuTi-type structure is more stable than the Cu2MnAl-type structure and that the ground state of this alloy is ferromagnetic. The band structure of Cs2CrGe shows half metallic behavior for the two approaches GGA and mBJ-GGA with an indirect band gap. The total magnetic moment calculated is in good agreement with the Slater-Pauling rule for full-Heusler alloys with an important magnetic moment equal to 4 μB. Elastic properties indicate that our compound is ductile, anisotropic and not too rigid.

  20. Magnetocaloric effect study of ferromagnetic-charge ordered core-shell type manganite nanostructures

    Science.gov (United States)

    Das, Kalipada; Das, I.

    2017-08-01

    In the present study we have presented the magnetic and magnetocaloric properties of ferromagnetic (La0.67Sr0.33MnO3)-charge ordered (Pr0.67Ca0.33MnO3) core-shell nanostructures. We have also compared the magnetocaloric properties of Pr0.67Ca0.33MnO3 (PCMO) nanoparticles. Our study indicates that in case of the core-shell nanostructures, the magnetocaloric properties markedly modifies compared to its parent compound PCMO, additionally the low field magnetocaloric effect enhanced. More specifically, the large value of magnetocaloric entropy change (- Δ S(T)) was observed in wider temperature range in core-shell nanostructure which may be important from application point of view.

  1. Thin perovskite-type ferromagnetic film (La,Sr)CoO3

    Science.gov (United States)

    Łoziński, A.

    2016-01-01

    Properties of materials having a perovskite-type oxide crystal structure ABO3 can easily be modified by means of partial substitution of cations located at A or B sites. Nonstoichiometric lanthanum-strontium cobalt oxides (La,Sr)CoO3 also referred to as LSCO exhibit electrical conductivity and ferromagnetic properties. Perovskite-type compounds LaCoO3 and SrCoO3 can form solid solutions in every ratios to each other. Notation (La,Sr)CoO3, or La(1-x)SrxCoO3 means that some lanthanum ions are substituted with the strontium ones at A sites of crystal cell. This paper describes a sol-gel manufacturing process of LSCO thin films, presents measurements of their resistivity vs. composition, shows thermal coefficient of selected composition resistivity as well as its magnetoresistive properties.

  2. Polybenzimidazole compounds

    Science.gov (United States)

    Klaehn, John R.; Peterson, Eric S.; Wertsching, Alan K.; Orme, Christopher J.; Luther, Thomas A.; Jones, Michael G.

    2010-08-10

    A PBI compound that includes imidazole nitrogens, at least a portion of which are substituted with an organic-inorganic hybrid moiety. At least 85% of the imidazole nitrogens may be substituted. The organic-inorganic hybrid moiety may be an organosilane moiety, for example, (R)Me.sub.2SiCH.sub.2--, where R is selected from among methyl, phenyl, vinyl, and allyl. The PBI compound may exhibit similar thermal properties in comparison to the unsubstituted PBI. The PBI compound may exhibit a solubility in an organic solvent greater than the solubility of the unsubstituted PBI. The PBI compound may be included in separatory media. A substituted PBI synthesis method may include providing a parent PBI in a less than 5 wt % solvent solution. Substituting may occur at about room temperature and/or at about atmospheric pressure. Substituting may use at least five equivalents in relation to the imidazole nitrogens to be substituted or, preferably, about fifteen equivalents.

  3. Finite-size effects on the magnetoelectric coupling in a ferroelectric/ferromagnetic structure revealed by ferromagnetic resonance

    Directory of Open Access Journals (Sweden)

    Sukhov A.

    2014-07-01

    Full Text Available For a composite multiferroic chain corresponding to a BaTiO3/Fe-interface we report theoretical calculations of the spectra of ferromagnetic resonance relying on the solution of the coupled Landau-Khalatnikov equation for the FE polarization and the Landau-Lifshitz-Gilbert equation for the magnetization motion. We focus on the role of the system size. Additionally, we find that although the magnetoelectric coupling strength remains linear upon the electric field variation, its dependence on the thickness of the ferromagnet is not linear.

  4. Magnetic phase transitions in layered intermetallic compounds

    Science.gov (United States)

    Mushnikov, N. V.; Gerasimov, E. G.; Rosenfeld, E. V.; Terent'ev, P. B.; Gaviko, V. S.

    2012-10-01

    Magnetic, magnetoelastic, and magnetotransport properties have been studied for the RMn2Si2 and RMn6Sn6 (R is a rare earth metal) intermetallic compounds with natural layered structure. The compounds exhibit wide variety of magnetic structures and magnetic phase transitions. Substitution of different R atoms allows us to modify the interatomic distances and interlayer exchange interactions thus providing the transition from antiferromagnetic to ferromagnetic state. Near the boundary of this transition the magnetic structures are very sensitive to the external field, temperature and pressure. The field-induced transitions are accompanied by considerable change in the sample size and resistivity. It has been shown that various magnetic structures and magnetic phase transitions observed in the layered compounds arise as a result of competition of the Mn-Mn and Mn-R exchange interactions.

  5. Uranium ferromagnet with negligible magnetocrystalline anisotropy: U4Ru7Ge6

    Science.gov (United States)

    Vališka, Michal; Diviš, Martin; Sechovský, Vladimír

    2017-02-01

    Strong magnetocrystalline anisotropy (MA) is a well-known property of uranium compounds. The almost isotropic ferromagnetism in U4Ru7Ge6 reported in this paper represents a striking exception. We present results for magnetization, ac susceptibility, thermal expansion, specific heat, and electrical resistivity measurements performed on a U4Ru7Ge6 single crystal at various temperatures and magnetic fields; we discuss the results in relation to first-principles electronic structure calculations. U4Ru7Ge6 behaves as an itinerant 5 f -electron ferromagnet (TC=10.7 K , μS=0.85 μB/f .u . at 1.9 K ). The ground-state easy magnetization direction is along the [111] axis of the cubic lattice. The anisotropy field μ0Ha along the [001] direction is only about 0.3 T , which is at least three orders of magnitude smaller than for other U ferromagnets. At Tr=5.9 K the easy magnetization direction changes to [001], and remains [001] up to TC. This transition is due to a change in magnetic symmetry, and is quite apparent in the low-field magnetization, ac susceptibility, and thermal expansion data, whereas only weak anomalies are observed at Tr in the temperature dependence of the specific heat and electrical resistivity. The magnetoelastic interaction induces a rhombohedral (tetragonal) distortion of the paramagnetic cubic crystal lattice in the case of the [111] ([001]) easy magnetization direction. The rhombohedral distortion is connected with two crystallographically inequivalent U sites. Our density functional theory calculations, including spin-orbit interaction (SOI) of the U 5 f electrons, also produces two inequivalent U sites, because SOI leads to a reduction of the symmetry of the former cubic structure. The calculated ground state is in agreement with the experimentally observed [111] easy magnetization direction. The first excited state has moments along the [001] direction, which agrees with the moment orientation for T >Tr . The energy of the first excited state is

  6. Off-axis electron holography of ferromagnetic multilayer nanowires

    DEFF Research Database (Denmark)

    Akhtari-Zavareh, Azadeh; Carignan, L. P.; Yelon, A.

    2014-01-01

    We have used electron holography to investigate the local magnetic behavior of isolated ferromagnetic nanowires (NWs) in their remanent states. The NWs consisted of periodic magnetic layers of soft, high-saturation magnetization CoFeB alloys, and non-magnetic layers of Cu. All NWs were fabricated...

  7. Magnetic exitations in the itinerant ferromagnet UFe2

    DEFF Research Database (Denmark)

    Paolasini, L.; Lander, G.H.; Shapiro, S.M.;

    1996-01-01

    UFe2 (Laves phase, fee crystal structure) is a ferromagnet with T-C=165 K, Previous neutron elastic measurements have established that the Fe moment is 0.6 mu(B) and that the moment on the U atom is almost zero because of the cancellation of the spin and orbital moments, which are both about 0...

  8. Nagaoka ferromagnetism in large-spin fermionic and bosonic systems

    NARCIS (Netherlands)

    Miyashita, Seiji; Ogata, Masao; De Raedt, Hans

    2009-01-01

    We study the magnetic properties of itinerant quantum magnetic particles, described by a generalized Hubbard model with large spin (S>1/2), which may be realized in optical lattices of laser-cooled atom systems. In fermion systems (half-integer spins), an extended form of Nagaoka ferromagnetism may

  9. Low temperature magnetic force microscopy on ferromagnetic and superconducting oxides

    Science.gov (United States)

    Sirohi, Anshu; Sheet, Goutam

    2016-05-01

    We report the observation of complex ferromagnetic domain structures on thin films of SrRuO3 and superconducting vortices in high temperature superconductors through low temperature magnetic force microscopy. Here we summarize the experimental details and results of magnetic imaging at low temperatures and high magnetic fields. We discuss these data in the light of existing theoretical concepts.

  10. Tuning Ferromagnetism at Interfaces between Insulating Perovskite Oxides

    NARCIS (Netherlands)

    Ganguli, Nirmal; Kelly, Paul J.

    2014-01-01

    We use density functional theory calculations to show that the LaAlO 3 |SrTiO 3 interface between insulating perovskite oxides is borderline in satisfying the Stoner criterion for itinerant ferromagnetism and explore other oxide combinations with a view to satisfying it more amply. The larger latt

  11. Controllable 0-π Josephson junctions containing a ferromagnetic spin valve

    Science.gov (United States)

    Gingrich, E. C.; Niedzielski, Bethany M.; Glick, Joseph A.; Wang, Yixing; Miller, D. L.; Loloee, Reza; Pratt, W. P., Jr.; Birge, Norman O.

    2016-06-01

    Superconductivity and ferromagnetism are antagonistic forms of order, and rarely coexist. Many interesting new phenomena occur, however, in hybrid superconducting/ferromagnetic systems. For example, a Josephson junction containing a ferromagnetic material can exhibit an intrinsic phase shift of π in its ground state for certain thicknesses of the material. Such `π-junctions' were first realized experimentally in 2001 (refs ,), and have been proposed as circuit elements for both high-speed classical superconducting computing and for quantum computing. Here we demonstrate experimentally that the phase state of a Josephson junction containing two ferromagnetic layers can be toggled between 0 and π by changing the relative orientation of the two magnetizations. These controllable 0-π junctions have immediate applications in cryogenic memory, where they serve as a necessary component to an ultralow power superconducting computer. Such a fully superconducting computer is estimated to be orders of magnitude more energy-efficient than current semiconductor-based supercomputers. Phase-controllable junctions also open up new possibilities for superconducting circuit elements such as superconducting `programmable logic', where they could function in superconducting analogues to field-programmable gate arrays.

  12. Final Report. Novel Behavior of Ferromagnet/Superconductor Hybrid Systems

    Energy Technology Data Exchange (ETDEWEB)

    Birge, Norman [Michigan State Univ., East Lansing, MI (United States)

    2016-09-26

    Final report for grant DE-FG02-06ER46341. This work has produced a most convincing experimental demonstration that spin-triplet supercurrent can appear in Josephson junctions containing ferromagnetic materials, even when the superconducting electrodes are conventional, spin-singlet superconductors.

  13. Tuning Ferromagnetism at Interfaces between Insulating Perovskite Oxides

    NARCIS (Netherlands)

    Ganguli, N.; Kelly, Paul J.

    2014-01-01

    We use density functional theory calculations to show that the LaAlO 3 |SrTiO 3 interface between insulating perovskite oxides is borderline in satisfying the Stoner criterion for itinerant ferromagnetism and explore other oxide combinations with a view to satisfying it more amply. The larger

  14. Spin Filtering of Hot Holes in a Metallic Ferromagnet

    NARCIS (Netherlands)

    Banerjee, T.; Haq, E.; Siekman, M.H.; Lodder, J.C.; Jansen, R.

    2005-01-01

    Spin-dependent transport of nonequilibrium holes in ferromagnetic thin films and trilayers is investigated using ballistic hole magnetic microscopy. For Co, the hole attenuation length is short and increases from 6 to 10 Å in the energy range 0.8 to 2 eV. The hole transmission of a Ni81Fe19/Au/Co tr

  15. Nagaoka ferromagnetism in large-spin fermionic and bosonic systems

    NARCIS (Netherlands)

    Miyashita, Seiji; Ogata, Masao; De Raedt, Hans

    2009-01-01

    We study the magnetic properties of itinerant quantum magnetic particles, described by a generalized Hubbard model with large spin (S>1/2), which may be realized in optical lattices of laser-cooled atom systems. In fermion systems (half-integer spins), an extended form of Nagaoka ferromagnetism may

  16. Ferromagnetism in CuO-ZnO multilayers

    Science.gov (United States)

    Chandran, Sudakar; Kirby, B. J.; Padmanabhan, K.; Lawes, G.; Naik, R.; Kumar, Sanjiv; Naik, V. M.

    2008-03-01

    The magnetic properties of CuO-ZnO heterostructures are examined to elucidate the origin of the ferromagnetic signature in Cu doped ZnO. The CuO and ZnO layer thickness varied from 15 nm to 350 nm, and we observed no significant diffusion of either Cu^2+ in the ZnO layers or of Zn^2+ in the CuO layers using Rutherford backscattering spectrometry. Bulk magnetization measurements established that the multilayers exhibit a ferromagnetic moment at room temperature, with a saturation magnetization (˜2-5 emu/cc of CuO) that depends on the CuO size, but not the CuO-ZnO interfacial area. Polarized neutron reflection studies suggest that the ferromagnetism arises from the CuO layers, and not from the interdiffusion of CuO and ZnO. These results indicate that the ferromagnetism in these multicomponent structures arises from the uncompensated surface spins of CuO nanoparticles in the layer rather than from regions of interdiffusing ZnO and CuO.

  17. Heat Transport in Graphene Ferromagnet-Insulator-Superconductor Junctions

    Institute of Scientific and Technical Information of China (English)

    LI Xiao-Wei

    2011-01-01

    We study heat transport in a graphene ferromagnet-insulator-superconducting junction. It is found that the thermal conductance of the graphene ferromagnet-insulator-superconductor (FIS) junction is an oscillatory function of the barrier strength x in the thin-barrier limit. The gate potential U0 decreases the amplitude of thermal conductance oscillation. Both the amplitude and phase of the thermal conductance oscillation varies with the exchange energy Eh. The thermal conductance of a graphene FIS junction displays the usual exponential dependence on temperature, reflecting the s-wave symmetry of superconducting graphene.%@@ We study heat transport in a graphene ferromagnet-insulator-superconducting junction.It is found that the thermal conductance of the graphene ferromagnet-insulator-superconductor(FIS)junction is an oscillatory function of the barrier strength X in the thin-barrier limit.The gate potential Uo decreases the amplitude of thermal conductance oscillation.Both the amplitude and phase of the thermal conductance oscillation varies with the exchange energy Eh.The thermal conductance of a graphene FIS junction displays the usual exponential dependence on temperature, reflecting the s-wave symmetry of superconducting graphene.

  18. Thermodynamics of the Heisenberg ferromagnet in an applied magnetic field.

    Science.gov (United States)

    Flax, L.

    1972-01-01

    The anisotropic-Heisenberg-ferromagnet formalism developed previously is examined to include an applied magnetic field for the isotropic case in the random-phase approximation. Thermodynamic quantities such as magnetization, susceptibility, and the derivative of magnetization with respect to temperature are studied near the Curie point.

  19. Frustrated Ferromagnetic Spin Chain near the Transition Point

    Institute of Scientific and Technical Information of China (English)

    ZHU Ren-Gui

    2011-01-01

    @@ The one-dimensional quantum spin-1/2 model with nearest-neighbor ferromagnetic and next-nearest-neighbor antiferromagnetic interaction is considered.The Hamiltonian is firstly rewritten in a form with rotated spin operators,then bosonized by using the linear spin wave approximation and then treated by using the Green function approach.An integral expression of the quantum correction to the classical ground state energy is derived.The critical behavior of the ground state energy in the vicinity of the transition point from the ferromagnetic to the singlet ground state is analyzed by numerical calculation and the result is-8γ2.%The one-dimensional quantum spin-1/2 model with nearest-neighbor ferromagnetic and next-nearest-neighbor antiferromagnetic interaction is considered. The Hamiltonian is firstly rewritten in a form with rotated spin operators, then bosonized by using the linear spin wave approximation and then treated by using the Green function approach. An integral expression of the quantum correction to the classical ground state energy is derived. The critical behavior of the ground state energy in the vicinity of the transition point from the ferromagnetic to the singlet ground state is analyzed by numerical calculation and the result is -8r2.

  20. Geometric space-time integration of ferromagnetic materials

    NARCIS (Netherlands)

    Frank, J.E.

    2003-01-01

    The Landau-Lifshitz equation (LLE) governing the flow of magnetic spin in a ferromagnetic material is a PDE with a noncanonical Hamiltonian structure. In this paper we derive a number of new formulations of the LLE as a partial differential equation on a multisymplectic structure. Using this form we

  1. Current-induced magnetization dynamics in disordered itinerant ferromagnets

    NARCIS (Netherlands)

    Tserkovnyak, Y.; Skadsem, H.J.; Brataas, A.; Bauer, G.E.W.

    2006-01-01

    Current-driven magnetization dynamics in ferromagnetic metals is studied in a self-consistent adiabatic local-density approximation in the presence of spin-conserving and spin-dephasing impurity scattering. Based on a quantum kinetic equation, we derive Gilbert damping and spin-transfer torques ente

  2. Geometric space-time integration of ferromagnetic materials

    NARCIS (Netherlands)

    Frank, J.E.

    2004-01-01

    The Landau-Lifshitz equation (LLE) governing the flow of magnetic spin in a ferromagnetic material is a PDE with a noncanonical Hamiltonian structure. In this paper we derive a number of new formulations of the LLE as a partial differential equation on a multisymplectic structure. Using this form we

  3. Ferromagnetic behavior of formyl-group-carrying stable thioaminyl radicals.

    Science.gov (United States)

    Miura, Yozo; Nakamura, Shogo; Teki, Yoshio

    2003-10-17

    Four formyl-group-carrying thioaminyl radicals were generated, and one radical could be isolated as radical crystals. Magnetic susceptibility measurements of the isolated radical showed a ferromagnetic regular linear-chain interaction of 2J/k(B) = 3.2 K, which was explained in terms of the X-ray crystallographic results.

  4. Distribution of ferromagnetic moments in crystals under external twisting

    Energy Technology Data Exchange (ETDEWEB)

    Zavorotnev, Yu.D., E-mail: zavorotnev.yurii@gmail.com [Donetsk Institute for Physics and Engineering, NAS of Ukraine, 72 R.Luxemburg Street, 83114 Donetsk (Ukraine); Pashinskaya, E.H.; Varyukhin, V.N. [Donetsk Institute for Physics and Engineering, NAS of Ukraine, 72 R.Luxemburg Street, 83114 Donetsk (Ukraine); Popova, O.Yu. [Donetsk National Technical University, 58 Artema Street, 83001 Donetsk (Ukraine)

    2014-01-15

    In an easy-axis ferromagnet, the effect of superposition of severe plastic deformation by twisting (SPDT) perpendicular to the “easy axis” on the ferromagnetic order parameter (OP) distribution is studied. The consideration is carried out within the frameworks of phenomenological theory of Landau. It is shown that SPDT effects the results in occurrence of the normal component of the magnetic OP and periodical change of OP modulus. The law of distribution of the magnetic moment is determined by proximity of the temperature of the crystal and any phase transition. - Highlights: • The effect of application of external twisting deformation to a ferromagnetic crystal of easy-axis type is studied theoretically. • The deformation axis is directed normally to the easy axis of the crystal. • The consideration is carried out within the frameworks of a phenomenological model. • It is shown that in this case, a spiral long-period structure is formed. • Besides, spatial distribution of the modulus of ferromagnetic vector changes depending on the temperature and the twisting moment.

  5. Longitudinal domain wall formation in elongated assemblies of ferromagnetic nanoparticles

    DEFF Research Database (Denmark)

    Varón, Miriam; Beleggia, Marco; Jordanovic, Jelena

    2015-01-01

    Through evaporation of dense colloids of ferromagnetic ~13 nm ε-Co particles onto carbon substrates, anisotropic magnetic dipolar interactions can support formation of elongated particle structures with aggregate thicknesses of 100-400 nm and lengths of up to some hundred microns. Lorenz microsco...

  6. Topological Superconductivity in Ferromagnetic Metal Chains: Part I

    Science.gov (United States)

    Li, Jian; Chen, Hua; Drozdov, Ilya; Yazdani, Ali; Bernevig, Bogdan; MacDonald, Allan

    2015-03-01

    Recent experiments have demonstrated superconductivity induced in ferromagnetic atomic chains as a new route to the research of Majorana physics. In this talk we discuss the theory behind these experiments. We will first present a generic picture for how superconductivity is induced in ferromagnetic metal chains through coupling to a superconductor with strong spin-orbit coupling, and explain why this hybrid system is a plausible new platform in searching for topological superconductivity. We will then present a tight-binding model associated with the existing experiments. We reveal a new chain magnetic symmetry that is able to stabilize multiple Majorana end modes in the absence of disorder, resulting in a one-dimensional crystalline topological superconductor. We show phase diagrams in terms of such topological phases and point out their relevance to the existing experiments. In the last part of this talk we will briefly discuss some other directions of research based on the new platform, including braiding Majorana quasi-particles in ferromagnetic chains, as well as realizing topological superconductivity in two-dimensional ferromagnetic thin films.

  7. Anomalous Specific Heat around Ferromagnetic Instability in Metals

    Science.gov (United States)

    Ishigaki, Aya; Moriya, Tôru

    1996-02-01

    The low-temperature specific heat around the ferromagnetic instability is studied by using the self-consistent renormalization (SCR) theory of spin fluctuations with particular attention to the crossover between the Fermi liquid (γT+ηT3ln T+···) and the quantum critical (-Tln T) regimes.

  8. Ferroelectricity and ferromagnetism in EuTiO3 nanowires

    Science.gov (United States)

    Morozovska, Anna N.; Glinchuk, Maya D.; Behera, Rakesh K.; Zaulychny, Basil; Deo, Chaitanya S.; Eliseev, Eugene A.

    2011-11-01

    We predicted the ferroelectric-ferromagnetic multiferroic properties of EuTiO3 nanowires and generated the phase diagrams in coordinates of temperature and wire radii. The calculations were performed within the Landau-Ginzburg-Devonshire theory with phenomenological parameters extracted from tabulated experimental data and first-principles calculations. Since bulk EuTiO3 is antiferromagnetic at temperatures lower than 5.5 K and paraelectric at all temperatures, our goal was to investigate the possibility of inducing the ferroelectric and ferromagnetic properties of EuTiO3 by reducing the bulk to nanosystems. Our results indicate that ferroelectric spontaneous polarization of ˜0.1-0.5 C/m2 is induced in EuTiO3 nanowires due to the intrinsic surface stress, which is inversely proportional to the nanowire radius. Spontaneous polarization exists at temperatures lower than 300 K for wire diameter of ˜4 lattice constants with 10 N/m surface stress coefficient. Due to the strong biquadratic magnetoelectric coupling, the spontaneous polarization in turn induces the ferromagnetic phase at temperatures lower than 30 K for 2-nm nanowire and at temperatures lower than 10 K for 4-nm nanowire in EuTiO3. Thus, we predicted that the EuTiO3 nanowires can be the new ferroelectric-ferromagnetic multiferroic.

  9. Spin-accumulation-induced resistance in mesoscopic ferromagnet- superconductor junctions

    NARCIS (Netherlands)

    Jedema, F.J.; van Wees, Bart; Hoving, B.H.; Filip, A.T.; Klapwijk, T.M

    1999-01-01

    We present a description of spin-polarized transport in mesoscopic ferromagnet-superconductor (F/S) systems, where the transport is diffusive and the interfaces are transparent. It is shown that the spin reversal associated with Andreev reflection generates an excess spin density close to the F/S in

  10. Neutron scattering studies of ferromagnetic superconductor UGe2 under pressure

    Science.gov (United States)

    Sokolov, D. A.; Huxley, A. D.; Ritz, R.; Pfleiderer, C.; Keller, T.

    2010-03-01

    Observation of an unconventional superconductivity in ferromagnetic UGe2 when ferromagnetism is suppressed by pressure indicates a dramatic modification of its electronic structure near the Quantum Critical Point [1]. We present high resolution measurements of the lattice constants of ferromagnetic superconductor UGe2 under pressure probed by a novel technique, which utilizes Larmor precession of polarized neutrons and surpasses the resolution of conventional scattering methods by an order of magnitude. We have observed sharp anomalies at the Curie temperature, TC and at TX, which marks the crossover regime. Our studies under pressure of 10, and 12 kbar indicate that the sharp anomaly corresponding to TC shifted to lower temperature in agreement with a phase diagram. At the pressure corresponding to an onset of superconductivity, 10kbar, the lattice expansion corresponding to ferromagnetic transition undergoes a first order transition and increases by a factor of 3. The results indicate a complex response of the electronic structure of UGe2 to external pressure and suggest a strong magnetoelastic coupling as one of multiple energy scales that stabilize superconductivity in UGe2. [1] S. S. Saxena, et al., Nature 406, 587 (2000)

  11. Temperature dependence of ferromagnetic resonance measurements in nanostructured line arrays

    Directory of Open Access Journals (Sweden)

    Raposo V.

    2014-07-01

    Full Text Available We report the effect of temperature on the ferromagnetic resonance (FMR spectra of nanostructured line arrays. Different temperature dependences are observed for permalloy an nickel based samples. The qualitative features of the temperature dependence of the resonance field and linewidth can be described by the usual expression of slow relaxing linewidth mechanism and Bloch equation.

  12. From ballistic transport to tunneling in electromigrated ferromagnetic breakjunctions

    DEFF Research Database (Denmark)

    Bolotin, Kirill I; Kuemmeth, Ferdinand; Pasupathy, Abhay N

    2006-01-01

    We fabricate ferromagnetic nanowires with constrictions whose cross section can be reduced gradually from 100 x 30 nm(2) to the atomic scale and eventually to the tunneling regime by means of electromigration. The contacts are mechanically and thermally stable. We measure low-temperature magnetor...

  13. Magnetic evolution of itinerant ferromagnetism and interlayer antiferromagnetism in cerium doped LaCo{sub 2}P{sub 2} crystals

    Energy Technology Data Exchange (ETDEWEB)

    Tian, Yong; Kong, Yixiu; Liu, Kai; Zhang, Anmin [Department of Physics, Beijing Key Laboratory of Opto-electronic Functional Materials & Micro-nano Devices, Renmin University of China, Beijing 100872 (China); He, Rui [Department of Physics, University of Northern Iowa, Cedar Falls, Iowa 50614 (United States); Zhang, Qingming, E-mail: qmzhang@ruc.edu.cn [Department of Physics, Beijing Key Laboratory of Opto-electronic Functional Materials & Micro-nano Devices, Renmin University of China, Beijing 100872 (China)

    2017-05-01

    ThCr{sub 2}Si{sub 2}-type phosphide ACo{sub 2}P{sub 2} (A=Eu, La, Pr, Nd, Ce) has the same structure as iron arsenides, but their magnetic behaviors are quite distinct. In this paper, we grew a series of La{sub 1−x}Ce{sub x}Co{sub 2}P{sub 2} single crystals (x=0.0 to1.0), made structural and magnetic characterizations. We found the introduction of cerium induces a rapid decrease of c-axis and a change from ferromagnetic to antiferromagnetic states. Compared to other trivalent doped compounds, the enhancement of ferromagnetism with doping is suppressed and the transition from ferromagnetism to antiferromagnetism appear earlier. By employing first-principles band-structure calculations, we identify the increase of Ce valence suppress the itinerant ferromagnetism and leading to formation of P-P bonding with the shortening of c-axis. The bonding effectively drives an increase of interlayer antiferromagnetic interaction, eventually leads to antiferromagnetic ordering of cobalt in high-doping region.

  14. Ferromagnetic germanide in Ge nanowire transistors for spintronics application.

    Science.gov (United States)

    Tang, Jianshi; Wang, Chiu-Yen; Hung, Min-Hsiu; Jiang, Xiaowei; Chang, Li-Te; He, Liang; Liu, Pei-Hsuan; Yang, Hong-Jie; Tuan, Hsing-Yu; Chen, Lih-Juann; Wang, Kang L

    2012-06-26

    To explore spintronics applications for Ge nanowire heterostructures formed by thermal annealing, it is critical to develop a ferromagnetic germanide with high Curie temperature and take advantage of the high-quality interface between Ge and the formed ferromagnetic germanide. In this work, we report, for the first time, the formation and characterization of Mn(5)Ge(3)/Ge/Mn(5)Ge(3) nanowire transistors, in which the room-temperature ferromagnetic germanide was found through the solid-state reaction between a single-crystalline Ge nanowire and Mn contact pads upon thermal annealing. The atomically clean interface between Mn(5)Ge(3) and Ge with a relatively small lattice mismatch of 10.6% indicates that Mn(5)Ge(3) is a high-quality ferromagnetic contact to Ge. Temperature-dependent I-V measurements on the Mn(5)Ge(3)/Ge/Mn(5)Ge(3) nanowire heterostructure reveal a Schottky barrier height of 0.25 eV for the Mn(5)Ge(3) contact to p-type Ge. The Ge nanowire field-effect transistors built on the Mn(5)Ge(3)/Ge/Mn(5)Ge(3) heterostructure exhibit a high-performance p-type behavior with a current on/off ratio close to 10(5), and a hole mobility of 150-200 cm(2)/(V s). Temperature-dependent resistance of a fully germanided Mn(5)Ge(3) nanowire shows a clear transition behavior near the Curie temperature of Mn(5)Ge(3) at about 300 K. Our findings of the high-quality room-temperature ferromagnetic Mn(5)Ge(3) contact represent a promising step toward electrical spin injection into Ge nanowires and thus the realization of high-efficiency spintronic devices for room-temperature applications.

  15. Superconductivity-induced magnetization depletion in a ferromagnet through an insulator in a ferromagnet-insulator-superconductor hybrid oxide heterostructure.

    Science.gov (United States)

    Prajapat, C L; Singh, Surendra; Paul, Amitesh; Bhattacharya, D; Singh, M R; Mattauch, S; Ravikumar, G; Basu, S

    2016-05-21

    Coupling between superconducting and ferromagnetic states in hybrid oxide heterostructures is presently a topic of intense research. Such a coupling is due to the leakage of the Cooper pairs into the ferromagnet. However, tunneling of the Cooper pairs though an insulator was never considered plausible. Using depth sensitive polarized neutron reflectivity we demonstrate the coupling between superconductor and magnetic layers in epitaxial La2/3Ca1/3MnO3 (LCMO)/SrTiO3/YBa2Cu3O7-δ (YBCO) hybrid heterostructures, with SrTiO3 as an intervening oxide insulator layer between the ferromagnet and the superconductor. Measurements above and below the superconducting transition temperature (TSC) of YBCO demonstrate a large modulation of magnetization in the ferromagnetic layer below the TSC of YBCO in these heterostructures. This work highlights a unique tunneling phenomenon between the epitaxial layers of an oxide superconductor (YBCO) and a magnetic layer (LCMO) through an insulating layer. Our work would inspire further investigations on the fundamental aspect of a long range order of the triplet spin-pairing in hybrid structures.

  16. Superconductivity-induced magnetization depletion in a ferromagnet through an insulator in a ferromagnet-insulator-superconductor hybrid oxide heterostructure

    Science.gov (United States)

    Prajapat, C. L.; Singh, Surendra; Paul, Amitesh; Bhattacharya, D.; Singh, M. R.; Mattauch, S.; Ravikumar, G.; Basu, S.

    2016-05-01

    Coupling between superconducting and ferromagnetic states in hybrid oxide heterostructures is presently a topic of intense research. Such a coupling is due to the leakage of the Cooper pairs into the ferromagnet. However, tunneling of the Cooper pairs though an insulator was never considered plausible. Using depth sensitive polarized neutron reflectivity we demonstrate the coupling between superconductor and magnetic layers in epitaxial La2/3Ca1/3MnO3 (LCMO)/SrTiO3/YBa2Cu3O7-δ (YBCO) hybrid heterostructures, with SrTiO3 as an intervening oxide insulator layer between the ferromagnet and the superconductor. Measurements above and below the superconducting transition temperature (TSC) of YBCO demonstrate a large modulation of magnetization in the ferromagnetic layer below the TSC of YBCO in these heterostructures. This work highlights a unique tunneling phenomenon between the epitaxial layers of an oxide superconductor (YBCO) and a magnetic layer (LCMO) through an insulating layer. Our work would inspire further investigations on the fundamental aspect of a long range order of the triplet spin-pairing in hybrid structures.

  17. Shot noises of spin and charge currents in a ferromagnet-quantum-dot-ferromagnet system

    Institute of Scientific and Technical Information of China (English)

    Hong-kang ZHAO; Jian WANG

    2008-01-01

    We have investigated the shot noises of charge and spin current by considering the spin polarized electron tunneling through a ferromagnet-quantum-dotferromagnet system.We have derived the spin polarized current noise matrix,from which we can derive general expressions of shot noises associated with charge and spin currents.The spin and charge currents are intimately related to the polarization angles,and they behave quite differently from each other.The shot noise of charge current is symmetric about the gate voltage whose structure is modified by the Zeeman field considerably.There exists oscillations in spin current shot noise in the absence of source-drain bias at zero temperature,and it is asym metric in the positive and negative regimes of sourcedrain voltage. The shot noise of spin current behaves quite differently from the shot noise of charge current,since the spin current components Isx,Isy oscillate sinusoidally with the frequency ωγ in the γth lead,while the Isz component of spin current is independent of time.

  18. Multipurpose Compound

    Science.gov (United States)

    1983-01-01

    Specially formulated derivatives of an unusual basic compound known as Alcide may be the answer to effective treatment and prevention of the disease bovine mastitis, a bacterial inflammation of a cow's mammary gland that results in loss of milk production and in extreme cases, death. Manufactured by Alcide Corporation the Alcide compound has killed all tested bacteria, virus and fungi, shortly after contact, with minimal toxic effects on humans or animals. Alcide Corporation credits the existence of the mastitis treatment/prevention products to assistance provided the company by NERAC, Inc.

  19. Exchange bias in a mixed metal oxide based magnetocaloric compound YFe0.5Cr0.5O3

    Science.gov (United States)

    Sharma, Mohit K.; Singh, Karan; Mukherjee, K.

    2016-09-01

    We report a detailed investigation of magnetization, magnetocaloric effect and exchange bias studies on a mixed metal oxide YFe0.5Cr0.5O3 belonging to perovskite family. Our results reveal that the compound is in canted magnetic state (CMS) where ferromagnetic correlations are present in an antiferromagnetic state. Magnetic entropy change of this compound follows a power law (∆SM∼Hm) dependence of magnetic field. In this compound, inverse magnetocaloric effect (IMCE) is observed below 260 K while conventional magnetocaloric effect (CMCE) above it. The exponent 'm' is found to be independent of temperature and field only in the IMCE region. Investigation of temperature and magnetic field dependence studies of exchange bias, reveal a competition between effective Zeeman energy of the ferromagnetic regions and anisotropic exchange energy at the interface between ferromagnetic and antiferromagnetic regions. Variation of exchange bias due to temperature and field cycling is also investigated.

  20. YbNiAl{sub 2}: A new Yb-based antiferromagnet with a field-induced ferromagnetic order

    Energy Technology Data Exchange (ETDEWEB)

    Rojas, D.P., E-mail: rojasd@unican.e [Departamento CITIMAC, Av de los Castros S/N, Santander 39005 (Spain); Rodriguez Fernandez, J.; Espeso, J.I.; Gomez Sal, J.C. [Departamento CITIMAC, Av de los Castros S/N, Santander 39005 (Spain)

    2009-10-15

    We report measurements on the thermal and magnetic properties in the temperature range 2-300 K for the YbNiAl{sub 2} compound which crystallizes in the orthorhombic MgCuAl{sub 2}-type structure (space group Cmcm). At zero magnetic field, AC-magnetic susceptibility data show a peak in the real component consistent with an antiferromagnetic order below T{sub N}=4.8K. A field-induced ferromagnetic order is observed from the zero field cooled and field cooled curves of DC-magnetic susceptibility at different magnetic fields with a transition to a ferromagnetic state between 9 and 10 kOe. It is further confirmed by the isothermal magnetization curves as a function of the magnetic field at several temperatures, showing two metamagnetic transitions at H{sub 1}=8kOe and H{sub 2}=9.3kOe. The results are compared to those reported for other Yb-Ni-Al compounds.

  1. Magnetic relaxation in a three-dimensional ferromagnet with weak quenched random-exchange disorder

    Indian Academy of Sciences (India)

    S N Kaul; Anita Semwal

    2003-12-01

    Isothermal remanent magnetization decay, r(), and `in-field’ growth of zero-field-cooled magnetization, ZFC(), with time have been measured over four decades in time at temperatures ranging from 0.25 c to 1.25 c (where c is the Curie temperature, determined previously for the same sample from static critical phenomena measurements) for a nearly ordered intermetallic compound Ni3Al, which is an experimental realization of a three-dimensional (= 3) ferromagnet with weak quenched random-exchange disorder. None of the functional forms of r() predicted by the existing phenomenological models of relaxation dynamics in spin systems with quenched randomness, but only the expressions r()=0[1 \\exp(-/1)+(/2)-] and ZFC()='0[1-\\{'1\\exp(-/'1)+(/'2)-'] closely reproduce such data in the present case. The most striking features of magnetic relaxation in the system in question are as follows: Aging effects are absent in both r() and ZFC() at all temperatures in the temperature range covered in the present experiments. A cross-over in equilibrium dynamics from the one, characteristic of a pure = 3 ferromagnet with complete atomic ordering and prevalent at temperatures away from c, to that, typical of a = 3 random-exchange ferromagnet, occurs as → c. The relaxation times 1()('1()) and 2()('2()) exhibit logarithmic divergence at critical temperatures $^{_{1}}_{\\text{c}}(^{'_{1}}_{\\text{c}}(H))$ and $^{_{2}}_{\\text{c}}(^{'_{2}}_{\\text{c}}(H))$; $^{'_{1}}_{\\text{c}}$ and $^{'_{2}}_{\\text{c}}$ both increase with the external magnetic field strength, , such that at any given field value, $^{'_{1}}_{\\text{c}}=^{'_{2}}_{\\text{c}}$. The exponent characterizing the logarithmic divergence in $'_{1}()$ and $'_{2}()$ possesses a field-independent value of ≃ 16 for both relaxation times. Of all the available theoretical models, the droplet fluctuation model alone provides a qualitative explanation for some aspects of the present magnetic relaxation data.

  2. Quantum Lifshitz Field Theory of a Frustrated Ferromagnet.

    Science.gov (United States)

    Balents, Leon; Starykh, Oleg A

    2016-04-29

    We propose a universal nonlinear sigma model field theory for one-dimensional frustrated ferromagnets, which applies in the vicinity of a "quantum Lifshitz point," at which the ferromagnetic state develops a spin wave instability. We investigate the phase diagram resulting from perturbations of the exchange and of magnetic field away from the Lifshitz point, and uncover a rich structure with two distinct regimes of different properties, depending upon the value of a marginal, dimensionless, parameter of the theory. In the regime relevant for one-dimensional systems with low spin, we find a metamagnetic transition line to a vector chiral phase. This line terminates in a critical end point, beyond which there is at least one multipolar or "spin nematic" phase. We show that the field theory is asymptotically exactly soluble near the Lifshitz point.

  3. Ferromagnetic and antiferromagnetic order in bacterial vortex lattices

    Science.gov (United States)

    Wioland, Hugo; Woodhouse, Francis G.; Dunkel, Jörn; Goldstein, Raymond E.; Goldstein Lab Team

    2013-11-01

    In conventional electronic materials, spins can organize into ordered phases that give rise to ferromagnetic or antiferromagnetic behavior. Here, we report similar observations in a completely different system: a suspension of swimming bacteria. When a dense Bacillus subtilis suspension is confined to a small circular chamber, it can spontaneously form a stable vortex (``spin'') state that can persist for several minutes. By coupling up to 100 such chambers in microfluidic devices, we are able to realize bacterial spin lattices of different geometries. Depending on that geometry and the effective coupling strength between neighboring vortices, we observe the formation of stable ``antiferromagnetic'' and ``ferromagnetic'' bacterial vortex states, that appear to be controlled by the subtle competition between bacterial boundary layer flows and bulk dynamics.

  4. Tuning Ferromagnetism at Interfaces between Insulating Perovskite Oxides

    Science.gov (United States)

    Ganguli, Nirmal; Kelly, Paul J.

    2014-09-01

    We use density functional theory calculations to show that the LaAlO3|SrTiO3 interface between insulating perovskite oxides is borderline in satisfying the Stoner criterion for itinerant ferromagnetism and explore other oxide combinations with a view to satisfying it more amply. The larger lattice parameter of a LaScO3|BaTiO3 interface is found to be less favorable than the greater interface distortion of LaAlO3|CaTiO3. Compared to LaAlO3|SrTiO3, the latter is predicted to exhibit robust magnetism with a larger saturation moment and a higher Curie temperature. Our results provide support for a "two phase" picture of coexistent superconductivity and ferromagnetism.

  5. Tuning ferromagnetism at interfaces between insulating perovskite oxides.

    Science.gov (United States)

    Ganguli, Nirmal; Kelly, Paul J

    2014-09-19

    We use density functional theory calculations to show that the LaAlO3|SrTiO3 interface between insulating perovskite oxides is borderline in satisfying the Stoner criterion for itinerant ferromagnetism and explore other oxide combinations with a view to satisfying it more amply. The larger lattice parameter of a LaScO3|BaTiO3 interface is found to be less favorable than the greater interface distortion of LaAlO3|CaTiO3. Compared to LaAlO3|SrTiO3, the latter is predicted to exhibit robust magnetism with a larger saturation moment and a higher Curie temperature. Our results provide support for a "two phase" picture of coexistent superconductivity and ferromagnetism.

  6. Tailoring Giant Magneto-impedance Effect in Ultrasoft Ferromagnetic Microwires

    Science.gov (United States)

    Chaturvedi, A.; Ruiz, A.; Mukherjee, P.; Srikanth, H.; Phan, M. H.; Larin, V. S.

    2012-02-01

    Research on soft ferromagnetic microwires exhibiting giant magneto-impedance (GMI) effect, which is a large change of the ac impedance of a ferromagnetic conductor in a static magnetic field, for advanced magnetic sensor applications is an area of topical interest. In this study we show how the GMI effect and its field sensitivity are optimized in Co-B-Si-Mn microwires by varying the magnetic core to glass shell diameter ratio (d). The microwires have been fabricated by the glass-coated melt spinning method. The largest values of GMI (245%) and its field sensitivity 25%/Oe are achieved at f = 13MHz for the microwires with d = 0.86. The d dependence of the magneto-impedance has been analyzed based on those of the magneto-resistance and magneto-reactance. Our studies indicate that the microwires with optimized GMI response are attractive candidate materials for structural health self-monitoring and magnetic biosensing applications.

  7. Magnetism in structures with ferromagnetic and superconducting layers

    Energy Technology Data Exchange (ETDEWEB)

    Zhaketov, V. D.; Nikitenko, Yu. V., E-mail: nikiten@nf.jinr.ru [Joint Institute for Nuclear Research (Russian Federation); Radu, F. [Helmholtz-Zentrum Berlin für Materialen un Energie (Germany); Petrenko, A. V. [Joint Institute for Nuclear Research (Russian Federation); Csik, A. [MTA Atomki, Institute for Nuclear Research (Hungary); Borisov, M. M.; Mukhamedzhanov, E. Kh. [Russian Research Centre Kurchatov Institute (Russian Federation); Aksenov, V. L. [Russian Research Centre Kurchatov Institute, Konstantinov St. Petersburg Nuclear Physics Institute (Russian Federation)

    2017-01-15

    The influence of superconductivity on ferromagnetism in the layered Ta/V/Fe{sub 1–x}V{sub x}/V/Fe{sub 1–x}V{sub x}/Nb/Si structures consisting of ferromagnetic and superconducting layers is studied using polarized neutron reflection and scattering. It is experimentally shown that magnetic structures with linear sizes from 5 nm to 30 μm are formed in these layered structures at low temperatures. The magnetization of the magnetic structures is suppressed by superconductivity at temperatures below the superconducting transition temperatures in the V and Nb layers. The magnetic states of the structures are shown to undergo relaxation over a wide magnetic-field range, which is caused by changes in the states of clusters, domains, and Abrikosov vortices.

  8. Ferromagnetic interaction model of activity level in workplace communication

    Science.gov (United States)

    Akitomi, Tomoaki; Ara, Koji; Watanabe, Jun-ichiro; Yano, Kazuo

    2013-03-01

    The nature of human-human interaction, specifically, how people synchronize with each other in multiple-participant conversations, is described by a ferromagnetic interaction model of people’s activity levels. We found two microscopic human interaction characteristics from a real-environment face-to-face conversation. The first characteristic is that people quite regularly synchronize their activity level with that of the other participants in a conversation. The second characteristic is that the degree of synchronization increases as the number of participants increases. Based on these microscopic ferromagnetic characteristics, a “conversation activity level” was modeled according to the Ising model. The results of a simulation of activity level based on this model well reproduce macroscopic experimental measurements of activity level. This model will give a new insight into how people interact with each other in a conversation.

  9. Monte Carlo simulation of the hysteresis phenomena on ferromagnetic nanotubes.

    Science.gov (United States)

    Salazar-Enríquez, C D; Restrepo, J; Restrepo-Parra, E

    2012-06-01

    In this work the hysteretic properties of single wall ferromagnetic nanotubes were studied. Hysteresis loops were computed on the basis of a classical Heisenberg model involving nearest neighbor interactions and using a Monte Carlo method implemented with a single spin movement Metropolis dynamics. Nanotubes with square and hexagonal unit cells were studied varying their diameter, temperature and magneto-crystalline anisotropy. Effects of the diameter were found stronger in the square unit cell magnetic nanotubes (SMNTs) than in the hexagonal unit cell magnetic nanotubes (HMNTs). The ferromagnetic behavior was observed in SMNTs at higher temperature than in HMNTs. Moreover in both cases, SMNTs and HMNTs, the magneto-crystalline anisotropy in the longitudinal direction showed a linear correspondence with the coercive field.

  10. Disorder-Induced Stabilization of the Quantum Hall Ferromagnet

    Science.gov (United States)

    Piot, B. A.; Desrat, W.; Maude, D. K.; Kazazis, D.; Cavanna, A.; Gennser, U.

    2016-03-01

    We report on an absolute measurement of the electronic spin polarization of the ν =1 integer quantum Hall state. The spin polarization is extracted in the vicinity of ν =1 (including at exactly ν =1 ) via resistive NMR experiments performed at different magnetic fields (electron densities) and Zeeman energy configurations. At the lowest magnetic fields, the polarization is found to be complete in a narrow region around ν =1 . Increasing the magnetic field (electron density) induces a significant depolarization of the system, which we attribute to a transition between the quantum Hall ferromagnet and the Skyrmion glass phase theoretically expected as the ratio between Coulomb interactions and disorder is increased. These observations account for the fragility of the polarization previously observed in high mobility 2D electron gas and experimentally demonstrate the existence of an optimal amount of disorder to stabilize the ferromagnetic state.

  11. Spin filter and spin valve in ferromagnetic graphene

    Science.gov (United States)

    Song, Yu; Dai, Gang

    2015-06-01

    We propose and demonstrate that a EuO-induced and top-gated graphene ferromagnetic junction can be simultaneously operated as a spin filter and a spin valve. We attribute such a remarkable result to a coexistence of a half-metal band and a common energy gap for opposite spins in ferromagnetic graphene. We show that both the spin filter and the spin valve can be effectively controlled by a back gate voltage, and they survive for practical metal contacts and finite temperature. Specifically, larger single spin currents and on-state currents can be reached with contacts with work functions similar to graphene, and the spin filter can operate at higher temperature than the spin valve.

  12. Ferromagnetic Ground States in Face-Centered Cubic Hubbard Clusters

    Science.gov (United States)

    Souza, T. X. R.; Macedo, C. A.

    2016-01-01

    In this study, the ground state energies of face-centered cubic Hubbard clusters are analyzed using the Lanczos method. Examination of the ground state energy as a function of the number of particle per site n showed an energy minimum for face-centered cubic structures. This energy minimum decreased in n with increasing coulombic interaction parameter U. We found that the ground state energy had a minimum at n = 0.6, when U = 3W, where W denotes the non-interacting energy bandwidth and the face-centered cubic structure was ferromagnetic. These results, when compared with the properties of nickel, shows strong similarity with other finite temperature analyses in the literature and supports the Hirsh’s conjecture that the interatomic direct exchange interaction dominates in driving the system into a ferromagnetic phase. PMID:27583653

  13. Coupling between ferromagnetic electrodes through ZnS barrier

    Energy Technology Data Exchange (ETDEWEB)

    Fix, T. [IPCMS-GMI (UMR 7504 du CNRS), ULP-ECPM, 23 rue du Loess, BP43 F-67034 Strasbourg (France)]. E-mail: thomas.fix@ipcms.u-strasbg.fr; Colis, S. [IPCMS-GMI (UMR 7504 du CNRS), ULP-ECPM, 23 rue du Loess, BP43 F-67034 Strasbourg (France); Schmerber, G. [IPCMS-GMI (UMR 7504 du CNRS), ULP-ECPM, 23 rue du Loess, BP43 F-67034 Strasbourg (France); Ulhaq, C. [IPCMS-GMI (UMR 7504 du CNRS), ULP-ECPM, 23 rue du Loess, BP43 F-67034 Strasbourg (France); Dinia, A. [IPCMS-GMI (UMR 7504 du CNRS), ULP-ECPM, 23 rue du Loess, BP43 F-67034 Strasbourg (France)

    2005-02-01

    Magnetization measurements are performed on CoFe{sub 2}/ZnS/CoFe{sub 2}/NiFe structures to investigate the interactions between ferromagnetic electrodes through the ZnS barrier. Negative shifts observed in magnetization minor loops indicate a ferromagnetic interaction. The influence of the hard-layer deposition temperature on this shift and on the hard-layer coercive field is considered. The amplitude of the shift decreases as the thickness of the ZnS layer increases. The decrease in this shift at low temperature confirms the presence of an indirect exchange coupling between the magnetic electrodes mediated by spin-polarized quantum tunneling through the ZnS layer.

  14. Hybrid superconductor-ferromagnet transistor-like device

    Energy Technology Data Exchange (ETDEWEB)

    Nevirkovets, I P [Department of Physics and Astronomy, Northwestern University, Evanston, IL 60208 (United States); Belogolovskii, M A [Donetsk Institute for Physics and Engineering, National Academy of Sciences of Ukraine, 72 R. Luxemburg Street, Donetsk 83114 (Ukraine)

    2011-02-15

    We demonstrate theoretically and experimentally that a ferromagnetic layer as thin as a few nanometres, which is almost transparent for non-superconducting charge transport, can be used as a cut-off filter to block transport of charge-carrier superconducting correlations. This property may be exploited in some applications, as is exemplified by the case of double-barrier S{sub 1}IS{sub 2}FIS{sub 3} multi-terminal devices (with S, I, and F denoting a superconductor, an insulator, and a ferromagnetic metal, respectively), whose principle of operation is based on a nonequilibrium superconducting state driven by tunnel injection of quasiparticles. Using the F layer makes the device asymmetric and considerably improves input-output isolation in comparison with the formerly investigated symmetric S{sub 1}IS{sub 2}IS{sub 3} devices.

  15. Tuning ferromagnetism in zinc oxide nanoparticles by chromium doping

    Science.gov (United States)

    Kaur, Palvinder; Pandey, S. K.; Kumar, Sanjeev; Negi, N. S.; Chen, C. L.; Rao, S. M.; Wu, M. K.

    2015-11-01

    Zn1- x Cr x O nanoparticles with x = 0.0, 0.01, 0.03 and 0.05 were synthesized by the sol-gel technique. Powder X-ray diffraction (XRD) studies reveal that chromium (Cr) incorporates into the ZnO crystal lattice without disturbing the parent hexagonal (wurtzite) structure. Transmission electron microscopy (TEM) measurements show that the average size of these nanoparticles is in the range 15-25 nm. Optical absorption studies show that the band gap of ZnO nanoparticles varies with Cr doping. Photoluminescence (PL) studies depict the presence of defects in Cr-doped nanoparticles. Undoped ZnO exhibits diamagnetic behavior while Cr-doped ZnO samples exhibit weak ferromagnetism to anti-ferromagnetism depending on the Cr content.

  16. Superconductivity and ferromagnetism in nanostructured Bi{sub 3}Ni

    Energy Technology Data Exchange (ETDEWEB)

    Schoenemann, R.; Herrmannsdoerfer, T.; Naumann, M.; Wosnitza, J. [Dresden High Magnetic Field Laboratory (HLD), Helmholtz-Zentrum Dresden-Rossendorf (Germany); Skrotzki, R. [Dresden High Magnetic Field Laboratory (HLD), Helmholtz-Zentrum Dresden-Rossendorf (Germany); Department of Chemistry and Food Chemistry, TU Dresden (Germany); Kaiser, M.; Heise, M.; Ruck, M. [Department of Chemistry and Food Chemistry, TU Dresden (Germany); Kummer, K. [European Synchrotron Radiation Facility (ESRF), Grenoble (France); Graf, D. [National High Magnetic Field Laboratory and Department of Physics, Florida State University, Tallahassee, Florida (United States)

    2014-07-01

    We have demonstrated the coexistence of superconductivity and ferromagnetism in Bi{sub 3}Ni nanostructures which have been prepared by making use of novel chemical-reaction paths. Here, we present recent experiments on novel nanostructures, such as supercrystals consisting of packed Bi{sub 3}Ni nanofibers. We have investigated their magnetic and electrical-transport properties by means of XMCD, SQUID magnetometry, pulsed-field susceptometry, and ac-resistance measurements in a wide field and temperature range. Resistivity measurements demonstrate that superconductivity persists well above the Pauli limiting field - with strong anisotropy. These results will be presented in the context of a coexistence of superconductivity and ferromagnetism. Part of this work was performed at the NHMFL and ESRF beamline ID08.

  17. Magnetoanisotropic Andreev reflection in ferromagnet-superconductor junctions.

    Science.gov (United States)

    Högl, Petra; Matos-Abiague, Alex; Žutić, Igor; Fabian, Jaroslav

    2015-09-11

    Andreev reflection spectroscopy of ferromagnet-superconductor (FS) junctions [corrected] is an important probe of spin polarization. We theoretically investigate spin-polarized transport in FS junctions in the presence of Rashba and Dresselhaus interfacial spin-orbit fields and show that Andreev reflection can be controlled by changing the magnetization orientation. We predict a giant in- and out-of-plane magnetoanisotropy of the junction conductance. If the ferromagnet is highly spin polarized-in the half-metal limit-the magnetoanisotropic Andreev reflection depends universally on the spin-orbit fields only. Our results show that Andreev reflection spectroscopy can be used for sensitive probing of interfacial spin-orbit fields in a FS junction.

  18. Bound States of a Ferromagnetic Wire in a Superconductor.

    Science.gov (United States)

    Sau, Jay D; Brydon, P M R

    2015-09-18

    We consider the problem of bound states in strongly anisotropic ferromagnetic impurities in a superconductor, motivated by recent experiments that claim to observe Majorana modes at the ends of ferromagnetic wires on a superconducting substrate [S. Nadj-Perge et al., Science 346, 602 (2014)]. Generalizing the successful theory of bound states of spherically symmetric impurities, we consider a wirelike potential using both analytical and numerical approaches. We find that away from the ends of the wire the bound states form bands with pronounced van Hove singularities, giving rise to subgap peaks in the local density of states. For sufficiently strong magnetization of the wire, we show that this process generically produces a sharp peak at zero energy in the local density of states near the ends of the wire. This zero-energy peak has qualitative similarities to the claimed signature of a Majorana mode observed in the aforementioned experiment.

  19. Soliton switching in a site-dependent ferromagnet

    Science.gov (United States)

    Senjudarvannan, R.; Sathishkumar, P.; Vijayalakshmi, S.

    2017-02-01

    Switching of soliton in a ferromagnetic medium offers the possibility of developing a new innovative approach for information storage technologies. The nonlinear spin dynamics of a site-dependent Heisenberg ferromagnetic spin chain with Gilbert damping under the influence of external magnetic field is expressed in the form of the Landau-Lifshitz-Gilbert equation in the classical continuum limit. The corresponding evolution equation is developed through stereographic projection technique by projecting the unit sphere of spin onto a complex plane. The exact soliton solutions are constructed by solving the associated evolution equation through the modified extended tanh-function method. The impact of damping and external magnetic field on the magnetic soliton under the invariant inhomogeneity is investigated and finally, the magnetization switching in the form of shape changing solitons are demonstrated.

  20. Large magnetocaloric effect in sintered ferromagnetic EuS

    Science.gov (United States)

    Matsumoto, Koichi; Li, Liang; Hirai, Shinji; Nakamura, Eiji; Murayama, Daiki; Ura, Yutaro; Abe, Satoshi

    2016-10-01

    We present magnetocaloric effect measurements of the ferromagnetic semiconductor EuS in the vicinity of its ordering temperature. Single phase EuS powder was synthesized by CS2 gas sulfurization of Eu2O3. A sintered compact with relative density over 95% was prepared by pulsed electric current sintering of the powder. Temperature and magnetic field dependence of the magnetization and specific heat were characteristic of a paramagnetic to ferromagnetic second order phase transition. The entropy change induced by an external magnetic field and the specific heat were both close to those of a single crystal. We obtained an entropy-temperature (S-T) diagram of the EuS sintered compact. Carnot cycle liquefaction of hydrogen using EuS was compared with several other materials, with results indicating that sintered EuS is an excellent magnetic refrigerant for hydrogen liquefaction.

  1. Bolometric detection of ferromagnetic resonance in YIG slab

    Science.gov (United States)

    Tu, Sa; Białek, Marcin; Zhang, Youguang; Zhao, Weisheng; Yu, Haiming; Ansermet, Jean-Philippe

    2017-10-01

    The resistance of the Pt bar deposited on the YIG slab was monitored while the magnetic field was ramped through the ferromagnetic resonance with the YIG slab facing a coplanar waveguide resonator excited at 4.3 GHz excitation. The resistance change provides detection of the ferromagnetic resonance with a high signal-to-noise ratio. It is ascribed to a change in the temperature of the Pt bars. The thermal origin of the signal is confirmed by the observation that the signal vanishes when field modulation is applied at frequencies above 6 Hz. The spin pumping effect was vanishingly small, and the anisotropic magnetoresistance of the Pt bar, though quite easily observed, would imply a rectification voltage that is much smaller than the bolometric effect.

  2. Neutron scattering study of the ferromagnetic superconductor UGe2

    Science.gov (United States)

    Kernavanois, N.; Grenier, B.; Huxley, A.; Ressouche, E.; Sanchez, J. P.; Flouquet, J.

    2001-11-01

    Unpolarized and polarized neutron scattering experiments have been performed at ambient pressure on a single crystal of the itinerant electron superconductor UGe2 in both the ferromagnetic and the paramagnetic phases. Unpolarized neutrons have confirmed the ZrGa2-type orthorhombic crystal structure of UGe2 and a ferromagnetic ordering below TC=53 K with the moments aligned along the a axis. No evidence of any modulated component for the magnetic structure has been found. Polarized neutron data have shown a large and almost spherical magnetization distribution at the U sites and no induced moment at the Ge sites. Refinements of the magnetic structure factors within the dipolar approximation allow the magnitude of the orbital and spin uranium moments to be quantified, and a comparison to the measured static magnetization reveals that there is no diffuse contribution.

  3. Optical spectra of the heavy fermion uniaxial ferromagnet UGe2

    Science.gov (United States)

    Guritanu, V.; Armitage, N. P.; Tediosi, R.; Saxena, S. S.; Huxley, A.; van der Marel, D.

    2008-11-01

    We report a detailed study of UGe2 single crystals using infrared reflectivity and spectroscopic ellipsometry. The optical conductivity suggests the presence of a low-frequency interband transition and a narrow free-carrier response with strong frequency dependence of the scattering rate and effective mass. We observe sharp increase in the low-frequency mass and reduction in scattering rate below the upper ferromagnetic transition TC=53K indicating the emergence of a heavy fermion state triggered by the ferromagnetic order. The characteristic changes are exhibited most strongly at an energy scale below 12 meV. They recover their unrenormalized value above TC and for ω>40meV . In contrast no sign of an anomaly is seen at the lower transition temperature of unknown nature, Tx˜30K , observed in transport and thermodynamic experiments.

  4. Calculation of Gilbert damping in ferromagnetic films

    Directory of Open Access Journals (Sweden)

    Edwards D. M.

    2013-01-01

    Full Text Available The Gilbert damping constant in the phenomenological Landau-Lifshitz-Gilbert equation which describes the dynamics of magnetization, is calculated for Fe, Co and Ni bulk ferromagnets, Co films and Co/Pd bilayers within a nine-band tight-binding model with spin-orbit coupling included. The calculational effciency is remarkably improved by introducing finite temperature into the electronic occupation factors and subsequent summation over the Matsubara frequencies. The calculated dependence of Gilbert damping constant on scattering rate for bulk Fe, Co and Ni is in good agreement with the results of previous ab initio calculations. Calculations are reported for ferromagnetic Co metallic films and Co/Pd bilayers. The dependence of the Gilbert damping constant on Co film thickness, for various scattering rates, is studied and compared with recent experiments.

  5. The paramagnetic properties of ferromagnetic mixed-spin chain system

    Energy Technology Data Exchange (ETDEWEB)

    Hu, Ai-Yuan, E-mail: huaiyuanhuyuanai@126.com; Wu, Zhi-Min; Cui, Yu-Ting; Qin, Guo-Ping

    2015-01-15

    The double-time Green's function method is used to investigate the paramagnetic properties of ferromagnetic mixed-spin chain system within the random-phase approximation and Anderson–Callen's decoupling approximation. The analytic expressions of the transverse susceptibility, longitudinal susceptibility and correlation length are obtained under transverse and longitudinal magnetic field. Using the analytic expressions of the transverse and longitudinal susceptibility to fit the experimental results, our results well agree with experimental data and the results from the high temperature series expansion within a simple Padé approximation. - Highlights: • We investigate the magnetic properties of a ferromagnetic mixed-spin chain system. • We use the double-time temperature-dependent Green's function technique. • Different single-ion anisotropy values for different spin values are considered. • Our results agree with experimental data and the results from the other theoretical methods.

  6. Zn-Mn-O: Ferromagnet at room temperature

    Directory of Open Access Journals (Sweden)

    Milivojević Dušan D.

    2007-01-01

    Full Text Available Semiconductor Zn-Mn-O crystallites were synthesized by a solid state reaction method starting from the thermal decomposition of the appropriate oxalates. Samples were thermally treated in air at temperatures ranging from 400 to 900°C. The nominal concentrations of manganese werex = 0.01, 0.02, 0.04 and 0.10. The samples were investigated by the X-ray powder diffraction method, magnetization measurements and by electron paramagnetic resonance. X-ray diffractgrams show a dominant wurtzite structure of Zn-Mn-O. Room temperature ferromagnetism was observed in Zn-Mn-O samples with manganese concentrations x ≤ 0.04, thermally treated at low temperature (500°C. The saturation magnetiza­tion for the sample with x = 0.01 was 0.05 μB/Mn. The room temperature ferromagnetism seems to be due to the diffusion of Zn into the Mn-oxides grains.

  7. The Mobility Edge in Disordered Ferromagnetic Doped Semiconductors

    Science.gov (United States)

    Nielsen, Erik; Bhatt, R. N.

    2007-03-01

    While the clearest example of ferromagnetism in doped semiconductors is seen in diluted magnetic semiconductors such as Ga1-xMnxAs, under certain conditions, semiconductors doped with non-magnetic impurities may also exhibit ferromagnetic ground states. We present numerical results of the nature of single particle states in such a positionally disordered three-dimensional system with a maximally spin-polarized ground state using a realistic potential for hydrogenic centers. In particular, we identify the mobility edges, which mark the energies at which single particle states become delocalized, and whose location relative to the Fermi energy determine electronic transport in the system. We describe the dependence of the mobility edges on impurity density and potential, and discuss the variation of conductivity with impurity and carrier density. H. Ohno, Science 281, 951 (1998) Erik Nielsen and R. N. Bhatt, APS March Meeting 2006. R. N. Bhatt and T. M. Rice, Physical Review B 23, 1920 (1981).

  8. Intermetallic Compounds

    Science.gov (United States)

    Takagiwa, Y.; Matsuura, Y.; Kimura, K.

    2014-06-01

    We have focused on the binary narrow-bandgap intermetallic compounds FeGa3 and RuGa3 as thermoelectric materials. Their crystal structure is FeGa3-type (tetragonal, P42/ mnm) with 16 atoms per unit cell. Despite their simple crystal structure, their room temperature thermal conductivity is in the range 4-5-W-m-1-K-1. Both compounds have narrow-bandgaps of approximately 0.3-eV near the Fermi level. Because their Seebeck coefficients are quite large negative values in the range 350-FeGa3 and RuGa3 as n and p-type materials. The dimensionless figure of merit, ZT, was significantly improved by substitution of Sn for Ga in FeGa3 (electron-doping) and by substitution of Zn for Ga in RuGa3 (hole-doping), mainly as a result of optimization of the electronic part, S 2 σ.

  9. Organic Compounds

    Science.gov (United States)

    Shankland, Kenneth

    For many years, powder X-ray diffraction was used primarily as a fingerprinting method for phase identification in the context of molecular organic materials. In the early 1990s, with only a few notable exceptions, structures of even moderate complexity were not solvable from PXRD data alone. Global optimisation methods and highly-modified direct methods have transformed this situation by specifically exploiting some well-known properties of molecular compounds. This chapter will consider some of these properties.

  10. Compound odontoma

    Directory of Open Access Journals (Sweden)

    Monica Yadav

    2012-01-01

    Full Text Available Odontomas have been extensively reported in the dental literature, and the term refers to tumors of odontogenic origin. Though the exact etiology is still unknown, the postulated causes include: local trauma, infection, inheritance and genetic mutation. The majority of the lesions are asymptomatic; however, may be accompanied with pain and swelling as secondary complaints in some cases. Here, we report a case of a compound odontome in a 14 year old patient.

  11. Magnetic relaxation in chain-of-spheres ferromagnetic particles

    CERN Document Server

    Yang, J S

    2002-01-01

    The thermal activation of elongated ferromagnetic particles is analyzed using a chain-of-spheres model. The spheres within the chain are assumed to be coupled magnetically with dipolar interaction. The effect of uniaxial magnetocrystalline anisotropy along the chain is also taken into account. It was shown that the behavior of thermal switching critically depends on the relative strength of shape anisotropy and magnetocrystalline anisotropy, field orientation, sweep field rate and temperature.

  12. Analysis of ultra-narrow ferromagnetic domain walls

    Energy Technology Data Exchange (ETDEWEB)

    Jenkins, Catherine; Paul, David

    2012-01-10

    New materials with high magnetic anisotropy will have domains separated by ultra-narrow ferromagnetic walls with widths on the order of a few unit cells, approaching the limit where the elastic continuum approximation often used in micromagnetic simulations is accurate. The limits of this approximation are explored, and the static and dynamic interactions with intrinsic crystalline defects and external driving elds are modeled. The results developed here will be important when considering the stability of ultra-high-density storage media.

  13. The partition function of a ferromagnet up to three loops

    Energy Technology Data Exchange (ETDEWEB)

    Hofmann, C P, E-mail: christoph@ucol.mx [Facultad de Ciencias, Universidad de Colima, Bernal Diaz del Castillo 340, Colima, Colima 28045 (Mexico)

    2011-04-01

    The low-temperature behavior of ferromagnets with a spontaneously broken symmetry O(3) {yields} O(2) is analyzed within the perspective of effective Lagrangians. The leading coefficients of the low-temperature expansion for the partition function are calculated up to three loops and the manifestation of the spin-wave interaction in this series is discussed. The effective field theory method has the virtue of being completely systematic and model-independent.

  14. Is gadolinium a helical antiferromagnet or a collinear ferromagnet?

    Indian Academy of Sciences (India)

    S N Kaul

    2003-03-01

    Controversial issues concerning the nature of magnetic ordering in gadolinium are briefly reviewed. The recent experimental results are shown to resolve most of such issues in that they rule out the possibility of a helical spin structure in Gd and clearly bring out the role of long-range dipolar interactions in stabilising collinear ferromagnetic order for temperatures between the spin-reorientation temperature and the Curie point.

  15. Reversal of exchange bias in nanocrystalline antiferromagnetic-ferromagnetic bilayers

    CERN Document Server

    Prados, C; Hernando, A; Montone, A

    2002-01-01

    The sign of the exchange bias in field cooled nanocrystalline antiferromagnetic-ferromagnetic bilayers (Co-O and Ni-O/permalloy) is reversed at temperatures approaching the antiferromagnetic (AFM) blocking temperature. A similar phenomenon is observed after magnetic training processes at similar temperatures. These effects can be explained assuming that the boundaries of nanocrystalline grains in AFM layers exhibit lower transition temperatures than grain cores.

  16. Polarized Neutron Reflectivity Simulation of Ferromagnet/ Antiferromagnet Thin Films

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Ki Yeon; Lee, Jeong Soo

    2008-02-15

    This report investigates the current simulating and fitting programs capable of calculating the polarized neutron reflectivity of the exchange-biased ferromagnet/antiferromagnet magnetic thin films. The adequate programs are selected depending on whether nonspin flip and spin flip reflectivities of magnetic thin films and good user interface are available or not. The exchange-biased systems such as Fe/Cr, Co/CoO, CoFe/IrMn/Py thin films have been simulated successfully with selected programs.

  17. Transport through hybrid superconducting/ferromagnetic double-path junction

    Energy Technology Data Exchange (ETDEWEB)

    Facio, T.J.S. [Departamento de Física e Química, Universidade Estadual Paulista – UNESP, 15385-000, Ilha Solteira, SP (Brazil); Orellana, P.A. [Departamento de Física, Universidad Técnica Federico Santa Maria, Av. Vicuña Mackenna, 3939, Santiago (Chile); Jurelo, A.R. [Departamento de Física, Universidade Estadual de Ponta Grossa – UEPG, 84030-000, Ponta Grossa, PR (Brazil); Figueira, M.S. [Instituto de Física, Universidade Federal Fluminense, 24210-340, Niterói, RJ (Brazil); Cabrera, G.G. [Instituto de Física ‘Gleb Wataghin’, Universidade Estadual de Campinas – UNICAMP, 13083-859, Campinas, SP (Brazil); Siqueira, E.C., E-mail: ecosta@utfpr.edu.br [Departamento de Física, Universidade Tecnológica Federal do Paraná – UTFPR, 84016-210, Ponta Grossa, PR (Brazil)

    2017-02-05

    In this paper we study a double-path junction formed by a ferromagnetic and a superconductor lead. The first path connects the superconductor and ferromagnet directly while the second path connects these metals through a quantum dot. The whole system works as an Aharonov–Bohm interferometer allowing the study of the interference between these two paths under the presence of spin imbalance and Andreev bound states. We considered the effect of Fano interference on the electronic transmittance through the quantum dot and observed two regimes of conduction depending on the strength of the direct coupling. For the weak coupling regime, the transmittance presented the usual four resonances due to the Andreev bound states whereas for the strong coupling regime the profile was inverted and resonances became anti-resonances. However, even in the strong coupling regime it was possible to observe a central resonance due to the interference between the Andreev bound states. We have also studied the signatures of Fano interference on the average occupation within the quantum dot. The spin accumulation was analyzed and how it depends on the direct coupling and an external magnetic field applied to the system. The results obtained may be used in a possible experimental implementation of this system in order to probe spin related effects in ferromagnetic superconductor nanostructures. - Highlights: • An Aharonov–Bohm interferometer composed by a quantum-dot coupled to a superconductor and ferromagnetic lead is studied. • The transmittance through the QD is determined by the interplay between Andreev and Fano interference. • Spin accumulation within the quantum dot is studied as a function of bias/gate voltages and an external magnetic flux.

  18. Magnetization behavior of nanocrystalline systems combining ferromagnetic and antiferromagnetic phases

    Energy Technology Data Exchange (ETDEWEB)

    Loeffler, J.; Wagner, W.; Svygenhoven, H. van [Paul Scherrer Inst. (PSI), Villigen (Switzerland); Meier, J.; Doudin, B.; Ansermet, J.P. [Ecole Polytechnique Federale, Lausanne (Switzerland)

    1997-09-01

    The magnetic properties of nanostructured materials on the basis of Fe and Ni have been investigated with a SQUID magnetometer, complementary to the small-angle neutron scattering study reported in the same volume. Measurements of the coercive field in a temperature range from 5 to 300 K confirm the validity of the random anisotropy model for our nanostructured systems. Furthermore, we obtain information about the presence and distribution of the antiferromagnetic oxides, joining the ferromagnetic grains. (author) 2 figs., 3 refs.

  19. Long range anti-ferromagnetic spin model for prebiotic evolution

    Energy Technology Data Exchange (ETDEWEB)

    Nokura, Kazuo [Shonan Institute of Technology, Fujisawa 251-8511 (Japan)

    2003-11-28

    I propose and discuss a fitness function for one-dimensional binary monomer sequences of macromolecules for prebiotic evolution. The fitness function is defined by the free energy of polymers in the high temperature random coil phase. With repulsive interactions among the same kind of monomers, the free energy in the high temperature limit becomes the energy function of the one-dimensional long range anti-ferromagnetic spin model, which is shown to have a dynamical phase transition and glassy states.

  20. Direct evidence for ferromagnetic spin polarization in gold nanoparticles

    OpenAIRE

    Yamamoto, Y; Miura, T; Teranishi, T.; Miyake, M.; Hori, H.; Suzuki, M.; Kawamura, N.; Miyagawa, H; T. Nakamura; Kobayashi, K

    2004-01-01

    We report the first direct observation of ferromagnetic spin polarization of Au nanoparticles with a mean diameter of 1.9 nm using X-ray magnetic circular dichroism (XMCD). Owing to the element selectivity of XMCD, only the gold magnetization is explored. Magnetization of gold atoms estimated by XMCD shows a good agreement with the results obtained by conventional magnetometry. This result is evidence of intrinsic spin polarization in nano-sized gold.

  1. Direct Observation of Ferromagnetic Spin Polarization in Gold Nanoparticles

    OpenAIRE

    Yamamoto, Y; Miura, T; Suzuki, M.; Kawamura, N.; Miyagawa, H; T. Nakamura; Kobayashi, K; Teranishi, T.; Hori, H.

    2004-01-01

    We report the first direct observation of ferromagnetic spin polarization of Au nanoparticles with a mean diameter of 1.9 nm using x-ray magnetic circular dichroism (XMCD). Owing to the element selectivity of XMCD, only the gold magnetization is explored. Magnetization of gold atoms as estimated by XMCD shows a good agreement with results obtained by conventional magnetometry. This evidences intrinsic spin polarization in nanosized gold.

  2. Ferroelectricity and ferromagnetism in EuTiO3 nanowires

    OpenAIRE

    Morozovska, Anna N.; Glinchuk, Maya D.; Behera, Rakesh K.; Zaylichniy, Basyl Y.; Deo, Chaitanya S.; Eliseev, Eugene A.

    2011-01-01

    We predicted the ferroelectric-ferromagnetic multiferroic properties of EuTiO3 nanowires and generated the phase diagrams in coordinates of temperature and wire radii. The calculations were performed within the Landau-Ginzburg-Devonshire theory with phenomenological parameters extracted from tabulated experimental data and first principles calculations. Since bulk EuTiO3 is antiferromagnetic at temperatures lower than 5.5 K and paraelectric at all temperatures, our goal was to investigate the...

  3. New Preisach model for structured particulate ferromagnetic media

    Energy Technology Data Exchange (ETDEWEB)

    Stancu, Alexandru [Faculty of Physics, Department of Electricity and Electronics, ' Alexandru Ioan Cuza' University, Blvd. Carol I, 700506 Iasi (Romania)]. E-mail: alstancu@uaic.ro; Stoleriu, Laurentiu [Faculty of Physics, Department of Electricity and Electronics, ' Alexandru Ioan Cuza' University, Blvd. Carol I, 700506 Iasi (Romania); Postolache, Petronel [Faculty of Physics, Department of Electricity and Electronics, ' Alexandru Ioan Cuza' University, Blvd. Carol I, 700506 Iasi (Romania); Tanasa, Radu [Faculty of Physics, Department of Electricity and Electronics, ' Alexandru Ioan Cuza' University, Blvd. Carol I, 700506 Iasi (Romania)

    2005-04-15

    In this paper a Preisach-type model, named Preisach model for patterned media (PMPM, or PM{sup 2}), that successfully describes magnetization processes in structured particulate ferromagnetic media and in strongly correlated particulate media is presented. The PM{sup 2} provides explicit expressions for the magnetization curves, which makes it numerically very efficient. It obeys the exact wiping-out property and describes non-congruent minor hysteresis loops measured within given field limits.

  4. Magnetic Sensors Based on Amorphous Ferromagnetic Materials: A Review

    OpenAIRE

    Carlos Morón; Carolina Cabrera; Alberto Morón; Alfonso García; Mercedes González

    2015-01-01

    Currently there are many types of sensors that are used in lots of applications. Among these, magnetic sensors are a good alternative for the detection and measurement of different phenomena because they are a “simple” and readily available technology. For the construction of such devices there are many magnetic materials available, although amorphous ferromagnetic materials are the most suitable. The existence in the market of these materials allows the production of different kinds of senso...

  5. Modeling of Hysteresis Losses in Ferromagnetic Laminations under Mechanical Stress

    OpenAIRE

    Rasilo, Paavo; Singh, Deepak; Aydin, Ugur; Martin, Floran; Kouhia, Reijo; Belahcen, Anouar; Arkkio, Antero

    2015-01-01

    A novel approach for predicting magnetic hysteresis loops and losses in ferromagnetic laminations under mechanical stress is presented. The model is based on combining a Helmholtz free energy -based anhysteretic magnetoelastic constitutive law to a vector Jiles-Atherton hysteresis model. This paper focuses only on unidirectional and parallel magnetic fields and stresses, albeit the model is developed in full 3-D configuration in order to account also for strains perpendicular to the loading d...

  6. A study of periodic and aperiodic ferromagnetic antidot lattices

    Science.gov (United States)

    Bhat, Vinayak S.

    This thesis reports our study of the effect of domain wall pinning by ferromagnetic (FM) metamaterials [1] in the form of periodic antidot lattices (ADL) on spin wave spectra in the reversible regime. This study was then extended to artificial quasicrystals in the form of Penrose P2 tilings (P2T). Our DC magnetization study of these metamaterials showed reproducible and temperature dependent knee anomalies in the hysteretic regime that are due to the isolated switching of the FM segments. Our dumbbell model analysis [2] of simulated magnetization maps indicates that FM switching in P2T is nonstochastic . We have also acquired the first direct, two-dimensional images of the magnetization of Permalloy films patterned into P2T using scanning electron microscopy with polarization analysis (SEMPA). Our SEMPA images demonstrate P2T behave as geometrically frustrated networks of narrow ferromagnetic film segments having near-uniform, bipolar (Ising-like) magnetization, similar to artificial spin ices (ASI). We find the unique aperiodic translational symmetry and diverse vertex coordination of multiply-connected P2T induce a more complex spin-ice behavior driven by exchange interactions in vertex domain walls, which differs markedly from the behavior of disconnected ASI governed only by dipolar interactions. Keywords: Ferromagnetic Antidot Lattices, Metamaterials, Ferromagnetic Resonance, Artificial Quasicrystal, Artificial Spin Ice. [1] VV Kruglyak et al. "Magnonic metamaterials". In: Metamaterial, edited by X.-Y. Jiang (InTech, 2012) (2012). [2] Claudio Castelnovo, Roderich Moessner, and Shivaji L Sondhi. "Magnetic monopoles in spin ice". In: Nature 451.7174 (2008), pp. 42--45.

  7. Ferromagnetic shadow mask for spray coating of polymer patterns

    DEFF Research Database (Denmark)

    Keller, Stephan Sylvest; Bosco, Filippo; Boisen, Anja

    2013-01-01

    We present the fabrication of a wafer-scale shadow mask with arrays of circular holes with diameters of 150–400 μm. Standard UV photolithography is used to define 700 μm thick SU-8 structures followed by electroplating of nickel and etching of the template. The ferromagnetic properties of the sha...... of the shadow mask allow magnetic clamping to the substrate and spray coating of well defined polymer patterns....

  8. Dynamical mean-field theory for flat-band ferromagnetism

    Science.gov (United States)

    Nguyen, Hong-Son; Tran, Minh-Tien

    2016-09-01

    The magnetically ordered phase in the Hubbard model on the infinite-dimensional hyper-perovskite lattice is investigated within dynamical mean-field theory. It turns out for the infinite-dimensional hyper-perovskite lattice the self-consistent equations of dynamical mean-field theory are exactly solved, and this makes the Hubbard model exactly solvable. We find electron spins are aligned in the ferromagnetic or ferrimagnetic configuration at zero temperature and half filling of the edge-centered sites of the hyper-perovskite lattice. A ferromagnetic-ferrimagnetic phase transition driven by the energy level splitting is found and it occurs through a phase separation. The origin of ferromagnetism and ferrimagnetism arises from the band flatness and the virtual hybridization between macroscopically degenerate flat bands and dispersive ones. Based on the exact solution in the infinite-dimensional limit, a modified exact diagonalization as the impurity solver for dynamical mean-field theory on finite-dimensional perovskite lattices is also proposed and examined.

  9. Ferromagnetic resonance features of degenerate GdN semiconductor

    Energy Technology Data Exchange (ETDEWEB)

    Vidyasagar, Reddithota, E-mail: dr.vidyasagar1979@gmail.com [Department of Electrical and Electronic Engineering, Graduate School of Engineering, Kobe University, 1-1 Rokkodai, Kobe 657-8501 (Japan); Kita, Takashi [Department of Electrical and Electronic Engineering, Graduate School of Engineering, Kobe University, 1-1 Rokkodai, Kobe 657-8501 (Japan); Sakurai, Takahiro; Shimokawa, Tokuro [Centre for Support to Research and Education Activities, Kobe University, 1-1 Rokkodai, Kobe 657-8501 (Japan); Ohta, Hitoshi [Molecular Photoscience Research Center and Graduate School of Science, Kobe University, 1-1 Rokkodai, Kobe 657-8501 (Japan)

    2017-06-15

    Using X-band Ferromagnetic Resonance (FMR) Spectroscopy, we demonstrate the microscopic ferromagnetic resonance features of degenerated GdN semiconductor. The FMR spectrum suggests a single resonance mode below 10 K; interestingly, this particular structure is found to exhibit a peculiar magnetic resonance (PMR) on the top of the uniform FMR while temperature increases from 12–36 K. The low-field PMR mode attributed to the differently magnetized part of the film with an easy in-plane axis. The narrow-field gap between PMR and uniform FMR suggests the strong coupling owning to the differently magnetized part with easy in-plane axis and the magnetized part with an out-of-plane axis. The saturation magnetization, cubic magnetocrystalline anisotropy, and uniaxial anisotropy of GdN epitaxial film have been evaluated by the angular-dependence FMR. - Highlights: • Observation of peculiar magnetic resonance (PMR) on the top of ferromagnetic resonance (FMR). • Newly evolving PMR manifests differently magnetized part of the film with an easy in-plane axis. • Narrow gap between PMR and FMR owing to the strong interaction between two spin–wave resonances. • Uniaxial anisotropy increases with GdN thickness decreases.

  10. (Ga,Fe)Sb: A p-type ferromagnetic semiconductor

    Energy Technology Data Exchange (ETDEWEB)

    Tu, Nguyen Thanh; Anh, Le Duc; Tanaka, Masaaki [Department of Electrical Engineering and Information Systems, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-8656 (Japan); Hai, Pham Nam [Department of Electrical Engineering and Information Systems, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-8656 (Japan); Department of Physical Electronics, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro, Tokyo 152-0033 (Japan)

    2014-09-29

    A p-type ferromagnetic semiconductor (Ga{sub 1−x},Fe{sub x})Sb (x = 3.9%–13.7%) has been grown by low-temperature molecular beam epitaxy (MBE) on GaAs(001) substrates. Reflection high energy electron diffraction patterns during the MBE growth and X-ray diffraction spectra indicate that (Ga,Fe)Sb layers have the zinc-blende crystal structure without any other crystallographic phase of precipitates. Magnetic circular dichroism (MCD) spectroscopy characterizations indicate that (Ga,Fe)Sb has the zinc-blende band structure with spin-splitting induced by s,p-d exchange interactions. The magnetic field dependence of the MCD intensity and anomalous Hall resistance of (Ga,Fe)Sb show clear hysteresis, demonstrating the presence of ferromagnetic order. The Curie temperature (T{sub C}) increases with increasing x and reaches 140 K at x = 13.7%. The crystal structure analyses, magneto-transport, and magneto-optical properties indicate that (Ga,Fe)Sb is an intrinsic ferromagnetic semiconductor.

  11. Ferromagnetism in ZnO doped with alkaline elements

    Science.gov (United States)

    Wang, Yiren; Piao, Jingyuan; Xin, Guozhong; Lu, Yunhao; Ao, Zhimin; Bao, Nina; Ding, Jun; Li, Sean; Yi, Jiabao

    We have observed room temperature ferromagnetism (RTFM) in ZnO doped with alkaline elements Using first-principles calculations we found the magnetization in these systems is originated from the O2p hole states around Zn vacancies. Calculations indicate that the formation energy of Zn vacancies alone is rather high while further investigation indicates the formation can be much stabilized by the alkaline dopants in the form of defect complexes. By calculating the formation energy of concerned defects and complexes, we found the role of the dopants that under a certain doping concentration: Zn vacancy, substitutional and interstitial dopants can form a defect complex, which can lower formation energy, therefore stabilizing Zn vacancies. Moreover K dopants have shown unique functions on the ferromagnetism since the substitutional K can induce magnetic moments to the system by forming partial zinc vacancy via lattice distortion. Hence K doped ZnO can be magnetic at low doping concentrations. Experimentally, Li, Na doped ZnO films and K doped ZnO nanorods with different doping levels are synthesized, RTFM can be observed in all these systems. The magnetization is found to be greatly influenced by the doping concentrations. The experimental results have shown good consistence with our theoretical calculations. Our studies can inspire the defect induced ferromagnetism as a new route for the fabrication of new diluted magnetic semiconductors.

  12. Inconvenient magnetocaloric effect in ferromagnetic shape memory alloys

    Energy Technology Data Exchange (ETDEWEB)

    Khovaylo, Vladimir, E-mail: khovaylo@misis.ru [National University of Science and Technology “MISiS”, Moscow 119049 (Russian Federation)

    2013-11-15

    Highlights: ► Critical analysis of the available experimental results on isothermal magnetic entropy change in ferromagnetic shape memory alloys Ni–Mn–X (X = Ga, In, Sn, Sb) is given. ► Based on available in literature experimental data on total entropy change at martensitic transformation it is shown that the isothermal magnetic entropy change in Ni–Mn–X (X = Ga, In, Sn, Sb) should not greatly exceed 30 J/kg K. -- Abstract: Critical analysis available in the literature experimental results on magnetocaloric effect in ferromagnetic shape memory alloys Ni–Mn–X (X = Ga, In, Sn, Sb) is given. Based on a model developed by Pecharsky et al. [22], it is shown that the isothermal magnetic field-induced entropy change in the Ni–Mn–X alloys should not greatly exceed 30 J/kg K. Considering thermodynamics of temperature- and magnetic field-induced martensitic transformations, it is demonstrated that a contribution of the structural subsystem to the magnetocaloric effect in the Ni–Mn–X alloys studied so far is irreversible in magnetic fields below 5 T. This makes ferromagnetic shape memory alloys an inconvenient system for the practical application in modern magnetic refrigeration technology.

  13. Ferroplasmons: Intense Localized Surface Plasmons in Metal-Ferromagnetic Nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Sachan, Ritesh [University of Tennessee, Knoxville (UTK); Malasi, Abhinav [ORNL; Ge, Jingxuan [Materials Science and Engineering Department, University of Tennessee, Knoxville, TN, USA; Yadavali, Sagar P [ORNL; Gangopadhyay, Anup [Washington University, St. Louis; Krishna, Dr. Hare [Washington University, St. Louis; Garcia, Hernando [Southern Illinois University; Duscher, Gerd J M [ORNL; Kalyanaraman, Ramki [University of Tennessee, Knoxville (UTK)

    2014-01-01

    Interaction of photons with matter at length scales far below their wavelengths has given rise to many novel phenomena, including localized surface plasmon resonance (LSPR). However, LSPR with narrow bandwidth (BW) is observed only in a select few noble metals, and ferromagnets are not among them. Here, we report the discovery of LSPR in ferromagnetic Co and CoFe alloy (8% Fe) in contact with Ag in the form of bimetallic nanoparticles prepared by pulsed laser dewetting. These plasmons in metal-erromagnetic nanostructures, or ferroplasmons (FP) for short, are in the visible spectrum with comparable intensity and BW to those of the LSPRs from the Ag regions. This finding was enabled by electron energy-loss mapping across individual nanoparticles in a monochromated scanning transmission electron microscope. The appearance of the FP is likely due to plasmonic interaction between the contacting Ag and Co nanoparticles. Since there is no previous evidence for materials that simultaneously show ferromagnetism and such intense LSPRs, this discovery may lead to the design of improved plasmonic materials and applications. It also demonstrates that materials with interesting plasmonic properties can be synthesized using bimetallic nanostructures in contact with each other.

  14. Suppression of superconductivity in superconductor/ferromagnet multilayers

    Energy Technology Data Exchange (ETDEWEB)

    Hwang, T. J.; Kim, D. H. [Yeungnam University, Gyeongsan (Korea, Republic of)

    2016-03-15

    Suppression of the superconducting transition temperature (Tc) of NbN thin films in superconductor/ferromagnet multilayers has been investigated. Both superconducting NbN and ferromagnetic FeN layers were deposited on thermally oxidized Si substrate at room temperature by using reactive magnetron sputtering in an Ar-N2 gas mixture. The thickness of FeN films was fixed at 20 nm, while the thickness of NbN films was varied from 3 nm to 90 nm. Tc suppression was clearly observed in NbN layers up to 70 nm thickness when NbN layer was in proximity with FeN layer. For a given thickness of NbN layer, the magnitude of Tc suppression was increased in the order of Si/FeN/NbN, Si/NbN/FeN, and Si/FeN/NbN/FeN structure. This result can be used to design a spin switch whose operation is based on the proximity effect between superconducting and ferromagnetic layers.

  15. Theoretical Study of Interplay Between Superconductivity and Itinerant Ferromagnetism

    Directory of Open Access Journals (Sweden)

    Subhra Kakani

    2014-08-01

    Full Text Available Following Green’s function technique and equation of motion method, the coexistence of superconductivity (SC and itinerant ferromagnetism (FM is investigated in a single band homogenous system. Self consistent equations for SC and FM order parameters, Δ and m or I respectively are derived. It is shown that there generally exists a coexistent (Δ ≠ 0, and m or I ≠ 0 solutions to the coupled equations of the order parameter in the, temperature range 0 < T < min(TC, TFM, where TC and TFM are respectively the superconducting and ferromagnetic transition temperatures. Expressions for specific heat, density of states, free energy and critical field are derived. The specific heat has linear temperature dependence as opposed to the exponential decrease in the BCS theory. The density of states for a finite m increases as opposed to that of a ferromagnetic metal. Free energy study reveals that FMSC state has lowest energy than the normal FM state and therefore realized at low enough temperature .Effect of small external field is also studied. The theory is applied to explain the observations in uranium based intermetallics systems UCoGe and UIr. The agreement between theory and experiments is quite encouraging.

  16. Defects and ferromagnetism in transition metal doped zinc oxide

    Science.gov (United States)

    Thapa, Sunil

    Transition metal doped zinc oxide has been studied recently due to its potential application in spintronic devices. The magnetic semiconductor, often called Diluted Magnetic Semiconductors (DMS), has the ability to incorporate both charge and spin into a single formalism. Despite a large number of studies on ferromagnetism in ZnO based DMS and the realization of its room temperature ferromagnetism, there is still a debate about the origin of the ferromagnetism. In this work, the synthesis and characterization of transition metal doped zinc oxide have been carried out. The sol-gel method was used to synthesize thin films, and they were subsequently annealed in air. Characterization of doped zinc oxide films was carried out using the UV-visible range spectrometer, scanning electron microscopy, superconducting quantum interference device (SQUID), x-ray diffraction(XRD) and positron annihilation spectroscopy. Hysteresis loops were obtained for copper and manganese doped zinc oxide, but a reversed hysteresis loop was observed for 2% Al 3% Co doped zinc oxide. The reversed hysteresis loop has been explained using a two-layer model.

  17. Doping with Graphitic Nitrogen Triggers Ferromagnetism in Graphene

    Science.gov (United States)

    2017-01-01

    Nitrogen doping opens possibilities for tailoring the electronic properties and band gap of graphene toward its applications, e.g., in spintronics and optoelectronics. One major obstacle is development of magnetically active N-doped graphene with spin-polarized conductive behavior. However, the effect of nitrogen on the magnetic properties of graphene has so far only been addressed theoretically, and triggering of magnetism through N-doping has not yet been proved experimentally, except for systems containing a high amount of oxygen and thus decreased conductivity. Here, we report the first example of ferromagnetic graphene achieved by controlled doping with graphitic, pyridinic, and chemisorbed nitrogen. The magnetic properties were found to depend strongly on both the nitrogen concentration and type of structural N-motifs generated in the host lattice. Graphenes doped below 5 at. % of nitrogen were nonmagnetic; however, once doped at 5.1 at. % of nitrogen, N-doped graphene exhibited transition to a ferromagnetic state at ∼69 K and displayed a saturation magnetization reaching 1.09 emu/g. Theoretical calculations were used to elucidate the effects of individual chemical forms of nitrogen on magnetic properties. Results showed that magnetic effects were triggered by graphitic nitrogen, whereas pyridinic and chemisorbed nitrogen contributed much less to the overall ferromagnetic ground state. Calculations further proved the existence of exchange coupling among the paramagnetic centers mediated by the conduction electrons. PMID:28110530

  18. Transport through hybrid superconducting/ferromagnetic double-path junction

    Science.gov (United States)

    Facio, T. J. S.; Orellana, P. A.; Jurelo, A. R.; Figueira, M. S.; Cabrera, G. G.; Siqueira, E. C.

    2017-02-01

    In this paper we study a double-path junction formed by a ferromagnetic and a superconductor lead. The first path connects the superconductor and ferromagnet directly while the second path connects these metals through a quantum dot. The whole system works as an Aharonov-Bohm interferometer allowing the study of the interference between these two paths under the presence of spin imbalance and Andreev bound states. We considered the effect of Fano interference on the electronic transmittance through the quantum dot and observed two regimes of conduction depending on the strength of the direct coupling. For the weak coupling regime, the transmittance presented the usual four resonances due to the Andreev bound states whereas for the strong coupling regime the profile was inverted and resonances became anti-resonances. However, even in the strong coupling regime it was possible to observe a central resonance due to the interference between the Andreev bound states. We have also studied the signatures of Fano interference on the average occupation within the quantum dot. The spin accumulation was analyzed and how it depends on the direct coupling and an external magnetic field applied to the system. The results obtained may be used in a possible experimental implementation of this system in order to probe spin related effects in ferromagnetic superconductor nanostructures.

  19. Giant magnetoresistance of novel ferromagnets AMg4Mn6O15 (A=K, Rb, and Cs) with highly symmetric structure

    Science.gov (United States)

    Tanaka, Yudai; Sato, Hirohiko

    2017-04-01

    A novel family of cubic manganese oxides, AMg4Mn6O15 (A=K, Rb, and Cs), were discovered. In this type of structure, the MnO6 octahedra share edges, constructing a highly symmetric framework where Mn atoms form a three-dimensional network of truncated octahedra. The crystallographic site of Mn is unique and the average oxidation state of Mn is 3.5, indicating a mixed-valence electronic state where Mn3+ and Mn4+ sites are completely indistinguishable. These compounds become ferromagnetic with fully polarized magnetic moments of Mn ions. The ferromagnetic transition temperature TC is 170 K, that is considerably high for manganese oxides. The electric resistivity of KMg4Mn6O15 is about 105 Ωcm at 300 K and exhibits a non-metallic temperature dependence. It reveals a large negative magnetoresistance; about 40% of the resistivity is suppressed by 5 T of magnetic field at TC.

  20. Dynamical spin injection at a quasi-one-dimensional ferromagnet-graphene interface

    Energy Technology Data Exchange (ETDEWEB)

    Singh, S.; Ahmadi, A.; Mucciolo, E. R.; Barco, E. del [Department of Physics, University of Central Florida, Orlando, Florida 32816 (United States); Cherian, C. T. [Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117542 (Singapore); Graphene Research Center, National University of Singapore, Singapore 117542 (Singapore); Özyilmaz, B. [Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117542 (Singapore); NanoCore, 4 Engineering Drive 3, National University of Singapore, Singapore 117576 (Singapore); Graphene Research Center, National University of Singapore, Singapore 117542 (Singapore); NUS Graduate School for Integrative Sciences and Engineering (NGS), National University of Singapore, Singapore 117456 (Singapore)

    2015-01-19

    We present a study of dynamical spin injection from a three-dimensional ferromagnet into two-dimensional single-layer graphene. Comparative ferromagnetic resonance (FMR) studies of ferromagnet/graphene strips buried underneath the central line of a coplanar waveguide show that the FMR linewidth broadening is the largest when the graphene layer protrudes laterally away from the ferromagnetic strip, indicating that the spin current is injected into the graphene areas away from the area directly underneath the ferromagnet being excited. Our results confirm that the observed damping is indeed a signature of dynamical spin injection, wherein a pure spin current is pumped into the single-layer graphene from the precessing magnetization of the ferromagnet. The observed spin pumping efficiency is difficult to reconcile with the expected backflow of spins according to the standard spin pumping theory and the characteristics of graphene, and constitutes an enigma for spin pumping in two-dimensional structures.

  1. Defect-induced ferromagnetism in crystalline SrTiO3

    Energy Technology Data Exchange (ETDEWEB)

    Osten, Julia; Potzger, Kay; Shalimov, Artem; Talut, Georg; Reuther, Helfried; Arpaci, Seda; Buerger, Danilo; Schmidt, Heidemarie [Helmholtz-Zentrum Dresden-Rossendorf, Bautzner Landstrasse 400, 01328 Dresden (Germany); Levin, Alexander.A. [Institut fuer Strukturphysik, Technische Universitaet Dresden, 01062 (Germany); Nestler, Tina; Meyer, Dirk C. [Institut fuer Experimentelle Physik, Technische Universitaet Bergakademie Freiberg, 09596 Freiberg (Germany)

    2011-07-01

    Ion irradiation of high-quality SrTiO3 single crystals leads to room-temperature ferromagnetism. Structural analysis revealed oxygen deficient (polycrystalline) SrTiO3, Sr2Ti6O13, or Ruddlesden-Popper like secondary phases at the sample surface induced by the irradiation. The lack of potentially ferromagnetic secondary phases suggests defects to be the origin of the observed ferromagnetic signal.

  2. Conceptual study of ferromagnetic pebbles for heat exhaust in fusion reactors with short power decay length

    Directory of Open Access Journals (Sweden)

    N. Gierse

    2015-03-01

    The key results of this study are that very high heat fluxes are accessible in the operation space of ferromagnetic pebbles, that ferromagnetic pebbles are compatible with tokamak operation and current divertor designs, that the heat removal capability of ferromagnetic pebbles increases as λq decreases and, finally, that for fusion relevant values of q∥ pebble diameters below 100 μm are required.

  3. Development of eddy current testing system using magnetic saturation in ferromagnetic materials

    Energy Technology Data Exchange (ETDEWEB)

    Sung, Je Joong; Ahn, Hyung Keun; Shin, Yong Hoon [Sae An Engineering Corperation, Seoul (Korea, Republic of); Seo, Dong Man [Kunjang College, Kunsan (Korea, Republic of)

    2002-11-15

    Ferromagnetic materials have difficulties of eddy current test using traditional eddy current equipment due to their electric character of high permeability and anomalous magnetic flux. Development of on-line eddy current test equipment for ferromagnetic materials is a goal of this research. as the first step for it, in this paper, a prove for ferromagnetic materials was developed and practical test was performed with it at a manufactory. For magnetic saturation of inside of ferromagnetic material, DC power supply was used. As increasement of applied voltage, signals of defects were distinguished.

  4. Transforming from paramagnetism to room temperature ferromagnetism in CuO by ball milling

    Directory of Open Access Journals (Sweden)

    Daqiang Gao

    2011-12-01

    Full Text Available In this work, we experimentally demonstrate that it is possible to induce ferromagnetism in CuO by ball milling without any ferromagnetic dopant. The magnetic measurements indicate that paramagnetic CuO is driven to the ferromagnetic state at room temperature by ball milling gradually. The saturation magnetization of the milled powders is found to increase with expanding the milling time and then decrease by annealing under atmosphere. The fitted X-ray photoelectron spectroscopy results indicate that the observed induction and weaken of the ferromagnetism shows close relationship with the valence charged oxygen vacancies (Cu1+-VO in CuO.

  5. Ferromagnetism in Co-doped (La,Sr)TiO3

    Energy Technology Data Exchange (ETDEWEB)

    Fix, T.; Liberati, M.; Aubriet, H.; Sahonta, S.-L.; Bali, R.; Becker, C.; Ruch, D.; MacManus-Driscoll, J.L.; Arenholz, E.; Blamire, M.G.

    2009-04-21

    The origin of ferromagnetism in Co-doped (La,Sr)TiO{sub 3} epitaxial thin films is discussed. While the as-grown samples are not ferromagnetic at room temperature or at 10 K, ferromagnetism at room temperature appears after annealing the films in reducing conditions and disappears after annealing in oxidizing conditions. Magnetic measurements, x-ray absorption spectroscopy, x-ray photoemission spectroscopy and transmission electron microscopy experiments indicate that within the resolution of the instruments the activation of the ferromagnetism is not due to the presence of pure Co.

  6. Transport critical-current density of superconducting films with hysteretic ferromagnetic dots

    Directory of Open Access Journals (Sweden)

    Nuria Del-Valle

    2012-06-01

    Full Text Available Superconductor-ferromagnet hybrids present a rich and complex phenomenology. Particularly, a hysteretic behavior on the transport critical-current density, as a function of a uniform perpendicular applied field, has been experimentally found in superconducting films with some embedded ferromagnets. Here we analyze the interaction superconductor-ferromagnets by means of an iterative model based on the critical-state model with field-dependent internal critical-current density and compare the results with actual transport measurements. By using arguments of field compensation, we show how the change in the magnetization of the ferromagnetic inclusions is responsible for the observed hysteresis on the transport critical current.

  7. Magnesium compounds

    Science.gov (United States)

    Kramer, D.A.

    2012-01-01

    Seawater and natural brines accounted for about 57 percent of magnesium compounds produced in the United States in 2011. Dead-burned magnesia was produced by Martin Marietta Magnesia Specialties LLC from well brines in Michigan. Caustic-calcined magnesia was recovered from seawater by Premier Magnesia LLC in Florida, from well brines in Michigan by Martin Marietta and from magnesite in Nevada by Premier Magnesia. Intrepid Potash Wendover LLC and Great Salt Lake Minerals Corp. recovered magnesium chloride brines from the Great Salt Lake in Utah. Magnesium hydroxide was produced from seawater by SPI Pharma Inc. in Delaware and Premier Magnesia in Florida, and by Martin Marietta from its brine operation in Michigan.

  8. Spin-Transfer-Torques at a Ferromagnet/Antiferromagnet Interface

    Science.gov (United States)

    Tsoi, Maxim

    2009-03-01

    Spintronics in ferromagnetic systems is built on a complementary set of phenomena in which the magnetic configuration of the system influences its transport properties and vice versa. Giant magnetoresistance (GMR) [1] and spin- transfer-torque (STT) [2] phenomena are typical examples of such interconnections. Recently, MacDonald and co-workers [3] predicted that corresponding effects ought to occur in systems where ferromagnetic (F) components are replaced by antiferromagnets (AFM). I will present our experimental search for these new AFM effects which may potentially lead to a new all-antiferromagnetic spintronics where antiferromagnets are used in place of ferromagnets. In particular I will focus on our experiments with exchange-biased spin valves [4] where extreme current densities were found to affect the exchange bias at F/AFM interface [5-7]. As exchange bias is known to be associated with interfacial AFM magnetic moments, our observation can be taken as the first evidence of STT effect in AFM materials. [4pt] [1] M. N. Baibich et al., Phys. Rev. Lett. 61, 2472 (1988); G. Binasch et al., Phys. Rev. B 39, 4828 (1989). [0pt] [2] J. C. Slonczewski, J. Magn. Magn. Mater. 159, L1 (1996); L. Berger, J. Appl. Phys. 81, 4880 (1997); M. Tsoi et al., Phys. Rev. Lett. 80, 4281 (1998). [0pt] [3] A. S. N'uñez et al., Phys. Rev. B 73, 214426 (2006); [0pt] [4] Z. Wei et al., Phys. Rev. Lett. 98, 116603 (2007). [0pt] [5] S. Urazhdin and N. Anthony, Phys. Rev. Lett. 99, 046602 (2007). [0pt] [6] X-L.Tang et al., Appl. Phys. Lett. 91, 122504 (2007). [0pt] [7] N. V. Dai et al., Phys. Rev. B77, 132406 (2008).

  9. Synthesis, X-ray powder structure, and magnetic properties of the new, weak ferromagnet iron(II) phenylphosphonate.

    Science.gov (United States)

    Bellitto, C; Federici, F; Altomare, A; Rizzi, R; Ibrahim, S A

    2000-04-17

    A new molecule-based weak ferromagnet of formula Fe[C6H5PO3].H2O was synthesized. It was characterized by thermogravimetric analysis and UV-visible and infrared spectroscopy, and the magnetic properties were studied using a superconducting quantum interference device magnetometer. The crystal structure of the compound was determined "ab initio" from X-ray powder diffraction data and refined by the Rietveld method. The crystals of Fe[C6H5PO3].H2O are orthorhombic, space group Pmn2(1), with a = 5.668(8) A, b = 14.453(2) A, c = 4.893(7) A, and Z = 2. The title compound is isostructural with the previously reported lamellar M[C6H5PO3].H2O, M = Mn(II), Zn(II), and Cd(II). The inorganic layers are made of Fe(II) ions octahedrally coordinated by five phosphonate oxygen atoms and one from oxygen of the water molecule. These layers are then separated by bilayers of the phenyl groups, and van der Waals contacts are established between them. The refinement has shown that the phenyl rings are disordered in the lattice. The oxidation state of the metal ion is +2, and the electronic configuration is d6 (S = 2) high-spin, as determined from dc magnetic susceptibility measurements from 150 K to room temperature. Below 100 K, the magnetic moment of Fe[C6H5PO3].H2O rises rapidly to a maximum at TN = 21.5 K, and then it decreases again. The peak at TN is associated with the 3D antiferromagnetic long-range ordering. Below the critical temperature, the title compound behaves as a "weak" ferromagnet, which represents the third type of magnetic materials characterized by having a finite zero-field magnetization, ferromagnets and ferrimagnets being the other two types. The large coercive field (i.e., 6400 G) observed in the hysteresis loop at T = 10 K is rare in molecule-based materials; it can be ascribed to a pronounced spin-orbit coupling for the 5T2g ground state of the Fe(II) ion in the octahedral environment.

  10. Charge state modification in Mn site substituted CMR manganites: strong deleterious influence on the ferromagnetic-metallic state

    Energy Technology Data Exchange (ETDEWEB)

    Lakshmi, L Seetha [XS and CGS, Materials Science Division, Indira Gandhi Centre For Atomic Research, Kalpakkam, Tamil Nadu 603102 (India); Doerr, K [Institute of Metallic Materials, IFW Dresden, Postach 270116, Dresden 01171 (Germany); Nenkov, K [Institute of Metallic Materials, IFW Dresden, Postach 270116, Dresden 01171 (Germany); Sastry, V S [XS and CGS, Materials Science Division, Indira Gandhi Centre For Atomic Research, Kalpakkam, Tamil Nadu 603102 (India); Mueller, K-H [Institute of Metallic Materials, IFW Dresden, Postach 270116, Dresden 01171 (Germany)

    2007-06-13

    The effect of charge state modification at the Mn site on the physical properties of CMR manganites is reported. With a view to avoiding additional complexity of local spin coupling effects, Mn site substitution of La{sub 0.67}Ca{sub 0.33}MnO{sub 3} is carried out with appropriate diamagnetic ions-Zn{sup 2+}, Zr{sup 4+}, Ta{sup 5+} and W{sup 6+}-of different valence states. The substitution results in size changes of the unit cell and enhanced local structural distortions, which increase in the order Zn, Zr, Ta and W. The ground state is ferromagnetic-metallic below a certain critical concentration x{sub c} of the substituents, beyond which the magnetic ground state shows a glassy behaviour. The phase transition temperatures (T{sub MI} and T{sub c}) decrease with substitution, but to different extents. The observed suppression rates of the Curie temperature, T{sub c}, of {approx}39 K/at.% and {approx}45 K/at.% respectively for Ta{sup 5+} and W{sup 6+} substituted compounds are the highest reported in the Mn site substituted CMR manganites. Besides the modification of majority carrier concentration due to the increased (decreased) Mn{sup 3+} concentration and enhanced local structural effects, the local electrostatic potential of the substituents seems to contribute to the unusually strong reduction in the itinerant ferromagnetism and the observed glassy states.

  11. Ferromagnetism in Cr-doped passivated AlN nanowires

    KAUST Repository

    Kanoun, Mohammed

    2014-01-01

    We apply first principles calculations to predict the effect of Cr doping on the electronic and magnetic properties of passivated AlN nanowires. We compare the energetics of the possible dopant sites and demonstrate the favorable configuration ferromagnetic ordering. The charge density of the pristine passivated AlN nanowires is used to elucidate the bonding character. Spin density maps demonstrate an induced spin polarization for N atoms next to dopant atoms, though most of the magnetism is carried by the Cr atoms. Cr-doped AlN nanowires turn out to be interesting for spintronic devices. © 2014 the Partner Organisations.

  12. Generalized magneto-optical ellipsometry in ferromagnetic metals

    Energy Technology Data Exchange (ETDEWEB)

    Neuber, G.; Rauer, R.; Kunze, J.; Backstrom, J.; Ruebhausen, M

    2004-05-01

    We present spectral generalized magneto-optical ellipsometry as an optical tool to investigate magnetic and electronic properties of ferromagnetic materials. The advantage of the simultaneous observation of the dielectric and the magnetic responses within one measurement procedure is crucial for materials with coupled degrees of freedom near a phase transition or during annealing procedures to improve the film quality by removing grain boundaries. Moreover, we show the implementation of this technique within an UHV-cryostat for a temperature range between 4.2 and 800 K and fields up to 40 mT. Examplary measurements on iron and Permalloy demonstrate the comfortable application of this technique.

  13. Tuning ferromagnetism at interfaces between insulating perovskite oxides

    OpenAIRE

    Ganguli, Nirmal; Kelly, Paul J.

    2014-01-01

    We use density functional theory calculations to show that the LaAlO3|SrTiO3 interface between insulating perovskite oxides is borderline in satisfying the Stoner criterion for itinerant ferromagnetism and explore other oxide combinations with a view to satisfying it more amply. The larger lattice parameter of an LaScO3|BaTiO3 interface is found to be less favorable than the greater interface distortion of LaAlO3|CaTiO3. Compared to LaAlO3|SrTiO3, the latter is predicted to exhibit robust mag...

  14. Anomalous Hall Effect in a 2D Rashba Ferromagnet.

    Science.gov (United States)

    Ado, I A; Dmitriev, I A; Ostrovsky, P M; Titov, M

    2016-07-22

    Skew scattering on rare impurity configurations is shown to dominate the anomalous Hall effect in a 2D Rashba ferromagnet. The mechanism originates in scattering on rare impurity pairs separated by distances of the order of the Fermi wavelength. The corresponding theoretical description goes beyond the conventional noncrossing approximation. The mechanism provides the only contribution to the anomalous Hall conductivity in the most relevant metallic regime and strongly modifies previously obtained results for lower energies in the leading order with respect to impurity strength.

  15. Tunable metamaterial bandstop filter based on ferromagnetic resonance

    Directory of Open Access Journals (Sweden)

    Qingmin Wang

    2015-07-01

    Full Text Available Tunable wideband microwave bandstop filters have been investigated by experiments and simulations. The negative permeability is realized around the ferromagnetic resonance frequency which can be influenced by the demagnetization factor of the ferrite rods. For the filter composed of two ferrite rods with different size, it exhibits a -3 db stop bandwidth as large as 500 MHz, peak absorption of -40 db and an out-of-stopband insertion loss of -1.5 db. This work provides a new way to fabricate the microwave bandstop filters.

  16. Optical Magnus effect in metamaterials fabricated from ferromagnetic microwires

    Science.gov (United States)

    Ivanov, A. V.; Shalygin, A. N.; Vedyaev, A. V.; Ivanov, V. A.

    2007-08-01

    In homogeneous negative phase velocity media, the Doppler and Cherenkov-Vavilov effects and the refraction and pressure of light are anomalous: they are inverse with respect to the corresponding effects in conventional media. Using the geometrical optics approximation, it is shown that the optical Magnus effect in inhomogeneous negative phase velocity media is also anomalous. The effect is demonstrated by considering a metamaterial consisting of parallel amorphous ferromagnetic microwires in a magnetic field. The metamaterial proves to be a left-handed one in the realistic region of the electromagnetic spectrum. The optical properties of such a left-handed medium can be controlled by the external magnetic field.

  17. Ferromagnetism in undoped One-dimensional GaN Nanowires

    Directory of Open Access Journals (Sweden)

    K. Jeganathan

    2014-05-01

    Full Text Available We report an intrinsic ferromagnetism in vertical aligned GaN nanowires (NW fabricated by molecular beam epitaxy without any external catalyst. The magnetization saturates at ∼0.75 × emu/gm with the applied field of 3000 Oe for the NWs grown under the low-Gallium flux of 2.4 × 10−8 mbar. Despite a drop in saturation magnetization, narrow hysteresis loop remains intact regardless of Gallium flux. Magnetization in vertical standing GaN NWs is consistent with the spectral analysis of low-temperature photoluminescence pertaining to Ga-vacancies associated structural defects at the nanoscale.

  18. Dynamic Feedback in Ferromagnet-Spin Hall Metal Heterostructures

    Science.gov (United States)

    Cheng, Ran; Zhu, Jian-Gang; Xiao, Di

    2016-08-01

    In ferromagnet-normal-metal heterostructures, spin pumping and spin-transfer torques are two reciprocal processes that occur concomitantly. Their interplay introduces a dynamic feedback effect interconnecting energy dissipation channels of both magnetization and current. By solving the spin diffusion process in the presence of the spin Hall effect in the normal metal, we show that the dynamic feedback gives rise to (i) a nonlinear magnetic damping that is crucial to sustain uniform steady-state oscillations of a spin Hall oscillator at large angles and (ii) a frequency-dependent spin Hall magnetoimpedance that reduces to the spin Hall magnetoresistance in the dc limit.

  19. Spin Waves in 2D ferromagnetic square lattice stripe

    OpenAIRE

    Ahmed, Maher Z.

    2011-01-01

    In this work, the area and edges spin wave calculations were carried out using the Heisenberg Hamiltonian and the tridiagonal method for the 2D ferromagnetic square lattice stripe, where the SW modes are characterized by a 1D in-plane wave vector $q_x$. The results show a general and an unexpected feature that the area and edge spin waves only exist as optic modes. This behavior is also seen in 2D Heisenberg antiferromagnetic square lattice. This absence of the acoustic modes in the 2D square...

  20. Power optimization for domain wall motion in ferromagnetic nanowires

    Science.gov (United States)

    Tretiakov, O. A.; Liu, Y.; Abanov, Ar.

    2011-04-01

    The current mediated domain-wall dynamics in a thin ferromagnetic wire is investigated. We derive the effective equations of motion of the domain wall. They are used to study the possibility to optimize the power supplied by electric current for the motion of domain walls in a nanowire. We show that a certain resonant time-dependent current moving a domain wall can significantly reduce the Joule heating in the wire, and thus it can lead to a novel proposal for the most energy efficient memory devices. We discuss how Gilbert damping, nonadiabatic spin transfer torque, and the presence of Dzyaloshinskii-Moriya interaction can effect this power optimization.

  1. Power optimization for domain wall motion in ferromagnetic nanowires

    OpenAIRE

    Tretiakov, Oleg A.; Liu, Y.; Abanov, Ar.

    2010-01-01

    The current mediated domain-wall dynamics in a thin ferromagnetic wire is investigated. We derive the effective equations of motion of the domain wall. They are used to study the possibility to optimize the power supplied by electric current for the motion of domain walls in a nanowire. We show that a certain resonant time-dependent current moving a domain wall can significantly reduce the Joule heating in the wire, and thus it can lead to a novel proposal for the most energy efficient memory...

  2. Periodic instantons and domain structure in a ferromagnetic film

    Science.gov (United States)

    Zheng, G.-P.; Liang, J.-Q.; Nie, Y.-H.; Yin, W.

    2003-11-01

    We in this paper study periodic instantons and domain structures in a theoretical film consisting of biaxial-anisotropic ferromagnets. In a proper approximation the equation of motion of the magnetization vector as a space-time function in the film is reduced to the 1 + 2-dimensional sine-Gordon field equation in strong anisotropy limit. Static periodic instantons, which are solutions of Euclidean field equantion, and various new domain structures are obtained analytically. We also investigate the energy density and stability of the periodic instantons.

  3. Theoretical Investigation of Negative Refraction in Metallic and Ferromagnetic Composites

    Institute of Scientific and Technical Information of China (English)

    SU Hua; LI Cheng-fang

    2004-01-01

    A new design of LHM (left-handed material) is suggested, in which the wave vector k and the energy flow S (the Poynting vector) are in the opposite direction. Metallic cores or lines are coated with ferromagnetic layers to obtain negative permittivity and permeability. This design may bring some improvements over the binary design, such as higher homogeneity, smaller volume size, lower power loss, higher convenience and economy. The analytical expressions for the permittivity ε and permeability μ are shown to be negative in certain direction and frequency regions. Two specific structures are theoretically discussed and proved to be left-handed.

  4. The ferromagnetic shape-memory effect in Ni Mn Ga

    Science.gov (United States)

    Marioni, M. A.; O'Handley, R. C.; Allen, S. M.; Hall, S. R.; Paul, D. I.; Richard, M. L.; Feuchtwanger, J.; Peterson, B. W.; Chambers, J. M.; Techapiesancharoenkij, R.

    2005-04-01

    Active materials have long been used in the construction of sensors and devices. Examples are piezo-electric ceramics and shape memory alloys. The more recently developed ferromagnetic shape-memory alloys (FSMAs) have received considerable attention due to their large magnetic field-induced, reversible strains (up to 10%). In this article, we review the basic physical characteristics of the FSMA Ni-Mn-Ga (crystallography, thermal, mechanical and magnetic behavior). Also, we present some of the works currently under way in the areas of pulse-field and acoustic-assisted actuation, and vibration energy absorption.

  5. Spin Transport in Mesoscopic Superconducting-Ferromagnetic Hybrid Conductor

    Directory of Open Access Journals (Sweden)

    Zein W. A.

    2008-01-01

    Full Text Available The spin polarization and the corresponding tunneling magnetoresistance (TMR for a hybrid ferromagnetic / superconductor junction are calculated. The results show that these parameters are strongly depends on the exchange field energy and the bias voltage. The dependence of the polarization on the angle of precession is due to the spin flip through tunneling process. Our results could be interpreted as due to spin imbalance of carriers resulting in suppression of gap energy of the superconductor. The present investigation is valuable for manufacturing magnetic recording devices and nonvolatile memories which imply a very high spin coherent transport for such junction.

  6. Giant Mutual Proximity Effects in Ferromagnetic/Superconducting Nanostructures

    OpenAIRE

    Petrashov, Victor; Sosnin, I. A.; Cox, I.; Parsons, A.; Troadec, C.

    1999-01-01

    A strong mutual influence of superconductors (S) and ferromagnetic (F) conductors in hybrid F/S (Ni/Al) nanostructures is observed. The proximity-induced conductance on the F side, Delta G, is 2 orders of magnitude larger than that predicted by theory. A crossover from positive to negative Delta G takes place upon an increase in the F/S interface barrier resistance. Reentrance of the superconductors to the normal state reciprocated by changes on the F side has been found in low applied magnet...

  7. Critical Exponents of Ferromagnetic Ising Model on Fractal Lattices

    Science.gov (United States)

    Hsiao, Pai-Yi

    2001-04-01

    We review the value of the critical exponents ν-1, β/ν, and γ/ν of ferromagnetic Ising model on fractal lattices of Hausdorff dimension between one and three. They are obtained by Monte Carlo simulation with the help of Wolff algorithm. The results are accurate enough to show that the hyperscaling law df = 2β/ν + γ/ν is satisfied in non-integer dimension. Nevertheless, the discrepancy between the simulation results and the γ-expansion studies suggests that the strong universality should be adapted for the fractal lattices.

  8. Ferromagnetic properties of hybrid cementite and diamond nanocomposite

    Directory of Open Access Journals (Sweden)

    Shao-Hui Kang

    2013-12-01

    Full Text Available A nanocomposite of cementite (Fe3C nanoparticles and diamond obtained via powder mixed dielectric-electrical discharge machining (PMD-EDM is investigated. The processed surface morphology exhibits various structures, including a white layer (machined surface and a heat-affected zone (HAZ. The concentration of the Fe element in the white layer is higher than that in the HAZ. The value of magnetization is about 0.1~0.5 mA/m2. Increasing the frequency of the pulse affects the ferromagnetic behavior of magnets fabricated using the PMD-EDM process.

  9. Topologically nontrivial magnons at an interface of two kagome ferromagnets

    Science.gov (United States)

    Mook, Alexander; Henk, Jürgen; Mertig, Ingrid

    2015-06-01

    Magnon band structures of topological magnon insulators exhibit a nontrivial topology due to the Dzyaloshinskii-Moriya interaction, which manifests itself by topologically protected edge magnons. Bringing two topological magnon insulators into contact can lead to nontrivial unidirectional magnons located at their common interface. We study theoretically interfaces of semi-infinite kagome ferromagnets in various topological phases, with a focus on the formation and the confinement of nontrivial interface magnons. We analyze generic magnon dispersions with respect to the number of band gaps and the respective winding numbers. Eventually, we prove that interfaces of topologically identical phases can host nontrivial interface magnons as well.

  10. Emergent propagation modes of ferromagnetic swimmers in constrained geometries

    Science.gov (United States)

    Bryan, M. T.; Shelley, S. R.; Parish, M. J.; Petrov, P. G.; Winlove, C. P.; Gilbert, A. D.; Ogrin, F. Y.

    2017-02-01

    Magnetic microswimmers, composed of hard and soft ferromagnets connected by an elastic spring, are modelled under low Reynolds number conditions in the presence of geometrical boundaries. Approaching a surface, the magneto-elastic swimmer's velocity increases and its trajectory bends parallel to the surface contour. Further confinement to form a planar channel generates new propagation modes as the channel width narrows, altering the magneto-elastic swimmer's speed, orientation, and direction of travel. Our results demonstrate that constricted geometric environments, such as occuring in microfluidic channels or blood vessels, may influence the functionality of magneto-elastic microswimmers for applications such as drug delivery.

  11. Magnetic Field Effect on Critical Behavior of Perovskite Ferromagnet

    Institute of Scientific and Technical Information of China (English)

    Tian Hongwei; Zheng Weitao; Chen Yanping; Ding Tao; Wang Xin; Kan Dongwu

    2005-01-01

    The polycrystalline samples of La2/3Ca1/3MnO3 were prepared by a conventional solid state reaction method. The magnetizations (ZFC, FC and initial magnetization) of the polycrystalline La2/3Ca1/3MnO3 were measured with superconducting quantum interference device magnetometer. The scaling theory was employed to study the changes of critical behavior arising from the applied external field. The critical parameter β decreases with increasing the external magnetic field results in an increase in the magnitude of ferromagnetic ordering.

  12. Magnetic moment distribution of ferromagnetic Ni--Rh alloys

    Energy Technology Data Exchange (ETDEWEB)

    Cable, J.W.; Wollan, E.O.

    1977-01-01

    The diffuse scattering of polarized and unpolarized neutrons was used to determine the spatial distribution of the magnetic moment for ferromagnetic Ni-Rh alloys. The average Ni moment remains near 0.6 ..mu../sub B/ to 12 at. % Rh and then decreases toward zero at the critical concentration of 37 at. % Rh. There is an initial rapid decrease in the Rh moment that follows a P/sub 12/ dependence and corresponds to a moment of 2 ..mu../sub B/ for isolated Rh atoms. The data indicate moment fluctuations at both the Ni and the Rh sites that are associated with local environment.

  13. Odd-Parity Superconductivity and the Ferromagnetic Quantum Critical Point

    Science.gov (United States)

    Huxley, A. D.; Yates, S. J. C.; Lévy, F.; Sheikin, I.

    2007-05-01

    The study of the emergence of superconductivity close to quantum critical points affords a powerful means to identify the mechanism that drives the formation of unconventional superconductivity in heavy fermion materials. The recent discovery of superconducting states close to quantum critical points in ferromagnets UGe2 and URhGe is reviewed in this light. For URhGe we examine whether the predominant type of magnetic excitations involved are longitudinal excitations, hitherto considered theoretically to be the most promising candidate to mediate equal-spin-paired superconductivity.

  14. Engineering Curvature-Induced Anisotropy in Thin Ferromagnetic Films

    Science.gov (United States)

    Tretiakov, Oleg A.; Morini, Massimiliano; Vasylkevych, Sergiy; Slastikov, Valeriy

    2017-08-01

    We investigate the effect of large curvature and dipolar energy in thin ferromagnetic films with periodically modulated top and bottom surfaces on magnetization behavior. We predict that the dipolar interaction and surface curvature can produce perpendicular anisotropy which can be controlled by engineering special types of periodic surface structures. Similar effects can be achieved by a significant surface roughness in the film. We demonstrate that, in general, the anisotropy can point in an arbitrary direction depending on the surface curvature. Furthermore, we provide simple examples of these periodic surface structures to show how to engineer particular anisotropies in thin films.

  15. Indirect Coupling between Two Cavity Photon Systems via Ferromagnetic Resonance

    CERN Document Server

    Hyde, Paul; Harder, Michael; Match, Christophe; Hu, Can-Ming

    2016-01-01

    We experimentally realize indirect coupling between two cavity modes via strong coupling with the ferromagnetic resonance in Yttrium Iron Garnet (YIG). We find that some indirectly coupled modes of our system can have a higher microwave transmission than the individual uncoupled modes. Using a coupled harmonic oscillator model, the influence of the oscillation phase difference between the two cavity modes on the nature of the indirect coupling is revealed. These indirectly coupled microwave modes can be controlled using an external magnetic field or by tuning the cavity height. This work has potential for use in controllable optical devices and information processing technologies.

  16. Approximating the partition function of the ferromagnetic Potts model

    CERN Document Server

    Goldberg, Leslie Ann

    2010-01-01

    We provide evidence that it is computationally difficult to approximate the partition function of the ferromagnetic q-state Potts model when q>2. Specifically we show that the partition function is hard for the complexity class #RHPi_1 under approximation-preserving reducibility. Thus, it is as hard to approximate the partition function as it is to find approximate solutions to a wide range of counting problems, including that of determining the number of independent sets in a bipartite graph. Our proof exploits the second order phase transition of the "random cluster" model, which is a probability distribution on graphs that is closely related to the q-state Potts

  17. Itinerant ferromagnetism in a polarized two-component Fermi gas.

    Science.gov (United States)

    Massignan, Pietro; Yu, Zhenhua; Bruun, Georg M

    2013-06-07

    We analyze when a repulsively interacting two-component Fermi gas becomes thermodynamically unstable against phase separation. We focus on the strongly polarized limit, where the free energy of the homogeneous mixture can be calculated accurately in terms of well-defined quasiparticles, the repulsive polarons. Phase diagrams as a function of polarization, temperature, mass imbalance, and repulsive polaron energy, as well as scattering length and range parameter, are provided. We show that the lifetime of the repulsive polaron increases significantly with the interaction range and the mass of the minority atoms, raising the prospects of detecting the transition to the elusive itinerant ferromagnetic state with ultracold atoms.

  18. Theoretical investigations of half-metallic ferromagnetism in new Half-Heusler YCrSb and YMnSb alloys using first-principle calculations

    Science.gov (United States)

    Atif Sattar, M.; Rashid, Muhammad; Hashmi, M. Raza; Ahmad, S. A.; Imran, Muhammad; Hussain, Fayyaz

    2016-10-01

    Structural, electronic, and magnetic properties of new predicted half-Heusler YCrSb and YMnSb compounds within the ordered MgAgAs C1b-type structure are investigated by employing first-principal calculations based on density functional theory. Through the calculated total energies of three possible atomic placements, we find the most stable structures regarding YCrSb and YMnSb materials, where Y, Cr(Mn), and Sb atoms occupy the (0.5, 0.5, 0.5), (0.25, 0.25, 0.25), and (0, 0, 0) positions, respectively. Furthermore, structural properties are explored for the non-magnetic and ferromagnetic and anti-ferromagnetic states and it is found that both materials prefer ferromagnetic states. The electronic band structure shows that YCrSb has a direct band gap of 0.78 eV while YMnSb has an indirect band gap of 0.40 eV in the majority spin channel. Our findings show that YCrSb and YMnSb materials exhibit half-metallic characteristics at their optimized lattice constants of 6.67 Å and 6.56 Å, respectively. The half-metallicities associated with YCrSb and YMnSb are found to be robust under large in-plane strains which make them potential contenders for spintronic applications.

  19. Magnetic, magnetocaloric, and lattice properties of the La(Fe{sub x}Si{sub 1-x}){sub 13} ferromagnets

    Energy Technology Data Exchange (ETDEWEB)

    Valiev, E. Z., E-mail: valiev@imp.uran.ru; Berger, I. F.; Voronin, V. I.; Kazantsev, V. A. [Russian Academy of Sciences, Institute of Metal Physics, Ural Branch (Russian Federation)

    2011-12-15

    The magnetic and lattice properties of a sample of La(Fe{sub 0.86}Si{sub 0.14}){sub 13} ferromagnet have been measured. The influence that neutron irradiation has on the physical properties of this ferromagnet is studied. It is shown that the irradiation of this sample by a fluence of 3 Multiplication-Sign 10{sup 19} n/cm{sup 2} increases the lattice constant a and the Curie temperature (T{sub C}) as the volume magnetostriction decreases. A model of ferromagnet is proposed which satisfactorily describes the dependence a(T) of the initial and irradiated samples and their magnetic properties. The temperature dependence of the change in entropy when switching the magnetic field on and off is calculated. It is established that the change in both the magnetic and lattice parts of the total entropy at the magnetic phase transition must be taken into account for La(Fe{sub x}Si{sub 1-x}){sub 13} compounds.

  20. Ferromagnetism: Sulfur Doping Induces Strong Ferromagnetic Ordering in Graphene: Effect of Concentration and Substitution Mechanism (Adv. Mater. 25/2016).

    Science.gov (United States)

    Tuček, Jiří; Błoński, Piotr; Sofer, Zdeněk; Šimek, Petr; Petr, Martin; Pumera, Martin; Otyepka, Michal; Zbořil, Radek

    2016-07-01

    R. Zbořil and co-workers show that doping a graphene lattice with sulfur induces magnetic centers which display ferromagnetic order below ≈62 K. As described on page 5045, sulfur doping promotes magnetically active configurations resembling the gamma-thiothiapyrone motif. Enhanced magnetic properties of sulfur-doped graphene are attributed to two unpaired electrons from each sulfur atom injected into the graphene conducting band where they are delocalized between the S and C atoms. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. Unexpected large room-temperature ferromagnetism in porous Cu{sub 2}O thin films

    Energy Technology Data Exchange (ETDEWEB)

    Hou, Xue [College of Physics Science & Information Engineering, Hebei Normal University, Shijiazhuang 050024 (China); Key Laboratory of Advanced Films of Hebei Province, Shijiazhuang 050024 (China); Sun, Huiyuan, E-mail: huiyuansun@126.com [College of Physics Science & Information Engineering, Hebei Normal University, Shijiazhuang 050024 (China); Key Laboratory of Advanced Films of Hebei Province, Shijiazhuang 050024 (China); Liu, Lihu; Jia, Xiaoxuan; Liu, Huiyuan [College of Physics Science & Information Engineering, Hebei Normal University, Shijiazhuang 050024 (China); Key Laboratory of Advanced Films of Hebei Province, Shijiazhuang 050024 (China)

    2015-05-15

    Porous Cu{sub 2}O films have been fabricated on porous anodic alumina substrates using DC-reactive magnetron sputtering with pure Cu targets, and unexpectedly large room temperature ferromagnetism has been observed in the films. The maximum saturation magnetic moment along the out-of-plane direction was as high as 94 emu/cm{sup 3}. Photoluminescence spectra show that the ferromagnetism originates with oxygen vacancies. The ferromagnetism could be adjusted by changing the concentration of oxygen vacancies through annealing in an oxygen atmosphere. These observations suggest that the origin of the ferromagnetism is due to coupling between oxygen vacancies with local magnetic moments in the porous Cu{sub 2}O films, which can occur either directly through exchange interactions between oxygen vacancies, or through the mediation of conduction electrons. Such a ferromagnet without the presence of any ferromagnetic dopant may find applications in spintronic devices. - Highlights: • Porous Cu{sub 2}O films were deposited on porous anodic alumina (PAA) substrates. • Significant room-temperature ferromagnetism has been observed in porous Cu{sub 2}O films. • Ferromagnetism of Cu{sub 2}O films exhibited different magnetic signals with the field. • The saturation magnetization is 94 emu/cm{sup 3} with an out-of-plane.

  2. The analysis of the influence of the ferromagnetic rod in an annular magnetohydrodynamic (MHD pump

    Directory of Open Access Journals (Sweden)

    Bergoug Nassima

    2012-01-01

    Full Text Available This paper deals with the 2D modelisation of an annular induction magnetohydrodynamic (MHD pump using finite volume method in cylindrical coordinates and taking into consideration the saturation of the ferromagnetic material. The influence of the ferromagnetic rod on the different characteristics, in the channel of the MHD pump was studied in the paper.

  3. Simultaneous suppression of ferromagnetism and superconductivity in UCoGe by Si substitution

    NARCIS (Netherlands)

    de Nijs, D.E.; Huy, N.T.; de Visser, A.

    2008-01-01

    We investigate the effect of substituting Si for Ge in the ferromagnetic superconductor UCoGe. dc-magnetization, ac-susceptibility, and electrical resistivity measurements on polycrystalline UCoGe1-xSix samples show that ferromagnetic order and superconductivity are progressively depressed with incr

  4. Exact Results for Spin-Wave Renormalisation in Heisenberg and Planar Ferromagnets

    DEFF Research Database (Denmark)

    Rastelli, E.; Lindgård, Per-Anker

    1979-01-01

    An exact perturbation expansion, to the order 1/S2, is derived for the Heisenberg ferromagnet. The equivalence of the Dyson-Maleev (DM), Holstein-Primakoff (HP) and matching-of-matrix-element (MME) transformations is proven. They give identical T5/2 and T4 coefficients. For the planar ferromagnet...

  5. Darboux transformation and exact solutions of the integrable Heisenberg ferromagnetic equation with self-consistent potentials

    Science.gov (United States)

    Yersultanova, Z. S.; Zhassybayeva, M.; Yesmakhanova, K.; Nugmanova, G.; Myrzakulov, R.

    2016-10-01

    Integrable Heisenberg ferromagnetic equations are an important subclass of integrable systems. The M-XCIX equation is one of a generalizations of the Heisenberg ferromagnetic equation and are integrable. In this paper, the Darboux transformation of the M-XCIX equation is constructed. Using the DT, a 1-soliton solution of the M-XCIX equation is presented.

  6. Spin-accumulation and Andreev-reflection in a mesoscopic ferromagnetic wire

    NARCIS (Netherlands)

    Belzig, W.; Nazarov, Y.V.; Bauer, G.E.W.

    2000-01-01

    The electron transport though ferromagnetic metal-superconducting hybrid devices is considered in the non-equilibrium Green's function formalism in the quasiclassical approximation. Attention if focused on the limit in which the exchange splitting in the ferromagnet is much larger than the supercond

  7. On-chip detection of ferromagnetic resonance of a single submicron Permalloy strip

    NARCIS (Netherlands)

    Costache, M. V.; Sladkov, M.; van der Wal, C. H.; van Wees, B. J.

    2006-01-01

    The authors measured ferromagnetic resonance of a single submicron ferromagnetic strip, embedded in an on-chip microwave transmission line device. The method used is based on detection of the oscillating magnetic flux due to the magnetization dynamics, with an inductive pickup loop. The dependence o

  8. Standing magnetic wave on Ising ferromagnet: Nonequilibrium phase transition

    Science.gov (United States)

    Halder, Ajay; Acharyya, Muktish

    2016-12-01

    The dynamical response of an Ising ferromagnet to a plane polarised standing magnetic field wave is modelled and studied here by Monte Carlo simulation in two dimensions. The amplitude of standing magnetic wave is modulated along the direction x. We have detected two main dynamical phases namely, pinned and oscillating spin clusters. Depending on the value of field amplitude the system is found to undergo a phase transition from oscillating spin cluster to pinned as the system is cooled down. The time averaged magnetisation over a full cycle of magnetic field oscillations is defined as the dynamic order parameter. The transition is detected by studying the temperature dependences of the variance of the dynamic order parameter, the derivative of the dynamic order parameter and the dynamic specific heat. The dependence of the transition temperature on the magnetic field amplitude and on the wavelength of the magnetic field wave is studied at a single frequency. A comprehensive phase boundary is drawn in the plane described by the temperature and field amplitude for two different wavelengths of the magnetic wave. The variation of instantaneous line magnetisation during a period of magnetic field oscillation for standing wave mode is compared to those for the propagating wave mode. Also the probability that a spin at any site, flips, is calculated. The above mentioned variations and the probability of spin flip clearly distinguish between the dynamical phases formed by propagating magnetic wave and by standing magnetic wave in an Ising ferromagnet.

  9. Coherence and stiffness of spin waves in diluted ferromagnets

    Science.gov (United States)

    Turek, I.; Kudrnovský, J.; Drchal, V.

    2016-11-01

    We present the results of a numerical analysis of magnon spectra in supercells simulating two-dimensional and bulk random diluted ferromagnets with long-range pair exchange interactions. We show that low-energy spectral regions for these strongly disordered systems contain a coherent component leading to interference phenomena manifested by a pronounced sensitivity of the lowest excitation energies to the adopted boundary conditions. The dependence of configuration averages of these excitation energies on the supercell size can be used for an efficient determination of the spin-wave stiffness D . The developed formalism is applied to the ferromagnetic Mn-doped GaAs semiconductor with optional incorporation of phosphorus; the obtained concentration trends of D are found to be in reasonable agreement with recent experiments. Moreover, a relation of the spin stiffness to the Curie temperature TC has been studied for Mn-doped GaAs and GaN semiconductors. It is found that the ratio TC/D exhibits qualitatively the same dependence on Mn concentration in both systems.

  10. Triplet superconductivity in oxide ferromagnetic interlayer of mesa-structure

    Science.gov (United States)

    Ovsyannikov, G. A.; Y Constantinian, K.; Sheerman, A. E.; Shadrin, A. V.; Kislinski, Yu V.; Khaydukov, Yu N.; Mustafa, L.; Kalabukhov, A.; Winkler, D.

    2015-03-01

    We present experimental data on Nb-Au/La0.7Sr0.3MnO3/SrRuO3/YBa2Cu3O7-δ mesa- structure with in plane linear size 10÷50 μm. The mesa-structures were patterned from the epitaxial heterostructures fabricated by pulsed laser ablation and magnetron sputtering. Superconducting critical current was observed for mesa-structures with the interlayer thicknesses up to 50 nm. In the mesa-structures with just one, either La0.7Sr0.3MnO3 or SrRuO3 interlayer with a thickness larger than 10 nm no superconducting current was observed. The registered superconducting current for the mesa-structures with a thinner interlayer is attributed to pinholes. Obtained results are discussed in terms of superconducting long-range triplet generation at interfaces of superconductor and a composite ferromagnet consisting of ferromagnetic materials with non-collinear magnetization.

  11. Electrical manipulation of a ferromagnet by an antiferromagnet

    Science.gov (United States)

    Tshitoyan, V.; Ciccarelli, C.; Mihai, A. P.; Ali, M.; Irvine, A. C.; Moore, T. A.; Jungwirth, T.; Ferguson, A. J.

    Several recent studies of antiferromagnetic (AFM) spintronics have focused on transmission and detection of spin-currents in AFMs. Efficient spin transmission through AFMs was inferred from experiments in FM/AFM/NM (normal metal) structures. Measurements in FM/AFM bilayers have demonstrated that a metallic AFM can also act as an efficient ISHE detector of the spin-current, with spin-Hall angles comparable to heavy NMs. Here we demonstrate that an antiferromagnet can be employed for a highly efficient electrical manipulation of a ferromagnet. We use an all-electrical excitation and detection technique of ferromagnetic resonance in a NiFe/IrMn bilayer. We observe antidamping-like spin torque acting on the NiFe generated by the in-plane current driven through the IrMn antiferromagnet. A large enhancement of the torque, characterized by an effective spin-Hall angle exceeding most heavy transition metals, correlates with the presence of the exchange-bias field at the NiFe/IrMn interface. It highlights that, in addition to strong spin-orbit coupling, the AFM order in IrMn governs the observed phenomenon.

  12. Analysis of thermal energy harvesting using ferromagnetic materials

    Energy Technology Data Exchange (ETDEWEB)

    Lallart, Mickaël, E-mail: mickael.lallart@insa-lyon.fr; Wang, Liuqing; Sebald, Gaël; Petit, Lionel; Guyomar, Daniel

    2014-09-05

    This Letter aims at giving a preliminary investigation of the thermal energy harvesting capabilities of a technique using the temperature-dependent permeability of ferromagnetic materials. The principles lie in the modification of the magnetic field caused by the variation of the permeability due to the temperature change, hence generating a voltage across a coil surrounding the circuit. The technique can be made truly passive by the use of magnets for applying bias magnetic field. Theoretical results, validated by experimental measurements, show a voltage output of 1.2 mV at optimal load of 2 Ω under 60 K temperature variation in 5 s (with a maximum slope of 25 K s{sup −1}). Further improvements, such as the use of low resistivity coil and magnet with high remnant magnetic field, indicate that it is possible to convert up to 7.35 μJ cm{sup −3} K{sup −2} cycle{sup −1}. - Highlights: • Ferromagnetic materials show a sharp change in their permeability near the Curie temperature. • A bias magnetic field permits changing the magnetic flux with the temperature. • The variable magnetic flux can be converted into electrical energy by using a coil. • Theoretical and experimental measurements show an energy density up to 7.35 μJ cm{sup −3} K{sup −2} cycle{sup −1}. • Optimization issues should focus on coil quality and global magnetic reluctance variation.

  13. Magnetostatic modes in ferromagnetic samples with inhomogeneous internal fields

    Science.gov (United States)

    Arias, Rodrigo

    2015-03-01

    Magnetostatic modes in ferromagnetic samples are very well characterized and understood in samples with uniform internal magnetic fields. More recently interest has shifted to the study of magnetization modes in ferromagnetic samples with inhomogeneous internal fields. The present work shows that under the magnetostatic approximation and for samples of arbitrary shape and/or arbitrary inhomogeneous internal magnetic fields the modes can be classified as elliptic or hyperbolic, and their associated frequency spectrum can be delimited. This results from the analysis of the character of the second order partial differential equation for the magnetostatic potential under these general conditions. In general, a sample with an inhomogeneous internal field and at a given frequency, may have regions of elliptic and hyperbolic character separated by a boundary. In the elliptic regions the magnetostatic modes have a smooth monotonic character (generally decaying form the surfaces (a ``tunneling'' behavior)) and in hyperbolic regions an oscillatory wave-like character. A simple local criterion distinguishes hyperbolic from elliptic regions: the sign of a susceptibility parameter. This study shows that one may control to some extent magnetostatic modes via external fields or geometry. R.E.A. acknowledges Financiamiento Basal para Centros Cientificos y Tecnologicos de Excelencia under Project No. FB 0807 (Chile), Grant No. ICM P10-061-F by Fondo de Innovacion para la Competitividad-MINECON, and Proyecto Fondecyt 1130192.

  14. Three-dimensional magnetic recording using ferromagnetic resonance

    Science.gov (United States)

    Suto, Hirofumi; Kudo, Kiwamu; Nagasawa, Tazumi; Kanao, Taro; Mizushima, Koichi; Sato, Rie

    2016-07-01

    To meet the ever-increasing demand for data storage, future magnetic recording devices will need to be made three-dimensional by implementing multilayer recording. In this article, we present methods of detecting and manipulating the magnetization direction of a specific layer selectively in a vertically stacked multilayer magnetic system, which enable layer-selective read and write operations in three-dimensional magnetic recording devices. The principle behind the methods is ferromagnetic resonance excitation in a microwave magnetic field. By designing each magnetic recording layer to have a different ferromagnetic resonance frequency, magnetization excitation can be induced individually in each layer by tuning the frequency of an applied microwave magnetic field, and this selective magnetization excitation can be utilized for the layer-selective operations. Regarding media for three-dimensional recording, when layers of a perpendicular magnetic material are vertically stacked, dipolar interaction between multiple recording layers arises and is expected to cause problems, such as degradation of thermal stability and switching field distribution. To solve these problems, we propose the use of an antiferromagnetically coupled structure consisting of hard and soft magnetic layers. Because the stray fields from these two layers cancel each other, antiferromagnetically coupled media can reduce the dipolar interaction.

  15. Voltage-controlled domain wall traps in ferromagnetic nanowires

    Science.gov (United States)

    Bauer, Uwe; Emori, Satoru; Beach, Geoffrey S. D.

    2013-06-01

    Electrical control of magnetism has the potential to bring about revolutionary new spintronic devices, many of which rely on efficient manipulation of magnetic domain walls in ferromagnetic nanowires. Recently, it has been shown that voltage-induced charge accumulation at a metal-oxide interface can influence domain wall motion in ultrathin metallic ferromagnets, but the effects have been relatively modest and limited to the slow, thermally activated regime. Here we show that a voltage can generate non-volatile switching of magnetic properties at the nanoscale by modulating interfacial chemistry rather than charge density. Using a solid-state ionic conductor as a gate dielectric, we generate unprecedentedly strong voltage-controlled domain wall traps that function as non-volatile, electrically programmable and switchable pinning sites. Pinning strengths of at least 650 Oe can be readily achieved, enough to bring to a standstill domain walls travelling at speeds of at least ~20 m s-1. We exploit this new magneto-ionic effect to demonstrate a prototype non-volatile memory device in which voltage-controlled domain wall traps facilitate electrical bit selection in a magnetic nanowire register.

  16. Spin Funneling for Enhanced Spin Injection into Ferromagnets

    Science.gov (United States)

    Sayed, Shehrin; Diep, Vinh Q.; Camsari, Kerem Yunus; Datta, Supriyo

    2016-07-01

    It is well-established that high spin-orbit coupling (SOC) materials convert a charge current density into a spin current density which can be used to switch a magnet efficiently and there is increasing interest in identifying materials with large spin Hall angle for lower switching current. Using experimentally benchmarked models, we show that composite structures can be designed using existing spin Hall materials such that the effective spin Hall angle is larger by an order of magnitude. The basic idea is to funnel spins from a large area of spin Hall material into a small area of ferromagnet using a normal metal with large spin diffusion length and low resistivity like Cu or Al. We show that this approach is increasingly effective as magnets get smaller. We avoid unwanted charge current shunting by the low resistive NM layer utilizing the newly discovered phenomenon of pure spin conduction in ferromagnetic insulators via magnon diffusion. We provide a spin circuit model for magnon diffusion in FMI that is benchmarked against recent experiments and theory.

  17. Intermittent flow regimes near the convection threshold in ferromagnetic nanofluids.

    Science.gov (United States)

    Krauzina, Marina T; Bozhko, Alexandra A; Putin, Gennady F; Suslov, Sergey A

    2015-01-01

    The onset and decay of convection in a spherical cavity filled with ferromagnetic nanofluid and heated from below are investigated experimentally. It is found that, unlike in a single-component Newtonian fluid where stationary convection sets in as a result of supercritical bifurcation and where convection intensity increases continuously with the degree of supercriticality, convection in a multicomponent ferromagnetic nanofluid starts abruptly and has an oscillatory nature. The hysteresis is observed in the transition between conduction and convection states. In moderately supercritical regimes, the arising fluid motion observed at a fixed temperature difference intermittently transitions from quasiharmonic to essentially irregular oscillations that are followed by periods of a quasistationary convection. The observed oscillations are shown to result from the precession of the axis of a convection vortex in the equatorial plane. When the vertical temperature difference exceeds the convection onset value by a factor of 2.5, the initially oscillatory convection settles to a steady-state regime with no intermittent behavior detected afterward. The performed wavelet and Fourier analyses of thermocouple readings indicate the presence of various oscillatory modes with characteristic periods ranging from one hour to several days.

  18. Preparation and characterization of flexible ferromagnetic nanocomposites for microwave applications

    Energy Technology Data Exchange (ETDEWEB)

    Thomas, Teena; Kanoth, Bipinbal P. [Department of Polymer Science & Rubber Technology, Cochin University of Science & Technology, Cochin, 682022, Kerala (India); Nijas, C.M. [Department of Electronics, Cochin University of Science & Technology, Cochin, 682022, Kerala (India); Joy, P.A. [Physical and Materials Chemistry Division, National Chemical Laboratory, Pune 411008 (India); Joseph, Joseph M. [Inter University Centre for Nanomaterials and Devices, Cochin University of Science & Technology, Cochin 682022, Kerala (India); Kuthirummal, Narayanan, E-mail: kuthirummaln@cofc.edu [Department of Physics and Astronomy, College of Charleston, Charleston, SC 29424 (United States); Thachil, Eby T., E-mail: ethachil@gmail.com [Department of Polymer Science & Rubber Technology, Cochin University of Science & Technology, Cochin, 682022, Kerala (India)

    2015-10-15

    Highlights: • Fe{sub 3}O{sub 4} nanoparticles (∼20 nm) were synthesised by co-precipitation method. • Nanoparticles were homogeneously distributed in natural rubber through latex stage processing. • Mechanical properties and magnetic properties of composites improved with loading Fe{sub 3}O{sub 4} nanoparticles. • Imaginary part of permeability increases with nanoparticle loading improving the microwave absorption characteristics. • Infrared spectra reveal strong interaction between NR and iron oxide nanoparticles. - Abstract: Magnetic Fe{sub 3}O{sub 4} nanoparticles (∼20 nm) were synthesized using the chemical co-precipitation method with a view of developing flexible and easily processable ferromagnetic materials with high mouldability to be used as microwave absorbers. The nanoparticles prepared were incorporated into natural rubber through latex stage processing. This novel processing method gives better dispersion of particles in the rubber matrix. The composites were characterized using XRD, SEM, vibrating sample magnetometer, dynamic mechanical analyzer, cavity perturbation, thermogravimetry (TGA), and Fourier transform infrared photoacoustic spectroscopy (FTIR-PAS). A notable improvement in the mechanical properties of composites was observed upon adding Fe{sub 3}O{sub 4} particles. Magnetic and microwave characteristics of the composites indicate the formation of a flexible ferromagnetic material with good microwave absorption characteristics.

  19. Callen-like method for the classical Heisenberg ferromagnet

    Science.gov (United States)

    Campana, L. S.; Cavallo, A.; De Cesare, L.; Esposito, U.; Naddeo, A.

    2012-02-01

    A study of the d-dimensional classical Heisenberg ferromagnetic model in the presence of a magnetic field is performed within the two-time Green function's framework in classical statistical physics. We extend the well known quantum Callen method to derive analytically a new formula for magnetization. Although this formula is valid for any dimensionality, we focus on one- and three- dimensional models and compare the predictions with those arising from a different expression suggested many years ago in the context of the classical spectral density method. Both frameworks give results in good agreement with the exact numerical transfer-matrix data for the one-dimensional case and with the exact high-temperature-series results for the three-dimensional one. In particular, for the ferromagnetic chain, the zero-field susceptibility results are found to be consistent with the exact analytical ones obtained by M.E. Fisher. However, the formula derived in the present paper provides more accurate predictions in a wide range of temperatures of experimental and numerical interest.

  20. Robust quantum anomalous Hall effect in ferromagnetic transition metal halides

    CERN Document Server

    Huang, Chengxi; Wu, Haiping; Deng, Kaiming; Jena, Puru; Kan, Erjun

    2016-01-01

    The quantum anomalous Hall (QAH) effect is a novel topological spintronic phenomenon arising from inherent magnetization and spin-orbit coupling. Various theoretical and experimental efforts have been devoted in search of robust intrinsic QAH insulators. However, up to now, it has only been observed in Cr or V doped (Bi,Sb)2Te3 film in experiments with very low working temperature. Based on the successful synthesis of transition metal halides, we use first-principles calculations to predict that RuI3 monolayer is an intrinsic ferromagnetic QAH insulator with a topologically nontrivial global band gap of 11 meV. This topologically nontrivial band gap at the Fermi level is due to its crystal symmetry, thus the QAH effect is robust. Its Curie temperature, estimated to be ~360 K using Monte-Carlo simulation, is above room temperature and higher than most of two-dimensional ferromagnetic thin films. We also discuss the manipulation of its exchange energy and nontrivial band gap by applying in-plane strain. Our wor...

  1. Inverse problem of pulsed eddy current field of ferromagnetic plates

    Science.gov (United States)

    Chen, Xing-Le; Lei, Yin-Zhao

    2015-03-01

    To determine the wall thickness, conductivity and permeability of a ferromagnetic plate, an inverse problem is established with measured values and calculated values of time-domain induced voltage in pulsed eddy current testing on the plate. From time-domain analytical expressions of the partial derivatives of induced voltage with respect to parameters, it is deduced that the partial derivatives are approximately linearly dependent. Then the constraints of these parameters are obtained by solving a partial linear differential equation. It is indicated that only the product of conductivity and wall thickness, and the product of relative permeability and wall thickness can be determined accurately through the inverse problem with time-domain induced voltage. In the practical testing, supposing the conductivity of the ferromagnetic plate under test is a fixed value, and then the relative variation of wall thickness between two testing points can be calculated via the ratio of the corresponding inversion results of the product of conductivity and wall thickness. Finally, this method for wall thickness measurement is verified by the experiment results of a carbon steel plate. Project supported by the National Defense Basic Technology Research Program of China (Grant No. Z132013T001).

  2. On magnon mediated Cooper pair formation in ferromagnetic superconductors

    Directory of Open Access Journals (Sweden)

    Rakesh Kar

    2014-08-01

    Full Text Available Identification of pairing mechanism leading to ferromagnetic superconductivity is one of the most challenging issues in condensed matter physics. Although different models have been proposed to explain this phenomenon, a quantitative understanding about this pairing is yet to be achieved. Using the localized-itinerant model, we find that in ferromagnetic superconducting materials both triplet pairing and singlet pairing of electrons are possible through magnon exchange depending upon whether the Debye cut off frequency of magnons is greater or lesser than the Hund's coupling (J multiplied by average spin (S per site. Taking into account the repulsive interaction due to the existence of paramagnons, we also find an expression for effective interaction potential between a pair of electrons with opposite spins. We apply the developed formalism in case of UGe2 and URhGe. The condition of singlet pairing is found to be fulfilled in these cases, as was previously envisaged by Suhl [Suhl, Phys. Rev. Lett. 87, 167007 (2001]. We compute the critical temperatures of URhGe at ambient pressure and of UGe2 under different pressures for the first time through BCS equation. Thus, this work outlines a very simple way to evaluate critical temperature in case of a superconducting system. A close match with the available experimental results strongly supports our theoretical treatment.

  3. Magnetic Exchange Between Superconducting and Ferromagnetic Oxide Layers

    Science.gov (United States)

    Giblin, Sean; Taylor, Jon; Duffy, Jon; Dugdale, Stephen; Nakamura, T.; Santamaria, Jacobo

    2012-02-01

    The origins of high temperature superconductivity and the rich phase diagrams in complex oxides are still a matter of contention that have stimulated many novel experimental studies and observations. Recently the improvement of layer by layer growth techniques of thin films has enabled investigations of both bulk and surface properties. For most common superconductors the order parameter is thought to be antagonistic to that of the exchange mechanism in ferromagnets. Accurately grown thin fllms have enabled these competing interactions to be probed experimentally. In particular, the growth of epitaxial oxide layers, with well-characterized atomically flat interfaces, consisting of superconducting layers of YBa2Cu3O7 (YBCO) and lattice-matched ferromagnetic La2/3Ca1/3MnO3 (LCMO) has flourished. Using XMCD we demonstrate that the known superexchange between Mn and Cu across the YBCO/LCMO is modified when an apparent critical thickness of the superconducting layer is reduced. All samples show an apparent exchange below the superconducting transition but above it is dependent on the YBCO thickness. Possible origins of this behaviour will be discussed.

  4. Magnetic Sensors Based on Amorphous Ferromagnetic Materials: A Review.

    Science.gov (United States)

    Morón, Carlos; Cabrera, Carolina; Morón, Alberto; García, Alfonso; González, Mercedes

    2015-11-11

    Currently there are many types of sensors that are used in lots of applications. Among these, magnetic sensors are a good alternative for the detection and measurement of different phenomena because they are a "simple" and readily available technology. For the construction of such devices there are many magnetic materials available, although amorphous ferromagnetic materials are the most suitable. The existence in the market of these materials allows the production of different kinds of sensors, without requiring expensive manufacture investments for the magnetic cores. Furthermore, these are not fragile materials that require special care, favouring the construction of solid and reliable devices. Another important feature is that these sensors can be developed without electric contact between the measuring device and the sensor, making them especially fit for use in harsh environments. In this review we will look at the main types of developed magnetic sensors. This work presents the state of the art of magnetic sensors based on amorphous ferromagnetic materials used in modern technology: security devices, weapon detection, magnetic maps, car industry, credit cards, etc.

  5. Ordering in rolled-up single-walled ferromagnetic nanomembranes

    Energy Technology Data Exchange (ETDEWEB)

    Janutka, Andrzej, E-mail: Andrzej.Janutka@pwr.edu.pl

    2016-12-01

    Magnetization of soft-ferromagnetic nano- and microtubes of nanometer-thin walls (a single-widening rolled-up nanomembranes) is theoretically studied using analytical and numerical approaches including different stress-induced anisotropies. Within the analytical study, we consider magnetostatic effects qualitatively, with an effective anisotropy, while they are fully treated in the micromagnetic simulations (limited to the tubes of submicrometer diameters however). Basic types of the periodic ordering have been established and their presence in nanotubes of polycrystalline Permalloy and cobalt has been verified within the simulations. The domain structure is basically determined by a material-deposition-induced helical stress or a cooling-induced axial stress via the volume magnetostriction while it is influenced by the distribution of magnetic charges as well. Also, it is dependent on the initial state of the magnetization process. - Highlights: • An effective model of the magnetic anisotropy in ferromagnetic tube of nm-thick wall has been formulated. • Basic types of magnetization structures of the tubes are analytically described. • Possible orderings are examined with micromagnetic simulations of Co and Py nanotubes.

  6. Ferromagnetic Resonance of a Single Magnetochiral Metamolecule of Permalloy

    Science.gov (United States)

    Kodama, Toshiyuki; Tomita, Satoshi; Kato, Takeshi; Oshima, Daiki; Iwata, Satoshi; Okamoto, Satoshi; Kikuchi, Nobuaki; Kitakami, Osamu; Hosoito, Nobuyoshi; Yanagi, Hisao

    2016-08-01

    We investigate the ferromagnetic resonance (FMR) of a single chiral structure of a ferromagnetic metal—the magnetochiral (MCh) metamolecule. Using a strain-driven self-coiling technique, micrometer-sized MCh metamolecules of metallic permalloy (Py) are fabricated without any residual Py films. The magnetization curves of ten Py MCh metamolecules obtained by an alternating gradient magnetometer show soft magnetic behavior. In cavity FMR with a magnetic-field sweep and coplanar-waveguide (CPW) FMR with a frequency sweep, the Kittel-mode FMR of the single Py metamolecule is observed. The CPW-FMR results, which are consistent with the cavity-FMR results, bring about the effective g factor, effective magnetization, and Gilbert damping of the single metamolecule. Together with calculations using these parameters, the angle-resolved cavity FMR reveals that the magnetization in the Py MCh metamolecule is most likely to be the hollow-bar type of configuration when the external magnetic field is applied parallel to the chiral axis, although the expected magnetization state at remanence is the corkscrew type of configuration.

  7. Quantum anomalous Hall effect in ferromagnetic transition metal halides

    Science.gov (United States)

    Huang, Chengxi; Zhou, Jian; Wu, Haiping; Deng, Kaiming; Jena, Puru; Kan, Erjun

    2017-01-01

    The quantum anomalous Hall (QAH) effect is a novel topological spintronic phenomenon arising from inherent magnetization and spin-orbit coupling. Various theoretical and experimental efforts have been devoted in search of intrinsic QAH insulators. However, up to now, it has only been observed in Cr or V doped (Bi,Sb ) 2T e3 film in experiments with very low working temperature. Based on the successful synthesis of transition metal halides, we use first-principles calculations to predict that the Ru I3 monolayer is an intrinsic ferromagnetic QAH insulator with a topologically nontrivial global band gap of 11 meV. This topologically nontrivial band gap at the Fermi level is due to its crystal symmetry, thus the QAH effect is robust. Its Curie temperature, estimated to be ˜360 K using Monte Carlo simulation, is above room temperature and higher than most two-dimensional ferromagnetic thin films. The inclusion of Hubbard U in the Ru-d electrons does not affect this result. We also discuss the manipulation of its exchange energy and nontrivial band gap by applying in-plane strain. Our work adds an experimentally feasible member to the QAH insulator family, which is expected to have broad applications in nanoelectronics and spintronics.

  8. Current-driven dynamics of chiral ferromagnetic domain walls.

    Science.gov (United States)

    Emori, Satoru; Bauer, Uwe; Ahn, Sung-Min; Martinez, Eduardo; Beach, Geoffrey S D

    2013-07-01

    In most ferromagnets the magnetization rotates from one domain to the next with no preferred handedness. However, broken inversion symmetry can lift the chiral degeneracy, leading to topologically rich spin textures such as spin spirals and skyrmions through the Dzyaloshinskii-Moriya interaction (DMI). Here we show that in ultrathin metallic ferromagnets sandwiched between a heavy metal and an oxide, the DMI stabilizes chiral domain walls (DWs) whose spin texture enables extremely efficient current-driven motion. We show that spin torque from the spin Hall effect drives DWs in opposite directions in Pt/CoFe/MgO and Ta/CoFe/MgO, which can be explained only if the DWs assume a Néel configuration with left-handed chirality. We directly confirm the DW chirality and rigidity by examining current-driven DW dynamics with magnetic fields applied perpendicular and parallel to the spin spiral. This work resolves the origin of controversial experimental results and highlights a new path towards interfacial design of spintronic devices.

  9. Magnetic Sensors Based on Amorphous Ferromagnetic Materials: A Review

    Directory of Open Access Journals (Sweden)

    Carlos Morón

    2015-11-01

    Full Text Available Currently there are many types of sensors that are used in lots of applications. Among these, magnetic sensors are a good alternative for the detection and measurement of different phenomena because they are a “simple” and readily available technology. For the construction of such devices there are many magnetic materials available, although amorphous ferromagnetic materials are the most suitable. The existence in the market of these materials allows the production of different kinds of sensors, without requiring expensive manufacture investments for the magnetic cores. Furthermore, these are not fragile materials that require special care, favouring the construction of solid and reliable devices. Another important feature is that these sensors can be developed without electric contact between the measuring device and the sensor, making them especially fit for use in harsh environments. In this review we will look at the main types of developed magnetic sensors. This work presents the state of the art of magnetic sensors based on amorphous ferromagnetic materials used in modern technology: security devices, weapon detection, magnetic maps, car industry, credit cards, etc.

  10. Novel Majorana mode and magnetoresistance in ferromagnetic superconducting topological insulator

    Science.gov (United States)

    Goudarzi, H.; Khezerlou, M.; Asgarifar, S.

    2017-03-01

    Among the potential applications of topological insulators, we investigate theoretically the effect of coexistence of proximity-induced ferromagnetism and superconductivity on the surface states of 3-dimensional topological insulator, where the superconducting electron-hole excitations can be significantly affected by the magnetization of ferromagnetic order. We find that, Majorana mode energy, as a verified feature of TI F/S structure, along the interface sensitively depends on the magnitude of magnetization mzfs in FS region, while its slope in perpendicular incidence presents steep and no change. Since the superconducting gap is renormalized by a factor η (mzfs) , hence Andreev reflection is more or less suppressed, and, in particular, resulting subgap tunneling conductance is more sensitive to the magnitude of magnetizations in FS and F regions. Furthermore, an interesting scenario happens at the antiparallel configuration of magnetizations mzf and mzfs resulting in magnetoresistance in N/F/FS junction, which can be controlled and decreased by tuning the magnetization magnitude in FS region.

  11. Mn-doping induced ferromagnetism and enhanced superconductivity in Bi4 -xMnxO4S3 (0.075 ≤x ≤0.15 )

    Science.gov (United States)

    Feng, Zhenjie; Yin, Xunqing; Cao, Yiming; Peng, Xianglian; Gao, Tian; Yu, Chuan; Chen, Jingzhe; Kang, Baojuan; Lu, Bo; Guo, Juan; Li, Qing; Tseng, Wei-Shiuan; Ma, Zhongquan; Jing, Chao; Cao, Shixun; Zhang, Jincang; Yeh, N.-C.

    2016-08-01

    We demonstrate that Mn doping in the layered sulfides Bi4O4S3 leads to stable Bi4-xMnxO4S3 compounds that exhibit both long-range ferromagnetism and enhanced superconductivity for 0.075 ≤x ≤0.15 , with a possible record superconducting transition temperature (Tc) ˜15 K among all BiS2-based superconductors. We conjecture that the coexistence of superconductivity and ferromagnetism may be attributed to Mn doping in the spacer Bi2O2 layers away from the superconducting BiS2 layers, whereas the enhancement of Tc may be due to excess electron transfer to BiS2 from the Mn4 +/Mn3 + substitutions in Bi2O2 . This notion is empirically corroborated by the increased electron-carrier densities upon Mn doping, and by further studies of the Bi4-xAxO4S3 compounds (A = Co, Ni; x =0.1 , 0.125), where the Tc values remain comparable to that of the undoped Bi4O4S3 system (˜4.5 K) due to lack of 4+ valences in either Co or Ni ions for excess electron transfer to the BiS2 layers. These findings therefore shed new light on feasible pathways to enhance the Tc values of BiS2-based superconductors, although complete elucidation of the interplay between superconductivity and ferromagnetism in these anisotropic layered compounds awaits the development of single crystalline materials for further investigation.

  12. Correlation between magnetostriction and magnetic structure in pseudobinary compounds Tb(Co1-xFex)2

    Science.gov (United States)

    Wang, Yue; Ma, Tianyu; Wu, Chen; Yan, Mi; Zhang, Changsheng; Chen, Xiping; Sun, Guangai; Yang, Sen; Wang, Yu; Chang, Tieyan; Zhou, Chao; Liao, Xiaoqi; Zheng, Xinqi

    2017-07-01

    Giant low-field magnetostriction has been achieved in pseudobinary Laves phase compounds RR'T2 (R and R': rare earth elements; T: transition metal elements) around the ferromagnetic - ferromagnetic (ferro.-ferro.) transition temperature. Evolution of the magnetic structure across such transition requires comprehensive investigation. In this work, pseudobinary system Tb(Co1-xFex)2 is selected to investigate the evolution of local magnetic moment, for which two end terminals TbCo2 and TbFe2 possess the rhombohedral (R) structure at the ferromagnetic state but with different magnetic ordering temperatures (TC). Magnetometry measurements reveal that a composition independent ferromagnetic - ferromagnetic transition occurs at ˜100 K despite the increased Curie temperature TC with raised Fe concentration in the Tb(Co1-xFex)2. Synchrotron XRD data reveal that both the lattice parameter and the lattice strain along the direction are abnormally temperature dependent, accompanied with experimentally observed magnetostriction abnormality at 100 K. In-situ neutron powder diffraction (NPD) results show that the local magnetic moments of T2 (9e site) atoms are also abnormally temperature dependent, which is larger at 100 K than that at a lower temperature 50 K. Such findings indicate close correlations between the magnetic structure and the magnetostrictive effect in the pseudobinary RT2 compounds.

  13. Correlation between magnetostriction and magnetic structure in pseudobinary compounds Tb(Co1-xFex2

    Directory of Open Access Journals (Sweden)

    Yue Wang

    2017-07-01

    Full Text Available Giant low-field magnetostriction has been achieved in pseudobinary Laves phase compounds RR’T2 (R and R’: rare earth elements; T: transition metal elements around the ferromagnetic - ferromagnetic (ferro.-ferro. transition temperature. Evolution of the magnetic structure across such transition requires comprehensive investigation. In this work, pseudobinary system Tb(Co1-xFex2 is selected to investigate the evolution of local magnetic moment, for which two end terminals TbCo2 and TbFe2 possess the rhombohedral (R structure at the ferromagnetic state but with different magnetic ordering temperatures (TC. Magnetometry measurements reveal that a composition independent ferromagnetic - ferromagnetic transition occurs at ∼100 K despite the increased Curie temperature TC with raised Fe concentration in the Tb(Co1-xFex2. Synchrotron XRD data reveal that both the lattice parameter and the lattice strain along the direction are abnormally temperature dependent, accompanied with experimentally observed magnetostriction abnormality at 100 K. In-situ neutron powder diffraction (NPD results show that the local magnetic moments of T2 (9e site atoms are also abnormally temperature dependent, which is larger at 100 K than that at a lower temperature 50 K. Such findings indicate close correlations between the magnetic structure and the magnetostrictive effect in the pseudobinary RT2 compounds.

  14. Encouragement of Enzyme Reaction Utilizing Heat Generation from Ferromagnetic Particles Subjected to an AC Magnetic Field.

    Science.gov (United States)

    Suzuki, Masashi; Aki, Atsushi; Mizuki, Toru; Maekawa, Toru; Usami, Ron; Morimoto, Hisao

    2015-01-01

    We propose a method of activating an enzyme utilizing heat generation from ferromagnetic particles under an ac magnetic field. We immobilize α-amylase on the surface of ferromagnetic particles and analyze its activity. We find that when α-amylase/ferromagnetic particle hybrids, that is, ferromagnetic particles, on which α-amylase molecules are immobilized, are subjected to an ac magnetic field, the particles generate heat and as a result, α-amylase on the particles is heated up and activated. We next prepare a solution, in which α-amylase/ferromagnetic particle hybrids and free, nonimmobilized chitinase are dispersed, and analyze their activities. We find that when the solution is subjected to an ac magnetic field, the activity of α-amylase immobilized on the particles increases, whereas that of free chitinase hardly changes; in other words, only α-amylase immobilized on the particles is selectively activated due to heat generation from the particles.

  15. Evidence for ferromagnetic instability in a repulsive Fermi gas of ultracold atoms

    CERN Document Server

    Valtolina, G; Amico, A; Burchianti, A; Recati, A; Enss, T; Inguscio, M; Zaccanti, M; Roati, G

    2016-01-01

    Ferromagnetism is among the most spectacular manifestations of interactions within many-body fermion systems. In contrast to weak-coupling phenomena, it requires strong repulsion to develop, making a quantitative description of ferromagnetic materials notoriously difficult. This is especially true for itinerant ferromagnets, where magnetic moments are not localized into a crystal lattice. In particular, it is still debated whether the simplest case envisioned by Stoner of a homogeneous Fermi gas with short-range repulsive interactions can exhibit ferromagnetism at all. In this work, we positively answer this question by studying a clean model system consisting of a binary spin-mixture of ultracold 6Li atoms, whose repulsive interaction is tuned via a Feshbach resonance. We drastically limit detrimental pairing effects that affected previous studies by preparing the gas in a magnetic domain-wall configuration. We reveal the ferromagnetic instability by observing the softening of the spin-dipole collective mode...

  16. Encouragement of Enzyme Reaction Utilizing Heat Generation from Ferromagnetic Particles Subjected to an AC Magnetic Field.

    Directory of Open Access Journals (Sweden)

    Masashi Suzuki

    Full Text Available We propose a method of activating an enzyme utilizing heat generation from ferromagnetic particles under an ac magnetic field. We immobilize α-amylase on the surface of ferromagnetic particles and analyze its activity. We find that when α-amylase/ferromagnetic particle hybrids, that is, ferromagnetic particles, on which α-amylase molecules are immobilized, are subjected to an ac magnetic field, the particles generate heat and as a result, α-amylase on the particles is heated up and activated. We next prepare a solution, in which α-amylase/ferromagnetic particle hybrids and free, nonimmobilized chitinase are dispersed, and analyze their activities. We find that when the solution is subjected to an ac magnetic field, the activity of α-amylase immobilized on the particles increases, whereas that of free chitinase hardly changes; in other words, only α-amylase immobilized on the particles is selectively activated due to heat generation from the particles.

  17. Calibration of Hall sensor array for critical current measurement of YBCO tape with ferromagnetic substrate

    Energy Technology Data Exchange (ETDEWEB)

    Zhu, Yunpeng; Wang, Gang; Liu, Liyuan [Key laboratory of Magnetic levitation Technologies and Maglev Trains (Ministry of Education), Superconductor and New Energy R& D Center, Mail Stop 165#, Southwest Jiaotong University, Chengdu, 610031 (China); Yang, Xinsheng, E-mail: xsyang@swjtu.edu.cn [Key laboratory of Magnetic levitation Technologies and Maglev Trains (Ministry of Education), Superconductor and New Energy R& D Center, Mail Stop 165#, Southwest Jiaotong University, Chengdu, 610031 (China); Zhao, Yong [Key laboratory of Magnetic levitation Technologies and Maglev Trains (Ministry of Education), Superconductor and New Energy R& D Center, Mail Stop 165#, Southwest Jiaotong University, Chengdu, 610031 (China); Superconductivity Research Group, School of Materials Science and Engineering, University of New South Wale, Sydney 2052, NSW (Australia)

    2015-12-15

    Abstract : HAS (Hall sensor array) is a powerful tool to detect the uniformity of HTS (high temperature superconductor) tape through mapping the distribution of remanent or shielding field along the surface of the tape. However, measurement of HTS tape with ferromagnetic parts by HSA is still an issue because the ferromagnetic substrate has influence on the magnetic field around the HTS layer. In this work, a continuous HSA system has been designed to measure the critical current of the YBCO tape with ferromagnetic substrate. The relationship between the remanent field and critical current was calibrated by the finite element method. The result showed that the HSA is an effective method for evaluating the critical current of the HTS tape with ferromagnetic substrate. - Highlight: • A continuous Hall sensor array system has been designed. • The inhomogeneity of YBCO tape with ferromagnetic substrate can be detected by HAS. • Finite element method is an effective method for calibrating the remanent field.

  18. Effects of annealing on the ferromagnetism and photoluminescence of Cu-doped ZnO nanowires

    Science.gov (United States)

    Xu, H. J.; Zhu, H. C.; Shan, X. D.; Liu, Y. X.; Gao, J. Y.; Zhang, X. Z.; Zhang, J. M.; Wang, P. W.; Hou, Y. M.; Yu, D. P.

    2010-01-01

    Room temperature ferromagnetic Cu-doped ZnO nanowires have been synthesized using the chemical vapor deposition method. By combining structural characterizations and comparative annealing experiments, it has been found that both extrinsic (CuO nanoparticles) and intrinsic (Zn1-xCuxO nanowires) sources are responsible for the observed ferromagnetic ordering of the as-grown samples. As regards the former, annealing in Zn vapor led to a dramatic decrease of the ferromagnetism. For the latter, a reversible switching of the ferromagnetism was observed with sequential annealings in Zn vapor and oxygen ambience respectively, which agreed well with previous reports for Cu-doped ZnO films. In addition, we have for the first time observed low temperature photoluminescence changed with magnetic properties upon annealing in different conditions, which revealed the crucial role played by interstitial zinc in directly mediating high Tc ferromagnetism and indirectly modulating the Cu-related structured green emission via different charge transfer transitions.

  19. Interfacial Ferromagnetism in LaNiO3/CaMnO3 Superlattices

    Energy Technology Data Exchange (ETDEWEB)

    Grutter, Alexander J.; Yang, Hao; Kirby, B. J.; Fitzsimmons, M. R.; Aguiar, Jeffery A.; Browning, Nigel D.; Jenkins, C. A.; Arenholz, Elke; Mehta, V. V.; Alaan, U. S.; Suzuki, Y.

    2013-08-01

    We observe interfacial ferromagnetism in superlattices of the paramagnetic metal LaNiO3 and the antiferromagnetic insulator CaMnO3. LaNiO3 exhibits a thickness dependent metal-insulator transition and we find the emergence of ferromagnetism to be coincident with the conducting state of LaNiO3. That is, only superlattices in which the LaNiO3 layers are metallic exhibit ferromagnetism. Using several magnetic probes, we have determined that the ferromagnetism arises in a single unit cell of CaMnO3 at the interface. Together these results suggest that ferromagnetism can be attributed to a double exchange interaction among Mn ions mediated by the adjacent itinerant metal.

  20. Interfacial ferromagnetism in LaNiO3/CaMnO3 superlattices.

    Science.gov (United States)

    Grutter, A J; Yang, H; Kirby, B J; Fitzsimmons, M R; Aguiar, J A; Browning, N D; Jenkins, C A; Arenholz, E; Mehta, V V; Alaan, U S; Suzuki, Y

    2013-08-23

    We observe interfacial ferromagnetism in superlattices of the paramagnetic metal LaNiO3 and the antiferromagnetic insulator CaMnO3. LaNiO3 exhibits a thickness dependent metal-insulator transition and we find the emergence of ferromagnetism to be coincident with the conducting state of LaNiO3. That is, only superlattices in which the LaNiO3 layers are metallic exhibit ferromagnetism. Using several magnetic probes, we have determined that the ferromagnetism arises in a single unit cell of CaMnO3 at the interface. Together these results suggest that ferromagnetism can be attributed to a double exchange interaction among Mn ions mediated by the adjacent itinerant metal.