43 research outputs found
Ballistic spin-transport properties of magnetic tunnel junctions with MnCr-based ferrimagnetic quaternary Heusler alloys
We investigate the suitability of nearly half-metallic ferrimagnetic
quaternary Heusler alloys, CoCrMnZ (Z=Al, Ga, Si, Ge) to assess the feasibility
as electrode materials of MgO-based magnetic tunnel junctions (MTJ). Low
magnetic moments of these alloys originated from the anti-ferromagnetic
coupling between Mn and Cr spins ensure a negligible stray field in spintronics
devices as well as a lower switching current required to flip their spin
direction. We confirmed mechanical stability of these materials from the
evaluated values of elastic constants, and the absence of any imaginary
frequency in their phonon dispersion curves. The influence of swapping
disorders on the electronic structures and their relative stability are also
discussed. A high spin polarization of the conduction electrons are observed in
case of CoCrMnZ/MgO hetrojunctions, independent of terminations at the
interface. Based on our ballistic transport calculations, a large coherent
tunnelling of the majority-spin -like states can be expected
through MgO-barrier. The calculated tunnelling magnetoresistance (TMR) ratios
are in the order of 1000\%. A very high Curie temperatures specifically for
CoCrMnAl and CoCrMnGa, which are comparable to Co, could also yield a
weaker temperature dependece of TMR ratios for CoCrMnAl/MgO/CoCrMnAl (001) and
CoCrMnGa/MgO/CoCrMnGa (001) MTJ.Comment: 24 pages, 13 figure
Finite electric field effects in the large perpendicular magnetic anisotropy surface Pt/Fe/Pt(001): A first-principles study
金沢大学理工研究域数物科学系We investigate crystalline magnetic anisotropy in the electric field (EF) for the FePt surface which has a large perpendicular anisotropy, by means of the first-principles approach. Anisotropy is reduced linearly with respect to the inward EF, associated with the induced spin density around the Fe layer. Although the magnetic anisotropy energy (MAE) density reveals large variation around the atoms, the intrinsic contribution to the MAE is found to mainly come from the Fe layer. The surface without the capping Pt layer also shows similar linear dependence. © 2009 The American Physical Society
Magnetic anisotropy of Fe/Pt (001) and Pt/Fe/Pt (001) using a first-principles approach
金沢大学理工研究域 数物科学系We investigated the magnetic anisotropy of an iron layer on a Pt(001) surface and some related systems by employing the local spin density approximation in a theoretical ab initio approach. We found that the surface system Pt/Fe/Pt (001) showed a perpendicular magnetic anisotropy and its anisotropy energy per iron atom amounted to a value which is 2 times larger than the value of bulk FePt. The surface relaxation much enhances the anisotropy energies, related to a large attractive force between the iron and platinum layers. A remarkable cap effect-that the covering platinum layer changes anisotropy energy-was also found to exist. We investigated the microscopic origin of the perpendicular anisotropy in relation to the local densities of states of the Fe atom. These quantities were discussed as a fingerprint of magnetic anisotropy in comparison with the results of the Fe chain at the step edge on a vicinal surface Pt(664). The atomic orbital magnetic moments were enhanced at the respective surface atoms. © 2008 The American Physical Society
Spin-splitting band dispersions of the heavy elements on Si(111)-(1×1) surface
金沢大学大学院自然科学研究科 We have carried out the first-principles fully relativistic electronic structure calculations for the surfaces, R/Si(111) (R = Pb and Bi). The band dispersions of the surface states in the bulk band gap shows the large spin splitting, associated with the spin-orbit interaction on the atoms of the overlayer. Besides the usual Rashba effect around the center of the surface Brillouin zone, the vortical spin polarizations were obtained around the M ̄ points. At the K̄, associated with the symmetry, the complete out-of-plane spin polarization was obtained for the surface states. © 2010 IOP Publishing Ltd
Electric-field effects on magnetic anisotropy in Pd/Fe/Pd(0 0 1) surface
金沢大学理工研究域数物科学系Electric-field (EF) effects have been studied on magnetic anisotropy in the metallic surfaces Pt/Fe/Pt(0 0 1) and Pd/Fe/Pd(0 0 1) by means of the first-principles electronic structure calculation which employs the generalized gradient approximation. The variation of anisotropy energy with respect to the EF is found to be opposite to each other. The modulus rate of the variation is larger by a few factors in the Pt substrate than in the Pd one. These results agree qualitatively well with the available experimental data. The electronic structures are presented and the origins in EF effects are discussed along a line of the second perturbative fashion. © 2011 IOP Publishing Ltd
Electronic and magnetic properties of the topological semimetal SmMgBi
Dirac semimetals show nontrivial physical properties and can host exotic
quantum states like Weyl semimetals and topological insulators under suitable
external conditions. Here, by combining angle-resolved photoemission
spectroscopy measurements (ARPES) and first-principle calculations, we
demonstrate that Zintl-phase compound SmMgBi belongs to the close
proximity to a topological Dirac semimetallic state. ARPES results show a
Dirac-like band crossing at the zone-center near the Fermi level () which is further confirmed by first-principle calculations. Theoretical
studies also reveal that SmMgBi belongs to a topological class
and hosts spin-polarized states around the . Zintl's theory
predicts that the valence state of Sm in this material should be Sm,
however we detect many Sm-4 multiplet states (flat-bands) whose energy
positions suggest the presence of both Sm and Sm. It is also
evident that these flat-bands and other dispersive states are strongly
hybridized when they cross each other. Due to the presence of Sm ions,
the temperature dependence of magnetic susceptibility shows
Curie-Weiss-like contribution in the low temperature region, in addition to the
Van Vleck-like behaviour expected for the Sm ions. The present study
will help in better understanding of the electronic structure, magnetism and
transport properties of related materials.Comment: 10 pages, 7 figure