High spin polarization of the anomalous Hall current in Co-based Heusler compounds

Abstract

Based on first principles density functional calculations of the intrinsic anomalous and spin Hall conductivities, we predict that the charge Hall current in Co-based full Heusler compounds Co 2 XZ (X = Cr and Mn; Z = Al, Si, Ga, Ge, In and Sn), except Co 2 CrGa, would be almost fully spin polarized, even though Co 2 MnAl, Co 2 MnGa, Co 2 MnIn and Co 2 MnSn do not have a halfmetallic band structure. Furthermore, the ratio of the associated spin current to the charge Hall current is slightly larger than 1.0. This suggests that these Co-based Heusler compounds, especially Co 2 MnAl, Co 2 MnGa and Co 2 MnIn which are found to have large anomalous and spin Hall conductivities, might be called anomalous Hall half-metals and could have valuable applications in spintronics such as spin valves as well as magnetoresistive and spin-torquedriven nanodevices. These interesting findings are discussed in terms of the calculated electronic band structures, magnetic moments and also anomalous and spin Hall conductivities as a function of the Fermi level.

Magnetocrystalline anisotropy and its electric-field-assisted switching of Heusler-compound-based perpendicular magnetic tunnel junctions

“…Interfacial spin polarization. The spin-dependent tunneling conductance of the MgObased MTJs is determined by two factors: the symmetry matching between the transmission Bloch states in FM electrodes and evanescent states in the MgO barrier, and the spin polarization (SP) within the electrodes and at the electrode/barrier interfaces [35,[59][60][61][62]. As for the former factor, the spin-filter effect can be tremendously boosted if the FM electrode materials possess half-metallic Δ 1 bands, of which the Bloch states suffer from the smallest decay within the C 4v -symmetry MgO barrier.…”

Anomalous resistivity upturn in epitaxial L21-Co2MnAl films

“…The full-Heusler alloy L 2 1 -Co 2 MnAl has attracted considerable attention in the emerging field of spintronics due to the vanishingly small density of states in minority spin band at Fermi level12. Firstly, Heusler ferromagnets with high spin polarization ( P ) have promise for amazingly high giant magnetoresistance (GMR) in current-perpendicular-plane (CPP) spin valves (SVs) and tunneling magnetoresistance in magnetic tunneling junctions (MTJs)3.…”

“…high- P Heusler alloys could be an excellent approach to solve the over-rotation problem and to realize ultrafast (~100 ps) deterministic switching of the orthogonal spin torque (OST) CPP SVs. The L 2 1 -Co 2 MnAl films are also of great interest in high-sensitivity Hall sensor application due to the giant intrinsic anomalous Hall conductivity arising from Berry phase curvature12. However, the control of the structural disorder is a crucial issue for the practical Co 2 MnAl films in order to obtain the fascinating properties expected in perfectly ordered samples.…”

“…(i.e. ~786 emu/cm 3 )12. L 2 1 -Co 2 MnAl bulk was obtained by induction melting and 10 day annealing at 600–1190 °C under a magnetic field of 5 kOe9.…”

CPP-GMR study of half-metallic full-Heusler compound Co2(Fe,Mn)Si

“…In addition, other interesting properties arising from half-metallicity were also predicted: high spin-polarization of anomalous Hall current and large cooling effects due to spin-entropy expansion etc. 2,3) Previous theoretical calculations based on the first principles predicted that various kinds of materials have a potential for exhibiting half-metallicity. As representative candidates of half-metals that can be easily synthesized/grown practically, some of Heusler compounds (NiMnSb and Co2MnSi etc.)…”