Spin filtering and spin separation in 2D materials by topological spin Hall effect

Abstract

The needs of high speed performance electronic devices for various applications require novel materials and new physical phenomena. For these purposes we propose to study new physical effects based on electron scattering on magnetic skyrmions and vortices distributed in a 2D ferromagnetic material. We show that the topological spin Hall effect can be efficiently employed for the filtering, switching, and separation of spin currents. For some values of the parameters (conduction electron concentrations, and skyrmion/vortex sizes) it is possible to separate Hall currents for different electron spin projections as it is like for different carrier charges (electrons and holes) in the normal Hall effect. The calculations are performed using the Boltzmann kinetic equation for the nonequilibrium distribution function and the Lippmann-Schwinger equation for the transition matrix in the whole range of the adiabaticity parameter. The spin filtering due to the skyrmion/vortex scattering can be several orders of magnitude more efficient in the narrow range of the electron concentrations than that of the ordinary ferromagnetic spin polarization in spintronics.

“Magic” Orientation Angles to Suppress Spin-Driven Hall Currents in Anisotropic 2D Materials with an Ideal Skyrmion Gas

“…In the previous investigations, the mechanism of the conduction electrons scattering in an ideal skyrmion gas resulted in the dramatic charge current dependencies on the concentration and spin projection of the conduction electrons and also on the skyrmion sizes. In particular, spin filtering and spin separation in the direction perpendicular to the electric field were found . In addition, thermoelectric devices can exhibit the abrupt voltage switching in the spin Seebeck and Nernst effects .…”

“…The mechanism of a spin-driven Hall effect is different from that of a charge Hall effect where a free electron deviates from its straight line trajectory due to the presence of a magnetic field or nonzero magnetic moments. The spin-driven Hall effect (SDHE) appears due to interaction of the conduction electrons with localized magnetic moment textures, skyrmions. − The schematic pictures for a skyrmion and electronic device are shown in Figure . The skyrmions are very specific spin arrangements with distinct topological properties characterized by topological charges. ,,− …”

“…The polar symmetry for both skyrmions and the electron gas significantly simplified both numerical solutions of the Lippmann–Schwinger equation for the transition matrix and the Boltzmann equation for the nonequilibrium distribution function. In that case, the direction of the electric field was irrelevant …”

“…In particular, spin filtering and spin separation in the direction perpendicular to the electric field were found. 27 In addition, thermoelectric devices can exhibit the abrupt voltage switching in the spin Seebeck and Nernst effects. 33 For the calculations of spin currents in the xand y-directions, we considered an isotropic material where the conduction electrons were presented as an ideal electron gas with an isotropic effective mass.…”

“…In that case, the direction of the electric field was irrelevant. 27 However, the orientation of a 2D anisotropic crystal can significantly change conduction electron scattering properties, revealing new unusual effects depending on the orientation angle. In this work, we assume that the skyrmions still have the polar symmetry while the electron gas is anisotropic, i.e., the effective masses in x-and y-directions are different, as schematically shown in Figure 2.…”