Spin Hall and spin swapping torques in diffusive ferromagnets

TL;DR

This paper derives comprehensive drift-diffusion equations for charge and spin dynamics in ferromagnets with spin-orbit coupling, revealing complex effects like spin swapping and novel torque generation mechanisms.

Contribution

It introduces a complete set of generalized equations capturing major spin transport phenomena, including spin swapping, in ferromagnets with extrinsic spin-orbit coupling.

Findings

Spin swapping effect is enhanced by spin polarization.

Complex spin textures can generate torques without external polarizers.

The equations unify multiple spin transport phenomena in ferromagnets.

Abstract

A complete set of the generalized drift-diffusion equations for a coupled charge and spin dynamics in ferromagnets in the presence of extrinsic spin-orbit coupling is derived from the quantum kinetic approach, covering major transport phenomena, such as the spin and anomalous Hall effects, spin swapping, spin precession and relaxation processes. We argue that the spin swapping effect in ferromagnets is enhanced due to spin polarization, while the overall spin texture induced by the interplay of spin-orbital and spin precessional effects displays a complex spatial dependence that can be exploited to generate torques and nucleate/propagate domain walls in centrosymmetric geometries without use of external polarizers, as opposed to the conventional understanding of spin-orbit mediated torques.