Intrinsic Spin Torque Without Spin-Orbit Coupling

TL;DR

This paper introduces an intrinsic non-adiabatic spin torque mechanism that arises from electric-field perturbations of electronic states, independent of spin-orbit coupling or extrinsic relaxation, and can dominate in certain models.

Contribution

It derives a new intrinsic spin torque contribution that is electric-field-induced and distinct from previous current-induced or spin-orbit-based mechanisms.

Findings

The intrinsic torque does not depend on electron state occupation changes.

It can be the dominant non-adiabatic torque in some models.

It is related to the Berry phase spin-orbit torque in Rashba systems.

Abstract

We derive an intrinsic contribution to the non-adiabatic spin torque for non-uniform magnetic textures. It differs from previously considered contributions in several ways and can be the dominant contribution in some models. It does not depend on the change in occupation of the electron states due to the current flow but rather is due to the perturbation of the electronic states when an electric field is applied. Therefore it should be viewed as electric-field-induced rather than current-induced. Unlike previously reported non-adiabatic spin torques, it does not originate from extrinsic relaxation mechanisms nor spin-orbit coupling. This intrinsic non-adiabatic spin torque is related by a chiral connection to the intrinsic spin-orbit torque that has been calculated from the Berry phase for Rashba systems.