Current-induced torques in the presence of spin-orbit coupling

TL;DR

This paper explores how strong spin-orbit coupling alters the relationship between spin-transfer torques, angular momentum currents, and mechanical torques, revealing persistent torques and interface effects in ferromagnetic systems.

Contribution

It generalizes the relationship between spin-transfer torque and spin current divergence to include total angular momentum and mechanical torques in systems with strong spin-orbit coupling.

Findings

Persistent spin transfer torque in spin valves.

Mechanical torque at ferromagnetic-nonmagnetic interfaces.

Modification of spin torque behavior in ferromagnetic semiconductors.

Abstract

In systems with strong spin-orbit coupling, the relationship between spin-transfer torque and the divergence of the spin current is generalized to a relation between spin transfer torques, total angular momentum current, and mechanical torques. In ferromagnetic semiconductors, where the spin-orbit coupling is large, these considerations modify the behavior of the spin transfer torques. One example is a persistent spin transfer torque in a spin valve: the spin transfer torque does not decay away from the interface, but approaches a constant value. A second example is a mechanical torque at single ferromagnetic-nonmagnetic interface.