Current-Induced Torques in Magnetic Metals: Beyond Spin Transfer

TL;DR

This paper reviews a microscopic perspective on current-induced torques in magnetic metals, emphasizing their applicability beyond spin conservation, including effects on antiferromagnetic order parameters.

Contribution

It introduces a novel microscopic framework for understanding current-induced torques that applies to systems lacking spin conservation, such as antiferromagnets.

Findings

Current-induced torques can act on antiferromagnetic order parameters.

The microscopic picture is applicable to systems without conserved spin.

This approach broadens the understanding of spintronic effects in complex magnetic systems.

Abstract

Current-induced torques on ferromagnetic nanoparticles and on domain walls in ferromagnetic nanowires are normally understood in terms of transfer of conserved spin angular momentum between spin-polarized currents and the magnetic condensate. In a series of recent articles we have discussed a microscopic picture of current-induced torques in which they are viewed as following from exchange fields produced by the misaligned spins of current carrying quasiparticles. This picture has the advantage that it can be applied to systems in which spin is not approximately conserved. More importantly, this point of view makes it clear that current-induced torques can also act on the order parameter of an antiferromagnetic metal, even though this quantity is not related to total spin. In this informal and intentionally provocative review we explain this picture and discuss its application to antiferromagnets.