Intrinsic torques emerging from anomalous velocity in magnetic textures

TL;DR

This paper links band topology to intrinsic torques in magnetic textures, introducing the topological Hall torque (THT) that arises from anomalous velocity and is observable in bulk materials without interfaces.

Contribution

It classifies intrinsic torques phenomenologically and identifies the topological Hall torque as a new intrinsic effect arising from electron band topology in magnetic textures.

Findings

THT is an intrinsic torque arising from band topology.

Numerical demonstration shows THT surpasses conventional spin-transfer torque.

Giant current-induced torque observed in ferromagnetic SrRuO3 can be explained by THT.

Abstract

Momentum-space topology of electrons under strong spin-orbit coupling contributes to the electrically induced torques exerting on magnetic textures insensitively to disorder or thermal fluctuation. We present a direct connection between band topology and the torques by classifying the whole torques phenomenologically. As well as the intrinsic anomalous Hall effect, the torques also emerge intrinsically from the anomalous velocity of electrons regardless of a nonequilibrium transport current. We especially point out the intrinsic contribution arising exclusively in magnetic textures, which we call the "topological Hall torque (THT)." The THT emerges in bulk crystals without any interface or surface structures. We numerically demonstrate the enhancement of the THT in comparison with the conventional spin-transfer torque in the bulk metallic ferromagnet, which accounts for the giant current-induced torque measured in ferromagnetic SrRuO3.