Spin-Transfer Torques in Helimagnets

TL;DR

This paper theoretically explores how spin-orbit coupling-induced reactive spin-transfer torque, governed by crystal symmetry, influences magnetization dynamics in chiral-lattice helimagnets, affecting spin-spiral motion and spin wave behavior.

Contribution

It introduces a previously unconsidered reactive spin-transfer torque in non-centrosymmetric helimagnets and analyzes its effects on magnetic dynamics.

Findings

The new torque acts as an effective magnetic field along the current direction.

It tilts the spin-spiral structure during current-induced motion.

The spin wave dispersion remains unaffected by the new torque.

Abstract

We theoretically investigate current-induced magnetization dynamics in chiral-lattice helimagnets. Spin-orbit coupling in non-centrosymmetric crystals induces a reactive spin-transfer torque that has not been previously considered. We demonstrate how the torque is governed by the crystal symmetry and acts as an effective magnetic field along the current direction in cubic B20-type crystals. The effects of the new torque are computed for current-induced dynamics of spin-spirals and the Doppler shift of spin waves. In current-induced spin-spiral motion, the new torque tilts the spiral structure. The spin waves of the spiral structure are initially displaced by the new torque, while the dispersion relation is unaffected.