Landau-Lifshitz theory of the thermomagnonic torque

TL;DR

This paper derives a comprehensive thermomagnonic torque model for magnetic textures under temperature gradients, combining entropic and magnon flow effects, and analyzes their impact on domain-wall motion.

Contribution

It introduces a unified derivation of entropic and spin-transfer thermomagnonic torques within the stochastic Landau-Lifshitz-Gilbert framework, highlighting their opposite signs and effects.

Findings

Entropic torque causes domain walls to move toward hotter regions.

Dissipative components of the two torques share similar structure but have opposite signs.

The entropic torque is twice as large as the spin-transfer torque.

Abstract

We derive the thermomagnonic torque associated with smooth magnetic textures subjected to a temperature gradient, in the framework of the stochastic Landau-Lifshitz-Gilbert equation. Our approach captures on equal footing two distinct contributions: (1) A local entropic torque that is caused by a temperature dependence of the effective exchange field, the existence of which had been previously suggested based on numerics and (2) the well-known spin-transfer torque induced by thermally-induced magnon flow. The dissipative components of two torques have the same structure, following a common phenomenology, but opposite signs, with the twice larger entropic torque leading to a domain-wall motion toward the hotter region. We compare the efficiency of the torque-driven domain-wall motion with the recently proposed Brownian thermophoresis.