Thermopower and Thermally Induced Domain Wall Motion in (Ga,Mn)As

TL;DR

This paper investigates thermally induced domain wall motion and heat pumping in (Ga,Mn)As, revealing significant thermal spin transfer effects and practical domain wall velocities under temperature gradients.

Contribution

It introduces the effective thermal spin transfer torque parameter and predicts domain wall motion speeds and heat pumping effects in (Ga,Mn)As.

Findings

Effective thermal spin transfer torque parameter is of order unity.

Domain walls can move at 10 m/s in 10 K/μm temperature gradients.

Seebeck coefficient is 100-500 μV/K at 10 K, matching experiments.

Abstract

We study two reciprocal thermal effects in the ferromagnetic semiconductor (Ga,Mn)As by scattering theory: domain wall motion induced by a temperature gradient as well as heat currents pumped by a moving domain wall. The effective out-of-plane thermal spin transfer torque parameter $P_Q \beta_{Q}$, which governs the coupling between heat currents and a magnetic texture, is found to be of the order of unity. Unpinned domain walls are predicted to move at speed 10 m/s in temperature gradients of the order 10 ${\rm K/ \mu m}$. The cooling power of a moving domain wall only compensates the heating due to friction losses at ultra-low domain wall velocities of about 0.07 m/s. The Seebeck coefficient is found to be of the order 100-500 ${\rm \mu V / K}$ at T=10 K, in good agreement with recent experiment.