Temperature gradient-driven motion of magnetic domains in a magnetic metal multilayer by entropic forces

TL;DR

This study demonstrates that magnetic domains in multilayer tracks move towards heat sources primarily due to entropic forces induced by temperature gradients, with motion quantified up to 1 nm/s.

Contribution

It provides experimental evidence that entropic forces dominate magnetic domain motion under temperature gradients in multilayer structures, surpassing spin Seebeck effects.

Findings

Domains move towards heaters with increasing thermal gradient.

Maximum observed domain velocity is around 1 nm/s at 20 K/μm gradient.

Entropic forces are the primary driver of domain displacement, not spin Seebeck effects.

Abstract

We studied the displacement of magnetic domains under temperature gradients in perpendicularly magnetized Ta/[Pt/Co$_{68}$B$_{32}$/Ir]$_{\times 10}$/Pt multilayer tracks with microfabricated Pt heaters/thermometers by magnetic force microscopy (MFM). Subtracting out the effects of the Oersted field from the heating current reveals the pure temperature gradient-driven motion, which is always towards the heater. The higher the thermal gradient along the track (owing to proximity to the heater or larger heater currents), the greater the observed displacements of the domains, up to a velocity of around 1~nm/s in a temperature gradient of 20~K/$\mu$m. Quantitative estimates of the strength of different driving mechanisms show that entropic forces dominate over those arising from the spin Seebeck and spin-dependent Seebeck effects.