Universality of thermally assisted magnetic domain wall motion under spin torque

TL;DR

This paper theoretically demonstrates that thermally assisted magnetic domain wall motion driven by spin torque exhibits a universal exponential dependence on spin current, independent of material specifics, at low temperatures.

Contribution

It reveals a universal linear relation in the logarithm of velocity versus spin current over temperature, confirming the spin torque as the driving mechanism.

Findings

Wall velocity depends exponentially on spin current below threshold.

The linear term in spin current is universal and independent of material constants.

The behavior can be used to experimentally confirm spin torque as the driving force.

Abstract

Thermally assisted motion of magnetic domain wall under spin torque is studied theoretically. It is shown that the wall velocity $v$ depends exponentially on the spin current, $\Is$, below the threshold value, in the same way as in a thermally activated motion driven by a force. A novel property of the spin torque driven case at low temperature is that the linear term in spin current is universal, i.e., $\ln v \sim \frac{\pi\hbar}{2e}(\Is/\kB T)$. This behavior, which is independent of pinning and material constants, could be used to confirm experimentally the spin torque as the driving mechanism.