Magnetic domain wall motion in a nanowire: depinning and creep

TL;DR

This paper theoretically investigates how weak driving forces, including magnetic fields and currents with spin transfer torques, influence magnetic domain wall depinning and creep in nanowires, considering thermal effects and spin-orbit coupling.

Contribution

It provides a detailed analysis of the separate effects of adiabatic and nonadiabatic spin transfer torques on domain wall motion, highlighting corrections important for experimental interpretation.

Findings

Adiabatic spin transfer torque induces significant corrections to domain wall dynamics.

Neglecting these corrections can lead to misestimating the nonadiabaticity parameter.

Rashba spin-orbit coupling effects are also analyzed in the context of domain wall motion.

Abstract

The domain wall motion in a magnetic nanowire is examined theoretically in the regime where the domain wall driving force is weak and its competition against disorders is assisted by thermal agitations. Two types of driving forces are considered; magnetic field and current. While the field induces the domain wall motion through the Zeeman energy, the current induces the domain wall motion by generating the spin transfer torque, of which effects in this regime remain controversial. The spin transfer torque has two mutually orthogonal vector components, the adiabatic spin transfer torque and the nonadiabatic spin transfer torque. We investigate separate effects of the two components on the domain wall depinning rate in one-dimensional systems and on the domain wall creep velocity in two-dimensional systems, both below the Walker breakdown threshold. In addition to the leading order contribution coming from the field and/or the nonadiabatic spin transfer torque, we find that the adiabatic spin transfer torque generates corrections, which can be of relevance for an unambiguous analysis of experimental results. For instance, it is demonstrated that the neglect of the corrections in experimental analysis may lead to incorrect evaluation of the nonadiabaticity parameter. Effects of the Rashba spin-orbit coupling on the domain wall motion are also analyzed.