Depinning of domain walls with an internal degree of freedom

TL;DR

This paper investigates how internal phase dynamics influence the depinning behavior of magnetic domain walls under weak pinning, revealing complex force-velocity characteristics and bistability phenomena.

Contribution

It introduces a model incorporating internal phase coupling into domain wall depinning analysis, uncovering novel bistable and non-monotonous behaviors not seen in standard models.

Findings

Bistable regimes at zero temperature with logarithmic transition behavior.

Multiple bistable transitions linked to topological phase modes.

Non-monotonous force-velocity curves at finite temperature.

Abstract

Taking into account the coupling between the position of the wall and an internal degree of freedom, namely its phase $\phi$, we examine, in the rigid wall approximation, the dynamics of a magnetic domain wall subject to a weak pinning potential. We determine the corresponding force-velocity characteristics, which display several unusual features when compared to standard depinning laws. At zero temperature, there exists a bistable regime for low forces, with a logarithmic behavior close to the transition. For weak pinning, there occurs a succession of bistable transitions corresponding to different topological modes of the phase evolution. At finite temperature, the force-velocity characteristics become non-monotonous. We compare our results to recent experiments on permalloy nanowires.