Model of bound interface dynamics for coupled magnetic domain walls

TL;DR

This paper develops a theoretical model for the dynamics of coupled magnetic domain walls in ultrathin ferromagnetic layers, predicting bound states and providing analytical velocity expressions that match experimental observations.

Contribution

It introduces a detailed, parameter-free theoretical framework for bound interface dynamics in coupled magnetic domain walls, extending previous experimental findings.

Findings

Bound creep state exists at zero magnetic field.

Analytical velocity expression matches experimental data.

Coupled domain walls can move together at the same speed.

Abstract

A domain wall in a ferromagnetic system will move under the action of an external magnetic field. Ultrathin Co layers sandwiched between Pt have been shown to be a suitable experimental realization of a weakly disordered 2D medium in which to study the dynamics of 1D interfaces (magnetic domain walls). The behavior of these systems is encapsulated in the velocity-field response v(H) of the domain walls. In a recent paper [P.J. Metaxas et al., Phys. Rev. Lett. 104, 237206 (2010)] we studied the effect of ferromagnetic coupling between two such ultrathin layers, each exhibiting different v(H) characteristics. The main result was the existence of bound states over finite-width field ranges, wherein walls in the two layers moved together at the same speed. Here, we discuss in detail the theory of domain wall dynamics in coupled systems. In particular, we show that a bound creep state is expected for vanishing H and we give the analytical, parameter free expression for its velocity which agrees well with experimental results.