Depinning exponents of thin film domain walls depend on disorder strength

TL;DR

This paper models domain wall depinning in disordered thin films, revealing that depinning exponents depend on disorder strength and internal magnetization excitations, with implications for magnetic material behavior.

Contribution

It introduces a new model capturing internal degrees of freedom of domain walls and demonstrates how disorder strength influences depinning exponents.

Findings

Weak disorder yields exponents similar to quenched Edwards-Wilkinson model.

Stronger disorder causes disorder-dependent exponents.

Increased disorder leads to nucleation of Bloch lines within domain walls.

Abstract

Domain wall dynamics in ferromagnets is complicated by internal degrees of freedom of the domain walls. We develop a model of domain walls in disordered thin films with perpendicular magnetic anisotropy capturing such features, and use it to study the depinning transition. For weak disorder, excitations of the internal magnetization are rare, and the depinning transition takes on exponent values of the quenched Edwards-Wilkinson equation. Stronger disorder results in disorder-dependent exponents concurrently with nucleation of an increasing density of Bloch lines within the domain wall.