Deterministic roughening in the dc-driven precessional regime of domain walls

TL;DR

This paper investigates the deterministic instabilities and roughening phenomena in domain walls driven by magnetic fields, revealing a universal spectral stability diagram and a phase transition to a rough phase.

Contribution

It introduces a collective-coordinate model and simulations that identify a universal instability diagram and characterize the transition to roughening in domain walls.

Findings

Flat domain walls become unstable above the Walker breakdown field.

Large domain walls develop spatiotemporal chaos and Bloch-line dynamics.

A dynamical phase transition from flat to rough phase occurs at a critical field.

Abstract

We numerically study the dynamics of extended domain walls in homogeneous ferromagnets driven by a uniform magnetic field at zero temperature. Using both micromagnetic Landau-Lifshitz-Gilbert simulations and a collective-coordinate description, we show that flat chiral domain walls become linearly unstable above the Walker breakdown field and below a higher threshold, provided their length exceeds a characteristic scale. This instability is captured by a quasi-universal spectral stability diagram, parameterized solely by the Gilbert damping, which predicts the onset of deviations from rigid-wall behavior. Beyond the linear regime, large domain walls with bands of unstable modes develop spatiotemporal chaos, intricate Bloch-line dynamics, and deterministic roughening. At a critical field, the system undergoes a dynamical phase transition from a flat to a rough moving phase with universal features. Our results provide a framework for addressing domain-wall dynamics in the presence of thermal fluctuations and quenched disorder by disentangling their effects from intrinsic deterministic instabilities.