Propelling Ferrimagnetic Domain Walls by Dynamical Frustration

TL;DR

This paper demonstrates that ferrimagnetic domain walls can self-propel under weak oscillating magnetic fields due to dynamical frustration, leading to rapid growth of magnetic correlations and resilience to noise, resembling active matter systems.

Contribution

It introduces a novel mechanism where dynamical frustration induces active motion of domain walls in ferrimagnets, a phenomenon not previously reported.

Findings

Domain walls move actively in a preferred direction due to dynamical frustration.

Magnetic correlation length grows linearly over time, faster than in equilibrium.

System exhibits high resilience to noise, with larger correlation lengths than equilibrium counterparts.

Abstract

Many-particle systems driven out of thermal equilibrium can show properties qualitatively different from any thermal state. Here, we study a ferrimagnet in a weak oscillating magnetic field. In this model, domain walls are not static, but are shown to move actively in a direction chosen by spontaneous symmetry breaking. Thus they act like self-propelling units. Their collective behaviour is reminiscent of other systems with actively moving units studied in the field of 'active matter', where, e.g., flocks of birds are investigated. The active motion of the domain walls emerges from 'dynamical frustration'. The antiferromagnetic xy-order rotates clockwise or anticlockwise, determined by the sign of the ferromagnetic component. This necessarily leads to frustration at a domain wall, which gets resolved by propelling the domain wall with a velocity proportional to the square root of the driving power across large parameter regimes. This motion and strong hydrodynamic interactions lead to a linear growth of the magnetic correlation length over time, much faster than in equilibrium. The dynamical frustration furthermore makes the system highly resilient to noise. The correlation length of the weakly driven one-dimensional system can be orders of magnitude larger than in the corresponding equilibrium system with the same noise level.