Antiferromagnetic Barkhausen noise induced by weak random-field disorder

TL;DR

This paper numerically explores how weak random-field disorder influences magnetisation reversal and Barkhausen noise in three-dimensional antiferromagnetic models, revealing unique avalanche behaviors and scale invariance linked to self-organised criticality.

Contribution

It uncovers the distinct structure and dynamics of Barkhausen noise in antiferromagnets with weak disorder, differing from ferromagnetic systems, and links these phenomena to self-organised criticality.

Findings

Observation of step-wise hysteresis and triangular magnetisation bursts.

Identification of disorder-dependent multifractal fluctuations and scale invariance.

Demonstration of avalanche activity linked to self-organised critical dynamics.

Abstract

This study numerically investigates magnetisation reversal processes driven by an external magnetic field in three-dimensional antiferromagnetic spin models with weak random field disorder. Considering an extremely weak disorder and low temperature, we observe a step-wise hysteresis loop and the appearance of short magnetisation bursts of a characteristic triangular shape; the number of bursts increases with disorder, indicative of Barkhausen-type noise. These phenomena are attributed to the simultaneous reversal at a given external field of segments composed of spins with identical neighbourhoods. A local random field orients one or more spin neighbours, resulting in small, ferromagnetic-like clusters distributed throughout the system. As disorder increases, these clusters may merge to form a labyrinthine structure within the antiferromagnetic background, facilitating brief avalanche propagation. The results demonstrate that, compared with familiar random-field ferromagnets, the observed antiferromagnetic Barkhausen noise and the related avalanche sequence have a profoundly different structure, organised into peaks associated with the transition between magnetisation plateaus. They exhibit prominent cyclical trends and disorder-dependent multifractal fluctuations, with the singularity spectrum quantifying the degree of disorder. The activity avalanches exhibit scale invariance resembling that recently found in experiments with disordered ferr\textit{i}magnets and martensites, as well as in quantum Barkhausen noise, which are associated with active geometric regions rather than individual-spin dynamics. The observed scaling behaviour is interpreted in terms of self-organised critical dynamics.