The critical Barkhausen avalanches in thin random-field ferromagnets with an open boundary

TL;DR

This study investigates how sample geometry influences critical Barkhausen avalanches in thin random-field ferromagnets, revealing size-dependent effects on noise signals, avalanche distributions, and multi-fractal properties during magnetization reversal.

Contribution

It introduces a numerical analysis of the impact of sample thickness on Barkhausen noise and avalanche scaling in random-field ferromagnets, bridging 2D and 3D behaviors.

Findings

Small thickness alters spectral segments and enhances multi-fractality.

Avalanche distributions show two distinct power-law regions.

Thicker samples' properties approach 3D critical behavior.

Abstract

The interplay between the critical fluctuations and the sample geometry is investigated numerically using thin random-field ferromagnets exhibiting the field-driven magnetisation reversal on the hysteresis loop. The system is studied along the theoretical critical line in the plane of random-field disorder and thickness. The thickness is varied to consider samples of various geometry between a two-dimensional plane and a complete three-dimensional lattice with an open boundary in the direction of the growing thickness. We perform a multi-fractal analysis of the Barkhausen noise signals and scaling of the critical avalanches of the domain wall motion. Our results reveal that, for sufficiently small thickness, the sample geometry profoundly affects the dynamics by modifying the spectral segments that represent small fluctuations and promoting the time-scale dependent multi-fractality. Meanwhile, the avalanche distributions display two distinct power-law regions, in contrast to those in the two-dimensional limit, and the average avalanche shapes are asymmetric. With increasing thickness, the scaling characteristics and the multi-fractal spectrum in thicker samples gradually approach the hysteresis loop criticality in three-dimensional systems. Thin ferromagnetic films are growing in importance technologically, and our results illustrate some new features of the domain wall dynamics induced by magnetisation reversal in these systems.