Critical Hysteresis from Random Anisotropy

TL;DR

This paper explores critical hysteresis in ferromagnets with random anisotropies, revealing various universality classes and the role of uniaxial anisotropy as a tuning parameter, which may explain experimental discrepancies.

Contribution

It introduces a spin model with random anisotropies to analyze critical hysteresis, highlighting the importance of metastability and anisotropy tensorial nature, and identifies new universality classes.

Findings

Random field Ising criticality is common.

Proximity to $ ext{O}(N)$ criticality affects behavior.

Uniaxial anisotropy can be tuned via applied stress.

Abstract

Critical hysteresis in ferromagnets is investigated through a $N$-component spin model with random anisotropies, more prevalent experimentally than the random fields used in most theoretical studies. Metastability, and the tensorial nature of anisotropy, dictate its physics. Generically, random field Ising criticality occurs, but other universality classes exist. In particular, proximity to $\mathcal{O}(N)$ criticality may explain the discrepancy between experiment and earlier theories. The uniaxial anisotropy constant, which can be controlled in magnetostrictive materials by an applied stress, emerges as a natural tuning parameter.