Magnetic avalanches in granular ferromagnets: Thermal activated collective behavior

TL;DR

This study uses large-scale simulations to explore how thermal activation causes collective magnetic avalanches in granular ferromagnets, revealing critical behavior linked to percolation theory and dissipation effects.

Contribution

It introduces a microscopic reaction-diffusion simulation model for thermal avalanche dynamics in granular ferromagnets, highlighting the role of dissipation-controlled criticality.

Findings

Avalanche behavior is governed by a percolation transition.

Thermal activation induces collective inter-granular magnetization dynamics.

Criticality falls within the 3D percolation universality class.

Abstract

We present a numerical study on the thermal activated avalanche dynamics in granular materials composed of ferromagnetic clusters embedded in a non-magnetic matrix. A microscopic dynamical simulation based on the reaction-diffusion process is developed to modeling the magnetization process of such systems. The large-scale simulations presented here explicitly demonstrate inter-granular collective behavior induced by thermal activation of spin tunneling. In particular, we observe an intriguing criticality controlled by the rate of energy dissipation. We show that thermal activated avalanches can be understood in the framework of continuum percolation and the emergent dissipation induced criticality is in the universality class of three-dimensional percolation transition. Implications of these results to the phase-separated states of colossal magnetoresistance materials and other artificial granular magnetic systems are also~discussed.