Thermal simulation of magnetization reversals for size-distributed assemblies of core-shell exchange biased nanoparticles

TL;DR

This paper presents a temperature-dependent model for magnetization reversal in size-distributed ferromagnetic and core-shell nanoparticles, revealing complex thermal and angular behaviors influenced by size distribution and exchange coupling.

Contribution

It introduces a novel thermal fluctuation model for size-distributed nanoparticles, capturing asymmetric and non-monotonic magnetization reversal behaviors.

Findings

Temperature affects coercive and exchange-bias fields complexly.

Size distribution causes asymmetric magnetization reversal.

Angular dependence shows T-dependent apex behavior.

Abstract

A temperature dependent coherent magnetization reversal model is proposed for size-distributed assemblies of ferromagnetic nanoparticles and ferromagnetic-antiferromagnetic core-shell nanoparticles. The nanoparticles are assumed to be of uniaxial anisotropy and all aligned along their easy axis. The thermal dependence is included by considering thermal fluctuations, implemented via the N\'eel-Arrhenius theory. Thermal and angular dependence of magnetization reversal loops, coercive field and exchange-bias field are obtained, showing that F-AF size-distributed exchange-coupled nanoparticles exhibit temperature-dependent asymmetric magnetization reversal. Also, non-monotonic evolutions of He and Hc with T are demonstrated. The angular dependence of Hc with T exhibits a complex behavior, with the presence of an apex, whose position and amplitude are strongly T dependent. The angular dependence of He with T exhibits complex behaviors, which depends on the AF anisotropy and exchange coupling. The resulting angular behavior demonstrates the key role of the size distribution and temperature in the magnetic response of nanoparticles.