Shape-dependent exchange bias effect in magnetic nanoparticles with core-shell morphology

TL;DR

This study investigates how the shape and interface roughness of ferromagnetic core-antiferromagnetic shell nanoparticles influence the exchange bias effect, revealing shape-dependent magnetic properties and the impact of interface imperfections.

Contribution

It provides a detailed simulation-based analysis of shape and interface roughness effects on exchange bias in core-shell nanoparticles, highlighting the shape sensitivity and microstructural influence.

Findings

Cubes show higher coercivity than spheres of the same size.

Interface roughness reduces shape-dependent differences in magnetic properties.

Sensitivity of exchange bias to interface microstructure varies with particle shape.

Abstract

We study the low-temperature isothermal magnetic hysteresis of cubical and spherical nanoparticles with ferromagnetic (FM) core - antiferromagnetic (AF) shell morphology, in order to elucidate the sensitivity of the exchange bias effect to the shape of the particles and the structural imperfections at the core-shell interface. We model the magnetic structure using a classical Heisenberg Hamiltonian with uniaxial anisotropy and simulate the hysteresis loop using the Metropolis Monte Carlo algorithm. For nanoparticles with geometrically sharp interfaces, we find that cubes exhibit higher coercivity and lower exchange bias field than spheres of the same size. With increasing interface roughness, the shape-dependence of the characteristic fields gradually decays and eventually, the distinction between cubical and spherical particles is lost for moderately rough interfaces. The sensitivity of the exchange bias field to the microstructural details of the interface is quantified by a scaling factor (b) relating the bias field to the net moment of the AF shell (Heb = bMAF + Ho). Cubical particles exhibit lower sensitivity to the dispersed values of the net interfacial moment.