Enhancement of exchange bias in ferromagnetic/antiferromagnetic core-shell nanoparticles through ferromagnetic domain wall formation

TL;DR

This study uses Monte Carlo simulations to explore how ferromagnetic domain wall formation influences exchange bias in core-shell nanoparticles, revealing new ways to optimize their magnetic properties for technological applications.

Contribution

It demonstrates how controlling domain wall formation and ferromagnetic parameters can enhance exchange bias, challenging traditional models and offering new optimization strategies.

Findings

Exchange bias shows anomalous dependence on uniaxial anisotropy in weak coupling systems.

Domain walls form near the interface and propagate in the ferromagnetic core.

Magnetization reversal asymmetry reduces coercive field and enhances exchange bias.

Abstract

The spin configuration in the ferromagnetic part during the magnetization reversal plays a crucial role in the exchange bias effect. Through Monte Carlo simulation, the exchange bias effect in ferromagnetic-antiferromagnetic core-shell nanoparticles is investigated. Magnetization reversals in the ferromagnetic core were controlled between the coherent rotation and the domain wall motion by modulating ferromagnetic domain wall width with parameters of uniaxial anisotropy constant and exchange coupling strength. An anomalous monotonic dependence of exchange bias on the uniaxial anisotropy constant is found in systems with small exchange coupling, showing an obvious violation of classic Meiklejohn-Bean model, while domain walls are found to form close to the interface and propagate in the ferromagnetic core with larger uniaxial anisotropy in both branches of the hysteresis. The asymmetric magnetization reversal with the formation of a spherical domain wall dramatically reduces the coercive field in the ascending branch, leading to the enhancement of the exchange bias. The results provide another degree of freedom to optimize the magnetic properties of magnetic nanoparticles for applications.