Exchange bias phenomenology and models of core/shell nanoparticles

TL;DR

This paper reviews exchange bias phenomena in core/shell nanoparticles, compares experimental observations with existing models, and presents simulations that provide microscopic insights into the effects, matching experimental results.

Contribution

It introduces a simple, tunable model for core/shell nanoparticles that explains exchange bias phenomenology and aligns well with experimental data.

Findings

Simulations reproduce key experimental exchange bias effects.

Interfacial spin order significantly influences magnetic behavior.

Model quantifies loop shifts consistent with observations.

Abstract

Some of the main experimental observations related to the occurrence of exchange bias in magnetic systems are reviewed, focusing the attention on the peculiar phenomenology associated to nanoparticles with core/shell structure as compared to thin film bilayers. The main open questions posed by the experimental observations are presented and contrasted to existing theories and models for exchange bias formulated up to date. We also present results of simulations based on a simple model of a core/shell nanoparticle in which the values of microscopic parameters such as anisotropy and exchange constants can be tuned in the core, shell and at the interfacial regions, offering new insight on the microscopic origin of the experimental phenomenology. A detailed study of the of the magnetic order of the interfacial spins shows compelling evidence that most of the experimentally observed effects can be qualitatively accounted within the context of this model and allows also to quantify the magnitude of the loop shifts with striking agreement with the macroscopic observed values.