Microscopic origin of exchange bias in core/shell nanoparticles

TL;DR

This study uses Monte Carlo simulations to uncover the microscopic mechanisms behind exchange bias in core/shell nanoparticles, linking interfacial spin behavior to macroscopic magnetic properties.

Contribution

It provides a detailed microscopic explanation for exchange bias, emphasizing the role of uncompensated interfacial spins and their impact on hysteresis loop asymmetry.

Findings

Exchange coupling increases enhance exchange bias.

Uncompensated interfacial spins cause loop asymmetry.

Microscopic parameters accurately predict macroscopic loop shifts.

Abstract

We report the results of Monte Carlo simulations with the aim to clarify the microscopic origin of exchange bias in the magnetization hysteresis loops of a model of individual core/shell nanoparticles. Increase of the exchange coupling across the core/shell interface leads to an enhancement of exchange bias and to an increasing asymmetry between the two branches of the loops which is due to different reversal mechanisms. A detailed study of the magnetic order of the interfacial spins shows compelling evidence that the existence of a net magnetization due to uncompensated spins at the shell interface is responsible for both phenomena and allows to quantify the loop shifts directly in terms of microscopic parameters with striking agreement with the macroscopic observed values.