Exchange bias effect in cylindrical nanowires with ferromagnetic core and polycrystalline antiferromagnetic shell

TL;DR

This study models the exchange bias effect in cylindrical nanowires with a ferromagnetic core and polycrystalline antiferromagnetic shell, revealing how shell polycrystallinity influences magnetic properties and aligns with experimental findings.

Contribution

It introduces a Monte Carlo simulation approach to analyze the impact of shell polycrystallinity on exchange bias in nanowires, extending the Stoner-Wohlfarth model.

Findings

Polycrystallinity enhances exchange bias in off-axis directions.

Shell structure affects coercivity and hysteresis loop characteristics.

Results align qualitatively with experimental Co/CoO nanowire data.

Abstract

We model the exchange bias effect in thin cylindrical nanowires composed of a ferromagnetic core and an antiferromagnetic shell implementing a classical spin Hamiltonian and Monte Carlo simulations. We address systematically the effect of shell polycrystallinity on the characteristic fields of the isothermal hysteresis loop (coercivity, exchange-bias) and their angular dependence upon the direction of the applied / cooling field. We relate the observed trends to modifications of the underlying magnetization reversal mechanism. We fit our simulation results to an extended Stoner-Wohlfarth model with effective off-axis unidirectional anisotropy and demonstrate that shell polycrystallinity could lead to maximum exchange bias effect in an off-axis direction. Our results are in qualitative agreement with recent experimental studies of Co/CoO nanowires.