Disorder-induced mechanism for positive exchange bias fields

TL;DR

This paper introduces a disorder-based mechanism for positive exchange bias in magnetic bilayers, explaining experimental observations through a domain wall formation at disordered interfaces during field cooling.

Contribution

It presents a novel disorder-induced explanation for positive exchange bias, supported by simulations and theoretical models, without assuming specific FM-AFM coupling.

Findings

Domain wall formation at disordered interfaces explains positive exchange bias.

The mechanism aligns with various experimental observations.

Supported by Monte Carlo, micromagnetic, and mean field analyses.

Abstract

We propose a mechanism to explain the phenomenon of positive exchange bias on magnetic bilayered systems. The mechanism is based on the formation of a domain wall at a disordered interface during field cooling (FC) which induces a symmetry breaking of the antiferromagnet, without relying on any ad hoc assumption about the coupling between the ferromagnetic (FM) and antiferromagnetic (AFM) layers. The domain wall is a result of the disorder at the interface between FM and AFM, which reduces the effective anisotropy in the region. We show that the proposed mechanism explains several known experimental facts within a single theoretical framework. This result is supported by Monte Carlo simulations on a microscopic Heisenberg model, by micromagnetic calculations at zero temperature and by mean field analysis of an effective Ising like phenomenological model.