Polycrystalline exchange-biased bilayers: magnetically effective vs. structural antiferromagnetic grain volume distribution

TL;DR

This paper demonstrates a method to determine the distribution of magnetically active grain sizes in polycrystalline exchange-biased bilayers using vectorial Kerr magnetometry, revealing that magnetic activity extends over only part of the structural grains.

Contribution

It introduces a non-destructive approach to estimate microscopic magnetic parameters from macroscopic measurements, focusing on the effective grain size distribution relevant for exchange bias.

Findings

Magnetically active grain size distribution differs from structural distribution.

Magnetic order extends over only part of the structural grain volume.

Method enables non-destructive characterization of magnetic grain properties.

Abstract

The magnetic characteristics of polycrystalline exchange-biased antiferromagnet/ferromagnet-bilayers are determined by a complex interplay of parameters, describing structural and magnetic properties of the material system, including in particular the grain volume distribution of the antiferromagnet. An ideal characterization of such systems would be a non-destructive determination of the relevant parameters for each individual grain. This is in most cases not feasible, since typical characterization methods do average over larger areas. Here, we show that it is however possible to determine averaged microscopic parameters from averaged macroscopic magnetic quantities measured by vectorial Kerr magnetometry in comparison to an elaborate model. In particular, we estimate the magnetically effective antiferromagnetic grain size distribution, being essential for the interface exchange coupling to the ferromagnetic layer. We found that the distribution of magnetically active grain sizes differs from the structural one, indicating that the antiferromagnetic order, relevant for the exchange bias, extends only over a part of the grains' structural volumes.