Crystal Structure Manipulation of the Exchange Bias in an Antiferromagnetic Film

TL;DR

This study demonstrates how manipulating the crystal structure of epitaxial Cr2O3 films can control the direction of exchange bias in ferromagnet/antiferromagnet heterostructures, which is crucial for magnetic device applications.

Contribution

It introduces a method to tune exchange bias orientation via crystal structure control in epitaxial Cr2O3 films, unlike in polycrystalline films.

Findings

Exchange bias can be tuned from out-of-plane to in-plane.

Epitaxial growth enables highly anisotropic exchange bias.

Collinear exchange coupling is responsible for the observed effects.

Abstract

Exchange bias is one of the most extensively studied phenomena in magnetism, since it exerts a unidirectional anisotropy to a ferromagnet (FM) when coupled to an antiferromagnet (AFM) and the control of the exchange bias is therefore very important for technological applications, such as magnetic random access memory and giant magnetoresistance sensors. In this letter, we report the crystal structure manipulation of the exchange bias in epitaxial hcp Cr2O3 films. By epitaxially growing twined (10-10) oriented Cr2O3 thin films, of which the c axis and spins of the Cr atoms lie in the film plane, we demonstrate that the exchange bias between Cr2O3 and an adjacent permalloy layer is tuned to in-plane from out-of-plane that has been observed in (0001) oriented Cr2O3 films. This is owing to the collinear exchange coupling between the spins of the Cr atoms and the adjacent FM layer. Such a highly anisotropic exchange bias phenomenon is not possible in polycrystalline films.