Reversing the training effect in exchange biased CoO/Co bilayers

TL;DR

This study investigates the training effect in exchange biased CoO/Co bilayers, revealing how magnetic domains nucleate and can be partially erased, affecting magnetization behavior and offering insights into magnetic domain control.

Contribution

It demonstrates that the untrained state can be partially reinduced by specific hysteresis measurements, showing a new way to manipulate antiferromagnetic domains.

Findings

Magnetic domain nucleation occurs during initial magnetization reversal.

Partial erasure of antiferromagnetic domains is possible with perpendicular field measurements.

The untrained state can be reinduced, altering the hysteresis loop characteristics.

Abstract

We performed a detailed study of the training effect in exchange biased CoO/Co bilayers. High-resolution measurements of the anisotropic magnetoresistance (AMR) are consistent with nucleation of magnetic domains in the antiferromagnetic CoO layer during the first magnetization reversal. This accounts for the enhanced spin rotation observed in the ferromagnetic Co layer for all subsequent reversals. Surprisingly, the AMR measurements as well as magnetization measurements reveal that it is possible to partially reinduce the untrained state by performing a hysteresis measurement with an in plane external field perpendicular to the cooling field. Indeed, the next hysteresis loop obtained in a field parallel to the cooling field resembles the initial asymmetric hysteresis loop, but with a reduced amount of spin rotation occurring at the first coercive field. This implies that the antiferromagnetic domains, which are created during the first reversal after cooling, can be partially erased.