Local manipulation and reversal of the exchange bias field by ion irradiation in FeNi/FeMn double layers

Abstract

Both the direction and the strength of the exchange bias field ${H}_{\mathrm{eb}}$ of an FeNi/FeMn double layer are manipulated locally by He ion irradiation in an applied magnetic field. The magnitude of ${H}_{\mathrm{eb}}$ is enhanced over its initial value in the low ion dose regime. Above a threshold irradiation dose a reduction and eventually a suppression of ${H}_{\mathrm{eb}}$ is found. The direction of ${H}_{\mathrm{eb}}$ is initialized by the field direction during irradiation. These observations are discussed considering the structural modifications caused by the ion bombardment. The data are well described by a model, which is based on the competition between the enhancement of the exchange bias field strength due to defect creation in the antiferromagnetic layer and the decrease induced by intermixing at the ferromagnet/antiferromagnet interface.