Interdependence of reversal asymmetry and training effect in Ir22Mn78/Ni81Fe19 bilayers probed with magnetoresistance

Abstract

Using magnetoresistance as a probe we demonstrate the correlation between reversal asymmetry and training effect in ion-beam sputtered IrMn/NiFe bilayers. During the training procedure, both exchange bias field and the degree of asymmetry decrease monotonically following a very similar trend. The analysis of the magnetoresistance behaviour establishes that the two distinct training mechanisms are operative. The first one is exhibited by an abrupt single cycle training effect and an accompanying pronounced reversal asymmetry, attributed to the presence of biaxial anisotropy in the IrMn layer. The second one displays a gradual cycling dependence due to thermal depinning of uncompensated antiferromagnetic spins.