Training Effect and Hysteretic Behaviour of Angular Dependence of Exchange Bias in Co/IrMn Bilayers

The training effect and the hysteresis behaviour of the angular dependence of exchange bias are extensively investigated upon the variation of the IrMn layer thickness t_IrMn in a series of Co/IrMn bilayers. When t_IrMn is very small, both of them are negligible. Then they increase very sharply with increasing t_IrMn and then reach maxima at almost the same value of t_IrMn. Finally they both decrease when t_IrMn is further increased. The similar variation trends suggest that these phenomena arise from irreversible change of antiferromagnet spin orientations, according to the thermal activation model.