Thermally activated reversal of the antiferromagnet in exchange biased IrMn/CoFe bilayers

Abstract Thermally activated reversal of the antiferromagnet (AFM) in exchange biased bilayers plays an important role in determining the magnetic characteristics of the bilayer. Bulk magnetometry measurements of these effects are difficult to make because the AFM has zero macroscopic magnetic moment and, therefore, changes in the AFM have to be inferred from the behaviour of the pinned ferromagnet layer. By making careful measurements of hysteresis loops on IrMn( X A)/CoFe(100 A) ( X =50,70,100) bilayers, the time-dependent behaviour of the AFM has been illustrated. We show that the reversal in the AFM is governed by one of two mechanisms, which are responsible for the increased coercivity seen in the bilayers. We also show that the reversal is dependent upon the thickness of the AFM layer.