Asymmetric magnetic disorder observed in thermally activated magnetization reversal of exchange-biased IrMn/CoFe films

We report an asymmetry of magnetic disorder in exchange-biased IrMn(tIrMn=5–20 nm)/CoFe(50 nm) films observed by means of a Kerr microscope, capable of direct domain observation. From the correlation between the magnetization half-reversal time and applied magnetic field, we find that the magnetization switching in all the films occurs via a thermally activated reversal mechanism for both branches of hysteresis loops. Surprisingly, in the forward branch reversal where the applied magnetic field is antiparallel to the direction of exchange-bias field, degree of magnetic disorder decreases as exchange-bias field increases, which is definitely contrasted with the case of backward branch reversal. This result is likely ascribed to the fact that the local values of exchange-bias field and coercive field are oppositely fluctuating with each other in the film. - Highlights: ► Quite different "magnetic disorder" in the same structural-disordered system. ► Elucidation of magnetization reversal mechanism via direct domain observation. ► The simple model which explains the origin of asymmetric magnetic disorder.