Magnetisation processes in exchange-biased systems

The nature of the exchange biasing process in thin-film materials in which an antiferromagnetic material is grown on top of a ferromagnetic layer is extremely complex due to thermally activated reversal in the antiferromagnet. Measurements of the hysteresis loops for Ta/NiFeCo/Cu/NiFeCo/FeMn/Ta spin-valve structures were undertaken and by careful control of temperature and time during the measurements we were able to characterize the reversal in the antiferromagnet via its effect on the ferromagnetic layer. In this way, we were able to show that the exchange field of the ferromagnet progressively reorders the antiferromagnetic layer with the process being driven by thermal activation. This can lead to an almost complete reversal in the direction of the exchange biasing.