Magnetization reversal processes in exchange-biased spin-valve structures

In this paper we provide an initial, qualitative description of the basic magnetization reversal processes that occur when a soft ferromagnetic layer is coupled to an antiferromagnet. We find that the magnetization reversal in the ferromagnetic layer adjacent to the antiferromagnet, i.e., the pinned layer, is dominated by thermal activation processes. We have developed, and report here, a model that accounts for seven distinct features of the magnetization curve of the pinned layer. The model is based upon the formation of domains in the antiferromagnetic layer whose growth is dominated by thermal activation processes. The thermal activation of these domain processes can result in shifts of the hysteresis loop in either direction, depending on the magnetic history of the sample and the rate of field sweep. In consequence, we call into question the current definition of the exchange field H_ex typically used to characterize such systems.