Increase in ferromagnetic/antiferromagnetic exchange bias due to a reduction of the interfacial exchange interaction

We experimentally investigated the influence of the location of nonmagnetic impurities (Au) inserted in the NiO layer of NiO/Co bilayers on the exchange bias. The inserted Au layer actually consists of a discontinuous plane of Au islands leading to local disruption of the exchange interactions within the NiO layer or at the Co/NiO interface. When the Au layer is introduced at the Co/NiO interface, this results in a significant initial increase in the exchange bias field. If the Au layer is moved deeper within the NiO layer, the exchange bias progressively decreases towards its value without Au. Our experiments are interpreted in terms of a reduced dragging of the NiO magnetization during Co magnetization reversal due to the reduced interfacial interaction. This interpretation is supported by numerical simulations which also predict the formation and annihilation of bubble-like domain walls. (C) 2003 American Institute of Physics.