Role of domain and interface spin structure on exchange bias in CoNi/Gd/CoNi trilayers

Abstract

In this study, dc remanence measurements were performed on a sputter deposited CoNi(top)/Gd/CoNi trilayers. The remanence state of the CoNi(top)/Gd bilayer, which is the hard layer, determines the exchange bias field strength. If the sample is cooled from room temperature at the remanence state corresponding to the hard layer coercive field, the exchange bias becomes zero. Domains form in the hard layer at this remanence state. The angular dependence of the coercive field does not indicate magnetization reversal by domain wall motion. The bottom soft CoNi layer exchange couples to each domain in the hard layer at the interface. This causes the exchange bias field to become zero on the average. If the trilayer is cooled at its full remanence state, the formation of Hb anisotropy is observed in the angular dependence of coercivity.