Thickness dependence of positive exchange bias in ferromagnetic/antiferromagnetic bilayers

For the ferromagnetic (FM)/antiferromagnetic (AFM) bilayers, both negative and positive exchange bias H E have been observed for low and high cooling field H C F , respectively. The thickness dependence of H E and coercivity H C have been investigated for the cases of negative and positive H E . It is found that the negative H E and the positive one have similar FM thickness dependence that is attributed to the interfacial nature of exchange bias. However, the AFM thickness dependence of positive H E is completely contrary to that of the negative one, which clearly demonstrates that the AFM spins play different roles for the cases of positive and negative H E . In particular, the AFM thickness of positive H E was first highlighted by an AFM spin canting model. These results should be attributed to the interfacial spin configuration after field cooling procedure.