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-CF, 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. (C) 2011 Elsevier Ltd. All rights reserved.