Positive exchange bias observed in Pt-inserted Cr2O3/Co exchange coupled bilayers

摘要

We investigated the effect of Pt insertion on a CrO/Co exchange coupling system. The perpendicular exchange bias μH decreased with increasing Pt insertion layer thickness, and we observed positive μH for samples with relatively thick Pt insertion layers. We also examined the cooling field μH dependence of μH for the samples. At small μH, all samples exhibited negative μH. With increasing μH, a shift of μH from negative to positive was observed. In the past, similar behaviors were observed for FeF/Fe systems exhibiting positive μH. In addition, the μH dependence of μH was well fitted by an equation taking into account the Zeeman energy at the surface of an antiferromagnet as well as an antiferromagnetic exchange coupling. The results strongly suggest that (1) CrO surface spin is affected by the external magnetic field and (2) the coupling at the CrO/Pt/Co interface is antiferromagnetic.