The effect of interface roughness on the perpendicular exchange bias of NiO/CoPt/Pt stacking structure

An orthogonal coupling structure of NiO/CoPt/Pt/glass with perpendicular exchange bias effect has been prepared. The exchange bias is found to be strongly dependent on the interface roughness between NiO and CoPt layer. The conventional inverse proportionality of the exchange bias field with the ferromagnetic thickness is not applicable to this top-pinned stacking structure. Moreover, an anomalous ferromagnetic thickness dependence of blocking temperature is also observed. A simulation on the basis of a spin configuration model with defects at the interface agrees well with the experimental observations. These findings suggest considerable contribution of the interface roughness to the perpendicular exchange bias.