Inverted hysteresis loops in CoO-based multilayers

Abstract

We have observed inverted hysteresis loops in a number of multilayer [Co-O]/Cu and [Co-O]/Al multilayers. In this phenomenon, the forward and reverse branches of a hysteresis loop are shifted along the magnetic field axis in such a way that they cross each other and we report the dependence of this phenomenon on magnetic layer thickness. In many cases the Cu or Al layer is thick enough that interlayer interactions between magnetic layers are not possible. It is suggested that interface exchange between Co and Co-O phases within the magnetic layer is important in these multilayers and that this phenomenon is closely related to shifted hysteresis loops which are also produced by interface exchange. We do not find this behavior in nominally homogeneous Co-O films indicating that the multilayer nature of the material is important. A two-phase model is presented which is able to qualitatively explain some of the observed results.