Effect of varying ferromagnetic anisotropy on exchange-bias in [Pt/Co]3/NiO(11 Å) multilayers

Abstract

An investigation has been performed on the effect of varying ferromagnetic anisotropy on the exchange biasing field, its temperature dependence, and blocking temperature in [Pt(5Å)/Co(tCo)]3/NiO(11Å) multilayers. The ferromagnetic easy axis switches from out-of-plane to in-plane on increasing the Co layer thickness tCo. After field cooling along out-of-plane and in-plane directions, respectively, a number of interesting features have been observed. The in-plane exchange field is much lower than the out-of-plane one, and goes to zero at a much lower blocking temperature. Both the in-plane and out-of-plane blocking temperatures drop with increasing Co layer thickness. The temperature dependence of the out-of-plane exchange field displays two distinct regions, which are separated by a temperature TCr close to the in-plane blocking temperature TB=35K at tCo=20Å. The exchange field decreases linearly in both regions but with a much steeper slope below TCr. These features are considered to be related to the variation of interfacial NiO spin structures with the ferromagnetic anisotropy easy axis and the temperature behavior of the NiO anisotropies.