Exchange coupling in ferromagnetic/antiferromagnetic/ferromagnetic [Pd/Co]_n/NiO/Co trilayers with different [Pd/Co] anisotropy

摘要

Exchange coupling in NiO/Co bilayers and [Pd/Co(t_(Co))]_n/NiO/Co trilayers prepared by magnetron sputtering has been investigated. With decreasing thickness (t_(Co)) of the Co layers in [Pd/Co] multilayers (MLs) and increasing number of [Pd/Co] repeats (n), the ferromagnetic easy axis of the [Pd/Co] MLs switches from in-plane to out-of-plane direction. Ferromagnetic and non-collinear interlayer couplings between the [Pd/Co] MLs and the Co layer across the antiferromagnetic NiO spacer are found in trilayers. After cooling at in-plane and out-of-plane remanent state, respectively, for t_(Co)=1 nm and n=2, a larger in-plane exchange bias field of 724 Oe is observed which vanishes at temperatures above 90 K which is the same as the in-plane blocking temperature observed in the NiO/Co bilayer. For t_(Co)=0.3 nm and n=7, the in-plane blocking temperature in the trilayer enhances up to 210 K, which strongly depends on orientation and strength of the ferromagnetic [Pd/Co] ML anisotropy axis.