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

Exchange coupling in NiO/Co bilayers and [Pd/Co(tCo)]n/NiO/Co trilayers prepared by magnetron sputtering has been investigated. With decreasing thickness (tCo) 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 tCo=1nm and n=2, a larger in-plane exchange bias field of 724Oe is observed which vanishes at temperatures above 90K which is the same as the in-plane blocking temperature observed in the NiO/Co bilayer. For tCo=0.3nm and n=7, the in-plane blocking temperature in the trilayer enhances up to 210K, which strongly depends on orientation and strength of the ferromagnetic [Pd/Co] ML anisotropy axis. •The easy axis of the [Pd/Co] MLs switches from in-plane to out-of-plane direction.•Ferromagnetic and non-collinear interlayer couplings are found in the trilayers.•A larger in-plane HE of 724Oe is observed for the trilayers tCo=1nm and n=2.•The in-plane blocking temperature TB increases up to 210K for tCo=0.3nm and n=7.