Observation of the coupling of ferromagnetic spins by antiferromagnetic spins with a spatial resolution of single grains

This paper presents the first quantitative evaluation of the pinned uncompensated spin (UCS) density on the scale of single grains obtained from high lateral resolution magnetic force microscopy. All measurements presented were performed on one ferromagnetic-antiferromagnetic (FM/AFM) multilayer sample that contained a Co/Pt multilayer as ferromagnetic layer and CoO as an AFM layer. TEM of the CoO AFM layers shows grains with a diameter around 20 nm and that CoO is grown epitaxially on the CoPt, and vice versa. From the structural knowledge obtained by TEM and the UCS density distribution evaluated from MFM data it is concluded that a Takano-type model well explains the exchange bias (EB) effect in our AFM/FM system. A careful engineering of the intergranular coupling of the AFM grains may lead to an enhanced EB-effect.