Magnetic depth profiling of FM/AF/FM trilayers by PNR

Ferromagnetic/antiferromagnetic/ferromagnetic (FM/AF/FM) trilayers are investigated by polarized neutron reflectivity (PNR) with polarization analysis to obtain the layer resolved magnetization profile at various states of magnetization. The trilayers are composed of FeCoV (FM) layers which are separated by NiO (AF) layers of varying thickness. The spin-dependent reflectivities are analyzed by modeling the magnetic states of the FeCoV layers. First, we study magnetization configurations during the magnetization reversal as a function of AF thickness. It is found that for thin AF layers the magnetization reversal of the FM layers occurs simultaneously, whereas for thick AF layers the reversal occurs in a two-step process. In a second part of the experiments we follow, by PNR, the reorientation of the top FM layer in an in-plane perpendicular field starting from a state with the magnetization in the adjacent FM layers oriented antiparallel. It is observed that the magnetization of the top FeCoV layer gradually rotates into the direction of the applied field while the bottom FeCoV layer remains pinned in its state perpendicular to the field.