Magnetization and magnetization reversal in epitaxial Fe/Cr/Co asymmetric spin-valve systems

We have investigated asymmetric Fe/Cr/Co/Cr superlattices with two magnetic layers of Fe and Co, which are different with respect to their magnetic properties: magnetization, coercivity, and magnetic anisotropy. The magnetic layers are weakly coupled via a mediating Cr spacer layer providing an antiferromagnetic alignment of adjacent layers. The magnetic structure of these spin-valve-like Fe/Cr/Co/Cr superlattices was analyzed from the remanent state up to saturation via polarized neutron scattering and polarized neutron reflectivity (PNR). Furthermore, the domain structure in remanence was imaged via polarized x-ray photoemission electron microscopy (XPEEM). This analysis reveals that the Co magnetization strongly affects the Fe domain structure, while the layer magnetization is collinear from the remanent antiparallel state up to the ferromagnetic saturation state. However, for certain Co layer thicknesses, the as-grown remanent state exhibits a noncollinear antiferromagnetic spin structure, which cannot be recovered after applying a magnetic field. However, the noncollinear structure is reproducible with freshly grown superlattices.