Giant magnetoresistance in symmetric spin-valves: nanostructure and domain dynamics

High resolution transmission electron microscopy (HRTEM) was used to investigate the nanostructure of symmetric spin-valves (SSV) of the type NiO/Co/Cu/Co/Cu/Co/NiO. The Co/Cu layers grow coherently over each other within columnar grains, the topography of the columns being conformal with that of the underlying NiO layer. Clear evidence is presented which shows that the middle Co layer switches between antiferromagnetic (AF) ↔ ferromagnetic (F) aligned states by domain wall nucleation and growth; the Co layers, magnetically pinned by NiO, undergo reversal at high fields (48 mT), but no accompanying wall motion was observed. The wall nucleation of the middle Co layer is explained in terms of the presence of local AF-coupled regions arising from fluctuations in Cu layer thickness.