GIANT MAGNETORESISTANCE IN SYMMETRICAL SPIN-VALVES - NANOSTRUCTURE AND DOMAIN DYNAMICS

High resolution transmission electron microscopy (HRTEM) was used to i nvestigate the nanostructure of symmetric spin-valves (SSV) of the typ e NiO/Co/Cu/Co/Cu/Co/NiO. The Co/Cu layers grow coherently over each o ther within columnar grains, the topography of the columns being confo rmal with that of the underlying NiO layer. Clear evidence is presente d which shows that the middle Co layer switches between antiferromagne tic (AF) double left right arrow ferromagnetic (F) aligned states by d omain wall nucleation and growth; the Co layers, magnetically pinned b y NiO, undergo reversal at high fields (48 mT), but no accompanying wa ll 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. (C) 1997 Acta Metallurgica I nc.