Annealing effect on the magnetic properties of Ta 50 angstroms/Cu 50 angstroms/Co 75 angstroms/Cu 50 angstroms/Ta 50 angstroms sandwiches

High-vacuum anneals up to 440 °C have been performed on Ta 50 angstroms/Cu 50 angstroms/Co 75 angstroms/Cu 50 angstroms/Ta 50 angstroms sandwiches deposited by magnetron sputtering. In-plane magnetization measurements at room temperature revealed strong changes in the magnetic properties after annealing. Whereas the as-deposited sample presents a coercive field of 11.5 Oe, a coercive squareness of 0.91 and a saturation magnetization close to the Co bulk value, annealing up to 440 °C leads to a progressive increase of the coercive field to 295 Oe and a decrease of the squareness to 0.42. The saturation magnetization is reduced by a factor of two. These results can be explained by a grain-boundary interdiffusion between the Co and Cu layers, resulting in a decrease of the intergranular exchange coupling. Annealing at 440 °C leads to the formation of a granular CoCu alloy as confirmed by the appearance of a magnetoresistance of about 1%.