Spin-dependent scattering in the nonmagnetic layers of annealed Co/Cu multilayers

Annealing a multilayer is expected to promote diffusion at the interfaces. We have found that the interface roughness and giant magnetoresistance of Co/Cu (111) multilayers, grown by molecular-beam epitaxy on sapphire substrates, remain unchanged during anneals of up to 320 degrees C despite the zero-field resistivity having doubled. We explain this large increase in resistivity as due to the formation of an alloy between the top Cu layer of the multilayer and the Au protective cap. We propose that scattering in the AuCu alloy is spin dependent. We discuss this idea in the light of mean free path effects and the density of states of the entire sample. (C) 1996 American Institute of Physics.