X-ray and magnetoresistance measurements of annealed Co/Cu multilayers

Annealed Co/Cu multilayers grown on sapphire by molecular beam epitaxy have been studied by grazing-incidence X-ray scattering and magnetotransport measurements. Specular X-ray reflectivity data indicated no change in interface roughness for these multilayers grown on Nb buffer layers on sapphire. This was confirmed in extensive diffuse scattering studies. Exploiting the tunability of synchrotron radiation, we have used anomalous dispersion to highlight the Co/Cu interfaces from those associated with the buffer and cap layers. This has shown that virtually all of the Cu/Co interface roughness is correlated through the multilayer. No change in the correlated roughness occurred on annealing, but monotonic rises in both the resistivity rho and Delta rho were observed which scaled such that little change occurred in the GMR. We explain the large changes in resistivity as the result of alloying between the top Cu layer of the multilayer and the Au cap.