Influence of the Roughness of the Buffer Layer on the Magnetoresistance of Co/Cu Multilayers

Abstract

We have studied the influence of the Pb buffer layer thickness in the Co/Cu multilayers on the magnetoresistance of the system. Co/Cu multilayers (ML) were thermally evaporated at very low deposition rates on Si substrates covered with Pb buffer layer of different thickness (5, 10, 20, 30, 40 nm). The structural characterisation of samples was performed by X-ray reflectometry (XRR) and Scanning Force Microscopy (SFM). Using ex situ scanning force microscopy we have measured directly the topography of the top surface of the multilayered structure as well as the top surface of buffer layer. Quantitative estimates of the character of sample surface have been done using dynamic-scaling theory. Magnetoresistance measurements were carried out at room temperature using a standard four-probe dc method with current in the plane of the sample. We have found that Pb buffer layer strongly influences the magnetotransport properties of Co/Cu multilayers. Since the thickness of single layers is of similar magnitude as the interfacial roughness in our samples the nature of the coupling is still not clear, but we suggest the creation of granular entities which are the main source of MR in these samples.