Structural and magnetoresistance studies of Ni/Co multilayers

A study of ferromagnetic/ferromagnetic Ni/Co multilayers grown by DC magnetron sputtering with component layer thicknesses between 40 and 5 Angstrom is presented. Structural characterization by small-angle x-ray reflectivity reveals high-quality layered structures with a well-defined composition modulation along the film growth direction. Quantitative interpretation of the superlattice structure parameters, including interface roughness and intermixing, has been performed by modelling the x-ray reflectivity data. Measurements of the magnetotransport properties of these multilayers indicate that the magnetoresistance (MR) effect: Delta rho similar to 0.35 mu Omega-cm, is roughly constant over the entire compositional range. We attribute the origin of this effect to anisotropic magnetoresistance (AMR). The MR ratio Delta p/p, which is as high as 3.0% in a SiO2/(Ni40 Angstrom/Co5 Angstrom)x6 multilayer with saturation field similar to 80 Oe, is therefore more strongly dependent on the zero-field resistivity. By fitting a semi-classical model of conduction in multilayers to the resistivity thickness variation, we extracted the mean free paths for conduction in each of the constituent layers as well as the contribution of interfacial scattering in the superlattice structure.