Effect of substrate roughness on the magnetic properties of thin fcc Co films

We present a study of the influence of substrate roughness on the magnetic properties of thin fcc Co films (7 and 17 nm thick) grown on Cu(001)/Si(001). A significant decrease in cubic anisotropy with increasing film roughness was observed with Brillouin light scattering and magneto-optical Kerr effect magnetometry. In addition, the rougher samples showed a substantial broadening of the spin wave peaks. Both effects were found to be more pronounced for the thinner Co layers. Our observations are discussed in the framework of a theoretical model which takes into account the morphology of the Co films as measured by atomic force microscopy. While roughness effects are usually discussed in the context of Neel's orange-peel model, we propose a qualitatively different effect in this work whereby the magnetization follows coherently the substrate morphology (undulating state) resulting in the absence of magnetic surface charges. This magnetic configuration gives rise to a reduction in the magnetic anisotropy of epitaxial thin films, which is in good qualitative agreement with the experimental observations.