Effect of substrate roughness on the magnetic properties of thin fcc Co films
Steinmuller SJ., Vaz CAF., Ström V., Moutafis C., Tse DHY., Gürtler CM., Kläui M., Bland JAC., Cui Z.
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 Néel'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. © 2007 The American Physical Society.