Influence of film morphology on perpendicular magnetic anisotropy

Perpendicular magnetic anisotropy (PMA) appears in epitaxial films mainly due to the broken symmetry at the interface. As a result, ultrathin magnetic layers tend to be perpendicularly magnetized. With increasing film thickness, the shape anisotropy overcomes this interface contribution and forces the sample magnetization into the surface plane. We show that previous experimental studies of the magnetic anisotropy energies in the Co/Cu(111) system are affected by the large roughness of the Co films, resulting in underestimated values for the Co-Cu interface anisotropy. By using a surfactant (Pb) to assist the growth of Co layers we are able to prepare Co films and Cu/Co bilayers of homogeneous thickness and negligible roughness, and to determine a more accurate value for the Co-Cu interface anisotropy. With the aid of a simple model calculation, we demonstrate that roughness will substantially affect experimentally determined values of PMA.