Magnetic reversal of ultrathin films with planar magnetization

Classical spin simulations are used to study magnetic reversal in ultrathin (1--6 monolayers) films with planar magnetization and surface roughness typical of epitaxially grown samples. Reduced site symmetry at surface steps leads to strong, local anisotropies that both nucleate reversal and pin domain wall motion. The results we obtain from realistic models with periodic roughness are interpreted using a much simpler model with a single, finite-length step. These models show how growth induced roughness can lead to oscillations in the coercive field as the film thickness is increased, as seen in some experiments. They also demonstrate explicitly how local step anisotropies become less important and magnetostatic interactions become more important as the film thickness increases.