Thickness evolution of coercivity in ultrathin magnetic films

The thickness evolution of in-plane magnetization reversal in ultrathin films is studied with a theoretical model that takes account of surface roughness typical of epitaxial growth. Guided by N\'{e}el's model, step edge sites of monolayer-height islands are assigned a two-fold anisotropy in addition to a four-fold anisotropy at all sites. Coercivity is found to depend essentially on both the film thickness and the partial coverage of the topmost layer. Its qualitative features are determined primarily by sample geometry and the size of the step anisotropy compared to the domain wall energy. Magnetostatic interactions change the results quantitatively, but not qualitatively. Their effect is understood by comparing calculations with and without their inclusion.