Dendritic domain structures in ultrathin cobalt films

We report on the study of dendritic domain structures in gold-enveloped cobalt ultrathin films of thicknesses slightly below the thickness at which the reorientation from a perpendicular magnetization state to the in-plane state takes place. In these films, magnetization reversal proceeds through the dendritic growth of domains. A magnetic after-effect was observed. We reveal the mechanism and key parameters controlling the dendritic growth of magnetic domains.