Overpotential driven perpendicular magnetization of electrodeposited ultrathin cobalt films

Depending on the overpotential applied during electrodeposition of ultrathin cobalt films (η=0.1–2.2 V), either in-plane or out-of-plane magnetization can be stabilized. The regime of high supersaturation in particular allows to engineer electrodeposited cobalt films on Au(111) that show perpendicular magnetization (in the thickness range from 2 to 8 atomic layers) exactly like their ultrahigh vacuum grown counterparts. The film topography depends on the overpotential as shown by atomic force microscopy: continuous films are obtained at low overpotential whereas high overpotential leads to the formation of islands. The perpendicular magnetization results from a subtle thickness dependent competition between the shape and the interface anisotropy.