Anomalous magnetic anisotropy in ultrathin transition metals

In situ polar Kerr effect measurements were used to probe directly the magnetic anisotropy of ultrathin MBE-grown cobalt films with and without overlayers of various nonmagnetic metals (X=Ag, Cu, Pd). To investigate the Co/X interface, perpendicular hysteresis curves were measured as a function of overlayer coverage. The magnitude of the perpendicular anisotropy was found to be strongly peaked near approx1 atomic layer (1.5-2 A) coverage. The magnitude of the perpendicular anisotropy was strongly peaked near approx2 atomic layer (1.5-2 A) coverage for Ag and Cu overlayers. For Cu, the overlayer with the strongest effect, the total anisotropy energy rapidly decreases by a factor of 3 from its peak value after a total coverage of only approx2 atomic layers (4 A) of Cu.