A mode-of-growth-dependent magneto-optical response from ultrathin Co films on Pd surfaces

We have grown ultra-thin epitaxial Co films on (0 0 1) and (1 1 1) surfaces of Pd. Their magnetic properties are studied by magneto-optical Kerr effect (MOKE). They are correlated with surface morphology analyzed by scanning tunneling microscopy (STM). In agreement with theoretical predictions, reversed polar Kerr rotation loops with respect to those of thicker Co films were observed below the thickness of 2.5 monolayers. This is interpreted as being due to a dominating negative contribution of Co/Pd interface with respect to the positive contribution from the non-interface part of the Co film. There is no change of sign of the polar Kerr rotation at low Co coverage on Pd(1 1 1) due to the growth which starts by formation of double-layer patches in this case.