Response and enhancement of surface magneto-optic Kerr effect for Co-Pt(111) ultrathin films and surface alloy

Magnetic anisotropy as a function of Co coverage was comparatively studied on a flat and sputtered Pt(111) surface by a surface magneto-optic Kerr effect. The magnetic anisotropy of the flat Pt(111) surface changes gradually from out-of-plane to in-plane when the film thickness is over four monolayers, whereas both the out-of-plane and in-plane anisotropy occur on the sputtered Pt(111) surface. This difference is attributed to the fact that the magnetocrystalline anisotropy is diminished from the sputtered surface. A large enhancement in the polar magnetooptic Kerr signal was observed after one atomic layer of Co adatoms on the flat Pt(111) surface was annealed at 710 K. The formation of Co-Pt alloy at the interface following the enhancement was confirmed by low-energy electron diffraction and Auger electron spectroscopy. The mechanism of the enhancement is discussed.