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 magneto-optic 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.