Comparative Study in Magnetic Properties of Co Ultrathin Films on Flat and Sputtered Pt(111) Surfaces

Abstract

The in situ magneto-optic Kerr effect was used to study the magnetic properties of Co ultrathin films grown on a flat and a sputtered Pt(111) surface. The perpendicular magnetic anisotropy appears for Co on the flat Pt(111) surface with a thickness of less than 4.0 ML and it changes to in-plane after the coverage of Co is more than 6.5 ML, whereas both the out-of-plane and in-plane anisotropy occur on the sputtered Pt(111) surface. The coercive force decreases as the Co coverage increases for the flat Pt(111) surface, but it is independent of the thickness for the sputtered one. A surface in island growth and surface roughness seem beneficial to the reversal of a magnetic domain wall. Thermal energy also helps the domain wall motion. The perpendicular Kerr intensity increases in a linear relation with thickness of Co before the magnetization turns to in-plane for the flat surface, and it is a smooth curve with a maximum at 5.5 atomic monolayers of Co for the sputtered surface. The Curie temperature of Co thin films on the flat Pt(111) was measured. The Curie temperature increases as the thickness of Co increases. An enhancement of perpendicular magnetic anisotropy was observed when a Co-Pt alloy is developed. The hybridization of electronic states in the formation of a Co-Pt surface alloy and the large spin-orbit coupling in this system are possible mechanisms for the enhancement.