Magnetic phase diagram study of ultrathin Co/Si(111) films

The magnetic properties of ultrathin Co/Si(111) films were studied by the surface magneto-optic Kerr effect technique. A magnetic phase diagram has been successfully established between 120 and 500 K. Several phases were observed, i.e. a nonferromagnetic Co–Si compound, a low Curie temperature Co film, canted out-of-plane anisotropy, and in-plane anisotropy. The nonferromagnetic Co–Si compound can be reduced by decreasing the substrate temperature. With an Ag buffer layer, the thermal stability of the magnetization for a Co/Si(111) film is lowered. From Auger electron spectroscopy measurement, Ag atoms in the Co/Ag/Si(111) film segregate to top layers even below 350 K. The segregation of Ag atoms to the top layer may damage the magnetic domains in the Co layer and causes the lower thermal stability of the magnetization in the Co/Ag/Si(111) film.