Magnetic properties of ultrathin Co films on Si(111) and [formula omitted] surfaces

The orientation of the magnetization and the occurrence of interfacial ferromagnetic dead layers for ultrathin Co films on Si(111) and [formula omitted] surfaces have been systematically studied using in situ surface magnetic-optic Kerr effect. We have experimentally demonstrated that an in-plane magnetization can be obtained by using [formula omitted] as a buffer layer for ultrathin Co films between 2.8 and 10.5 monolayers (MLs) deposited on Si(111) at 300 K. The ferromagnetic dead layers at the interface are most likely due to the formation of a Co–Si alloy. This region can be reduced from 2.1 to 1.4 ML by lowering the substrate temperature from 300 to 120 K. From a dynamic study of the silicide formation in Co/Si(111), a two-step diffusion mechanism is suggested with two different diffusion activation energies of the Co atoms resulting from different chemical environments.