Magnetic properties of ultrathin Co films on Si(111) and CoSi2 surfaces

The orientation of the magnetization and the occurrence of interfacial ferr omagnetic dead layers for ultrathin Co films on Si(111) and CoSi2 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 CoSi2 as a buffer layer for ultrathin Co films bet ween 2.8 and 10.5 monolayers (MLs) deposited on Si(111) at 300 K. The ferro magnetic 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 s ilicide formation in Co/Si(111), a two-step diffusion mechanism is suggeste d with two different diffusion activation energies of the Co atoms resultin g from different chemical environments. (C) 1999 American Institute of Phys ics. [S0021-8979(99)78308-8].