Magnetic phase diagram of ultrathin Co/Si(111) film studied by surface magneto-optic Kerr effect

A magnetic phase diagram of the ultrathin Co/Si(111) film deposited at 300 K has been established by the surface magneto-optic Kerr effect technique. The temperature, where ferromagnetism vanishes, increases from 375 to 625 K as the coverage of the Co film increases from 3.5 to 16 monolayers. A quan titative calculation of the normalized Auger signal of CoSi2 shows that the calculated values lie between the experimental measured Auger signals befo re and after ferromagnetism vanishes for films with coverage between 3.5 an d 9.1 monolayers. For samples with higher coverage, the experimental data a re smaller than that by calculation. This may be qualitatively explained by Co atoms escaping from the CoSi2 phase to diffuse into the Si substrate. T he disappearance of ferromagnetism is mainly attributed to silicide formati on. (C) 1999 American Institute of Physics. [S0003-6951(99)01409-6].