Magneto-optic Kerr effect measurements on Fe3-xCoxSi (0<=x<=2.5) epitaxially stabilized on Si(111)

200 Angstrom thick Fe3-xCoxSi (0 less than or equal to x less than or equal to 2.5) films have been epitaxially grown on Si(111) by co-deposition at room temperature. Low- and medium-energy electron diffraction indicate the formation of cubic silicides with a crystallinity comparable to that of epitaxial alpha-Fe on Si(111). These silicides form a random alloy as evidenced by the lack of DO3-type long-range order, usually observed in the Fe3Si stoichiometric compound. Using ex situ magneto-optic Ken effect, hysteresis curves for different magnetic field directions have been measured at room temperature. The data demonstrate ferromagnetic behavior with strong in-plane uniaxial anisotropy in spite of the threefold symmetry of the cubic structure of these Fe3-xCoxSi silicides. The easy axis is found to be parallel to the [-101] direction.