STRUCTURE AND MAGNETISM OF FE3-XCOXSI LESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-2.5) EPITAXIALLY STABILIZED ON SI(111)

Fe3-xCoxSi (0 less than or equal to x less than or equal to 2.5) films have been epitaxially grown for the first time on Si(111) by codeposi tion at room temperature. Low-and medium-energy electron diffraction, X-ray photoelectron diffraction, X-ray diffraction as well as Si 2p co re-level photoemission measurements indicate the formation of cubic ep itaxial Fe3-xCoxSi(111) phases. They are found to crystallize in a cub ic structure derived by substitution from alpha-Fe, with a lattice par ameter close to half that of silicon. These silicides form a random al loy as evidenced by the lack of DO3-type long-range order, usually obs erved in the Fe,Si stoichiometric compound. By using ex situ magneto-o ptic Kerr-effect experiments, hysteresis curves for different magnetic held directions have been measured at room temperature. The data demo nstrate ferromagnetic behavior with a strong in-plane uniaxial anisotr opy in spite of the threefold symmetry of the cubic structure of these Fe3-xCoxSi silicides. It is found that the easy axis is parallel to a [-101] crystallographic direction.