Magnetic properties in epitaxial binary iron and ternary iron-cobalt silicide thin films grown on Si(111)

Binary Fe(Si1-xFex) iron and ternary Fe3-yCoySi iron cobalt silicide thin films (thickness: 200 Angstrom) with local CsCl structure epitaxially grown at room temperature on Si(1 1 1) have been studied through X-ray magnetic circular dichroism (XMCD) and magneto-optic Kerr effect (MOKE) vector magnetometry. The binary Fe(Si1-xFex) films have ferromagnetic properties at room temperature in the range 0.09 less than or equal to x < 1 and the cobalt-substituted Fe3-yCoySi films an ferromagnetic as well in the whole range 0 < y < 3 at room temperature. The off-normal evaporation geometry leads to strong in-plane uniaxial magnetic anisotropy (including the non-epitaxial pure cobalt silicide Co3Si) favored by the absence of orientation dependence of the fourth-order cubic term of the magnetocrystalline anisotropy energy in (1 1 1) crystallographic plane. The easy axis corresponds invariably to the direction normal to the incidence plane of the atomic flux during evaporation. The substitution of iron by silicon in Fe(Si1-xFex) films increases the coercive field but does not strongly affect the uniaxial anisotropy constant. In Fe3-yCoySi alloys, a similar trend is observed and the increase of coercive force may be related to defects generated by alloying. The change of the magnetic moments of Fe and Co versus y, as obtained by XMCD, can be understood in terms of simple models. (C) 2000 Elsevier Science B.V. All rights reserved.