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 f ilms (thickness: 200 Angstrom) with local CsCl structure epitaxially grown at room temperature on Si(1 1 1) have been studied through X-ray magnetic c ircular dichroism (XMCD) and magneto-optic Kerr effect (MOKE) vector magnet ometry. 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-s ubstituted Fe3-yCoySi films an ferromagnetic as well in the whole range 0 < y < 3 at room temperature. The off-normal evaporation geometry leads to st rong in-plane uniaxial magnetic anisotropy (including the non-epitaxial pur e cobalt silicide Co3Si) favored by the absence of orientation dependence o f the fourth-order cubic term of the magnetocrystalline anisotropy energy i n (1 1 1) crystallographic plane. The easy axis corresponds invariably to t he direction normal to the incidence plane of the atomic flux during evapor ation. The substitution of iron by silicon in Fe(Si1-xFex) films increases the coercive field but does not strongly affect the uniaxial anisotropy con stant. In Fe3-yCoySi alloys, a similar trend is observed and the increase o f coercive force may be related to defects generated by alloying. The chang e of the magnetic moments of Fe and Co versus y, as obtained by XMCD, can b e understood in terms of simple models. (C) 2000 Elsevier Science B.V. All rights reserved.