Long-range order in thin epitaxial Fe{sub 3}Si films grown on GaAs(001)

As-grown thin epitaxial Fe{sub 3}Si films fabricated by molecular beam epitaxy on GaAs(001) are studied by grazing incidence x-ray diffraction. The long-range order parameters of the films of different stoichiometry are determined by measuring fundamental and superlattice crystal truncation rods and comparing them to simulations in dynamical approximation. Two order parameters, associated with the degree of migration of Si atoms into different Fe sublattices, are obtained. A residual intermixing of the sublattices is found, even near complete stoichiometry. The relative positions of the Fe{sub 3}Si and GaAs lattices are determined. Fe atoms in Fe{sub 3}Si are located at the positions of the Ga atoms in GaAs, with an additional shift of 0.1{+-}0.04 A of the tetragonally distorted Fe{sub 3}Si lattice normal to the interface.