Preparation and structural characterization of ferromagnetic Mn₅Si₃Cₓ films

Carbon-doped Mn-Si films prepared by magnetron sputtering at elevated substrate temperatures exhibit ferromagnetic order for compositions around Mn5Si3Cx (x{\textgreater}0) in contrast to the antiferromagnetic Mn5Si3 compound. In these sputtered samples the carbon concentration can be strongly enhanced compared to sintered powder samples. The local structural order around the Mn site in Mn5Si3Cx films was investigated for x=0 and 0.75 by x-ray-absorption spectroscopy at different temperatures T. At low T, both films retain their hexagonal structure and do not exhibit the orthorhombic distortion observed for bulk Mn5Si3 powder. For the carbon-doped film a local distortion of the octahedra formed by six Mn atoms of the Mn5Si3 structure is found when surrounding a C atom. This indicates an anisotropic change of the atomic Mn environment by C, in contrast to a simple lattice expansion as inferred from previous structural analysis.