Preparation and structural characterization of ferromagneticMn5Si3Cxfilms

Abstract

Carbon-doped Mn-Si films prepared by magnetron sputtering at elevated substrate temperatures exhibit ferromagnetic order for compositions around ${\mathrm{Mn}}_{5}{\mathrm{Si}}_{3}{\mathrm{C}}_{x}$ $(x>0)$ in contrast to the antiferromagnetic ${\mathrm{Mn}}_{5}{\mathrm{Si}}_{3}$ 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 ${\mathrm{Mn}}_{5}{\mathrm{Si}}_{3}{\mathrm{C}}_{x}$ 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 ${\mathrm{Mn}}_{5}{\mathrm{Si}}_{3}$ powder. For the carbon-doped film a local distortion of the octahedra formed by six Mn atoms of the ${\mathrm{Mn}}_{5}{\mathrm{Si}}_{3}$ 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.