Strongly enhanced Curie temperature in carbon-doped Mn5Ge3 films

The structural and magnetic properties of Mn5Ge3Cx films prepared at elevated substrate temperatures TS are investigated. In particular, films with x⩾0.5 and TS=680 K exhibit a strongly enhanced Curie temperature TC=445 K compared to bulk Mn5Ge3 with TC=304 K while at the same time the average Mn moment decreases from 2.6 to 1 μB. Structural analysis of these films suggests that the carbon is interstitially incorporated into the voids of Mn octahedra of the hexagonal Mn5Si3-type structure giving rise to a lattice compression. The enhanced ferromagnetic stability in connection with the lattice compression is interpreted in terms of an Mn–Mn interaction mediated by C based on a change in the electronic structure.