Strongly enhanced Curie temperature in carbon-doped Mn5Ge3 films

The structural and magnetic properties of Mn5Ge3Cx films prepared at elevated substrate temperatures T-S are investigated. In particular, films with x greater than or equal to 0.5 and T-S = 680 K exhibit a strongly enhanced Curie temperature T-C = 445 K compared to bulk Mn5Ge3 with T-C = 304 K while at the same time the average Mn moment decreases from 2.6 to 1 mu (B). 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. (C) 2000 Elsevier Science B.V. All rights reserved.