Mn5Ge3Cx films with x >= 0.5 were experimentally shown to exhibit a strongly enhanced Curie temperature T-C compared to Mn5Ge3. In this letter we present the results of our first principles calculations within Green's function approach, focusing on the effect of carbon doping on the electronic and magnetic properties of the Mn5Ge3. The calculated exchange coupling constants revealed an enhancement of the ferromagnetic Mn-Mn interactions mediated by carbon. The essentially increased T-C in Mn5Ge3C is well reproduced in our Monte Carlo simulations and together with the decrease of the total magnetization is found to be predominantly of an electronic nature.
Department of Physics National and Kapodistrian University of Athens University Campus GR-157 84 Zografou, Athens