Carbon diffusion and reactivity in Mn5Ge3 thin films

The Curie temperature of Mn5Ge3 has been successfully enhanced by carbon doping. In this context the diffusion of a carbon thin film in Mn5Ge3 has been studied at room temperature. A value of the diffusivity of about D = 2.4x10(-23) +/- 0.5x10(-23) m(2) s(-1) is reported. This value is in the typical range of interstitial diffusion coefficients. Moreover Auger Ge and Mn peaks shifts and Ge-3d core level have been investigated to get some details on the reactivity of carbon atoms in Mn5Ge3. Mn Auger transitions display a shift of 4 eV whereas Ge transitions do not. Similarly Ge-3d core level does not contain C related contribution but presents a Mn one. These observations confirmed the fact that carbon atoms are not inert species for Mn. It suggests that a ternary GeMn-C alloy could occur and should be taken into account when doping the Mn5Ge3 with carbon.