Selective modification of the unquenched orbital moment of manganese introduced by carbon dopant in epitaxial Mn5Ge3C0.2/Ge(111) films

Mn-55 NMR was used to investigate the effect of carbon doping on the local magnetic anisotropy in Mn5Ge3 epitaxial films (space-group P6(3)/mcm). It was found that carbon enters interstitially in the vicinity of the 6(g) crystallographic positions, occupying the 2(b) octahedral voids. The magnetic properties of the Mn atoms located in the corners of a host octahedron are strongly modified by the presence of carbon. Their magnetic moment is reduced by 0.7 mu(B) with respect to the pristine Mn5Ge3 film and the anisotropy of their orbital moment, measured as a difference between its value along the hexagonal c direction and on the c plane is reduced to 0.058 mu(B), whereas, in the pristine Mn5Ge3 films, it oscillated every 60 degrees between 0.151 mu(B) and 0. These changes are responsible for a significant decrease in magnetocrystalline anisotropy, which was reported to drop by an order of magnitude upon doping the Mn5Ge3 films with carbon.