The effects of spurious O atoms upon the electronic and magnetic properties of Mn-doped material were studied using ab initio calculations. Several different sites together with the formation of some defects complexes were investigated and analyzed with regard to the energetics, structure and electronic and magnetic properties of Mn and O incorporation into bulk Ge. The study showed that the presence of O always lowered the heat of formation of Mn impurities in Ge; thus favoring Mn incorporation. However, this result was found to be strongly dependent upon the sites occupied by Mn and O and by their chemical potential. It was found that O bonded with Ge, via hybridization of their p states. A relatively more ionic bond was found between Mn and O. As a result, Mn at low O-concentrations kept its magnetic moment and ferromagnetic alignment, provided that no Mn-neighboring atoms were present. Moreover, O markedly lowered theheat of formation for Mn adsoprtion in interstitial sites, both tetrahedral and hexagonal, making their energy cost very similar.

Role of Oxygen Defects in Diluted Mn:Ge. A.Continenza, G.Profeta: Physical Review B, 2008, 78[8], 085215 (7pp)