Chemical and magnetic interactions in Mn- and Fe-codoped Ge diluted magnetic semiconductors

Chemical and magnetic homogeneities of Mn and Fe, codoped in Ge, have been studied experimentally and theoretically. As we alter the codopant concentration in our diluted magnetic semiconductors, polarized neutron reflectivity measurements indicate no segregation and lower clustering tendencies for higher Fe doping. First-principles density-functional calculations based on Korringa-Kohn-Rostoker coherent-potential approximation show that Fe codoping introduces ferromagnetic interaction between Fe atoms as well as between Fe and Mn in contrast to only Mn-doped Ge. The clustering behavior observed in Mn-doped Ge is counteracted by the presence of Fe and hence increases the fraction of homogeneity, in agreement with the experiments. These observations indicate that Fe codoping makes Mn-doped Ge more attractive toward application.