First-principles investigation of transition-metal-doped group-IV semiconductors: R(x)Y1(-x) (R=Cr,Mn,Fe;Y=Si,Ge)

A number of transition-metal- (TM) doped group-IV semiconductors, RxY1-x (R=Cr,Mn,Fe; Y=Si,Ge), have been studied by the first-principles calculations. The results obtained show that antiferromagnetic (AFM) order is energetically more favored than ferromagnetic (FM) order in Cr-doped Ge and Si with x=0.03125 and 0.0625. In 6.25% Fe-doped Ge, the FM interaction dominates in all ranges of R-R distances, while for Fe-doped Ge at 3.125% and Fe-doped Si at both concentrations of 3.125% and 6.25%, only in a short R-R range can the FM states exist. In the Mn-doped case, the Ruderman-Kittel-Kasuya-Yoshida-like mechanism seems to be suitable for the Ge host matrix, while for the Mn-doped Si, the short-range AFM interaction competes with the long-range FM interaction. The different origin of the magnetic orders in these diluted magnetic semiconductors (DMS's) makes the microscopic mechanism of the ferromagnetism in the DMS's more complex and attractive.