Iron group impurities in beta-FeSi2 studied by EPR

Using EPR we have investigated bulk single crystals of beta-FeSi2 grown by chemical vapor transport. By an interpretation of the hyperfine structure combined with intentional doping during crystal growth, we prove that most of the paramagnetic centers observed arise from isolated iron group impurities. The 3d transition metals Cr, Mn, and Co, and with less certainty Ni and Cu, have been identified. The angular variations of the corresponding spectra show orthorhombic symmetry and can be explained with an electronic spin S=1/2. The substructure of the EPR lines due to the ligand hyperfine interaction indicates an eightfold Si coordination. The simple center model of an impurity atom substituting for iron is consistent with the observed spin, symmetry, and coordination. Whereas Cr and Mn can occupy either of both crystallographically inequivalent Fe sites Co, Ni, and Cu prefer one site. For Cu, however, an interstitial incorporation also seems possible.