IRON-GROUP IMPURITIES IN BETA-FESI2 STUDIED BY EPR

Using EPR we have investigated bulk single crystals of beta-FeSi2 grow n by chemical vapor transport. By an interpretation of the hyperfine s tructure combined with intentional doping during crystal growth, we pr ove that most of the paramagnetic centers observed arise from isolated iron group impurities. The 3d transition metals Cr, Mn, and Co, and w ith less certainty Ni and Cu, have been identified. The angular variat ions of the corresponding spectra show orthorhombic symmetry and can b e 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 substitut ing for iron is consistent with the observed spin, symmetry, and coord ination. Whereas Cr and Mn can occupy either of both crystallographica lly inequivalent Fe sites Co, Ni, and Cu prefer one site. For Cu, howe ver, an interstitial incorporation also seems possible.