Lattice vibration characterization and magnetic properties of M-type barium hexaferrite with excessive iron

Nonstoichiometric M-type barium hexaferrite compounds, with nominal compositions BaFe12+xO19+1.5x (0⩽x⩽0.4), have been synthesized by spark plasma sintering technique. The electron probe microanalysis shows that the excessive trivalent iron (Fe3+) ions are in the lattices of BaFe12+xO19+1.5x compounds. Both Raman and FTIR spectra reveal that the excessive Fe3+ ions spin upward. They occupy the octahedron interstices similar to the FeO6 octahedron at the 12k site and the bipyramid interstices similar to the FeO5 bipyramid at the 2b site, in the x range of 0–0.3 and x=0.4, respectively. This explains well significant enhancement in the specific saturation magnetizations for BaFe12+xO19+1.5x with increasing the x in the range of 0–0.4. The gradual increase in the coercivities has been interpreted with the augment of Fe3+ concentration in unit cell.