Improvement in magnetic parameters of polycrystalline barium hexaferrite by nonmagnetic cation substitution and microwave processing

Polycrystalline Zn-Zr substituted barium hexaferrite (BaFe12-xZnx/2Znx/2O19 where x = 0.3, 0.5, 0.7 and 1.0) specimen have been synthesized by two different methods, namely conventional and microwave sintering. The latter has resulted in magnetoplumbite phase in 5 min at a lower temperature (1000 degrees C). The values of magnetic parameters of different samples are extracted from the corresponding M - H loops using law of approach to saturation magnetization. A high value of saturation magnetization (M-s = 76 emu/g) is obtained for a conventionally sintered sample. Still higher value of saturation magnetization (M-s = 104 emu/g) has been obtained for the microwave sintered cation substituted sample. The increase in the magnetization has been attributed to the magnetic reordering of iron cations in the non-magnetic Zn2+Zr4+ substituted samples. The coercivity of the microwave processed substituted samples has been drastically reduced to 163 Oe (from 2961 Oe for conventionally sintered pristine sample). The observed decrement can be ascribed to the increase in particle size and reduction in magnetocrystalline anisotropy (2.58 x 10(6) erg/cc). Raman spectra of the substituted samples have shown a shift in the vibrational frequencies (characteristic of magnetoplumbite phase) with cation substitution. This suggests that the non-magnetic Zn-Zr cations replace Fe3+ from certain interstitial sites (4f(1), 4f(2), 2b and 12k).