Shape control and associated magnetic and dielectric properties of MFe12O19 (M = Ba, Pb, Sr) hexaferrites

Single-phase MFe12O19 (M = Ba, Pb, Sr) powders composed of hexagonal grains were prepared by the citratenitrate process by adjustment of the pH to 7 and with an M-to-iron molar ratio of 1:11, a nitrate-to-citrate ratio of 1:1.5, and a heating temperature of 850 degrees C. The physical properties were comprehensively investigated by different techniques. Rietveld refinement shows that the samples can be indexed in hexagonal symmetry (space group P6(3)/mmc), which was confirmed by Fourier-transform infrared spectroscopy. The variation of the saturation magnetization of the MFe12O19 hexaferrite is explained mainly by the formation of a magnetically dead layer in the grains. The coercive field of the samples studied increases with increase of the average particle size, which originates mainly from the sum of all the changes in anisotropy energies. Dielectric results for the samples studied show the presence of short-range conduction of the localized charge carriers in the relaxation process and thus a departure from an ideal Debye-type behavior, was also confirmed by the results of ac conductivity studies.