Nanostructural M-type barium hexaferrite synthesized by spark plasma sintering method

Abstract

This investigation shows that the spark plasma sintering (SPS) method may not only absolutely prevent the formation of intermediate phase α-Fe2O3 but also significantly lower the crystallization temperature of M-type barium hexaferrite. A kind of textured sample composed of major phase M-type barium hexaferrite and trace amount of BaFe0.24Fe0.76O2.88 has been successfully synthesized in one step by SPS process at 800°C for 10min. Scanning electron microscopy, energy dispersive spectroscopy, x-ray-diffraction, transimission electron microscopy, and vibrating-sample magnetometer techniques are used to study the microstructure, composition, phase formation, crystal orientation, and magnetism of the textured sample, respectively. It is confirmed that nanostructural M-type barium hexaferrites in the holes of the textured sample are in nanobelt and nanorod microstructures; these nanobelts and nanorods are nonstoichiometric and completely random and are characterized by barium or iron surplus, and that their composition may be described as BaFe12+xO19+1.5x (−4.49⩽x⩽6.60). The prolongation orientation of a nanobelt is parallel to the zone axis [101¯0]. The values of σs and Hc of the textured sample are 65.52emu∕g and 1412.17Oe, respectively. The Hc value decreases to one-fourth of that of randomly packed platelike M-type barium hexaferrite with same composition synthesized by sol-gel process at 900°C for 4h, while the σs value was independent of the synthesis conditions. This indicates that M-type barium hexaferrite magnets synthesized by SPS process may be applied to electromagnetic wave absorption and/or magnetic recording.