Self-propagating high temperature synthesis of MFe12O19 (M=Sr,Ba) from the reactions of metal superoxides and iron metal

Hexagonal ferrites MFe12O19 are widely utilised both as permanent hard magnets and in high density recording media. This is due to their high Curie temperatures, strong magnetic anisotropy and high coercivities. Typical commercial preparations involve reacting metal carbonates and iron oxide at high temperatures for prolonged periods and can involve as many as 12 processing steps. In this paper, a self-propagating high temperature synthesis is used to prepare crude ferrites from a mixture of MO2 (M=Ba,Sr), iron oxide and iron powder in air. Heating the crude mixture to 1150°C for 2 h affords pure crystalline MFe12O19. The ferrites were characterised by X-ray powder diffraction (Rietveld analysis), FT-IR, magnetometry, EDAX/SEM and Mössbauer spectroscopy. The ferrites showed good purity, coercivity, remanence and hysteresis loops compared to commercial samples. The new synthetic route also allows a range of mixed metal ferrites SrxBa1−xFe12O19 to be made. It is rapid (ca. 10 s), inexpensive and does not require the use of special reaction containers or an oxygen atmosphere.