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 magn ets and in high density recording media. This is due to their high Curie te mperatures, strong magnetic anisotropy and high coercivities. Typical comme rcial preparations involve reacting metal carbonates and iron oxide at high temperatures for prolonged periods and can involve as many as 12 processin g steps. In this paper, a self-propagating high temperature synthesis is us ed 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 degreesC for 2h affords pure crystalline MFe12O19. The ferrites were characterised by X-ray powder diffraction (Rietveld analysis), FT-IR, magnetometry, EDAX/SEM and Mossbauer spectroscopy. The ferrites showed good purity, coercivity. remane nce and hysteresis loops compared to commercial samples. The new synthetic route also allows a range of mixed metal ferrites SrxBa1-xFe12O19 to be mad e. It is rapid (ca,10 s), inexpensive and does not require the use of speci al reaction containers or an oxygen atmosphere. (C) 2001 Elsevier Science B .V. All rights reserved.