Hexagonal ferrite particles for perpendicular recording prepared by ion exchange

Particles of nonstoichiometric M-type barium hexaferrite with the chemical formula BaFe/sub 10.5/M/sub 0.25/O/sub 17.05/ (M=Mg, Cd, Co, Ni, Nd Zn) have been prepared by ion exchange in Ba containing molten salts from precursor ferrites with the beta - or beta "-alumina structure. The particles possess a plateletlike shape with diameters as low as 0.2 mu m and as diameter-to-thickness ratio between 5 and 10. The Curie temperature is close to 470 degrees C. Saturation magnetization values sigma /sub s/ up to 64 emu g and coercive fields jH/sub c/ ranging from 0.5 to 1.5 kOe were found.<
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