Influence of stoichiometry and heat treatment conditions on the magnetic properties and phase constitution of Ba-ferrite powders prepared by sol-gel

The magnetic properties and the microstructure of Ba-ferrite powders prepared by the sol-gel route were investigated. Amorphous gels were processed with a varying Fe/Ba ratio and then powder materials were obtained by heat treating at temperatures between 900 and 1000degreesC for 1-4 h. The results showed that increasing time and temperature was beneficial to the saturation magnetisation (M,,), whereas the coercivity (H-ci) was only slightly affected. The variation of the Fe/Ba ratio led to the formation of different proportions of BaFe12O19 and BaFe2O4, which directly affected the magnetic properties. Transmission electron microscopy (TEM) micrographs showed mainly hexagonal-like grains with crystallite sizes ranging from similar to50 to 150 nm. (C) 2002 Elsevier Science B.V. All rights reserved.