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 1000 °C for 1–4 h. The results showed that increasing time and temperature was beneficial to the saturation magnetisation (Ms), whereas the coercivity (Hci) 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 ∼50 to 150 nm.