Formation of cadmium-containing W-type hexagonal ferrite

The main steps of the phase formation processes which take place in samples of W-type hexaferrites containing cadmium, prepared by chemical coprecipitation, have been analysed. The processes were followed by Mössbauer spectroscopy, powder X-ray diffraction, thermomagnetic analysis and magnetic measurements. For samples heated in the temperature range 1000-1100°C, the phase formation processes are the same as those verified for the other zinc, nickel, cobalt W-type compounds: forT h=1000°C the only phases present are SrFe12O19 (M-type ferrite) and CdFe2O4 (spinel ferrite); in contrast, forT h>1100°C, the solid state reaction between the M-type and the spinel phases does not take place and the spinel phase decomposes, leading to the formation of ?-Fe2O3.