Preparation and characterization of cobalt ferrite by the polymerized complex method

Magnetic nanoparticles of Co-ferrite were prepared by the polymerized complex method. Heating in vacuum of a precursor solution containing citric acid (CA), ethylene glycol (EG) and cobalt and iron salts with a molar ratio of Co/Fe/CA/EG=1/2/9/22.5 at 130 °C produced a brownish transparent polymeric gel, which have been characterized by IR and NMR spectroscopy. The results of both techniques suggest two types of reactions: the formation of metal-CA complexes and successive esterification reactions between CA and EG. The organic fraction was removed by controlled thermal treatments (200–800 °C) whereby the bimetallic oxide was formed. The powders obtained were characterized by X-ray diffraction (XRD), vibrational sample magnetometry (VSM) and transmission electron microscopy (TEM). XRD analysis showed the presence of CoFe₂O₄ at 400 °C. The saturation magnetization values of the samples increased as a function of calcination temperature and reached a maximum of 79.8 emu/g at 800 °C. The TEM images showed spherical nanoparticles with sizes between 20 and 40 nm.