Comparative study of the synthesis of CoFe2O4 and NiFe2O4 in silica through the polymerized complex route of the sol–gel method

In this work the synthesis of CoFe₂O₄-SiO₂ and NiFe₂O₄-SiO₂ nanocomposites was studied via the sol–gel method, using the polymerized complex route. The polymerized precursors obtained by the reaction of citric acid, ethylene glycol, tetraethylorthosilicate, ferric nitrate, and cobalt nitrate or nickel chloride were characterized by nuclear magnetic resonance (NMR) and infrared (IR) spectroscopy. NMR and IR spectra of the precursors, without and with metallic ions, show the formation of polymeric chains with ester and ether groups and complexes of metal-polymeric precursor. The nanocomposites were obtained by the thermal decomposition of the organic fraction and characterized by X-ray diffraction (XRD) and vibrating sample magnetometry (VSM). XRD patterns show the formation of CoFe₂O₄ and NiFe₂O₄ in an amorphous silica matrix above 400 °C in both cases. When the calcination temperature was 800 °C the particle size of the crystalline phases, calculated using the Scherrer equation, reached ∼35 nm for the two oxides. VSM plots show the ferrimagnetic behavior that is expected for this type of magnetic material; the magnetization at 12.5 KOe of the CoFe₂O₄-SiO₂ and NiFe₂O₄-SiO₂ compounds was 29.5 and 17.4 emu/g, respectively, for samples treated at 800 °C.