Non-stoichiometric CoFe₂O₄ nanoparticles supported on an amorphous silica matrix

Non-Stoichiometric CoFe₂O₄ nanoparticles dispersed in an silica matrix with a silica content of 87 wt% and Co/Fe molar ratio of 1:1, were prepared by the sol-gel method using an ethanolic solution of tetraethoxysilane and either iron(III) and cobalt(II) nitrates or iron(II) and cobalt(II) acetates. The influence of different metal precursors on the xerogels were examined by X-Ray Diffraction (XRD), Transmission Electron Microscopy (TEM) and N₂ physisorption measurements at 77 K. Magnetic properties of the samples were investigated by field cooled FC and zero field cooled ZFC measurements. Depending on the metal precursor, different spinel oxides of a few nanometers were observed in the samples treated at 350°C. After heating at 900°C non-stoichiometric CoFe₂O₄ was formed in both samples, whose average particle size was only slightly larger than in samples treated at 350°C.