Preparation of x(Ni0.65Zn0.35Fe2O4)/(100 − x)SiO2 nanocomposite powders by a modified sol–gel method

The synthesis of (Ni0.65Zn0.35Fe2O4)/(100 − x)SiO2 (x = 35% Si 65%, mass percent) nanocomposites, by a sol–gel method, starting from tetraethylorthosilicate, metal nitrates and polyols is reported here. The gels obtained were thermally treated at 130 °C, when the redox reaction between metal nitrates and polyol took place in the pores, forming Fe(III), Ni(II), Zn(II), carboxylate compounds, which are precursors of the ferrite. The precursors formation and thermal decomposition inside the silica matrix have been studied by thermal analysis and FT-IR spectrometry. The controlled thermal treatment of the gels, which contained the ferrite precursors, lead to the formation of spherical Ni, Zn ferrite nanoparticles embedded in silica matrix. Thus, XRD spectra and TEM images showed that the ferrite particles diameters were under 30 nm in size. The magnetic behaviour of the ferrite nanoparticles embedded in the silica matrix, measured in quasi-static magnetic field (50 Hz), modified from superparamagnetic to ferrimagnetic, depending on the annealing temperature.