Spherical (ZnδNi1-δFe2O4)γ nanoparticles in an amorphous (SiO2)1-γ matrix, prepared with the sol–gel method Original Research Article

By using the sol–gel method we have obtained spherical nanoparticles (NPs) of stoichiometric (ZnδNi1-δFe2O4)γ mixed ferrite (δ=0.15; 0.35; 0.65 and γ=0.15), dispersed in an amorphous (SiO2)1-γ matrix (nanocomposites). The nanocomposites were investigated at room temperature by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), electron diffraction (ED), Mössbauer spectroscopy and quasi-static magnetic measurements. We have studied in detail the magnetic behavior of ferrite NPs in a silica matrix, both under quasi-static (50 Hz) and dynamic (20 MHz) conditions. The results show a pure superparamagnetic (SPM) behavior of the sample that has a concentration of the Zn ions of δ=0.15. At higher concentrations, there is a significant deviation from this behavior and this deviation increases with the increase of δ. We attribute the observed behavior to the Néel-type magnetic relaxation processes. After processing the TEM image and performing magneto-granulometric measurements, it has resulted that on the surface of NPs embedded in the silica matrix a layer is formed; this layer has a thickness in the size range of nanometers and it has no magnetic ordering.