Synthesis and characterization of (NiZnFe 2O 4) 0.5/(SiO 2) 0.5 granular nanocomposites

Abstract

(NiZnFe 2O 4) 0.5/(SiO 2) 0.5 nanocomposites were synthesized by three different methods: sol–gel, wet impregnation of nitrates in powders of amorphous silica and wet dispersion of previously ball-milled powders into amorphous silica. The as-prepared samples were then annealed for 1 h at 1273 K, in air atmosphere, to obtain the desired nanocomposites. Crystallographic phases, particle sizes and lattice parameters were determined from X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements. Specific surface area of the powders was estimated by the BET method and Fourier transform infrared spectroscopy was used to detect the ferrite phase. Hysteresis properties were characterized in the temperature range from 5 to 300 K. The samples synthesized by the sol–gel technique consisted of NiZn ferrite nanoparticles embedded in the amorphous SiO 2 matrix. The same phases were observed in samples obtained by wet mixture of previously milled powders, but in this case a quite broad crystal size distribution results and the ferrite particles are dispersed in a fine silica sintered powder rather than embedded in the SiO 2 matrix. The sample synthesized by wet impregnation of nitrates presented a large mean ferrite crystallite size and small quantities of other phases, as hematite and willemite. All samples displayed ferromagnetic hysteresis in the temperature range studied and it was found that the saturation magnetization of the nanostructured NiZn ferrite was lower than that of the bulk material, in the three composites analyzed.