We have investigated the structural and magnetic properties of Ni0.5Zn0.5Fe2O4 nanoparticles embedded in SiO2 fabricated by a sol-gel processing. The obtained (Ni0.5Zn0.5Fe2O4)(x)(SiO2)(100-x) (6 less than or equal to x less than or equal to 78%) samples were characterized by X-ray diffraction, Mossbauer spectroscopy (MS) and vibrating sample magnetometry. The results showed the formation of stoichiometric NiZn-ferrite in the SiO2 matrix, for x < 41%. Samples with higher ferrite fraction have small amounts of Fe2O3. MS revealed the superparamagnetism of the ferrite nanoparticles at room temperature. The combination of different ferrite content and annealing temperatures allowed the obtention of samples with saturation magnetization ranging from 1.3 to 68 emu/g and coercivity from 0 to 123 Oe, value two orders of magnitude higher than those presented by bulk Ni0.5Zn0.5Fe2O4. (C) 1999 Published by Elsevier Science B.V. All rights reserved.1922277280