Magnetic properties of Mg-ferrite nanoparticles

MgFe2O4 nanoparticles encapsulated in amorphous SiO2 were prepared by means of a wet chemical method, and the magnetic properties were studied. The diameters of these particles were estimated from X- ray diffraction patterns as ranging from 3 to 8 nm. Magnetization measurements were carried out for each sample under a +/- 50 kO field. The blocking temperature, T-b, was determined to be around 30K from the temperature dependence of both the field- cooled ( FC) and the zero-field- cooled ( ZFC) magnetization. The M - H curve indicated the presence of ferromagnetic behavior with hysteresis below the blocking temperature, Tb. A large coercive force of about 1000 Oe was found at 5K. Heat treatment was carried out for the prepared samples using an electric furnace in air. A clear difference in magnetization was found between the quenched samples and annealed samples. This phenomenon suggests that the Mg2+ ions in the spinel structure would be randomly distributed into both the A- and the B- site. (c) 2006 Elsevier B. V. All rights reserved.