Magnetic Study of SiO_2/γ-Fe_2O_3 Nanocomposites Prepared by the SOL-GEL Method

摘要

Nanocomposites of 7-Fe,O, in a silica matrix were prepared by Hie sol-gel method using letramethylorthosilicate (TMOS) as a precursor of silica and introducing iron as Fc(NC),), with Fc/Si ratios of 2, 5, 10 and 20%. Tlie obtained gels were calcinated at temperatures between 6Q0"C and IO()()"C. Magnetic measurements performed with a vibrating magnetometer showed that superparamagnetic Y-Fe,O, nanoparticles began to form at 700"C, as confirmed by X-rays and Miissbauer spectroscopy. Superparamagnetic magnetization curves were filled by a Langcvin function considering a log-normal particle size distribution. Tins allowed to determine the saturation magnetization and the particle si?,e distribution of the samples. The latter results were in good agreement with observations made by Transmission Electronic Microscope. For all studied concentrations, the y-FejO, particles size increased with the calcination temperature up to a maximal average diameter of 40 A. This maximum was reached at 900r'C for the highest concentrations and 10()0r'C for the lowest. Calcinations at higher temperatures led to the degradation of the 7-FejOj phase with creation of defects in [he pnrlicles and formation of a-Fe,O,. This phenomenon was accompanied by n decrease in (he saturation magnetization and the presence of an hysteresis in the magnetization curve.