J. Phys. IV France 07 (1997) C1-555-C1-556
Magnetic Study of SiO2/γ-Fe2O3 Nanocomposites Prepared by the SOL-GEL MethodN. Viart1, D. Niznansky2 and J.L. Rehspringer1
1 Institut de Physique et Chimie des Matériaux de Strasbourg, Groupe des Matériaux Inorganiques, 23 rue du Loess, 67037 Strasbourg cedex, France
2 Institute of Inorganic Chemistry, Academy of Science of Czech Republic, 25068 Rez u Prahy, Czech Republic
Nanocomposites of γ-Fe2O3 in a silica matrix were prepared by the sol-gel method using tetramethylorthosilicate (TMOS) as a precursor of silica and introducing iron as Fe(NO3)3 with Fe/Si ratios of 2, 5, 10 and 20%. The obtained gels were calcinated at temperatures between 600°C and 1000°C. Magnetic measurements performed with a vibrating magnetometer showed that superparamagnetic γ-Fe2O3 nanoparticles began to form at 700°C as confirmed by X-rays and Mössbauer spectroscopy. Superparamagnetic magnetization curves were fitted by a Langevin function considering a log-normal particle size distribution. This allowed to determine the saturation magnetization and the particle size distribution of the samples. The latter results were in good agreement with observations made by Transmission Electronic Microscope. For all studied concentrations, the γ-Fe2O3 particles size increased with the calcination temperature up to a maximal average diameter of 40 Å. This maximum was reached at 900°C for the highest concentrations and l000°C for the lowest. Calcinations at higher temperatures led to the degradation of the γ-Fe2O3 phase with creation of defects in the particles and formation of α-Fe2O3. This phenomenon was accompanied by a decrease in the saturation magnetization and the presence of an hysteresis in the magnetization curve.
© EDP Sciences 1997