Superparamagnetic behaviour of gamma-Fe2O3 nanoparticles dispersed in a silica matrix

The structural and magnetic properties of two Fe2O3-SiO2 nanocomposites, containing respectively 16.9 and 28.5 wt.% Fe2O3, were investigated. The samples were synthetized by a sol-gel method, using ethylene glycol as a solvent, and heating the gels gradually to 900 degreesC. The procedure allowed us to obtain gamma -Fe2O3 nanoparticles homogeneously dispersed in the amorphous silica matrix. The particles have a narrow size distribution and mean sizes from 3 to 6 nm depending on the iron oxide content. The magnetic properties of the samples were investigated by static and dynamic susceptibility measurements. All the samples showed superparamagnetic behaviour. The superparamagnetic relaxation was investigated also by Mossbauer spectroscopy. Hysteresis loops were measured at 2.5 K and both samples showed high values of coercive field. The role of magnetic interparticle interactions on the magnetic properties is discussed.