Coercividade de nanopartículas de CoFe2O4 dispersas em uma matriz de SiO2

Abstract

In this work, we study the magnetic properties of CoFe2O4 nanoparticles dispersed in silica (SiO2) matrix. Samples were produced by the sol-gel method and synthesized at different temperatures. The average distance between the particles and thus the nature of inter-particle interactions were controlled for using different concentrations of iron and cobalt salts and the starting material tetraethylorthosilicate (TEOS). The samples were characterized by thermogravimetry (TG), X-ray fluorescence (XRF), X-ray diffraction (XRD), transmission electron microscopy (TEM) and magnetization as a function of magnetic field and temperature. Thermogravimetric analysis showed that the weight loss increases with increasing concentration of salts in the starting solution. The results of X-ray diffraction combined with the transmission electron microscope images confirmed the presence of CoFe2O4 nanoparticles dispersed into the SiO2 matrix. Magnetization measurements showed a typical behavior generally showed by a magnetic nanoparticles system, that is, the observation of a peak in the curve FC-ZFC with a thermal hysteresis in the low temperature region. In particular, we observed a dependence of the coercive field with temperature of CoFe2O4 nanoparticles that did not follow the predictions of the model Bean-Livingston. We believe that this fact is linked more to the effect of size distribution than the possible effects of interaction between the nanoparticles. In this regard, a model considering a particle size distribution in the coercivity of nanoparticles was used. The model was able to fit the experimental data to wide temperature range.