Analysis of zero field and field cooled magnetization curves of CoFe2O4 nanoparticles with a T-dependence on the saturation magnetization

In this work, CoFe2O4 nanoparticles embedded inside an amorphous SiO2 were produced by the sol-gel method through the hydrolysis and condensation of tetraethyl orthosilicate (TEOS). In order to improve the sample homogeneity, a set of samples was prepared for using citric acid. Morphological and magnetic properties have been obtained via transmission electronic microscopy (TEM) and AC and DC magnetization measurements, respectively. TEM analysis indicate that nanoparticles present a spherical-like shape. The broad peaks and the presence of thermal hysteresis at low temperatures in the Zero-Field-Cooled and Field-Cooled (ZFC/FC) curves are consistent with the superparamagnetism phenomenon. Once the maximum magnetization, M (H = 70 kOe), extracted from the MvsH loops is not constant along the studied temperature range we have used, for the first time, a T-dependence of the saturation magnetization, MS, to fit the ZFC/FC magnetization curves. Finally, the extracted parameter from both ZFC/FC magnetization curves and AC susceptibilities fits are used to calculate the nanoparticles mean sizes. These results are in good agreement with that extracted from transmission electronic microscopy.