Magnesium ferrite nanoparticles inserted in a glass matrix—Microstructure and magnetic properties

Glasses with composition xFe2O3–5MgO–(95 − x)SiO2, where x is equal to 1.25, 2.5, 5 and 10 mol%, were prepared by the sol–gel method. The gel samples were heat-treated at temperature between 500 and 1000 °C. The samples were studied using X-ray diffraction (XRD), scanning electron microscopy combined with X-ray microanalysis by energy dispersive spectrometer (SEM-EDS), visible–near infrared spectrometry (VIS-NIR) and dc magnetic measurements. In most samples the presence of magnesium ferrite was detected by XRD. However, in the brown and transparent 1.25Fe2O3–5MgO–93.75SiO2 sample heat-treated at 500 °C, there was no evidence, by XRD, of the presence of magnesium ferrite. In 10Fe2O3–5MgO–85SiO2 composition, heat-treated at 500 and 1000 °C, hematite was also present. By the Scherrer method it was determined that the average size of magnesium ferrite crystals, in all the samples heat treated at 1000 °C, varied from 8 to 10 nm. All the samples heat treated at 1000 °C exhibited ferro or ferrimagnetic interactions combined with superparamagnetism with a blocking temperature. The sample with composition 1.25Fe2O3–5MgO–93.75SiO2 treated at 500 °C showed a paramagnetic behaviour down to 5 K.