Crystal structure of superparamagnetic Mg_0.2Ca_0.8Fe₂O₄ nanoparticles synthesized by sol–gel method

Powders of magnetic iron oxide nanoparticles (Mg_0.2Ca_0.8Fe₂O₄) were prepared by a sol–gel method using ethylene glycol and nitrates of Fe, Ca and Mg as starting materials. Those powders were heat treated at different temperatures (573, 673, 773 and 873 K). In order to evaluate the effect of the heat treatment temperature on the nanoferrites properties, X-ray diffraction (XRD), vibrating sample magnetometry (VSM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) techniques were used. It was found that the reaction products exhibit nanometric sizes and superparamagnetic behavior. It is also demonstrated that, as the heat treatment temperature increases, the particle size and the saturation magnetization of the nanoferrites are increased. - Highlights: • Mg_0.2Ca_0.8Fe₂O₄ superparamagnetic nanoparticles were successfully synthesized. • Particle average sizes of Ca–Mg ferrites were within the range of 8–25 nm. • The nanoferrite treated at 873 K showed a stoichiometry close to Mg_0.2Ca_0.8Fe₂O₄. • The heat treatment temperature has a strong effect on the crystal structure. • These nanoparticles are potential materials for magnetic hyperthermia