Facile synthesis of stoichiometric zinc ferrite nanocrystal clusters with superparamagnetism and high magnetization

Stoichiometric ZnFe2O4 magnetic nanocrystal clusters (MNCs) with an average diameter of 127 nm have been successfully synthesized by using a one-step solvothermal method without any additives, where nitrates (Fe(NO3)3 and Zn(NO3)2) were used as reactants. Different characterization techniques were used, such as XRD, ICP-AES, TEM, HRTEM, XPS, and SQUID. The results demonstrate that the stoichiometric ZnFe2O4 is superparamagnetic, and the saturation magnetization (35.9 ± 0.1 emu/g at 300 K, 78.0 ± 0.1 emu/g at 5 K) is higher than that reported in some references. However, when FeCl3 and ZnCl2 were used as reactants that replaced the nitrates at the same experimental conditions, ZnFe2O4 · 40Fe3O4 was synthesized. The NO 3 − decreased the Fe2+ concentration through oxidation and reduction reactions in the polyol method for the formation of ZnFe2O4. A possible mechanism for the stoichiometric ZnFe2O4 formation was proposed and discussed, based on the time-resolved experiments.