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 5K) 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 center dot 40Fe(3)O(4) was synthesized. The NO3- decreased the Fe2+ concentration through oxidation and reduction reactions in the polyol method for the formation of ZnFe2O4. A possible mechanism for the stoichiometrid ZnFe2O4 formation was proposed and discussed, based on the time-resolved experiments. (C) 2014 Elsevier Ltd. All rights reserved.