Sol–Gel Based Liquid-Mix Method for the Synthesis of Znfe2O4 Spinel

The superparamagnetic ZnFe2O4 (ZFO) powder with spinel structure was synthesized by a sol–gel based liquid-mix method using deionized water, citric acid, iron nitrate, zinc nitrate, and propylene glycol. Based on the principles of the Pechini method, the obtained solutions were treated under reflux at 95 °C followed by drying to obtain the desired powder. Simultaneous thermal analysis (STA) showed that there are three main thermal events at 165, 300, and 800 °C, which are related to the evaporation of water and/or volatile chemicals, combustion of organic materials, and chemical reactions to form ZFO phase, respectively. Among different calcination temperatures, thermal treatment at 900 °C led to the formation of a powder which its XRD pattern is well-matched with the ZFO standard peaks. Scanning electron microscopy (SEM) showed that calcination at 400-600 °C led to some agglomerated sediment particles in the range of 50-100 nm, whereas the morphologies of the samples calcined at 700-900 °C consisted of some fused particles with larger size (~1 μm). The vibrating sample magnetometer (VSM) results approved that although magnetization saturation (Ms) values were negligible in the samples calcined at lower temperatures (low– temperature samples), Ms value of the sample calcined at 900 °C was about ±7.5 emu/g. On the other hand, the S-shaped hysteresis curves of the high-temperature samples (calcined at 700-900 °C) and consequently zero/near-zero value for the coercivity (Hc) and remanence (Mr) parameters confirmed the superparamagnetic behavior of the as-synthesized ZFO compound.