Solvothermal synthesis, characterization and magnetic properties of nearly superparamagnetic Zn-doped Fe₃O₄ nanoparticles

We report a facile solvothermal method for synthesizing nearly superparamagnetic Zn-doped Fe₃O₄ nanoparticles with controllable doping concentration. All samples demonstrate a typical spinel structure with small size (less than 20 nm). The Zn ion doping effect on the structure, morphology and magnetism of Fe₃O₄ nanoparticles have been systematically studied by XRD, TEM, FTIR, XPS and FMR. It is found that the saturation magnetization of Fe₃O₄ first increases then decreases with increasing Zn doping concentration due to the different site occupation of Zn ions. In contrast, dynamic magnetic measurements demonstrate that the Lande g-factor shows a monotonic increasing trend by the increase of Zn doping concentration.