Improvements in the Organic-Phase Hydrothermal Synthesis of Monodisperse MxFe3–xO4 (M = Fe, Mg, Zn) Spinel Nanoferrites for Magnetic Fluid Hyperthermia Application

In the quest for optimal heat dissipaters for magnetic fluid hyperthermia applications, monodisperse M x Fe 3- x O 4 (M = Fe, Mg, Zn) spinel nanoferrites were successfully synthesized through a modified organic-phase hydrothermal route. The chemical composition effect on the size, crystallinity, saturation magnetization, magnetic anisotropy, and heating potential of prepared nanoferrites were assessed using transmission electron microscopy (TEM), dynamic light scattering, X-ray diffraction (XRD), thermogravimetric analysis (TGA), energy-dispersive X-ray spectroscopy (EDS), atomic absorption spectroscopy (AAS), X-ray photoelectron spectroscopy (XPS), and vibrating sample magnetometer (VSM) techniques. TEM revealed that a particle diameter between 6 and 14 nm could be controlled by varying the surfactant ratio and doping ions. EDS, AAS, XRD, and XPS confirmed the inclusion of Zn and Mg ions in the Fe 3 O 4 structure. Magnetization studies via VSM revealed both the superparamagnetic nature of the nanoferrites and the dependence on substitution of the doped ions to the final magnetization. The broader zero-field cooling curve of Zn-doped Fe 3 O 4 was related to their large size distribution. Finally, a maximum rising temperature ( T max ) of 66 °C was achieved for an aqueous ferrofluid of nondoped Fe 3 O 4 nanoparticles after magnetic field activation for 12 min.