Microwave assisted synthesis of magnetite nanoparticles.

Magnetite nanoparticles of size ranging from 7-10 nm are prepared from aqueous solutions of Fe2+ and Fe3+ by microwave irradiation at different reaction temperatures ranging from 50 to 200 °C. The effect of reaction temperature on the structural and magnetic properties of nanoparticles is studied using X-ray diffraction (XRD), Transmission electron microscopy (TEM), Small angle X-ray scattering (SAXS), Thermo gravimetry (TGA), Differential scanning calorimetry (DSC), Vibrating sample magnetometer (VSM) and Fourier transform infrared spectroscopy (FTIR) techniques. The average size of the prepared particles, obtained from SAXS, is found to vary from 11 to 15±1 nm as the reaction temperature is increased from 50 to 200 °C. The weight gain curves under an external magnetic field show slope changes at 300 and 596 °C because of the magnetite to maghemite phase transition and ferri to paramagnetic phase transitions, respectively. The ferromagnetic γ-Fe2O3 to antiferromagnetic α-Fe2O3 phase transition temperature is found to be enhanced by 154 °C for the nanoparticles prepared at 200 °C, due to an enhanced activation energy for the cubic to a more compact hexagonal transition. The increase in the phase stability of nanoparticles prepared at elevated temperature is attributed to the diffusion of Na+ in the spinel structure. These results are useful to tailor magnetic particles with enhanced thermal stability for practical applications.