Preparation and magnetic properties of magnetite nanoparticles by sol-gel method

Magnetite (Fe₃O₄) nanoparticles have been synthesized by sol-gel method combined with annealing under vacuum, without use of surfactants and using precursors like FeCl₃·6H₂O, ethanol and propylene epoxide and using several annealing temperatures and different annealing time. The approach is straightforward, inexpensive and versatile. The annealing process, the phase structures, morphologies, particle sizes and magnetic properties of Fe₃O₄ nanoparticles have been characterized by thermogravimetric-differential thermal analysis (TG-DTA), X-ray diffraction (XRD), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM). The results indicate that with annealing at 300°C for 2 h under vacuum, magnetite (Fe₃O₄) nanoparticles in the interval of 9~11 nm were synthesized and that the six, the corresponding saturation magnetization value and coercivity value of Fe₃O₄ nanoparticles increase with the increase of synthesized temperature. In addition it is possible to obtain a narrower nanoparticle size dispersion and smaller nanoparticles for shorter annealing time under vacuum and this method could be extended to prepare other transition and main-group metal oxide materials.