Mössbauer spectroscopy of iron oxide nanoparticles containing both magnetite and maghemite

Iron oxide nanoparticles are available in two common phases, including magnetite (Fe₃O₄) and maghemite (Fe₂O₃). Upon exposure to oxygen atoms, the magnetite phase readily oxidizes into the maghemite phase with the partial conversion of ferrous ions into ferric ions. We report on the approach to determine the ratio of magnetite and maghemite in iron oxide nanoparticles synthesized by the hydrothermal process. The crystallinity of these nanoparticles has been investigated by X-ray diffraction studies and transmission electron microscopy observations. The hysteresis loops of the iron nanoparticles demonstrated the “S-shaped” pattern corresponding to superparamagnetic behavior. The Mössbauer spectrum of the sample is compared with the theoretically predicted model to determine the contributions from magnetite and maghemite. Such characterization is necessary for the synthesis of magnetic nanoparticles of uniform size with potential for biomedical applications.