Controllable synthesis and magnetic properties of pure hematite and maghemite nanocrystals from a molecular precursor

Rodlike and cubiform hematite nanocrystals free of organic contaminants were controllably synthesized via hydrothermal processing of an air-stable metallorganic molecular precursor (ferric acetylacetonate: Fe-(ACAC)3) in distilled water, simply by adjusting the reaction temperatures (140–180 °C) and reaction times (1.5–12 h); while pure quadrate maghemite nanocrystals were obtained by direct thermolysis of the Fe-(ACAC)3 in air at 300 °C for 3 h. The phase, morphology, size, and purity of the as-prepared products were characterized by powder X-ray diffraction, transmission electronic microscope, Fourier transform infrared spectroscopy and Raman spectroscopy. The magnetization measurements revealed that the as-prepared hematite nanocrystals all showed a typical superparamagnetic behavior at room temperature, except some variation in the values of remanences and coercive forces with different product morphologies; while the as-prepared maghemite nanocrystals showed a ferromagnetic behavior at room temperature.