Investigation of structure and magnetic properties of nanocrystalline iron oxide powders for use in magnetic fluids

Iron oxide nanopowders with particles of different size, obtained by co-precipitation and sonochemical methods, were studied by X-ray diffraction, transmission electron microscopy and Mossbauer spectroscopy. The average size of nanoparticles obtained by a co-precipitation method, was about 10 nm. The main phase component of such nanoparticles was maghemite phase gamma-Fe2O3. It was shown, that these nanoparticles were superparamagnetic. In contrast, the nanoparticles obtained by sonochemical method, consisted of larger particles with an average size of around 25 nm. Their main phase component was magnetite Fe3O4. This powder clearly showed hard magnetic properties. (C) 2012 Elsevier B. V. All rights reserved.