Magnetic nanoparticles prepared by laser pyrolysis

Ultrafine /spl gamma/-Fe/sub 2/O/sub 3/ and /spl alpha/-Fe particles of sizes between 3.5 and 15 nm have been directly synthesized by laser induced pyrolysis of iron pentacarbonyl vapors. It was found that a controlled oxidation inside the reaction cell gives rise to the formation of maghemite, whereas the oxidation outside the reaction cell results in the formation of metal iron nanoparticles. Additionally, particle size and crystallinity can be varied by controlling other experimental conditions, such as the laser power, the pressure into the reactor cell, and the precursor temperature. The particles were characterized by X-ray diffraction, IR spectroscopy, and transmission electron microscopy. Magnetic properties of these materials showed a strong dependence not only on the particle size but also on the degree of crystallinity, which has been often undervalued, in particular for the case of maghemite samples.