<title>Structural and magnetic properties of nanosized iron-polyoxocarbosilane core-shell composites prepared by laser pyrolysis</title>

Abstract

Because of their quantum-scale dimensions, nanoparticles exhibit properties different from those of the bulk. As a result of their unique properties, numerous efforts have been made to disperse nanoparticles in polymers to enhance or modify their structural and magnetic properties. A new in situ synthesis method was used to incorporate small iron nanoparticles into a polyoxocarbosilane polymer matrix. Nano-magnetic iron-based composites were obtained by a one-step procedure consisting of the IR laser co-pyrolysis of a sensitized (with ethylene) gaseous mixture containing gaseous iron pentacarbonyl and hexamethyldisiloxane in argon. The simultaneously occurring formation of iron from iron pentacarbonyl and that of organosilicon polymer from hexamethyldisiloxane yield iron nanoparticles surrounded by an organosilicon polymer shell. The particles become superficially oxidized in the atmosphere. They were characterized by Raman analysis, electron microscopy and magnetic measurements. The properties of the nanocomposite particles depend on the experimental synthesis parameters such as flow rates of precursors, total pressure and laser power. Magnetization curves, exchange bias <i>H</i>ex at <i>T</i> = 5 K and AC susceptibility were studied in the temperature range 5-400 K. It was found that the nanocomposite should be in a ferromagnetic blocked state with a minor superparamagnetic contribution of the smallest nanoparticles.