Mossbauer spectroscopy studies of carbon-encapsulated magnetic nanoparticles obtained by different routes

Carbon-encapsulated magnetic nanoparticles (CEMNPs) are nanomaterials with a core-shell structure. Their intrinsic properties result both from the unique nature of the encapsulated magnetic phases and the high chemical stability of the external carbon shells. CEMNPs may find many prospective applications, e.g., in magnetic data storage, catalysis, xerography, magnetic resonance imaging, and in biomedical applications. Herein, we present detailed structural studies of such nanostructures by Mossbauer spectroscopy, x-ray diffraction (XRD), scanning electron microscopy, and transmission electron microscopy. CEMNPs have been obtained by three different techniques: carbon are, combustion synthesis, and radio frequency thermal plasma. The evaluation of the phase composition of the products was strongly limited due to the broadening and overlapping of the lines in XRD diffraction patterns. The presence of the semicrystalline phases, which could not been identified by XRD, was established by Mossbauer spectroscopy. Furthermore, the magnetic core phase composition was evaluated quantitatively. The products were purified before structural analyses to remove the nonencapsulated particles. The purification caused significant changes in the mass and the saturation magnetization. The Mossbauer spectra of the purified products were compared with the literature data concerning the as-produced CEMNPs. (C) 2008 American Institute of Physics.