Investigations on magnetic properties and structure for carbon encapsulated nanoparticles of Fe, Co, Ni

In the present work, experiments aim at the encapsulation of foreign materi als within hollow graphitic cage have been carried out for iron group metal s (Fe, Co, Ni) using a modified are-discharge (carbon arc) reactor. HRTEM ( high resolution transmission electron miscroscope), and XRD (X-ray diffract ometer) studies, for three carbon encapsulated materials, showing nanoparti cles of both a metallic phase (alpha-Fe, gamma-Fe; hcp-Co, fcc-Co; fcc-Ni) and also a carbide phase (M3C, M = Fe, Co, Ni) are encapsulated in graphiti c carbon. The magnetic measurement for the three as-made nanoparticles, ind icating that the values of saturation magnetic moment of three nanoparticle are 37.6, 55.5 and 15.7% of the bulk ferromagnetic elements counterparts, respectively. The different comparison values (M-r/M-s) of remanent magneti zation (M-r) and saturation magnetization (M-s) suggest, the encapsulated F e and Co nanoparticles are shown to be ferromagnetic with a ratio of remnan t to saturation magnetization M-r/M-s similar to 0.3; whereas, the encapsul ated Ni nanoparticles exhibits superparamagnetic behavior at room temperatu re. (C) 2000 Elsevier Science S.A. All rights reserved.