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 materials within hollow graphitic cage have been carried out for iron group metals (Fe, Co, Ni) using a modified are-discharge (carbon arc) reactor. HRTEM (high resolution transmission electron miscroscope), and XRD (X-ray diffractometer) studies, for three carbon encapsulated materials, showing nanoparticles 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 graphitic carbon. The magnetic measurement for the three as-made nanoparticles, indicating 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 magnetization (M-r) and saturation magnetization (M-s) suggest, the encapsulated Fe and Co nanoparticles are shown to be ferromagnetic with a ratio of remnant to saturation magnetization M-r/M-s similar to 0.3; whereas, the encapsulated Ni nanoparticles exhibits superparamagnetic behavior at room temperature. (C) 2000 Elsevier Science S.A. All rights reserved.