Synthesis, crystal structures and magnetic properties of Co particles encapsulated in carbon nanocapsules

Carbon-coated cobalt particles were produced by are-evaporation of a Co-packed graphite rod in a modified fullerene generator. Cobalt particles grown were in an fee phase, with a trace amount of hcp-Co. The particles were nominally spherical in shape, and typically 10-100 nm in diameter. Thickness and structure of outer carbon layers could be controlled by varying the relative area of a Co-packed hole drilled in the graphite rod. Saturation magnetization (M-s) and the coercive force (H-c) was measured between room temperature and 800 degrees C for powder samples: Temperature dependence of the measured M-s was consistent with that for fcc-Co. The highest value of M-s of 160 emu/g at room temperature, nearly the same value for bulk fee-Co, was obtained for Co particles covered with thin carbon layers. H-c varied from 600 Oe to 300 Oe, depending on the size of Co particles.