Carbon-coated cobalt nanocapsules were synthesized by the chemical vapor-condensation process with cobalt carbonyl (Co (CO) ) used as precursor and carbon monoxide (CO) as carrier gas. The characterization and magnetic properties of 2 8 carbon-coated cobalt nanocapsules were investigated systematically. The transmission electron microscope (TEM) images showed that the as-prepared nanoparticles consist of a metal core and an amorphous carbon shell. X-ray diffraction and TEM selected area diffraction revealed the presence of f.c.c. Co phase, h.c.p. Co phase, and minority Co C, Co C phases. The 2 3 2 21
saturation magnetization at room temperature of the nanocapsules is 146.9 Am kg , which is 90% of the bulk ferromagnetic element counterpart. The coercive force at room temperature of the nanocapsules is 0.12 T, while the ratio of remnant to saturation magnetization M /M is about 0.4. The saturation magnetization and the coercive force increase with r s increasing the decomposition temperature, mainly due to the increase of the size of the magnetic particles. The decomposition of the cobalt carbonyl (Co (CO) ) and CO gas can decrease efficiently the oxygen content in nanocapsules.
2 8
The metallic Co nanoparticles completely coated by carbon can resist the dilute acid erosion as well as the oxidation. The thermal stability of the Co nanocapsules is also studied.