Carbon-coated Fe, Co, and Ni ferromagnetic nanoparticles prepared by a modified arc discharge

Carbon-coated Fe, Co, and Ni particles were produced by an are discharge process modified in geometry of the anode and flow pattern of the helium gas. Field emission scanning electron microscopy shows that the resulting materials consist only of carbon-coated metal particles without any nanotubes or other unwanted carbon formations present. X-ray diffraction analysis confirmed that the as-made particles are carbon-coated elements rather than metal carbides. High resolution transmission electron microscopy reveals that these as-made metal particles are covered by one to two graphitic layers. Nitric acid and annealing treatments manifest that the particles completely coated by carbon resist both post-deposition treatments. Magnetic moment measurements indicate that the Fe, Co, and Ni particles are ferromagnetic with a ratio of remnant to saturation magnetization M-R/M-S similar to 0.3 at room temperature. When the particles were made under a given experimental condition, they are of roughly the same size. Under conditions when the supply rates of the metal vs. carbon are changed, for instance by changing the size of the liquid metal pool on the surface of the graphite anode, the exact morphology of each type of metal particles is strongly affected. In this report, the growth mechanism of these particles as well as their morphological properties in dependence of the preparation conditions are discussed.