The Synthesis of Superparamagnetic Cobalt Nanoparticles Encapsulated in Carbon Through High-pressure CVD

Superparamagnetic nanocomposites of carbon-coated cobalt (Co@C) nanoparticles are synthesized through CVD by the use of cobaltocene and an additional hydrocarbon as the precursor. The nanocomposite is characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman spectroscopy (RS), and superconducting quantum interference device (SQUID) magnetometry. The cobalt nanoparticles exhibit face-centered cubic (fcc) structure and an average size of about 4nm within a narrow size distribution of 3-5nm. They are tightly embedded in the carbon matrix in core/shell structures and well protected against oxidation. Magnetic results reveal superparamagnetic behavior with blocking temperature T-B approximate to 140K and a room temperature saturation magnetization of 79 emu g(-1). We evaluate synthesis parameters such as decomposition temperature, pressure, and ratio of cobalt to carbon in the gaseous precursor and show that they strongly affect the characteristics of the C matrix, the size of cobalt particles, and thus the magnetic properties of the nanocomposite.