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

Abstract

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 4 nm within a narrow size distribution of 3–5 nm. 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 TB ∼ 140 K 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.