NiO@C and Ni@C Nanoparticles: Synthesis, Characterization and Magnetic Properties

Carbon-coated nickel oxide nanoparticles (NiO@C) were synthesized by near-critical hydrothermal method using starch and nickel nitrate as precursors. Also,carbon-coated Ni nanoparticles (Ni@C) were obtained by annealing NiO@C nanoparticles in hydrogen atmosphere. The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy(TEM), Raman spectroscopy, simultaneous thermal analysis (STA) and physical property measurement system (PPMS). The average sizes of the NiO and Ni nanoparticles were 18[Formula: see text]nm and 15[Formula: see text]nm according to the XRD analysis, respectively. Raman spectroscopy and thermogravimetric analysis demonstrated that the carbon shells of NiO@C and Ni@C nanoparticles were composed of amorphous and partially graphitized carbon. The formation mechanism of NiO@C and Ni@C nanoparticles was briefly discussed. The Ni@C nanoparticles have enhanced coercive force than bulk nickel, and their coercive force has shown a linear dependence on the square root of temperature.