Magnetic properties of carbon nanocages: Pure and with the Ni or Co inclusions

Carbon nanocages (CNCs) are promising materials for catalysis, filtration and electrochemistry. This work is devoted to the experimental and theoretical study of the magnetic properties of both pure CNCs and those encapsulated by transition metals Ni and Co. This study presents high-resolution transmission electron microscopy (HR-TEM) images of the homogeneous composite consisting of Co particles with a diameter of 3–5 nm coated with one or more layers of graphitized carbon. We also present HR-TEM images of hollow nanocages obtained after the complete etching of the metal with acid. The coercivity of the homogeneous composites (Ni and Co encapsulated) exhibited a rapid decrease below 50 K, while in the temperature range of 50–350 K, pronounced superparamagnetic properties are observed. On the other hand, in the etched material consisting of hollow carbon cages, the contribution of the diamagnetism of the carbon fraction increases with temperature. Theoretical estimates of saturation magnetization of metal nanoparticles and the electronic diamagnetic susceptibility of the carbon spheres are consistent with the experimental results.