Magnetic properties of dense carbon nanospheres prepared by chemical vapor deposition

Carbon nanospheres (∅ ∼ 50 nm) prepared by chemical vapor deposition exhibit Curie-type paramagnetism, with a localized spin density NS = 4.01 × 1019 spins/g. The spheres are solid, as shown by their cross-sections. Their low surface area excludes the presence of exposed graphene layers at the surface being the origin of paramagnetic centers. Inside the carbon spheres, HRTEM reveals a concentric wavy pattern of graphitic (sp2-bonded) clusters (size < 2 nm) embedded in disordered carbon. The high density of carbon atoms with sp2–sp3 hybrid orbitals acting as paramagnetic centers, at interfaces between graphitic (sp2-bonded carbon) clusters and amorphous carbon, can explain the magnetic measurements.