Magnetic resonance study of fullerene-like glassy carbon

Multi-shell fullerene-like nanoparticles of glassy carbon were synthesized by a low-temperature pyrolysis of sucrose. These samples were studied by magnetic resonance spectroscopy. ¹³C NMR spectrum of glassy carbon shows a complicated line the most intensive component of which originated from sp² carbons. Measured values of nuclear spin-lattice relaxation times are discussed with a model of system containing intrinsic paramagnetic centers, as it is supported by EPR. EPR reveals extrinsic and intrinsic magnetism in the samples. The former is probably due to para- and ferromagnetic impurities entrapped during the synthesis. The latter is attributed to the carbon system (e.g., dangling bonds). The carbon-originated EPR signal has Lorentzian lineshape and g-factor of 2.0030 ± 0.0001. Its line width as well as electron spin-lattice relaxation time was found to be extremely sensitive to partial oxygen pressure and humidity. The intrinsic magnetism obeys the Curie law at 130-400 K. The total amount of carbon-originated paramagnetic defects exceeds 2 × 10¹⁹ spin/g. They are suggested to exist in all layers of imperfect fullerene(onion)-like particle around their breaches which are large enough allowing oxygen to penetrate freely into the particles.