Magnetic and electronic properties of multiwall carbon nanotubes

Multiwall carbon nanotubes were studied by dc magnetization and electron spin resonance (ESR) measurements. Hole doping is inferred from both the high-field dc susceptibility and ESR parameters complying favorably with the band model of two-dimensional graphite. Paramagnetic deviations are evinced on the diamagnetic susceptibility at weak fields and low temperatures, conforming qualitatively with the Aharonov-Bohm effect on the energy gap for magnetic field parallel to the tube axis. Comparison with theoretical predictions for ensembles of carbon nanotubes reveals appreciable differences, indicative of the diverse distribution of nanotubes as well as the presence of active doping.