Magnetic properties of carbon nanotubes produced by the arc-discharge method under different conditions

The diamagnetic susceptibility and EPR signals of multi-walled carbon nanotubes produced at different helium pressures and rates of feed of the graphite anode are studied. It is found that a decrease in the helium pressure and in the feed rate of the graphite anode leads to an increase in the diamagnetic susceptibility and the g factor of the EPR signal associated with the carbon nanotubes. The investigation into the magnetic properties within the framework of the band model of quasi-two-dimensional graphite demonstrates that an increase in the diamagnetic susceptibility and in the g factor of the EPR signal is due to a decrease in the content of layered defects in the carbon nanotubes. Analysis of the EPR spectra indicates that, in addition to carbon nanotubes, the cathode deposit contains a considerable fraction of polyhedral nanoparticles at helium pressure in a chamber below 200 Torr. A similar situation is observed for cathode deposits obtained at low feed rates of the graphite anode.