Magnetic properties of carbon nanostructures

We investigate the magnetic response and the ring currents induced by the presence of an external magnetic field in different carbon nanostructures using a π-electron tight binding model in conjunction with the London approximation. We consider fullerenes, corrugated and non-corrugated carbon nanotori, and finite graphene sheets. For corrugated carbon nanotori, we have constructed the structures in two different ways: by joining the ends of carbon nanotubes containing pentagonal, hexagonal and heptagonal carbon rings (rectangular and hexagonal Haeckelites); and by coalescing C60 molecules along the three different axes of symmetry (C2, C3 and C5). The non-corrugated carbon nanotori have been constructed by joining the ends of standard carbon nanotubes containing hexagonal rings only. For the graphene ribbons, we considered those exhibiting armchair or zig-zag edges. Our results reveal strong paramagnetic signals in structures containing non-hexagonal carbon rings. For carbon nanotori, the presence of strong paramagnetism causes the electrons to flow around the torus. We also observed that the ring currents of graphene ribbons are small and localised at the edges. Finally, the magnetic moment of nanotori constructed from Haeckelite structures is also described as a function of doping (adding additional electrons or holes).