Magnetism in corrugated carbon nanotori: The importance of symmetry, defects, and negative curvature

We demonstrate that carbon nanotori constructed by either coalescing C ₆₀ molecules along the 5-fold axis (incorporating pentagons and octagons) or by joining the ends of Haeckelite tubes (containing heptagons, hexagons, and pentagons) exhibit large magnetic moments when an external magnetic field is applied. In particular, we have used a π-orbital nearest-neighbor tight-binding Hamiltonian with the London approximation in order to study the influence of uniform external magnetic fields on various types of torous-like carbon nanostructures with negative and positive Gaussian curvature. We have calculated the ring currents and the induced magnetic moments on these structures. The results reveal the presence of an unexpected magnetic response, which is due to the presence of nonhexagonal carbon rings. Our results could also explain the existence of ferromagnetic nanocarbons. We envisage that coalesced peapods may exhibit unusual magnetic properties.