Ferromagnetic spin ordering on carbon nanotubes with topological line defects

We report first-principles total-energy electronic-structure calculations in the density functional theory performed for carbon nanotubes with a topological line defect consisting of pentagon and octagon rings. We find that the ground state of the nanotubes with the topological line defect is ferromagnetic with small but finite magnetic moment of about 0.04 mu(B)/A. Detailed analyses of energy bands and spin densities unequivocally reveal the nature of the ferromagnetic spin ordering which is associated with the peculiar edge-localized states of graphite flakes.