D0 magnetism in Ca doped narrow carbon nanotubes: First principle chirality effect study

Curvature has always had crucial effects on the physical properties of narrow carbon nanotubes (CNTs) and here spin-polarized density functional calculations were employed to study electronic and magnetic properties of calcium-decorated narrow (5,5) and (9,0)CNTs with close diameters (∼7 Å) and different chiralities. Our results showed that chirality had great impact on the electronic structure and magnetization of the doped CNTs. In addition, internally or externally doping of the calcium atoms was studied comparatively and although for the (9,0)CNT the internal doping was the most stable configuration, which involves a novel kind of spin-polarization originated from Ca-4s electrons, but for the (5,5)tube the external doping was the most stable one without any spin-polarization. On the other hand, calcium doping in the center of the (5,5)CNT was an endothermic process and led to the spin-polarization of unoccupied Ca-3d orbitals via direct exchange interaction between adjacent Ca atoms. In the considered systems, the existence of magnetization in the absence of any transition-metal elements was an example of valuable d0 magnetism title.