Electronic structure, stability, and magnetism of rutile-type ultrathin TiO2 nanotubes

In this study, based on density functional theory, we predicted the electronic structure, stability, and magnetism of ultrathin rutile-type TiO2 nanotubes (u-TiO2NTs) with different curvatures. The curvature energy calculations showed that the (m, 0) u-TiO2NTs follow the classical elasticity theory. As the diameter of the NTs increases, the wall thickness becomes thinner, and the binding energy and band gap increase until saturation. For the (10, 0) u-TiO2NT, the neutral Ti vacancies (VTi0) could induce a large magnetic moment and long-range ferromagnetic coupling, whereas the neutral O vacancies (VO0) cannot. In addition to calculations of the vacancy formation energy, we investigated the magnetism and magnetic coupling of the (10, 0) u-TiO2NT with VTi− or VO+. We found that the introduction of VTi− vacancies led to unstable ferromagnetic coupling in the NTs, whereas the VO+ vacancies preferred to couple in a stable ferromagnetic manner. Our results suggest a possible route for obtaining high Curie temperature ferromagnetism in TiO2 materials.