The origin of magnetism induced by intrinsic defects in anatase-type ultrathin TiO2 nanotube

Abstract The structural, electronic and magnetic properties of intrinsic defects in anatase-type ultrathin TiO2 nanotube have been investigated systematically by first-principles calculations. The neutral Ti vacancies ( V Ti 0 ) could induce a large magnetic moments and long-range ferromagnetic coupling, nevertheless, it is difficult to create a significant amount of V Ti 0 in nanotube due to its higher formation energy. The neutral oxygen vacancies ( V O 0 ) are more easily to form than V Ti 0 vacancies, and the type of their magnetic coupling is related not only to the kinds of oxygen vacancies but also to the distance of vacancies, and their antiferromagnetic couplings are stable in most cases. Thus, the monovalence positively- and negatively-charged vacancy defects ( V O + , V O - , V Ti + , and V Ti - ) in nanotube are predicted. By comparing the formation energies of these neutral and charged vacancies, the V O + vacancies are more easily formed in nanotube under O-poor condition, and their ferromagnetic couplings are energetically favorable. The V Ti - vacancies are more stable under O-rich condition, and they prefer to couple in a antiferromagnetic way. Our work offers a possible route toward high Curie temperature ferromagnetism in TiO2 materials.