Ab initio calculation for vacancy-induced magnetism in ferroelectric Na0.5Bi0.5TiO3

We performed ab initio calculations on the magnetism of Na0.5Bi0.5TiO3 (NBT) with rhombohedral perovskite structure. Calculated results show that an ideal NBT is non-magnetic. The sodium (Na) or titanium (Ti) vacancy could induce the magnetism rather than the bismuth (Bi) or oxygen (O) vacancy. The magnetism of rhombohedral NBT with neutral Na or Ti vacancy is mainly originated from the polarization of O 2p electrons. In the rhombohedral NBT with neutral Na or Ti vacancies, the ferromagnetic coupling is more stable.