Room-temperature magnetoelectric coupling in nanocrystalline Na0.5Bi0.5TiO3

Nanocrystalline Na0.5Bi0.5TiO3 was prepared by sol-gel method. The nanocrystalline Na0.5Bi0.5TiO3 plates present room temperature ferromagnetism (FM). The reduction of FM for the plate with subsequent long time and high temperature air-annealing indicating that the observed ferromagnetism is connected with the vacancies at/near the surface of nanograins. For Na0.5Bi0.5TiO3 powders after annealing at 900 °C in air, a subsequent annealing in vacuum at 900 °C for 20 min weakens the room-temperature FM, but a subsequent annealing in oxygen atmosphere at 900 °C for 20 min enhances the room-temperature FM, which means that the observed FM in nanocrystalline Na0.5Bi0.5TiO3 may originate from cation vacancy at/near the surface of nanograins. The results of density functional theory calculation with the local density approximation plus on-site effect (LDA + U) method on the magnetism of Na0.5Bi0.5TiO3 (100) surface show that Na vacancies can introduce a nonzero magnetic moment. The Na0.5Bi0.5TiO3 plates annealed a...