Room-temperature magnetoelectric coupling in nanocrystalline (Na1−xKx)0.5Bi0.5TiO3 (x = 0.1, 0.16, 0.20, 0.25)

Abstract

Nanocrystalline (Na_1−xK_x)_0.5Bi_0.5TiO₃ (x = 0.1, 0.16, 0.20, 0.25) plates exhibit ferromagnetism at room temperature. The reduction of ferromagnetism for the (Na_1−xK_x)_0.5Bi_0.5TiO₃ plates over time and the high temperature air-annealing indicates that the observed ferromagnetism is connected with the cation vacancies at/near the surface of nanograins. The density functional theory calculation with the local density approximation plus on-site effect method on the magnetism of the (Na_5/6K_1/6)_0.5Bi_0.5TiO₃ supercell shows that Na vacancies can introduce a nonzero magnetic moment. The (Na_1−xK_x)_0.5Bi_0.5TiO₃ (x = 0.1, 0.16, 0.20, 0.25) plates when annealed at 900 °C for 1 hour present d⁰ multiferroicity with the coexistence of ferromagnetism and ferroelectricity at room-temperature. A room-temperature magnetodielectric effect is observed in (Na_1−xK_x)_0.5Bi_0.5TiO₃ plates and the appropriate substitution of potassium can increase the magnetodielectric effect. In addition, electric field treatment leads to an enormous enhancement of saturation magnetization for (Na_1−xK_x)_0.5Bi_0.5TiO₃ multiferroic plates, resulting in a strong magnetoelectric coupling.