Room-Temperature Ferromagnetism in Nickel-Doped Wide Band Gap Ferroelectric Bi_0.5K_0.5TiO₃ Nanocrystals

抄録

We report the effect of nickel doping on the structural, optical, and magnetic properties of Bi_0.5K_0.5TiO₃ nanocrystal. The X-ray diffraction results indicated that Ni was substituted into the Ti sites in Bi_0.5K_0.5TiO₃ and the NiTiO₃ phase was formed when Ni concentration was higher than 3 mol%. The band gap value decreased from 3.31 eV to 2.96 eV when the Ni concentration changed from 0 to 3 mol% and then increased with higher Ni concentration. Both weak-ferromagnetism and diamagnetism coexisted in un-doped Bi_0.5K_0.5TiO₃ samples. The ferromagnetic signal strongly influenced the paramagnetic signal for Ni-doped Bi_0.5K_0.5TiO₃ samples at room temperature. The room-temperature ferromagnetism in Ni-doped Bi_0.5K_0.5TiO₃ samples could be contributed by intrinsic reason due to presence of Ni ion in Bi_0.5K_0.5TiO₃ crystal and by extrinsic reason due to segregation of NiTiO₃ clusters when Ni concentration was over 3 mol% threshold. This method may provide a useful way to get both single-phase multiferroics and composite multiferroics materials.