Room-temperature ferromagnetism in nickel-doped wide band gap ferroelectric Bi0.5K0.5TiO3 nanocrystals

Abstract

We report the effect of nickel doping on the structural, optical, and magnetic properties of Bi0.5K0.5TiO3 nanocrystal. The X-ray diffraction results indicated that Ni was substituted into the Ti sites in Bi0.5K0.5TiO3 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 Bi0.5K0.5TiO3 samples. The ferromagnetic signal strongly influenced the paramagnetic signal for Ni-doped Bi0.5K0.5TiO3 samples at room temperature. The room-temperature ferromagnetism in Ni-doped Bi0.5K0.5TiO3 samples could be contributed by intrinsic reason due to presence of Ni ion in Bi0.5K0.5TiO3 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.