Hydrothermal synthesis and properties of NiFeO@BaTiO composites with well-matched interface.

NiFeO@BaTiO multiferroic composite particles were produced by a simple hydrothermal method in two steps: preparing NiFeO nanoparticles and then synthesizing core-shell nanocomposites. Multiferroic composite ceramics were sintered from these powders. X-ray diffraction, Raman scattering and energy dispersive x-ray analyses indicated that the core-shell composites with a NiFeO core and BaTiO shell were formed in the hydrothermal environment. Different types of sharp interfaces were self-assembled owing to the minimization of direct elastic energy. The saturation magnetization of the composites linearly increased with the NiFeO content while the dielectric constant decreased. A dielectric peak appeared at around 460 °C because of the oxygen vacancies in the BaTiO ceramics. It resulted in an enhancement of magnetic permeability in the composites, indicating magnetoelectric coupling that was also observed by direct magnetoelectric measurements.