Magnetoelectric effect in multiferroic heteroepitaxial BaTiO_3-NiFe_2O_4 composite thin films

摘要

Heterostructured NiFe_2O_4-BaTiO_3 composite thin films epitaxially grown on (11 l)-SrTiO_3 single-crystal substrate were prepared-using pulsed-laser deposition, where the BaTiO_3 layer grew as columnar structure while the NiFe_2O_4 layer formed a continuous film. Structural characterization by X-ray diffraction and electron microscopy showed good horizontal heterostructures of (11 l)-oriented BaTiO_3 and (11 l)-oriented NiFe_2O_4 on (11 l)-SrTiO_3 whatever their deposition sequences. Such heterostructures present simultaneously strong ferroelectric and ferromagnetic responses at room temperature. In particular, an obvious direct magnetoelectric coupling effect was observed in the heterostructured films. The growth sequence of the BaTiO_3 and NiFe_2O_4 layers on the substrate has an effect on multiferroic behavior of the composite thin films.