Magnetoelectric effect in multiferroic heteroepitaxial BaTiO3–NiFe2O4 composite thin films

Heterostructured NiFe2O4–BaTiO3 composite thin films epitaxially grown on (1 1 1)-SrTiO3 single-crystal substrate were prepared using pulsed-laser deposition, where the BaTiO3 layer grew as columnar structure while the NiFe2O4 layer formed a continuous film. Structural characterization by X-ray diffraction and electron microscopy showed good horizontal heterostructures of (1 1 1)-oriented BaTiO3 and (1 1 1)-oriented NiFe2O4 on (1 1 1)-SrTiO3 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 BaTiO3 and NiFe2O4 layers on the substrate has an effect on multiferroic behavior of the composite thin films.