Modification of Ferroelectric Properties of BaTiO3–CoFe2O4 Multiferroic Composite Thin Film by Application of Magnetic Field

Abstract

We prepared BaTiO3–CoFe2O4 composite thin film on (La0.5Sr0.5)CoO3/CeO2/YSZ/Si(100) substrate by pulsed laser deposition. Simultaneous epitaxial growths of BaTiO3 and CoFe2O4 were achieved. Reciprocal space map measurement revealed that the lattice parameters of BaTiO3 parallel and perpendicular to the substrate are 0.4239 and 0.4060 nm, respectively. The fact that both lattice parameters are larger than those of the bulk (a = 0.3994, c = 0.4038 nm) suggests that the BaTiO3 film contains a considerable amount of oxygen vacancies, and a relatively large tensile stress is observed along the direction parallel to the substrate. These results indicate that the BaTiO3 film has (h00) orientation; however, we consider that the small amount of (00l) orientation component is also included although the (00l) orientation component is not clearly detected by X-ray diffraction. The magnetization–magnetic field (M–H) hysteresis measurement revealed that the film had a high perpendicular coercivity of 7.0 kOe. In addition, a distinct perpendicular magnetic anisotropy was observed. The distribution of magnetic domains was observed by magnetic force microscopy. Polarization–electric field (P–E) hysteresis measurement revealed that the BaTiO3–CoFe2O4 composite film had weak ferroelectricity with considerable leakage current. It was also found that the shape of the P–E curve was changed by the application of a lateral magnetic field of 0.2 T. The change would have been caused by the following two possibilities: (1) magnetostriction of CoFe2O4 and (2) magnetic resistivity of CoFe2O4 or (La0.5Sr0.5)CoO3.