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

We prepared BaTiO 3 –CoFe 2 O 4 composite thin film on (La 0.5 Sr 0.5 )CoO 3 /CeO 2 /YSZ/Si(100) substrate by pulsed laser deposition. Simultaneous epitaxial growths of BaTiO 3 and CoFe 2 O 4 were achieved. Reciprocal space map measurement revealed that the lattice parameters of BaTiO 3 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 BaTiO 3 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 BaTiO 3 film has ( h 00) orientation; however, we consider that the small amount of (00 l ) orientation component is also included although the (00 l ) 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 BaTiO 3 –CoFe 2 O 4 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 CoFe 2 O 4 and (2) magnetic resistivity of CoFe 2 O 4 or (La 0.5 Sr 0.5 )CoO 3 .