Multiferroic BaTiO 3 –BiFeO 3 composite thin films and multilayers: strain engineering and magnetoelectric coupling

BiFeO3 and BaTiO3 were used to grow homogeneous composite thin films and multilayer heterostructures with 15 double layers by pulsed laser deposition. The perpendicular strain of the films was tuned by employing different substrate materials, i.e. SrTiO3 (0 0 1), MgO(0 0 1) and MgAl2O4 (0 0 1). Multiferroic properties have been measured in a temperature range from room temperature down to 2 K. The composite films show a high ferroelectric saturation polarization of more than 70 C cm-2. The multilayers show the highest magnetization of 2.3 emu cm-3, due to interface magnetic moments and exchange coupling of the included weak ferromagnetic phases. The magnetoelectric coupling of the BaTiO3-BiFeO3 films was investigated by two methods. While the ferroelectric hysteresis loops in magnetic fields up to 8 T show only minor changes, a direct longitudinal AC method yields a magnetoelectric coefficient ME = ∂E/∂H of 20.75 V cm-1 Oe-1 with a low μ0HDC of 0.25 T for the 67% BaTiO3-33% BiFeO3 composite film at 300 K. This value is close to the highest reported in the literature.