Giant magnetoelectric coupling interaction in BaTiO₃/BiFeO₃/BaTiO₃ trilayer multiferroic heterostructures

Multiferroic trilayer thin films of BaTiO₃/BiFeO₃/BaTiO₃ were prepared by RF-magnetron sputtering technique at different thicknesses of BiFeO₃ layer. A pure phase polycrystalline growth of thin films was confirmed from X-ray diffraction results. The film showed maximum remnant electric polarization (2P_r) of 13.5 μC/cm² and saturation magnetization (M_s) of 61 emu/cc at room temperature. Thermally activated charge transport dominated via oxygen vacancies as calculated by their activation energy, which was consistent with current–voltage characteristics. Magnetic field induced large change in resistance and capacitance of grain, and grain boundary was modeled by combined impedance and modulus spectroscopy in the presence of varied magnetic fields. Presence of large intrinsic magnetoelectric coupling was established by a maximum 20% increase in grain capacitance (C_g) with applied magnetic field (2 kG) on trilayer having 20 nm BiFeO₃ layer. Substantially higher magnetoelectric coupling in thinner films has been observed due to bonding between Fe and Ti atoms at interface via oxygen atoms. Room temperature magnetoelectric coupling was confirmed by dynamic magnetoelectric coupling, and maximum longitudinal magnetoelectric coupling of 515 mV/cm-Oe was observed at 20 nm thickness of BiFeO₃. The observed magnetoelectric properties are potentially useful for novel room temperature magnetoelectric and spintronic device applications for obtaining higher voltage at lower applied magnetic field