Strong magnetoelectric coupling in multiferroic Co/BaTiO3 thin films

We have found evidence for a strong magnetoelectric (ME) coupling at room temperature between polycrystalline Co layers (5-40 nm) and single-crystalline (001)-oriented BaTiO3 layers (15-17 nm). We took advantage of the quasi-single polarization orientation, perpendicular to the film plane, of the ferroelectric BaTiO3 domains in the tetragonal phase. Using ferromagnetic resonance spectroscopy with the Co magnetization aligned either parallel or antiparallel to the BaTiO3 polarization, we assessed a strong anisotropy of about 0.14 T in the Co resonance field positions, indicating a coupling constant of 0.27 s/F. When sweeping the temperature through the phase transitions of BaTiO3, the two resonance positions are shifted in opposite directions. The ME coupling induces a notable magnetic anisotropy resulting in high values of the out-of-plane remanent magnetization. Our results are promising for future multiferroic devices.