Phase separation enhanced magneto-electric coupling in La_(0.7)Ca_(0.3)MnO_(3)/BaTiO_(3) ultra-thin films

摘要

We study the origin ofthe magnetoelectric coupling in manganite films on ferroelectric substrates. We find large magnetoelectric coupling in La_(0.7)Ca_(0.3)MnO_(3)/BaTiO_(3) ultra thin films in experiments based on the converse magnetoelectric effect.The magnetization changes by around 30–40% upon applying electric fields on the order of 1kV/cm to the BaTiO_(3) substrate, corresponding to magnetoelectric coupling constants on the order of α=(2–5)·10−7 s/m. Magnetic anisotropy is also affected by the electric field induced strain, resulting in a considerable reduction of coercive fields.We compare the magnetoelectric effectin pre-poled and unpoled BaTiO_(3) substrates. Polarized neutron reflectometry reveals a two-layer behavior with a depressed magnetic layer of around 30Å atthe interface. Magnetic force microscopy (MFM) shows a granular magnetic structure of the La0.7Ca0.3MnO3.The magnetic granularity of the La_(0.7)Ca_(0.3)MnO_(3) film and the robust magnetoelastic coupling at the La_(0.7)Ca_(0.3)MnO_(3)/BaTiO_(3) interface are at the origin of the large magnetoelectric coupling, which is enhanced by phase separation in the manganite.