Magnetic and transport properties of La$_{0.7}$Ca$_{0.3}$MnO$_{3}$/BaTiO$_{3}$ and La$_{0.7}$Sr$_{0.3}$MnO$_{3}$/BaTiO$_{3}$ bilayered films

The magnetic and the transport properties of La$_{0.7}$Ca$_{0.3}$MnO$_{3}$/BaTiO$_{3}$ (LCMO/BTO) and La$_{0.7}$Sr$_{0.3}$MnO$_{3}$/BaTiO$_{3}$ (LSMO/BTO) bilayered films, prepared by the rf-magnetron sputtering, have been investigated. For comparison, the same data for the LCMO and the LSMO films, deposited on the bare LaAlO$_{3}$ (LAO) substrates, are obtained as well. The microstructural analysis reveals that LCMO/BTO and LSMO/BTO have the biaxial tensile in-plane and compressive out-of-plane strains, while LCMO/LAO and LSMO/LAO are reversely in the compressive in-plane and tensile out-of-plane strains. The films with biaxial tensile in-plane lattice strains undergo the magnetic transition at a higher temperature than those with biaxial compressive ones. This suggests that the Mn-O-Mn bond angle, controlled by the lattice strain, plays more important role in the formation of spin ordering in the manganite film than the modification of Mn-O bond length. The observed enhancement of magnetoresistance at room temperature in LSMO/BTO provides an advance for the development of new hybrid ferromagnetic/ferroelectric devices.