Microstructural and magnetotransport properties of La0.7Ca0.3MnO3/BaTiO3 and La0.7Sr0.3MnO3/BaTiO3 bilayered films

The microstructural and the magnetotransport properties of La0.7Ca0.3MnO3 and La0.7Sr0.3MnO3 films, deposited on a BaTiO3 layer (LCMO/BTO and LSMO/BTO, respectively), and on LaAlO3 and SrTiO3 (001) single crystals (LCMO/LAO, LSMO/LAO and LSMO/STO) by rf-magnetron sputtering using the "soft" (or powder) targets, have been investigated. The films grown on BTO demonstrate biaxial tensile in-plane and compressive out-of-plane strains, while those grown on LAO show the opposite trend, i.e., compressive in-plane and tensile out-of-plane strains. The films with a biaxial tensile in-plane strain undergo the magnetic transition at a higher temperature than those with a biaxial compressive one. This implies that the variation of Mn-O-Mn bond angle, controlled by the lattice strain, plays a more important role in the formation of spin ordering in the manganite film than the modification in the Mn-O bond length does. It was shown that the magnetic inhomogeneity, observed through the difference between field-cooled and zero-field-cooled temperature-dependent magnetization, is not greatly relevant to the electronic nature, but is controlled by the lattice distortion and the microstructural defects. The observed enhancement of magnetoresistance for the LSMO/BTO bilayer at room temperature makes this material system promising in the development of new hybrid ferromagnetic/ferroelectric devices.