Résumé
Colossal magnetoresistance La0.66Sr0.33MnO3 (LSMO) thin films have been grown by pulsed laser deposition on SrTiO3 using combinatorial substrate epitaxy (CSE) approach. These polycrystalline substrates have been synthesized by spark plasma sintering (SPS) and polished in order to obtain mirror surface. They present micrometer-size grains with different crystallographic orientations where each grain acts as a single crystal to promote local epitaxy with all the different crystallographic orientations in only one sample. The size of the crystallographic domains can be controlled from 2 to 40 µm depending of annealing temperature during synthesis by SPS. A complete study of grain size, orientation, local epitaxy, and morphology have been investigated by electron backscatter diffraction (EBSD) and atomic force microscopy (AFM) measurements. The study of the magnetic and transport properties shows an increase of the Curie temperature of the LSMO films deposited onto polycrystalline substrates, compare to films deposited on single-crystal SrTiO3 substrate. We show that magnetotransport is strongly affected by CSE approach depending on the crystallographic domain size. A constant high magnetoresistance (MR) appears in the CSE approach from 5 to 320K compare to single-crystal We have also evidenced the apparition of a low field magnetoresistance (LFMR) below 200K. This effect is strongly reinforced by the shrinking of the size domain, related to the presence of the grain boundaries. Finally, we study hysteretic magnetotransport which is also sensitive to domain size and anisotropy. CSE approach is therefore a new way to tune the magnetotransport of complex oxides.