Grain-boundary effects on magnetotransport in La0.7Sr0.3MnO3 biepitaxial films

The low field magnetotransport of La0.7Sr0.3MnO3 (LSMO) films grown pn SrTiO3 substrates has been investigated. A high quality LSMO film exhibits anisotropic magnetoresistance (AMR) and a peak in the magnetoresistance close to the Curie temperature of LSMO. Biepitaxial films prepared using a seed layer of MgO and a buffer layer of CeO2 display a resistance dominated by grain boundaries. One film was prepared with seed and buffer layers intact, while a second sample was prepared as a 2D square array of grain boundaries. These films exhibit (i) a low temperature tail in the low field magnetoresistance, (ii) a magnetoconductance with a constant high field slope, and (iii) a comparably large AMR effect. A model based on a two-step tunneling process, including spin-flip tunneling, is discussed and shown to be consistent with the experimental findings of the biepitaxial films.