Effect of grain boundaries on the local electronic transport in nanostructured films of colossal magnetoresistive manganites

Abstract

We have studied the spatially resolved local electronic properties of nanostructured films of a colossal magnetoresistive (CMR) material by local conductance mapping (LCMAP) using a variable temperature scanning tunneling microscope (STM), as a function of temperature and magnetic field. The experiments were carried out on nanostructured (NS) films of rare-earth hole doped manganites like La_0.67Sr_0.33MnO₃ (LSMO), (prepared by Chemical Solution Deposition (CSD)) having average grain sizes around 100 nm or less. Due to the presence of a large number of natural grain boundaries (GBs), these films exhibit interesting transport properties that are not observed in single crystals and epitaxial films of the same composition, such as low field magnetoresistance (LFMR), and significant MR at higher fields over the entire temperature range. Spatially resolved measurements of electronic properties, like the LCMAP, traces the contribution of the grain boundaries to the electronic transport in these NS films. It is found that the application of a low magnetic field enhances the DOS in the GB region, leading to the observed low field response of the MR.