Extrinsic Magnetotransport in Manganites and its Dependence on Mechanical Strain

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The extrinsic electrical transport in manganites of the type (La, A)(Mn, B)O3 (where A = Ca2+, Sr2+ or Pb2+ and B = Ru+, Ta+ or W+) has been studied onbulk ceramic and thin film samples. In particular, its dependence on reversibl strain applied with a piezoelectric substrate has been investigated. The firstpart discusses results on bulk polycrystalline samples, (La0.7Ca0.3MnO3)/LaAlO3 (001) films forming step edge junctions (SEJ) on substrates containing lithographicallydefined parallel steps and La0.7Sr0.3MnO3/SrTiO3 (001) films on a bicrystal substrate containing one grain boundary. Magnetoresistance measurements have been carried out in static and in pulsed magnetic fields of µ0H = 50 T. The magnetoconductance G(H) depends on the susceptibility of a magnetically lessordered layer around the grain boundaries. In particular, the second-order grainboundary tunnelling model of Lee et al.