Correlation between extrinsic electroresistance and magnetoresistance in   fine-grained La0.7Ca0.3MnO3
  We report our observation of a correlation between the extrinsic electroresistance (EER) and magnetoresistance (EMR) via grain size in fine-grained La0.7Ca0.3MnO3. The nature of dependence of EER and EMR on grain size (~0.2-1.0 micron) indicates that for finer grains with low-resistive boundaries both of them follow similar trend whereas they differ for coarser grains with high-resistive boundaries. This could be due to a crossover in the mechanism of charge transport across the grain boundaries - from spin-depedent scattering process to spin-polarized tunneling one - as a function of grain size. 
P. Sujatha Devi, A. Kumar, Dipten Bhattacharya, Shilpi Karmakar, and   B.K. Chaudhuri