  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.
