Magnetotransport properties of a single grain boundary in a bulk La–Ca–Mn–O material

Besides the ‘‘intrinsic’’ colossal magnetoresistance effect observed in single crystals, the polycrystalline manganate compounds also exhibit an ‘‘extrinsic’’ magnetoresistance related to the presence of grain boundaries. We report electrical transport and magnetic measurements carried out on a bigrain sample extracted from a floating zone method-grown rod of calcium doped lanthanum manganate. Electrical resistance was measured both within a grain and across the grain boundary, between 20 and 300 K and from 0 to 8 T. Magnetoresistance values up to 99% are reached within the grain. The temperature dependence of the resistance across the grain boundary displays a ‘‘foot-like’’ feature towards the bottom of the transition. Low field and high field magnetoresistance effects are examined. We compare our results for a ‘‘bulk’’ grain boundary to those obtained by other authors for bicrystal thin films and bulk polycrystalline materials. © 2001 American Institute of Physics. @DOI: 10.1063/1.1410885#