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

Besides the "intrinsic" colossal magnetoresistance effect observed in singl e crystals, the polycrystalline manganate compounds also exhibit an "extrin sic" magnetoresistance related to the presence of grain boundaries. We repo rt electrical transport and magnetic measurements carried out on a bigrain sample extracted from a floating zone method-grown rod of calcium doped lan thanum manganate. Electrical resistance was measured both within a grain an d across the grain boundary, between 20 and 300 K and from 0 to 8 T. Magnet oresistance values up to 99% are reached within the grain. The temperature dependence of the resistance across the grain boundary displays a "foot-lik e" feature towards the bottom of the transition. Low field and high field m agnetoresistance 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. (C) 2001 American Institute of Physics.