ROLE OF SURFACE PHENOMENA IN THE MAGNETORESISTIVITY OF POLYCRYSTALLINE MANGANITES LA1-XCAXMNO3

The dc electrical resistivity and magnetoresistivity of polycrystallin e manganites La1-xCaxMnO3 (x=0-0.3) are investigated as functions of t he temperature, magnetic field and electric field, along with the micr owave surface resistance. The investigations show that the dc electric al resistivity and magnetoresistivity are governed by the surface prop erties of the intergranular boundaries. The dc electrical resistivity is observed to decrease substantially (tenfold) for a comparatively sm all electric field (E congruent to 100 V/cm). Estimates are obtained f or the internal electrical resistivity of the granules, the thickness of the contact layer (which depends on the temperature and the magneti c field), and the height of the potential barrier between the interfac es separating the surface layer and inner layer of a granule. (C) 1998 American Institute of Physics. [S1063-7834(98)02310-7].