The nature of the low-temperature minimum of resistivity in ceramic manganites

Electrical transport measurements were carried out on a ceramic samples of La0.5Pb0.5MnO3 containing 10 at.% of Aa in a dispersed form and La0.8Sr0.2M nO3. Their resistivity at zero applied magnetic field exhibits a shallow mi nimum at the interval of T similar to 25-30 K. This minimum shifts towards lower T upon applying a magnetic field (H) and disappears at a certain fiel d H-er while residual resistivity decreases notably with increasing of H. I t is found that the bulk-scattering model is not adequate for describing of such behavior of rho in the presence of H. It seems that the proposed mode l of charge-carrier tunneling between antiferromagnetically coupled grains accounts for the results obtained in spite of significant difference in the crystallinity (grain size) of the samples. (C) 2001 Elsevier Science B.V. All rights reserved.