Transport properties and magnetoresistance of nano-polycrystalline La0.7Sr0.3MnO3-δ

The resistivity and magnetoresistance of bulk polycrystalline La0.7Sr0.3MnO3-δ, fabricated to produce nanoscale grains sintered at different temperatures, have been investigated as functions of temperature. With decreasing temperature below room temperature the resistivity (ρ) exhibits a maximum near 250K, below which it shows “metallic" behaviour, i.e. ρ∝T2 in the temperature range from 50K to 170K. However, ρ subsequentlyexhibits a minimum near 50K, below which it is well fit by the predictions of the tunneling of conduction electrons through insulating interfacial layers, viz lnρ ∝T1/2, a result interpreted as conduction-electron tunneling between adjacent LSM granules. The minimum of ρ occuring in these samples may result from the competition of the tunneling effect and the intrinsic metallic transport mechanism of LSM. The temperature dependence of the associated tunneling magnetoresistance is also reported.