中文摘要：

利用溶胶．凝胶法制备了纳米多晶La0．7Sr0．3MnO3-δ（LSM）块体样品．详细研究了在不同烧结温度下的LSM样品电阻率随测量温度的变化关系和磁电阻效应．随着测量温度从室温降低，电阻率β都在250K附近存在最大值，低于该温度后，样品表现为金属导电特性，随后在50K左右存在一极小值．即随着温度从50K左右降低到4．2K．ρ反而逐渐升高，表现为绝缘体性的导电特性．研究表明，在低温下（〈50K），ρ随温度降低而升高的现象与隧穿效应的理论模型（1n ρ ∝T^1/2）符合得很好，表明这种现象是由于传导电子在通过邻近LSM晶粒间表面／界面层时的隧道效应所致．而在50—250K的温度范围内，其电阻率与T^2成正比，表现为LSM本征的金属导电特性．因此这种低温下电阻率的极小值现象来源于隧穿效应和LSM晶粒本征的金属导电特性的相互竞争．本文还详细研究了相应的隧道磁电阻效应．

英文摘要：

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.c. ρ∝ T^2 in the temperature range from 50K to 170K. However, p subsequently exhibits a minimum near 50K, below which it is well fit by the predictions of the tunneling of conduction electrons through insulating interfacial layers, viz ln ρ∝ T^2, a result interpreted as conduction-electron tunneling between adjacent ISM granules. The minimum of p 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.