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详细研究了由纳米晶粒组成的块体多晶La0 7Sr0 3MnO3(LSM)的电阻率和磁电阻效应 ,以及它们的温度依赖性 .随着温度从室温降低 ,电阻率 (ρ)在 2 5 0K附近存在一最大值 ,低于该温度后 ,样品表现为金属导电特性 ,随后在 5 0K附近存在一极小值 .也就是说在低于 5 0K的温度范围内 ,随着温度降低 ρ反而升高 ,表现为绝缘体性的导电特性 .经研究发现 ,这种随温度降低 ρ反而增加的现象与隧穿效应的理论模型 (lnρ∝T- 1 2 )符合得很好 .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导致的 .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 .还详细研究了相应的隧道磁电阻效应的温度依赖性 .
The resistivity and magnetoresistive effect of bulk polycrystalline La0 7Sr0 3MnO3 (LSM) composed of nanocrystalline grains and their temperature dependencies were investigated in detail.The resistivity (ρ) at 250 K There is a maximum near, below which the sample behaves as a metallic conductor and then has a minimum around 50 K. That is to say, in the temperature range below 50K, High, showing the conductivity of the insulating properties of the study found that the temperature decreases with the increase of ρ phenomenon and the tunneling effect of the theoretical model (lnραT- 1 2) is in good agreement.This phenomenon is due to conduction The tunneling effect of electrons upon passing through the LSM interfacial interfacial layer is caused by the tunneling effect of the low resistivity at low temperatures resulting from the competition between the tunneling effect and the metallic conductive properties intrinsic to the LSM grains. The temperature dependency of the magnetoresistance of the tunnel is studied in detail.