多晶钙钛矿锰氧化物中的巨磁电阻与磁场关系

本论文研究了多晶锰氧化物磁电阻和磁场的关系，在低温和低场下，磁性纳米团簇的磁矩转动和晶粒边界的自旋二级隧穿对磁电阻起主要作用因高于Tc时，由弱化强度随温度关系的实验结果指出顺磁态中已出现铁磁团簇，因此它类似于磁性颗粒膜中的巨磁电阻（CMR）机制；在顺磁－铁磁相变区，既有颗粒贡献又有界面的隧道贡献，这一理论模型与多晶La0.825Sr0.175MnO3中的实验结果很好地吻合。

THE FIELD DEPENDENCE OF MAGNETORESISTANCEIN POLYCRYSTALLINE MANGANITES

The field dependence of magnetoresistance (MR) in the polycrystalline manganites was investigated. At the low temperature and low magnetic field, MR is originated from the moment rotation of magnetic nanoclusters and the second-order tunneling through the interfacial spins sites at the grain boundary and domain wall. At T>Tc, the M-T data shows there already exist magnetic nanoclusters in paramagnetic state, so the MR is similar to the giant magnetoresistance (GMR) in granular materials (or thin films). In the range of paramagnetic-ferromagnetic transition, both magnetic nanoclusters and grain boundary contribute to the MR. This model is well in agreement with the experimental results of polycrystalline La0.825Sr0.175MnO3.