【作者】 袁力；

【导师】 袁松柳；

【作者基本信息】 华中科技大学 ， 材料物理与化学， 2006， 硕士

【摘要】 在本论文中,我们用溶胶-凝胶法制备了小尺寸的La_2/3Ca_1/3MnO₃颗粒,随后分别采用物理的和化学的方法在La_2/3Ca_1/3MnO₃颗粒系统中引入了Cu相关的顺磁性相和Sb₂O₅绝缘体相。我们从实验角度探讨了第二相的引入对复合颗粒系统的电磁输运行为和磁电阻的影响,实验测量表明:1、较之纯La_2/3Ca_1/3MnO₃颗粒系统,零场下电阻温度关系测量表明,少量的Cu相关顺磁性物质的引入使得复合颗粒系统的电阻率大幅度降低;随着引入的Cu相关顺磁性物质的量的增加,磁测量表明,复合颗粒系统展现出新的磁相,且对外磁场的响应加强,外场下电阻温度关系测量表明,复合颗粒系统表现出明显增强的磁阻效应。2、在La_2/3Ca_1/3MnO₃颗粒系统中引入Sb2O5绝缘体相,零场下电阻温度关系测量表明,对x<3%范围,随Sb₂O₅含量增加,复合颗粒系统的电阻率增大,绝缘体-金属转变温度降低;而对x>3%范围,随Sb₂O₅含量增加,复合颗粒系统的电阻率减小,绝缘体-金属转变温度提高。磁电阻测量表明,少量Sb₂O₅的引入可明显增强磁电阻效应。基于La_2/3Ca_1/3MnO₃颗粒周围包覆有第二相薄层的考虑,我们对上述两种磁电阻变化行为提出了一可能的解释。更多还原

【Abstract】 In our work, we prepared nominal La_2/3Ca_1/3MnO₃ grains with sol-gel method, then we introduced the Cu dependent material and the Sb₂O₅ material respectively to the La_2/3Ca_1/3MnO₃ grains system with physical and chemical method. We discuss the effect of the second phase in these compounds, experimental results indicated that:1. When the second phase is the Cu dependent material, the study of temperature dependence of resistivity at zero field shows that, the resistivity of the composites decreases prodigiously with small addition level. With the addition level decreases, the composites becomes sensitively to the magnetic field, the measurement for temperature dependence of magnetoresistance （MR） indicates that MR effect can be largely enhanced in the composites with the second phase addition.2. When the second phase is the Sb₂O₅ material, the study of temperature dependence of resistivity at zero field shows that, the metal-insulator transition temperature （Tp） and the resistivity of the composites are dependent on Sb₂O₅ addition level x. When x<3%, Tp shifts towards low temperature and resistivity increases with the increase of x. But Tp shifts towards high temperature and resistivity decreases with further increasing of x. The measurement for temperature dependence of magnetoresistance （MR） indicates that MR effect can be largely enhanced in the composites with small Sb₂O₅ addition.Based on the structure that the La_2/3Ca_1/3MnO₃ grains are surrounded by the the second phase, just like the sandwich structure, we give a possible interpretation to the enhanced magnetoresistance （MR） effect observed in these composites.更多还原