【作者】 孙超伦；

【导师】 熊永红； 熊曹水；

【作者基本信息】 华中科技大学 ， 材料物理与化学， 2007， 硕士

【摘要】 近年来,具有钙钛矿结构的稀土锰氧化物一直就是人们理论和研究的热点,这主要是因为该材料在磁场下所表现出来的超大磁电阻效应（CMR, Colossal Magnetoresistance ）具有很广阔的应用前景,主要体现在磁记录、磁存储、磁传感器及其他方面的实际应用。锰基钙钛矿结构的材料是典型的强关联电子体系,自旋、电荷和轨道等自由度的相互耦合对材料的性质起决定性的作用。因此过去的那些忽略电子之间相互作用的经典近似理论几乎不再有发挥的平台,所以CMR效应的产生机理研究在一定程度上向凝聚态物理的发展提出了新的挑战。本文主要介绍作者在硕士期间,在相关理论的指导下对锰氧化物复合材料的一些理论探讨和实验结果。可包括四个主要部分:第一部分着重介绍当前关于稀土锰氧化物的研究进展以及随之发展起来的相关理论;第二部分主要论述实验样品的制备方法和测量手段;第三部分重点论述实验测量结果、理论分析以及研究本课题的现实意义。第四部分介绍材料高温测试系统的搭建和测量机制;我们通过传统的固相反应法制备了(La_0.67Ca_0.33MnO₃ )_1-x/（SrBi₂Ta₂O₉）_x,其中x=0%,1.5%,2%,3%,5%,7%,10%,15%,20%,25%。然后对这样品的电磁输运性质、结构等进行了一系列的研究。实验结果发现,随着掺杂物质SrBi₂Ta₂O₉（SBT）的增加,复合物的电阻率的变化趋势并不单调。当掺杂量很低的时候,电阻率随着掺杂量的增加而增加;然而当掺杂量到达一定程度的时候电阻率却又呈现一种下降的趋势,随着掺杂量的继续增加,电阻率又开始增加,直至在整个温度范围（77K-300K）内没有转变峰,呈现绝缘体的性质。我们还对(La_0.67Ca_0.33MnO₃ )_1-x/（SrBi₂Ta₂O₉）_x的磁输运性质也进行了一系列的研究,发现铁磁金属-顺磁绝缘体转变温度向低温移动,并且磁电阻效应随着掺杂量的增加而加强。但我们推测磁电阻不会无限制的随着掺杂量增加而增加必然会存在一个饱和的磁电阻值。更多还原

【Abstract】 Manganese pervoskite rare-earth oxides have been the hot topic for recent years, due to the potential application on magnetic storage, and magnetic sensor and so on. The colossal magnetoresistance is the common character of this kind of materials.Manganites are typical strongly correlated electron systems, spin, and charge, and orbital freedom degrees of coupling are crucial to the characters. The classical theories that neglect some interactions on studying the properties of manganites do not work any more. So to understand the mechanism of CMR in manganites is a main challenge in condensed matter physics.In this paper, we mainly talk about the work done by me as a master during the recent two years. The contents include four sections: firstly introducing the situation about the development of rare earth manganites, secondly telling the samples preparing and measuring methods, thirdly analyzing the results of measurement and summarizing the meaning in application generally, and fourthly describing the mechanism of measurement system designed by ourselves in high temperature region.We prepared the (La_0.67Ca_0.33MnO₃ )_1-x/（SrBi₂Ta₂O₉）_x （x=0%,1.5%,2%,3%,5%,7%,10%,15%,20%,25%） by conventional solid-state reaction. The electrical and magnetic transport properties were investigated systemically. It is interesting to note that with increasing SrBi₂Ta₂O₉ （SBT） dopant, the change trend of the resistivity is different. When in low dopant, the resistivity increases as the SBT addition. When SBT reaches up to a certain value the resistivity decreases with increasing the dopant contents. However, the trend is not remained and changed as x>25%. The temperature transition of ferromagnetic-paramagnetic shifts to low temperature region and the magnetoresistance （MR） increases with the adding of dopant. But we still assume that MR won’t be keep increasing continually and there must be a maximal value.更多还原