河北工业大学
博士学位论文
钙钛矿结构锰氧化物La<,0.67-x>R<,x>Ca<,0.33>MnO<,3>中的
电磁性质及红外吸收
姓名：***
申请学位级别：博士
拉布拉多幼犬图片专业：材料物理与化学
指导教师：***
20061101
钙钛矿结构锰氧化物La0.67-x R x Ca0.33MnO3中
的电磁性质及红外吸收
摘要
本论文系统地研究了具有巨磁电阻效应钙钛矿型锰氧化物La0.67-x R x Ca0.33MnO3（R=Pr，Y，Ho，Gd，Dy）中的电磁性质及红外吸收。
通过对La0.67-x Pr x Ca0.33MnO3（x=0～0.67）零场和加场下电磁性质的研究，发现随着Pr对La的逐渐替代，化合物中出现铁磁相、电荷有序相、反铁磁相共存的现象，且相应的转变温度随Pr的含量成规律性变化。当Pr含量较少（x<0.4）时，样品随着温度的降低发生绝缘态－金属态的转变，Pr含量较高时（x>0.5），样品电阻率随温度降低而单调增加。发现电阻率在电荷有序转变温度附近有明显跃变，而外加磁场会抑制电荷有序相的产生，使金属－绝缘态转变温度向高温处移动。不同温度区域的电阻率曲线符合不同模型的拟合，拟合结果与实验数据符合很好。
通过对含Pr样品红外吸收光谱的研究，发现了频率在～530cm-1处的吸收峰，我们分析这一吸收峰跟物质的铁磁性密切相关。研究了来源于Mn-O键径向振动的拉伸模式吸收峰，由于相分离现象会造成该吸收峰的劈裂，劈裂的尺度达到～45cm-1。通过红外吸收谱研究了不同温度下样品的有效载流子密度，其变化规律对应于铁磁金属态－顺磁绝缘态转变。
通过研究离子半径相近的磁性离子Ho3+和非磁性离子Y3+对La0.67Ca0.33MnO3中La的替代，发现样品具有丰富的电磁性质，出现铁磁序和反铁磁序共存的磁性相分离现象。使得相同掺杂含量下，含Y笼能组什么词
样品的磁化强度比含Ho的低，而电阻率则比含Ho样品的高，我们根据磁性离子之间的耦合作用对此给出了解释。在对红外光谱的分析中发现了磁性相分离造成的Mn-O键吸收峰的劈裂。
如何做到爱岗敬业通过研究重稀土元素Dy和Gd对La0.67Ca0.33MnO3中La的替代，发现样品中出现自旋团簇玻璃态及亚铁磁态。在x=0.2，0.3时，样品的磁化强度出现补偿温度现象，这是亚铁磁性的一个重要特征，我们用双晶格模型作出解释。红外吸收光谱分析发现Mn-O键长吸收峰的形状、位置稳定，没有分裂迹象；与铁磁性相关的～530cm-1处的吸收峰减弱到几乎消失。
关键词：钙钛矿结构，红外吸收光谱，巨磁电阻效应，铁磁性，相分离
ELECTRONIC, MAGNETIC PROPERTIES AND
INFRARED ABSORPTION OF PEROVSKITE
最好听的纯音乐MANGANITES La0.67-x R x Ca0.33MnO3
ABSTRACT
In this thesis, perovskite manganites La0.67-x R x Ca0.33MnO3 (R=Pr，Y，Ho，Gd，Dy) with colossal magnetoresistance effect have been investigated systematically. The main results are generalized as follows:
波罗密多心经
In the polycrystalline samples La0.67-x Pr x Ca0.33MnO3 (x=0~0.67), we studied the temperature dependence of magnetization and resistivity in zero-field-cooling (ZFC) and field-cooling (FC), respectively. It was found that the coexistence of ferromagnetism, charge-ordering and antiferromagnetism in the compounds with increasing the Pr doping content, and the corresponding transfer temperature varies regularly. The samples occur insulator-metal transition with decreasing temperature as x<0.4, on the other hand, when the doping content increas up to 0.5 or more, the resistivity of the samples increas monotonously. It was also found that an abrupt change of the resistivity occurs near T CO, and the field will suppress the occurrence of charge-ordering, pull the I-M transition to higher temperature. It was found that the different model should be ud to simulate the resistivity in different temperature scope, and the results of simulation and measurement match each other very well.
Ba on the analysis of Infrared absorption of the samples, the absorption peak at ~530cm-1 was found and it should be some relations with the ferromagnetic features of the compounds. The stretch-mode absorption peak near ~620cm-1 was investigated thoroughly, and found that the peak split into two peaks with the gap about ~45cm-1 due to pha paration in the compounds. And the effective carrier number obtained from the infrared absorption spectra changes with temperature, according to the transition of FMM-PMI.
With the same radii, Ho3+ and Y3+ were chon to substitute La3+ in La0.67Ca0.33MnO3.
钙钛矿结构锰氧化物La0.67-x R x Ca0.33MnO3中的电磁性质及红外吸收
Many novel features of electronics and magnetism, such as the pha paration of FM and AFM, were found. It was also found that the magnetization of Y-doping compounds is lower than that of Ho-doping, and on the contrary, the resistivity of Y-doping is higher than that of Ho-doping. The features should ascribe to the coupling of the ion with moment. The STM peak in infrared spectra also split into two peaks due the pha paration.
By the investigation on the Dy/Gd-doped La0.67Ca0.33MnO3, it was found that the coexistence of spin glass cluster with the ferrimagnetism. And the compensation temperature was found in the M-T curves when x=0.2, 0.3, we has interpreted with the sublattice model. The metal-insulator transition occurs in the samples with x<0.2, and the variable range hopping (VRH) model and the polaron model can be ud to simulate the resistivity in different temperature scope. Infrared spectra analysis indicates that the STM peak keep its shape, position stably without splitting and the peak at ~530cm-1 weakened and even disappeared in the compounds.
Key words: perovskite, infrared absorption, colossal magnetoresistance, ferromagnetism, pha p
aration
河北工业大学博士学位论文
1
嘉兴西塘古镇第一章 绪 论
1.1 引 言
自旋电子学（spinelectronics ）也称磁电子学（magnetoelectronics ）是凝聚态物理领域一门新兴的分支学科，自二十世纪八十年代以来得到了长足发展。众所周知，电子具有两个基本的自然属性，即电荷与自旋。二十世纪人类最伟大的创造之一就是成功地研究、控制并应用了半导体中电子和空穴的输运特性，形成了微电子学的科学分支。微电子学的研究内容是不考虑电子的自旋状态，仅利用其荷电性可以由电场来控制电子的输运过程。而我们所说的自旋电子学或称为磁电子学的研究内容是介观尺度范围内自旋电子的输运特性，以及基于这些自旋特性设计、开发在新的机理下工作的电子器件。这是由磁学和电子学形成的交叉学科，具有很强的应用背景，可能对电子技术的发展产生深远的影响。
1.2 磁电阻效应
1.2.1磁电阻效应
磁电阻效应( magnetoresistance, MR )是指材料的电阻率ρ在外加磁场H 的作用下发生变化的现象。其表示方法有两种：
()()()
%10000×−=R R H R MR ， ()()()%1000×−=
H R R H R MR ， 其中()H R 和()0R 分别代表无磁场和有磁场时电阻率的数值。磁电阻的数值可正可负，分别称作正磁电阻效应和负磁电阻效应。现在，人们已经在单质金属、合金以及多种氧化物中发现了磁电阻效应，并对其机理进行了大量研究。
在很多材料中，磁电阻效应的大小不仅仅依赖于外加磁场，还与外加偏置电流和磁场的夹角有关。因此，磁电阻效应又可分为径向磁电阻效应和横向磁电阻效应，分别对应于磁场方向平行和垂直于偏置电流方向。何光暐
径向磁电阻效应：
骨传声()()0p p p H ρρρ−=Δ，
