三价Fe离子对La2CoMnO6系统磁性能的影响

论文总字数：24813字

摘 要

双钙钛矿La₂CoMnO₆ 由于具有丰富的物理性质，如磁电阻效应（MR）、磁电容效应、较高的居里温度Tc（La₂NiMnO₆：280 K）、（La₂CoMnO₆：230 K）而被广泛研究，在下一代自旋电子器件方面存在很大的应用前景。离子替代是探索钙钛矿材料物理性质较为有效的途径之一，本文利用三价Fe离子替代Co² 离子制备La₂Co_1-xFe_xMnO₆（x=0.1，0.2，0.5，1.0）样品，采用的是固相反应法，并用X射线衍射仪、扫描电子显微镜、综合物性测量系统等仪器对样品进行了分析测量。

第一章简要介绍钙钛矿和双钙钛矿的相关理论，第二章介绍样品的制备合成及性质表征，第三章对介绍实验得到的样品性质表征数据。

对样品的晶体结构采用X射线衍射仪进行分析测量，结果表明样品的确为双钙钛矿结构，且利用固相反应法制备合成的步骤没太大问题，没有明显的杂相产生，不同量的Fe掺杂对于衍射峰来说并没有发生移动等变化。对样品的表面形貌则利用了扫描电子显微镜，测量结果表明样品具有大颗粒、均匀分布的特点。对样品的磁电性能利用综合物性测量系统进行测量分析，通过样品的磁滞回线可得到一个结果，那就是Fe掺杂的越多，样品的饱和磁化强度会随之降低，矫顽力减小。猜测造成这种结果的原因是由于Fe的掺杂导致样品的结构发生了变化，有序度降低。对其磁性研究的结果发现样品具有较大的磁电阻效应。

本文中成功制备了Fe掺杂的合格样品，并对其晶体结构、样品表面形貌、磁电性能进行了研究，相信这些结果对后面从事双钙钛矿的研究具有重大意义。

关键词：双钙钛矿 La₂CoMnO₆ Fe掺杂 固相反应法 磁电性能

EFFECT OF TRIVALENT FE ION ON THE MAGNETIC AND DIELECTRIC CHARACTERISTICS OF THE DOUBLE PEROVSKITE LA₂COMNO₆ SYSTEM

Abstract

Double perovskite La₂CoMnO₆ has been extensively studied because of its rich physical properties. Ion substitution is one of the effective ways to explore the physical properties of perovskite materials. In this paper, La₂Co_1-xFe_xMnO₆ (x=0.1, 0.2, 0.5, 1.0) samples were prepared by substitution of trivalent Fe ion for Co² ion by solid state reaction, The samples were measured and analyzed by X-ray diffraction, scanning electron microscopy, physical property measurement system and other instruments.

Measuring and analyzing the crystal structure of the samples were used by X-ray diffraction , The results show that the sample is indeed a double perovskite structure, and the steps of the use of solid state reaction method to prepare the synthesis were no problem. No apparent miscellaneous phase produced. The different amount of Fe doped with the diffraction peak does not happen to move and so on. The surface morphology of the samples was measured by scanning electron microscope. The results showed that the sample had the characteristics of large particles and uniform distribution. Measurement and analysis of the magnetoelectric properties of the samples are used by physical property measurement system. One result is obtained through the hysteresis loop of the samples that is with increase of Fe substitution, the saturation magnetization and coercive force of the sample decrease. The reason for this result is that the structure of the sample was changed due to the doping of Fe, and the ordering is reduced. The results show that the samples have a large magnetodielectric effects.

Fe doped qualified samples were successfully prepared in this paper. The crystal structure, the surface morphology and magnetoelectric properties of the samples were studied. It can be believed that these results would be significant for the study of double perovskite in the future.

KEY WORDS: Double perovskite, La₂CoMnO_6, Fe-substitution, solid state reaction, magnetoelectric properties

目 录

摘 要 I

Abstract II

目 录 III

第一章 绪论 1

1.1引言 1

1.2钙钛矿和双钙钛矿氧化物的研究进程及现状 1

1.3 钙钛矿和双钙钛矿氧化物概述 5

1.3.1钙钛矿和双钙钛矿氧化物的晶体结构 5

1.3.2 Jahn –Teller畸变 6

1.3.3 双交换作用 6

1.3.4 磁电阻效应 7

1.4 本文的研究目的和主要研究内容 7

第二章 样品的制备及其性质表征的办法 9

2.1 样品制备 9

2.1.1 制备方法 9

2.1.2 制备过程 11

2.2 性质表征 12

2.2.1分析样品的晶体结构——X射线衍射（XRD） 12

2.2.2分析样品表面形貌及组分——扫描电子显微镜（SEM） 14

2.2.3磁性和电性测量——综合物性测量系统（PPMS） 15

第三章 样品的性质表征 17

3.1 X射线衍射（XRD）图像 17

3.2 扫描电子显微镜（SEM）图像 17

3.3 综合物性测量系统测量数据图像分析 20

3.3.1 FC和ZFC条件下的M-T图 20

3.3.2 5 K下的磁滞回线 20

3.3.3 磁电阻效应图 21

3.3.4 ρ-T图 22

第四章 结论 24

致谢 25

参考文献 26

第一章 绪论

1.1引言

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