论文总字数：41188字

摘 要

随着磁性材料的发展，人们对材料磁性能的提高和成本的降低要求越来越高。从材料研究的角度来说，如何用低成本的原材料通过简单的流程制备出磁性能良好的磁性材料是近年来的研究热点。本文首先对磁学知识、纳米材料性质、磁性材料分类和纳米复合永磁材料发展做了简单介绍，并对纳米复合磁性材料的制备方法进行了概述。我们研究了水热法制备BaFe₁₂O₁₉实验中各因素与物相和形貌的关系并改进了水热过程，在Ba/Fe化学计量配比下一步反应得到了单相BaFe₁₂O₁₉，随后通过调整OH^-浓度水热制备了单畴单分散的BaFe₁₂O₁₉纳米片。最后，以水合肼为还原剂在二次水热过程中部分的将BaFe₁₂O₁₉还原为Fe₃O₄，成功制备得到了BaFe₁₂O₁₉/Fe₃O₄硬磁/软磁复合材料。对水合肼还原BaFe₁₂O₁₉的机理、BaFe₁₂O₁₉/Fe₃O₄复合纳米晶的结构和形貌进行了研究，发现水合肼还原前后样品片状形貌未发生变化，Fe₃O₄是在BaFe₁₂O₁₉表面原位转化形成，它们间有特殊的结晶学关系：[111]_Fe3O4//[001]_BaFe12O19。磁性能的表征发现复合样品的磁滞回线表现为单一相的磁化曲线特征且在低还原程度样品中出现剩磁比的增强，表现较强的交换耦合作用。良好的磁性能与两相特殊的结晶学关系密不可分，这使它们易磁化轴平行，两相磁有序结构完整的匹配。

关键词：复合磁性材料；水热法；BaFe₁₂O₁₉/Fe₃O₄复合纳米晶；结晶学关系；硬磁/软磁交换耦合

Abstract

As the development of magnetic materials, the demand for magnetic property enhancement and cost reduction of magnetic materials is becoming more and more higher. From the point of view of material research, how to prepare materials with good magnetic properties using low-cost raw materials is a recent research hotspot. In this thesis, we first review the knowledge of magnetism, properties of nanomaterials, classification of magnetic materials, development of nanocomposite permanent and discuss its preparation method. We investigate the relations between experimental factors and phase components, morphologies of the products. Under a modified hydrothermal process, single phase BaFe₁₂O₁₉ particles were synthesized with stoichiometric ratio of Ba/Fe and after an adjustment of OH^- concentration, single domain and monodisperse BaFe₁₂O₁₉ nanoplates were subsequently obtained. Finally, the BaFe₁₂O₁₉ were partially transformed into Fe₃O₄ in a second hydrothermal process where hydrazine hydrate was used as a reduction agent, indicating the successful preparation of BaFe₁₂O₁₉/Fe₃O₄ hard/soft composite. The reduction mechanism of BaFe₁₂O₁₉ towards hydrazine hydrate and the structure, morphology of BaFe₁₂O₁₉/Fe₃O₄ nanocomposites were studied, which demonstrate that the plate-like shape of particles remains unchanged after the reduction with Fe₃O₄ produced in the manner of in-situ transformation, giving a special crystallographic relationship between two phases: [111]_Fe3O4//[001]_BaFe12O19. The magnetic characterization shows that the hysteresis loops of composite particles feature single-like shape and the remanence ratio was enhanced in the sample with low reduction degree, which imply strong exchange coupling between BaFe₁₂O₁₉ and Fe₃O₄. These excellent magnetic properties are highly related to the special crystallographic relationship which gives parallel easy magnetization axes and well magnetic matching.

Key Words: composite magnetic material; hydrothermal method; BaFe₁₂O₁₉/Fe₃O₄ nanocomposite; crystallographic relationship; hard/soft exchange coupling

目　录

摘 要 Ⅰ

Abstract Ⅱ

第一章 绪论 1

1.1 磁学基本理论 1

1.1.1 磁滞回线 1

1.1.2 饱和磁化强度 1

1.1.3 剩余磁化强度 1

1.1.4 矫顽力 1

1.1.5 磁能积 2

1.2 纳米材料 2

1.2.1 纳米材料定义 2

1.2.2 纳米材料分类 2

1.2.3 纳米材料性质 2

1.3 磁性材料 2

1.3.1 磁性材料定义 2

1.3.2 磁性材料分类 2

1.3.3 稀土永磁材料发展历史 4

1.4 纳米复合永磁材料 4

1.4.1纳米复合永磁材料的定义 5

1.4.2 纳米复合永磁材料的发展 5

1.4.3 纳米复合永磁材料的理论模型研究 5

1.5 BaFe₁₂O₁₉硬磁材料 7

1.5.1 BaFe₁₂O₁₉硬磁材料简介 7

1.5.2纳米钡铁氧体的制备方法 7

1.6 纳米复合永磁材料的制备方法 8

1.6.1 溶胶—凝胶法(Sol-Gel法) 8

1.6.2 均匀共沉淀法 9

1.6.3 溶体快淬法 9

1.6.4 机械化合金和高能球磨法 10

第二章 BaFe₁₂O₁₉纳米晶的水热制备研究 11

2.1 水热法合成BaFe₁₂O₁₉纳米晶 11

2.1.1 水热法合成BaFe₁₂O₁₉纳米晶的工艺流程 11

2.1.2 BaFe₁₂O₁₉纳米晶的测试表征 12

2.1.3水热法合成BaFe₁₂O₁₉纳米晶的实验原料与仪器 12

2.2 BaFe₁₂O₁₉纳米晶的物相和形貌表征 13

2.2.1 Ba/Fe摩尔比对水热产物物相的影响 13

2.2.2单相BaFe₁₂O₁₉的一步合成及反应温度、时间对其物相的影响 14

2.2.3 OH-浓度对BaFe₁₂O₁₉形貌的影响 17

2.2.4 水热BaFe₁₂O₁₉的磁性表征 19

2.3 本章小结 20

第三章 水合肼还原制备BaFe₁₂O₁₉/Fe₃O₄硬磁/软磁纳米晶研究 21

3.1 水合肼还原制备BaFe₁₂O₁₉/Fe₃O₄纳米晶 21

3.1.1水合肼还原制备BaFe₁₂O₁₉/Fe₃O₄纳米晶的工艺流程 21

3.1.2 BaFe₁₂O₁₉/Fe₃O₄纳米晶的测试表征 22

3.1.3水合肼还原制备BaFe₁₂O₁₉/Fe₃O₄纳米晶的实验原料与仪器 22

3.2 BaFe₁₂O₁₉/Fe₃O₄纳米晶的组分、微结构及磁性能研究 23

3.2.1 水合肼还原产物的物相及还原过程 23

3.2.2 BaFe₁₂O₁₉/Fe₃O₄纳米晶的结构和形貌 25

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