类钙钛矿氧化物材料的磁电物性研究

发布时间：2018-01-05 11:39

本文关键词：类钙钛矿氧化物材料的磁电物性研究　出处：《中国科学技术大学》2016年博士论文　论文类型：学位论文

【摘要】：多铁性材料是指具有两种或两种以上铁性序的材料。最为常见的多铁性是指材料中同时具有铁电性和磁有序的材料。电和磁是基本的物理现象,依据麦克斯韦方程组,变化的电磁场因互相感应而耦合在一起。在固体物质中,电场可以诱导电偶极矩产生,而磁场则可以导致物质被磁化。然而要在物质中实现电偶极矩和磁化强度的耦合却并非易事。单相磁性和铁电材料的发展长久保持着平行,直到近十几年,磁电耦合多铁材料才发生了突破性进展。2003年,单相多铁材料BiFeO3薄膜中实现了室温巨大的铁电极化与磁性共存,而TmMnO3单晶中也测得了磁致铁电性,且获得了巨大的磁电耦合系数。在此之后,单相多铁领域迅速发展,衍生出一系列的Ⅰ类和Ⅱ类多铁材料。其中Ⅰ类多铁材料的铁电起因包括晶格畸变、孤对电子和电荷有序,而这三种机制都允许与磁性共存。这些材料拥有着巨大的电极化强度和很高的铁电居里温度,而有的材料甚至在室温同时具备铁电性和磁性。另一方面Ⅱ类多铁材料则有着丰富而新奇的物理机制,其机制包括自旋电流、交换收缩和p-d轨道杂化。这些多铁材料拥有着极高的磁电耦合强度,有的材料中甚至可以实现电场对磁矩的翻转或是磁场对电极化的翻转。目前多铁系统中存在着两个重要的问题,首先是实用室温磁电翻转多铁材料尚未出现,因此对于多铁新体系的探索依然具有重要意义。其次,已有多铁体系有可能存在着多种铁电起源贡献,因此对于已有体系的探索依然有重要意义。我们针对这些问题进行了探索与研究。论文内容共分为四章,每章的主要内容如下：第一章综合介绍了钙钛矿多铁材料的研究背景及交换偏置的研究背景。首先介绍了多铁材料的基本分类和典型材料,从而为新型多铁性材料的探索提供参考；而钙钛矿材料研究背景则可以充分利用系统相图推测新型多铁材料的磁电参数,如磁性尼尔温度和铁电居里温度。最后介绍了近期报道的一些单相交换偏置材料。第二章详细研究了单晶铁氧化物SmFeO3的交换偏置效应。我们首先测试了不同温度不同磁场下SmFeO3的交换偏置行为,发现SmFeO3的交换偏置大小会被磁矩补偿放大,与Heusler合金一致。经过文献调研我们发现这一体系暂无关于交换偏置可靠的解释,因此我们参考SmCiO3和Heusler合金系统中的团簇解释,并与类似系统NdFeO3中的实验结果进行了对照。在数据处理中我们用到了平均场近似,因此我们又对低温下Sm的磁性进行了探索,验证了我们关于Sm直到0.4 K都没有形成长程序的理解。第三章详细测试了新材料Ba3Ti2MnO9的结构和磁电物性。结构测试验证了Ba3Ti2MnO9中Mn-Ti沿着c轴的有序排列,从而确认其空间群为非中心对称的。变温拉曼测试表明系统随温度降低无明显相变。磁性测量表明系统中存在着较强的阻挫发生,验证了结构推导出的准二维三角自旋排布。进一步的测试表明,系统缺失/多余自旋会导致磁化率上升；而多余的自旋会以自旋二聚体的性质凝聚。铁电性的起源可能是由于共面八面体不足以填充BaO框架导致的。第四章研究了In掺杂GaFeO3的磁电物性,通过测试发现GaFeO3的电极化强度可以由In掺杂而变大,饱和磁化强度也可以随着In掺杂而获得优化,且拉曼测试表明掺杂样品中也存在着自旋声子耦合。然而系统的磁有序温度却有所下降,这一缺陷可以通过调节GaFe比例实现。
[Abstract]:Multiferroic materials are those with two or more than two kinds of iron materials. The sequence of multiferroic materials commonly refers to material with ferroelectric and magnetic order. Electricity and magnetism are fundamental physical phenomena, based on the Maxwell equations, the electromagnetic field changes by mutual induction and coupling in together. In the solid, the electric field can induce electric dipole moment, while the magnetic field can lead to substance magnetized. However in order to realize the coupling of electric dipole moment and the magnetization in matter is not easy. The development of magnetic and ferroelectric materials of single phase long maintained in parallel, until recent years, multiferroic magnetoelectric coupling the material took place in a breakthrough in.2003, single phase multiferroic BiFeO3 thin films were realized in the great room temperature ferroelectric polarization and magnetic coexistence, and also measured the magnetic and ferroelectric single crystal TmMnO3, and obtained the magnetoelectric coupling coefficients. In the great After this, the rapidly developing field of multiferroic, derived from a series of class I and class II multiferroic materials. The ferroelectric origin of class I multiferroic materials including lattice distortion, lone pair electron and charge ordering, and these three mechanisms are allowed and the coexistence of magnetism. These materials have a ferroelectric Curie temperature of electrode great strength and high, and even some materials at room temperature and have ferroelectricity and magnetism. On the other hand type multiferroic materials are rich and novel physical mechanism, the mechanism including spin current, exchange shrinkage and P-D orbitalhybridization. These multiferroic materials have high magnetic coupling strength. Flip or electric field on the magnetic moment of magnetic field on the electrode material. Some can even turn the iron system there are two important questions. The first is the practical room temperature magnetoelectric multiferroic material turnover has not yet appeared, so Still has important significance for exploring a new system of iron. Secondly, there are many iron systems there may exist a variety of ferroelectric origin contribution, so the exploration for the existing system still has important significance. We solve these problems for the exploration and research. The thesis is divided into four chapters, the main contents of each chapter are as follows: first chapter introduces the research background the research background of perovskite multiferroic materials and exchange bias. Firstly introduces the basic classification of multiferroic materials and typical materials, to provide reference for exploring new multiferroic materials; magnetic parameters and perovskite materials research background can make full use of that new system phase diagram of multiferroic material, such as the Neal temperature of magnetic and ferroelectric Curie temperature. Finally introduces some recent reports of single-phase exchange bias materials. The second chapter is a detailed study of the single crystal of iron oxide to SmFeO3 Exchange bias effect. We first tested the exchange bias behavior at different temperatures under different magnetic field SmFeO3, found that the exchange bias will be the size of the SmFeO3 magnetic moment compensation amplification, consistent with the Heusler alloy. After literature research we found that this system no explanation about the exchange bias and reliable, so we refer to clusters SmCiO3 and Heusler alloy system the explanation, and with a similar system in NdFeO3. Experimental results were compared in the data processing, we use the mean field approximation, therefore we have to Sm at low temperature magnetic properties are explored, validates our understanding about Sm until 0.4 K are not long program. The third chapter detailed test structure and magnetoelectric properties of the new material Ba3Ti2MnO9. Verify the Ba3Ti2MnO9 Mn-Ti structure in order along the c axis, thus confirming the non centrosymmetric space group. Temperature dependent Raman test table The system with the decrease of temperature had no obvious change. The magnetic measurements show that the system has strong frustration, verified the quasi two dimensional triangular spin arrangement is derived. Further tests show that the system can lead to excess loss / spin magnetization rates; the coagulation properties and excess spin to spin two dimers. The origin of ferroelectricity may be due to not enough to fill eight coplanar surface BaO framework result. The fourth chapter studies the physical properties of In magnetoelectric doped GaFeO3, the test found that the polarization of GaFeO3 can be changed by In doping, the saturation magnetization can be obtained with In doping and optimization, Raman test also shows that there are doped spin phonon coupling system. However the magnetic ordering temperature is decreased, this defect can be adjusted by the ratio of GaFe.

【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TM27

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