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  本文關鍵詞：類鈣鈦礦氧化物材料的磁電物性研究　出處：《中國科學技術大學》2016年博士論文　論文類型：學位論文

  更多相關文章： 多鐵材料 浮區(qū)法 SmFeO_3 Ba_3Ti_2MnO_9 GaFeO_3 交換偏置

【摘要】：多鐵性材料是指具有兩種或兩種以上鐵性序的材料。最為常見的多鐵性是指材料中同時具有鐵電性和磁有序的材料。電和磁是基本的物理現(xiàn)象,依據(jù)麥克斯韋方程組,變化的電磁場因互相感應而耦合在一起。在固體物質中,電場可以誘導電偶極矩產生,而磁場則可以導致物質被磁化。然而要在物質中實現(xiàn)電偶極矩和磁化強度的耦合卻并非易事。單相磁性和鐵電材料的發(fā)展長久保持著平行,直到近十幾年,磁電耦合多鐵材料才發(fā)生了突破性進展。2003年,單相多鐵材料BiFeO3薄膜中實現(xiàn)了室溫巨大的鐵電極化與磁性共存,而TmMnO3單晶中也測得了磁致鐵電性,且獲得了巨大的磁電耦合系數(shù)。在此之后,單相多鐵領域迅速發(fā)展,衍生出一系列的Ⅰ類和Ⅱ類多鐵材料。其中Ⅰ類多鐵材料的鐵電起因包括晶格畸變、孤對電子和電荷有序,而這三種機制都允許與磁性共存。這些材料擁有著巨大的電極化強度和很高的鐵電居里溫度,而有的材料甚至在室溫同時具備鐵電性和磁性。另一方面Ⅱ類多鐵材料則有著豐富而新奇的物理機制,其機制包括自旋電流、交換收縮和p-d軌道雜化。這些多鐵材料擁有著極高的磁電耦合強度,有的材料中甚至可以實現(xiàn)電場對磁矩的翻轉或是磁場對電極化的翻轉。目前多鐵系統(tǒng)中存在著兩個重要的問題,首先是實用室溫磁電翻轉多鐵材料尚未出現(xiàn),因此對于多鐵新體系的探索依然具有重要意義。其次,已有多鐵體系有可能存在著多種鐵電起源貢獻,因此對于已有體系的探索依然有重要意義。我們針對這些問題進行了探索與研究。論文內容共分為四章,每章的主要內容如下：第一章綜合介紹了鈣鈦礦多鐵材料的研究背景及交換偏置的研究背景。首先介紹了多鐵材料的基本分類和典型材料,從而為新型多鐵性材料的探索提供參考；而鈣鈦礦材料研究背景則可以充分利用系統(tǒng)相圖推測新型多鐵材料的磁電參數(shù),如磁性尼爾溫度和鐵電居里溫度。最后介紹了近期報道的一些單相交換偏置材料。第二章詳細研究了單晶鐵氧化物SmFeO3的交換偏置效應。我們首先測試了不同溫度不同磁場下SmFeO3的交換偏置行為,發(fā)現(xiàn)SmFeO3的交換偏置大小會被磁矩補償放大,與Heusler合金一致。經過文獻調研我們發(fā)現(xiàn)這一體系暫無關于交換偏置可靠的解釋,因此我們參考SmCiO3和Heusler合金系統(tǒng)中的團簇解釋,并與類似系統(tǒng)NdFeO3中的實驗結果進行了對照。在數(shù)據(jù)處理中我們用到了平均場近似,因此我們又對低溫下Sm的磁性進行了探索,驗證了我們關于Sm直到0.4 K都沒有形成長程序的理解。第三章詳細測試了新材料Ba3Ti2MnO9的結構和磁電物性。結構測試驗證了Ba3Ti2MnO9中Mn-Ti沿著c軸的有序排列,從而確認其空間群為非中心對稱的。變溫拉曼測試表明系統(tǒng)隨溫度降低無明顯相變。磁性測量表明系統(tǒng)中存在著較強的阻挫發(fā)生,驗證了結構推導出的準二維三角自旋排布。進一步的測試表明,系統(tǒng)缺失/多余自旋會導致磁化率上升；而多余的自旋會以自旋二聚體的性質凝聚。鐵電性的起源可能是由于共面八面體不足以填充BaO框架導致的。第四章研究了In摻雜GaFeO3的磁電物性,通過測試發(fā)現(xiàn)GaFeO3的電極化強度可以由In摻雜而變大,飽和磁化強度也可以隨著In摻雜而獲得優(yōu)化,且拉曼測試表明摻雜樣品中也存在著自旋聲子耦合。然而系統(tǒng)的磁有序溫度卻有所下降,這一缺陷可以通過調節(jié)GaFe比例實現(xiàn)。
[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.

【學位授予單位】：中國科學技術大學
【學位級別】：博士
【學位授予年份】：2016
【分類號】：TM27

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