本文選題：第二類多鐵 + 磁電耦合�。� 參考：《南京大學(xué)》2017年博士論文

【摘要】：近十幾年來,人們對于多功能小型器件的需求越來越強烈,磁電耦合材料因其在信息存儲、磁電傳感器等方面的潛在應(yīng)用受到了廣泛的關(guān)注。特別是多鐵性材料中的第二類多鐵,其獨特的物理機制、較強的磁電耦合特性更是引起了人們濃厚的興趣。然而,這類材料普遍存在鐵電極化小和相變溫度低的缺點,給應(yīng)用帶來了不小的阻礙。本論文以過渡金屬氧化物中多鐵性材料的性能提升和未來應(yīng)用為驅(qū)動,一方面通過現(xiàn)代薄膜外延技術(shù)嘗試對其性能進行改良和優(yōu)化,另一方面深入探索并理解這類體系中的物理內(nèi)涵。因此,本論文的安排如下:第一章對多鐵性材料進行了概述,重點介紹了幾種第二類多鐵和非常規(guī)鐵電機制及其研究現(xiàn)狀,最后討論了薄膜技術(shù)在多鐵性材料中的應(yīng)用。第二章主要討論薄膜樣品的制備方法、結(jié)構(gòu)表征手段以及各種磁學(xué)電學(xué)物性的測量方法。在薄膜制備方面,主要介紹本論文所采用的脈沖激光沉積法。在結(jié)構(gòu)表征方面,主要介紹X射線衍射技術(shù)的各種掃描模式和倒易空間圖(RSM)相關(guān)的制作方法,以及電子顯微鏡(SEM和TEM)技術(shù)的應(yīng)用。在磁電物性表征方面,簡要介紹了本論文所采用的低溫環(huán)境系統(tǒng)PPMS和MPMS,主要討論薄膜電極的制作以及PUND和熱釋電這兩種電學(xué)性質(zhì)測量方法。第三章系統(tǒng)地研究了外延薄膜技術(shù)對第二類多鐵性材料GdMn03的結(jié)構(gòu)特征和多鐵性質(zhì)的調(diào)控。在這個工作中,我們利用PLD方法在(001)方向的SrTi03襯底上制備了高質(zhì)量的(001)取向的GdMn03外延薄膜。詳細的高分辨TEM分析發(fā)現(xiàn)其面內(nèi)存在自組裝的納米尺度孿晶疇結(jié)構(gòu),它可以最大程度地釋放薄膜面內(nèi)較大的晶格失配。在磁和鐵電性質(zhì)的測量中,我們發(fā)現(xiàn)它展現(xiàn)出了非常獨特的多鐵行為,包括較高的鐵電相變溫度(Tc～75 K)、較大的鐵電極化(Pa～4900 μC/m2)和相對較強的弱鐵磁性(～105 K)。我們認為GdMnO3薄膜中自發(fā)鐵電極化強度的增強來源于ab面內(nèi)自旋螺旋序。另外,薄膜內(nèi)部存在的自組裝納米尺度孿晶疇結(jié)構(gòu)是導(dǎo)致其高溫鐵電相和弱鐵磁性出現(xiàn)的主要誘因。第四章細致地研究了典型的第二類多鐵性材料GdMn205多晶中室溫鐵電相對低溫磁致鐵電性的影響,并在熱釋電測量過程中提出了一種特殊的極化樣品的方法。實驗結(jié)果表明,足夠強的室溫鐵電極化會誘發(fā)Mn-Mn短程磁關(guān)聯(lián)——局域自旋序,它會對低溫磁致鐵電性產(chǎn)生重要的影響。在不同的極化模式下,誘發(fā)出的局域自旋序會改變Mn3+-Mn4+-Mn3+對稱交換伸縮作用,使得與之相關(guān)的極化PMM最終與Gd3+-Mn4+-Gd3+對稱交換伸縮誘導(dǎo)出的極化PGM平行或者反平行,從而帶來低溫部分鐵電極化P=PGM ± PMM的不同行為。第五章研究了混合型非常規(guī)鐵電體Ca3Ti207/SrTi03外延薄膜的結(jié)構(gòu)特征及鐵電性質(zhì),并發(fā)現(xiàn)了該體系中存在的超低矯頑場�；旌闲头浅Ｒ�(guī)鐵電體中的鐵電極化來源于兩種或兩種以上非鐵電結(jié)構(gòu)的集體扭曲,比如在Ca3Ti207家族中Ti-O八面體的旋轉(zhuǎn)和傾斜。我們利用脈沖激光沉積的方法在(110)方向的SrTi03襯底上制備了高質(zhì)量的(010)取向的Ca3Ti2O7外延薄膜,它在界面處的外延關(guān)系為[001]CTO//[001]STO和[100]CTO//[-110]STO,表現(xiàn)出了良好的外延性質(zhì)。薄膜的面內(nèi)鐵電回線表明即便在低溫下,它也有著～5 kV/cm的超低矯頑場,這幾乎比單晶塊體中的數(shù)值低了兩個數(shù)量級。我們利用斷面高分辨TEM(包括SAED)技術(shù)以及第一性原理計算等方法對Ca3Ti2O7薄膜內(nèi)部的晶格畸變、晶格缺陷等因素進行了觀測與分析,并最終認為外延薄膜與塊體之間的巨大差異極有可能來源于薄膜中的晶格缺陷而不是襯底應(yīng)變,表明了 Ca3Ti2O7的鐵電性質(zhì)對晶格缺陷的高敏感性。第六章是對本文的總結(jié)和展望。
[Abstract]:In the past decade, the demand for multi-functional small devices is becoming more and more intense. The potential applications of magnetoelectric coupling materials have attracted wide attention because of their potential applications in information storage and magnetoelectric sensors. Especially, the second kinds of multi iron in the multi ferroelectric materials have been caused by their unique physical machine system and strong magnetic and electrical coupling characteristics. However, this kind of material has the disadvantage of low ferroelectric polarization and low phase transition temperature, which has brought no small obstacles to the application. This paper is driven by the performance promotion and future application of the transition metal oxide. On the one hand, we try to improve and optimize its performance through the modern film epitaxy technology. On the one hand, the physical connotation of this kind of system is deeply explored and understood. Therefore, the arrangement of this paper is as follows: the first chapter is an overview of the multi iron material, focusing on several kinds of second kinds of multi iron and unconventional iron motor system and its research status. Finally, the application of thin film technology in the multi iron material is discussed. The second chapter is the main discussion. The preparation methods of membrane samples, the means of structural characterization, and the measurement of various magnetic properties of electrical properties. In the preparation of the film, the pulse laser deposition method used in this paper is mainly introduced. In the aspect of the structure characterization, the various scanning modes of X ray diffraction technology and the fabrication methods related to the inverted space map (RSM), and the electron are mainly introduced. The application of microscopes (SEM and TEM) technology. In the characterization of magnetoelectric properties, the low temperature environment system PPMS and MPMS used in this paper are briefly introduced. The fabrication of thin film electrodes and the two methods of measurement of PUND and pyroelectric properties are mainly discussed. The third chapter systematically studies the epitaxial film technology for the second kinds of multiferroic materials GdMn03 In this work, we use the PLD method to prepare a high quality (001) oriented GdMn03 epitaxial film on the (001) direction of the SrTi03 substrate. The detailed high resolution TEM analysis shows that the surface of its surface is in the self-assembled nanoscale twin domain structure, and it can release the film surface to the maximum. Large lattice mismatch. In the measurement of magnetic and ferroelectric properties, we find that it shows a very unique multi iron behavior, including high ferroelectric phase transition temperature (Tc ~ 75 K), large ferroelectric polarization (Pa to 4900 C/m2) and relatively strong ferromagnetism (~ 105 K). We think the enhanced source of the spontaneous iron electrode in GdMnO3 thin films In addition, the self assembled nanoscale twin domain structure in the film is the main cause of the high temperature ferroelectric phase and weak ferromagnetism. In the fourth chapter, the influence of the ferroelectric relative low temperature ferroelectric properties at room temperature in the second typical Polyferric material is carefully studied in the fourth chapter, and the pyroelectric measurement is made in the pyroelectric measurement. A special method of polarization samples is proposed in the process of quantity. The experimental results show that strong enough room temperature and iron electrode can induce Mn-Mn short range magnetic Association - local spin order, which will have an important influence on the ferroelectric properties of low temperature magnetically induced. In different polarization modes, the local spin order induced by different polarization modes will change the symmetry of Mn3+-Mn4+-Mn3+. In the fifth chapter, the structure characteristics and ferroelectric properties of the mixed type unconventional ferroelectric Ca3Ti207/ SrTi03 epitaxial film are studied in the fifth chapter. The ultra low coercive field in the system is found. The ferroelectric polarization in the hybrid unconventional ferroelectric is derived from the collective distortion of two or more than two kinds of non ferroelectric structures, such as the rotation and tilt of the Ti-O eight body in the Ca3Ti207 family. We have prepared high quality on the (110) SrTi03 substrate by the method of pulsed laser deposition. The (010) oriented epitaxial Ca3Ti2O7 epitaxial film, whose epitaxial relationship at the interface is [001]CTO//[001]STO and [100]CTO//[-110]STO, shows good epitaxy properties. The ferroelectric wire in the surface of the film shows that even at low temperature, it also has a 5 kV/cm ultra-low coercive field, which is almost two orders of magnitude lower than that in the single crystal block. We have observed and analyzed the lattice distortion and lattice defects in the Ca3Ti2O7 thin film by using the high resolution TEM (including SAED) and the first principle calculation, and finally believed that the huge difference between the epitaxial film and the bulk is likely to come from the lattice defects in the thin film rather than the substrate strain. It is clear that the ferroelectric properties of Ca3Ti2O7 are Gao Min sensitive to lattice defects. The sixth chapter is the summary and Prospect of this paper.
【學(xué)位授予單位】：南京大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2017
【分類號】：O484

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