【作者】 杨昊；

【导师】 金绍维；

【作者基本信息】 安徽大学 ， 材料物理与化学， 2010， 硕士

【摘要】 巨磁阻效应(Giant Magnetoresistance, GMR)自1990’s被Albert Fert和Peter Grunberg发现以来,由于其在工业上具有广泛的重要应用,例如计算机硬盘、磁传感器、读取磁头、磁存储材料等等,有关它的研究已成为强关联电子自旋体系的热点之一,尤其是人们发现了具有GMR效应的钙钛矿结构锰氧化物,这种材料的GMR应用主要是基于薄膜的特性。这些锰氧化物表现出顺次-铁磁相变、绝缘体-金属相变、相分离以及电子、电荷、自旋有序的耦合等丰富的物理现象,对于基础研究有着重要意义；巨磁阻薄膜的研究和探索为磁自旋阀、磁隧道结及异质结的研制和应用提供了有效途径。本论文系统研究了掺杂的La0.8Sr0.2MnO3(LSMO)多晶靶材及其外延薄膜的结构与电磁性能。详细研究了制备条件及厚度效应对外延薄膜的微结构、输运性和磁学性质的影响,介绍了多晶块材和薄膜的制备、结构表征及性能测试,重点介绍了X-射线衍射(X-ray diffraction, XRD)和脉冲激光沉积(Pulse laser deposition,PLD)。最后还制备了薄膜异质结La0.8Sr0.2MnO3/NSTO(LSMO/NSTO),并对其整流特性进行了分析和讨论。本论文共分为四章,各章的主要内容概述如下：第一章：介绍和概述了包括块材、外延薄膜、异质结等巨磁阻材料的物理性质、研究及应用状况。首先回顾了GMR的历史、应用价值及其产生的物理机制,对巨磁阻材料之一的钙钛矿锰氧化物的晶体结构、电学性质、磁结构和输运性进行了阐述。接着指出了同种材料所组成的薄膜与块材的不同性质。最后对钙钛矿锰氧化物异质结LSMO/NSTO的应用及性质做了介绍,展望了进一步的应用前景。第二章：制备了不同厚度的La0.8Sr0.2MnO3外延薄膜,对块材和薄膜的表征手段及测试方法进行了介绍。首先回顾了块材和薄膜的的制备技术,重点介绍了PLD系统及镀膜步骤。接着对块材和薄膜的表征手段XRD、倒易空间图、扫描隧道显微镜和原子力显微镜等做了介绍。最后对测量薄膜电阻率和磁性的仪器做了简单说明。第三章：讨论了掺杂含量、晶格失配对薄膜晶体的生长及微结构的影响,详细研究了厚度效应对薄膜的结构、输运性、磁性的影响。XRD结果表明掺杂含量和薄膜厚度对块材La1-xSrxMnO3微结构的影响不大,厚度不同的LSMO/STO薄膜都具有很高的外延性和结晶质量。电阻率的测量表明,随着薄膜厚度的增加,电阻率减小,而绝缘体-金属转变温度(Tp)增加,且随着薄膜厚度的增加,转变温度Tp趋于块材的转变温度。磁性测量表明外磁场平行于膜面时,磁化强度远大于垂直膜面时的磁化强度；磁化强度随膜厚的增加而减小。第四章：首先回顾了锰氧化物异质结的发展历史、目前的研究情况及其巨大的应用价值。接着对La0.8Sr0.2MnO3/NSTO薄膜异质结的制备过程作了简要概述。最后讨论了厚度效应对薄膜异质结LSMO/NSTO整流特性的影响,得出结论LSMO越厚,异质结的整流特性越好。更多还原

【Abstract】 Since the discovery of Giant magnetoresistance (GMR) by Albert Fert and Peter Griinberg in 1990’s, the studies of it have become one of main topics in strongly correlated electron system due to its extensive and important application in industry, for example, computer hard disk, magnetic sensor, read-heads, magnetic memory material, etc, especially the discovery of GMR in perovskite manganese oxides materials whose GMR depending on thin film properties. These manganese oxides show paramagnetic-ferromagnetic phase transition, insulator-metal phase transition, phase separation and interplay between electron, spin and charge orders etc physical phenomenon of great significance in fundamental physics research; the studies and exploration of GMR epitaxial thin films offer an effective path to development and application of magnetic spin-valve, magnetic tunneling junction and heterojunction.The structure and electromagnetic properties of doped polycrystalline bulk and epitaxial thin films of La0.8Sr0.2MnO3 (LSMO) are systematically investigated in this thesis. Effects of preparation conditions and thickness on microstructure, transport properties and magnetism of films are carefully investigated respectively. Preparation and measurement methods of films and bulks samples are also introduced, placing emphasis on X-ray diffraction (XRD) and pulse laser deposition (PLD). In addition, thin films heterojunction La0.8Sr0.2MnO3/NSTO (LSMO/NSTO) are fabricated and the rectifying characteristics of LSMO/NSTO are also analyzed and discussed.The whole thesis consists of four chapters and the main contents of every chapter are as follows:Chapter one:The physical properties, research and application of GMR materials, including bulk, epitaxial thin films and heterojunction are introduced and summarized. Firstly, the history, application value and physical mechanism of GMR are reviewed and the crystal structure, electrical properties, magnetic structure and transport properties of perovskite manganese oxides, one of the GMR materials, are expatiated. Secondly, the difference of properties between thin films and bulks whose consist of same materials are pointed out. Lastly, we introduce the application and properties of LSMO/NSTO heterojunction and make a prospect of further application.Chapter two:La0.8Sr0.2MnO3 epitaxial thin films with different thickness are fabricated and the representing means and measurement methods towards bulks and films are introduced. Firstly, the preparation of bulks and fabricating technologies of thin films are reviewed, especially PLD and fabricating thin films process. Secondly, representing means, including XRD, reciprocal space maps, scanning tunneling microscope and atomic force microscope are introduced. Lastly, the instruments for measuring the resistivity and magnetism of films are simply described respectively.Chapter three:the influence of doping content and lattice mismatch on thin films’ crystal growth and microstructure and the effect of thickness on thin films’structure, transport properties and magnetism are investigated in detail. The result of XRD manifest that doping content and thickness nearly don’t influence the microstructure of La1-xSrxMnO3 bulks and that those LSMO/STO thin films with different thickness possess of high crystalline and epitaxial quality. Measurements indicate that the resistivity decreases and the insulator-metal transition temperature (Tp) increases with increasing of the film thickness. The Tp will remain a fixed value which is the Tp of bulk of LSMO when LSMO films thickness reaches a critical value. Magnetic measurements make it clear that LSMO thin films’magnetization is far greater than vertical when applied magnetic field is parallel with film surface and the magnetization reduces with the increase of thickness.Chapter four:firstly, the development history, present research and application of magnetite-based p-n junction are reviewed. Secondly, the process of fabricating La0.8Sr0.2MnO3/NSTO thin films junction is introduced. Last, thickness effects on the rectifying characteristics of LSMO/NSTO are discussed coming to a conclusion that the rectifying characteristics of LSMO/NSTO are getting better for thicker junction.更多还原