【作者】 曹桂新；

【导师】 张金仓； 沈学础；

【作者基本信息】 上海大学 ， 无线电物理， 2006， 博士

【摘要】 强关联钙钛矿锰氧化物体系存在诸多奇异而有趣的物理现象和丰富而又复杂的物理内涵,成为近年来物理学和信息材料物理领域十分活跃而又引人注目的前沿研究领域。特别是该类材料中所表现出的电荷/自旋/轨道和晶格自由度之间存在的相互作用和竞争现象,和由此而诱发产生的绝缘-金属转变、有序化和相分离等一系列新奇物理现象,向现代物理学和信息科学的传统概念提出了挑战,从而给物理学家、材料科学家和信息科学家们提出了新的研究课题,诸多与此相关的一些新现象的解释和新概念的提出,将导致以强关联物理学、自旋物理学和自旋电子学等为代表的基础学科和未来信息技术的革命,使得强关联钙钛矿锰氧化物体系的研究成为二十一世纪科学技术特别是凝聚态物理强关联电子系统的主要研究热点之一。本论文工作以具有典型低温相分离特征的Pr掺杂锰氧化物La 5/8-xP rxCa 3/8 MnO3体系和半掺杂的(La,Pr)0.5Ca0.5MnO3体系为具体研究对象,在制备高质量单晶和多晶样品的基础上,采用磁场诱导技术,研究了低温相分离特征与step型输运异常现象的关联、电荷/自旋/轨道有序结构、磁场诱导产生的自旋重定向/载流子退局域化与可能的自旋/轨道量子转变的本质,以及与电荷有序和轨道有序等多种序参量之间的关联等等,本论文共分为六章,主要内容为:第一章综述了近年来强关联钙钛矿锰氧化物物理与自旋电子学领域的研究进展,重点就强关联钙钛矿锰氧化物的相分离问题、CMR机理研究和自旋/轨道之间的强耦合作用导致存在于低温下的一些奇异物理现象,并就本文工作的研究目的和出发点进行了概括性描述。第二章主要介绍了实验样品的制备、样品质量表征、以及物性测量手段和基本原理,主要包括电磁输运性质和比热性质测量等。第三章研究了利用光学浮区法制备的Pr5/8Ca3/8MnO3单晶的结构、输运和磁特性。发现在几个特斯拉的较低外磁场诱导下,体系在60 K以下出现的step型电荷有序反铁磁-铁磁转变(COAFM-FM),存在于~4.2 K以下异常陡峭的磁化step变化行为,在场冷模式下发现了存在于Pr 5/8Ca 3/8 MnO3单晶中T=2 K下的双重磁化更多还原

【Abstract】 The study of the manganites, widely known belonging to strongly correlated electron systems, that exist many novel and interesting physical phenomena and complex physical mechanism is among the active and attractive areas of research within the area of physics and information material physics. Significantly, the strong coupling and competition among the spin, charge, orbital, and lattice degrees of freedom in these systems can induce a wide variety of newly novel phenomena such as insulator-metal transition, orderings and phase separation etc. All these challenge the traditional understanding of physics and information science and will provide newly subject for the physicist, material scientist and information scientist. A lot of related new physical phenomena and concepts have been brought forward, which will arouse a revolution of some basic subjects (such as strongly correlated systems, spinelectronics physics) and the information technology in the future. This probably makes strongly correlated manganites the one of the hotspots in the field of condensed matter physics in the 21st century. In this dissertation, based on the preparation of high quality single crystal and polycrystalline samples, the typical phase-separated La5/8-xPrxCa 3/8 MnO3 and half doped (La,Pr)0.5Ca0.5MnO3 systems were investigated in magnetic fields. The correlation between low temperature phase separation and novel step-like transport, and the correlation among ordering parameters such as charge ordering and orbital ordering etc. were studied Meanwhile, the charge/spin/orbital ordering structure, the mechanism of magnetic induced spin reorientation/carrier delocalization, and the possible quantum spin/orbital transition were studied in these systems. The content of the dissertation are divided into six chapters and main results are summarized as follows.The first chapter describes the content status and progress of the studies concerning the strongly correlated manganites and correlative spin electronic physics, stressing on the phase separation in the mananites, the mechanism of the colossal更多还原