【作者】 吴小峰；

【导师】 冯守华；

【作者基本信息】 吉林大学 ， 无机化学， 2013， 博士

【摘要】 钙钛矿型锰氧化物由于其内部的电荷、自旋、轨道及晶格等自由度间的强烈耦合，多种竞争机制下产生了丰富的物理现象，这些性质为开发自旋电子学器件提供了基本素材，同时钙钛矿锰氧化物也为凝聚态物理的研究提供了“天然实验室”，是自然界赐予人类的一块瑰宝。本论文的研究对象为La1-x-yCaxKyMnO3（LCKMO），其由于A位两种不同价态离子K和Ca的共同掺杂，使Mnn+呈现更为复杂的电子态分布，具备三重价态及原子级p-n结整流等多种新奇特性。本论文针对LCKMO材料的低维制备和电磁性能进行了研究，取得的结果如下：1)制备了不同维度的LCKMO材料，分别用水热法、脉冲激光沉积法和模板辅助沉积法制备了三维单晶，二维高质量薄膜和一维纳米管及零维纳米点材料。2)采用多种实验方法研究了LCKMO单晶和薄膜的电学性质，二者除表现基本磁阻特征外，更是呈现出明显的整流效应。3)对薄膜的磁热研究表明其在磁制冷应用方面有潜在的应用价值。5T下最大磁熵变为3.45Jkg^-1K^-1，相对制冷效率为379.5Jkg^-1，磁熵半峰宽为110K。各章节的主要内容概括如下：第一章介绍了钙钛矿锰氧化物的研究背景及相关基础理论，概述了新兴的自旋电子学及锰氧化物相关的器件应用，最后简述了论文的选题思路。第二章用多种实验方法如两电极法、变温原子力法、聚焦离子束辅助四电极法和交流频谱法研究了LCKMO单晶的电学性质，结果表明单晶材料具备明显的整流特性，在正向电压下快速开启，而在反向电压下则保持截止状态。第三章介绍了脉冲激光沉积法（PLD）制备LCKMO薄膜并对薄膜进行了系统表征。首先介绍了等离子体的形成及薄膜的生长动力学过程，然后有目的地优化薄膜的生长。ICP，XRD，SEM，TEM，XPS和RBS等表征说明钛酸锶基底上获得了较高晶体质量的LCKMO薄膜。第四章研究了薄膜的电磁学性能。在面内用四电极法研究了薄膜的输运特性，在面外方向，以SrRuO3作为底电极进行原子力测试，表明薄膜呈现良好的单向导通效应，最后对整流机制做了阐述。用等温磁化法研究了薄膜样品的磁熵性能，较大的磁熵半峰宽和相对制冷效率表明其在Ericsson磁制冷循环有较好的应用潜能。第五章介绍了La0.8Ca0.2MnO3（LCMO）和LCKMO低维纳米材料的制备。用阳极氧化铝模板（AAO）作为基底，PLD沉积后去除模板，则得到纳米管材料。实验中，对纳米管进行了系列表征，并对形成机理进行了解释。将超薄AAO转移到钛酸锶基底后，沉积后去除模板即可得到相应的纳米点材料，其纳米材料性能还在进一步研究。第六章对全文进行了总结，并对原子级p-n结材料在未来的研究和应用进行了展望。随着科技的发展进步，人类逐渐在纳米尺度认识和改造世界，通过操控原子和分子以创造新物质和新性能。本课题组基于实验结果提出的原子级p-n结概念，为新型电子信息材料的开发和新型器件构型提供了素材和设计思路。本文工作用多种实验方法进一步证实了结效应，并且丰富了样品的存在形式，同时表明材料有较好的磁热效应，为制备复合功能自旋电子学器件奠定了基础。更多还原

【Abstract】 There are strong interactions among charge，orbital，spin and lattice existing inperovskite-type manganite. Those multiple competition mechanisms lead to a seriesof physical phenomenon which can be used as a basis for developing spintronicdevices. Simultaneously, perovskite-type manganite is a “Natural Laboratory” forcondensed matter research，and be considered a precious gift given by natural worldto mankind. This thesis is targeted on La1-x-yCaxKyMnO3（LCKMO）, which co-dopedby monovalent potassium and bivalent calcium in A-site. Many novel properties suchas atomic-scale p-n junction, which is caused by complicated electronic statedistribution of Mnn+, were present in this compound. Here, we reported thepreparation of low dimensional LCKMO materials and their electromagnetic behavior,and the major results are as follows: a) LCKMO materials with four different kinds ofdimensions were prepared. Single crystal, film, nanotube and nanodot were preparedby hydrothermal synthesis and pulsed laser deposition method. b) The electronicproperties of single crystal and film were measured by several means, all the resultsreveal the rectify effect existing in LCKMO. c) The excellent MCE performance,which may cause by K ions substituted and strain effect in the LCKMO film, revealsits great applicative potentialities as magnetic cooling refrigerant. The main contentsfor each section in this dissertation are presented as follows: In chapter1, we introduce the research background and related basic theories ofperovskite-type manganit. A brief sketch of the rising spintronics andmanganite-based devices and its applications were given, and the choice item andbasic thought of this thesis are stated at last.In chapter2, we studied the electrical properties of LCKMO single crystals usingseveral kinds of experimental method such as two electrodes, variable temperatureatomic force microscope, focused ion beam assisted four electrodes and alternatingcurrent spectrometry. The perceptible rectify effects are consistently shown in singlecrystal test. When the crystal is forward biased, the current abruptly increase at thethreshold voltage, and the crystal cut off with the reverse bias applied.In chapter3, LCKMO films are prepared by pulsed laser deposition （PLD）method and then characterized systematically. The formation of laser-induced plasmaand kinetic process of the film growth are briefly introduced at the beginning, and usethem as the basis for optimization the growth conditions of the film purposefully. ICP,XRD, SEM, TEM, XPS and RBS are used to analyzing the resultant film, and theresults indicate that the LCKMO films with high crystalline quality were obtained onSrTiO3（STO） single crystal substrate.In chapter4, the electromagnetic properties of the LCKMO film were studied.The in plane transport properties was studied using four wire method, and the out ofplane was measured by atomic force microscope using a SrRuO3film as bottomelectrode. The expected rectify effect was observed and its mechanism was discussed.With the magnetic field change of5T, the maximum magnetic entropy change andrelative cooling power of the film is3.45J·kg^-1·K^-1and379.5J·kg^-1, respectively. Anotable case is that the full width at half maximum of|ΔSM|is110K, which isdesirable for the Ericsson cycle. The excellent MCE performance of the LCKMO filmreveals its great applicative potentialities as magnetic cooling refrigerant.In chapter5, Low dimensional materials of perovskite-type manganite nanotubeand nanodot were prepared by template assisted pulsed laser deposition. After thedeposition on anodic aluminum oxide （AAO） nanopore membrane, we obtained the nanotube by removing the template in alkaline condition. The structure、morphologyand magnetic properties are characterized and the formation mechanism of the NTs isalso proposed. When we transfer the ultrathin AAO template to STO and then executePLD deposition，nanodot structure formed on STO substrate corresponding to the poredistribution. Further research is required to fully understand their performanceinduced by scale shrinking.In chapter6, a brief summary based on the full text was present, and the futureresearch and applications of atomic p-n junction were look forward.With the development of science and technology and the progress of society，humankind are understanding and transforming the objective world in nano-scalegradually， individual atoms and molecules were manipulated to produce newmaterials and new properties. Based on the experimental results, our group proposedthe idea of atomic scale p-n junction firstly. We provided ingredient and designthinking for new generation electronic information materials and devices architecture.In this thesis, diverse forms of LCKMO were developed, the existing of junctioneffect was verified by using multiple means, and its magnetocaloric effect was alsostudies. Those works lays a good foundation for the preparation of spintronics devicewith complex functions.更多还原