【作者】 吕章明；

【导师】 曹烈兆； 阮可青；

【作者基本信息】 中国科学技术大学 ， 凝聚态物理， 2009， 博士

【摘要】 过渡金属氧化物是凝聚态物理中的研究热点之一,它包含了丰富而奇异的物理现象,如铜氧化物的高温超导电性,锰氧化物的巨磁电阻等等。由于这些奇异的现象中蕴涵着广阔的应用前景,对其深刻的认识和科学的利用将为人类科技的发展以及物质财富的积累起到巨大的推动作用。但到目前为止,对于这些奇异的现象背后的本质还没有非常成熟的理论,因而,对于过渡金属氧化物的研究一直受到广泛的关注和支持。在本论文中,我们对Ru基磁性高温超导体RuSr₂Gd_1.4Ce_0.6Cu₂O₁₀和Ruddelsen-Popper型化合物Sr₃Fe_2-xRu_xO₇的输运性质、磁性质以及其他受到关注的性质进行了一系列的研究和探索。部分研究结果已在J.Appl.Phys.,SolidState Commun.等杂志上发表,还有部分成果正在整理发表中。本论文分为六章,下面简要介绍一下各章主要内容。第一章为绪论部分,我们主要对人们对于高温超导电性的认知现状和最新的一些研究方法做了一个全貌性的介绍。虽然也不尽完整,但应该使读者能够对高温超导电性得到一个大概的认识,特别是对于利用最新研究手段得到一些研究成果.而且我们也对这些高级的研究手段做了一些介绍,比如角分辨光电子能谱（ARPES）,中子散射技术等。第二章中我们对Ru基磁性高温超导体做了一个背景介绍。这一部分中我们对以前其他工作者做的重要工作做了一个总结,对比分析了Ru基磁性高温超导体两个体系Ru-1212和Ru-1222的各方面性质和研究进展。重要的是,在这一章中我们引出了很多以前研究上的一些具有争议性的结果以及尚未得到明确结论的问题,以作为我们工作的方向和研究重点,接下来的两章我们主要通过各种测量手段有针对性地研究和分析这些问题。第三章题为“RuSr₂Gd_1.4Ce_0.6Cu₂O₁₀的制备和超导电性稳定性研究”。首先介绍了我们制备RuSr₂Gd_1.4Ce_0.6Cu₂O₁₀的过程以及对样品各方面的表征。由于Ru基高温超导体的体超导电性经常表现出对环境的严重的依赖关系,我们对此进行了一系列的研究,得到了一些有意义的结果。第四章题为“RuSr₂Gd_1.4Ce_0.6Cu₂O₁₀的磁性质、输运性质和超导态性质的研究”。我们一开始对于Ru离子的自旋态进行了测量和分析,并对磁性质进行了综合的分析,得出了一些有意义结论.我们进一步通过热导的磁场效应研究了和分析RuO-2层内的电子对输运性质的影响和贡献。在这一章最后一部分我们探讨了Meissner态和自发涡旋态的存在状况。第五章题为“Ruddlesdcn-Popper型化合物Sr₃（Pe,Ru）₂O₇体系的磁性质和输运性质研究”,这是我们较早的一些工作。该体系为对Mott绝缘体的一种掺杂,我们对于Ru掺杂对该体系的结构、输运性质以及磁性质进行了一些探讨,并取得一定的认识.第六章主要讲述了我们对于电子型掺杂超导体Sm_2-xCe_xCuO₄材料的制备条件和退火条件的探索,以对电子型超导体的各种特性进行研究。从实验结果看,这些材料的制备条件已取得一些结果,而退火条件需要进一步摸索,而各方面的物理性质需要小组继续进行研究。更多还原

【Abstract】 Transition metal oxides have been extensively studied for their interesting and abnormal properties,such as high-T_c superconductivity,colossal magnetoresistance,et al.Because there is huge practice value behind these abnormal phenomena,a better understanding and cognition of these phenomena will improve the development of human being’s technology and raise the productivity.However,so far,there is no mature theory to these complex phenomena.The research of transition metal oxides has been receiving wide support and attention,and it is necessary to continue to do so.In this dissertation,we have studied the transport properties,magnetic properties and some other attractive aspects of the magnetic superconductor RuSr₂Gd_1.4Ce_0.6Cu₂O₁₀ and the Ruddelsen-Popple compounds Sr₃Fe_2-xRu_xO₇.Some of our results have been published in international magazines such as J.Appl.Phys.and Solid State Commun.And some is preparing to be published.This dissertation includes five chapters.Chapter one is a comprehensive introduction to the progress in the research of high-T_c superconductivity.Though not all-contained,it can give a simple and crude profile to readers of the study of the high-T_c superconductivity.In the part,we paid much of our attention to introduce the recent progresses in the reseach of high-T_c superconductivity using most advanced tools and methods.We also simply introduce these tools and methods such as angle-resolved photoemission spectroscopy（ARPES）,neutron scattering,et al.In chapter two,we give an introduction to Ru-based high-T_c cuprates by summarizing the previous works and by comparing the two Ru-based high-T_c cuprate systems Ru-1212 and Ru-1222.Most importantly,we summed up the most controversial results and some unanswered questions and our research focused on these points.The following two chapters are about our researching work on these problems.Chapter three is entitled "Preparation and Stability of Superconductivity of Magnetic Superconductor RuSr₂Gd_1.4Ce_0.6Cu₂O₁₀".First,we described the method of preparing and characterizing the compound RuSr₂Gd_1.4Ce_0.6Cu₂O₁₀.Since the bulk superconductivity is sensitive to preparing and conserving conditions,we first focused on this issue and obtained some very interesting results.We present all our experimental steps and results in the second part.Chapter four is entitled "The Magnetic,Transport and Superconducting Properties of the Magnetic Superconductor RuSr₂Gd_1.4Ce_0.6Cu₂O₁₀".In this chapter,we focus on the controversial issues in the Ru-1222 system.We first conclude our research work on the spin-state of the magnetic Ru ions and on the overall magnetic property of the compounds.Then we turn on to the transport property.In this part we mainly shed some light on the issue whether the RuO2 layers conduct or not through magnetothermal conductance measurement.In the last part of this chapter, we present our work on searching the Meissner state and spontaneous vortex state in the superconducting state.Chapter five is titled "The Studies on the Magnetic and Transport Properties of the Ruddlesden-Popper Type Compounds Sr₃（Fe,Ru）₂O₇" This is our research work in the early years. The system is the doping of Ru to Mott insulator Sr₃Fe₂O₇.By varying the Ru content,we studied the evolution of the structural,transport and magnetic properties.We summarize our experiments and understandings of this system in this chapter.Chapter six is mainly about our work on finding the best method to grow the single crystals of n-type high-T_c superconducting compounds Sm_2-xCe_xCuO₄ as well as its best annealing condition.The results show that we have found the best growing condition but the annealing condition is still uncontrolled.The remaining work is required to be completed by other members of our group.更多还原