【作者】 许升高；

【导师】 曹光旱；

【作者基本信息】 浙江大学 ， 凝聚态物理， 2011， 硕士

【摘要】 超导电性自发现之日起就引起了物理学界的广泛关注,超导电性的研究也历经百年而不衰。2008年初铁基超导体的发现,是自铜氧化物超导体之后高温超导领域的又一重大突破,给超导研究带来了巨大的机遇和挑战。铁基超导体的研究一方面可以从实验上积累更多的化学组成和结构与超导电性的相关知识,另一方面也可以有助于理论上探索高温超导的微观机制,而这些对于寻找新的高温超导体和提高超导转变温度大有裨益。基于对铁基超导体研究工作和作者研究组之前的研究成果的总结,本文着重于铁基超导体122体系两种母体化合物EuFe₂As₂和BaFe₂As+2进行等电子掺杂工作。EuFe₂As₂和BaFe₂As₂化合物都是具有ThCr₂Si₂结构的化合物,它们分别在200K和140K的温度下发生结构相变和SDW相变。我们通过对它们进行等电子掺杂,得到了重要结果,并描绘了掺杂的电子相图。全文共分四章,第一章为绪论,回顾了超导发展的历程,超导电性的基本性质以及固体的磁性分类,第二章总结了铁基超导体自发现以来的实验研究进展,主要介绍了1111体系和122体系的主要研究工作。第三章介绍了EuFe₂As₂体系中As位P掺杂的研究工作。我们合成了一系列EuFe₂(As_1-xP_x)₂多晶样品,并对其进行了结构表征和电阻率测量。我们发现P掺杂会使晶胞缩小,引入化学压力。我们描绘了完整的EuFe2(As_1-xP_x)₂电子相图,指出P掺杂能够压制SDW并引入超导,超导区域为0.2≤x≤0.4,同时,在这一掺杂范围内超导和铁磁共存。x>0.4时,材料的超导消失,仅剩下铁磁转变。第四章介绍了BaFe₂As₂体系中Fe位等量掺杂Cr和Ni的研究工作。我们通过对一系列Ba(Fe（1-x）Cr_x/2Ni_x/2)₂As₂样品的物性表征,给出了Ba(Fe（1-x）Cr_x/2Ni_x/2)₂As₂体系的电子相图。我们发现等量Cr、Ni的掺杂,会在BaFe2As2中引入铁磁相互作用。掺杂能够压制SDW相变,并使材料出现自旋玻璃态。随着掺杂比率的增加,自旋玻璃态向铁磁态演变。BaCrNiAs₂在64K时发生铁磁相变。更多还原

【Abstract】 Since its discovery, superconductivity has aroused wide attention in phys ics, and is all the while one of the most popular subjects. The discovery of iron-based superconductors in the year of 2008 is another important breakthrough after the copper-oxide superconductivity in high temperature superconductivity, which brought great chance and challenge for the superconductive study. The crystal structure and chemical composition of the layers are crucial and sensitive for the emerge of supe rconductivity.Based on the earlier study work, my dissertation focuses on the iso-electronic doping effects on the EuFe2As2 and BaFe2As2 systems. EuFe2As2 and BaFe2As2 possess the same ThCr2Si2-type structure, however, the structural and magnetic transition happen at 200K and 140K respectively. By iso-electronic doping methods, some important results and electronic phase diagrams are obtained.My dissertation includes four chapters. The first chapter is the introduction, including the process of superconductivity development, two basic properties of superconductors, the solid magnetism and so oa The second chapter summarizes the experimental research progress of iron-based superconductivity, especially on the 1111 and 122 systems.In the third chapter, we demonstrate the results on P doping at As site in EuFe2As2. A series of EuFe2(As_1-xP_x)₂ polycrystalline were synthesized, and powder X diffraction and resistivity measurement were performed. The isovalent substitution of As with P leads to the shrinkage of the lattice and generates chemical pressure. The phase diagram is obtained, which shows that P doping at As site suppress the SDW transition and induces superconductivity. In the area of 0.2≤x≤0.4, superconductivity emerges, and coexists with ferromagnetism. Ferromagnetic transition happe ns in the area of x>0.4.The fourth chapter introduces the work on iso-electronic Fe-site doping with Cr and Ni in Ba(Fe_1-xCr_x/2Ni_x/2)₂As₂. We performed some property characteristics and obtained phase diagram. We found that the Cr and Ni doping induces ferromagnetic interreaction. Doping suppresses the SDW transition quickly and spin glass state emerge. With increasing the doping level, spin glass state evolves into ferro magnetism. BaCrNiAs2 shows a ferromagnetic transition at 64K.更多还原