Research On Physical Properties Of Magnetic Superconductor RuSr₂Gd_1.4Ce_0.6Cu₂O₁₀ And RP-type Compounds Sr₃Fe_2-xRu_xO₇ And Preparation Of Electron-doped Super

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.