【作者】 田翠锋；

【导师】 孙爱民；

【作者基本信息】 西北师范大学 ， 凝聚态物理， 2006， 硕士

【摘要】 由于熔融织构YBCO具有高的转变温度和临界电流密度，所以被广泛应用，如超导磁悬浮、超导电机、超导飞轮等等。本论文简要介绍了超导材料的发展现状及选题意义和选题内容，讲述了所研究材料的结构特点、制备工艺及其特性，重点阐述了熔融织构YBCO的有效钉扎势的研究，具体分析并确定了有效钉扎势中的三个参数——玻璃态指数、临界电流密度、钉扎势（有效钉扎势的标度势）。1．对于熔融织构YBCO样品，我们用定场磁驰豫方法获得了玻璃态指数μ（T，H），结果表明与用磁场扫描方法得到的结果变化趋势一致，并且符合集体钉扎理论。2．在集体钉扎理论中，在热激活磁通运动中，有一个描述磁通运动的重要参数有效钉扎势，它是临界电流密度J_c、玻璃态指数μ和钉扎能U₀的函数。确定钉扎能是比较困难的，这里我们介绍了一种新办法来确定钉扎能U₀，在三个参数都确定的前提下，有效钉扎势的问题才得到解决。3．用震动样品磁强计测量了熔融织构YBCO样品的磁滞回线，并根据集体钉扎里论确定了临界电流密度J_C，由此得到的曲线中，分别在T=77K和83K观察到了鱼尾效应。进一步研究表明鱼尾效应是玻璃态指数和钉扎势之间竞争的结果，同时我们也看到随着温度的下降峰向高磁场方向移动。更多还原

【Abstract】 Due to the high transition temperature and the quite high critical current density, the YBa₂Cu₃O_7-d （YBCO or Y123） superconductor can be applied for many potential aspects, such as superconducting magnetic suspension, superconducting motor and superconducting flywheel. This dissertation gives a brief introduction of the developed history and the latest investigation on the effective pinning energy of the MTG YBCO, and the significance and main content of this thesis; tells of the research material structure, synthesize technique and physical properties; expatiate on the effective pinning energy of the MTG YBCO, analysis and determining of the three parameters （the glassy exponent, the critical current density, pinning energy） of effective pinning potential (U_eff).1. By magnetic relaxation method we obtained the glassy exponentμ（T, H） of the melt textured Yba₂Cu₃O_7-x sample. The results have a similar behavior compared with ones using the method of magnetic field sweep, and are compatible with the model of collective pinning theory.2. In collective pinning theory, effective pinning potential, U_eff , is a key parameter in describing thermally activated flux motion, but it is a function of the exponentμ, scale energy U₀ and critical current density J_C, under the base of Griessen’s and our group’s methods of obtaining J_C andμ, respectively. Determining U₀ is a troublesome problem. In this paper, we introduced a new way of determining pinning energy U₀, thus, the complex problem of getting U_eff has been solved successfully.3. According to the collective pinning model, we determine the critical current density J_C for melt textured YBa₂Cu₃O_7-x bulk by using magnetic hystersis loops （MHLs） in a vibrating sample magnetometer （VSM）, and only observe the fishtail effect （peak effect） at T=77K and 83K. Further investigation shows that the fishtail effect is the competitive result of the glassy exponentμand the pinning energy U₀, which are varying with magnetic field and temperature. We also observe that the fishtail effect shift towards higher fields as temperature decreased.更多还原