中国物理B ›› 1994, Vol. 3 ›› Issue (2): 124-130.doi: 10.1088/1004-423X/3/2/006

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FLUX CREEP, FLUX PINNING AND CRITICAL CURRENT DENSITY OF Y-, Gd-, AND Tl-BASED SUPERCONDUCTIVE THIN FILMS

张晖1, 孙志坚1, 杨森祖1, 施智祥2, 吉和林2, 张贻瞳2, 金新2, 徐小农2, 丁世英2, 姚希贤2, 王长安3, 王瑞兰3, 李宏成3   

  1. (1)Department of Information Physics, Nanjing University, Nanjing 210008, China; (2)Department of Physics, and National Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210008, China; (3)Nationai Laboratory for Superconductivity, Institute of Physics, Academia Sinica, Beijing 100080, China
  • 收稿日期:1993-03-15 出版日期:1994-02-20 发布日期:1994-02-20
  • 基金资助:
    Project supported by the National Center for Research and Development on Superconductivity of China, and the Foundation for Doctoral Eduction.

FLUX CREEP, FLUX PINNING AND CRITICAL CURRENT DENSITY OF Y-, Gd-, AND Tl-BASED SUPERCONDUCTIVE THIN FILMS

SHI ZHI-XIANG (施智祥)a, JI HE-LIN (吉和林)a, ZHANG YI-TONG (张贻瞳)a, JIN XIN (金新)a, XU XIAO-NONG (徐小农)a, DING SHI-YING (丁世英)a, YAO XI-XIAN (姚希贤)a, WANG CHANG-AN (王长安)b, WANG RUI-LAN (王瑞兰)b, LI HONG-CHENG (李宏成)b, ZHANG HUI (张晖)c, SUN ZHI-JIAN (孙志坚)c, YANG SEN-ZU (杨森祖)c   

  1. a Department of Physics, and National Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210008, China; b Nationai Laboratory for Superconductivity, Institute of Physics, Academia Sinica, Beijing 100080, China; c Department of Information Physics, Nanjing University, Nanjing 210008, China
  • Received:1993-03-15 Online:1994-02-20 Published:1994-02-20
  • Supported by:
    Project supported by the National Center for Research and Development on Superconductivity of China, and the Foundation for Doctoral Eduction.

摘要: Magnetic hysteresis loops have been measured for YBa2Cu3O6+x, GdBa2Cu3O6+x and Tl2Ba2Ca2Cu3O10-y films at different temperatures with a vibrating sample magnetometer. Based on Bean model, magnetic critical current density Jcm has been derived approximately. The field and temperature dependence of Jcm for all samples can be written as: Jcm= Jc0(T)×f(B,T), Where f(B,T) = 1 - Aln(B/B0(T)), which is similar to the transport critical density strongly affected by flux creep: Jct = Jc0(B,t)(1 - (kBT/U0)ln(BΩd/Ec)). The extraordinary similarity suggests that Jcm is determined not only by flux pinning but also by flux creep. In the first formula, f(B,T) may be correlated with the effect of flux creep on Jcm, and Jc0(T) is determined by flux pinning. Jc0(T) is independent of magnetic field and is proportional to (Tc - T). Similar results have also been found for other samples. It may be the common characteristic of high-Tc superconductors. Magnetic relaxation of YBa2Cu3O6+x and GdBa2Cu3O6+x films has been measured at LN2 temperature. Using the equation of Hagen et al., effective activation energy U0 has been deduced, which is about 0.3eV, one order bigger than the value obtained by A = kBT/U0. U0 is almost independent of the field in the field range selected.

Abstract: Magnetic hysteresis loops have been measured for YBa2Cu3O6+x, GdBa2Cu3O6+x and Tl2Ba2Ca2Cu3O10-y films at different temperatures with a vibrating sample magnetometer. Based on Bean model, magnetic critical current density Jcm has been derived approximately. The field and temperature dependence of Jcm for all samples can be written as: Jcm= Jc0(Tf(B,T), Where f(B,T) = 1 - Aln(B/B0(T)), which is similar to the transport critical density strongly affected by flux creep: Jct = Jc0(B,t)(1 - (kBT/U0)ln(B$\varOmega$d/Ec)). The extraordinary similarity suggests that Jcm is determined not only by flux pinning but also by flux creep. In the first formula, f(B,T) may be correlated with the effect of flux creep on Jcm, and Jc0(T) is determined by flux pinning. Jc0(T) is independent of magnetic field and is proportional to (Tc - T). Similar results have also been found for other samples. It may be the common characteristic of high-Tc superconductors. Magnetic relaxation of YBa2Cu3O6+x and GdBa2Cu3O6+x films has been measured at LN2 temperature. Using the equation of Hagen et al., effective activation energy U0 has been deduced, which is about 0.3eV, one order bigger than the value obtained by A = kBT/U0. U0 is almost independent of the field in the field range selected.

中图分类号: 

  • 74.25.Qt
74.25.Sv (Critical currents) 74.25.Ha (Magnetic properties including vortex structures and related phenomena)