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
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
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(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(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.
Received: 15 March 1993
Accepted manuscript online:
Fund: Project supported by the National Center for Research and Development on Superconductivity of China, and the Foundation for Doctoral Eduction.
Cite this article:
SHI ZHI-XIANG (施智祥), JI HE-LIN (吉和林), ZHANG YI-TONG (张贻瞳), JIN XIN (金新), XU XIAO-NONG (徐小农), DING SHI-YING (丁世英), YAO XI-XIAN (姚希贤), WANG CHANG-AN (王长安), WANG RUI-LAN (王瑞兰), LI HONG-CHENG (李宏成), ZHANG HUI (张晖), SUN ZHI-JIAN (孙志坚), YANG SEN-ZU (杨森祖) FLUX CREEP, FLUX PINNING AND CRITICAL CURRENT DENSITY OF Y-, Gd-, AND Tl-BASED SUPERCONDUCTIVE THIN FILMS 1994 Acta Physica Sinica (Overseas Edition) 3 124
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