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

doi:10.1088/1004-423X/3/2/006

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

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)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

^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/Abstract

摘要： Magnetic hysteresis loops have been measured for YBa₂Cu₃O_6+x, GdBa₂Cu₃O_6+x and Tl₂Ba₂Ca₂Cu₃O_10-y films at different temperatures with a vibrating sample magnetometer. Based on Bean model, magnetic critical current density J_cm has been derived approximately. The field and temperature dependence of J_cm for all samples can be written as: J_cm= J_c0(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: J_ct = J_c0(B,t)(1 - (k_BT/U₀)ln(BΩd/E_c)). The extraordinary similarity suggests that J_cm 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 J_cm, and J_c0(T) is determined by flux pinning. J_c0(T) is independent of magnetic field and is proportional to (T_c - T). Similar results have also been found for other samples. It may be the common characteristic of high-T_c superconductors. Magnetic relaxation of YBa₂Cu₃O_6+x and GdBa₂Cu₃O_6+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 = k_BT/U₀. U₀ is almost independent of the field in the field range selected.

Abstract: Magnetic hysteresis loops have been measured for YBa₂Cu₃O_6+x, GdBa₂Cu₃O_6+x and Tl₂Ba₂Ca₂Cu₃O_10-y films at different temperatures with a vibrating sample magnetometer. Based on Bean model, magnetic critical current density J_cm has been derived approximately. The field and temperature dependence of J_cm for all samples can be written as: J_cm= J_c0(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: J_ct = J_c0(B,t)(1 - (k_BT/U₀)ln(B$\varOmega$d/E_c)). The extraordinary similarity suggests that J_cm 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 J_cm, and J_c0(T) is determined by flux pinning. J_c0(T) is independent of magnetic field and is proportional to (T_c - T). Similar results have also been found for other samples. It may be the common characteristic of high-T_c superconductors. Magnetic relaxation of YBa₂Cu₃O_6+x and GdBa₂Cu₃O_6+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 = k_BT/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)

施智祥, 吉和林, 张贻瞳, 金新, 徐小农, 丁世英, 姚希贤, 王长安, 王瑞兰, 李宏成, 张晖, 孙志坚, 杨森祖. FLUX CREEP, FLUX PINNING AND CRITICAL CURRENT DENSITY OF Y-, Gd-, AND Tl-BASED SUPERCONDUCTIVE THIN FILMS[J]. 中国物理B, 1994, 3(2): 124-130.

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[J]. Acta Physica Sinica (Overseas Edition), 1994, 3(2): 124-130.

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

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

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