Critical current density measurement of thin films by AC susceptibility based on the penetration parameter h

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• 作者：Xiao-Fen Li ; ^{xiaofenli@gmail.com} ; Jean-Claude Grivel ; Asger B. Abrahamsen ; Niels H. Andersen
• 关键词：Critical current density ; AC susceptibility ; Superconducting thin film ; London penetration depth
• 刊名：Physica C
• 出版年：2012
• 期刊代码：80_09214534
• 类别：ms
• 出版时间：July, 2012
• 卷：477
• 期：Complete
• 页码：6-14
• 文件大小：627 K

摘要

We have numerically proved that the dependence of AC susceptibility 蠂 of a E(J) power law superconducting thin disc on many parameters can be reduced to one penetration parameter h, with E the electric field and J the current density. Based on this result, we propose a way of measuring the critical current density J_c of superconducting thin films by AC susceptibility. Compared with the normally used method based on the peak of the imaginary part, our method uses a much larger range of the AC susceptibility curve, thus allowing determination of the temperature (T) dependence of J_c from a normally applied 蠂(T) measurement. A fitting equation J_c = 1.9H_a鈭?em>蠂鈥测垼^0.69/d, 鈭?.4 < 蠂鈥?#xA0;< 鈭?.001 derived from the critical state case (Bean model) can be used in most situations, where H_a is the amplitude of the applied AC field, 蠂鈥?is the real part of the normalized susceptibility and d is the thickness of the film. The method is valid for the cases where the film is fully penetrated. We also discuss how the finite London penetration depth affects the susceptibility when the film is screened. Measurements with varying T, H_a and DC background field H_dc are performed to support the arguments.