Numerical calculation of critical current density and third harmonic voltage in superconducting films

When an AC magnetic field of a suitable magnitude is applied locally to a wide surface of a superconducting film, a third harmonic voltage is induced in a pick-up cod. This measurement is used for an evaluation of the critical current density of the film. Mawatari et al. analyzed the relationship between the third harmonic voltage amplitude (V-3) and the driving current amplitude for the field (I-0) by using the critical state model and a simple assumption that the magnetic field is locally parallel to a flat surface. In this study, this relationship is numerically analyzed by finite element method (FEM) for a condition similar to the experiment by Mawatari et al. This result is compared with the above theoretical and experimental results. Some deviations from theory are found. However, the scaling of V-3-I-0 curves holds and I-0 at which V-3 starts to appear is proportional to the critical current density. (C) 2003 Elsevier B.V. All rights reserved.