Nondestructive, inductive measurement of critical current densities of superconducting films in magnetic fields

An inductive method to detect a third harmonic voltage V₃ is widely used to measure critical current densities J_c of large-area superconducting films. Very recently Mawatari et al. have elucidated the generation mechanism of V₃ and derived the relationship between the coil ac current and V₃. We have supported this theory by experiment, and then used this method to measure J_c of YBCO films in dc magnetic fields at various temperatures (0-5 T, 66-77.3 K). The temperature and the field dependence of J_c was in good agreement with those measured by dc magnetization and transport measurement. It is demonstrated that this method can also be applicable to measure J_c in applied dc magnetic fields.