A Non-contact Measuring System for Critical Current Density Using a Permanent Magnet

Abstract

We developed a novel non-destructive and non-contact method for the measurement of critical current density (J_c) using a permanent magnet. A high-temperature superconductor (HTS) thin-film was fixed on the stage of the system and a small cylindrical permanent magnet (Sm₂Co₁₇) was set above the HTS film. The repulsive force (F_r) and attractive force between the small magnet and HTS film were measured by a high-resolution load sensor changing the distance (L) between the HTS film and the magnet. The maximum repulsive force (F_m) could be estimated from an experimental result of the F_r vs. L curve. We investigated the relationship of J_c to F_m in several HTS samples. The standard J_c of the HTS films was determined using the inductive measurement system made from THEVA GmbH. We found that the J_c is approximately proportional to the F_m normalized by the film thickness. This result indicates that the permanent magnet technique can easily estimate the J_c of HTS films. We also found that the system can measure J_c with sufficient reproducibility and in a short time. Moreover, it was checked to confirm that J_c mapping of a YBCO thin film could be also measured.