超電導材料特性計測技術―マッピング技術の進展を中心として―永久磁石を用いた非接触型臨界電流密度測定システム

Abstract

We developed a novel non-destructive and non-contact method for the measurement of critical current density (Jc) 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 (Fr) 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 (Fm) could be estimated from an experimental result of the Fr vs. L curve. We investigated the relationship of Jc to Fm in several HTS samples. The standard Jc of the HTS films was determined using the inductive measurement system made from THEVA GmbH. We found that the Jc is approximately proportional to the Fm normalized by the film thickness. This result indicates that the permanent magnet technique can easily estimate the Jc of HTS films. We also found that the system can measure Jc with sufficient reproducibility and in a short time. Moreover, it was checked to confirm that Jc mapping of a YBCO thin film could be also measured.