Abstract Body

REBa₂Cu₃O_y (REBCO, RE = Rare earth) high-temperature superconducting tapes have high critical temperature and high critical current density (J_c) characteristics in magnetic fields and are expected to be applied to superconducting devices such as high-field magnets and superconducting motors. Since local defects limit the J_c property in REBCO tapes, in which the superconducting layer is formed as a thin film with a few micrometers thickness, it is important to clarify the cause of the J_c limitation in the superconducting thin films. Therefore, we have been studying magneto-optical imaging (MOI), which has high spatial resolution among magnetic field distribution measurements. In this study, to evaluate the temperature and magnetic field dependence of the in-plane J_c distribution in the REBCO thin film with metal stripes, we obtained and analyzed magneto-optical images acquired under various conditions using MOI. We observed the trapped magnetic field distribution for a 5 mm × 5 mm superconducting thin films with metal stripes that divide the film into five sections in the plane. The number of pixels for MOI observation was 2048 × 2048 pixel and the signal depth was 16 bits. MOI observations were performed at each external magnetic field by cooled the sample to a predetermined temperature. The external magnetic field was varied from 0 T to 0.42 T in 0.02 T intervals and then demagnetized to 0 T. First, we considered the calibration for the conversion from signal intensity to magnetic field. As a result, the obtained magnetic field distribution was confirmed to be in good agreement with the theoretical one. Then we calculated the J_c distribution from the magnetic field distribution obtained by the experiment. The J_c was confirmed to be in general agreement with the values calculated from the theoretical formula of Brandt et al [1][2]. Those results indicated that the five filaments were electrically separated and the in-plane J_c was highly uniform without local defects. The temperature and magnetic field dependence of the J_c will be discussed.

References

[1] E. H. Brandt, et al., Europhys. Lett. 22 (1993) 735
[2] Y. Mawatari, J. Cryo. Soc. Jpn 44 (2009) 2

Acknowledgment

This work was supported in part by the Joint Research Hub Program of NIMS and by JSPS Grants-in-Aid for Scientific Research JP22H02019 and JP22H02021.

Keywords: Magneto-Optical Imaging, REBa₂Cu₃O_y, Critical current density distribution