Scaling Behavior of Induced Electric Field in Cuprate Superconducting Tapes during Magnetization Relaxation

We have investigated a scaling behavior of induced electric field during magnetization relaxation in cuprate superconducting tapes based on scanning Hall probe microscopy (SHPM). Magnetization measurement is a standard method to evaluate critical current density (Jc) properties in a superconducting sample, if the sample is uniform. Moreover, remarkable time-decay of magnetization (M) occurs in high temperature superconductor (HTS) because of its rounded electric field-current density (E-J) characteristics, where negligible decay in low temperature superconductor (LTS). Namely, Jc cannot be determined only from the value of M in case of HTS but also time dependence should be clarified with regard to electric field criterion in the measurements. Generally, E can be derived from the time dependent M analytically in a homogeneous sample, by introducing a geometric coefficient G. However, the quantitative agreement of this derivation is not yet fully confirmed. Besides, in case of multi-filamentary Bi-2223 tapes, it is still unclear if this derivation is correct without clarifying the magnetization current path inside the tapes. In this study, we carried out spatially resolved measurement on time dependent magnetic field profile and solve E and J distributions directly based on basic Faraday's law and inverted Biot-Savart law, respectively. The relaxation properties are well described by the Anderson-Kim flux creep model due to thermal fluctuation. We also validate the correction factor G for E estimation based on macroscopic magnetization. Additionally, we measured magnetization relaxation in RE-123 and Bi-2223 tapes at different operation temperature, applied field and sample geometry. We study a universal relationship among J, sample geometry, n-index, and induced E during the magnetization relaxation. This scaling behaviour provides an easy method to estimate E for magnetization measurements.