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 and the geometry can be defined. Moreover, remarkable time-decay of magnetization (M) occurs in high temperature supeconductor (HTS) because of its rounded electric fieldcurrent density (E-J) characteristics, where negligible decay in low temperature supeconductor (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. E can be derived from the time dependent M analytically based on Faradays law in a homogeneous sample. However, we claim that the quantitative agreement of this derivation is not yet fully confirmed, as well as the applicability in case of Bi-2223 multi-filamentary tape for unclear magnetization current path. In contrast, spatially resolved measurement on time dependent magnetic field profile is advantageous in solving E and J distributions directly based on basic Faradays law and inverted Biot-Savart law, respectively. From relaxation of magnetic field profile on the sample surface based on SHPM, we derived time-dependent E and J, whose relaxation properties are well described by the Anderson-Kim flux creep model due to thermal fluctuation. Additionally, the model also indicates E can vary depending on several parameters, such as the sample geometry. We measure 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 magnetization relaxation. This scaling behaviour helps to estimate the value of E during magnetization measurements easily.