Critical current density properties of thick YBa2Cu3Oy films with different thicknesses

Abstract

Even in REBa₂Cu₃O_y (REBCO) films, which exhibit high critical current density (J_c) under low-temperature and high-magnetic-field conditions, their performance deteriorates significantly at high-temperatures because of pronounced flux creep induced by thermal agitation. This degradation is particularly pronounced in thin superconducting films, as the thickness constrains the pinning correlation length. In this study, we examined the effect of YBCO film thickness on J_c within the range of 0.94 to 3.7 μm. While some variations were observed depending on crystal orientation, thicker superconducting layers demonstrated a smaller reduction in J_c with increasing magnetic field in high-temperature regions, resulting in superior J_c values under high-temperature and high-magnetic-field conditions. Moreover, the apparent pinning potential $U_0^{*}$, determined from magnetization relaxation measurements, was larger for thicker films in these conditions, indicating that $U_0^{*}$ is influenced by the thickness of the superconducting layer. These findings are further supported by the flux creep flow model analysis. Collectively, these results suggest that not only introducing strong pinning forces but also increasing the thickness of the superconducting layer is an effective strategy for enhancing performance near liquid nitrogen temperatures.