High field properties of irreversibility field and pinning force for YBa2Cu3O7 film

The critical current density and irreversibility field of YBa₂Cu₃O₇ films were resistively measured in fields up to 23 T at 5-84 K when the magnetic field B was applied parallel to the c-axis. The irreversibility field B_i at low temperature, which cannot be measured directly, was estimated using the temperature scaling law of the pinning force density. We found that the B_i values are proportional to (1-(T/T_c) ²)^1.4 at high temperature above 40 K and then rapidly increase at low temperature below 40 K. The obtained B_i values at low temperature for B||c are very large, compared with that for other high-T_c superconductors. Moreover, the B _i value estimated on the basis of the temperature scaling law of F_p exceeds at least 600 T at 5.0 K even for B||c