High field properties of irreversibility field and pinning force for YBa/sub 2/Cu/sub 3/O/sub 7/ film

The critical current density and irreversibility field of YBa/sub 2/Cu/sub 3/O/sub 7/ 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/sub 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/sub i/ values are proportional to (1-(T/T/sub c/)/sup 2/)/sup 1.4/ at high temperature above 40 K and then rapidly increase at low temperature below 40 K. The obtained B/sub i/ values at low temperature for B/spl par/c are very large, compared with that for other high-T/sub c/ superconductors. Moreover, the B/sub i/ value estimated on the basis of the temperature scaling law of F/sub p/ exceeds at least 600 T at 5.0 K even for B/spl par/c.