Defect independence of the irreversibility line in proton-irradiated Y-Ba-Cu-O crystals

Flux pinning in Y-Ba-Cu-O crystals is studied as a function of fluence of 3-MeV protons, which create random local defects. Order-of-magnitude increases in the critical current density are deduced from magnetic hysteresis loops, with values up to 2×{}10⁵ A/cm² observed at 77 K and 1 T. However, the irreversibility line in the field-temperature plane and the pinning potentials deduced from flux-creep studies are hardly changed. These results are compared to melting and pinning models.