COMPARISON OF SUPERCONDUCTING FLUX-PINNING DUE TO ION IRRADIATION ANDEFFECTS EFFECTS

Heavy-ion irradiation experiments have been carried out for single cry stals of YBa2Cu4O8 in order to compare the magnetic-field dependence o f the flux pinning for damage channels with the intrinsic ''fishtail'' pinning that occurs in this material before irradiation The two pinni ng effects seem to be additive in that irradiation increases the hyste resis at all fields and the fishtail hump persists in the irradiated s amples with roughly the same magnitude as before the damage channels a re produced. For irradiated samples, there are two regions where pinni ng rises with increasing field, one near zero field due to a matching effect of the defect density with the vortex lattice spacing and a sec ond at the same field as the original fishtail. Both effects appear in the same sample in different magnetic-field ranges.