Critical Currents, Pinning Forces and Irreversibility Fields in (YxTml-x)Ba2Cu3O7 Single Crystals with Columnar Defects in Fields up to 50 T

We have studied the influence of columnar defects, created by heavy-ion (Kr) irradiation with doses up to 6 10^11 Kr-ions/cm2, on the superconducting critical parameters of single crystalline (YxTm1-x)Ba2Cu3O7. Magnetisation measurements in pulsed fields up to 50 T in the temperature range 4.2 - 90 K revealed that: (i) in fields up to T the critical current Jc(H,T) is considerably enhanced and (ii) down to temperatures T ~ 40 K the irreversibility field Hirr(T) is strongly increased. The field range and magnitude of the Jc(H,T) and Hirr(T) enhancement increase with increasing irradiation dose. To interpret these observations, an effective matching field was defined. Moreover, introducing columnar defects also changes the pinning force fp qualitatively. Due to stronger pinning of flux lines by the amorphous defects, the superconducting critical parameters largely exceed those associated with the defect structures in the unirradiated as-grown material: Jc,irrad(77 K, 5 T) ^3 10* Jc,ref(77 K, 5 T).