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

摘要

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 superconductingcritical parameters of single crystalline (YxTm1-x)Ba2Cu3O7. Magnetisationmeasurements in pulsed fields up to 50 T in the temperature range 4.2 - 90 Krevealed that: (i) in fields up to T the critical current Jc(H,T) isconsiderably enhanced and (ii) down to temperatures T ~ 40 K theirreversibility field Hirr(T) is strongly increased. The field range andmagnitude of the Jc(H,T) and Hirr(T) enhancement increase with increasingirradiation dose. To interpret these observations, an effective matching fieldwas defined. Moreover, introducing columnar defects also changes the pinningforce fp qualitatively. Due to stronger pinning of flux lines by the amorphousdefects, the superconducting critical parameters largely exceed thoseassociated with the defect structures in the unirradiated as-grown material:Jc,irrad(77 K, 5 T) ^3 10* Jc,ref(77 K, 5 T).