Critical currents, pinning forces and irreversibility fields in (Y xTm 1− x)Ba 2Cu 3O 7 single crystals with columnar defects in fields up to 50 T

Abstract

We have studied the influence of columnar defects, created by heavy-ion (Kr) irradiation with doses up to 6×10 11 Kr-ions/cm 2, on the superconducting critical parameters of single crystalline (Y x Tm 1− x )Ba 2Cu 3O 7. Magnetisation measurements in pulsed fields up to 50 T in the temperature range 4.2–90 K revealed that: (i) in fields up to μ 0 H≈20 T the critical current J c( H, T) is considerably enhanced and (ii) down to temperatures T∼40 K the irreversibility field H irr( T) is strongly increased. The field range and magnitude of the J c( H, T) and H irr( T) enhancement increase with increasing irradiation dose. To interpret these observations, an effective matching field B φ· was defined. Moreover, introducing columnar defects also changes the pinning force f p 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: J c,6×10 11 Kr-ions/cm 2 (77 K, 5 T)≥10 J c,ref (77 K, 5 T).