Critical currents, pinning forces and irreversibility fields in (YxTm1-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 x 10(11) Kr-ions/cm(2), on the superconduc ting critical parameters of single crystalline (YxTm1-x)Ba2Cu3O7. Magnetisa tion measurements in pulsed fields up to 50 T in the temperature range 4.2- 90 K revealed that: (i) in fields up to mu(0) H approximate to 20 T the cri tical current J(c)(H,T) is considerably enhanced and (ii) down to temperatu res T similar to 40 K the irreversibility field H-irr(T) is strongly increa sed. The field range and magnitude of the J(c)(H,T) and H-irr(T) enhancemen t increase with increasing irradiation dose. To interpret these observation s, an effective matching field B phi. was defined. Moreover, introducing co lumnar defects also changes the pinning force f(p) qualitatively. Due to st ronger pinning of flux lines by the amorphous defects, the superconducting critical parameters largely exceed those associated with the defect structu res in the unirradiated as-grown material: J(c,6x10)(11) (2)(Kr-ions / cm)( 77 K, 5 T) greater than or equal to 10 J(c,ref) (77 K, 5 T). (C) 1999 Publi shed by Elsevier Science B.V. All rights reserved.