Influence of columnar deffects on critical currents, pinning forces and irreversibility fields in (Tm_(1-X)Y_x) Ba_2Cu_3O_7 single crystals up to 50 T

摘要

The influence of columnal defects, created by hevy-ion (Kr) irradiation, on the superconducting critical parameters of single crystalline (Tm_(1-x) Y_x )Ba_2Cu_3O_7 has been studyied. Magnetisation measurements in pulsed fields up to 50 in the temperature range 4.2-90 K showed that: (i) up to fields #mu#_0 H approx approx 20 T the critical current J_c(H,T) is considerably enhanced and (ii) down to temperatures T approx 40 K the irreversibility field H_(irr) (T) is stronly increased. The field range and magnitude of the J_c(H,T) and H_(irr)(T) enhancement increase with increasing irradiatin dose. To interpret these observations, and effective matching field B_#PHI# was defined. Moreover, introducing columnar defects also changes the pinning force f_p qualitatively. Due to stronger pinning of flux lines by the linear defects, the superconducting critical parameters largely exceed those associated with the defect structures in the unirradiated as-grown material.