FLUX TRAPPING IN TRANSPORT MEASUREMENTS OF YBA2CU3O7-X SUPERCONDUCTORS - A FINGERPRINT OF INTRAGRAIN PROPERTIES

A study of flux trapping in polycrystalline YBa2Cu3O7-x was made through measurements of transport J(c) versus H characteristics. It was shown that most of the trapped flux which provokes hysteresis in such experiments comes from the superconducting grains, and not from persistent loops in the weak link network. The lower critical field of the grains and the intragrain critical current were calculated for oxygenated and partially deoxygenated samples, showing good coincidence with the commonly accepted values. Further evidence of the intragranular character of the flux trapping resulted from the study of the time variation of the voltage associated with flux creep, from which good estimates of the effective pinning energy of the grains were obtained.