MAGNETIC-RELAXATION AND PINNING IN AG BI(PB)SCCO TAPES - DEFORMATION-INDUCED EFFECTS/

Magnetic hysteresis and magnetic relaxation in as-sintered and cold-pr essed after sintering Ag/Bi-2223 tapes have been studied in the temper ature range of 5-45 K for two field orientations: H parallel to c-axis and H parallel to ab-plane. Significantly higher effective pinning en ergy, U-eff, for H parallel to ab as compared to that for H parallel t o c, is connected with the mechanism of intrinsic pinning for the vort ex motion normal to the CuO2 atomic planes. Cold pressing results in t he reduction of magnetization and transport inter-granular currents du e to the introduction of additional weak links and microcracks into a sample. For the H parallel to c case the drastic drop in relaxation ra te as well as the increase in the field of the first large scale vorte x penetration, H-vp, was observed after cold pressing, indicating the enhancement of intra-granular and surface pinning by generated defects . Accordingly,the increase of U-eff in the limit of low currents was o bserved after cold pressing. Warm pressing which normally generates si gnificantly lower concentration of residual defects than cold pressing , does not result in any inhibition of relaxation. For in-plane field H parallel to ab vortices penetration into a tape interior through mic rocracks is the dominating deformation-induced effect resulting in the acceleration of magnetic relaxation and the significant decrease of U -eff.