Study of the vortex state of Bi-2223 by magnetic analysis

Abstract

From detailed magnetization studies in fields up to 2 T in t h e temperature range between 4 and 90 K an empirical magnetic phase diagram for 81-2223 HTSC has been derived. The 'depinning Iine'E*(T) h a s been estimated where the critical current density J, becomes zero in fields well below Hc2. In t h e region with non-zero critical current densities we mainly found evidence for collective pinning behaviour. Only at fields smaller than about 1.5 T and at lower temperatures might single vortex pinning occur. The enhancement of the first critical field ,H,, in the low temperature range might originate from surface effects, as can be qualitatively explained. The temperature dependence of the critical current density J, gives evidence for t h e existence of two hinds of pinning centre. A large number of pinning centres with low activation energy, therefore being active mainly at lower temperatures, might be responsible for the enhancement ofJ, below 30 K.