STUDY OF THE VORTEX STATE OF BI-2223 BY MAGNETIC ANALYSIS

From detailed magnetization studies in fields up to 2 T in the temperature range between 4 and 90 K an empirical magnetic phase diagram for Bi-2223 HTSC has been derived. The 'depinning line' B*(T) has been estimated where the critical current density J(c) becomes zero in fields well below H(c2). In the 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(c1) in the low temperature range might originate from surface effects, as can be qualitatively explained. The temperature dependence of the critical current density J(c) gives evidence for the existence of two kinds 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 of J(c) below 30 K.