ORIGIN OF VORTEX MELTING LINE IN BI2223 AG TAPES/

Using AC diamagnetic and transport measurements we have derived a thre e-dimensional H-J(c)-T diagram for high-quality Bi2223/Ag tapes. The d iagram shows an abrupt decrease of critical current caused by the melt ing of a vortex glass. The melting line was defined as the contour lin e for the J(c)(H, T) surface at J(c)approximate to Y 10 A cm(-2), wher e J(c) showed the steepest decrease with H and T. This line coincided with the locus of the chi''(T) maximum, at a frequency approximate to 110 Hz and an AG field amplitude approximate to 0.1 Oe. The melting li ne reflects the process of the separation of unit-cell stacks. The mos t important are the low-number stacks that contain one to three unit c ells. These stacks have the lowest Kosterlitz-Thouless transition temp eratures and the lowest corresponding vortex melting temperatures. A m agnetic field causes the separation of the stacks and reduces T-m in e ach stack to the melting temperature of the lower stack. At the univer sal T-KT, the vortex melting line is the combination of T-m(H) for dif ferent, mainly bw-number, stacks.