SAMPLE-SIZE EFFECT ON THE DETERMINATION OF THE IRREVERSIBILITY LINE OF HIGH-T-C SUPERCONDUCTORS

The irreversibility lines of a high-J(c) superconducting Bi2Sr2Ca2Cu3O x/Ag tape were systematically measured upon a sequence of subdivisions of the sample. The irreversibility field H-r(T) (parallel to the c ax is) was found to change approximately as L(0.13), where L is the effec tive dimension of the superconducting tape. Furthermore, it was found that the irreversibility line for a grain-aligned Bi2Sr2Ca2Cu3Ox speci men can be approximately reproduced by the extrapolation of this relat ion down to a grain size of a few tens of micrometers. The observed si ze effect could significantly obscure the real physical meaning of the irreversibility lines. In addition, this finding surprisingly indicat ed that the Bi2Sr2Ca2Cu2Ox/Ag tape and grain-aligned specimen may have similar flux line pinning strength.