Determination of irreversibility field variations in mono- and multifilamentary (Bi,Pb)2Sr2Ca2Cu3Ox tapes by transport current methods

The irreversibility field, H*, has been measured for a variety of mono- and multifilamentary (Bi,Pb)(2)Sr2Ca2Cu3Ox (2223) tapes using two different transport current techniques. It is common to characterize the quality of 2223 tapes by their zero-field, 77 K critical current density [J(c)(0 T, 77 K)], even though this ignores the fact that significant self-fields depress Jc(0 T, 77 K) and the possibility that the in-field J(c)(B) characteristics may be optimized independently of the J(c)(0 T, 77 K) value. To provide more useful information, we propose a second characterization, that of the irreversibility field, H*. Having both H* and J(c)(0 T, 77 K) information helps in separating the two independent contributions that better connectivity and stronger flux pinning can make to the J(c) of a tape. We illustrate this point with results from a variety of mono- and multifilamentary Bi-2223/Ag tapes in damaged and undamaged conditions, which show that H* (77 K) can vary from similar to 100 to similar to 200 mT and not directly correlate with J(c)(0 K). The two proposed protocols for H* measurement are robust and compatible with common transport measurement procedures. (C) 1997 American Institute of Physics.