Disclosure of hidden magnetic moments in low and high T sub(c) hysteretic and semi-reversible type II superconductors during warming to T sub(c)

We report on measurements of the evolution of the magnetization < M > upon warming from T sub(0) (4.2 or 77 K) to T sub(c) for type II superconductors with the locus of < M > initially situated along bridges between the envelopes of the major hysteresis curves. Strongly hysteretic and semi-reversible specimens of low and high T sub(c) type II superconductors have been studied (Nb sub(3)Zr, VTi, YBCO, Nb and BiSCCO). Concentric, oppositely directed magnetic moments coexist in the specimens when < M > lies along the bridges. We focused on the cases where < M > identical with 0, hence, before warming, the constituent moments cancel each other exactly. Since they diminish in magnitude at different rates as T is increased to T sub(c), their sequential `release' leads to a rich variety of phenomena. A simple model exploiting the critical state, an equilibrium Meissner current and conservation of flux accounts for all the intricate behaviour encountered.