The position Bmax of the maximum of magnetic hysteresis loops (MHL) close to zero external magnetic field Bext, in as prepared (Bi,Pb)-2223/Ag tapes, shifts with decreasing temperature anomalously towards positive Bext on the descending-field branch of MHL. The field Bmax increases steeply below 15 K reaching +0.15 T at 2.5 K. Bmax(T) is quite similar for rolled and pressed tapes and for tapes with and without a silver sheath. MHL are asymmetric at low temperatures with larger moments on the upper MHL branch. This asymmetry appears below a threshold temperature T* ≈ 0.6 Tirr, where Tirr is an ″irreversible″ temperature. The rate of flux creep changes very significantly at the MHL maximum. We propose that Bmax > 0 can also be observed on a virtual granular superconducting material formed by planes of flat disk-shaped grains with just small contacts at the disk circumferences. Bmax is positive due to a change of sign of stray fields close to the grain circumferences.
|ジャーナル||Superlattices and Microstructures|
|出版ステータス||Published - 1997 1月 1|
ASJC Scopus subject areas