ANTI-MEISSNER EFFECT AND LOW-FIELD MAGNETIC-RELAXATION IN SINTERED BI-2212

A detailed study of the low field magnetic properties of some sintered Bi-2212 samples has been performed. For sufficiently low applied magn etic fields, typically for fields H < 0.2 Oe, the field-cooled magneti sation becomes positive at some temperature below T(C) (anti-Meissner effect), contrary to the usual Meissner effect. The field dependence o f this effect is comparable to the predicted behaviour for a system in an orbital glass state. Additionally, the relaxation of the zero-fiel d-cooled magnetisation displays an unexpected field dependence, the re laxation rate S = partial-derivative M/partial-derivative log(t) incre ases as H(alpha) with alpha almost-equal-to 0.9 at very low fields. In contrast to the behaviour found in sintered YBCO, this result is not accounted for in conventional flux creep models, where the prediction is alpha greater-than-or-equal-to 2.