PARAMAGNETIC MEISSNER EFFECT IN HIGH-TEMPERATURE SUPERCONDUCTORS

We have studied the low-field Meissner effect of polycrystalline Bi hi gh-temperature superconductors using a special superconducting-quantum -interference-device magnetometer. In certain samples a surprising fea ture was observed: Instead of the usual diamagnetic moment a paramagne tic moment develops in the field cooling mode below T(c) for fields H < 1 Oe. The data are consistent with orbital paramagnetic moments due to spontaneous currents. Such currents may originate in so-called pi c ontacts in the weak-link network of polycrystalline material. In some of these samples also an anomaly in the low-field microwave absorption was observed, which is obviously correlated with the existence of spo ntaneous currents.