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Abstract:
For the high-T c superconductor La1.85Sr0.15CuO4, we present results for the low-field magnetization and the lower and upper critical fieldsB c1 (T) andB c2(T). ForB c1 (0) we find a value of about 20 mT. Extrapolating our resistive data for the transition midpoint taken in fields up to 12 T, we deduce a value of about 50 T forB c2 (0). TheB c2 values obtained by inductive measurements are significantly lower. We explain this by a largeB c2 anisotropy due to the layered structure of these compounds. Losses in the Meissner state observed in magnetization and susceptibility measurements disappear after powdering the sample. This is taken as strong evidence for intergrain Josephson coupling in the bulk sample.
