The magnetization studies of cast-annealing Bi 1.5Pb 0.28Sr 1.72Ca 2.0Cu 3.5O y ceramic sample

Abstract

The sample with nominal composition Bi1.5Pb0.28Sr1.72-Ca2.0Cu3.5Oy was prepared by cast-annealing method and identified to contain almost pure 110K phase from X-ray powder diffraction pattern. The A.C. magnetic susceptibility and the Meissner diamagnetic magnetization in various magnetic fields were measured as the functions of temperature down to 77K. With the increase of the field the magnitude of D.C. magnetic susceptibility Xdc is found to be reduced and Xdc transition is significantly broadened. The magnetization curve demonstrates that the present ceramic sample is a weak-pinning type-II superconductor as a whole. The slope of (-4 M) versus magnetic field shows that the value of the diamagnetic volume fractions of the whole sample and the superconducting grains is 34.5% and 18.5%, respectively, which means existence of great shielding effect from weak-link networks. Flux creep was detected at nitrogen temperature and studied directly by the magnetization measurement as a function of time in various constant magnetic fields. The result indicates that in weaker fields the magnetization changes logarithmically in time. The logarithmic creep rate is found to rise gradually as applied field is increased until the magnetic field exceeds the magnetization peak field. In higher field, however, the logarithmic dependence of flux creep on time can no longer be found.