Measurement and understanding of magnetisation in AC and DC fields and the determination of intragrain H_c1 in high T_c RBa₂Cu₃O₇ superconductors

Abstract

We present DC and low frequency AC magnetization measurements on various RBa₂Cu₃O₇ superconductors. We identify features intrinsic to these compounds, and establish the features originating from intergranular links in sintered pellets. The isothermal magnetization curves, and the temperature dependence of magnetization in field-cooled and zero field-cooled states are shown to be consistent with the calculations done following a recent extension of Bean's model. Low field anomalies predicted within this model are observed, and yield H_c1 values of a few Oe. These values are shown to be consistent with the temperature variation of magnetization. A comparison is made with the other existing data and it is demonstrated that earlier quoted values of H_c1 are gross overestimates.