Anomalous magnetic hysteresis loops and small H_c1 values in high T_c superconductors

Abstract

We have studied the hysteresis loops of RBa₂Cu₃O₇ (R=Gd, Ho and Y) and detected anomalies in some of them. The observed anomalies support a recent prediction by Ravi Kumar and Chaddah based on an extension of Bean's model. The anomalies indicate low H_c1 values and we have confirmed this by studying the onset of low-field hysteresis in less than 10 Oe at 77 K for these high T_c, superconductors.