Diamagnetic shielding and Meissner effect in the high T_c superconductor Sr_0.2La_1.8CuO₄

SQUID susceptibility measurements of the high Tc superconductor Sr0.2La1.8CuO4, with a 40 K resistive onset, are reported for fields from 1 μT to 4.5 T (10mG to 45 kG). Data show an average lower critical field of 30 mT at 5 K, but with nonlinearities appearing as low as 100 μT. Zero field cooling and subsequent application of a field shows a diamagnetic shielding effect reaching 100% in the lowest fields with a 37 K onset and 31 K midpoint. The observed Meissner effect in single phase material exceeds 40% but decreases with oxygen annealing even though Tc increases. © 1993.