Heat Capacities of Ba₂RCu₃O_x (R=Gd, Ho, Er, Dy)

Abstract

Heat capacities of high-T_c superconductors Ba₂RCu₃O_x (R=Gd, No, Er, Dy) are measured at temperatures below the respective superconducting transition temperatures. The observed sharp peaks at 2.25 K(Gd), 0.95 K(Dy), 0.55 K(Er) and 0.1 K(Ho) are associated with the magnetic ordering of the rare-earth ions in two dimensions. A co-existence of superconductivity and magnetic ordering is also confirmed down to the measured temperature of 30 mK.