Heat Capacity Measurements on Some High-T_c Superconductors

Abstract

The heat capacity has been obtained for superconducting samples of La_1.85Sr_.15CuO₄ ¹ and REBa₂Cu₃0_7-x ^2,3 (RE = Gd,Dy,Ho,Er). The ∆C/yT values of 2 to 5 for the La_1.85Sr_0.15CuO₄ compound places this material well into the strong coupling limit From the data for REBa₂Cu₃O_7-x, the degeneracies of the crystal field ground state are determined and the magnetic moment in the ground state and the energy separation to the first excited crystal field state are estimated. The magnetic transitions are observed at T_m = 2.2, 0.95, 0.17, and 0.59 K for the Gd, Dy, Ho, and Er compounds, respectively. The antiferromagnetic ordering of the Gd ions is independent of the presence or the absence of superconductivity and is unchanged in both insulating and metallic systems.