SPECIFIC HEAT OF RBa_2Cu_3O_(7-x) AND RBaSrCu_3O_(7-x) COMPOUNDS (R = Sm, Dy, Er)

摘要

The low-temperature specific-heat C(T) data of high-T_c superconductors RBa_2Cu_3O_(7-x)(R123O_(7-x)) were reviewed. A discussion of the C(T) data obtained on single-crystalline samples of Er123O_(7-x) and Sm123O_(7-x) compounds in applied magnetic fields for better evaluation of the crystal--electric-field parameters is given. The C(T) measurements of Sr-substituted compounds RBaSrCu_3 O_7 revealed the λ-type of peak related to the antifer-romagnetic order at 1.2 K and 0.6 K respectively for Dy- and Er-compounds. The magnetic singlet ground state in these compounds is produced by weak exchange interactions of-0.05 T/μ_B and -0.035 T/μ_B, respectively. For Nd-and Sm-compounds, only a broad anomaly around 0.6 K was observed which is well fitted with a Schottky-type anomaly with an energy splitting of 1.4 K.