Specific Heat of RBa₂Cu₃O_7-xand RBaSrCu₃O_7-xCompounds (R = Sm, Dy, Er)

Abstract

The low-temperature specific-heat C(Τ) data of high-Τc superconductors RBa2 Cu3 O 7-x (R123O 7-x ) were reviewed. A discussion of the C(Τ) data obtained on single-crystalline samples of Er123O 7-x and Sm123O7-x compounds in applied magnetic fields for better evaluation of the crystal--electric-field parameters is given. The C(Τ) measurements of Sr-substituted compounds RBaSrCu3 O7 revealed the λ-type of peak related to the antiferromagnetic 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/μB and -0.035 T/μΒ, respectively. For Ndand 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.