Thermal properties of layered cobaltites RBaCo2O5.5 (R = Y, Gd, and Tb)

Specific heat studies of a series of RBaCo2O5.5 (R = Y, Gd, and Tb) layered cobaltites are reported. They were aimed at explaining an influence of different rare-earth ions on thermal properties of these compounds and at studying phase transitions appearing in them. The studies were performed over the temperature range from 3 to 395 K, in the magnetic field ranging from 0 to 9 T. Anomalies accompanying different phase transitions were analyzed. Based on the performed supplementary Raman scattering measurements, frequencies of main optical phonon modes were determined and used for evaluation of the lattice contribution to the specific heat. Lattice, magnon, and Schottky contributions to the specific heat were separated and described theoretically. As a result, the molecular field corresponding to the R-Co exchange interactions was estimated to be similar to 1 T.