Long-range magnetic ordering in the high-Tc superconductors RBa2Cu3O7−δ (R=Nd, Sm, Gd, Dy, and Er)

Abstract

Low-teperature specific-heat C measurements have been made on the high-Tc superconductors RBa2Cu3O7−δ (R=Nd, Sm, Gd, Dy, and Er; δ≊0.1) for 0.5≲T≤30 K. Features in the specific heat associated with magnetic ordering of the trivalent R ions were observed for all of these compounds. The values of the magnetic ordering temperature TM, defined as the temperature of the peak of the specific-heat anomaly due to magnetic ordering, are 0.52, 0.61, 2.25, 0.90, and 0.60 K for the compounds with R=Nd, Sm, Gd, Dy, and Er, respectively. Calculations of the magnetic entropy from the C vs T data suggest that the R ions in these compounds have doublet ground states, except for R=Gd, which has an eightfold degenerate ground state. The values of TM for the compounds with R=Nd, Sm, Dy, and Er are in reasonable agreement with the deGennes factor scaling of TM for the compound with R=Gd. The deGennes factor scaling of TM is consistent with expectations based on the Ruderman-Kittel-Kasuya-Yosida interaction, although the agreement may be fortuitous since recent specific-heat measurements by Dunlap et al. on metallic and semiconducting (oxygen-defiicient) GdBa2Cu3O7−δ suggest that dipole-dipole interactions are responsible for the magnetic order in these materials.

Source-reported materials — not catalogue approval

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