Calorimetric study of copper ordering in the T' (214) system

Abstract

Calorimetric and magnetic measurements have been carried out on the insulating compound (Gd 1.85Ce 0.15)CuO 4−δ. As the only nonsuperconducting member of the T' (214) (R 1.85Ce 0.15)CuO 4−δ system (R=Pr, Nd, Sm, Eu, Gd), its Cu spins undergo a canted antiferromagnetic ordering at T N of 162 K. Spin reorientation occurs at T sr near 14 K to become truly antiferromagnetic. While the transitions were clearly identified by magnetic measurements, no specific heat anomaly was observed at either T N or T sr. A negligibly small latent heat must then occur at T sr. The observation at T N is, however, in contrast with the early results on antiferromagnetic ordering of Gd 3+ in the same compound at 5.3 K, where a specific heat peak and consequently a magnetic entropy of 1.85 Rln 8 prevail as expected. A strong two-dimensional quantum spin fluctuation is thus cited as the cause of the unusual behavior at T N. Dynamic short-range intraplanar antiferromagnetic ordering persists to much higher than this three-dimensional ordering temperature.