CHINESE JOURNAL OF PHYSICS VOL. 39, NO. 6 DECEMBER 2001

Specific Heat Anomaly for a Layer Antiferromagnet

Y. M. Nie¹, P. Y. Hsiao¹, Y. F. Chiang¹ and T. K. Lee<sup>1,2

1</sup>Institute of Physics, Academia Sinica, Taipei, Taiwan 115, R.O.C.

²National Center for Theoretical Sciences, P.O. Box 2-131, Hsinchu, Taiwan 300, R.O.C.
(Received July 19, 2001)

The pronounced specific heat anomaly observed in cuprate oxide superconductors with Gd layers below the Néel temperature T_N is studied by using the modified spin-wave theory for an anisotropic layer antiferromagnetic system. The present work elucidates that the anomaly feature is mainly due to the large spin effect of the Gd³⁺-ion. Our result agrees well with the experiments. In addition, the observed disappearance of the specific heat anomaly in the presence of a magnetic field is also obtained. The specific heat above T_N is calculated by using a high temperature expansion. The breakdown of the generalized modified spin-wave theory for the large-spin layer antiferromagnetic systems is explicitly demonstrated in the evaluation of the sublattice magnetization and correlation function.

PACS. 75.30.Ds - Spin Waves.
PACS. 75.40.-s - Critical-point effects, specific heats, short-range order.
PACS. 75.50.Ee - Antiferromagnetics.

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