Elastic Properties of Distorted Triangular Lattice KNiCl_3-Family Compounds(Condensed matter: electronic structure and electrical, magnetic, and optical properties)

概要

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In order to discuss the condensation of the K_4-mode in KNiCl_3-family compounds, the temperature dependences of the elastic compliances of KNiCl_3, RbMnBr_3, RbFeBr_3, and RbCoBr_3 were measured. In each compound, the temperature dependence of the elastic compliance s_<33> showed a sharp discontinuity at the point of structural phase transition from a prototype P6_3/mmc structure. The structural phase transitions of the KNiCl_3-family compounds are induced by the condensation of the K_4-mode at the Brilluoin zone boundary in the P6_3/mmc structure. When the K_4-mode is regarded as an order parameter η, the Landau free energy includes coupling term η^2T_3, where T_3 is an external stress. The experimental results were interpreted satisfactorily on the basis of a phenomenological Landau theory.
2006-09-15