Study of the structural phase transitions in RbCuCl_3 and CsCuCl_3 single crystals with the electric-magnetic-type interactions using a ~(87)Rb and ~(133)Cs nuclear magnetic resonance spectrometer

摘要

RbCuCl_3 and CsCuCl_3 single crystals were grown by the slow evaporation method, and the spin-lattice relaxation times and the resonance lines of the ~(87)Rb and ~(133)Cs nuclei in the resulting crystals were investigated using Fourier transform nuclear magnetic resonance (FT NMR) spectrometry. The temperature dependence of the relaxation time of the ~(87)Rb nucleus in the RbCuCl_3 crystals exhibited a discontinuity near T_(C2)(=260 K), which was attributed to a structural phase transition. Although the ~(87)Rb relaxation data showed no change indicative of a phase transition at T_(C1)(=340 K), the splitting of the ~(87)Rb resonance lines did change abruptly at T_(C1), indicating that the ~(87)Rb nuclei depends on the local environments surrounding these nuclei. For the CsCuCl_3 crystals, the relaxation time of the ~(133)Cs nucleus underwent large, abrupt changes at T_N (=10.5 K) and near T_C (=423 K), which coincide with a magnetic and a structural phase transition, respectively. The RbCuCl_3 and CsCuCl_3 results are compared with those obtained previously for other ABCl_3 (A =Rb, Cs, B =Cd, Mn) perovskite crystals.