Abstract
The Rb87 spin-lattice relaxation time of Rb2CoCl4 single crystals grown using the slow evaporation method was measured using nuclear magnetic resonance. The recovery trace for the central line of Rb87 with dominant magnetic relaxation cannot be represented with a single exponential function, but can be represented with a linear combination of two exponential functions. The change in the Rb87 spin-lattice relaxation rate near Tc1 corresponds to the ferroelectric to incommensurate phase transition. There is a weak anomalous contribution to T1, and this seems to be the only detectable influence of a structural phase transition. The temperature dependence of T1−1 near Ti is more or less continuous and is not affected by the normal-incommensurate phase transition. For T>Ti, the spin-lattice relaxation rate is governed by molecular motion as described by the Bloembergen-Purcell-Pound theory. This behavior is different to that found for Rb in Rb2ZnCl4. The phase-transition temperatures of the Rb2CoCl4 and Rb2ZnCl4 single crystals are quite similar, but their phase-transition mechanisms are different. The nuclear-magnetic-resonance (NMR) interaction mechanism in Rb2ZnCl4 is well known to be of the electric quadrupolar type whereas in Rb2CoCl4 it is of magnetic origin. Therefore a completely different NMR behavior is obtained in the two crystals.
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