Nuclear-magnetic-resonance interaction mechanism in Rb2CoCl4 single crystals with the electric magnetic type -: art. no. 043906

The Rb-87 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 87Rb 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 87Rb spin-lattice relaxation rate near T-c1 corresponds to the ferroelectric to incommensurate phase transition. There is a weak anomalous contribution to T-1, and this seems to be the only detectable influence of a structural phase transition. The temperature dependence of T-1(-1) near T-i is more or less continuous and is not affected by the normal-incommensurate phase transition. For T > T-i, 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. (c) 2005 American Institute of Physics.