Ultraslow motion of domain wall in channel inclusion compound studied by means of NMR cross-relaxation

We report temperature dependent H-1 NMR relaxation measurements of the powd er thiourea-hexachloroethane inclusion compound, [2.95(NH2)(2)CS].C2Cl6, at different resonance frequencies, from 23 to 55.5 MHz. Significant reductio n of spin-lattice relaxation time at 38-47 MHz is caused by the cross-relax ation of protons via the quadrupole chlorine nuclei. We conclude that the e ffective H-1-Cl-35 cross-relaxation observed in powder sample is due to a s low mode process, when the molecules of the domain wall exhibit a correlate d translational and rotational motion over the channel. Such a propagation of the domain wall was predicted by atom-atomic potential calculation. We s how that the NMR cross-relaxation effect is an effective tool in studying u ltraslow motions, in particular in incommensurate structures. (C) 2001 Else vier Science Ltd. All rights reserved.