H-1-NMR STUDY OF THE SPIN DYNAMICS IN THE SUPERPARAMAGNETIC OCTANUCLEAR IRON CLUSTER FE8

The eight iron (III) S = 5/2 cluster Fe8, was studied by H-1 NMR and r elaxation rate measurements. We directed our experimental efforts to t he analysis of the nuclear spin-lattice relaxation rate T-1(-1) which presents a broad maximum at T > 100 K for all the NMR frequencies used . We discuss the temperature and frequency dependence of the relaxatio n rate in terms of the slow fluctuations of the local Fe magnetic mome nt and we try to relate the local dynamics observed by NMR with the ma croscopic relaxation of the magnetization measured by AC susceptibilit y and Mossbauer experiments. (C) 1998 Elsevier Science B.V. All rights reserved.