Proton spin-lattice relaxation at low temperature in the ferromagnetic spin ring Cu6

We report H-1 nuclear magnetic resonance spin-lattice relaxation rate (NSLR ) measurements as a function of temperature (1.5-4.2 K) and as a function o f applied magnetic field (0.2-8.2 T) in the molecular magnet [(PhSiO2)(6)Cu -6(O2SiPh)(6)] in short Cu6. The results are explained in terms of a simple model whereby the NSLR is driven by the fluctuations of the local hyperfin e field due to the reorientation of the total spin of the molecule in its g round state. From the analysis of the data, we infer the temperature and fi eld dependence of the characteristic rate of the fluctuations of the total magnetization of the Cu6 ring in its ground state. (C) 2000 American Instit ute of Physics. [S0021-8979(00)52508-0].