Deuteron spin-lattice relaxation in the Mn12O12-acetate magnetic cluster

The dynamics of the fully deuterated polycrystalline molecular cluster nanomagnet Mn12O12[(CD3COO)(16)(D2O)(4)].2CD(3)COOD.4D(2)O has been studied in a field of 6.3 T via deuteron spin-lattice relaxation time (T,) measurements between room temperature and 4 K. The relaxation is due to the fluctuations in the hyperfine electron nuclear coupling. The deuteron magnetization recovery was found to be of the stretched exponential type and the temperature dependence of the spin-lattice relaxation time parameter T-1 showed two pronounced minima, one around 70 K and another around 10 K. The two modes detected in this study are intermediate between the slow magnetization reorientation mode detected by susceptibility measurements and the fast spin modes detected by inelastic neutron scattering. Whereas the slow correlation time tau(1) is of the order of days in the vicinity of the superparamagnetic blocking temperature 5 K, the fast correlation time tau(2) is here still in the 10(-6) s range.