Spin Dynamics In Two Ref6-Based Single-Molecule Magnets From Nmr And Ac Susceptibility Measurements

Fluorine NMR is performed on two ReF6-based single-molecule magnets, a conductor, (BEDO)(4)[ReF6]center dot 6H(2)O, and its parent substance, an insulator, (PPh4)(2)[ReF6]center dot 2H(2)O. The correlation frequency of electronic spin fluctuations, omega(c), is derived from the spin-lattice relaxation rate. These data, combined with the inverse decay time of the magnetization, 1/tau(c), determined from the low-frequency ac susceptibility measurements, allows tracking of the spin dynamics span over seven orders of magnitude. We demonstrate that the two data sets, 1/tau(c) and the low-temperature region of omega(c), can be described by the same model, which includes Orbach, Raman, and "quantum tunneling of magnetization" contributions. This indicates that the two techniques characterize the same process. The influence of the conduction electrons on spin-lattice relaxation in (BEDO)(4)[ReF6]center dot 6H(2)O is revealed below 25 K as a trend of the relaxation to follow a linear temperature dependence.