Magnetism and spin dynamics in the cluster compound [Cr4S(O2CCH3)8(H2O)4](NO3)2•H2O

The magnetism and spin dynamics of [Cr4S(O2CCH3)(8)(H2O)(4)](NO3)(2).H2O have been investigated by magnetic susceptibility and proton NMR measurements and by theoretical calculations. The proton-spin lattice relaxation rate 1/T-1, as a function of the temperature T and external magnetic field B, provides a very useful probe of the dynamical behavior of the four Cr+3 (spins s=3/2) paramagnetic ions which are ferromagnetically coupled via isotropic Heisenberg exchange interaction. From our derived formulas for the two-ion time correlation functions, we find that 1/T-1 may be expressed as a function of the single scaling variable mu(B)B/(k(B)T), where mu(B) is the Bohr magneton and k(B) is Boltzmann's constant, for the regime of our measurements. Our experimental data are in good agreement with this prediction and our derived form of the scaling function.