Critical slowing-down in classical and quantum Heisenberg magnetic molecules

Abstract Two-spin equilibrium time correlation functions (TCF) are of fundamental importance for studying the spin dynamics of magnetic molecules since these quantities appear in formulas for inelastic neutron scattering and magnetic resonance experiments. For systems of classical and quantum spins ( s >1) interacting via antiferromagnetic Heisenberg exchange, we find the general result that the TCF exhibit critical slowing-down effects for T →0 K: the Fourier time transform of the TCF exhibits a growing peak that shifts towards zero frequency on cooling.