Local spin dynamics at low temperature in the slowly relaxing molecular chain [Dy(hfac)3NIT(C6H4OPh)]: A μ+ spin relaxation study

The spin dynamics of the molecular magnetic chain [Dy(hfac)(3){NIT(C6H4OPh)}] were investigated by means of the Muon Spin Relaxation (mu+SR) technique. This system consists of a magnetic lattice of alternating Dy(III) ions and radical spins, and exhibits single-chain-magnet behavior. The magnetic properties of [Dy(hfac)(3){NIT(C6H4OPh)}] have been studied by measuring the magnetization vs. temperature at different applied magnetic fields (H - 5, 3500, and 16500 Oe) and by performing mu+SR experiments vs. temperature in zero field and in a longitudinal applied magnetic field H - 3500 Oe. The muon asymmetry P(t) was fitted by the sum of three components, two stretched-exponential decays with fast and intermediate relaxation times, and a third slow exponential decay. The temperature dependence of the spin dynamics has been determined by analyzing the muon longitudinal relaxation rate lambda(interm)(T), associated with the intermediate relaxing component. The experimental lambda(interm)(T) data were fitted with a corrected phenomenological Bloembergen-Purcell-Pound law by using a distribution of thermally activated correlation times, which average to tau - tau(0) exp(Delta/k(B)T), corresponding to a distribution of energy barriers Delta. The correlation times can be associated with the spin freezing that occurs when the system condenses in the ground state.