Spin dynamics in S=3/2 one-dimensional Heisenberg antiferromagnets CsVCl3 and CsVBr3

The spin dynamics in S = 3/2. one-dimensional (1D) Heisenberg antiferromagn ets, CsVCl3 and CsVBr3, was investigated using inelastic neutron scattering . The magnetic excitations were measured at temperatures above the three-di mensional ordering temperature in order to discuss the 1D properties in the present systems. We report on the spin dynamics at low temperatures and it s temperature (T) dependence. From the observed dispersion relation, using the renormalization constant calculated from the quantum Monte Carlo method , we obtained the exchange constant (J) in good agreement with those taken from bulk-susceptibility measurements. The observed structure factor was we ll described by that calculated from the parameters describing the dispersi on relation. The energy width (Gamma) was independent of the 1D momentum tr ansfer (q) at large energy transfers, however, its q dependence exhibits th e minimum at the magnetic zone center. The parameters describing the energy scale in the spin dynamics at low T were found to be scaled by J. We also investigated the T dependence of the spin dynamics: Gamma(T) can be scaled by J, Gamma(T) at T>J is proportional to T as predicted by classical theory but at T>J, Gamma decreases with decreasing T and becomes finite. On the o ther hand, we found that kappa(T) is proportional to Tat any T, The scaling by J in the dynamics at low T as well as Gamma(T) suggests that the observ ed spin dynamics is of 1D origin. We conclude that the spin dynamics at hig h temperatures T>J, is well described by classical theory, however, at low temperatures;T<J, the finite width indicates some quantum fluctuations. The refore, we observed the crossover from the quantum state at low T to the cl assical state at high T in S = 3/2 systems. [S0163-1829(99)00521-4].