One-Dimensional Heisenberg Antiferromagnet with Spin S = 3/2. Experiments on AgCrP ₂ S ₆

The magnetic susceptibility of the spin-(S = 3/2) Heisenberg chain AgCrP2S6 follows in a wide temperature range the recent quantum Monte Carlo result (Sandvik and Kurkijärvi, 1991) with a nearest-neighbour exchange (JSiSi + 1) J/kB = 100 K. Inelastic neutron scattering in the quasi-one-dimensional phase indicates a spin-wave velocity C = 4.6J, well in excess of the classical value 3J. The results emphasize the strong quantum character of the S = 3/2 Heisenberg chain. The extrapolated zero-temperature susceptibility and the observed spin-wave velocity are compared with the theoretical predictions for half-integer spins and are compatible with universal critical properties for S = 1/2 and S = 3/2.