Spin dynamics in the linear-chain S=1 antiferromagnet Ni(${\mathrm{C}}_3$${\mathrm{H}}_{10}$${\mathrm{N}}_2$${)}_2$${\mathrm{N}}_3$(${\mathrm{ClO}}_4$)

Magnetic excitations in the quasi-one-dimensional Heisenberg spin-1 antiferromagnet Ni(${\mathrm{C}}_3$ ${\mathrm{H}}_{10}$ ${\mathrm{N}}_2$ ${)}_2$ ${\mathrm{N}}_3$ ${\mathrm{ClO}}_4$) (NINAZ) have been studied by single-crystal inelastic neutron scattering. A Haldane gap Δ≊3.6 meV in the spin excitation spectrum was observed in the vicinity of the antiferromagnetic wave vector at low temperature and the dispersion relation was measured. The temperature dependence of the energy gap Δ(T) was measured in the range 8–50 K and was found to be inconsistent with the predictions of the quantum nonlinear σ model. The results are discussed in comparison with those found in the literature for similar systems. © 1996 The American Physical Society.