Neutron scattering study of spin waves in one-dimensional antiferromagnet KCuF3

Inelastic neutron scattering has been used to obtain the spin-wave spectrum in KCu${\mathrm{F}}_3$. The nature of magnetic interactions in this material is quasi-one-dimensional (chainlike) as evidenced by a highly anisotropic spin-wave dispersion. The spin-wave dispersion along the chain direction fits very well with the exact solution for an $S=\frac{1}{2}$ linear-chain antiferromagnet given by des Cloizeaux and Pearson. Using linear spin-wave theory, the ratio of interchain to intrachain magnetic exchange parameters $\frac{J_a}{J_c}$ is found to be -0.01±0.001. A zone-center gap of 1.1 meV in the spin-wave mode with a spin component out of the easy ($\mathrm{xy}$) plane shows that the spin system is predominantly of Heisenberg nature with a small (0.02%) $\mathrm{xy}$-like component.