Short-Range-Order Effects in Neutron Scattering from Heisenberg Paramagnets: Application to RbMnF3

We have computed the wave-vector-dependent frequency moments of the spectral line shape, $\mathcal{S}(\mathrm{K}, \omega )$, of a Heisenberg paramagnet with isotropic exchange interaction of arbitrary range. The results are specialized to RbMn${\mathrm{F}}_3$ at $T=3.5\mathrm{}{T}_N$. Using the phenomenological representation of a two-parameter Gaussian diffusivity, the spectral line shape $\mathcal{S}(\mathrm{K}, \omega )$ is constructed. The theoretical results are compared and found to be in satisfactory agreement with the experimental data of Windsor, Briggs, and Kestigian.