Linewidth in exchange anisotropic paramagnets at the critical point

In this article the kinetic theory developed by Resibois and De Leener describing the temporal behavior of the spin autocorrelation functions near the critical point (TTc) in the Weiss limit is extended to exchange anisotropic systems with arbitrary spin. From our model, the scaling laws proposed by Riedel and Wegner can be justified microscopically. Furthermore, we suggest an interpretation of experimental data of linewidths above Tc on the uniaxial antiferromagnet MnF₂ in terms of the variables κ_∥q and κ_Δq, where κ_Δ is directly related to anisotropy. Owing to the satisfactory agreement obtained in the above, we give scaling functions relative to various systems (uniaxial and planar ferromagnets and planar antiferromagnets).