It is shown that magnetic-dipolar radiation damping can be a primary source of the broadening of the uniform mode in antiferromagnetic resonance (AFMR) as well as ferromagnetic resonance. From a detailed study of the dependence of the AFMR linewidth $\Delta H$ in Mn${\mathrm{F}}_2$ on the volume of the sample and its position relative to the termination of a shorted waveguide, a quantitative comparison between theory and experiment is obtained. An empirical procedure is outlined for separating the intrinsic (magnon scattering) contributions to $\Delta H$ from the radiation-induced broadening. Uniform-mode linewidths are now measured which not only agree with the dipolar pit-scattering theory of Loudon and Pincus, but also resolve the dilemma of Kotthaus and Jaccarino, who found the linewidth of the uniform mode to be much larger than those of the magnetostatic modes with which it is nearly degenerate.

• Received 7 January 1974

DOI:https://doi.org/10.1103/PhysRevB.10.132