Antiferromagnetic-Resonance Linewidths in MnF2

The fundamental relaxation mechanisms by which the uniform and magnetostatic modes decay in an antiferromagnet are identified by antiferromagnetic-resonance linewidth observations in Mn${\mathrm{F}}_2$ at 4.2°K in fields of 85 kOe. The dependence of the linewidth—0.2 Oe in the narrowest instance—on sample geometry, surface preparation, and impurity concentrations makes quantitative comparison with the Loudon-Pincus theory possible. The predominant relaxation process is surface pit scattering into the degenerate spin-wave manifold in all but the most impure crystals.