Soliton Contribution to the Electron Paramagnetic Resonance Linewidth in the Two-Dimensional Antiferromagnetic

An observed exponential decay in the electron paramagnetic resonance linewidth of the nearly classical two-dimensional antiferromagnet as a function of temperature is shown to be the result of solitons interacting with magnons, and provides an experimental confirmation of these excitations. The temperature dependence of the linewidth is calculated using the dynamic spin correlation function derived from soliton-magnon scattering in the Born approximation. Data in the critical regime for ( $n$-propylammonium${)}_2$ tetrachloromanganese (II) are presented and compared to the theory.