It is shown that the introduction of a very small amount of nonmagnetic impurities into the magnetic sites of a classical two-dimensional antiferromagnet creates a new type of static (impurity-pinned) soliton that affects the Arrhenius, $\exp (-E/T)$, temperature-dependent electron paramagnetic resonance linewidth by drastically changing the parameter $E$. Data just above the transition temperature for $({\mathrm{C}}_3{\mathrm{H}}_7{\mathrm{NH}}_3{)}_2{M}_x{\mathrm{Mn}}_{1-x}{\mathrm{Cl}}_4$ confirm the existence of these impurity-pinned solitons.

• Received 25 July 1997

DOI:https://doi.org/10.1103/PhysRevLett.80.2201