Two-dimensional solitons in the classical Heisenberg antiferromagnet with nonmagnetic impurities

Abstract

Experimental evidence is presented for the existence of nonlinear localized spin excitations (solitons) in the classical two-dimensional Heisenberg magnet doped with nonmagnetic impurities. These solitons are shown to provide the dominant mechanism for spin relaxation in electron paramagnetic resonance linewidths immediately above the ordering temperature for layered Mn compounds with a small impurity concentration. The new gapless excitations are pinned by the nonmagnetic impurities thereby becoming topologically unstable and lower in energy than the nonlinear excitations (skyrmions) that may exist in the pure material. Concentration-dependent results preclude a spin-wave mechanism for this effect.