Modulational instability of nonlinear spin waves in easy-axis antiferromagnetic chains

The modulational instability of extended nonlinear spin waves in antiferromagnetic chains with on-site easy-axis anisotropy has been investigated both analytically in the frame of linear-stability analysis and numerically by means of molecular-dynamics simulations. The linear-stability analysis predicts the instability region and the growth rates of modulation satellites. Our numerical simulations demonstrate that the analytical predictions correctly describe the onset of instability. For long-time scales when the instability is fully developed the linear-stability analysis fails and the modulated nonlinear spin waves can evolve into localized excitations. We explore the possibility of generating intrinsic localized spin-wave modes from extended spin waves through modulational instability and find that both discreteness and strong nonlinearity seem to be essential for the creation of long-lived localized excitations. The addition of weak dissipation is found to impose a finite amplitude threshold even for infinite chains.