Dark spin wave envelope solitons in the model with nonlinear dispersion

Spin wave envelope solitons in a magnetic thin film are modeled by the nonlinear Schroedinger equation. Recent experimental observations of dark solitons in yttrium iron garnet thin films, however, are different from the mathematical predictions. In particular, it is expected that carrier wave phase will be conserved during propagation but this does not appear to be the case in experiment. To understand this discrepancy, higher order dispersive and nonlinear terms have been added to the model equation. Numerical simulations show that phase still must be conserved in the modified model