Abstract
The propagation of bulk polaritons in ferromagnetic slab is considered through a short-wavelength approximation. Neither the damping nor the demagnetizing field do affect essentially the propagation and stability of the line soliton. The stable line soliton may be destroyed by background instability: the latter is suppressed in a narrow strip. The unstable line soliton decays into lumps, which can be described both numerically and through a variational approach. Lump interactions are mentioned.