Spin wave solitons in an antiferromagnetic film (abstract)

Abstract

The propagation of nonlinear dipole spin waves in a film consisting of a two sublattice, uniaxial, antiferromagnetic material has been investigated. The system when the external magnetic field is assumed to be parallel to the anisotropy axis of the antiferromagnetic film and is directed parallel, or perpendicular, to the film surface is considered. For the first case, surface and volume waves can propagate in the film, and for the second case, volume waves can propagate in the film for a rather weak external magnetic field when the magnetization of the sublattices are counter parallel to each other and are perpendicular to the film surface. The linear dispersion relations for all three types of waves are analyzed and their group velocity dispersion is calculated. The nonlinear shift of the frequency, due to the finite power of the wave, is also obtained for the three types of dipole waves for the case of a thin antiferromagnetic film, when kd≪1 (k is the wave number and d is the thickness of the film). The nonlinear Schrödinger equation governing the propagation of the nonlinear spin wave in the film is investigated. It is shown that the criterion for the existence of spin wave solitons is fulfilled, for parallel magnetization, which permits the existence of surface waves (one branch) and volume waves (both branches), but the criterion is not fulfilled for perpendicular magnetization. The power threshold for soliton creation is also calculated and estimates are given for the data appropriate to a MnF2 crystal.