Spin-wave Solitons Research Articles

Bright magnetostatic spin-wave envelope solitons in ferromagnetic films

The theory and simulation of the spin-wave soliton formation in thin ferromagnetic films is considered. The necessary and sufficient conditions for soliton formation are analysed and some novel numerical results for different, yet possible, physical input conditions are presented.

Moving and Stationary Self-Localized Magnons as Spin-Wave Solitons in Heisenberg Ferromagnets

A theory of elementary excitations in Heisenberg ferromagnets with anisotropic exchange interactions is formulated without assuming the smallness of spin deviations from the ground state. This is done by using a path integral formalism in the SU(2) coherent state representation combined with the use of the stationary-phase approximation. Equations for spin-deviation field variables are solved in an approximate analytical form to show the existence by the intrinsic nonlinearity of mobile and immobile self-localized magnons in one- and d -dimensional cases, respectively. Discussions are given on their characteristic properties such as the energy eigenvalues lying below the linear spin-wave energy band, dispersion curves and localized-mode profiles. These intrinsic nonlinear modes can be considered as a natural extension of conventional (linear) spin waves to the nonlinear, soliton regime.

Spin wave solitons in an antiferromagnetic film (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.

Existence of spin-wave solitons in an antiferromagnetic film.

The propagation of nonlinear dipole spin waves in a film consisting of a two-sublattice, uniaxial, antiferromagnetic material has been investigated. 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. The existence of envelope solitons of spin waves is predicted and conditions for their creation are discussed

Observation of dipole-exchange spin wave solitons in tangentially magnetised ferromagnetic films

The formation of spin wave envelope solitons was observed in tangentially magnetised YIG films having pinned surface spins. The solitons were formed in the spectral regions of high positive dispersion ( ∂ 2 ω/ ∂k 2 > 0) near the dipole “gaps” in the dipole-exchange spin wave spectrum of the film where the Lighthill criterion is satisfied. The qualitative theoretical description of the observed phenomena based on the model of nonlinear Schrödinger equation is presented.

Numerical modelling of spin wave soliton propagation in ferromagnetic films

Results of numerical modelling of the process of spin wave envelope solitons formation in ferromagnetic films are presented. The nonlinear Schrödinger equation (NSE) with dissipation is used as a mathematical model for numerical calculations. Numerical results show that the NSE model gives a fair qualitative description of the dipole-exchange spin wave solitons formation in YIG films, but fails to explain the effect of propagation loss reduction for short nonlinear pulses of purely dipolar spin waves.