Nonlinear surface spin waves (abstract)

Abstract

There has been extensive theoretical and experimental work devoted to investigations of surface spin waves in magnets. However, such excitations have usually been studied in the linear approximation, whereas large-scale dynamic excitations (magnetic solitons, nonlinear spin waves of different types) were discussed in infinite media only. The purpose of this work is to investigate a new type of surface excitation: nonlinear surface spin waves (surface solitons) in semi-infinite magnets. We analyzed the simplest model of a one-sublattice ferromagnet taking into account the nonhomogeneous exchange interaction and the easy-axis magnetic anisotropy. In addition, the boundary conditions on the surface describing uniaxial surface anisotropy were used. Linear surface spin waves in such a model are known to exist when the latter is of the easy-plane type only whereas nonlinear solutions of the equations of motion satisfying the boundary conditions are proved to exist whatever surface anisotropy takes place. These solutions describe nonlinear surface spin waves traveling along the surface. Moreover, for some values of precession frequency and surface anisotropy constant there are two or even three such soliton-like solutions. It should be noted that localization of these excitations near the surface is entirely due to nonlinearity, and the surface solitons under consideration have no linear analogy. We also proved the existence of so-called internal nonlinear spin waves describing soliton-like magnetic excitations localized on the interface between two semi-infinite magnets. In addition, the generalization of all results mentioned above was obtained for more complicated two- and many-sublattice magnets.