Surface spin waves in Heisenberg ferromagnets (a review)

The properties of localized surface states in the one-magnon spectrum of Heisenberg ferromagnets with different types of lattices and exchange interactions are considered. The systems with “isotropic” as well as “anisotropic” exchange interaction are investigated. The case of “anisotropic” exchange determined by the long-range interaction between the spins arranged along a crystallographic axis is analyzed. The dispersion relations and damping decrements of localized surface waves are obtained without using the cumbersome apparatus of Green’s functions for simple and complex ferromagnets with “isotropic” exchange between nearest neighbors. The contribution of the surface to the magnon energy distribution function is determined. Spin-wave states localized at two-dimensional defects (like a free surface, foreign plane in an infinite lattice, or the boundary between two magnetic crystals are investigted for systems with a long-range exchange interaction. The long-range interaction is found to be essential for an analysis of stability of the ferromagnetic ordering in the defect plane in the case of alternating ferro- and antiferromagnetic “anisotropic” interaction. Surface-projectable spectral densities of one-magnon states are estimated.

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