Long Wavelength Bulk and Surface Spin Waves in Metallic Superlattices

Abstract

At long wavelength where exchange interactions play a small role, and the dominant contribution to the excitation energy of the spin waves in a ferromagnet comes from the external Zeeman field and the demagnetizing field set up by the motion of the spins, the surface spin waves, also called the Damon-Eschbach mode, [1] have unique characteristics. Unlike the short wavelength, exchange-dominated surface spin waves, these dipolar surface magnons lie in frequency above the bulk bands and are unidirectional in nature. This effect shows up very well in Brillouin scattering measurements on ferromagnetic materials for both the case of the film [2] and the semi-infinite solid [3], where the surface magnon appears on either the Stokes or the anti-Stokes part of the spectrum, depending on whether the Zeeman field is parallel or antiparallel with respect to the saturation magnetization of the ferromagnet. The calculated light scattering spectra [4], in agreement with the experimental results, show the surface magnon peak to be much more intense than those due to the bulk magnons.