Surface Phonons and Magnos

Abstract

A brief introductory survey of surface phonons and magnons is presented. Long-wavelength surface modes include optical modes in ionic crystals, magnetostatic waves in magnetic insulators, and elastic surface waves. The effects of retardation on the optical modes lead to surface polaritons. Calculations based on discrete atomic models show that additional surface modes occur in the ionic crystals due to abrupt changes in the short-range forces at the surface and that the electrodynamic modes are pseudosurface states when they exist in the bulk band. Experiments relating to these modes are reviewed briefly. Magnetostatic modes are the magnetic analog of the electrodynamic optical modes in ionic crystals. When the exchange interaction is considered the magnetostatic surface modes are converted into pseudosurface states called dipole-exchange surface modes which lie within the bulk spin-wave band. Elastic surface waves in isotropic, anisotropic, piezoelectric, and layered media are discussed briefly. Various types of elastic waves include generalized Rayleigh, pseudosurface, electroacoustic, Love, Lamb, Sezawa, and Stoneley waves. Short-wavelength surface waves include acoustic and optical phonons and acoustic and optical magnons in ferro-and antiferromagnets. Surface magnons are discussed and experiments and theory relating to surface spin dynamics are reviewed. Surface phonon characteristics are described and relevant experiments are mentioned.