Surface Magnetic Modes

Abstract

The interactions within a system of spins are of two kinds: short-range exchange interaction and long-range electromagnetic interactions. The former determine short-wavelength modes while the latter are important at long wave-lengths. For very long wavelengths, of order C/ω_R, where ω_R is the appropriate (ferromagnetic or antiferromagnetic) resonance frequency, retardation of the electromagnetic interaction is important, and the bulk or surface modes are then called magnetic polaritons. In fact most observations have been of modes of somewhat shorter wavelength, for which electromagnetic effects can be treated in a magnetostatic approximation. The exchange-dominated short-wave-length modes, or spin waves, have been the subject of much theoretical study, but there has been very little experimental work. Partly for this reason, we restrict discussion of surface spin waves to some brief comments. The division into three wavelength regimes is not hard and fast« For example, important effects arise because of the modification of the magnetostatic modes by exchange interactions.