EXPERIMENTAL-OBSERVATION AND INTERPRETATION OF MAGNETIC POLARITON MODES IN FEF2

We demonstrate how the interpretation of high-resolution far-infrared reflectivity and ATR spectra allows the mapping out of experimentally determined dispersion curves for the antiferromagnet FeF2. The dispers ion curves clearly summarize the relationship between frequency and wa ve vector of magnetic polaritons, and show the position of the bulk an d surface modes and surface resonances in zero, low and relatively str ong applied fields, Surface resonances which exist only in the presenc e of damping are identified. In addition we show how far-infrared meas urements can provide independent measurements of material parameters s uch as the exchange and anisotropy fields and the sublattice magnetiza tion.