Influence of transverse fields on surface and bulk polaritons in antiferromagnetic films

We study the behavior of surface and bulk polaritons in thin antiferromagnetic films when a dc magnetic field is applied perpendicular to the easy axis. Dispersion relations are obtained for magnetostatic modes, as well as for retarded polaritons. It is shown that, the dispersion relations of localized modes exhibit reciprocity, i.e. Ω(k→)=Ω(−k→), but they are non equivalent since they are localized in different regions. The non reciprocal character of surface modes in a semi infinite sample is regained for very thick films.