The gyromagnetic Fabry-Pérot resonator: II. Dipole-exchange effects

The transmission of electromagnetic radiation at normal incidence through a magnetic film is considered for film thickness L small enough to require the inclusion of exchange effects arising from the wave-number component . We apply the continuum form of the dynamical equations with parametrized spin boundary conditions including pinned and unpinned spins as special cases. For applied field normal to the interfaces (Faraday geometry) the propagating modes are circularly polarized but because of the exchange there are two modes, say optical and spin, in each polarization. Equations for the transmission are given in a general form that allows for partial mirrors at the interfaces and applies to a film on a substrate as well as a free-standing film. Computed transmission spectra show that spin-wave fringes are unlikely to be observable for ferromagnets but can be significant in antiferromagnets. Some discussion is given of the implications for the characterization of antiferromagnetic film systems by means of far-infrared spectroscopy.