Spin Waves in a Bilayer with Biquadratic Interlayer Coupling

Linear spin waves in layered structures consisting of two ferromagnetic films coupled at the interface by a biquadratic exchange interaction are analysed theoretically within the localized spin model and in the low-temperature limit. Magnetizations of both films are assumed to be parallel to the film plane, but perpendicular one to another. The limit of two semi-infinite ferromagnets is also considered. In both cases interfacial modes have been found.