Energy characteristics of a surface electromagnetic wave in a tangently magnetized bi-gyrotropic layer with the example of calculation of a spin wave characteristics in a ferrite plate

The energy characteristics of a surface-surface electromagnetic wave propagating in an arbitrary direction along a tangentially magnetized bigyrotropic layer are theoretically investigated. It is shown that the modulus and orientation of the Poynting vector of such a wave (the distribution of which over the layer thickness is described by two different exponential dependencies) change abruptly at the layer surfaces (interfaces of the media). The described regularities are confirmed by the example of calculation of a similar spin wave characteristics in a ferrite plate, which is a special case of such a layer. For this spin wave, it is also found that the energy flux vector and the group velocity vector are always parallel and codirectional, whereas the direction of the group velocity vector calculated in the magnetostatic approximation does not coincide with the direction of the energy flux for the initial part of the wave spectrum.