We discuss difficulties arising from the description of spin waves in the magnetostatic approximation, in which neither the microwave electric field nor the Poynting vector is associated with the wave. To overcome these difficulties, we present for the first time a correct solution to the problem of electromagnetic wave propagation in an arbitrary direction along a tangentially magnetized bi-gyrotropic layer (a special case of this problem is the propagation of spin waves in a ferrite plate). It is shown that the wave distribution over the layer thickness is described by two different wave numbers k_x21 and k_x22, which can take real or imaginary values; in particular, three types of spin wave distributions can occur inside the ferrite plate — surface-surface (when k_x21 and k_x22 are real numbers), volume-surface (k_x21 is imaginary and k_x22 is real), and volume-volume (k_x21 and k_x22 are imaginary numbers), which fundamentally distinguishes the obtained description of spin waves from their description in the magnetostatic approximation.

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Keywords: spin waves, ferrite plates, electromagnetic waves, bi-gyrotropic layers, wave distribution over layer thickness PACS: 41.20.Gz, 41.20.Jb, 75.70.−i (all) DOI: 10.3367/UFNe.2024.09.039768 URL: https://ufn.ru/en/articles/2024/12/i/ Citation: Lock E H, Gerus S V "Electromagnetic waves in a tangentially magnetized bi-gyrotropic layer (with an example of analysis of spin wave characteristics in a ferrite plate)" Phys. Usp. 67 (12) (2024) Received: 30th, January 2024, revised: 9th, September 2024, accepted: 23rd, September 2024 Оригинал: Локк Э Г, Герус С В «Электромагнитные волны в касательно намагниченном бигиротропном слое (с примером анализа характеристик спиновых волн в ферритовой пластине)» УФН 194 1330–1344 (2024); DOI: 10.3367/UFNr.2024.09.039768