Peculiarities of the Spin Wave Spectrum in Transversely Confined YIG Microwaveguides with Inhomogeneous Magnetization Profile

A study of spin wave spectra in a two-layer structure of iron-yttrium garnet (YIG) with different magnitudes of the saturation magnetizations of the layers has been carried out. Different modes of spin wave propagation (reciprocal, nonreciprocal, single-wave) depending on the type of structure and width of the central waveguide are investigated. The classification of spin wave spectra is carried out, and the class of guided, outgoing, and edge spin modes is identified. In particular, it is shown that in a system of planar magnetic comb-type LS-type (Ms1 Ms2) microwave guide tubes with periodic boundary conditions, two non-contiguous frequency regions of existence of guided modes of the central waveguide are observed for a width w of the central waveguide. Two adjacent frequency regions exist in the system of planar magnetic comb-type HS-type (Ms1 Ms2) microwave guide tubes at any values of the width of the central waveguide: in the high-frequency region, the mode with outflowing modes of the structure is realized, while in the low-frequency region, the mode with guided modes of the central waveguide is realized. It is shown that in systems of both types in the region of strongly inhomogeneous magnetic fields there can exist modes of boundary waves having a mutual character of propagation. The results obtained can be used to expand and clarify the physics of wave processes in complicated magnetic structures.