Spin-wave resonance in multilayer films (one-dimensional magnon crystals). Identification rules

The characteristic modification of the spectrum of the exchange spin waves has been revealed in ferromagnet/ferromagnet multilayer films with a thickness of $N({d}_1+{d}_2)$ by the spin-wave resonance method. This modification is due to the first bandgap at the wavenumber ${k}_b=\pi/({d}_1+{d}_2)$ of a magnon crystal, which is formed by one-dimensional modulation of the magnetization. It has been shown that the transformation of the multilayer film with thermal annealing to the film of a single-phase alloy is accompanied by the disappearance of this modification of the spectrum.