Experimental Observation of Flat Bands in One-Dimensional Chiral Magnonic Crystals
S. Tacchi, Jorge Luis Flores, Daniela Petti, Felipe Brevis, Andréa Cattoni, Giuseppe Scaramuzzi, Davide Girardi, David Cortés‐Ortuño, R. A. Gallardo, Edoardo Albisetti, G. Carlotti, P. Landeros
Abstract
Spin waves represent the collective excitations of the magnetization field within a magnetic material, providing dispersion curves that can be manipulated by material design and external stimuli. Bulk and surface spin waves can be excited in a thin film with positive or negative group velocities and, by incorporating a symmetry-breaking mechanism, magnetochiral features arise. Here we study the band diagram of a chiral magnonic crystal consisting of a ferromagnetic film incorporating a periodic Dzyaloshinskii-Moriya coupling via interfacial contact with an array of heavy-metal nanowires. We provide experimental evidence for a strong asymmetry of the spin wave amplitude induced by the modulated interfacial Dzyaloshinskii-Moriya interaction, which generates a nonreciprocal propagation. Moreover, we observe the formation of flat spin-wave bands at low frequencies in the band diagram. Calculations reveal that depending on the perpendicular anisotropy, the spin-wave localization associated with the flat modes occurs in the zones with or without Dzyaloshinskii-Moriya interaction.