Experimental Observation of Flat Bands in One-Dimensional Chiral Magnonic Crystals

• Published in: Nano letters 2023-07, Vol.23 (14), p.6776-6783
• Main Authors: Tacchi, Silvia, Flores-Farías, Jorge, Petti, Daniela, Brevis, Felipe, Cattoni, Andrea, Scaramuzzi, Giuseppe, Girardi, Davide, Cortés-Ortuño, David, Gallardo, Rodolfo A., Albisetti, Edoardo, Carlotti, Giovanni, Landeros, Pedro
• Format: Article
• Language: English
• Subjects: Engineering Sciences; Letter; Materials; Micro and nanotechnologies; Microelectronics
• ISSN: 1530-6984; 1530-6992
• DOI: 10.1021/acs.nanolett.2c04215

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.