Twisted spin waves in a cylindrical magnonic crystal

Abstract

Twisted spin waves (or twisted magnons, TMs) have significant potential in high-capacity communication due to their orbital angular momentum (OAM) degree of freedom. Consequently, manipulating the propagation of TMs has become an important topic in spintronics. Here, we theoretically study the band structures of TMs in ferromagnetic cylindrical magnonic crystals with periodically modulated anisotropy. We find that the TMs with arbitrary OAMs exhibit forbidden bands at the boundary of the Brillouin zone, though, in different frequency ranges. This unique feature offers a promising avenue for developing filters capable of blocking the propagation of TMs with specific OAMs. Furthermore, we demonstrate the tunability of TM bandgaps, as their position and width can be easily adjusted by altering the magnitude of anisotropy or the period of the crystal structure. Full micromagnetic simulations are performed to verify the theoretical predictions, showing good agreement. Our work not only enhances our understanding of TM propagation characteristics but also paves the way for the design of advanced spintronic devices that harness the magnon OAM degree of freedom.