Fractal properties and tunable flat band structures in chiral magnonic quasicrystals

We investigate spin wave behavior in chiral magnonic quasicrystals (MQCs) based on Ir/Fe/Pt(Ir) and Au/Fe/Pt(Au) multilayers using wave vector resolved Brillouin light scattering (BLS). By systematically tuning the geometric structure and tailoring the interfacial Dzyaloshinskii-Moriya interaction (i-DMI), we obtain both the spin wave dispersion and the density of states (DOS). The results show that the Fibonacci sequence in chiral MQCs significantly enhances frequency modulation effects and promotes the formation of flat band structures. The position and number of local flat bands can be easily tuned, which has never been observed in conventional periodic magnonic crystals (MCs). Furthermore, the engineered i-DMI leads to pronounced nonreciprocal spin wave propagation, expanding the functional capabilities of MQCs. Moreover, a comprehensive analysis reveals that chiral MQCs exhibit unique dispersion characteristics, including multiple band gaps and fractal features, opening avenues for spin wave manipulation. These findings offer valuable insights for designing high-selectivity spintronic devices and establish a solid theoretical foundation for understanding spin wave dynamics, thereby accelerating the development of spin wave technologies for information processing and quantum computing.