Spin waves in quasiperiodic magnonic crystal arrays of metallic nanostripes

Theoretical studies are reported for the effects of quasiperiodicity on the dipole-exchange spin waves that can propagate in magnonic crystals. The systems under consideration are lateral arrays formed by nanowire stripes of metallic ferromagnets separated by nonmagnetic spacers and with growth rules derived from both the Fibonacci and Thue-Morse sequences. A microscopic (or Hamiltonian-based) approach is used to calculate the spectra of spin-wave bands and gaps for different generations of the sequences. Different origins for the quasiperiodicity, coming from variations in either the nanowire properties or the spacer properties, are compared and contrasted with one another as well as with the behavior in periodic magnonic crystals. The relative importance of dipole-dipole and exchange interactions can be varied by control of the wave vectors for the spin waves.