  Symmetry and localization properties of defect modes of a one-dimensional
bi-component magnonic superlattice are theoretically studied. The magnonic
superlattice can be seen as a periodic array of nanostripes, where stripes with
different width, termed as defect stripes, are periodically introduced. By
controlling the geometry of the defect stripes, a transition from dispersive to
practically flat spin-wave defect modes can be observed inside the magnonic
band gaps. It is shown that the spin-wave profile of the defect modes can be
either symmetric or antisymmetric, depending on the geometry of the defect. Due
to the localized character of the defect modes, a particular magnonic
superlattice is proposed, wherein the excitation of either symmetric or
antisymmetric flat magnonic modes is enabled at the same time. Also, it is
demonstrated that the relative frequency position of the antisymmetric mode
inside the band gap does not significantly change with the application of an
external field, while the symmetric modes move to the edges of the frequency
band gaps. The results are complemented by numerical simulations, where an
excellent agreement is observed between both methods. The proposed theory
allows exploring different ways to control the dynamic properties of the defect
modes in metamaterial magnonic superlattices, which can be useful for
applications on multifunctional microwave devices operating over a broad
frequency range.
