Propagation of Spin Waves in Doubly Periodic Magnonic Crystals

Towards the development of strategies for tailoring spin-wave band gaps in magnonic crystals, this work examines the band gap properties in a one-dimensional magnonic crystal with double periodicity. A long and narrow yttrium iron garnet (YIG) thin film strip is etched with an array of transverse groove lines separated by alternating distances, where the second distance is twice the first. This double periodicity in the magnonic crystal translates into dissimilar band gaps in the frequency domain, with the third and sixth band gaps being more pronounced than others. These band gaps are more pronounced because the corresponding wavenumbers simultaneously satisfy the Bragg scattering conditions for the periods equal to the two groove separations as well as their sum. Experimental observations are reproduced by numerical simulations. Together, the experimental and numerical results demonstrate how multiple periodicities could be an effective design parameter for creating magnonic crystals with desired band gaps.