Wall material dependence of the band gap in magnonic crystals

Controlling the propagation of spin waves is a significant and fundamental challenge in the development of magnonic devices. One of the most promising candidates for this challenge is the magnonic crystal (MC). The bandgap (BG) properties of MCs with surface periodic steps primarily depend on the magnetic properties of the material and the structural period. We have fabricated MCs by adding walls to the base layer, rather than forming grooves in the film. This technique enables the use of different materials for the base layer and the wall layers. By using Co walls on a Py base layer, instead of an MC consisting entirely of Py, we have successfully doubled the BG width, as supported by micromagnetic simulations. In this BG enhancement, the lower edge of the BG remains almost unchanged, while the upper edge of the BG is shifted upward. These findings provide a novel method of band engineering for MCs and enhance their design flexibility.