Nanometer-Thick YIG-Based Magnonic Crystals with Large Tunable Bandgaps

Control of information-carrying spin waves in magnonic crystals is essential for the development of magnon-based computing. Crystals comprised of a periodic array of ferromagnetic metals offer versatility in band structure design, but strong magnetic damping restricts their transmission efficiency. Yttrium iron garnet (YIG) with ultralow damping is the palpable alternative, yet its small magnetization limits dynamic dipolar coupling between discrete units in the technological imperative Damon-Eshbach (DE) geometry. Here, we experimentally demonstrate low-loss spin-wave manipulation in one-dimensional magnonic crystals of physically separated nanometer-thick YIG stripes. We enhance the transmission of DE spin waves in allowed minibands by filling the gaps between the stripes with CoFeB. The thus-formed magnonic crystals exhibit tunable bandgaps of 50 MHz - 200 MHz with nearly complete suppression of the spin-wave signal. We also show that efficient Bragg scattering on just two airgaps or two CoFeB stripes already produces clear frequency gaps in spin-wave transmission spectra.