Active Control of Spin Waves in Micro- and Nanoscale YIG-based Magnetic Structures

Magnonic devices based on active manipulation of spin waves, provide a broad set of solutions to many problems in CMOS technology as these can be operated at very high switch speeds on nanoscale while only very low thermal losses are experienced. Therefore, this work aims to utilize one–dimensional magnonic crystals and resonators that promise new routes towards nanoscale devices. In this work growth of ultra low damping nanometer thin YIG films by Pulsed Laser Deposition, patterning by means of optical and electron beam lithography, sputtering and ion beam etching as well as characterization of these devices by all-electric broadband spin wave spectroscopy are explained. By etching several magnonic crystals in 43 nm thick YIG deep and wide bandgaps are opened by Bragg Scattering. These magnonic crystals consist of several shallow air grooves with varying lattice period, groove width and groove depth. By optimizing crystal parameters, the bandgaps suppress spin-wave transmission down to background while transmission for allowed frequencies is comparable to continuous YIG. With a total size of less than 10 µm this is the smallest YIG magnonic crystal compared to literature. By developing a second approach utilizing narrow magnonic resonators consiting of CoFeB grown on top of continuous YIG film, damaging magnetic properties in YIG induced by air groove fabrication is avoided. Within that bilayer, the YIG spin-wave undergoes a asymmetric wavelength down shift. Superposition of reflected waves from the resonator edges leads to destructive interference for well-defined frequencies. This enables robust, deep and wide bandgaps with a resonator width as narrow as 250 nm, while keeping transmission in off-resonance frequencies unaffected. The results provided in this work offer promising prospects for engineering broad and deep bandgap in a large frequency range on the micro- and nanometer scale. Herewith, a big step towards highly efficient nanoscale YIG magnonics is achieved