Efficient geometrical control of spin waves in microscopic YIG waveguides

We study, experimentally and by micromagnetic simulations, the propagation of spin waves in 100-nm thick YIG waveguides, where the width linearly decreases from 2 to 0.5 μm over a transition region with varying lengths between 2.5 and 10 μm. We show that this geometry results in a downconversion of the wavelength, enabling efficient generation of waves with wavelengths down to 350 nm. We also find that this geometry leads to a modification in the group velocity, allowing for almost-dispersionless propagation of spin-wave pulses. Moreover, we demonstrate that the influence of energy concentration outweighs that of damping in these YIG waveguides, resulting in an overall increase in the spin-wave intensity during propagation in the transition region. These findings can be utilized to improve the efficiency and functionality of magnonic devices that use spin waves as an information carrier.