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 micrometers over a transition region with varying length between 2.5 and 10 micrometers. We show that this geometry results in a down-conversion of the wavelength, enabling efficient generation of waves with wavelengths down to 350 nm. We also find that this geometry leads to a modification of 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 of the spin-wave intensity during propagation in the transition region. These findings can be utilized to improve the efficiency and functionality of magnonic devices which use spin waves as an information carrier.