Time-gating of coherent spin-wave echoes from edge reflections in micro-patterned YIG

The extraction of intrinsic spin-wave damping and group velocity in a micro-structured yttrium iron garnet (YIG) device from direct transmission signals can be complicated by near-field inductive and capacitive coupling from closely spaced coplanar waveguide (CPW) antennas. In this work, we investigate a micrometer-sized YIG device and observe MHz-scale spectral ripples in its continuous-wave transmission spectra whose periodicity disperses with the applied magnetic field. We demonstrate that by performing time-domain transformations of broadband S-parameters, these ripples can be explicitly decoded as coherent spin-wave echoes originating from edge reflections. Because the echo wave-packet travels a significantly longer path than the direct signal, it effectively decouples from the CPW near-field feedthrough, stabilizing into a propagating magnon mode. Without the need for additional probes, we extract a relaxation time of τ≈50 ns and an effective Gilbert damping constant of α exp ≈8×10−4, while directly resolving group velocities that agree well with theoretical predictions where direct short-distance measurements deviate. Furthermore, reflection spectroscopy independently supports the origin of these signals. These observations are further corroborated by micromagnetic simulations. Our work establishes a robust protocol for magnon-based metrology, demonstrating how boundary effects can be utilized for on-chip delay elements.