Spin wave propagation in a ring-shaped magnonic waveguide

We experimentally investigate frequency-selective spin wave (SW) transmission in a micrometer-scale, ring-shaped magnonic resonator integrated with a linear yttrium iron garnet stripe. Using super-Nyquist-sampling magneto-optical Kerr effect (SNS-MOKE) microscopyand micro-focused Brillouin light scattering (μ-BLS), we probe SW dynamics in the dipolar regime under in-plane magnetization. Spatially resolved measurements reveal a sharp transmission peak at 3.92 GHz for an external field of 74 mT, demonstrating strong frequency selectivity. This behavior arises from interference and scattering among multiple SW modes in the ring, shaped by anisotropic dispersion, geometric confinement, and local magnetic field inhomogeneities. Caustic-like propagation further limits outcoupling due to fixed group velocity directions. Fourier analysis reveals discrete wavevector components consistent with quantized ring eigenmodes. μ-BLS measurements at 70 mT show a shift of the transmission peak, demonstrating tunability via the external magnetic field.