Tuning of spin-wave transmission and mode conversion in microscopic YIG waveguides with magnonic crystals

We report experimental results on spin-wave propagation, transmission gap tuning, and mode conversion in straight, curved, and Y-shaped yttrium iron garnet waveguides with magnonic crystals made of submicrometer-wide airgrooves. We observe forbidden frequency gaps with sizes up to 200 MHz in straight waveguides and narrowing of the gaps in curved and Y-shaped waveguides. The spin-wave transmission signal is strongly suppressed inside the gaps and remains high at allowed frequencies for all waveguide types. Using super-Nyquist sampling magneto-optical Kerr effect microscopy, we image symmetric and asymmetric spin-wave interference patterns, the self-focusing of propagating spin waves, and interconversions between width modes with different quantization numbers.