Investigation of mode-induced spin wave transmission blockage by in-situ nanoscale grooves

In the pursuit of advancing spin-wave optics, we investigate the propagation of magnetostatic surface spin waves in a uniform permalloy waveguide with in-situ nanopatterned grooves created through Atomic Force Microscopy nanolithography and Focused Ion Beam etching. Our study unveils that the introduction of narrow constrictions and grooves leads to a non-monotonic reduction of the transmitted spin-wave signal intensity as the spin-wave pathway is shrinked. We highlight the remarkable feature that a stronger signal extinction is obtained for a narrow groove compared to a spin waveguide interrupted by a full gap, where only inefficient transport through dipolar coupling is allowed. Combining experimental and numerical analyses, we unravel the intricate interplay between spin-wave diffraction and reflection at the waveguide edges, being at the origin of a transverse-mode variation responsible for the signal extinction when detected using coplanar antennas. Our findings offer insights into the controllable manipulation of detected spin-wave intensity, thereby opening promising avenues for the improvement of spin-wave switches and interferometers, and for the nanopatterning of graded index magnonics.