Edge-Prompted Spin Waves Probed via Magneto-Optical Effect in the Infrared

Recent advances in magnonics highlight the need for employing spin wave characteristics as new state variables, which is to be detected and mapped out with high precision in all-on-chip, small scale devices. Spin wave modes that are prompted by the sample edges in planar structures are of particular fundamental importance to the future design and characterization of magnonic device functionalities. In this work, we demonstrate an infrared light-based, magnetooptical technique that concurrently functions both as a spectroscopic and an imaging tool. The detected precessional phase contrast can be directly used to construct the map of the spin wave wavefront in the continuous-wave regime of spinwave propagation and in the stationary state, without needing any optical reference path. We experimentally detect the edge spin wave modes of a <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{Y}_{3} \mathbf{F e}_{5} \mathbf{O}_{12}$</tex> film sample, and study the evolution and interference from edge dominated modes to their bulk counterparts. Distinct wavevector groups and propagation characteristics are observed for the edge and bulk spin wave modes. Further, the magnon dispersion relation in the infrared is obtained by Fourier transforming the wavefronts measured in real space, which is a huge advantage to the wavevector-resolved Brillouin light scattering (BLS) technique, where the angle of incidence has to be varied, and is also much less cumbersome than the phase-resolved BLS. Our results demonstrate that the infrared optical strobe light can serve as a versatile platform for magneto-optical probing of magnetization dynamics, with potential implications in investigating hybrid magnonic systems.