Frequency and Field Angle Dependent Spin Wave Intensities in a Magnetic Y-Structure

Spin-based devices use spin waves or magnons to transmit and process information, which offer potential advantages over conventional devices due to their lower energy consumption. Magnonic logic gates are a specific type of spin-based device that uses the interference properties of spin waves. Here we investigate the effect of driving frequency and applied magnetic field angle on spin wave propagation through a 40-nm thick Ni₈₀ Fe₂₀ (Permalloy) Y-shaped structure made of microstrips with widths of w = 2.4-μm. A 10-μm wide gold microstrip antenna was used to excite spin waves in the two arms that form the top of the Y-structure, and then the spin waves converge in the base of the Y. We used Micro-focus Brillouin light scattering (micro-BLS) measurements to obtain spatial maps of spin wave intensities with the magnetic field applied in-plane perpendicular to the direction of spin wave propagation in the base of the Y, also known as the magnetostatic surface wave configuration. In this configuration the spatial maps show the spin wave intensity is stronger in the top arm and weaker in the bottom arm. As the applied field angle is tilted in-plane and the driving frequency is increased, the intensity in the bottom arm increases. The interference pattern also changes from being centered down the base of the Y to being concentrated along the edges. These changes in the spin wave propagation patterns can be understood by examining the spin wave dispersion relations for microstrips.