Structure modulation of Au/BYIG magneto-plasmonic crystals for efficient Faraday effects and refractive index detection

The structural characteristics of magneto-plasmonic crystals (MPCs) play a critical role in their performances, but current research often focuses on specific applications with fixed structural designs, leaving a gap in the systematic understanding of how geometric parameters influence their magneto-optical (MO) properties, particularly the evolution and underlying mechanisms of Faraday effects. To address the issue, this study employs the finite-difference time-domain method to numerically investigate the extraordinary optical transmission and MO properties of MPCs composed of a perforated Au film on a bismuth-substituted yttrium iron garnet layer. The influence of key structural parameters-including film thicknesses, hole size, shape (circular/square), periodicity, and arrangement (single/double holes per unit cell)-on the transmission spectra, Faraday rotation, and electric field distribution is systematically analyzed. For single-hole arrays, the optimal circular-hole arrays achieve a transmission of 27.3% and a Faraday rotation of 0.69°, while the optimal square-hole arrays yield 26.2% transmission and 0.67° rotation. Double-hole arrays, particularly with square holes, exhibit enhanced transmission sensitivity to environmental refractive index changes, reaching 174.61 nm/RIU, compared to 113-115 nm/RIU for single-hole structure. Electric field analysis reveals that enhanced coupling between surface plasmon polaritons and localized surface plasmon resonances underpins the improved MO performance. The study demonstrates that while double-hole arrays offer higher sensing sensitivity, single-hole arrays provide a larger figure of merit for MO applications. These findings provide valuable guidelines for designing high-performance MPC devices and plasmonic sensors by elucidating the relationship between structural geometry and performance.