Nickel–Iron (Ni₈₀Fe₂₀) nanoarrays, due to their strong magneto-optical responses, represent promising platforms for magneto-plasmonic applications. In this study, a multilayer structure comprising Ni–Fe nanoarrays on a polymethyl methacrylate (PMMA) layer, and a glass substrate was numerically investigated using the finite element method based on the full solution of the Maxwell's equations. Reflection spectra, electric field distributions, and Kerr magneto-optical effect quantities (rotation) were examined under external magnetic fields ranging from approximately 0 to 40 mT and for thicknesses of 26, 36 and 46 nm. The results indicate that in the reflection spectra analysis, surface and lattice plasmonic effects are responsible for the formation of minima and maxima. These effects are directly influenced by the calculated near-field magnitude. In contrast, the computed Kerr effect does not align with the near-field magnitude values. Analytical investigations reveal that beyond the near-field magnitude of the x and y components, the Kerr effect is also affected by the phase difference between these components. The Kerr effect is dominated by surface plasmon effects at lower thicknesses; at higher thicknesses, on one hand, high ohmic losses and absorption weaken the plasmonic effects, but it can also enhance magnetic peak intensity and shifts its position toward shorter wavelengths (blue-shift).
These findings provide deeper insight into the magnetic control of plasmonic resonances and offer effective guidance for designing magnetoplasmonic sensors and optoelectronic devices based on Ni–Fe nanoarrays.