Tunable Magneto-Optical Kerr Effect in Fe Films Underneath a Two-Dimensional Array of Polystyrene Spheres Covered by Au Nanocaps

For Fe layers covered by two-dimensional arrays of hexagonal close-packed polystyrene spheres which are hemispherically covered by Au films on the top, fine structures are observed in reflection, magneto-optical Kerr rotation and ellipticity spectra. The Kerr rotation achieves peaks or exhibits a narrow resonance-like spectral lineshape near the reflection minima, depending on the mechanism of the reflection dips. The Kerr rotation peaks and the resonance-like lineshape both are shifted with the sphere diameters. These phenomena can be attributed to the excitation of surface plasmon resonance and Fabry–Pérot modes.