Unconventional Transverse Magneto-Optical Kerr Effect in Cobalt Nanopillar Arrays

Novel magneto-optical (MO) properties can be actualized through well-designed nanostructures, greatly improving the application value of MO effects. As only p-polarized light can generate transverse magneto-optical Kerr effect (TMOKE) in traditional MO materials, it is quite challenging and valuable to effectuate TMOKE under s-polarization incidence at optical frequencies. The constructed nanopillar structures in this work can realize a clear TMOKE under both s-polarization and p-polarization incidences, as proved by experiments and simulations. Under s-polarized incident light with an elevation angle of 45 degrees, electric dipole resonance (EDR) and electric quadrupole resonance (EQR) are excited, resulting in the significant enhancement of TMOKE (five orders of magnitude higher than for the planar Co film). The intensity of s-polarized TMOKE shows an increase with the enhancing diameter and height of the nanopillar structure. The amplitude of p-polarized TMOKE is also appreciably increased due to the excitation of surface plasmon polaritons (SPPs) and localized surface plasmons (LSPs). Moreover, the Fe and Ni nanopillars display similar reflectivity and s-polarized TMOKE behaviors in simulations. The s-polarized TMOKE is unexpectedly observed in ferromagnetic metals for the first time, which builds up a considerable platform for the development and application of novel MO phenomena. The Co nanopillar structure constructed in this work displays an anomalous magneto-optical effect in both experiment and theory, i.e., s-polarized TMOKE, which is observed in ferromagnetic metals for the first time. The dimension of the nanopillar, the thickness of the coated Au film, and the material composition (Fe, Co, Ni) can all affect the intensity of s-polarized TMOKE. image