Kerr effect enhancement in Ni antidot hexagonal nanostructures

• Angular resolved transverse magneto-optical Kerr effect (TMOKE) measurements provide a versatile tool for optical characterization of plasmonic nanostructures and show how plasmons couple to the applied magnetic field. These measurements show TMOKE enhancements that are closely connected to the plasmonic resonances of the nanostructures. This is seen even without noble metal layers that are traditionally used as the most important enhancing parameter. Measurements with these methods on hexagonal arrays of circular holes in thin Ni films (Ni covered with Au [1] as well as pure Ni [2]) are presented and compared with reference Ni films. The hole sizes of the two samples are 250 nm for the Au covered Ni and 220 nm for the pure Ni, the periodicities are 470 nm for the Au covered and 450 nm for the pure Ni. The TMOKE asymmetry coincides well with the plasmonic resonance showing a large increase of the signal. Drops in reflectivity, enhanced magneto-optical activity and transmission are reported which are closely connected with the formation of surface plasmons. One signature feature of plasmons, the drop in reflectivity followed by the Fano resonance, is shown to yield an increased magneto-optical asymmetry and therefore an increased sensitivity in the measurement even though the signal-to-noise ratio from the light source is significantly decreased. By comparing the two cases one can see that even though the plasmonic signal (in reflectivity) is much smaller for the pure Ni (less than 10% change in reflectivity compared to that of the Au covered Ni) the magneto-plasmonic signal is only about 20% smaller (0.048% compared to 0.06% for the Au covered Ni) which shows that magneto-optical methods have a higher sensitivity to the plasmonic states and can also be used to characterize the magneto-plasmonic properties. With this type of patterned nanostructures, we have shown that it is possible to enhance the magneto-optical activity due to the coupling to the plasmonic resonance in pure magnetic Ni (self-passivation thickness ~1nm). This enables purely magnetic plasmonic structures (no noble metal required) and paves the way for circuits where the applied magnetization can be a great tool for controlling, enhancing and sensing the plasmonic effects.[1] E. Th. Papaioannou et al., Opt. Express 19, 23867 (2011)[2] E. Melander et al., Appl. Phys. Lett. 101, 063107 (2012)

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NATURVETENSKAP  -- Fysik -- Den kondenserade materiens fysik (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences -- Condensed Matter Physics (hsv//eng)

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