Enhanced transverse magneto-optical Kerr effect using ferromagnetic metal perforated with nanopore arrays

Abstract

Enhancement of transverse magneto-optical Kerr effects (T-MOKEs) based on surface plasmon resonance has attracted wide attention because of their high sensing performance. Most studies, however, mainly focus on prism-based magnetoplasmonic...

Ferromagnetic Subwavelength Periodic Nanogroove Structure with High Magneto-Optical Kerr Effect for Sensing Applications

“…This SPR-induced resonance of reflectance can considerably boost the amplitude of the TMOKE signal, as shown in Figure c, where the maximum and minimum values of the TMOKE signal occur almost simultaneously in pairs, as a result of which the TMOKE signal exhibits a distinct Fano shape which has an ultra-narrow line width compared with the U-shaped spectrum. This is a good indication that the TMOKE behavior is well improved owing to the induction of the (−1,0) SPR mode and that the shift in the TMOKE signal relative to the propagating SPR mode is not reciprocal. , …”

“…Owing to the periodicity at the subwavelength scale, the wave vector k of the m -th diffraction along the x -axis in the surface plane of the nanostructure can be coupled with the wave vector of the surface plasmon polariton (SPP) k spp to form the SPR mode, , which can effectively confine the electromagnetic energy to the interface between Co and medium around the structure as shown in Figure b. This typical optical mode can potentially lead to a high TMOKE response, which evaluates the amplitude of the relative change in reflectance R ( H + ) and R ( H – ) in response to the alternating magnetic fields, i.e., δ TMOKE = 2 × ( R ( H + ) – R ( H – ))/( R ( H + ) + R ( H – )). , Here, SPP is a quasiparticle that describes the coupling of photons to electrons, which is commonly formed at the interface between a metal with a negative dielectric constant and its surrounding medium. The wave vector k spp of SPP can be described as depending on the wave vector k 0 in free space and the refractive indices n m and n d of the metal and medium, that is, .…”

“…The magneto-optical Kerr effect (MOKE) can display diverse responses concerning the direction of the magnetization, incident plane, and sample surface, and it mainly occurs in three different forms: longitudinal MOKE, polar MOKE with respect to the change in light polarization, and transverse MOKE (TMOKE), which evaluates the intensity change of the light in the reflected or transmitted directions. − Magneto-optical devices based on TMOKE have attracted considerable attention and have driven the advancement in the sensing of biomolecules, gases, , water, − butanol, and chloroform . The primary requirement for these applications is that the device must exhibit a detectable TMOKE signal.…”

“…Unfortunately, prismatic structures are not conducive to the miniaturization of detection instruments because of their relatively large sizes. To overcome this problem, researchers have started to deposit metallic grating structures such as nanostripes, ,− nanopores, ,, and nanopillars , on the ferromagnetic film to realize the excitation of SPR using diffraction waves generated by grating-like structures instead of prismatic systems to intensify the available TMOKE signals and enhance the detection performance. For example, Diaz-Valencia covered a Co 6 Ag 94 film with Au nanograting to form magnetoplasmonic structures.…”

“…Their sensor, which consists of Au/Co nanodisk junction arrays on a metallic film, produced a well-resolved SPR spectrum with a line width of 7 nm and sensing sensitivity as high as 717 nm per refractive index unit (RIU). However, as research progressed, the increasing complexity of the device structure and the decreasing size of the structure imposed strict requirements on the cost and preparation technologies. ,, …”