Magneto-optics (MO) is an effervescent research field, with a wide range of potential industrial applications including sensing, theranostics, pharmaceutics, magnetometry, and spectroscopy, among others. This review discusses the historical development, from the discovery of MO effects up to the most recent application trends. In addition to the consolidated fields of magnetoplasmonic sensing and modulation of optical signals, we describe novel MO materials, phenomena, and applications. We also identified the emerging field of all-dielectric magnetophotonics, which hold promise to overcome dissipation from metallic inclusions in plasmonic nanostructures. Moreover, we identified some challenges, such as the need to merge magneto-chiroptical effects with microfluidics technology, for chiral sensing and enantioseparation of drugs in the pharmaceutical industry. Other potential industrial applications are discussed in light of recent research achievements in the available literature.

Giant enhancement of the magneto-optical Kerr effect (MOKE) by surface plasmon polaritons (SPPs) is theoretically shown in a trilayer structure consisting of double-layer dielectrics and a ferromagnetic metal (Al₂O₃/SiO₂/Fe). We calculated the resonant enhancement of the transverse MOKE (TMOKE) and polar MOKE (PMOKE) using the attenuated total reflection (ATR) configuration with the transfer matrix method using a 4 × 4 scattering matrix. At a specific film thickness of the low-index SiO₂ layer, where confinement of the SPPs on the Fe surface becomes close to the cutoff condition, the incident light from the Al₂O₃ couples with the SPPs at the SiO₂/Fe boundary most efficiently, resulting in resonant enhancement of the MOKE at an incident angle corresponding to the wave vector of the SPPs. The calculated PMOKE showed orthogonal transformation (90°-rotation) and almost full-orbed deformation (44°-ellipticity) of the polarization, and the TMOKE showed a change in reflectance of about 34 dB upon magnetization reversal.

Here, we show the high wavelength tunability and magnetic field modulation of surface plasmon polaritons (SPPs) of a waveguide mode that Double-layer Dielectrics and Ferromagnetic Metal, Al₂O₃/SiO₂/Fe, trilayer structures exhibit when excited in the Otto configuration of attenuated total reflection setup. First by modeling, and then experimentally, we demonstrate that it is possible to tune the wavelength at which the angular dependent reflectance of these structures reaches its absolute minimum by simply adjusting the SiO₂ intermediate dielectric layer thickness. This precise wavelength corresponds to the cut-off condition of SPPs' waveguide mode supported by the proposed structure, and it can be then switched between two values upon magnetization reversal of the Fe layer. In this specific situation, a large enhancement of the transverse magneto-optical effect is also obtained.

We have implemented the nonreciprocal propagation capabilities into plasmonic waveguides and have simulated the performances. We employed dielectric-loaded surface plasmon polariton waveguide (DLSPPW) and long-range DLSPPW (LR-DLSPPW) configurations, where ferromagnetic-metal Fe is used instead of noble metals in order to obtain nonreciprocal propagations by the transverse magneto-optical (MO) effect. The nonreciprocal performances were characterized by the finite-difference frequency-domain (FDFD) method in terms of the propagation losses in return for the nonreciprocal phase shift (NRPS) and nonreciprocal propagation loss (NRL). The NRPS and NRL of the DLSPPW configuration are larger than those of the previously reported semiconductor waveguide optical isolators owing to the large MO constant of Fe and the field confinement by surface plasmons although the propagation loss for NRL of 1 dB is at least 31 dB and the propagation length is limited to less than 10 μm. To reduce such a large propagation loss, we introduced the LR-DLSPPW configuration composed of Polymethyl methacrylate (PMMA) ridge and Benzocyclobutene (BCB) buffer layer. The Fe layer thickness and width are optimized to 50 nm and 500 nm, respectively, so that sizable MO effect and low propagation loss coexist. The propagation loss for NRL of 1 dB is suppressed to ~10 dB within a waveguide length of ~56 μm. Our comprehensive investigation offers fundamental information on practical magneto-plasmonic waveguides and how much nonreciprocal performances are expected, providing an insight into the integration of magneto-plasmonics with on-chip photonics and electronics.