Abstract
The spectral properties of the transverse magneto-optical Kerr effect (TMOKE) in periodic metal–dielectric hybrid structures are studied, in particular with respect to the achievable magnitude. It is shown that the TMOKE is sensitive to the magneto-optical activity of the bismuth-substituted rare-earth iron garnet, which is used as a dielectric material in the investigated structures. For samples with larger Bi substitution level and, consequently, larger gyration constant, the magnitude of the TMOKE increases and reaches 13% in the case of a Bi1.8Lu1.2Fe3.6Al1.4O12 magnetic film. Further, it is demonstrated that the TMOKE vanishes at the high-symmetry points of the Brillouin zone (at the Γ and X points). The main enhancement of the TMOKE takes place near the resonances of the surface plasmon polaritons (SPPs) at the metal/magnetic–dielectric interface. However, near the degenerate resonances of the SPPs at the air/metal and metal/magnetic–dielectric interfaces the TMOKE is increased by the air/metal SPPs as well. This phenomenon is explained in terms of a coupled oscillator model.
Highlights
Papers on the interplay between SPPs and magneto-optics addressed SPPs propagating along the smooth surface of a ferromagnetic film [31, 32] or along a smooth semiconductor surface in an external transverse magnetic field [33, 34]
This enhancement is mediated by the SPPs at the metal/magnetic–dielectric interface leading to Fano resonances in the transmittance and reflectance spectra that are sensitive to a transverse magnetic field
We concentrate our studies on several features of the transverse magneto-optical Kerr effect (TMOKE) in magneto-plasmonic crystals (MPCs) of similar structure consisting of a gold grating on top of a magnetic layer of bismuth-substituted rareearth iron garnet on a gadolinium gallium garnet (GGG) substrate
Summary
Each MPC sample under study in this paper consists of a nanometer-sized gold grating on top of a bismuth iron garnet (BIG) magnetic film of few micrometers thickness deposited onto a GGG substrate. In order to illustrate the origin of the higher TMOKE values, we compare its magnetic field dependence in samples with different bismuth substitution levels. For sample 2, whose bismuth substitution level is cBi ≈ 1, the magnetic field dependence is given by the red dots For this sample the saturation value of the TMOKE amplitude lies around 7%. In the same range of angles, enhanced optical transmission is observed, which exceeds 25% This value, which is considerably higher than would be expected from direct transmission through the grating slits, involves tunneling of the air/metal SPP to the metal/magnetic–dielectric interface due to the finite grating depths and subsequent radiative scattering into the forward direction [43]. It supports the above reasoning by showing simultaneous excitation of the air/metal and metal/magnetic–dielectric SPPs
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