The Fano Resonance And Magneto-optical Effects In Magnetoplasmonic Nanostructures

The development of nano-photonics demands more efficient and delicate control of light. In the last decade, we have witnessed the booming development of plasmonics in which the light is concentrated and manipulated in the sub-wavelength scale due to the excitation of surface plasmons (SPs). Particularly,-the magnetoplasmonics have so far drawn a great attention due to their multifunctionality that allows active control of SPs and significant enhancement of magneto-optical (MO) effects. This leads to a wide range of applications in new types of biosensors, nano-antennas, all-optical magnetic data storage, optical isolators and modulators, etc. However, significant challenges still remain because of the difficulty in the design of spectrally tunable systems exhibiting novel plasmonic and magneto-optical responses simultaneously.As we know, simple nanostructures such as disks, nanowires and rings, support localized surface plasmons (LSPs) that are sensitive to the variations in size and shape. The surface plasmon polaritons (SPPs), on the other hand, are propagating electromagnetic waves bound to the interface between metals and dielectrics. Interestingly, two or more coherent SPs modes may coexist in a complex plasmonic system, resulting in a fascinating Fano resonance. Compared with the conventional simple resonance modes, the Fano resonance possesses a steep, asymmetric line shape and an inherently excellent sensitivity to the changes in geometry or dielectric environment. Therefore it is of particular interest to implant the Fano resonance into magnetoplasmonic systems, as it has the potential to offer more novel plasmonic and MO properties with outstanding controllability.Recent investigations on the magnetoplasmonic system have demonstrated plenty of different interesting phenomena, they mainly focus on the demonstration of the excitation of either LSPs or SPPs, and consequently the enhancement of MO responses. However, few of them reveal that how the simple surface plasmon modes can be effectively coupled, and further how this coupling effect can be properly manipulated to trigger novel magneto-optical responses. The primary challenge for a convenient tunability in the design of Fano resonance, is the spectral engineering via controlled coupling of proper plasmon modes. This difficulty is more severe when taking into account the strong damping of SPs in FM metals arised from the large imaginary part of their dielectric constant.In this work, we devote to combine the extraordinary Fano resonance with magneto-optics in well-designed plasmonic nanostructures based on the interference lithography, electrochemical deposition and magnetron sputtering.3different kinds of structures are investigated in our experiments:2D square array of Ni nanodisks on Co film,1D Co line array and1D Ag/Co/Ag multilayer line array. In our samples the Fano resonance can be realized and properly tuned by a controlled coupling between LSPs and SPPs. Moreover, we demonstrate a5times enhancement and an extremely sharp reversal of longitudinal Kerr rotation, as well as a strong transversal Kerr effect up to5%, which is at least one order of magnitude larger than pure ferromagnetic films. The incorporations of Fano resonance into traditional ferromagnetic materials open up a new way to obtain and manipulate novel magneto-optical responses, which is far beyond what is offered by the intrinsic properties of the materials. The controlled enhancement and reversal of Kerr rotation observed in our experiments provide a possibility to develop new magneto-optics based technologies and devices.