Tuning the magneto-optical response of nanosize ferromagnetic Ni disks using the phase of localized plasmons

Horizontal aluminum magneto-plasmonic metasurface for efficient magneto-optical Kerr modulation and sensing in the ultraviolet range

Most of the plasmonic nanostructures utilized for magneto-optical (MO) enhancement have been limited to noble metals with resulting enhancement in the visible and infrared spectral range. Here, we designed a horizontal aluminum magneto-plasmonic metasurface, with the ability to control the Kerr rotation angle and enhance the RI sensing performance based on magneto-plasmons, by exploiting the polarization degree of freedom in the ultraviolet range. The surface composes of L-shaped magnetic dielectric embedded in the Al film. The reflection spectrum and the Kerr rotation angle map are both symmetric about the polarization angle of 45° and 135°. It is demonstrated that the sign change of the two maximal Kerr rotation angles at polarization angle of 0° and 90°, originates from the relative contribution of the two mutually orthogonal oscillating electric dipoles. In addition, the RI sensing FoM based on Kerr reversal at 372 nm of this structure reaches 5000/RIU, which is superior to the result in the visible or infrared range (1735/RIU). The results of our investigation demonstrate the potential of Al-based magneto-plasmonic effect and offer opportunities to push the MO spectral response out of the visible range into the ultraviolet range.

Magnetic Circular Dichroism Elucidates Molecular Interactions in Aggregated Chiral Organic Materials

Chiral materials formed by aggregated organic compounds play a fundamental role in chiral optoelectronics, photonics and spintronics. Nonetheless, a precise understanding of the molecular interactions involved remains an open problem. Here we introduce magnetic circular dichroism (MCD) as a new tool to elucidate molecular interactions and structural parameters of a supramolecular system. A detailed analysis of MCD together with electronic circular dichroism spectra combined to ab initio calculations unveils essential information on the geometry and energy levels of a self-assembled thin film made of a carbazole di-bithiophene chiral molecule. This approach can be extended to a generality of chiral organic materials and can help rationalizing the fundamental interactions leading to supramolecular order. This in turn could enable a better understanding of structure-property relationships, resulting in a more efficient material design.

Inert gas condensation made bimetallic FeCu nanoparticles – plasmonic response and magnetic ordering

Bimetallic FeCu nanoparticles of narrow size distribution produced by inert gas condensation (IGC) technique exhibit functional plasmonic and magnetic properties and can be considered as a promising system for the development of biosensors.

Analytical solution to electromagnetic wave transport in planar magneto-optical waveguide: modal dispersion, coupling, and nonreciprocal flow

The magneto-optical (MO) materials are essential for designing nonreciprocal devices, like isolators and circulators. Even though the study of MO effect has a long history, the recent works of fabricating nonreciprocal nanostructures, novel MO metamaterials, and topological photonics have garnered significant attention in both theoretical and experimental research of MO materials. In this work, we consider the planar MO waveguide mode. By setting the general form of the fields and utilizing the boundary conditions, the analytical solution of MO modes is obtained. We have shown the potential of such effective solution in analyzing the dispersions and transport behaviors of MO modes in the waveguide. Crossings and avoided crossings of modes will happen, which may due to the strong coupling of TE and TM modes in the waveguide. Faraday rotation can be observed during the propagation of MO modes and the energy flow will precess in the waveguide. These results can be applied in predicting the evolution of the modes in MO waveguides, which has potential in designing MO nonreciprocal devices.

All-dielectric magnetophotonic gratings for maximum TMOKE enhancement

All-dielectric nanophotonic devices are promising candidates for future lossless (bio)sensing and telecommunication applications. Active all-dielectric magnetophotonic devices, where the optical properties can be controlled by an externally applied magnetic field, have triggered great research interest. However, magneto-optical (MO) effects are still low for applications. Here, we demonstrate a concept for the enhancement of the transverse MO Kerr effect (TMOKE), with amplitudes of up to 1.85, i.e., close to the maximum theoretical values of ±2 (in transmission). Our concept exploits the lateral leaky Bloch-modes to enhance the TMOKE, under near-zero transmittance conditions. Potential applications in (bio)sensing structures are numerically demonstrated. The effects of optical losses were studied using different combinations of materials. Significantly, we demonstrate TMOKE enhancements of two orders of magnitude in relation to recent experimental studies, using the same building materials.

Magneto-Optical Activity in Nonmagnetic Hyperbolic Nanoparticles

Active nanophotonics can be realized by controlling the optical properties of materials with external magnetic fields. Here, we explore the influence of optical anisotropy on the magneto-optical activity in nonmagnetic hyperbolic nanoparticles. We demonstrate that the magneto-optical response is driven by the hyperbolic dispersion via the coupling of metallic-induced electric and dielectric-induced magnetic dipolar optical modes with static magnetic fields. Magnetic circular dichroism experiments confirm the theoretical predictions and reveal tunable magneto-optical activity across the visible and near infrared spectral range.

Strong Interfacial Coupling of Tunable Ni-NiO Nanocomposite Thin Films Formed by Self-Decomposition

The next-generation spintronic devices including memristors, tunneling devices, or stochastic switching exert surging demands on magnetic nanostructures with novel coupling schemes. Taking advantage of a phase decomposition mechanism, a unique Ni-NiO nanocomposite has been demonstrated using a conventional pulsed laser deposition technique. Ni nanodomains are segregated from NiO and exhibit as faceted "emerald-cut" morphologies with tunable dimensions affected by the growth temperature. The sharp interfacial transition between ferromagnetic (002) Ni and antiferromagnetic (002) NiO, as characterized by high-resolution transmission electron microscopy, introduces a strong exchange bias effect and magneto-optical coupling at room temperature. In situ heating-cooling X-ray diffraction (XRD) study confirms an irreversible phase transformation between Ni and NiO under ambient atmosphere. Synthesizing highly functional two-phase nanocomposites with a simple bottom-up self-assembly via such a phase decomposition mechanism presents advantages in terms of epitaxial quality, surface coverage, interfacial coupling, and tunable nanomagnetism, which are valuable for new spintronic device implementation.

Dielectric Effects in FeO x -Coated Au Nanoparticles Boost the Magnetoplasmonic Response: Implications for Active Plasmonic Devices

Plasmon resonance modulation with an external magnetic field (magnetoplasmonics) represents a promising route for the improvement of the sensitivity of plasmon-based refractometric sensing. To this purpose, an accurate material choice is needed to realize hybrid nanostructures with an improved magnetoplasmonic response. In this work, we prepared core@shell nanostructures made of an 8 nm Au core surrounded by an ultrathin iron oxide shell (≤1 nm). The presence of the iron oxide shell was found to significantly enhance the magneto-optical response of the noble metal in the localized surface plasmon region, compared with uncoated Au nanoparticles. With the support of an analytical model, we ascribed the origin of the enhancement to the shell-induced increase in the dielectric permittivity around the Au core. The experiment points out the importance of the spectral position of the plasmonic resonance in determining the magnitude of the magnetoplasmonic response. Moreover, the analytical model proposed here represents a powerful predictive tool for the quantification of the magnetoplasmonic effect based on resonance position engineering, which has significant implications for the design of active magnetoplasmonic devices.

Boosting the figure of merit of refractive index sensing via magnetoplasmon in H-shaped magnetoplasmonic crystals

Nanoscale refractive index (RI) sensors based on plasmonic structures usually suffer from a low figure of merit (FoM) due to the broad linewidth of the resonance peaks. Here, we report a magnetoplasmon-based RI sensing method with high FoM in the designed H-shaped magnetoplasmonic crystals. Instead of the light intensity spectrum, the Faraday signal is detected to analyze the changes of the surrounding RI. Sharp resonance with extremely narrow linewidth is obtained by plotting the reciprocal Faraday rotation near the null point region. Therefore, the FoM is hugely enhanced, and a theoretical value exceeding 1775/RIU is achieved, which is one order of magnitude higher than has ever been reported, to the best of our knowledge, for the RI sensor based on the Faraday effect. The Faraday reversal and the enhanced FoM arise from the Fano resonance. These findings are of potential value for practical high performance biochemical sensors.

Near-field mechanism of the enhanced broadband magneto-optical activity of hybrid Au loaded Bi:YIG

We unravel the underlying near-field mechanism of the enhancement of the magneto-optical activity of bismuth-substituted yttrium iron garnet films (Bi:YIG) loaded with gold nanoparticles. The experimental results show that the embedded gold nanoparticles lead to a broadband enhancement of the magneto-optical activity with respect to the activity of the bare Bi:YIG films. Full vectorial near- and far-field simulations demonstrate that this broadband enhancement is the result of a magneto-optically enabled cross-talking of orthogonal localized plasmon resonances. Our results pave the way to the on-demand design of the magneto-optical properties of hybrid magneto-plasmonic circuitry.

Enhanced magnetic modulation of light polarization exploiting hybridization with multipolar dark plasmons in magnetoplasmonic nanocavities

Enhancing magneto-optical effects is crucial for reducing the size of key photonic devices based on the non-reciprocal propagation of light and to enable active nanophotonics. Here, we disclose a currently unexplored approach that exploits hybridization with multipolar dark modes in specially designed magnetoplasmonic nanocavities to achieve a large enhancement of the magneto-optically induced modulation of light polarization. The broken geometrical symmetry of the design enables coupling with free-space light and hybridization of the multipolar dark modes of a plasmonic ring nanoresonator with the dipolar localized plasmon resonance of the ferromagnetic disk placed inside the ring. This hybridization results in a low-radiant multipolar Fano resonance that drives a strongly enhanced magneto-optically induced localized plasmon. The large amplification of the magneto-optical response of the nanocavity is the result of the large magneto-optically induced change in light polarization produced by the strongly enhanced radiant magneto-optical dipole, which is achieved by avoiding the simultaneous enhancement of re-emitted light with incident polarization by the multipolar Fano resonance. The partial compensation of the magneto-optically induced polarization change caused by the large re-emission of light with the original polarization is a critical limitation of the magnetoplasmonic designs explored thus far and that is overcome by the approach proposed here.

Magneto-plasmonic properties of Ag-Co composite nano-triangle arrays

The magneto-plasmonic properties of Ag-Co composite nano-triangle arrays are investigated. Both plasmonic and magnetic properties of the samples are found to strongly depend on the composition ratio of Ag and Co. Composite nano-triangle arrays exhibit strong plasmonic properties and low magneto-optics (MO) effect with high composition of Ag, and vice versa. The enhanced magneto-optic effect is also observed to be coincident with the localized surface plasmon resonance (LSPR) properties, i.e. the maximum Faraday effect occurs at the LSPR wavelength, which is due to locally high E-field. The composite triangle arrays with the 60% Co content show high plasmonic-MO performances characterized by magneto-optics-plasmonic correlation factor. All experimental results are confirmed by finite-difference time domain calculations.

Tunable magnetoplasmonics in lattices of Ni/SiO2/Au dimers

We present a systematic study on the optical and magneto-optical properties of Ni/SiO₂/Au dimer lattices. By considering the excitation of orthogonal dipoles in the Ni and Au nanodisks, we analytically demonstrate that the magnetoplasmonic response of dimer lattices is governed by a complex interplay of near- and far-field interactions. Near-field coupling between dipoles in Ni and low-loss Au enhances the polarizabilty of single dimers compared to that of isolated Ni nanodisks. Far-field diffractive coupling in periodic lattices of these two particle types enlarges the difference in effective polarizability further. This effect is explained by an inverse relationship between the damping of collective surface lattice resonances and the imaginary polarizability of individual scatterers. Optical reflectance measurements, magneto-optical Kerr effect spectra, and finite-difference time-domain simulations confirm the analytical results. Hybrid dimer arrays supporting intense plasmon excitations are a promising candidate for active magnetoplasmonic devices.

Strengthen of magnetic anisotropy of Au/Co/Au nanostructure by surface plasmon resonance

We experimentally demonstrated the increase of in-plane magnetic anisotropy in Au/Co/Au nanostructures by localized surface plasmon resonance (LSPR). When an array of Au/Co/Au square patch nanostructures was illuminated with linearly polarized light whose wavelength was 750 nm, the localized surface plasmons were resonantly excited in the nanostructures. From the measurement results of polar magneto-optical Kerr effect curves, we observed the magnetic anisotropy field increase in the Au/Co/Au nanostructure due to the excited surface plasmons. The in-plane magnetic anisotropy energy density was increased about 24%.

Tuning the magneto-optical Kerr effect by the nanograting cross section

The magneto-optical Kerr effect, especially the Kerr slope, is of great significance to magneto-optical devices. Herein, we developed a method to tune the magneto-optical effect by the nanograting cross section. Both the simulation and experiment confirm that the resonance strength of the plasmon can be modulated by the nanograting cross section, resulting in the large Kerr slope and Kerr rotation. By designing the nanograting cross section, we obtained the Kerr slope of 0.397°/nm, which is 4 orders of magnitude higher than the reported results. And the Kerr rotation of the magnetic nanograting reaches up to 1.218°, which is 24 times higher than the flat Co film. Such a huge enhancement on the Kerr slope and the Kerr rotation may have profound applications in magneto-optical devices in the future.

Dispersion of the Retardation of a Photoelastic Modulator

Recently, ellipsometry and polarization imaging using photoelastic modulators (PEMs) have been applied to a wide spectral range, from vacuum ultraviolet to the mid-infrared wavelengths. To ensure high accuracy polarization performance, the accurate calibration of the retardation of PEM is crucial. In this report, the dispersion of the retardation of the PEM is studied. According to the operational principle of PEM, their retardation can be separated into independent dispersion and driving terms. The effect attributed to the dispersion on PEM retardation calibration is experimentally explored. These experiments indicate that the dispersion term can be defined in advance using the refractive index of the photoelastic crystal under incident light, and that the driving term is directly proportional to the amplitude of the driving voltage. The calibration method for the retardation amplitude of the PEM, which considers dispersion, is also demonstrated. The results show that the relative deviation between the calibration and actual measurement values of PEM retardation amplitude are less than 1%. This study presents an accurate way to calibrate the PEM retardation and supports the application of PEMs in a wide range of wavelengths.

Non-reciprocal diffraction in magnetoplasmonic gratings

Phase-matching conditions-used to bridge the wave vector mismatch between light and surface plasmon polaritons (SPPs)-have been exploited recently to enable nonreciprocal optical propagation and enhanced magneto-optic responses in magnetoplasmonic systems. Here we show that using diffraction in conjunction with plasmon excitations leads to a photonic system with a more versatile and flexible response. As a testbed, we analyzed diffracted magneto-optical effects in magnetoplasmonic gratings, where broken time-reversal symmetry induces frequency shifts in the energy and angular spectra of plasmon resonance. These result in exceptionally large responses in the diffracted magneto-optical effect. The concepts presented here can be used to develop non-reciprocal optical devices that exploit diffraction, in order to achieve tailored electromagnetic responses.

Magnetoplasmonic nanograting geometry enables optical nonreciprocity sign control

We experimentally demonstrate a disruptive approach to control magnetooptical nonreciprocal effects. It has been known that the combination of a magneto-optically (MO) active substrate and extraordinary transmission (EOT) effects through deep-subwavelength nanoslits of a noble metal grating, leads to giant enhancements of the magnitude of the MO effects that would normally be obtained on just the bar substrate. This was demonstrated both in the transmission configuration, where the OET is directly observed, as well as in reflection configuration, where an increase of a transmitted power results in a decrease in reflected power. We show here that even more than just an enhancement, the MO effects can also undergo a sign reversal by achieving a hybridization of the different types of resonances at play in these EOT nanogratings. By tuning the geometrical profile of the grating's slits, one can engineer - for a fixed wavelength and fixed magnetization - the transverse MO Kerr effect (TMOKE) reflectivity of such a magnetoplasmonic system to be enhanced, extinguished or inversely enhanced. We have fabricated gold gratings with varying nanoslit widths on a Bi-substituted gadolinium iron garnet and experimentally confirmed such a behavior using a customized magneto-optic Mueller matrix ellipsometer. This demonstration allows new design paradigms for integrated nonreciprocal circuits and biochemical sensors with increased sensitivity and reduced footprint.

Nonreciprocal hybrid magnetoplasmonics

The Faraday effect describes the phenomenon that a magnetized material can alter the polarization state of transmitted light. Interestingly, unlike most light-matter interactions in nature, it breaks Lorentz reciprocity. This exceptional behavior is utilized for applications such as optical isolators, which are core elements in communication and laser systems. While there is high demand for sub-micron nonreciprocal photonic devices, the realization of such systems is extremely challenging as conventional magneto-optic materials only provide weak magneto-optic response within small volumes. Plasmonics could be a key to overcome this hurdle in the future: over the last years there have been several lines of work demonstrating that different types of metallic nanostrutures can be utilized to greatly enhance the magneto-optic response of conventional materials. In this review we give an overview over the state of the art in the field and highlight recent developments on hybrid plasmonic Faraday rotators. Our discussions are mainly focused on the visible and near-infrared wavelength regions and cover both experimental realizations as well as analytical descriptions. Special attention will be paid to recent developments on hybrid plasmonic thin film systems consisting of gold and europium chalcogenides.

Plasmon induced magneto-optical enhancement in metallic Ag/FeCo core/shell nanoparticles synthesized by colloidal chemistry

The combination of magnetic and plasmonic materials and their nanostructurization have revealed a prominent pathway to develop novel photonic materials for the active control of the light polarization using a magnetic field. Until now, physical growth methods have been the only exploitable approach to prepare these types of nanostructures. Here, we demonstrate the chemical synthesis of magneto-plasmonic core/shell nanocrystals with enhanced magnetic control of optical properties comparable to the best results reported for nanostructure growth by physical methods. Ag/FeCo core/shell nanocrystals were synthesized using a combination of hot injection and polyol approaches, demonstrating that the well-defined structures of both components, their interface and the optimized morphology, where the plasmonic and magnetic components are placed in the core and the shell regions, are responsible for the observed large enhancement of magnetic control of light polarization. Therefore, there is a possibility to develop tunable magneto-optical materials from hybrid magneto-plasmonic structures synthesized by chemical methods.

Magneto-Optical properties of noble-metal nanostructures: functional nanomaterials for bio sensing

Metallic nanostructures supporting Localized Surface Plasmon Resonances (LSPR) are characterized by their unique ability to control and manipulate light at the nanoscale. Noble metal nanostructures, such as gold nanostructures, are demonstrating to exhibit magneto-optic activity in the presence of modulated magnetic field of low intensity in transversal configuration (T-MOKE). Validation of experimental findings was achieved by numerical simulations based on Finite Element Method (FEM) techniques. The developed numerical models allowed studying the combination of the T-MOKE effect with the localized surface plasmon resonance of metal nanoparticles. Numerical optical and magneto-optical spectra provided a deep insight on the physical aspects behind the magneto-optical activity of metal nanostructures strictly related to direction of oscillations electrical dipoles generated in resonance conditions. Additionally the MO signal was characterized as a transducing signal for refractive index sensing in liquid conditions. The outcome is an increase in the limit of detection of magneto optical transducer with respect to traditional plasmonic sensors. A new strategy for magneto-plasmonic sensing based on the use of glass supported -Au nanostructures based on their MO properties has put forward.

Enhancing the magneto-optical Kerr effect through the use of a plasmonic antenna

We employ an extended finite-element model as a design tool capable of incorporating the interaction between plasmonic antennas and magneto-optical effects, specifically the magneto-optical Kerr effect (MOKE). We first test our model in the absence of an antenna and show that for a semi-infinite thin-film, good agreement is obtained between our finite-element model and analytical calculations. The addition of a plasmonic antenna is shown to yield a wavelength dependent enhancement of the MOKE. The antenna geometry and its separation from the magnetic material are found to impact the strength of the observed MOKE signal, as well as the antenna's resonance wavelength. Through optimization of these parameters we achieved a MOKE enhancement of more than 100 when compared to a magnetic film alone. These initial results show that our modeling methodology offers a tool to guide the future fabrication of hybrid plasmonic magneto-optical devices and plasmonic antennas for magneto-optical sensing.

Magnetic Control of the Chiroptical Plasmonic Surfaces

A major challenge facing plasmon nanophotonics is the poor dynamic tunability. A functional nanophotonic element would feature the real-time sizable tunability of transmission, reflection of light's intensity or polarization over a broad range of wavelengths, and would be robust and easy to integrate. Several approaches have been explored so far including mechanical deformation, thermal, or refractive index effects, and all-optical switching. Here we devise an ultrathin chiroptical surface, built on two-dimensional nanoantennas, where the chiral light transmission is controlled by the externally applied magnetic field. The magnetic field-induced modulation of the far-field chiroptical response with this surface exceeds 100% in the visible and near-infrared spectral ranges, opening the route for nanometer-thin magnetoplasmonic light-modulating surfaces tuned in real time and featuring a broad spectral response.

Tunable Magneto-Optical Kerr Effects of Nanoporous Thin Films

Magnetoplasmonics, combining magnetic and plasmonic functions, has attracted increasing attention owing to its unique magnetic and optical properties in various nano-architectures. In this work, Ag, CoFeB and ITO layers are fabricated on anodic aluminum oxide (AAO) porous films to form hybrid multi-layered nanoporous thin films by magnetron sputtering deposition process. The designed nanostructure supports localized surface plasmon resonance (LSPR) and tunable magneto-optical (MO) activity, namely, the sign inversion, which can be controlled by AAO porous film geometry (pore diameter and inter-pore spacing) flexibly. The physical mechanism of this special MO phenomena is further analyzed and discussed by the correlation of Kerr rotation and electronic oscillations controlled by the surface plasmon resonance that is related to the nanoporous structure.

Fast and full range measurements of ellipsometric parameters using a 45° dual-drive symmetric photoelastic modulator

The fast and full range measurements of ellipsometric parameters ψ and Δ using a 45° dual-drive symmetric photoelastic modulator (PEM) are proposed. The PEM operates in a pure traveling modulation mode with a constant retardation magnitude and the modulation axis performing circular motion. A field programmable gate array is used to control the PEM and fulfill the data processing. The parameters sin 2ψ sinΔ, sin 2ψ cosΔ, and sin 2ψ can be measured simultaneously, providing accurate measurements of ψ and Δ over the full range. The experimental results show that the repeatability and sensitivity of this system are at 10^-3°, and the data acquisition rate is 1 ms/point.

Resonant magneto-optic Kerr effects of a single Ni nanorod in the Mie scattering regime

We present a systematic, theoretical investigation of the polar magneto-optical (MO) Kerr effects of a single Ni nanorod in the Mie regime. The MO Kerr rotation, ellipticity, amplitude ratio, and phase shift are calculated as a function of the length and width of the nanorod. The electric field amplitude ratio of the MO Kerr effect is locally maximized when the nanorod supports a plasmonic resonance in the polarization state orthogonal to the incident light. The plasmonic resonances directly induced by the incident light do not enhance the amplitude ratio. In the Mie regime, multiple local maxima of the MO Kerr activity are supported by the resonant modes with different modal characteristics. From the viewpoint of first-order perturbation analysis, the spatial overlap between the incident-light-induced electric field and the Green function determines the local maxima.

Anisotropic Nanoantenna-Based Magnetoplasmonic Crystals for Highly Enhanced and Tunable Magneto-Optical Activity

We present a novel concept of a magnetically tunable plasmonic crystal based on the excitation of Fano lattice surface modes in periodic arrays of magnetic and optically anisotropic nanoantennas. We show how coherent diffractive far-field coupling between elliptical nickel nanoantennas is governed by the two in-plane, orthogonal and spectrally detuned plasmonic responses of the individual building block, one directly induced by the incident radiation and the other induced by the application of an external magnetic field. The consequent excitation of magnetic field-induced Fano lattice surface modes leads to highly tunable and amplified magneto-optical effects as compared to a continuous film or metasurfaces made of disordered noninteracting magnetoplasmonic anisotropic nanoantennas. The concepts presented here can be exploited to design novel magnetoplasmonic sensors based on coupled localized plasmonic resonances, and nanoscale metamaterials for precise control and magnetically driven tunability of light polarization states.

Light Localization and Magneto-Optic Enhancement in Ni Antidot Arrays

We reveal an explicit strategy to design the magneto-optic response of a magneto-plasmonic crystal by correlating near- and far-fields effects. We use photoemission electron microscopy to map the spatial distribution of the electric near-field on a nanopatterned magnetic surface that supports plasmon polaritons. By using different photon energies and polarization states of the incident light we reveal that the electric near-field is either concentrated in spots forming a hexagonal lattice with the same symmetry as the Ni nanopattern or in stripes oriented along the Γ-K direction of the lattice and perpendicular to the polarization direction. We show that the polarization-dependent near-field enhancement on the patterned surface is directly correlated to both the excitation of surface plasmon polaritons on the patterned surface as well as the enhancement of the polar magneto-optical Kerr effect. We obtain a relationship between the size of the enhanced magneto-optical behavior and the polarization and wavelength of optical excitation. The engineering of the magneto-optic response based on the plasmon-induced modification of the optical properties introduces the concept of a magneto-plasmonic meta-structure.

Magnetic circular dichroism of non-local surface lattice resonances in magnetic nanoparticle arrays

Subwavelength metallic particles support plasmon resonances that allow extreme confinement of light down to the nanoscale. Irradiation with left- and right hand circularly polarized light results in the excitation of circular plasmon modes with opposite helicity. The Lorenz force lifts the degeneracy of the two modes in magnetic nanoparticles. Consequently, the confinement and frequency of localized surface plasmon resonances can be tuned by an external magnetic field. In this paper, we experimentally demonstrate this effect for nickel nanoparticles using magnetic circular dichroism (MCD). Besides, we show that non-local surface lattice resonances in periodic arrays of the same nanoparticles significantly enhance the MCD signal. A numerical model based on the modified long wavelength approximation is used to reproduce the main features in the experimental spectra and provide design rules for large MCD effects in sensing applications.

Hybrid plasmonic lattices with tunable magneto-optical activity

We report on the optical and magneto-optical response of hybrid plasmonic lattices that consist of pure nickel and gold nanoparticles in a checkerboard arrangement. Diffractive far-field coupling between the individual emitters of the lattices results in the excitation of two orthogonal surface lattice resonance modes. Local analyses of the radiation fields indicate that both the nickel and gold nanoparticles contribute to these collective resonances and, thereby, to the magneto-optical activity of the hybrid arrays. The strong effect of noble metal nanoparticles on the magneto-optical response of hybrid lattices opens up new avenues for the realization of sensitive and tunable magneto-plasmonic nanostructures.

Enhanced Magneto-Optical Edge Excitation in Nanoscale Magnetic Disks

We report unexpected enhancements of the magneto-optical effect in ferromagnetic Permalloy disks of diameter D<400 nm. The effect becomes increasingly pronounced for smaller D, reaching more than a 100% enhancement for D=100 nm samples. By means of experiments and simulations, the origin of this effect is identified as a nanoscale ring-shaped region at the disk edges, in which the magneto-optically induced electric polarization is enhanced. This leads to a modification of the electromagnetic near fields and causes the enhanced magneto-optical excitation, independent from any optical resonance.

Magneto-optical properties of one-dimensional orderly nanocorrugation made from magnetic quadrilayer films

Magneto-optical (MO) Kerr effect and optical reflectance are investigated in the visible light region for one-dimensional orderly nanocorrugation of magnetic quadrilayer films. We find that the MO enhancement originates from the combined action between cavity effect and surface plasmon resonance. The coupling between surface plasmon polaritions and localized surface plasmons cannot only enhance the magnitude of Kerr angle, but also alter the sign of Kerr rotation. In addition, the MO properties on the nanocomposite films can be tuned by the thickness of the intermediate HfO2 layer due to the cavity effect in multilayer.

Active magnetoplasmonic ruler

Plasmon rulers are an emerging concept in which the strong near-field coupling of plasmon nanoantenna elements is employed to obtain structural information at the nanoscale. Here, we combine nanoplasmonics and nanomagnetism to conceptualize a magnetoplasmonic dimer nanoantenna that would be able to report nanoscale distances while optimizing its own spatial orientation. The latter constitutes an active operation in which a dynamically optimized optical response per measured unit length allows for the measurement of small and large nanoscale distances with about 2 orders of magnitude higher precision than current state-of-the-art plasmon rulers. We further propose a concept to optically measure the nanoscale response to the controlled application of force with a magnetic field.

Surface lattice resonances and magneto-optical response in magnetic nanoparticle arrays

Structuring metallic and magnetic materials on subwavelength scales allows for extreme confinement and a versatile design of electromagnetic field modes. This may be used, for example, to enhance magneto-optical responses, to control plasmonic systems using a magnetic field, or to tailor magneto-optical properties of individual nanostructures. Here we show that periodic rectangular arrays of magnetic nanoparticles display surface plasmon modes in which the two directions of the lattice are coupled by the magnetic field-controllable spin-orbit coupling in the nanoparticles. When breaking the symmetry of the lattice, we find that the optical response shows Fano-type surface lattice resonances whose frequency is determined by the periodicity orthogonal to the polarization of the incident field. In striking contrast, the magneto-optical Kerr response is controlled by the period in the parallel direction. The spectral separation of the response for longitudinal and orthogonal excitations provides versatile tuning of narrow and intense magneto-optical resonances.

Magneto-Plasmonics and Resonant Interaction of Light with Dynamic Magnetisation in Metallic and All-Magneto-Dielectric Nanostructures

A significant interest in combining plasmonics and magnetism at the nanoscale gains momentum in both photonics and magnetism sectors that are concerned with the resonant enhancement of light-magnetic-matter interaction in nanostructures. These efforts result in a considerable amount of literature, which is difficult to collect and digest in limited time. Furthermore, there is insufficient exchange of results between the two research sectors. Consequently, the goal of this review paper is to bridge this gap by presenting an overview of recent progress in the field of magneto-plasmonics from two different points of view: magneto-plasmonics, and magnonics and magnetisation dynamics. It is expected that this presentation style will make this review paper of particular interest to both general physical audience and specialists conducting research on photonics, plasmonics, Brillouin light scattering spectroscopy of magnetic nanostructures and magneto-optical Kerr effect magnetometry, as well as ultrafast all-optical and THz-wave excitation of spin waves. Moreover, readers interested in a new, rapidly emerging field of all-dielectric nanophotonics will find a section about all-magneto-dielectric nanostructures.

Ultrasensitive and label-free molecular-level detection enabled by light phase control in magnetoplasmonic nanoantennas

Systems allowing label-free molecular detection are expected to have enormous impact on biochemical sciences. Research focuses on materials and technologies based on exploiting localized surface plasmon resonances in metallic nanostructures. The reason for this focused attention is their suitability for single-molecule sensing, arising from intrinsically nanoscopic sensing volume and the high sensitivity to the local environment. Here we propose an alternative route, which enables radically improved sensitivity compared with recently reported plasmon-based sensors. Such high sensitivity is achieved by exploiting the control of the phase of light in magnetoplasmonic nanoantennas. We demonstrate a manifold improvement of refractometric sensing figure-of-merit. Most remarkably, we show a raw surface sensitivity (that is, without applying fitting procedures) of two orders of magnitude higher than the current values reported for nanoplasmonic sensors. Such sensitivity corresponds to a mass of ~ 0.8 ag per nanoantenna of polyamide-6.6 (n=1.51), which is representative for a large variety of polymers, peptides and proteins.

Infrared-induced variation of the magnetic properties of a magnetoplasmonic film with a 3D sub-micron periodic triangular roof-type antireflection structure

A carbon-matrix nickel composite magnetoplasmonic film with a 3D sub-micron periodic triangular roof-type antireflection structure (SPTAS) was fabricated via a simple and promising method that combines chemosynthesis with biomimetic techniques. The Troides helena (Linnaeus) forewing (T_FW) was chosen as the biomimetic template. The carbon-matrix Ni wing fabricated via electroless Ni deposition for 6 h (CNMF_6h) exhibits enhanced infrared absorption. Over a wavelength range (888-2500 nm), the enhancement of the infrared absorption of CNMF_6h is up to 1.85 times compared with the T_FW. Furthermore, infrared excitation induces a photothermal effect that results in variation in the magnetic properties of the carbon-matrix Ni wing. The magnetic properties were also confirmed using atomic force microscopy (AFM) and magnetic force microscopy (MFM). The good correlation between the AFM and MFM images demonstrates that the surface of the SPTAS of CNMF_6h exhibits strong magnetic properties. The infrared induced photothermal effect that results in magnetic variation is promising for use in the design of novel magnetoplasmonic films with potential applications in infrared information recording and heat-assisted magnetic recording.

Magnetoplasmonic design rules for active magneto-optics

Light polarization rotators and nonreciprocal optical isolators are essential building blocks in photonics technology. These macroscopic passive devices are commonly based on magneto-optical Faraday and Kerr polarization rotation. Magnetoplasmonics, the combination of magnetism and plasmonics, is a promising route to bring these devices to the nanoscale. We introduce design rules for highly tunable active magnetoplasmonic elements in which we can tailor the amplitude and sign of the Kerr response over a broad spectral range.