Transverse Magneto-optical Kerr Effect Research Articles

Design of a high-resolution magneto-plasmonic biosensor for analyte detection

Abstract This paper introduces the design of a magneto-plasmonic refractometric sensor aimed at achieving high resolution. This sensor consists of arrays of gold nanowires and layers of SiO2 and Co6Ag94, where the analyte is placed on the gold nanowires. A p-polarized optical field with a wavelength of 631 nm is used to excite the structure, which is applied in the range of 1º to 45º. A magnetic field is applied to z-axis to create the magneto-optical effect. The reflected optical field of the samples is used to calculate the signal of the transverse magneto-optical Kerr effect (TMOKE), which shows significant changes in the refractive index of the samples and the direction of the magnetic field. The highest displacement is 4º. The highest value of the figure of merit (FoM) is 3611 RIU-1, and the maximum sensitivity is obtained as 71 º/RIU.

Magnetically tunable Brewster angle in uniaxial magneto-optical metamaterials for advanced integration of high-resolution sensing devices.

In this Letter, we introduce a concept to produce high-resolution, highly integrable biosensing devices. Our idea exploits the highly absorbing modes in multilayered metamaterials to maximize the transverse magneto-optical Kerr effect (TMOKE). Results are discussed in the context of dielectric uniaxial (ε eff,∥ ε eff,⊥>0) and hyperbolic metamaterial (ε eff,∥ ε eff,⊥<0) regimes. For applications in gas sensing, we obtained sensitivities of S = 46.02 deg/RIU and S = 73.91 deg/RIU when considering the system working in the uniaxial and hyperbolic regimes, respectively, with figures of merit (resolution) in the order of 310 or higher. On the contrary, when considering the system for biosensing applications (incidence from an aqueous medium), we observed that the proposed mechanism can only be successfully used in the uniaxial regime, where a sensitivity of 56.87 deg/RIU was obtained.

Unconventional Transverse Magneto‐Optical Kerr Effect in Cobalt Nanopillar Arrays

AbstractNovel magneto‐optical (MO) properties can be actualized through well‐designed nanostructures, greatly improving the application value of MO effects. As only p‐polarized light can generate transverse magneto‐optical Kerr effect (TMOKE) in traditional MO materials, it is quite challenging and valuable to effectuate TMOKE under s‐polarization incidence at optical frequencies. The constructed nanopillar structures in this work can realize a clear TMOKE under both s‐polarization and p‐polarization incidences, as proved by experiments and simulations. Under s‐polarized incident light with an elevation angle of 45°, electric dipole resonance (EDR) and electric quadrupole resonance (EQR) are excited, resulting in the significant enhancement of TMOKE (five orders of magnitude higher than for the planar Co film). The intensity of s‐polarized TMOKE shows an increase with the enhancing diameter and height of the nanopillar structure. The amplitude of p‐polarized TMOKE is also appreciably increased due to the excitation of surface plasmon polaritons (SPPs) and localized surface plasmons (LSPs). Moreover, the Fe and Ni nanopillars display similar reflectivity and s‐polarized TMOKE behaviors in simulations. The s‐polarized TMOKE is unexpectedly observed in ferromagnetic metals for the first time, which builds up a considerable platform for the development and application of novel MO phenomena.

Enhancement of Transverse Magneto-Optic Kerr effect in subwavelength all-dielectric guided mode gratings with a buffer layer

We demonstrate a simple subwavelength all-dielectric photonic device with greatly enhanced transverse magneto-optical Kerr effect (TMOKE) in the transmission mode. The concept utilizes the diffracted waves of the periodic magnetic material bismuth-substituted iron garnet grating to excite the guided mode in the planar waveguide, and adds a buffer layer under the all-dielectric guided mode grating. In the study, it was found that increasing the refractive index of the buffer layer can reduce the coupling between the grating and the waveguide, so that full width at half maximum of the transmission spectra can be narrowed, and the value of TMOKE can be greatly enhanced up to 1.82. It is worth noting that the TMOKE value of the guide mode grating with buffer layer is 3 times that of those without buffer layer, thus opening up different avenues for designing efficient, integrated and low-loss magneto-optical devices. Enhanced TMOKE has great potential for applications such as biosensing/high-resolution sensing, magneto-optical modulation and magnetic measurement.

Magneto-optical heterostructures with second resonance of transverse magneto-optical Kerr effect

Two conventional magneto-plasmonic (MP) structures are firstly superimposed with mirror symmetry to form a symmetric MP heterostructure. These two MP components are separated from each other by a noble metallic layer. The unique feature of this novel heterostructure is that both magneto-plasmon modes of the up and down MP portions can be coupled as the spacer becomes thinner. This intertwining effect leads to appearance of a new peak in the angular transverse magneto-optical Kerr effect (TMOKE) curve of the heterostructure. This new peak which is reported for the first time in the TMOKE signal, is generally similar to plasmon induced transparency (PIT) phenomenon observed in plasmonic multilayered structures. We entitle this novel effect as “second resonance of TMOKE signal”. More importantly, the occurrence angle and magnitude of the second peak can be controlled by varying the thickness and material of separating layer between two MP parts. Also, the dispersion diagram of the heterostructure shows this coupling so that two branches convert into four branches by reducing the thickness of spacer. Furthermore, coupled oscillators model confirms emergence of the second peak in the TMOKE signal. These results can offer great promise for increasing sensitivity of conventional magneto-optical refractive index sensors.

Enhancement in the magneto-optical effect induced by combining multiple modes in a gold film–supported hybrid periodic gold/magnetic nanorod array

In this study, the possibility of enhanced transverse magneto-optical Kerr effect (TMOKE) and performance monitoring of a hybrid nanostructure developed by sandwiching a ferromagnetic film within a gold layer and square periodic nanorod arrays, is theoretically investigated. Based on the findings, the TMOKE signal can be enhanced approximately 33 times when compared to the referenced planar film, which is elucidated by the hybrid of modes in the magnetic film region. In addition, a high level of environmental sensor performance is simultaneously achieved by recording the wavelength resonance positions with the variation of refractive index, which is compatible with gaseous medium from 1 to 1.01, indicating that the structure of the proposal will have applications in environmental monitoring.

Transverse Magneto-Optical Kerr Effect Enhancement in Si–Ni Nanogratings by Mie and Surface Lattice Resonances

Transverse Magneto-Optical Kerr Effect Enhancement in Si–Ni Nanogratings by Mie and Surface Lattice Resonances

Enhanced Sensitivity of Magneto-Optical Surface Plasmon Resonance in the FeCu Superlattices

We demonstrated the sensitivity enhancement for magneto-optical surface plasmon resonance (MOSPR) using noble/ferromagnetic metals multilayers. The proposed structure is based on the Kretschmann configuration in the transverse magneto-optical Kerr effect (TMOKE) methods with the FeCu superlattices (SLs) as magneto-plasmonic materials and gelatin as biomolecules analyte. The dielectric constants of the FeCu SLs are taken from first principles calculation, which is performed by using a full-potential linearized augmented plane wave (FLAPW) method. The important role of the hybridization process in optical transitions has been identified, and it can be modulated by adjusting the thickness of superlattices. The dependence of the reflectivity on the dielectric constant is performed by 4×4 transfer matrix methods. It is found that the minimum reflectivity directly influences the slope of angular spectra, with a maximum slope of TMOKE signal is 12.23/degree. The change in the gelatin’s refractive index results in TMOKE signal response, then the enhancement of the sensitivity of the MOSPR system can be shown.

Strong transverse magneto-optical Kerr effect at normal incidence based on hybrid bound states in the continuum

Strong transverse magneto-optical Kerr effect at normal incidence based on hybrid bound states in the continuum

Second Harmonic Generation Versus Linear Magneto-Optical Response Studies of Laser-Induced Switching of Pinning Effects in Antiferromagnetic/Ferromagnetic Films

Composite magnetic nanostructures are a subject of high research interest, as they provide a number of exciting effects absent in live nature. Among others, much attention has been paid to the studies of exchange coupling in antiferromagnetic/ferromagnetic (AFM/FM) films, which leads to the pinning effect. It manifests itself as a widening and shift of the magnetic hysteresis loop with respect to zero value of the external magnetic field oriented along the pinning direction. In this work, we report on comparative studies of linear and nonlinear magneto-optical effects under the laser-induced switching of the pinning effect in IrMn/CoFe films of various thickness of the ferromagnetic CoFe layer. We found that the magneto-optical response of the pinned AFM/FM nanofilms appears with different hysteresis loop parameters in the transverse magneto-optical Kerr effect (MOKE) and interface-sensitive magnetization-induced second harmonic generation (SHG), indicating the diversity of the magnetic effects at interfaces compared to the bulk of the films.

Effect of granule sizes on magneto-optical spectra of nanocomposites

The magneto-optical transverse Kerr effect (TKE) spectroscopy allows non-contact investigation of nanostructures, giving valuable information about the microstructure of samples. In this paper, within the framework of effective medium approach we analyze the effect of granule size on the magneto-optical spectra of magnetic nanocomposites. We consider the influence of various microscopic parameters such as plasma frequency, relaxation time, the coefficient of the anomalous Hall effect inside the granule and on its surface on the amplitude and profile of the TKE spectrum. Three main mechanisms are considered: the quasi-classical size effect, spin–orbit interaction enhancement at the granule surface and change of the percolation threshold.

Magneto- and thermo-optic manipulation of imbert-fedorov shift for Laguerre-Gaussian beam in a graphene-VO2 multilayer structure

Imbert-Fedorov (IF) shift of Gaussian beams has been widely studied, while the IF shift of singular beams carrying Orbital Angular Momentum (OAM) also shows unique properties when reflected or refracted at optical interfaces. Here, through theoretical deduction and analysis, the IF shift of Laguerre-Gaussian beams with varying OAM in a graphene-VO2 multilayers structure is explored. The results demonstrate that the IF shift increases with the increase of topological charge l. Under the configuration of transverse magneto-optical Kerr effect (TMOKE), the IF shift increases by a factor of 10 compared to the Gaussian beam when l = 3. Additionally, under the polar magneto-optical Kerr effect (PMOKE) conditions, graphene demonstrates the magneto-optical (MO) effect and cross-polarization effect in the terahertz frequency range, and can effectively control the IF shift through the magnetic field. Both left- and right-handed circular polarization (LHCP and PHCP) exhibit asymmetry and non-reciprocity. Moreover, temperature control is achieved through the unique phase transition characteristics of VO2. These results offer novel insights into precision measurements, sensing techniques and the development of terahertz devices.

VIS-NIR TMOKE enhanced dielectric-metal hybrid structure for high performance dual-channel sensing.

Magneto-plasmon sensors based on the transverse magneto-optical Kerr effect (TMOKE) have been extensively studied in recent years. In this paper, we theoretically propose a hybrid structure composed of a one-dimensional bismuth iron garnet: yttrium iron garnet (BIG: YIG) nanowire arrays and thin film stack, which is grown on an infinite thick silicon wafer. The thin film stack, from top to bottom, consists of the following layers: BIG: YIG, SiO2, and Au. By exciting the magnetic dipole resonance mode between the cylindrical nanowires and the SPP mode on the surface of the Au film, dual-channel sensing has been achieved in both visible and infrared spectra. The results demonstrate that the TMOKE response spectrum of the structure supports ultra-narrow linewidths of 0.03 nm in the visible light range and 1.54 nm in the infrared range. By changing the refractive index of the analyte, the detected sensitivity of the sensor system in visible and infrared bands is 553 nm RIU-1 and 285 nm RIU-1, and the Figure of merit (FOM) can reach up to 69125 RIU-1 and 303 RIU-1, respectively. This work provides a theoretical basis and a feasible approach for the design of dual channel gas sensors.

Dual-polarization strong nonreciprocal thermal radiation under near-normal incidence

Performance of irreversible radiation is limited by the single polarization and large incident angles. Given potential applications of nonreciprocal thermal radiation, the implementation of irreversible radiation for both TE and TM polarizations at small angles is highly demanded. A solution that combines periodic silicon-based nanopore arrays with magneto-optical material (InAs) is proposed in this work. The results show that the absorptivity and emissivity of two polarizations are close to 98% with an incident angle of 1.5° and a high Q factor over 1680. By adjusting the applied magnetic field, the emissivity and transverse magneto-optical Kerr effect can be dynamically tuned. The validity of the calculation results is verified by the rigorous coupled-wave analysis and finite element method. Impedance matching theory and coupled mode theory are adopted to further analyze the physical origin. The proposed scheme and thermal radiator that allow nonreciprocal thermal radiation for both TE and TM polarizations at an extremely small incident angle offer valuable guidance to the development of dual-polarization nonreciprocal radiation devices.

Magneto-plasmonic grating-based structure for biosensing application

Gold with satisfactory plasmonic properties can be combined with magneto-optical material to be used as biosensors. In this theoretical work, our suggestion is to use optimized Au strips mounted on a periodic magneto-optical grating, with measurements of the transverse magneto-optical Kerr effect (TMOKE) as the basis for the sensing method. The thickness of the gold strips used is 20 nm after optimizing the structure. Considering the high cost of using gold, since the thickness of the obtained gold layer is small and only placed on the grating, this structure is expected to be economical. Also, in this research, its sensing application has been investigated, and significant results have been obtained.

Bilayer Magnetoplasmonic Grating for Enhancement of the Transverse Magneto-Optical Kerr Effect and Dual Sensing Performance by Surface Plasmon Resonance

Magnetoplasmonic nanostructures with magnetic and metallic compositions have received considerable attention because they can greatly enhance the transverse magneto-optical Kerr effect (T-MOKE) due to surface plasmon resonance (SPR) excitations, which can be used to realize extremely high detection performance. Here, a bilayer heterogeneous grating is proposed that comprises gold and cerium-substituted yttrium iron garnet layers on a gold film for remarkable SPR enhancement of the T-MOKE. Numerical simulations via the finite element method indicated that the proposed structure substantially improves the sensing performance of the incident angle and wavelength with high detection sensitivity and a figure of merit that is an order of magnitude better than previously reported results. Moreover, the proposed structure can be used to fabricate devices for sensing gaseous media.

All-magneto-optical grating bio-sensors based on enhanced transverse magneto-optical Kerr effect

Herein, a novel structure composed of an all-magneto-optical periodic grating, without using noble metals, is presented to enhance the transverse magneto-optical Kerr effect (TMOKE). This is done by calculating the relative changes in the reflection amplitudes for the p-polarized wave using the finite element method (FEM) with COMSOL Multiphysics. Bio-sensing applications of the proposed structure can be possible by detecting alternation in the refractive index of the analyte medium through monitoring of the TMOKE. The simultaneous operation of the magneto-optic layer as a sensing layer is the advantage of our idea, where direct interaction with the analyte happens, leading to the suppression of the wave reflection amplitudes, and finally leading to extreme TMOKE in a magneto-optical (MO) grating (the TMOKE amplitudes are near 0.8 in this work). And since TMOKE shows a Fano-like shape, we calculate sensitivity and figure of merit (FoM) by fitting them together. This results in high sensitivity, and the value of the FoM is remarkable (between 2×103 and 3×103 refractive index unit) at resonance angles for different refractive indices, which makes our proposed structure able to be utilized for bio-sensing applications.

Enhancement of transverse magneto-optical Kerr effect based on surface plasmon and its application in sensing

In recent years, the combination of magnetic and plasma properties of nanostructures has become a hot research topic. However, most such studies focuse on prism-based sandwich structures, which not only hinders device miniaturization but also has weak transverse magneto-optical Kerr (TMOKE) in amplitude. In this paper, a sub-wavelength periodic nanoporous Au/Co bilayer magneto-optical surface plasmon resonance (MOSPR) sensor is investigated, where the sensing principle is based on the measurement of TMOKE. By optimizing the geometric parameters of the nanostructure, a nearly perfect TMOKE spectrum with a FWHM of only 0.175 nm is obtained, which has a Fano-like pattern and an amplitude close to the theoretical maximum. It is proved that the excitation of high quality SPR enhances the magneto-optical effect. We then analyze the resonant angular shift associated with the TMOKE signal to monitor the change in the analyte refractive index, demonstrating the sensing sensitivity up to 220°RIU−1 and figure of merits (FOM) in excess of 103 in gas. The MOSPR system achieves higher resolution compared to the gold-based SPR system, yielding an order of magnitude higher FOM than the SPR system.

Nonlinear Electromagnetic Properties of Thinfilm Nanocomposites (CoFeZr)x(MgF2)100−x

The aim of this work is a comprehensive study of the effect of variable atomic composition and structural-phase state of (CoFeZr)x(MgF2)100−x nanocomposites (NCs) on their nonlinear electronic and magnetic/magneto-optical properties. Micrometer-thick nanocomposite layers on the glass substrates were obtained by ion-beam sputtering of a composite target in the argon atmosphere in a wide range of compositions x = 9–51 at·%. The value of the resistive percolation threshold, xper = 34 at·%, determined from the concentration dependencies of the electrical resistance of NCs, coincides with the beginning of nucleation of metallic nanocrystals CoFeZr in MgF2 dielectric matrix. The absolute value of maximum magnetoresistance of NCs is 2.4% in a magnetic field of 5.5 kG at x = 25 at·%, up to the percolation threshold. Two maxima appear in the concentration dependencies of magneto-optical transversal Kerr effect, one of which, at x = 34 at·%, corresponds to the formation of CoFeZr alloy nanocrystals of a hexagonal structure, and the second one at x = 45 at·% corresponds to the phase transition of nanocrystals from a hexagonal to a cubic body-centered structure. The magnetic percolation threshold in (CoFeZr)x(MgF2)100−x system at xfm = 34 at·%, with the appearance of a hysteresis loop and a coercive force of Hc ≈ 8 Oe, coincides with the resistive percolation threshold xper = 34 at·%. Concentration dependence of the coercive force showed that at low contents of metallic alloy x &lt; 30 at·%, NCs are superparamagnetic (Hc = 0). With an increase of the alloy content, in the region of magnetic and resistive percolation thresholds, NCs exhibit a magnetically soft ferromagnetic character and do not change it far beyond the percolation threshold, with the maximum value of the coercive force Hc &lt; 30 Oe.

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

The transverse magneto-optical Kerr effect (TMOKE) with gas sensing ability was comprehensively investigated in this study by directly patterning a subwavelength periodic nanogroove on a cobalt film. High-amplitude TMOKE was observed for the proposed structure, which was 243 times as intense as that of a smooth film. Further, the physical mechanism responsible for this significant improvement is elucidated by the effective activation of surface plasmon resonance at the gas–cobalt interface. The mechanism was established by investigating the electric field distributions at a resonant angle of incidence and the reflectance spectra associated with the metallic nanogroove grating structure. Moreover, we demonstrate that this scheme has a high detection sensitivity of up to 112.2° per refractive index unit and a large figure of merit, allowing the system to be integrated with microfluidics for sensing applications.