Transverse Magneto-optical Kerr Effect Research Articles

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 < 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 < 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.

Enhanced MOKE Via Tunable Plasmon Resonance Field in the Otto Configuration

Here, we demonstrate the enhancement of the transverse magneto-optical Kerr effect (TMOKE) signal, due to surface plasmon resonance in the Otto configuration, where the low index dielectric has a variable thickness. This constitutes a demonstration that, in principle, a separation of the magnetic sample from the plasmonic device and the modulation of the plasmon resonance with an enhancement of the MOKE signal is possible. We have achieved this by using air as a low index dielectric where the evanescent wave extends, preceding to excitation of surface plasmons. The magnetic sample under consideration is a thin layer of cobalt coated by an ultrathin silver layer, on a silicon substrate (Ag/Co/Si). The sample is brought close enough to the prism/air interface, allowing surface plasmon excitation in the air/Ag interface. This leads to an increase of the TMOKE signal up to ~ 2 ‰ with respect to the incident light. This is about 7 times the traditional MOKE signal in the absence of plasmons. This is comparable with previous works using the Kretschmann-Raether configuration. Furthermore, the fact that the plasmon field generated at the metal-air interface substitutes the laser light used in traditional MOKE allows new functionalities such as controlling the penetration depth of the plasmonic field into the sample. This should find applications in magnetometry and related technology.

Transverse magneto-optical behavior of nanoporous ferromagnetic film based on anodic aluminum oxide/aluminum template and its sensing application.

The transverse magneto-optical Kerr effect (TMOKE) has attracted widespread scientific interest because of its potential applications in biosensor technology, data storage, optical isolation, and telecommunications. More conventional architectures, including prism-based metal/magnetic multilayers and nanoarrays that integrate plasmonic and magnetic materials, are commonly used to amplify TMOKE through the high-quality propagation of the surface plasmon resonance optical mode. However, the main disadvantages of these architectures are their large ohmic losses and radiation damping, resulting in a large optical spectrum linewidth, which hinders the sensing performance. Here, we use a theoretical approach to show that it is possible to employ a low-loss Fabry-Perot optical mode on a magneto-optical platform for TMOKE signal and gaseous sensing enhancement by means of a single CoFeB ferromagnetic film directly overlayed on an already industrial anodic aluminum oxide/aluminum template. The proposed strategy can therefore potentially be exploited for high-precision and low-loss magneto-optical sensors.

Enhanced transverse magneto-optical Kerr effect using ferromagnetic metal perforated with nanopore arrays.

Enhancement of transverse magneto-optical Kerr effects (T-MOKEs) based on surface plasmon resonance has attracted wide attention because of their high sensing performance. Most studies, however, mainly focus on prism-based magnetoplasmonic structures or architectures that incorporate a noble metal lattice and ferromagnetic layer, hindering device fabrication, miniaturization, and integration into a microfluidic sensing configuration. Herein, we propose a single Co6Ag94 ferromagnetic-metal layer perforated with a square nanopore array system with a pronounced T-MOKE magnitude 51 times higher than that of a smooth film, and with potential to detect gaseous analytes. The proposed system is sufficient to detect gaseous media for early environmental monitoring and enables an accessible pathway for magneto-optical sensor design.

Fabry–Perot interference enhanced transverse magneto-optical Kerr effect in Ce:YIG nanopore array on an anodic aluminum oxide template

The all-dielectric magneto-optical (MO) structure has garnered considerable interest due to its enhanced MO effect and low ohmic loss compared to the magnetoplasmonic structure. In this study, the effect of Fabry–Perot (F–P) interference on the enhancement of the transverse magneto-optical Kerr effect (T-MOKE) as well as sensing performance is theoretically investigated in a dielectric MO structure composed of cerium-substituted yttrium iron garnet (Ce:YIG) nanopore array coating a nanoporous anodic aluminum oxide (AAO) film standing on an aluminum sheet referred to as the AAO/Al template. The system is particularly interesting because the MO response is significantly enhanced in the position of the F–P interference, in which the T-MOKE signal is close to a 5-fold increase compared with the reference Ce:YIG film. Additionally, the sensing performance shows that the all-dielectric nanopore-based system proposed here provides an alternative to fabricating gas and solution detectors with low ohmic loss.

Near-Perfect TMOKE in Photonic Crystal Structures for Sensing Devices With High Figure of Merit

Near-perfect transverse magneto-optical Kerr effect (TMOKE), which is realized by sandwiching a magnetic-optical film between a photonic crystal (PhC) structure and a metallic mirror, is studied. Near-unity amplitude in TMOKE is observed owing to the excitation of Tamm plasmon polaritons (TPPs) at the interface between the PhC and the metallic mirror. The physical origin behind such giant enhancement of TMOKE is disclosed by studying the magnetic field distributions at resonance and also confirmed by the reflection spectra of the top PhC and the bottom continuous metallic film. Besides, the suitability and the sensitivity of the proposed structure for sensing both gas and aqueous mediums are also illustrated in the last. And it is found that the excellent performance with the averaged figure of merit (FoM) on the order of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4.8\times10^{3}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$6.7\times10^{3}$ </tex-math></inline-formula> can be achieved for sensing gas and aqueous mediums, respectively. We hoped that this work will prompt the development of data magnetic storage, optical filters, waveguide isolators, and novel sensors with improved sensitivity.

Sensitivity and reproducibility of transverse magneto-optical Kerr effect (T-MOKE) ellipsometry

We report a comprehensive experimental study to analyze the limiting factors and physical mechanisms that determine the achievable performance of transverse magneto-optical Kerr effect (T-MOKE) ellipsometry. Specifically, we explore different approaches to achieve high sensitivity and reduced acquisition times. The best sensitivity is observed for an incident light polarization with balanced s-p components. We also verify experimentally that the method’s theoretical description is accurately describing data for any s-p combination of the incoming light. Furthermore, two alternative measurement strategies are explored by using different measurement sequences for the polarization sensitive optics, which both achieve a very comparable, high quality of results. Signal-to-noise ratios and systematic deviations are measured and analyzed based on a large number of nominally identical measurement repeats, both for entire signal sequences as well as for individual Fourier components of the magneto-optical signal generated by a sinusoidal magnetic field sequence. Hereby, we observe that while higher order Fourier components have a significantly reduced signal amplitude and correspondingly exhibit reduced signal-to-noise and repeatability performance, signal-to-noise ratios always exceed values of 100 even for the lowest signal Fourier component and the lowest signal sample that we investigated, illustrating the extremely precise nature of T-MOKE ellipsometry.

Bulk Plasmon Polariton Modes in Hyperbolic Metamaterials for Giant Enhancement of the Transverse Magneto-Optical Kerr Effect.

We demonstrate a concept for the giant enhancement of the transverse magneto-optical Kerr effect (TMOKE) using bulk plasmon polariton (BPP) modes in non-magnetic multilayer hyperbolic metamaterials (HMMs). Since the BPP modes are excited through the attenuated total reflection (ATR) mechanism, using a Si-based prism-coupler, we considered a single dielectric magneto-optical (MO) spacer between the prism and the HMM. The working wavelength was estimated, using the effective medium approach for a semi-infinite dielectric-plasmonic multilayer, considering the region where the system exhibits type II HMM dispersion relations. Analytical results, by means of the scattering matrix method (SMM), were used to explain the physical principle behind our concept. Numerical results for giant TMOKE values (close to their maximum theoretical values, ) were obtained using the finite element method (FEM), applying the commercial software COMSOL Multiphysics. Our proposal comprises a simple and experimentally feasible structure that enables the study of MO phenomena in HMMs, which may find application in future nanostructured magnetoplasmonic metamaterials for active nanophotonic devices.

Optimization of Magnetoplasmonic ε-Near-Zero Nanostructures Using a Genetic Algorithm.

Magnetoplasmonic permittivity-near-zero (-near-zero) nanostructures hold promise for novel highly integrated (bio)sensing devices. These platforms merge the high-resolution sensing from the magnetoplasmonic approach with the -near-zero-based light-to-plasmon coupling (instead of conventional gratings or bulky prism couplers), providing a way for sensing devices with higher miniaturization levels. However, the applications are mostly hindered by tedious and time-consuming numerical analyses, due to the lack of an analytical relation for the phase-matching condition. There is, therefore, a need to develop mechanisms that enable the exploitation of magnetoplasmonic -near-zero nanostructures’ capabilities. In this work, we developed a genetic algorithm (GA) for the rapid design (in a few minutes) of magnetoplasmonic nanostructures with optimized TMOKE (transverse magneto-optical Kerr effect) signals and magnetoplasmonic sensing. Importantly, to illustrate the power and simplicity of our approach, we designed a magnetoplasmonic -near-zero sensing platform with a sensitivity higher than and a figure of merit in the order of . These last results, higher than any previous magnetoplasmonic -near-zero sensing approach, were obtained by the GA intelligent program in times ranging from 2 to 5 min (using a simple inexpensive dual-core CPU computer).

Ultrafast element- and depth-resolved magnetization dynamics probed by transverse magneto-optical Kerr effect spectroscopy in the soft x-ray range

We report on time- and angle-resolved transverse magneto-optical Kerr effect spectroscopy in the soft x-ray range that, by analysis via polarization-dependent magnetic scattering simulations, allows us to determine the spatio-temporal and element-specific evolution of femtosecond laser-induced spin dynamics in nanostructured magnetic materials. In a ferrimagnetic GdFe thin film system, we correlate a reshaping spectrum of the magneto-optical Kerr signal to depth-dependent magnetization dynamics and disentangle contributions due to non-equilibrium electron transport and nanoscale heat diffusion on their intrinsic time scales. Our work provides a quantitative insight into light-driven spin dynamics occurring at buried interfaces of complex magnetic heterostructures, which can be tailored and functionalized for future opto-spintronic devices.