Magneto-optical Research Articles

Nanopore arrays with TMOKE-enhanced high performance sensing

Magneto-plasmon sensing structure based on surface plasmon resonance (SPR) and magneto-optical (MO) effect has become a hot research topic in recent years. In this work, we propose a magneto-plasmon crystal consisting of an Au/Co double-layer nanoporous structure with optically thick Au film as a substrate. Due to the excitation of high-quality SPR, a Fano-like transverse magneto-optical Kerr (TMOKE) spectrum with subnanometer bandwidth is realized. A sensitivity of up to 677 nm RIU−1 is detected under subtle refractive index changes in air, and all the calculated figure of merits (FOM) are higher than 104 RIU−1. In addition, in order to highlight the superiority of the sensing performance of the MO plasmon (MOSPR) sensor, we compare the MOSPR sensor with the SPR sensor and calculate their FOM in different refractive index environments. The results show that the FOM of the MOSPR sensor is two orders of magnitude higher than that of the SPR sensor, which proves that the performance of the MOSPR sensor is significantly better than that of the SPR sensor and provides a theoretical basis for biosensing and gas detection based on magneto plasmon.

Magneto-chiral Nonlinear Optical Effect with Large Anisotropic Response in Two-Dimensional Halide Perovskite.

The chiral organic-inorganic halide perovskites (OIHPs) are vital candidates for superior nonlinear optical (NLO) effects associated with circularly polarized (CP) light. NLO in chiral materials often couples with magnetic dipole (MD) transition, as well as the conventional electric dipole (ED) transition. However, the importance of MD transition in NLO process of chiral OIHPs has not yet been well recognized. Here, the circular polarized probe analysis of second harmonic generation circular dichroism (SHG-CD) provides the direct evidence that the contribution of MD leads to a large anisotropic response to CP lights in chiral OIHPs, (R-/S-MBACl)2PbI4. The thin films exhibit great sensitivity to CP lights over a wide wavelength range, and the g-value reaches up to 1.57 at the wavelength where the contribution of MD is maximized. Furthermore, it is also effective as CP light generator, outputting CP-SHG with maximum g-factor of 1.76 upon the stimulation of linearly polarized light. This study deepens the understanding of relation between chirality and magneto-optical effect, and such an efficient discrimination and generation of CP light signal is highly applicable for chirality-based sensor and optical communication devices.

Photonic spin Hall effect under the action of a full-angle three-dimensional magnetic field in space

In this paper, we have measured the magneto-optical spin Hall effect influenced by an arbitrary oriented magnetic field using CeDyAl thin films on Gd3Ga5O12 (GGG) substrates as reflective materials. Plots of the variation of the magneto-optic spin Hall effect (MOPSHE) with magnetic field strength, the hysteresis line, in three different unit-direction magnetic fields are simulated and experimentally measured. The comparison of the simulation results with the experiments allows the method of weak measurement to determine the MOPSHE under the influence of the magnetic field to be validated. MOPSHE under a three-dimensional magnetic field is measured and the measurement error is within 4 μm.

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.

Method for lightning flashover types identification on transmission lines utilizing OPGW optical polarization state signal characteristics

The Optical Fiber Composite Overhead Ground Wire (OPGW) has undergone rapid development and has been extensively applied in the realm of intelligent power system status monitoring. This article conducts research on lightning signal waveform in optical fibers within the context of lightning fault location using the OPGW optical polarization state method. A transmission line model is simulated employing ATP-EMTP to capture electrical characteristics when lightning strikes the OPGW. Subsequently, by employing the Faraday magneto-optical effect principle, electrical signals are transformed into optical polarization states within the internal fibers of OPGW. Using such data, the optical signal propagation characteristics when lightning strikes OPGW are deduced. Finally, a method for discerning between induced lightning and direct lightning strikes through the analysis of time-frequency domain characteristics in OPGW. This method addresses the limitation of traditional OPGW lightning monitoring, which is unable to deduce electrical signals, thus achieving precise identification of lightning-induced transient faults in transmission lines.

Layer Control of Magneto-Optical Effects and Their Quantization in Spin-Valley Splitting Antiferromagnets.

Magneto-optical effects (MOE), interfacing the fundamental interplay between magnetism and light, have served as a powerful probe for magnetic order, band topology, and valley index. Here, based on multiferroic and topological bilayer antiferromagnets (AFMs), we propose a layer control of MOE (L-MOE), which is created and annihilated by layer-stacking or an electric field effect. The key character of L-MOE is the sign-reversible response controlled by ferroelectric polarization, the Néel vector, or the electric field direction. Moreover, the sign-reversible L-MOE can be quantized in topologically insulating AFMs. We reveal that the switchable L-MOE originates from the combined contributions of spin-conserving and spin-flip interband transitions in spin-valley splitting AFMs, a phenomenon not observed in conventional AFMs. Our findings bridge the ancient MOE to the emergent realms of layertronics, valleytronics, and multiferroics and may hold immense potential in these fields.

Spin–orbit torque reconfigurable diffraction gratings

Spin–orbit torque (SOT) provides a convenient, fast, and efficient way to switch the magnetization and has been applied in memory, logic, and microwave devices. Here, we report the application of SOT in the spatial modulation of the optical field. We construct a diffraction grating composed of perpendicularly magnetized current channels that can be switched using the SOT current pulses, and the resulting periodic magnetization patterns are transferred into the polarization modulation of light through the magneto-optical effect. We demonstrate that the periodic structures and diffraction peaks of the grating can be reconfigured electrically. These results would open up an avenue to the application of the state-of-the-art spintronic technologies in fast tunable diffractive optics.

Magneto-optical fiber-based orbital angular momentum mode converters.

Orbital angular momentum (OAM) mode division multiplexing (MDM) systems can support large-capacity and high-speed rate information transmission, in which the OAM mode conversion devices play an important role. In this paper, the mode conversion principle of magneto-optical fiber-based long-period grating (MOF-LPG) is analyzed for further developing new magneto-optical (MO) OAM mode converters, including three types of C P 01 to O A M ±1,1, O A M ±1,1 to O A M ±2,1, and O A M ±1,1 to C P 02. It is shown that the magnetic tunability of the mode converters through the propagation constants of the eigenmodes is useful for compensating for process errors and increasing the operating wavelength range. The implementation of MOF-LPGs is also discussed from the aspect of the prospective experiments.

Interface polarity brings a way to modulate magneto-optical effect of cubic Ni2+/Fe3+ co-doped Bi25FeO40 film: Implications in piezoelectricity

Cubic Sillenite Bi25FeO40 (BFO) could become a new magneto-optical material due to its high concentration of Bi3+ and no birefringence. But its weak magnetism causes the magneto-optical properties to be far from the requirements of practical applications. Doping magnetic Fe3+ and Ni2+ ions to improve the magnetism and magneto-optical properties of BFO (Bi19Ni2.8Fe4.2O40) film on fluorine-doped tin oxide (BNFO/FTO) is discussed in this paper. Another focus of this paper is to discuss the magneto-optical properties modulated by the electric field. The cubic BNFO film has weak piezoelectric effects, which makes it difficult to modulate its magneto-optical effect by electric field. A polarity symmetry induced by the Schottky junction between Au metal layer and BNFO semiconductor layer (Au/BNFO) compensates for cubic symmetry, and the piezoelectric effect can be improved. By applying an electric field, its magnetic circular dichroism (MCD) ellipticity |ΨF| gradually decreases as a direct current voltage from 0 V to 10 V in a magnetic field of 2500 Oe, demonstrating the feasibility of this strategy. These results indicate a new way for highly symmetric magneto-optical materials to modulate magneto-optical effects in electric fields.

Magneto-optical-like effect in tight focusing of azimuthally polarized sine-Gaussian beams.

Magneto-optical effects, which have been known for over a century, are among the most fundamental phenomena in physics and describe changes in the polarization state of light when it interacts with magnetic materials. When a polarized plane wave propagates in or through a homogeneous and isotropic transparent medium, it is generally accepted that its transverse polarization structure remains unchanged. However, we show that a strong radial polarization component can be generated when an azimuthally polarized sine-Gaussian plane wave is tightly focused by a high numerical aperture lens, resulting in a magneto-optical-like effect that does not require external magnetic field or magnetic medium. Calculations show that the intensity structure and polarization distribution of the highly confined electric field strongly depend on the parameters m and φ0 in the sinusoidal term, where m can be used to control the number of the multifocal spots and φ0 can be used to control the position of each focal spot. Finally, we show that this peculiar electric field distribution can be used to realize multiple particles trapping with controllable numbers and locations.

Perspectives: Light Control of Magnetism and Device Development.

Accurately controlling magnetic and spin states presents a significant challenge in spintronics, especially as demands for higher data storage density and increased processing speeds grow. Approaches such as light control are gradually supplanting traditional magnetic field methods. Traditionally, the modulation of magnetism was predominantly achieved through polarized light with the help of ultrafast light technologies. With the growing demand for energy efficiency and multifunctionality in spintronic devices, integrating photovoltaic materials into magnetoelectric systems has introduced more physical effects. This development suggests that sunlight will play an increasingly pivotal role in manipulating spin orientation in the future. This review introduces and concludes the influence of various light types on magnetism, exploring mechanisms such as magneto-optical (MO) effects, light-induced magnetic phase transitions, and spin photovoltaic effects. This review briefly summarizes recent advancements in the light control of magnetism, especially sunlight, and their potential applications, providing an optimistic perspective on future research directions in this area.

Nonreciprocal toroidal dipole resonance and one-way quasi-bound state in the continuum.

Bound states in the continuum (BICs) provide an alternative way of trapping light at nanoscale. Although the last 10 years have witnessed tremendous progress on BICs from fundamentals to applications, nonreciprocal BICs and their potential applications have not been fully exploited yet. In this study, we demonstrated a one-way quasi-BIC by leveraging an all-dielectric magneto-optical (MO) metasurface. We show that the key point for achieving a one-way quasi-BIC is to excite a magnetization-induced leaky resonance. Here we adopt the longitudinal toroidal dipole (TD) resonance characterized by a vortex distribution of head-to-tail magnetic dipoles parallel to the plane of the MO metasurface. We show that, by breaking the time-reversal symmetry, at critical conditions, the TD resonance can be enhanced in the forward channel and perfectly canceled in the time-reversed channel, resulting in a one-way quasi-BIC. The demonstrated phenomena hold significant promise for practical applications such as magnetic field optical sensing, nonreciprocal optical switching, isolation, and modulation.

Controllable light group velocity in a degenerate two-level medium under the assistance of an external magnetic field

In this work, we proposed a simple model for control of subluminal and superluminal light propagation via an external magnetic field in a lambda configuration degenerate two-level atomic medium. We show that the absorption-dispersion properties and group index under the influence of the strength of coupling laser and external magnetic fields are controlled. By changing the direction and magnitude of the magnetic field, the medium switches from transparency with normal dispersion to enhanced absorption with anomalous dispersion at the line center, corresponding with the transfer from slow light to fast light. This work may provide for the application realization of magneto-optic switches and storage devices in quantum information processing.

The Role of Diamonds Dispersed in Ferronematic Liquid Crystals on Structural Properties

A study of the role of diamond nanoparticles on 5CB liquid crystal composites with Fe3O4 nanoparticles is presented. Composite ferronematic systems based on the nematic liquid crystal 5CB doped with Fe3O4 magnetic nanoparticles and additionally bound to diamond nanoparticles (DNPs), of a volume concentration of 3.2 mg/mL, 1.6 mg/mL and 0.32 mg/mL, were investigated using both magneto-optical effect and surface acoustic waves (SAWs) to study the role of diamond nanoparticles on the structural properties of ferronematic liquid crystals. The responses of light transmission and SAW attenuation to an external magnetic field were investigated experimentally under a linearly increasing and decreasing magnetic field, respectively. Investigations of the phase transition temperature shift of individual composites were also performed. The experimental results highlighted a decrease in the threshold field in the ferronematic LC composites compared to the pure 5CB as well as its further decrease after mixing Fe3O4 with diamond powder. Concerning the transition temperature, its increase with an increase in the volume fraction of both kinds of nanoparticles was registered. The role of diamond nanoparticles in the structural changes and the large residual light transition and/or attenuation (memory effect) were also observed. The presented results confirmed the potential of diamond nanoparticles in nematic composites to modify their properties which could lead to final applications.

Magneto-optical and luminescent properties of Tb doped Ge-B-X (X=Ga/La) glasses

Extensive efforts have been devoted to magneto-optical (MO) glass, owing to its remarkable potential in modern optics, encompassing diverse applications such as optical isolation, modulation, and sensing. Although the Tb ions doped glass has good MO properties, high concentrations of Tb ions tend to cluster, resulting in glass crystallization. To further improve the performance of MO glass, we must improve the solubility of Tb ions and inhibit the oxidation of paramagnetic Tb3+ to diamagnetic Tb4+ by adjusting the glass composition. In this work, we conducted a comparative study on GeO2-B2O3-X2O3 glasses doped with Tb2O3 (TGBX, where X represents Ga or La) to elucidate the effects of Ga2O3 and La2O3 on glass properties. Our findings reveal that TGBG glasses exhibit superior MO performance compared to TGBL glasses. Notably, the Verdet constant of TGBG glass with 45 mol.% Tb2O3 at 650 nm reaches 105 rad/(T·m). Although TGBL glass exhibits a lower Verdet constant, its higher glass network connectivity and higher concentration of Tb3+ ions suggest its potential for preparing larger-sized glasses with an increased Tb3+ molar ratio.

Atom-based optical polarization modulator.

In this work, we employ 87Rb atoms as rotation media to manipulate the polarization of optical fields in both magnetic and magnetic-free environments. Employing the nonlinear magneto-optical rotation mechanism, we achieve a state-of-the-art magneto-optical rotation coefficient of 1.74×108 rad⋅T-1⋅m-1 which is four orders of magnitude higher than commonly employed materials. Additionally, in a magnetic-free environment, we achieve all-optical cross-polarization modulation between the pump and probe light via Rb atoms. The nonlinear magneto-optical rotation configuration introduces inventive techniques for a new type of magneto-optical modulator while the all-optical configuration paves the way for exploring photonic integrated circuit (PIC) devices free from disruptions caused by electrical or magnetic crosstalk.

Recent advances of rare earth iron garnet magneto-optical single crystals

R3Fe5O12 (RIG) crystals are the most desirable elements for magneto-optical isolators in the near-infrared (NIR) to mid-infrared (MIR) region, with ever-growing demands for optical fiber communication and high-power laser system. Now, this system is the only commercialized Faraday rotator for optical isolators in 5G wireless communications. However, the growth of high-quality bulk RIG single crystals has been a big challenge for a long time, due to the typical incongruent melting characteristic and complex phase relationships. This work comprehensively summarizes the recent advances for the growth of RIG single crystals, including the proper choice of flux and innovative strategies on several growth techniques, like the flux-Bridgman, edge-defined film-fed growth (EFG) and top seeded solution growth (TSSG), etc. Effective modulation on the optical and magneto-optical performance is highlighted. Some ongoing perspectives are also proposed and discussed. It is anticipated that this work will provide deeper insight into the exploration of high-performance magneto-optical crystals for potential applications in NIR-MIR wavelength.

Investigation of deterministic and cumulative nature in helicity-dependent optical switching of ferrimagnetic Gd–Fe–Co films

The precise control of magnetization using circularly polarized laser pulses in perpendicularly magnetized films is a key approach to develop storage media. Although deterministic helicity-dependent magnetization switching (HDMS) in a single-pulse excitation has been observed in ferrimagnetic Gd–Fe–Co alloys, ferromagnetic [Co/Pt]N multilayers require cumulative effects of multiple pulses to achieve HDMS. In this study, we systematically investigated the single-shot and cumulative nature of HDMS using ferrimagnetic Gd–Fe–Co films with varying compositions and multilayer structures, in terms of angular momentum compensation, thermal diffusion, mobility of domain walls, and the size of the magneto-optical effect. These results provide insights for the realization of single-shot HDMS in various magnetic systems, such as ferromagnetic alloys.

Magnetic nanoparticles detection based on nonlinear Faraday rotation

Magnetic nanoparticles (MNPs) have attracted interest in various research fields due to their special superparamagnetic and strong magneto-optical effects, especially as contrast agents for enhancing medical imaging contrast. Using MNPs capable of generating Faraday rotation angles with higher harmonics as magnetic-optical contrast agents allows for a distinct contrast with biological tissues lacking these higher harmonics. This significantly improves the sensitivity of magnetic-optical imaging. By introducing the interaction coefficient, we propose a model for the nonlinear Faraday rotation of MNPs under the excitation of an external alternating magnetic field. Using our homemade device (which can detect rotation angles as low as approximately 2e-7 rad), we have verified that the higher harmonics of the Faraday rotation can mitigate interference from paramagnetic and diamagnetic backgrounds at lower concentrations. In the future, it is anticipated that MNPs can be utilized as magneto-optical contrast agents to achieve high-resolution in vivo imaging.

Optical Microscopy Using the Faraday Effect Reveals in Situ Magnetization Dynamics of Magnetic Nanoparticles in Biological Samples.

The study of exogenous and endogenous nanoscale magnetic material in biology is important for developing biomedical nanotechnology as well as for understanding fundamental biological processes such as iron metabolism and biomineralization. Here, we exploit the magneto-optical Faraday effect to probe intracellular magnetic properties and perform magnetic imaging, revealing the location-specific magnetization dynamics of exogenous magnetic nanoparticles within cells. The opportunities enabled by this method are shown in the context of magnetic hyperthermia; an effect where local heating is generated in magnetic nanoparticles exposed to high-frequency AC magnetic fields. Magnetic hyperthermia has the potential to be used as a cellular-level thermotherapy for cancer, as well as for other biomedical applications that target heat-sensitive cellular function. However, previous experiments have suggested that the cellular environment modifies the magnetization dynamics of nanoparticles, thus dramatically altering their heating efficiency. By combining magneto-optical and fluorescence measurements, we demonstrate a form of biological microscopy that we used here to study the magnetization dynamics of nanoparticles in situ, in both histological samples and living cancer cells. Correlative magnetic and fluorescence imaging identified aggregated magnetic nanoparticles colocalized with cellular lysosomes. Nanoparticles aggregated within these lysosomes displayed reduced AC magnetic coercivity compared to the same particles measured in an aqueous suspension or aggregated in other areas of the cells. Such measurements reveal the power of this approach, enabling investigations of how cellular location, nanoparticle aggregation, and interparticle magnetic interactions affect the magnetization dynamics and consequently the heating response of nanoparticles in the biological milieu.