Magneto-optical Faraday Effect Research Articles

Resonance Enhancement of the Faraday Effect in a agnetoplasmonic Composite

The paper presents the results of a theoretical and experimental study of the enhancement of the magneto-optical Faraday effect in a magnetoplasmonic nanocomposite, caused by localized plasmon resonance (LPR) in metal nanoparticles. The nanocomposite comprises a three-layer structure of self-assembled gold nanoparticles in a bismuth-substituted iron-garnet matrix. It is shown theoretically and experimentally that the enhancement of the magneto-optical Faraday effect is determined by the action of a magnetic field on the magnetoplasmonic composite as an effective medium as a whole. In this case, in the magnetoplasmonic nanocomposite, the Faraday effect is enhanced at the LPR wavelengths and is slightly weakened in the region of short wavelengths relative to the LPR. It is theoretically shown that the complex gyration index in the off-diagonal terms of the effective permittivity tensor for the magnetoplasmonic composite, in addition to rotation of the polarization plane, leads to the appearance of alternating ellipticity in the vicinity of the plasmon resonance, which is observed in the form of asymmetry of magneto-optical rotation.

Optical Readout of Single-Molecule Magnets Magnetic Memories with Unpolarized Light.

Magnetic materials are widely used for many technologies in energy, health, transportation, computation, and data storage. For the latter, the readout of the magnetic state of a medium is crucial. Optical readout based on the magneto-optical Faraday effect was commercialized but soon abandoned because of the need for a complex circular polarization-sensitive readout. Combining chirality with magnetism can remove this obstacle, as chiral magnetic materials exhibit magneto-chiral dichroism, a differential absorption of unpolarized light dependent on their magnetic state. Molecular chemistry allows the rational introduction of chirality into single-molecule magnets (SMMs), ultimate nanoobjects capable of retaining magnetization. Here, we report the first experimental demonstration of optical detection of the magnetic state of an SMM using unpolarized light on a novel air-stable Dy-based chiral SMM featuring a strong single-ion magnetic anisotropy. These findings might represent a paradigm shift in the field of optical data readout technologies.

Magnetooptical Faraday and Kerr effects in nanosized BiYIG/GGG structures

AnnotationMagnetooptical Faraday and Kerr effects are studied in the nanosized BiY2Fe5O12 films within the spectral region of 1.3 eV<E<4.5 eV and magnetic fields of up to 10 kOe. It is shown that the thin-films BiY2Fe5O12 with the thicknesses ranging from 5 to 51 nm obtained by magnetron sputtering on the single-crystalline Gd3Ga5O12 substrates have high magneto-optical quality. The specific Faraday rotation for the nanosized Bi0.5Y1.5Fe5O12-δ films reaches about 140000 deg/cm close to that for bulk BiY2Fe5O12. Meanwhile, the polar Kerr effect reaches about 30 min within the range of 1.6 eV–4.1 eV at the magnetic fields above 2 kOe.It is shown that the strong paramagnetic contribution of Gd3Ga5O12 substrates significantly affects the Faraday and Kerr effect for the films. The defining of magnetooptical parameters and Verdet constant for the Gd3Ga5O12 substrate permitted to separate the substrate contribution and reveal peculiarities of spectral dependences of both Faraday and Kerr effects for magnetic films of various thicknesses. The estimated critical thickness of the film-substrate interface region is as large as 35 lattice constants of BiY2Fe5O12. It is shown that the magnetooptical effects for the thin films with the thickness above the critical one correspond to those for bulk BiY2Fe5O12. For samples with the smallest thicknesses of the film (5 nm) the contributions from magnetically dead and magnetically passive layers lead to a drastic reduction in the observable Faraday and Kerr effects with a dominating contribution from the substrate. The high density of displacement dislocations at the film-substrate interface leads to the decrease the magnetooptical quality of the nanosized films.

Inverse Faraday Effect in Ferrite–Garnet Films in the Near-Infrared Range

The magneto-optical Faraday effect is determined by the electric dipole and magnetic dipole transitions in a transparent magnetic material. At the same time, the inverse Faraday effect is still described by an expression that includes only electric dipole transitions. The magnetic dipole contribution to the inverse Faraday effect is considered theoretically, and the dependence of the inverse Faraday effect on the wavelength in the near-infrared range (where the magnetic dipole contribution becomes significant) is obtained by the example of a ferrite–garnet film. It is shown that, although both contributions to the inverse Faraday effect always take place for homogeneous films, only the magnetic-dipole inverse Faraday effect manifests itself for films with a periodic nanostructure upon excitation by a TE waveguide mode, which may be useful for its experimental observation.

Assembly of Homochiral Magneto-Optical Dy6 Triangular Clusters by Fixing Carbon Dioxide in the Air.

A new hydrazone Schiff base bridging ligand (H2LSchiff (E)-N'-((1-hydroxynaphthalen-2-yl)methylene)pyrazine-2-carbohydrazide) and L/D-proline were used to construct a pair of homochiral Dy6 cluster complexes, [Dy6(CO3)(L-Pro)6(LSchiff)4(HLSchiff)2]·5DMA·2H2O (L-1, L-HPro = L-proline; DMA = N,N-dimethylacetamide) and [Dy6(CO3)(D-Pro)6(LSchiff)4(HLSchiff)2]·5DMA·2H2O (D-1, D-HPro = D-proline), which show a novel triangular Dy6 topology. Notably, the fixation of CO2 in the air formed a carbonato central bridge, playing a key role in assembling L-1/D-1. Magnetic measurements revealed that L-1/D-1 displays intramolecular ferromagnetic coupling and magnetic relaxation behaviours. Furthermore, L-1/D-1 shows a distinct magneto-optical Faraday effect and has a second harmonic generation (SHG) response (1.0 × KDP) at room temperature. The results show that the immobilization of CO2 provides a novel pathway for homochiral multifunctional 4f cluster complexes.

Nonreciprocal Pancharatnam-Berry metasurface for unidirectional wavefront manipulations

Optical metasurfaces employing the Pancharatnam-Berry (PB) geometric phase, called PB metasurfaces, have been extensively applied to realize spin-dependent light manipulations. However, the properties of conventional PB metasurfaces are intrinsically limited by the Lorentz reciprocity. Breaking reciprocity can give rise to new properties and phenomena unavailable in conventional reciprocal systems. Here, we propose a mechanism to realize nonreciprocal PB metasurfaces of subwavelength thickness by using the Faraday magneto-optical (FMO) effect of yttrium iron garnet (YIG) material in synergy with the PB geometric phase of spatially rotating meta-atoms. Using full-wave numerical simulations and multipole analysis, we show that the metasurface composed of dielectric cylinders and a thin YIG layer can achieve high isolation of circularly polarized lights, attributed to the enhancement of the magneto-optical effect by the resonant Mie modes and Fabry-Pérot (FP) cavity mode. In addition, the metasurface can enable unidirectional wavefront manipulations of circularly polarized lights, including nonreciprocal beam steering and nonreciprocal beam focusing. The results contribute to the understanding of the interplay between nonreciprocity and geometric phase in light manipulations and can find applications in optical communications, optical sensing, and quantum information processing.

Detection and classification of invisible weld defects by magneto-optical imaging under alternating magnetic field excitation

Aiming at the difficult to detect invisible weld defects, a magneto-optical (MO) imaging non-destructive testing (NDT) system excited by an alternating magnetic field is proposed for feature extraction and detection classification of invisible weld defects. The relationship between the MO image features and the magnetic field intensity is analyzed based on the Faraday MO effect. A magnetic dipole model is proposed to study the magnetic field distribution on weld defect. A three-dimensional finite element model of invisible weld defects (with a width of 0.01 mm) is established, and the distribution of leakage magnetic field for different types of invisible defects is analyzed. In order to detect different invisible weld defects under the excitation of alternating magnetic field, MO imaging NDT experiments are carried out. The effectiveness of the finite element model is verified by the experiment. The gray value of the MO image can match the corresponding leakage magnetic field intensity. The Tamura method and gray-level co-occurrence matrix (GLCM) method are used to extract the texture features of natural invisible weld defect’s MO image, and these texture features of MO images are used as input data for the defect classification model established using back propagation (BP) neural network. Experimental results show that the classification accuracy of the GLCM + Tamura-BP model is higher than that of the GLCM-BP model, and its overall classification accuracy reaches 91.1%, indicating that this model can effectively and accurately classify natural invisible weld defects.

Real-time deep-learning-based object detection and unsupervised statistical analysis for quantitative evaluation of defect length direction on magnetooptical faraday effect

Magnetooptical nondestructive inspection (MONDI) is widely used in various industries to detect defects in metal including ferromagnetic materials. Despite its high precision and sensitivity, its inspection accuracy is highly dependent on the direction of the magnetizer. In addition, the irregular shapes of defects make the assessment of their severity challenging. To address these limitations, we propose an efficient real-time deep learning (DL)-based object detection model called the MONDI detector. This model is designed to integrate a DL-based object detection model with statistical analysis based on regression model to classify and quantify the magnetizer direction. To comprehensively assess algorithm performance, this study investigates variations in the excitation field, defect shape, and defect depth. This analysis is expected to contribute to the state-of-the-art object detection paradigm in MONDI system.

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.

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.

Homochiral Dy2 single-molecule magnets with strong magneto-optical Faraday effects and strong third-harmonic generation

Four pairs of enantiomers of ferromagnetically coupled Dy2 single-molecule magnets, which show both strong magneto-optical Faraday effects and strong third-harmonic generation, are directionally constructed.

High-sensitivity and directional-identification fiber magnetic field sensor via polarimetric fiber ring laser with a fiber Faraday rotator

A highly sensitive fiber magnetic field sensor with directional identification utilizing multi-longitudinal-mode fiber ring laser (FRL) based on polarization-mode beat frequency (PMBF) is experimentally demonstrated. A bismuth-doped iron garnet (BIG), as a kind of fiber Faraday rotator, is embedded in the FRL and serves as a fiber magnetic field probe, whose birefringence shows strong dependence on the external magnetic field due to magneto-optical Faraday effect, leading to the frequency drift of PMBF. Thus, the external magnetic field can be characterized by monitoring the change in a certain PMBF. Additionally, the drift direction of the tracked PMBF is closely related to the applied magnetic field direction, which is attributed to the non-reciprocity of Faraday magneto-optical rotation. Therefore, it shows the good ability to distinguish the applied forward (positive) and reverse (negative) magnetic field. The experimental results reveal that the tracked PMBF signal near 100 MHz has opposite frequency drift signs in the forward (positive) range of 0–20 mT and reverse (negative) range of 0 - −20 mT, which can be used to identify the axial orientation of the applied magnetic field. Additionally, it shows the maximum magnetic field sensitivities of −100.76 and −105.73 kHz/mT in the positive and negative magnetic field ranges, respectively. The designed device makes full use of the advantages of the fiber laser that rapidly demodulates the magnetic field with the help of high-speed digital processing technology, as well as fast response, high integration and low cost of fiber Faraday rotator, offering potentials in high-sensitivity magnetic field measurement in a confined space.

Two Pairs of Homochiral Parallelogram-like Dy4 Cluster Complexes with Strong Magneto-Optical Properties.

Two pairs of homochiral Dy(III) tetranuclear cluster complexes derived from (+)/(-)-3-trifluoroacetyl camphor (D-Htfc/L-Htfc), [Dy4(OH)2(L1)4(D-tfc)2(DMF)2]·4DMF (D-1) [H2L1 = (E)-2-(2-hydroxy-3-methoxybenzylideneamino)phenol)]/[Dy4(OH)2(L1)4(L-tfc)2(DMF)2]·4DMF (L-1) and [Dy4(OH)2(L2)4(D-tfc)2(DMF)2]·2H2O·3MeCN (D-2) [H2L2 = (E)-3-(2-hydroxy-3-methoxybenzylideneamino)naphthalen-2-ol]/[Dy4(OH)2(L2)4(L-tfc)2(DMF)2]·2H2O·3MeCN (L-2), were synthesized at room temperature, which have a Dy4 parallelogram-like core. The magnetic studies revealed that D-1 exhibits single-molecule magnet (SMM) behavior under zero dc magnetic field, and its magnetic relaxation has a distinct Raman process in addition to the Orbach process, with the Ueff/k value of 57.5 K and the C value of 28.27 s-1K-2.14; while D-2 displays dual magnetic relaxation behavior at 0 Oe field, with the Ueff/k value 114.8 K for the slow relaxation process (SR) and the C value of 10.656 s-1K-5.80 for the fast relaxation process (FR), respectively. Theoretical calculations indicated that the conjugated groups (phenyl vs naphthyl) of the Schiff base bridging ligands (H2L1 and H2L2) significantly affect the intramolecular magnetic interactions between the Dy3+ ions and ultimately lead to different relaxations. Furthermore, magnetic circular dichroism (MCD) measurements showed that these two pairs of Dy4 enantiomers exhibit strong room temperature magneto-optical Faraday effects; notably, increasing the conjugated group on the Schiff base bridging ligand is beneficial to enhancing the magneto-optical Faraday effects.

A Pair of Multifunctional Cu(II)-Dy(III) Enantiomers with Zero-Field Single-Molecule Magnet Behaviors, Proton Conduction Properties and Magneto-Optical Faraday Effects.

Multifunctional materials with a coexistence of proton conduction properties, single-molecule magnet (SMM) behaviors and magneto-optical Faraday effects have rarely been reported. Herein, a new pair of Cu(II)-Dy(III) enantiomers, [DyCu2(RR/SS-H2L)2(H2O)4(NO3)2]·(NO3)·(H2O) (R-1 and S-1) (H4L = [RR/SS] -N,N'-bis [3-hydroxysalicylidene] -1,2-cyclohexanediamine), has been designed and prepared using homochiral Schiff-base ligands. R-1 and S-1 contain linear Cu(II)-Dy(III)-Cu(II) trinuclear units and possess 1D stacking channels within their supramolecular networks. R-1 and S-1 display chiral optical activity and strong magneto-optical Faraday effects. Moreover, R-1 shows a zero-field SMM behavior. In addition, R-1 demonstrates humidity- and temperature-dependent proton conductivity with optimal values of 1.34 × 10-4 S·cm-1 under 50 °C and 98% relative humidity (RH), which is related to a 1D extended H-bonded chain constructed by water molecules, nitrate and phenol groups of the RR-H2L ligand.

Fraunhofer diffraction by a slit between a vacuum and a non-magnetic medium with the magneto-optical Faraday effect

Fraunhofer diffraction by a slit on an opaque screen between vacuum and a nonmagnetic dielectric medium in the presence of magneto-optical activity induced in the medium by an external magnetic field is considered. A number of features of the diffraction pattern are revealed for different directions of an external magnetic field that induces magneto-optical activity (Faraday magneto-optical effect).

Electro-optic non-reciprocal polarization rotation in lithium niobate

Polarization is a fundamental degree of freedom for light and is widely leveraged in free space and fiber optics. Non-reciprocal polarization rotation, enabled via the magneto-optic Faraday effect, has been essentially unbeatable for broadband isolators and circulators. For integrated photonics foundries, however, there is still no good path to producing low-loss magneto-optic components, which has prompted a search for alternatives that do not use polarization rotation. Moreover, magneto-optic materials tend to be highly lossy, and while large (10–100 rad/cm) polarization rotation can be achieved, the key figure of merit (rotation-per-loss) is typically &amp;lt;1 rad/dB. Here, we demonstrate that broadband non-reciprocal polarization rotation can be produced using electro-optics in nanophotonic devices. Our demonstration leverages electro-optic inter-polarization scattering around 780 nm in lithium niobate, in which the reciprocity is broken with the help of a radiofrequency stimulus that carries synthetic momentum. While the demonstrated electro-optic polarization rotation rate is ≈1 rad/cm, the exceptionally low loss of lithium niobate enables non-reciprocal polarization rotators with figures of merit that are 1-2 orders of magnitude better than what is possible with magneto-optics. This approach can be replicated on III–V platforms, paving the way for high-performance lasers with co-integrated monolithic non-reciprocal devices.

Probing magnetization dynamics of iron oxide nanoparticles using a point-probe magneto-optical method

Magnetic nanoparticles (MNPs) are promising as local heat generators for magnetic hyperthermia under AC magnetic fields. The heating efficacy of MNPs is determined by the AC hysteresis loop area, which in turn is affected by the dynamic magnetic properties of the nanoparticles. Whilst inductive-based AC magnetometers can measure the average magnetic behavior of samples, the use of the magneto-optical Faraday effect with a focused laser spot allows point-probe measurements to be made, and without some of the magnetic field limitations imposed by inductive methods. In this work, the AC magnetic properties of different sized iron oxide MNPs in suspension were measured by AC magnetometry and AC susceptibility techniques. AC hysteresis loops measured by magneto-optical magnetometry were validated using a commercial inductive AC magnetometer, and compared to the magnetization relaxation behavior revealed by fitting the AC susceptibility data. The spatial sensitivity of the point-probe magneto-optical method is also demonstrated by measuring the AC hysteresis loop from large (&amp;gt;1 μm) MNP aggregates dried onto glass slides. These aggregated particles are found to be magnetically softer than in their suspension form, suggesting interparticle coupling mechanisms could occur when the nanoparticles form dense aggregates.

Theoretical studies of magneto-optical Kerr and Faraday effects in two-dimensional second-order topological insulators

Optical approaches are useful for studying the electronic and spin structure of materials. Here, based on the tight-binding model and linear response theory, we investigate the magneto-optical Kerr and Faraday effects in two-dimensional second-order topological insulators (SOTI) with external magnetization. We find that orbital-dependent Zeeman term induces band crossings for SOTI phase, which are absent for trivial phase. In the weak-magnetization regime, these crossings give rise to giant jumps (peaks) of Kerr and Faraday angles (ellipticity) for SOTI phase. In the strong-magnetization regime, we find that two nearly flat bands are formed at the high-symmetry point of Brillouin zone of SOTI phase. These flat bands give rise to two successive giant jumps (peaks) of Kerr and Faraday angles (ellipticity). These phenomena provide new possibilities to characterize and detect the two-dimensional SOTI phase.

Asymmetric Magneto-Optical Rotation in Magnetoplasmonic Nanocomposites

The results of the asymmetric magneto-optical rotation in the magnetoplasmonic nanocomposite study are presented. The asymmetry is observed in spectra of magneto-optical rotation when a magneto-optical medium with a plasmonic subsystem is magnetized along or against the radiation wave vector. The asymmetry is observed as vertical displacement of a magneto-optical hysteresis loop too. Such asymmetry is detected in magnetoplasmonic nanocomposite, which consists of a magneto-optical layer of Bi substituted iron-garnet intercalated with a plasmonic subsystem of gold self-assembled nanoparticles. It is shown that the physical reason for the asymmetric magneto-optical rotation is the manifestation of the Cotton–Mouton birefringence effect when the normal magnetization of the sample to a radiation wave vector appears due to the magnetic component of the electromagnetic field of resonating nanoparticles. This effect is additive to the basic magneto-optical Faraday Effect.

Distributed Poloidal Magnetic Field Measurement in Tokamaks Using Polarization-Sensitive Reflectometric Fiber Optic Sensor.

Determination of the poloidal magnetic field distribution in tokamaks is of prime importance for the successful operation of tokamaks. In this paper, we propose a polarization-sensitive reflectometry-based optical fiber sensor for measuring the spatial distribution of the poloidal magnetic field in tokamaks. The measurement method exploits the Rayleigh backscattering and Faraday magneto-optic effect in optical fibers. The former is an intrinsic property of optical fibers and enables distributed polarization measurements, while the latter arises in the presence of a magnetic field parallel to the optical fiber axis and rotates the polarization state of the light. When an optical fiber is looped around a toroidal section of the vacuum vessel, the local polarization rotation of the light is proportional to the local poloidal magnetic field in the tokamak. The proposed method is discussed theoretically and experimentally using the results from JET. The obtained magnetic field measurement shows a good agreement with that of the internal discrete coils. A potential solution to recover the magnetic field data from the noise-affected region of the optical measurement is proposed and is demonstrated through simulations using the JET magnetic field configuration.