Magneto-optical Materials Research Articles

Magneto-optic properties of highly Dy3+-doped GeO2-B2O3 glasses for NIR optical applications

Recent progress in the development of optical communication and high power laser systems in the near-infrared (NIR) region (1.5 to 2.0 μm) increased the demand for magneto-optic (MO) devices employing MO materials. These MO materials are required with lower optical absorption coefficients and higher Verdet constants at spectral range of interest. In this study, two series of highly Dy3+-doped GeO2–B2O3 glasses with and without P2O5 were fabricated using a simple melt-quenching technique. The glasses were characterized through various techniques (Raman, UV–VIS-NIR, and DTA) for the evaluation of characteristic properties with respect to the Dy2O3 concentration and glass composition. Faraday rotation measurement was carried out at 1550 nm to quantify the Verdet constant of the glasses. The Verdet constant values were found to increase linearly with increasing Dy3+ concentration for both the glass systems. The increase in Dy3+ concentration and, consequently, the number of unpaired electrons, leads to an increase in the Verdet constant. The GeO2-B2O3 glass doped with 30 mol% of Dy2O3 exhibited the highest Verdet constant of −5.36 rad/(T⋅m) at 1550 nm. The glasses exhibited a good optical transparency (>70 %) in the region covering from 400 to 2400 nm. The thermo-physical, optical, and polarizability properties of both glass systems were also investigated. The results indicate that the highly Dy3+-doped glasses are attractive for magneto-optics at 1550 nm.

Magneto-optical Goos–Hänchen shift in uniaxial anisotropic epsilon-near-zero metamaterials

Abstract We theoretically investigate the enhancement of the magneto-optical Goos-Hänchen (MOGH) shift in multilayer structure combining uniaxially anisotropic epsilon-near-zero (ENZ) metamaterials with magneto-optical (MO) materials. The structure enables the excitation of magneto-optical surface plasmon resonance (MOSPR) without the need for a prism or grating coupler, thereby achieving a significant enhancement of the MOGH shift. The effect of the thickness of the ENZ layer and the type of magnetic metal in this structure on the MOGH shift is also discussed. Based on the above structure, we design a high-sensitivity miniature biosensor that is used for the detection of hemoglobin concentration in human blood. The maximum sensitivity achievable with this sensor is 1.4×106 λ/RIU. The results of this investigation contribute to the development of biosensors towards miniaturization and integration.

Integrated non-reciprocal magneto-optics with ultra-high endurance for photonic in-memory computing

AbstractProcessing information in the optical domain promises advantages in both speed and energy efficiency over existing digital hardware for a variety of emerging applications in artificial intelligence and machine learning. A typical approach to photonic processing is to multiply a rapidly changing optical input vector with a matrix of fixed optical weights. However, encoding these weights on-chip using an array of photonic memory cells is currently limited by a wide range of material- and device-level issues, such as the programming speed, extinction ratio and endurance, among others. Here we propose a new approach to encoding optical weights for in-memory photonic computing using magneto-optic memory cells comprising heterogeneously integrated cerium-substituted yttrium iron garnet (Ce:YIG) on silicon micro-ring resonators. We show that leveraging the non-reciprocal phase shift in such magneto-optic materials offers several key advantages over existing architectures, providing a fast (1 ns), efficient (143 fJ per bit) and robust (2.4 billion programming cycles) platform for on-chip optical processing.

Study of the magnetic and structural properties of the simple perovskite YFeO3

In the present work, an experimental and theoretical study of the synthesis, magnetic, and structural properties of simple perovskite compounds YFeO3 has been investigated based on their potential applications, such as: solid oxide fuel cells, electrochemical sensors, sensor materials, magneto-optical materials, etc. Experimentally, the synthesis was carried out by the sol-gel method. X-rays and Rietveld refinements confirmed the orthorhombic structure. Scanning electron microscopy observations confirmed agglomerates of simple perovskite particles YFeO3. The study of the magnetic phase of the simple perovskite YFeO3 showed that it behaves like a weak ferromagnetic, this property delimits and directs magnetic fields into well-defined trajectories. On the other hand, the structural results, from a theoretical point of view, are in good agreement with the experimental ones. Through energy comparison, a possible competition was identified between the FM and AFM states, where the electronic properties are associated with the directional nature of the hybridization between the p orbitals of oxygen and the t2g states, where the superexchange mechanism prevails with e oxygen as mediator.

Transparent Tb2Ti2O7 ceramics for use in Faraday isolators

Magneto-optical and thermo-optical characteristics of transparent Tb2Ti2O7 ceramics were investigated. The dependence of the index of refraction on the wavelength in the 0.29–2 μm range, the wavelength and temperature dependence of the Verdet constant, as well as the dependence of thermally induced depolarization on laser radiation power were measured. The value of the Verdet constant in Tb2Ti2O7 surpasses that in Tb3Ga5O12 by more than 1.68 times. The thermo-optical characteristic Qeff was estimated to be (1.8–3.7)∙10−8 1/K, which is record small compared to Qeff of the known magneto-optical materials. The small value of Qeff makes Tb2Ti2O7 a highly promising magneto-optical material for Faraday isolators and rotators for high average power lasers.

Nonreciprocity in transmission mode with planar structures for arbitrarily polarized light [Invited

Approaching thermodynamic limits in light harvesting requires enabling nonreciprocal thermal emission. The majority of previously reported nonreciprocal thermal emitters operate in reflection mode, following original proposals by M. Green [Nano Lett. 12, 5985 (2012)10.1021/nl3034784] and others. In these proposals, cascaded nonreciprocal junctions that re-direct each junction’s emission towards a subsequent one are employed for efficient light-harvesting. Recently, simplified concepts have been proposed in solar photovoltaics and thermophotovoltaics, respectively, that leverage the concept of tandem junctions to approach thermodynamic limits. In these simplified scenarios, polarization-independent nonreciprocal response in transmission mode is required. We propose a pattern-free heterostructure that enables such functionality, using a magneto-optical material embedded between two dissimilar dielectric layers.

Optical fiber sensor based on magneto-optical surface plasmon resonance with ultra-high figure of merit

Compared to surface plasmon resonance (SPR), the sensors based on the magneto-optical SPR (MOSPR) technique have much higher figure-of-merit (FOM). However, there are no reports about applying MOSPR in the optical fiber structure now. In this work, a novel D-shaped optical fiber sensor based on the MOSPR technique is proposed. The D-shaped optical fiber is coated with a thin silver film and a magneto-optical (MO) material film of Cerium-doped Yttrium-Iron garnet (CeYIG). By applying a magnetic field on the sensing region, the magneto-optical Kerr effect (MOKE) of the CeYIG layer and the related MOSPR phenomenon could be excited when appropriate light is transmitted in the proposed optical fiber sensor. The influence of the structural parameters including the residual cladding thickness, silver and MO material film thicknesses are analyzed theoretically by the finite element method (FEM). With the optimal parameters, the sensor achieves the sensitivity of 5304 nm RIU−1. Since the peak width of MOSPR spectra is much narrower than that of the SPR spectra, the FOM of the sensor is largely enhanced to 3864 RIU−1 on average and 13260 RIU−1 in maximum, which surpasses the optical fiber SPR sensors vastly. The miniaturized and simple design of the D-shaped optical fiber MOSPR sensor, coupled with the ultra-high FOM, offers itself great potential in biochemical sensing applications.

Magneto-Optical Ceramics with High Transparency for Highly Sensitive Magnetometer via Quantum Weak Measurement.

Sensitive magnetometer technology is desirable for biomagnetic field detection and geomagnetic field measuring. Signal amplification materials such as magneto-optical crystals or ceramics are crucial for enhancing detection sensitivity, but severe optical scattering and low Verdet constant further limit its application. To develop high-sensitivity magnetometers for quantum weak measurement schemes, we have conducted investigations on the powder calcining dynamics and prepared a series of high-optical-quality (Ho/Dy)2Zr2O7 transparent ceramic samples. The Verdet constant of magneto-optical materials was measured across a continuous wavelength spectrum, exhibiting a peak at 283 ± 5 rad/(T·m). We further established an electron transition mechanism to elucidate the exceptional magneto-optical attributes of dysprosium. In addition, samples demonstrated superior performance in weak-value amplification, reaching a low detectable magnetic field threshold of 3.5 × 10-8 T and continuously worked over 6 h with high stability. Our work developed a highly sensitive magnetometer using optimized magneto-optical ceramics and provided guidance on design, fabrication, and application for magneto-optical ceramics in quantum weak measurement.

Non-reciprocal optical Tamm state in a photonic crystal heterojunction containing Weyl semimetals

In the past decades, optical Tamm states (OTSs) in photonic crystal (PC) heterojunctions containing magneto-optical materials have been widely utilized to achieve non-reciprocal transmission. Nevertheless, as incident angle increases, both forward and backward OTSs in PC heterojunctions containing magneto-optical materials shift toward shorter wavelengths (i.e., blueshift), giving rise to weak non-reciprocities. In this paper, we achieve a non-reciprocal OTS in a PC heterojunction containing Weyl semimetals (WSMs). Interestingly, as incident angle increases, the forward OTS shifts towards longer wavelengths while the backward OTS shifts toward shorter wavelengths. Therefore, the non-reciprocity can be greatly enhanced. The underlying physical mechanism can be explained by the Fabry-Perot resonant condition. Besides, the effects of the axial vector b and the loss of WSM on non-reciprocity are investigated. These results would possess great potential applications in the design of circulators and isolators.

Tunable Near-Field Radiative Heat Transfer between Graphene-Coated Magneto-Optical Metasurfaces.

The highly structured design of metasurfaces greatly facilitates the manipulation of near-field radiative heat transfer (NFRHT). In this study, we incorporate magneto-optical materials into metasurfaces to theoretically explore the mechanism for controlling NFRHT between anisotropic magneto-optical metasurfaces. Our findings indicate that the interaction between the magnetization-induced modes, arising from interband transitions of graphene, and the surface modes of InSb under a magnetic field leads to a transition in the heat transfer spectrum from a dual band to a triple band. The modification of the distribution and magnitude of transmission wave vectors in surface electromagnetic modes by magnetic fields serves to modulate the radiative heat flux. By combining active control by a magnetic field with passive structural design of metasurfaces, the regulation of heat flux can be increased by more than 8-fold compared with the planar configuration. Additionally, the magnetic field amplifies the anisotropy of the photon energy distribution induced by the symmetry breaking of the metasurface structure. This study is anticipated to provide a pathway for achieving flexible tuning of NFRHT by combining active and passive regulation. It also opens up possibilities for multiband information transmission and for improving the performance of energy conversion devices.

Non-reciprocity in a silicon photonic ring resonator with time-modulated regions.

Non-reciprocity and breaking of the time-reversal symmetry is conventionally achieved using magneto-optic materials. However, the integration of these materials with complementary metal-oxide semiconductor (CMOS)-compatible platforms is challenging. Temporal modulation is a well-suited approach for achieving non-reciprocity in integrated photonics. However, existing experimental implementations based on this method in silicon uses traveling-wave modulation in the whole structure or tandem ring or waveguide modulators, and they lead to high insertion loss and large footprint. In this work we achieve, to the best of our knowledge, the first experimental demonstration of non-reciprocity in a compact single silicon photonic ring resonator with time-modulated regions, fabricated with a CMOS-compatible commercial foundry. We demonstrate symmetry breaking of counter-rotating modes in an active silicon photonic ring resonator by applying phase-shifted RF signals to only two small p-i-n junctions on the ring, without employing traveling-wave modulation in the whole structure. The non-reciprocity is caused by the cross-coupling between the counter-rotating modes of the ring, which breaks their degeneracy. By reversing the polarity of the RF phase difference (e.g. (45°,-45°) asymmetric phases) opposite resonance wavelengths are obtained, with a 16-dB contrast between the transmissions of the asymmetric phases and a low insertion loss of 0.6 dB under 27 dBm RF power. We achieve the highest ratio of the asymmetric transmission to the insertion loss, among the state-of-the-art silicon non-reciprocal integrated optical structures based on time varying modulation. The non-reciprocal ring can be used as a magnetic-free, low-loss, compact, and CMOS-compatible integrated optical isolator.

Magnetic field expulsion in optically driven YBa2Cu3O6.48.

Coherent optical driving in quantum solids is emerging as a research frontier, with many reports of interesting non-equilibrium quantum phases1-4 and transient photo-induced functional phenomena such as ferroelectricity5,6, magnetism7-10 and superconductivity11-14. In high-temperature cupratesuperconductors, coherent driving of certain phonon modes has resulted in a transient state with superconducting-like optical properties, observed far above their transition temperatureTc and throughout the pseudogap phase15-18. However, questions remain on the microscopic nature of this transient state and how to distinguish it from a non-superconducting state with enhanced carrier mobility. For example, it is not known whether cuprates driven in this fashion exhibit Meissner diamagnetism. Here we examine the time-dependent magnetic field surrounding an optically driven YBa2Cu3O6.48 crystal by measuring Faraday rotation in a magneto-optic material placed in the vicinity of the sample. For a constant applied magnetic field and under the same driving conditions that result in superconducting-like optical properties15-18, a transient diamagnetic response was observed. This response is comparable in size with that expected in an equilibrium type II superconductor of similar shape and size with a volume susceptibility χv of order -0.3. This value is incompatible with a photo-induced increase in mobility without superconductivity. Rather, it underscores the notion of a pseudogap phase in which incipient superconducting correlations are enhanced or synchronized by the drive.

Tunable quasi-bound states in the continuum in magneto-optical metasurfaces

The enhancement of electromagnetic field with high Q factor in metasurfaces has attracted extensive attention of researchers. Magneto-optical metasurfaces (MOMS) provide approaches with controllable magnetic fields to modulate the optical response, which contributes towards the magneto-optical Kerr effect in nanophotonic devices. However, it is challenging for MOMS to obtain narrow spectra peak with high Q factors. Here, we propose MOMS-supported quasi-bound states in the continuum (quasi-BIC) and theoretically investigate the evolution process from BIC to quasi-BIC. By applying an external magnetic field, the BIC in our proposed metasurface can be transformed into a quasi-BIC with finite Q factor up to 33 620. Meanwhile, the quasi-BIC shows magnetization-related circular dichroism with a vortex point in the polarization graph, based on time-reversal symmetry breaking in the magneto-optical material under the condition of external magnetic field. The quasi-BIC also maintains nearly unity reflection and almost zero absorption, showing a promising future in sensing. Our results enrich the light control mechanisms of MOMS and provide a unique opportunity for applications requiring flexible tunability and high Q factors, such as sensors, laser sources, filters and chiral-related elements.

Polarization-independent nonreciprocal thermal radiation by cylindrical grating structure

Due to the significant application value of nonreciprocal thermal radiation in energy collection and conversion, it has always been an active research topic. The current research on polarization-independent nonreciprocal thermal radiation is characterized by low efficiency and a notable disparity in nonreciprocal efficiency between transverse electric (TE) and transverse magnetic (TM) polarizations. To address this issue, a polarization-independent nonreciprocal thermal radiation based on the two-dimensional grating structure is proposed, which is composed of silicon cylindrical grating ridges, magneto-optical materials InAs, and metal Ag. By the rigorous coupled-wave analysis (RCWA), the nonreciprocal efficiency exceeds 90 % at a wavelength of 11.763 μm under both TE and TM polarizations. Meanwhile, the difference in nonreciprocal efficiency between the two polarizations is less than 1 %. Through an examination of the magnetic field and electromagnetic distribution at resonance peaks that are polarization-independent, as well as an analysis of coupling mode theory, we have uncovered the underlying physical mechanisms responsible for this phenomenon. The device is capable of sustaining optimal performance across a wide range of structural parameters, offering a significant role for manufacturing applications. The research proposed in this article provides a novel approach for designing efficient polarization-independent nonreciprocal thermal radiation.

Effect of non-stoichiometric Ga content on the microstructure and optical transparency of terbium gallium garnet ceramics

The use of Faraday isolators in high-power lasers is currently a high-priority research topic and terbium gallium garnet (Tb3Ga5O12, TGG) transparent ceramic is a magneto-optical material with great potential for applications in the visible and near-infrared ranges. In this paper, the effect of chemical composition adjustment on the microstructure and properties of Tb3Ga5(1+x)O12 ceramics (where x is the non-stoichiometric index corresponding to the percentage difference in the amount of Ga used in the synthesis with respect to its content in the stoichiometric compound) was investigated. Powders obtained from starting materials of different stoichiometry were found to have similar morphology. However, the relative densities of the ceramics after pre-sintering in air increase with increasing Ga content. After the HIP post-treatment, the optimal properties with an in-line transmittance of 78.5 % (1.5 mm thick) at 1064 nm, and the Verdet constant of the ceramics with x = 0.8 % reaches −134.1 rad T−1 m−1 at 633 nm.

Coral-Inspired Terahertz-Infrared Bi-Stealth Electronic Skin.

The development of electronic skin with dual stealth functionality is crucial for enabling devices to operate effectively in dynamic electromagnetic environments, thereby facilitating intelligent electromagnetic protection for autonomous perception. However, achieving compatibility between terahertz (THz) and infrared (IR) stealth technologies remains largely unexplored due to their inherent contradictions. Herein, inspired by natural corals, a novel coral-like multi-scale composite foam (CMSF) was proposed that ingeniously reconciles these contradictions. The design capitalizes on the conductive network and heat insulation properties of the foam skeleton, the loss effects and low infrared emission of metal particles, and the infrared transparency of magneto-optical materials. This approach leads to the realization of a THz-IR bi-stealth electronic skin concept. The CMSF exhibits a maximum reflection loss of 84.8 dB in the terahertz band, while its infrared stealth capability ensures environmental adaptability under varying temperatures. Furthermore, the electronic skin exhibits exceptional sensitivity and reliability as a wearable device for perceiving environmental changes. This advanced material, combining multispectral stealth with sensing capabilities, holds immense potential for applications ranging from camouflage technology to smart wearables.

Graphene tunable dual-band nonreciprocal thermal emitter under TE polarization

Nonreciprocal thermal radiation is an emerging research direction, which can be achieved by adding anisotropic magneto-optical materials to some optical components. At present, most of the research focuses on nonreciprocal thermal radiation under TM polarization. In this paper, we propose a nonreciprocal emitter under TE polarization, which is a dual-band nonreciprocal emitter. There are twice guided mode resonances (GMRs) between 13 μm and 16 μm. It is a grating composed of a metal Ag and a magneto-optical material InAs. When the applied magnetic field is 3T, more than 90 % nonreciprocity is achieved at the incident wavelengths of 13.845 μm and 15.32 μm. In addition, we add a layer of graphene to the grating ridge to tune the peak position. It has a wide range of applications for the study of nonreciprocal thermal radiation, which can improve the energy conversion efficiency.

Studies on electromagnetic waves for ferromagnetic materials

With the developing technology, magneto-optical and ferromagnetic materials are gaining importance and are used especially in magneto-optics, ferromagnetism, fluid mechanics, etc. These processes are modeled via Kadomtsev–Petviashvili-type models. In this work, a generalized (3+1)-dimensional variable-coefficient modified Kadomtsev–Petviashvili (vcmKP) system and special cases are considered that simulates electromagnetic, water, and powder-acoustic/ion-acoustic/dust-ion-acoustic waves. As to the novelty of this paper, the travelling wave, soliton solutions of the considered systems are hold by using Bernoulli method which is the well-known ansatz-based method and the analytical method. As far as we know, the obtained solutions are seen for the first time in this study and are important for the development of the use of magneto-optical and ferromagnetic materials in industry and applied sciences, fiber optic communication fields.

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.

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.