Magneto-optical Devices Research Articles

Crystallization Double-Layer Magneto-Active Films for Magnetophotonics

Magneto-optics, magnetophotonics and magnetoplasmonics stay at the edge of scientific interests last years due to their unique features to manage the light and electromagnet field. Bi-substituted iron garnet (Bi:IG) is one of most promising magneto-optical material for these applications in order to its high efficiency in visible and infrared spectra. The possibility to integrate Bi:IG films to silicon semiconductor process leads to creation nanoscale hight performance magneto-optical devices. Bi:IG structures of different composition might be deposited by vacuum deposition on different substrates. The investigation of crystallization process of Bi:IG double-layer films at a different process parameter on gadolinium gallium garnet and fused quartz substrates allowing to determine dependences and suggestions for integration Bi:IG to semiconductor process or multicomponent optical nanostructures.

Linear-polarized terahertz isolator by breaking the gyro-mirror symmetry in cascaded magneto-optical metagrating

Abstract To realize nonreciprocal transmission, it is necessary to break the time-reversal symmetry of the transmission system, but it is very challenging to keep the linear polarized (LP) input and output unchanged in the free space transmission system. Magnetized semiconductor InSb can realize terahertz (THz) nonreciprocal transmission for the two conjugated photonic spin states, but it cannot realize efficient one-way transmission of LP state due to gyro-mirror symmetry. In this work, by introducing a pair of orthogonal uniaxial anisotropies from the meta-gratings on both sides of InSb, both the gyro-mirror and time-reversal symmetries are broken for the LP state, thus making this cascaded grating–InSb–grating structure serves as a high-performance isolator for the LP light. The experiment results indicate isolation of 50 dB at 0.4 THz for the same LP input and output under a weak biased magnetic field of 0.17 T. Moreover, we further illustrate the factors affecting the isolation bandwidth of the device, also demonstrated another broadband structure with the 10 dB isolation bandwidth from 0.2–0.7 THz, and the relative bandwidth achieves 110%. The mechanisms of THz nonreciprocal transmission and polarization manipulation proposed in this work will contribute to the development of efficient THz magneto-optical devices.

Liquid phase epitaxy growth of (GdYbBi)3(FeGe)5O12 films for magneto-optical applications

As an important component in magneto-optical devices, bismuth-substituted rare-earth iron garnet films play a significant role in guarantying a unidirectional light propagation in optical communication system. In this study, (GdYbBi)3(FeGe)5O12 film with a thickness of 120 μm was successfully grown by liquid phase epitaxy (LPE) technology. Lattice mismatch and internal stress between the epitaxial film and substrates were discussed in detail. Tested results shown that (GdYbBi)3(FeGe)5O12 films exhibit high crystal quality and large specific faraday rotation angle, which indicate that the prepared (GdYbBi)3(FeGe)5O12 films have a great potential to be used in optical communication system.

Strong magneto-optical effect and anomalous transport in the two-dimensional van der Waals magnets FenGeTe2 ( n=3 , 4, 5)

Two-dimensional ferromagnetic materials have recently been attracted much attention mainly due to their promising applications toward multifunctional devices, e.g., microelectronics, spintronics, and thermoelectric devices. Utilizing the first-principles calculations together with the group theory analysis, we systematically investigate the magnetocrystalline anisotropy energy, magneto-optical effect, and anomalous transport properties (including anomalous Hall, Nernst, and thermal Hall effects) of monolayer and bilayer ${\mathrm{Fe}}_{n}\mathrm{Ge}{\mathrm{Te}}_{2}$ ($n=3$, 4, 5). The monolayer ${\mathrm{Fe}}_{n}\mathrm{Ge}{\mathrm{Te}}_{2}$ ($n=3$, 4, 5) exhibits the out-of-plane, in-plane, and in-plane ferromagnetic orders with considerable magnetocrystalline anisotropy energies of $\ensuremath{-}3.17$, 4.42, and 0.58 meV/f.u., respectively. Ferromagnetic order is predicted in bilayer ${\mathrm{Fe}}_{4}\mathrm{Ge}{\mathrm{Te}}_{2}$ while antiferromagnetic order is preferred in bilayer ${\mathrm{Fe}}_{3}\mathrm{Ge}{\mathrm{Te}}_{2}$ and ${\mathrm{Fe}}_{5}\mathrm{Ge}{\mathrm{Te}}_{2}$. The group theory analysis reveals that in addition to monolayer ferromagnetic ${\mathrm{Fe}}_{n}\mathrm{Ge}{\mathrm{Te}}_{2}$ ($n=3$, 4, 5), the magneto-optical and anomalous transport phenomena surprisingly exist in bilayer antiferromagnetic ${\mathrm{Fe}}_{5}\mathrm{Ge}{\mathrm{Te}}_{2}$, which rare in realistic collinear antiferromagnets. If spin magnetic moments of monolayer and bilayer ${\mathrm{Fe}}_{n}\mathrm{Ge}{\mathrm{Te}}_{2}$ are reoriented from the in-plane to out-of-plane direction, then the magneto-optical and anomalous transport properties are enhanced significantly, presenting strong magnetic anisotropy. We also demonstrate that the anomalous Hall effect decreases with the temperature increases. The gigantic anomalous Nernst and thermal Hall effects are found in monolayer and bilayer ferromagnetic ${\mathrm{Fe}}_{n}\mathrm{Ge}{\mathrm{Te}}_{2}$, and the largest anomalous Nernst and thermal Hall conductivities, respectively, of $\ensuremath{-}3.31$ A/Km and 0.22 W/Km at 130 K are observed in bilayer ferromagnetic ${\mathrm{Fe}}_{4}\mathrm{Ge}{\mathrm{Te}}_{2}$. In particular, bilayer antiferromagnetic ${\mathrm{Fe}}_{5}\mathrm{Ge}{\mathrm{Te}}_{2}$ exhibits large zero-temperature anomalous Hall conductivity of 2.63 ${e}^{2}/h$ as well as anomalous Nernst and thermal Hall conductivities of 2.76 A/Km and 0.10 W/Km at 130 K, respectively. Our results suggest that two-dimensional van der Waals magnets ${\mathrm{Fe}}_{n}\mathrm{Ge}{\mathrm{Te}}_{2}$ ($n=3$, 4, 5) have great potential applications in magneto-optical devices, spintronics, and spin caloritronics.

Conversion of non-van der Waals VO2 solid to 2D ferromagnet by CO2-induced phase engineering

Two-dimensional (2D) ferromagnetic semiconductors that combine ferromagnetic order with desirable physical attributes could find transformative applications in atomically-thin magneto-optical and magnetoelectric devices. The mainstream strategies of creating magnetic moments in 2D materials are introducing charge carriers. Here we introduce a CO2-induced phase engineering strategy that achieves 2D ferromagnet via the transformation of non-van der Waals (non-vdW) VO2 solid to 2D defective structure with identified metastable phases. Our approach requires only exposing the structure to supercritical CO2 liquid that is able to first infiltrate and swell the material at the molecular scale, and then “plasticize” VO2 solid at the architectural scale to form a 2D defective network that ‘lock’ the metastable phases into a new topological structure, which would lead to a significantly enhanced ferromagnetic response. We attribute the phase transformation to the CO2 pressure-induced selective cleavage of covalent bond.

Mixed valence effects in Pr:YbF3 nanocrystals and influence to EPR, magnetic and Faraday rotation properties of diamagnetic glasses

The co-existence of light and heavy rare earth ions will arouse interesting optical, magnetic and magneto optical properties to matrix due to energy transfer between various rare earth ions and spin-orbit interactions of electric dipoles and magnetic dipoles. Pr and Yb co-doped orthorhombic Pr:YbF3 nano-crystals have been prepared by hydrothermal method, the structure and properties of Pr:YbF3 were characterized using X-ray diffraction, scanning electron microscopy, electron paramagnetic resonance, Raman & Infrared spectra and superconducting quantum interference device. The introduction of Pr into YbF3 induced changes on morphology, structure and properties due to different ionic radius, electronegativity and bond strength.The fabricated Pr:YbF3 nanocrystal doped glasses show good transparency and morphology. Pr:YbF3 nanocrystals were well dispersed in glass with slightly increased size (25 nm). X-ray photoelectron spectra confirmed the co-existence of Yb2+, Yb3+ and Pr3+ in 1% and 2% doped glasses, and additional Pr4+ in 4% doped one. Optical absorption edge red-shifted and emission intensity increased with the doping amount. Energy transfer between Pr3+ and Yb3+ ions was observed around 1000 nm. Due to the electron transition and energy transfer, the magnetization changed from diamagnetic to ferromagnetic and showed temperature-dependent behaviors. The Faraday rotation was significantly reinforced by Pr:YbF3 and a giant Verdet constant of -0.32 min/G.cm was obtained at 533 nm wavelength for 4% Pr:YbF3 doped glass which is promising for magneto optical devices.

Vortex beam manipulation through a tunable plasma-ferrite metamaterial

This paper is devoted to the study of vortex beam transmission from an adjustable magnetized plasma-ferrite structure with negative refraction index. We use the angular spectral expansion technique together with the 4times 4 matrix method to find out the transmitted intensity and phase profiles of incoming Laguerre-Gaussian beam. Based on numerical analysis we demonstrate that high transparency and large amount of Faraday rotation in the proximity of resonance frequency region, reverse rotation of spiral wave front, and side-band modes generation during propagation are the remarkable features of our proposed structure. These controllable properties of plasma-ferrite metamaterials via external static magnetic field and other structure parameters provide novel facilities for manipulating intensity and phase profiles of vortex radiation in transmission through the material. It is expected that the results of this work will be beneficial to develop active magneto-optical devices, orbital angular momentum based applications, and wavefront engineering.

Homochiral Ferromagnetic Coupling Dy2 Single-Molecule Magnets with Strong Magneto-Optical Faraday Effects at Room Temperature.

By the bridging action of the 6-chloro-2-hydroxypyridine (Hchp) ligand and the terminal coordination role of the homochiral ligand, (-)/(+)-3-trifluoroacetyl camphor (l-Htfc/d-Htfc), a pair of enantiomerically pure dysprosium(III) dinuclear complexes, [Dy2(l-tfc)4(chp)2(MeOH)2] (l-1) and [Dy2(d-tfc)4(chp)2(MeOH)2] (d-1), was obtained. Their circular dichroism (CD) spectra verified their enantiomeric nature. Magnetic investigation indicated that they exhibit ferromagnetic interaction and good zero field single-molecule magnet (SMM) properties. The Ueff/k values of l-1 and d-1 at 0 Oe are 180.5 and 181.3 K, respectively, which are large values for homochiral Dy(III) SMMs. A reasonable explanation for the magnetic properties of l-1 and d-1 was supplied by ab initio calculations. Remarkably, magnetic circular dichroism (MCD) investigation revealed that the chiral Dy2 enantiomers show a strong magneto-optical Faraday effect at room temperature, suggesting potential applications in magneto-optical devices.

Laser Dressed Magnetic Polaron In Semimagnetic Core/Shell Nanostructure

The combined effects of magnetic and intense laser fields on the properties of the ground state exciton in semimagnetic Cd0.7Mn0.3Te/CdTe Core/Shell Nanostructure (CSN) are analyzed using the variational method in the effective mass approximation. The magnetic field of 5 to 20 T, a laser with the frequency of 10 THz and its intensity ranging from 0.44 to 7.11 μW nm−2 are considered as external perturbing fields. The evolution of Exciton Magnetic Polaron (EMP) in response to the external fields is explored via Magnetization (M) and Zeeman energy shift (∆EZE). The variation in binding energy (BE) of an exciton, M and ∆EZE are examined for different shell widths, magnetic and laser fields. The laser-induced diamagnetism due to the dressed energy state of carriers reduces the polarization of EMP. Similarly, the external magnetic field reduces the exchange interaction between carriers and weakens EMP. The combined effect of perturbing fields on an EMP will give an insight on controlling the performance of magneto-optic devices.

Optical planar and ridge waveguides in terbium scandium aluminum garnet crystal fabricated by ion implantation and precise diamond blade dicing

Terbium scandium aluminum garnet crystal is a promising material which has excellent characteristics for magneto-optical devices. We report on the fabrication of optical planar and ridge waveguides in the terbium scandium aluminum garnet by using combination of helium ion implantation and precise diamond blade dicing. The conditions for the ion implantation are an energy of 400 keV and a fluence of 6 × 1016 ions/cm2. The rotating velocity and cutting speed of the diamond blade were set to be 20,000 rpm and 0.1 mm/s, respectively. The implantation depth and distributions of energy loss were calculated by the stopping and range of ions in matter 2013. The refractive index distribution and the dark-mode spectrum for the implanted planar waveguide were obtained by the reflectivity calculation method and the prism coupling system, respectively. The near-field intensity profiles of both the planar and ridge waveguides were measured by the end-face coupling technique. The optical guiding properties of the terbium scandium aluminum garnet waveguides suggest that they can serve as candidates for optical waveguide isolators.

Increasing reliability of forensic analysis while research on destroyed relief marking with magneto-optical devices

While research on destroyed relief marking of metal objects using the magneto-optical method, visualization of (invisible) fields of internal stress in the VIN plate area is performed and then a forensic analysis of obtained instrumental data is carried out (indirect organoleptic observation of the visualization results); thus, forensic analysis reliability of results directly depends on sensitivity of instruments and informativeness of instrumental data.
 The main quantitative characteristic in this case is probability of correct signal recognition (contours of marking signs) against the background of noise (structural noise of investigated surface and the noise of the visualization method itself) determined by the signal-to-noise ratio.
 This article presents results of a comparative experimental assessment of signal-to-noise ratio and probability of correct signal recognition while restoringthe destroyed relief markings for two complexes of magneto-optical imaging – models of 2006 and 2018.
 This article purpose is a quantitative and qualitative comparative assessment of results of visualization of internal stresses in areas of completely removed relief marking of metal objects. The results of successful practical research obtained by forensic experts from different countries make it possible to assess effectiveness and prospects of using the magneto-optical imaging method.
 In a new modification of the magneto-optical complex:
 
 signal level is 4.35 dB higher (contrast of reconstructed marking signs);
 2.71 dB lower noise level (surface relief/texture and magnetic copying noise);• probability of correct character recognition is P> 0.995 (increased by 14.9%).
 
 Technical improvements in implementation of magneto-optical visualization method made it possible to expand the range of materials for research objects(magnetic and electrically conductive materials were investigated).
 The high efficiency of method for restoring marking is illustrated by results of forensic examinations for materials with a low level of residual stresses (aluminum alloy, low-carbon steel) which chemical etching method did not give results for.
 The use of new modification allows examining the rust layer, up to cases of corrosion to the entire depth of marks.
 Considering non-destructive nature of magneto-optical researches, possibility of their repeated repetition without losing object properties, this method (in accordance with the order of application of types of studies) deserves more attention for application.

OPTICAL BISTABILITY IN A DEGENERATE TWO-LEVEL EIT MEDIUM UNDER THE INFLUENCE OF AN EXTERNAL MAGNETIC FIELD: AN ANALYTICAL APPROACH

We investigate the behavior of optical bistability in a degenerate two-level atomic medium using an external magnetic field to separate the lower level into two distinct levels that both connect to an upper level by the probe and coupling laser fields. Based on analytical solutions, the absorption spectrum and behavior of optical bistability in an electromagnetically induced transparency regime under an external magnetic field are investigated. By controlling the external magnetic field, we find that the appearance and disappearance of the optical bistability can be easily controlled according to the strength of the magnetic field in the transparent window domain. Furthermore, the effects of the intensity of the coupling laser field and the parameters of the system on the behavior of optical bistability are also considered. The proposed model is useful for applications in all-optical switches and magneto-optic storage devices.

Anomalous Magneto-Optical Effects in an Antiferromagnet–Topological-Insulator Heterostructure

We show that large magneto-optic Kerr effects (MOKEs) emerge when an antiferromagnet (AFM) is proximately coupled to a topological insulator (TI) film---where neither the perfect collinear N\'eel ordered single-domain AFM nor the unmagnetized TI individually shows any MOKE. Because of the lack of macroscopic magnetization, the AFM only couples to the spin of one of the TI's surfaces breaking time-reversal and inversion symmetry---which leads to a small microdegree MOKE signal. This small MOKE can be easily enhanced by 5 orders of magnitude, via cavity resonance, by optimizing the AFM and TI film thicknesses on the substrate. For slightly off-resonant structures, a ${6}^{\ensuremath{\circ}}$ Kerr rotation can be electrically switched on by varying the Fermi energy. This requires less than 20 meV, which is encouraging for low-power spintronics and magneto-optic devices. We further show that this simple structure is easily resilient to 5% material growth error.

Two-Dimensional Chromium Bismuthate: A Room-Temperature Ising Ferromagnet with Tunable Magneto-Optical Response

We present a density functional theory (DFT) based study of a two-dimensional phase of chromium bismuthate (CrBi), previously unknown material with exceptional magnetic and magnetooptical characteristics. Monolayer CrBi is a ferromagnetic metal with strong spin-orbit coupling induced by the heavy bismuth atoms, resulting in a strongly anisotropic Ising-type magnetic ordering with the Curie temperature estimated to be higher than 300 K. The electronic structure of the system is topologically nontrivial, giving rise to a nonzero Berry curvature in the ground magnetic state, leading to the anomalous Hall effect with the conductivity plateau of $\sim$1.5 $e^2/h$ at the Fermi level. Remarkably, the Hall conductivity and the magnetooptical constant are found to be strongly dependent on the direction of magnetization. Besides, monolayer CrBi demonstrates the polar magnetooptical Kerr effect in the visible and near-ultraviolet spectral ranges with the maximum rotation angles of up to 10 mrad. Our findinds suggest that monolayer CrBi is a promising system for practical applications in magnetooptical and spintronic devices.

Field validation of a magneto-optical detection device (Gazelle) for portable point-of-care Plasmodium vivax diagnosis.

A major challenge for malaria is the lack of tools for accurate and timely diagnosis in the field which are critical for case management and surveillance. Microscopy along with rapid diagnostic tests are the current mainstay for malaria diagnosis in most endemic regions. However, these methods present several limitations. This study assessed the accuracy of Gazelle, a novel rapid malaria diagnostic device, from samples collected from the Peruvian Amazon between 2019 and 2020. Diagnostic accuracy was compared against microscopy and two rapid diagnostic tests (SD Bioline and BinaxNOW) using 18ssr nested-PCR as reference test. In addition, a real-time PCR assay (PET-PCR) was used for parasite quantification. Out of 217 febrile patients enrolled and tested, 180 specimens (85 P. vivax and 95 negatives) were included in the final analysis. Using nested-PCR as the gold standard, the sensitivity and specificity of Gazelle was 88.2% and 97.9%, respectively. Using a cutoff of 200 parasites/μl, Gazelle’s sensitivity for samples with more than 200 p/uL was 98.67% (95%CI: 92.79% to 99.97%) whereas the sensitivity for samples lower than 200 p/uL (n = 10) was 12.5% (95%CI: 0.32% to 52.65%). Gazelle’s sensitivity and specificity were statistically similar to microscopy (sensitivity = 91.8, specificity = 100%, p = 0.983) and higher than both SD Bioline (sensitivity = 82.4, specificity = 100%, p = 0.016) and BinaxNOW (sensitivity = 71.8%, specificity = 97.9%, p = 0.002). The diagnostic accuracy of Gazelle for malaria detection in P. vivax infections was comparable to light microscopy and superior to both RDTs even in the presence of low parasitemia infections. The performance of Gazelle makes it a valuable tool for malaria diagnosis and active case detection that can be utilized in different malaria-endemic regions.

Highly Dy2O3 and Er2O3 doped boron-aluminosilicate glasses for magneto-optical devices operating at 2 µm

Magneto-optical glass materials with large Verdet constants at 2 μm have attracted increasing attention due to the significant advances of novel lasers operating at this wavelength region. In this paper, 13Al2O3-21B2O3-35.4SiO2-(30.6-X)Er2O3-XDy2O3 glasses have been synthesized, and their physical, optical, and magneto-optical properties were studied for making Faraday devices at 2 μm. A Verdet constant of as high as −5.9 rad/(T*m) at 1950 nm was measured with a 13Al2O3-21B2O3-35.4SiO2-30.6Dy2O3 glass. The temperature difference between crystallization and glass transition of 150 °C and the synthesis temperature of below 1500 °С make this glass very promising for making magneto-optical devices for 2 μm applications.

The effect of using coated graphene in enhancing Faraday rotation in gyroelectric and gyromagnetic materials

In this article, we introduce a Faraday rotator based on the gyroelectric (e.g. InSb) and gyromagnetic (e.g. MnF2) materials. We have designed a single layer of graphene placed on anisotropic materials, enhancing the Faraday rotation up to 30 degrees. More than 80% transmission has been achieved in the THz band (1 THz–7 THz). This design opens up a new way in ultrathin magneto-optical nanophotonic devices to realize polarization rotators with high transmittance in the THz band.

Magneto-optical properties of borophosphate glasses co-doped with [formula omitted] and [formula omitted]ions

Glasses from lithium-aluminum-zinc-boron-phosphorous oxide system co-doped with terbium (Tb3+) and dysprosium (Dy3+) oxides were studied for magneto-optical applications in lasers. The Fourier Transform Infrared and Raman Spectroscopy complementary analysis suggested the depolymerization of the boro-phosphate glass network by adding and increasing the rare-earth (RE) oxide content. Main UV–vis absorption maxima of Tb and Dy ions were identified at 348 and 1266 nm. Spectroscopic ellipsometry indicated a maximum refractive index of 1.56, at 400 nm, for the highest RE content. The Verdet constant amplified by increasing the RE content, reaching for the 9 mol% RE co-doped sample a value of -0.075 min/Oe/cm at 630 nm. The Faraday rotation angle was additionally confirmed by using a Faraday Cell Device, being also related to the specific paramagnetic behavior evidenced by Superconducting Quantum Interference Device magnetometry. The magneto-optical properties recommend such vitreous co-doped materials for magneto-optical devices.

Tunable Exchange-Bias-Like Effect in Bi -Substituted Gadolinium Iron Garnet Film

Using magneto-optical Faraday and Kerr measurements, we investigate the magnetic and magneto-optical properties of a thick $\mathrm{Bi}$-substituted gadolinium iron garnet film over a broad range of wavelengths (250--850 nm) and temperatures (150--300 K), including the magnetization compensation point, ${T}_{M}$. We observe an exchange-bias-like effect in the vicinity of ${T}_{M}$. By slightly changing the sample temperature, we can precisely tune the bias field, which reaches a magnitude 6 times higher than the coercive field. We explain this phenomenon by considering the short-range superexchange interaction and a change in the magnetic behavior when moving from the surface to the bulk of the film. This finding may lead to the development of single-film magneto-optical devices based on the exchange-bias effect.

Complete redshift photonic bandgap and dual-wavelength polarization selection in periodic multilayer structure containing hyperbolic metamaterial

According to the Bragg interference mechanism, photonic bandgaps (PBGs) in conventional all-dielectric periodic multilayer structures shift towards shorter wavelengths (blueshift) as the incident angle increases under both TM and TE polarizations. Hence, the polarization dependence of PBGs in conventional all-dielectric periodic multilayer structures is too weak to realize polarization selection in a broad angle range. Based on the anomalous angle-dependent property of the propagating phase within hyperbolic metamaterial (HMM), we design a complete redshift PBG under TM polarization whose two band edges shift towards longer wavelengths as the incident angle increases in a periodic multilayer structure composed of alternating dielectric and HMM layers. However, the PBG under TE polarization is still blueshifted. As a result, around the long-wavelength and the short-wavelength band edges, efficient polarization selection can be achieved in a broad angle range. This dual-wavelength wide-angle polarization selector based on the complete redshift PBG might possess applications in liquid crystal displays and read–write magneto-optical data storage devices.