Search Results (27)

This study presents a theoretical investigation of a terahertz (THz) surface plasmon resonance (SPR) optical biosensor utilizing a graphene-integrated Otto configuration. Through systematic numerical simulations, we demonstrate that actively modulating graphene’s conductivity via an external magnetic field enables tunable SPR behavior with high phase sensitivity. The proposed sensor achieves a phase sensitivity of up to $3.1043\times {10}^5$ deg RIU⁻¹ in liquid sensing and $2.5854\times {10}^4$ deg RIU⁻¹ in gas sensing. This simulation-based work establishes a foundational framework for the development of highly sensitive, magneto-optically tunable optical sensors, highlighting their potential in chemical detection and medical diagnostics. Full article

Nickel (Ni) ultrathin films exhibit phase-dependent electrical, magnetic, and optical characteristics that are significantly influenced by deposition methods. However, these films are inherently prone to rapid oxidation, with the oxidation rate dependent on substrate, temperature, and deposition parameters. The focus of this research is to investigate the temporal oxidation of RF-sputtered Ni ultrathin films on Corning glass under ambient atmospheric conditions and its impact on their structural, surface, and optical characteristics. Controlled film thicknesses were achieved through precise manipulation of deposition parameters, enabling the analysis of oxidation-induced modifications. Atomic force microscopy (AFM) revealed that films with high structural integrity and surface uniformity are exhibiting roughness values (Rq) from 0.679 to 4.379 nm of corresponding thicknesses ranging from 4 to 85 nm. Scanning electron microscopy (SEM) validated the formation of Ni grains interspersed with NiO phases, facilitating SPR-like effects. UV-visible spectroscopy is demonstrating thickness-dependent spectral (plasmonic peak) shifts. Finite Difference Time Domain (FDTD) simulations corroborate the observed thickness-dependent optical absorbance and the resultant shifts in the absorbance-induced plasmonic peak position and bandgap. Increased NiO presence primarily drives the enhancement of electromagnetic (EM) field localization and the direct impact on power absorption efficiency, which are modulated by the tunability of the plasmonic peak position. Our work demonstrates that controlled fabrication conditions and optimal film thickness selection allow for accurate manipulation of the Ni oxidation process, significantly altering their optical properties. This enables the tailoring of these Ni films for applications in transparent conductive electrodes (TCEs), magneto-optic (MO) devices, spintronics, wear-resistant coatings, microelectronics, and photonics. Full article

In this paper, we demonstrate the magnetic field-adjustable group delay of the reflected beam in the terahertz frequency range, using a multilayer architecture incorporating three layers of antisymmetric graphene. The observed enhancement in group delay results from localized field amplification, which occurs due to the excitation of surface plasmon polaritons on the graphene at the interface between two dielectric layers. By considering the quantum mechanical response of graphene, the polarity of the group delay can be reversed by exploiting the antisymmetric conductivity characteristics of graphene. Furthermore, the group delay can be dynamically modulated either by varying the external magnetic field or by adjusting the structural parameters. The achieved enhancement and tunability of the group delay offer significant potential for the development of graphene-based terahertz modulation devices and other optical delay applications. Full article

A preprocessing technique named “spiral annealing” was applied for the first time to magnetic microwires. In this process, the sample was arranged in a flat spiral shape during annealing, and subsequent measurements were conducted on the unbent sample with the induced stress distribution along and transverse to the sample. The research utilized both magnetic and magneto-optical methods. The anisotropy field magnitude in both the volume and surface of the microwire was measured, and for the first time, a direct correlation between the anisotropy field and the curvature of a spirally annealed microwire was established. Additionally, a connection between the type of surface domain structure and the degree of spiral curvature was identified. The preservation of the distribution of spiral annealing-induced magnetic properties both along and across the microwire is a key effect influencing the technological application of the microwire. The range of induced curvature within which a specific helical magnetic structure can exist was also determined. This insight links the conditions of spiral annealing to the selection of microwires as active elements in magnetic sensors. Full article

In this study, we investigate the electrically and magnetically tunable Goos–Hänchen (GH) shift of a reflected light beam at terahertz frequencies. Our study focuses on a photonic crystal heterostructure incorporating a monolayer anisotropic graphene. We observe a tunable and enhanced GH shift facilitated by a drastic change in the reflected phase at the resonance angle owing to the excitation of the topological edge state. Considering the quantum response of graphene, we demonstrate the ability to switch positive and negative GH shifts through the manipulation of graphene’s conductivity properties. Moreover, we show that the GH shift can be actively tuned by the external electric field and magnetic field, as well as by controlling the structural parameters of the system. We believe that this tunable and enhanced GH shift scheme offers excellent potential for preparing terahertz shift devices. Full article

An integrated optical isolator is a crucial part of photonic integrated circuits (PICs). Existing optical isolators, predominantly based on the silicon-on-insulator (SOI) platform, face challenges in integrating with active devices. We propose a broadband, compact TM mode Mach–Zehnder optical isolator based on InP-on-insulator platforms. We designed two distinct magneto-optical waveguide structures, employing different methods for bonding Ce:YIG and InP, namely O₂ plasma surface activation direct wafer bonding and DVS-benzocyclobutene (BCB) adhesive bonding. Detailed calculations and optimizations were conducted to enhance their non-reciprocal phase shift (NRPS). At a wavelength of 1550 nm, the direct-bonded waveguide structure achieved a 30 dB bandwidth of 72 nm with a length difference of 0.256 µm. The effects of waveguide arm length, fabrication accuracy, and dimensional errors on the device performance are discussed. Additionally, manufacturing tolerances for three types of lithographic processes were calculated, serving as references for practical manufacturing purposes. Full article

An approach was proposed to control the displacement of domain walls in magnetic microwires, which are employed in magnetic sensors. The velocity of the domain wall can be altered by the interaction of two magnetic microwires of distinct types. Thorough investigations were conducted utilizing fluxmetric, Sixtus–Tonks, and magneto-optical techniques. The magneto-optical examinations revealed transformation in the surface structure of the domain wall and facilitated the determination of the mechanism of external influence on the movement of domain walls in magnetic microwires. Full article

Magnetic nanoparticles (MNPs) are interesting for their potential employment in biomedical and environmental technologies. Although they have been characterized by many techniques, there are some issues that need to be solved. For instance, it is not yet possible to finely characterize their size distribution or to detect their local magnetic properties. In this work, commercial MNPs were employed, which were made of iron oxide cores with a mean diameter of 8 nm embedded in a matrix of dextran to form skeins with a mean diameter of 20 nm. These MNPs have been dispersed in keratin, a natural protein extracted from wool. Thin films have been realized by spin coating water solutions with various MNP concentrations. Analysis was conducted using a set of techniques, namely Atomic Force Microscopy, Environmental Scanning Electron Microscopy, a Physical Property Measurement System–Vibrating Sample Magnetometer, and the spatially resolved Magneto-Optic Kerr Effect (NanoMOKE). These MNPs show superparamagnetic properties, although a wide distribution of blocking temperature values indicates that the cores are not isolated and interact with others. NanoMOKE not only allows us to map the magnetic behavior of MNP clusters, but also to detect the presence of isolated MNPs dispersed in the keratin matrix. Full article

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. Full article

We investigate how an external magnetic field with an arbitrary direction affects the photonic band of a superlattice structure composed of alternating dielectric and magneto-optical plasma layers. By considering that the superlattice is electrodynamically anisotropic in the presence of an external magnetic field, we derive the dispersion equations; we show that the photonic spectrum of this superlattice loses its degeneracy and splits into two branches due to the external magnetic field. Interestingly, our results indicate that a superlattice that was previously wholly photo-isolating can become entirely photo-conducting, regardless of the direction of the external magnetic field applied. These results could be helpful to design and build new optical diode-like devices. Full article

In this paper, the magnetically tunable Goos–Hänchen (GH) shift of a reflected beam at terahertz frequencies is achieved by using a multilayer structure where three layers of anisotropic graphene are inserted. The enhanced GH shift phenomenon results from the local field enhancement owing to the excitation of graphene surface plasmon polaritons at the interface between two dielectric materials. By considering the quantum response of graphene, the GH shift can be switched from negative to positive by harnessing the anisotropic conductivity of graphene, and the GH shift can be actively tuned through the external magnetic field or by controlling the structural parameters. By setting appropriate magnetic field and structural parameters, we can obtain GH values of −140 microns to 220 microns in the terahertz band. This enhanced and tunable GH shift is promising for fabricating graphene-based terahertz shift devices and other applications in nanophotonics. Full article

ZnCoO:H and ZnCoAlO:H films were synthesized by radio frequency magnetron sputtering in a (1 − x)Ar + xH₂ mixed atmosphere with x = 0.2–0.5. The films contain different amounts of metallic Co particles (from 7.6% and higher) ~4–7 nm in size. The magnetic and magneto-optical (MO) behavior of the films was analyzed in combination with their structural data. The samples exhibit high values of magnetization (up to 377 emu/cm³) and MO response at room temperature. Two situations are considered: (1) the film magnetism is associated only with isolated metal particles and (2) magnetism is present both in the oxide matrix and in metal inclusions. It has been established that the formation mechanism of the magnetic structure of ZnO:Co²⁺ is due to the spin-polarized conduction electrons of metal particles and zinc vacancies. It was also found that in the presence of two magnetic components in the films, these components are exchange-coupled. In this case, the exchange coupling generates a high spin polarization of the films. The spin-dependent transport properties of the samples have been studied. A high value of the negative magnetoresistance of the films at room temperature (~4%) was found. This behavior was explained in terms of the giant magnetoresistance model. Thus, the ZnCoO:H and ZnCoAlO:H films with high spin polarization can be considered as sources of spin injection. Full article

A large number of carbon fiber reinforced polymers have been applied to aircraft and automobiles, and many nondestructive testing methods have been studied to detect their defects. Eddy current magneto-optical imaging nondestructive testing technology has been widely used in the detection of metal materials such as aircraft skin, but it usually requires a large excitation current and, at present, can only detect metal materials with high conductivity. In order to take full advantage of the innate benefits and efficiency of eddy current magneto-optic imaging and enable it to detect defects in carbon fiber reinforced polymers with weak conductivity, it is necessary to improve the magnetic field response of the eddy current magneto-optic imaging system and explore suitable excitation and detection methods. The scanning eddy current magneto-optical imaging nondestructive testing device built in this study has improved the magnetic field response of the system, and the eddy current magneto-optical phase imaging testing method has been proposed to detect the crack defects of carbon fiber reinforced polymers. The effectiveness of the method has been verified by simulation and experiment. Full article

Two dinuclear copper(II) complexes with macrocyclic Schiff bases K1 and K2 were prepared by the template reaction of (R)-(+)-1,1′-binaphthalene-2,2′-diamine and 2-hydroxy-5-methyl-1,3-benzenedicarboxaldehyde K1, or 4-tert-butyl-2,6-diformylphenol K2 with copper(II) chloride dihydrate. The compounds were characterized by spectroscopic methods. X-ray crystal structure determination and DFT calculations confirmed their geometry in solution and in the solid phase. Moreover, intermolecular interactions in the crystal structure of K2 were analyzed using 3D Hirshfeld surfaces and the related 2D fingerprint plots. The magnetic study revealed very strong antiferromagnetic Cu^II-Cu^II exchange interactions, which were supported by magneto-structural correlation and DFT calculations conducted within a broken symmetry (BS) framework. Complexes K1 and K2 exhibited luminescent properties that may be of great importance in the search for new OLEDs. Both K1 and K2 complexes showed emissions in the range of 392–424 nm in solutions at various polarities. Thin materials of the studied compounds were deposited on Si(111) by the spin-coating method or by thermal vapor deposition and studied by scanning electron microscopy (SEM/EDS), atomic force microscopy (AFM), and fluorescence spectroscopy. The thermally deposited K1 and K2 materials showed high fluorescence intensity in the range of 318–531 nm for K1/Si and 326–472 nm for the K2/Si material, indicating that they could be used in optical devices. Full article

Herein, we demonstrate a process for the synthesis of a highly crystalline bi-functional manganese (Mn)-doped zinc silicate (Zn₂SiO₄) nanostructures using a low-cost sol–gel route followed by solid state reaction method. Structural and morphological characterizations of Mn-doped Zn₂SiO₄ with variable doping concentration of 0.03, 0.05, 0.1, 0.2, 0.5, 1.0, and 2.0 wt% were investigated by using X-ray diffraction and high-resolution transmission electron microscopy (HR-TEM) techniques. HR-TEM-assisted elemental mapping of the as-grown sample was conducted to confirm the presence of Mn in Zn₂SiO_4. Photoluminescence (PL) spectra indicated that the Mn-doped Zn₂SiO₄ nanostructures exhibited strong green emission at 521 nm under 259 nm excitation wavelengths. It was observed that PL intensity increased with the increase of Mn-doping concentration in Zn₂SiO₄ nanostructures, with no change in emission peak position. Furthermore, magnetism in doped Zn₂SiO₄ nanostructures was probed by static DC magnetization measurement. The observed photoluminescence and magnetic properties in Mn-doped Zn₂SiO₄ nanostructures are discussed in terms of structural defect/lattice strain caused by Mn doping and the Jahn–Teller effect. These bi-functional properties of as-synthesized Zn₂SiO₄ nanostructures provide a new platform for their potential applications towards magneto-optical and spintronic and devices areas. Full article