Magnetic field sensor based on magnetoplasmonic crystal

Stable antiparallel domains in 3D corrugated magnetic thin films

Magnetic nanostructured materials are of great interest in fields such as non-conventional computing or magnetic field sensing due to the possibilities that 3D magnetic textures embedded on metamaterials offer. We present a novel study on the magnetization and magneto-optical properties of a ferromagnetic (permalloy), continuous thin film that is highly corrugated by its deposition on the surface of a triangular silicon nanograting with a low periodicity (250 nm) and a quite large amplitude (180 nm), which leads to the formation of an unusual magnetic texture. This grating profile activates several optical phenomena and thus hinders magnetic characterization, which usually requires the analysis of the magneto-optical Kerr effect (MOKE); however, in this paper we unveil the magnetization and disclose magnetic features sized smaller than the light wavelength. Not only does the optical activity include rotation of the polarization plane upon reflection but also, when using violet light (diffraction regime), there is excitation of surface plasmon polaritons at the metal film and consequently, a strong effect on the magneto-optical activity: the transverse Kerr signal is enhanced up to one order of magnitude and the longitudinal Kerr signal changes sign, in comparison with the values of red light (subwavelength regime). Optical modelling led us to understand that features of the field-cycled MOKE are associated with the non-uniform spatial distribution of magneto-optical activity in the film whereby, firstly, the Kerr effect with red light arises at the lower half of the grating and, secondly, the use of violet light focuses the effect at the film ridges and valleys. The surface-MOKE measured with an in-plane field cycled at different angles indicates a distinctive feature: there is only one magnetic easy axis (groove direction) but two directions symmetrically about the hard axis where the coercive field vanishes. This dependence, in agreement with the micromagnetic simulations, is consistent with the formation of a pattern of antiparallel magnetic domains with nanometric periodicity at the remanent magnetization. We have verified the existence of the magnetic pattern with magnetic force microscopy. Our findings offer a novel way to disentangle the magnetization reversal of 3D corrugated materials by performing Kerr magnetometry at different optical regimes.

A promising high-sensitive 1D photonic crystal magnetic field sensor based on the coupling of Fano\Tamm resonance in far IR region

This paper presents a novel investigation of a magnetic sensor that employs Fano/Tamm resonance within the photonic band gap of a one-dimensional crystal structure. The design incorporates a thin layer of gold (Au) alongside a periodic arrangement of Tantalum pentoxide ([Formula: see text]) and Cesium iodide ([Formula: see text]) in the configuration [Formula: see text]. We utilized the transfer matrix method in conjunction with the Drude model to analyze the formation of Fano/Tamm states and the permittivity of the metallic layer, respectively. These states can be manipulated based on the left-handed and right-handed circular polarization of electromagnetic waves, along with an applied magnetic field. Several key parameters were optimized, including material selection, layer thickness, unit cell periodicity, and the angle of incidence, to enhance the sensor performance. Additionally, we investigated how variations in magnetic field strength influence the position of Fano/Tamm resonance in the reflectivity spectrum of the interacting electromagnetic waves within a specific wavelength range of 60 μm to 140 μm. The proposed sensor displays good performance investigated by calculating several parameters like, sensitivity, figure of merit, quality factor and resolution. One of them, it shows a maximum sensitivity of 57 nm/Tesla within a magnetic field strength of 20 to 140 Tesla, positioning it as a promising candidate for various applications in magnetic field measurement and telecommunications, particularly in the unique far-infrared region.

Functional roles of magnetic nanoparticles for the identification of metastatic lymph nodes in cancer patients

Staging lymph nodes (LN) is crucial in diagnosing and treating cancer metastasis. Biotechnologies for the specific localization of metastatic lymph nodes (MLNs) have attracted significant attention to efficiently define tumor metastases. Bioimaging modalities, particularly magnetic nanoparticles (MNPs) such as iron oxide nanoparticles, have emerged as promising tools in cancer bioimaging, with great potential for use in the preoperative and intraoperative tracking of MLNs. As radiation-free magnetic resonance imaging (MRI) probes, MNPs can serve as alternative MRI contrast agents, offering improved accuracy and biological safety for nodal staging in cancer patients. Although MNPs' application is still in its initial stages, exploring their underlying mechanisms can enhance the sensitivity and multifunctionality of lymph node mapping. This review focuses on the feasibility and current application status of MNPs for imaging metastatic nodules in preclinical and clinical development. Furthermore, exploring novel and promising MNP-based strategies with controllable characteristics could lead to a more precise treatment of metastatic cancer patients.

Magneto-Optical Spectroscopy of Short Spin Waves by All-Dielectric Metasurface

The optical method of spin dynamics measurements via the detection of various magneto-optical effects is widely used nowadays. Besides it being a convenient method to achieve time-resolved measurements, its spatial resolution in the lateral direction is limited by a diffraction limit for the probe light. We propose a novel approach utilizing a Mie-resonance-based all-dielectric metasurface that allows for the extraction of a signal of a single submicron-wavelength spin wave from the wide spin precession spectra. This approach is based on the possibility of designing a metasurface that possesses nonuniform magneto-optical sensitivity to the different nanoscale regions of the smooth magnetic film due to the excitation of the Mie modes. The metasurface is tuned to be unsensitive to the long-wavelength spin precession, which is achieved by the optical resonance-caused zeroing of the magneto-optical effect for uniform magnetization in the vicinity of the resonance. At the same time, such a Mie-supporting metasurface exhibits selective sensitivity to a narrow range of short wavelengths equal to its period.

Bulk Plasmon Polariton Modes in Hyperbolic Metamaterials for Giant Enhancement of the Transverse Magneto-Optical Kerr Effect

We demonstrate a concept for the giant enhancement of the transverse magneto-optical Kerr effect (TMOKE) using bulk plasmon polariton (BPP) modes in non-magnetic multilayer hyperbolic metamaterials (HMMs). Since the BPP modes are excited through the attenuated total reflection (ATR) mechanism, using a Si-based prism-coupler, we considered a single dielectric magneto-optical (MO) spacer between the prism and the HMM. The working wavelength was estimated, using the effective medium approach for a semi-infinite dielectric-plasmonic multilayer, considering the region where the system exhibits type II HMM dispersion relations. Analytical results, by means of the scattering matrix method (SMM), were used to explain the physical principle behind our concept. Numerical results for giant TMOKE values (close to their maximum theoretical values, ±1) were obtained using the finite element method (FEM), applying the commercial software COMSOL Multiphysics. Our proposal comprises a simple and experimentally feasible structure that enables the study of MO phenomena in HMMs, which may find application in future nanostructured magnetoplasmonic metamaterials for active nanophotonic devices.

Nanophotonic devices based on magneto-optical materials: recent developments and applications

Interaction between light and magnetism in magneto-optical (MO) nanophotonic devices has been actively studied in the past few years. The recent development of MO all-dielectric resonators and metasurfaces has led to the emergence of various novel MO phenomena that were not observed in their bulk counterparts. For example, a large s-polarized transverse MO Kerr effect can be observed at magnetic resonance wavelength, which cannot exist in the bare MO films. We review recent developments in nanophotonic devices based on MO materials and focus on different modes and related MO effects in nanophotonic structures with emphasis on recently discovered new MO phenomena in magnetoplasmonics and all-dielectric nanostructures, such as dark mode, all-dielectric Mie resonance and waveguide mode. Further, we discuss the potential applications of these nanostructures for biological/chemical sensing, magnetic field sensing, and magnetic field-controlled active and nonreciprocal metasurfaces.

All-dielectric magnetophotonic gratings for maximum TMOKE enhancement

All-dielectric nanophotonic devices are promising candidates for future lossless (bio)sensing and telecommunication applications. Active all-dielectric magnetophotonic devices, where the optical properties can be controlled by an externally applied magnetic field, have triggered great research interest. However, magneto-optical (MO) effects are still low for applications. Here, we demonstrate a concept for the enhancement of the transverse MO Kerr effect (TMOKE), with amplitudes of up to 1.85, i.e., close to the maximum theoretical values of ±2 (in transmission). Our concept exploits the lateral leaky Bloch-modes to enhance the TMOKE, under near-zero transmittance conditions. Potential applications in (bio)sensing structures are numerically demonstrated. The effects of optical losses were studied using different combinations of materials. Significantly, we demonstrate TMOKE enhancements of two orders of magnitude in relation to recent experimental studies, using the same building materials.

Longitudinal Magneto-Optical Kerr Effect of Nanoporous CoFeB and W/CoFeB/W Thin Films

Nanoporous Co40Fe40B20 (CoFeB) and sandwich tungsten (W)/CoFeB/W thin films were fabricated via an anodic aluminum oxide (AAO) template-assisted magneto sputtering process. Their thickness-dependent magneto-optical Kerr effect (MOKE) hysteresis loops were investigated for enhanced Kerr rotation. Control of the Kerr null points of the polarized reflected light can be realized via the thicknesses of the CoFeB layers and W layers. Simulation of the thickness-dependent phase difference change by the finite element method reveals the existence of the two Kerr null points for W/CoFeB/W thin films, matching the experimental result very well. However, there are two additional Kerr null points for pure CoFeB thin films according to the simulation by comparing with the experimental result (only one). Theoretical analysis indicates that the different Kerr null points between the experimental result and the simulation are mainly due to the enhanced inner magnetization in the ferromagnetic CoFeB layer with the increased thickness, which is usually omitted in the simulation. Clearly, the introduction of non-ferromagnetic W layers can experimentally regulate the Kerr null points of ferromagnetic thin films. Moreover, construction of W/CoFeB/W sandwich thin films can greatly increase the highest magneto-optical susceptibility and the saturated Kerr rotation angle when compared with CoFeB thin films of the same thickness.

Design of Nanoarchitectures for Magnetoplasmonic Biosensing with Near-Zero-Transmittance Conditions

Nanostructures exhibiting large transverse magneto-optical Kerr effect (TMOKE) are required for magnetoplasmonic biosensing if the aim is the minituarization and integration into microfluidic devices. In this work, we present a general strategy to design nanoarchitectures with enhanced TMOKE, which consist of an arrangement of gold ribs deposited on an magneto-optical (MO) dielectric slab of Bi:YIG (bismuth-substituted yttrium iron garnet) with a SiO₂ substrate surrounded by water. Using the finite element method (FEM), we demonstrate numerically that the near-zero-transmittance condition is the most important requirement for high TMOKE values. This can be reached through geometric optimization of the nanoarchitecture by tuning the period, height, and width of the grating, thus leading to resonances at wavelengths where the MO dielectric slab has high MO activity. We also show that the TMOKE amplitude can be further increased if losses in metal ribs are reduced. For a magnetoplasmonic grating with optimized geometry, we demonstrated the potential detection of biologically relevant analytes with sensitivity in the order of 10² nm/RIU (refractive index unit). Since the nanoarchitecture proposed is experimentally feasible with, e.g., nanolithography techniques, one may expect that the design strategy may inspire the development of efficient magnetoplasmonic sensing platforms.

Sensing Using Light: A Key Area of Sensors

This invited featured paper offers a Doctrinal Conception of sensing using Light (SuL) as an "umbrella" in which any sensing approach using Light Sciences and Technologies can be easily included. The key requirements of a sensing system will be quickly introduced by using a bottom-up methodology. Thanks to this, it will be possible to get a general conception of a sensor using Light techniques and know some related issues, such as its main constituted parts and types. The case in which smartness is conferred to the device is also considered. A quick "flight" over 10 significant cases using different principles, techniques, and technologies to detect diverse measurands in various sector applications is offered to illustrate this general concept. After reading this paper, any sensing approach using Light Sciences and Technologies may be easily included under the umbrella: sensing using Light or photonic sensors (PS).

Photocrosslinking and photopatterning of magneto-optical nanocomposite sol-gel thin film under deep-UV irradiation

This paper is aimed at investigating the process of photocrosslinking under Deep-UV irradiation of nanocomposite thin films doped with cobalt ferrite magnetic nanoparticles (MNPs). This material is composed of a hybrid sol-gel matrix in which MNP can be introduced with high concentrations up to 20 vol%. Deep-UV (193 nm) is not only interesting for high-resolution patterning but we also show an efficient photopolymerization pathway even in the presence of high concentration of MNPs. In this study, we demonstrate that the photocrosslinking is based on the free radical polymerization of the methacrylate functions of the hybrid precursor. This process is initiated by Titanium-oxo clusters. The impact of the nanoparticles on the photopolymerization kinetic and photopatterning is investigated. We finally show that the photosensitive nanocomposite is suitable to obtain micropatterns with sub-micron resolution, with a simple and versatile process, which opens many opportunities for fabrication of miniaturized magneto-optical devices for photonic applications.

Ultrafast Magneto-Optics in Nickel Magnetoplasmonic Crystals

Here, we report on ultrafast all-optical modulation of the surface-plasmon (SP)-assisted transverse magneto-optical Kerr effect (TMOKE) and the reflectance in a one-dimensional nickel magnetoplasmonic crystal (MPC). A 50 fs nonresonant laser pump pulse with 7 mJ/cm² fluence reduces the magnetization by 65%, which results in the suppression of TMOKE in the SP-resonant probe from 1.15% to 0.4%. The differential reflectance of SP-resonant probe achieves 5.5%. Besides this, it is shown that electron thermalization and relaxation in MPC are several times slower than those in the plane nickel.

Bound states in the continuum enable modulation of light intensity in the Faraday configuration

We demonstrate a novel, to the best of our knowledge, magneto-optical effect that reveals itself in light intensity modulation without polarization rotation in the Faraday configuration. We design a photonic crystal with a magnetized optical cavity that supports bound states in the continuum (BICs), since it simultaneously provides the extended state (continuum) for TM polarization, and the bound (localized) state in the form of a cavity mode for TE-polarized light. Magnetization of the photonic crystal in the Faraday configuration results in efficient polarization conversion and trapping of the acquired TE components of the TM incident light inside the magnetized optical cavity. As a result, a BIC manifests itself as a significant magneto-optical modulation of transmitted light intensity, while its polarization is preserved. Therefore, the proposed structure is promising for magnetic control of light in various applications.