External Static Magnetic Field Research Articles

Magnetic field enhanced laser absorption on a metallic surface incorporated with shape-dependent nanostructures

Abstract This communication proposes an analytical model to investigate the nanoparticle-based nonlinear absorption phenomenon associated with an obliquely incident p-polarized laser beam on a metallic surface. In this scheme, the surface is ingrained with noble-metal spherical nanoparticles and cylindrical nanoparticles in the presence of an external static magnetic field. The absorption of laser energy in the presence of nanoparticles (NPs) is attributed to surface plasmon resonance and enhanced magnetic-field effects. The absorption phenomenon is significantly enhanced by the incorporation of nanostructures and a magnetic field. The ellipticity characterizing parameter, which significantly influences the resonant frequency of different nanometric structures, has also been analysed and discussed. The effects of varying the magnetic field intensity, incident angle, size, and spacing of the NP were examined to determine their influence on the anomalous absorption of the laser. Furthermore, a direct dependency was found between the absorption coefficient and transmission coefficient of the incident laser, as well as the dimensions of the NPs. Several applications have direct relevance to this study, including biosensors such as DNA sensors and immunosensors, photothermal therapy, photoacoustic imaging, optoelectronic devices, solar cells, and surface-enhanced Raman spectroscopy.

Theoretical study of a tunable optical device on the base of magnetoactive cholesteric liquid crystals

We investigated the light reflection from half-space of cholesteric liquid crystal (CLC) being in external static magnetic field directed along the helix axis at normal light incidence. In this case there appear three photonic band gaps (PBGs) and these bands can be tuned in large intervals. We found the eigenpolarizations (EPs) at reflection of light from half-space and investigated their peculiarities. We have shown that in the absence both of absorption and of external magnetic field and at minimal influence of dielectric boundary (when the dielectric permittivity of isotropic half-space which borders with CLC half-space is equal to the CLC's mean dielectric permittivity) these polarizations are orthogonal. While, in the presence of external magnetic field they become quasi-orthogonal everywhere outside the main PBG (which exist also at the absence of external magnetic field), and they are significantly non-orthogonal within the main PBG. At some values of helix pitch they become significantly non-orthogonal practically everywhere. Moreover, in this case there exist some special points where the EPs degenerate. This system can apply as tunable narrow-band or broad-band filter and mirror, a highly tunable broad/narrow-band optical diode, and other devices.

Anisotropic topological scaffolds synergizing non-invasive wireless magnetic stimulation for accelerating long-distance peripheral nerve regeneration

Long-distance peripheral nerve regeneration is the challenging clinical problem that needs to be resolved urgently. In this study, an anisotropic topological Chitosan@Artemisia sphaerocephala (CS@AS) scaffold containing Fe3O4 nanoparticles for achieving non-invasive wireless magnetic stimulation on nerve regeneration process under external static magnetic field (SMF) was developed using surface modification and micro-molding method, aiming to provide a synergistic stimulus for the repair of long-distance peripheral nerve injury. The results showed that the anisotropic topological scaffolds and non-invasive wireless magnetic stimulation under exogenous SMF could synergistically regulate the morphological change, proliferation and oriented growth of Schwann cells. In vivo experiments confirmed that magnetic CS@AS nerve conduit could better promote the functional recovery and reconstruction of the long-distance injured sciatic nerve under SMF, close to that of the autograft transplantation. Further on, the scaffolds were found to activate the magnetic induction receptors, promote the gene expression related to proliferation, migration and myelin formation, regulate the homeostasis of intracellular Ca2+ and enhance the signal transduction via cGMP-PKG, VEGF, MAPK, and TNF signaling pathways. Therefore, the combination of anisotropic topological nerve grafts and non-invasive wireless magnetic stimulation under external SMF can promote the repair and functional recovery of long-distance nerve injury, providing a new strategy for the treatment of peripheral nerve injury.

Near-zero-field microwave-free magnetometry with nitrogen-vacancy centers in nanodiamonds

We study the fluorescence of nanodiamond ensembles as a function of static external magnetic field and observe characteristic dip features close to the zero field with potential for magnetometry applications. We analyze the dependence of the feature’s width and the contrast of the feature on the size of the diamond (in the range 30 nm–3000 nm) and on the strength of a bias magnetic field applied transversely to the field being scanned. We also perform optically detected magnetic resonance (ODMR) measurements to quantify the strain splitting of the zero-field ODMR resonance across various nanodiamond sizes and compare it with the width and contrast measurements of the zero-field fluorescence features for both nanodiamonds and bulk samples. The observed properties provide compelling evidence of cross-relaxation effects in the NV system occurring close to zero magnetic fields. Finally, the potential of this technique for use in practical magnetometry is discussed.

Analysis of the performance and microbial community of continuous dark fermentation combined with steady static magnetic field

The effect of external static magnetic field on hydrogen production and its mechanism were studied by continuous dark fermentation with no pretreatment excess sludge as inoculum. The results showed that under conditions of 37 ± 1 ℃, HRT 8 h, OLR 15 g/(L· d) and no control of influent pH, 78 mT external static magnetic field by adding magnets on both sides of the reactor could accelerate the enrichment of Ethanoligenens and improve the activity of reduced coenzyme I (96 %), ferredoxin oxidoreductase (29 %) and pyruvate: ferredoxin oxidoreductase (7 %) so that the maximum hydrogen productivity could reach 1.657 L H2/L, which was 5 times higher than that of non-magnetic group. Moreover, the n-caproic acid production could also increase due to the enrichment of carbon chain elongation microorganisms. The decline of hydrogen production was mainly due to hydrogenotrophic methanogenesis and acetic acid accumulation. This study was benefit to understand the interaction mechanism between magnetic field and microorganisms during the process of biological hydrogen production.

External static magnetic field mitigates nitrogen loss during agro-waste composting

Nitrogen is a crucial component in the composting process of agricultural waste and serves as a key nutrient source for organic fertilizer production. However, nitrogen loss during composting is inevitable, and how to retain it needs further investigation. The effects of static magnetic field on nitrogen conversion during agro-waste composting were explored. Results showed that low magnetic field intensity treatment reduced NH3 by 29.68 % but raised N2O by 1.57 %, while high intensity treatment reduced both NH3 and N2O by 3.51 % and 4.35 %, respectively. Pearson correlation analysis revealed that external static magnetic field regulated NH3 emission by affecting temperature, pH, electrical conductivity and NH4+-N, while modulated N2O emission by influencing moisture content, volatile solids, nxrA, nirK, norB, nosZ and NO2--N. The findings stated that external static magnetic field effectively reduced nitrogen loss, enhanced its retention and exhibited the potential to become an effective technical measure to promote nitrogen utilization during composting.

Correlation of density fluctuation in a magnetized QCD matter near the critical end point

The dynamical correlation of density fluctuation in quark gluon plasma with a critical end point has been investigated within the scope of the Müller–Israel–Stewart theory in the presence of static ultra-high external magnetic field. The dynamic structure factor of the density fluctuation exhibits three Lorentzian peaks in absence of external magnetic field – a central Rayleigh peak and two Brillouin peaks situated symmetrically on the opposite sides of the Rayleigh peak. The spectral structure displays five peaks in presence of the magnetic field due to the coupling of the magnetic field with the hydrodynamic fields in second-order hydrodynamics. The emergence of the extra peaks is due to the asymmetry in the pressure gradient caused by the external magnetic field in the system. Interestingly, it is observed that near the critical end point, all the Brillouin peaks disappear irrespective of the presence or absence of the external magnetic field.

Surface wave propagation along a narrow transition layer in a slab Voigt geometry

The dispersion properties of electromagnetic surface waves, which propagate along a slab narrow transition layer separating two magnetoactive plasma uniform half spaces, are studied. Voigt geometry is considered, in which the waves propagate perpendicularly to an external uniform static magnetic field, which in turn is parallel to the interfaces between the plasmas and the transition layer. Electromagnetic power absorption within local resonances inside the transition layer is out of scope of the study. The influence of the plasma particle density profile smoothness on the surface wave dispersion properties is emphasized.

Magneto-plasmonic scattering by a disk-shaped particle made of an artificial dielectric

The main features of artificial dielectrics are high anisotropy and controllable heterogeneity, as well as adjustable values of their synthesized material parameters. In this work, we numerically study the scattering features of a disk-shaped particle made of an artificial dielectric (finely stratified structure, FSS) that is composed of magnetic and semiconductor constituents influenced by an external static magnetic field. The tensor-valued permittivity and permeability of the FSS are derived involving the effective medium theory. Due to a specific composition of the FSS, the material properties of the disk simultaneously acquire electric and magnetic gyrotropy, which depends on the proportion of the semiconductor and magnetic components included in the FSS. It is supposed that the ferromagnetic and plasma resonances of the constitutive materials are closely spaced. In particular, we examine the electric and magnetic dipole contributions to the scattering and absorption cross-sections obtained in the framework of the multipole decomposition method while accounting for the polarizability and magnetization induced in the particle by the field of incoming radiation. By varying the proportion of components of the artificial dielectric, we demonstrate the magneto-plasmonic functionality of the particle. Our presentation generalizes and complements several known solutions obtained separately for either magnetic or dielectric anisotropic particles. This approach can be used to study magneto-optical effects in metamaterials and metasurfaces composed of an ensemble of gyroelectric and gyromagnetic particles that is important for both plasmonic and photonic applications.

Orientational ordering and assembly of silica-nickel Janus particles in a magnetic field.

The orientation ordering and assembly behavior of silica-nickel Janus particles in a static external magnetic field were probed by ultra small-angle X-ray scattering (USAXS). Even in a weak applied field, the net magnetic moments of the individual particles aligned in the direction of the field, as indicated by the anisotropy in the recorded USAXS patterns. X-ray photon correlation spectroscopy (XPCS) measurements on these suspensions revealed that the corresponding particle dynamics are primarily Brownian diffusion [Zinn, Sharpnack & Narayanan (2023). Soft Matter, 19, 2311-2318]. At higher fields, the magnetic forces led to chain-like configurations of particles, as indicated by an additional feature in the USAXS pattern. A theoretical framework is provided for the quantitative interpretation of the observed anisotropic scattering diagrams and the corresponding degree of orientation. No anisotropy was detected when the magnetic field was applied along the beam direction, which is also replicated by the model. The method presented here could be useful for the interpretation of oriented scattering patterns from a wide variety of particulate systems. The combination of USAXS and XPCS is a powerful approach for investigating asymmetric colloidal particles in external fields.

Investigating the Effects of Cold Plasma on Cancer Cell Migration in the Presence of a Static Magnetic Field

Cold plasma is used in a wide range of applications [1]–[3] One of the primary uses of plasma is in the field of medicine. Moreover, many techniques have been suggested to enhance plasma performance, among which the inclusion of an external static magnetic field is one [4], [5]. This paper used a low-power (20-watt) RF 13.56 MHz plasma to investigate the effect of cold plasma on cancer cells' migration rate in the presence of a static magnetic field. The result of the scratch healing assay is shown in Figure 1 (Ⅰ and Ⅱ). The results are evaluated after 24 hours. Figure 1 (Ⅰ-A) is before plasma treatment (control), (Ⅰ-B) is without treatment, (Ⅰ-C) is 15 seconds of plasma treatment, and (Ⅰ-D) is plasma and SMF treatment. The area of free space in the created gap has been evaluated by image processing software. The percentage of free space compared to the total space is specified in the diagram (Figure1-Ⅱ). As shown in the figure, the empty space for the state where the plasma is combined with the magnetic field is twice the state of the plasma alone. One of the main components of plasma that changes the presence of a magnetic field is the density and temperature of electrons in cold plasma. The electron temperature was evaluated based on the Boltzmann plot method, and the electron density measurement was calculated using the Saha-Boltzmann equation (figure 1-Ⅲ). The Boltzmann diagram is drawn using the used plasma spectrum, which was used in the previous work [6]. The calculation indicates that the electron temperature Te and electron density ne is estimated as 1.04 eV and for the absence of SMF, and 1.24 eV and for the presence of SMF, respectively Although several factors are involved in the effect of plasma, in this work, the temperature and electron density of the plasma were evaluated. Because apart from the direct impact on the target, the electron also affects the density of the ions. The findings indicate that the presence of a stationary magnetic field in close proximity to a plasma significantly regulated the migratory rate of cancer cells.Figure 1. (Ⅰ) scratch healing assay, (Ⅱ) percentage of gap for treatments, (Ⅲ) electron temperature calculation with Boltzmann plot.[1] S. Padureanu et al., “Non-Thermal Plasma-Activated Water: A Cytogenotoxic Potential on Triticum aestivum,” Agronomy, vol. 13, no. 2, 2023, doi: 10.3390/agronomy13020459.[2] V. Ioannou and S. Laizet, “Numerical investigation of plasma-controlled turbulent jets for mixing enhancement,” Int. J. Heat Fluid Flow, vol. 70, no. October 2017, pp. 193–205, 2018, doi: 10.1016/j.ijheatfluidflow.2018.02.008.[3] L. Guo et al., “Mechanism of virus inactivation by cold atmospheric-pressure plasma and plasmaactivated water,” Appl. Environ. Microbiol., vol. 84, no. 17, 2018, doi: 10.1128/AEM.00726-18.[4] X. Cheng et al., “Enhancing cold atmospheric plasma treatment of cancer cells by static magnetic field,” Bioelectromagnetics, vol. 38, no. 1, pp. 53–62, 2017, doi: 10.1002/bem.22014.[5] R. Mehrabifard, H. Mehdian, K. Hajisharifi, and E. Amini, “Improving Cold Atmospheric Pressure Plasma Efficacy on Breast Cancer Cells Control-Ability and Mortality Using Vitamin C and Static Magnetic Field,” Plasma Chem. Plasma Process., vol. 40, no. 2, pp. 511–526, Nov. 2020, doi: 10.1007/s11090-019-10050-5.[6] R. Mehrabifard, Z. Kabarkouhi, F. Rezaei, K. Hajisharifi, H. Mehdian, and E. Robert, “Physical understanding of the static magnetic field’s synergistic enhancement of cold atmospheric pressure plasma treatment,” Apr. 2023, Accessed: Sep. 21, 2023. [Online]. Available: https://arxiv.org/abs/2304.05833v1 Figure 1

Magnetically-actuated microcages for cells entrapment, fabricated by laser direct writing via two photon polymerization.

The manipulation of biological materials at cellular level constitutes a sine qua non and provocative research area regarding the development of micro/nano-medicine. In this study, we report on 3D superparamagnetic microcage-like structures that, in conjunction with an externally applied static magnetic field, were highly efficient in entrapping cells. The microcage-like structures were fabricated using Laser Direct Writing via Two-Photon Polymerization (LDW via TPP) of IP-L780 biocompatible photopolymer/iron oxide superparamagnetic nanoparticles (MNPs) composite. The unique properties of LDW via TPP technique enabled the reproduction of the complex architecture of the 3D structures, with a very high accuracy i.e., about 90nm lateral resolution. 3D hyperspectral microscopy was employed to investigate the structural and compositional characteristics of the microcage-like structures. Scanning Electron Microscopy coupled with Energy Dispersive X-Ray Spectroscopy was used to prove the unique features regarding the morphology and the functionality of the 3D structures seeded with MG-63 osteoblast-like cells. Comparative studies were made on microcage-like structures made of IP-L780 photopolymer alone (i.e., without superparamagnetic properties). We found that the cell-seeded structures made by IP-L780/MNPs composite actuated by static magnetic fields of 1.3T were 13.66 ± 5.11 folds (p < 0.01) more efficient in terms of cells entrapment than the structures made by IP-L780 photopolymer alone (i.e., that could not be actuated magnetically). The unique 3D architecture of the microcage-like superparamagnetic structures and their actuation by external static magnetic fields acted in synergy for entrapping osteoblast-like cells, showing a significant potential for bone tissue engineering applications.

P and Fe doping, a strategy to develop light and magnetic responsive multifunctional materials: The case of LiMn2O4

The current work reports an unprecedented multifunctional material with optical activity and a modified magnetic response by a unique combination of doping with P and Fe into the spinel LiMn2O4. Through inductively coupled plasma – optical emission spectroscopy, X-ray absorption near-edge spectroscopy, X-ray diffraction and scanning transmission electron microscopy, the chemical composition, oxidation state and the crystalline structure are determined. Solid-state UV-Vis spectroscopy, magnetic susceptibility and electronic conductivity reveal the critical importance of the interaction between iron and phosphorus when simultaneously doping the crystalline structure of LiMn2O4. The presence of Fe and P considerably increases charge carrier concentration as a mechanism for enhancing electronic conductivity. Fe and P doping also creates Fe-Fe spin interactions that allow double electron optical excitations. This opens a pathway to create multifunctional materials for light-assisted charging lithium-ion batteries. P doping also induces the formation of magnetic clusters arising from the Fe-O-Fe, Fe-O-Mn and Mn-O-Mn spin exchange interactions. The magnetic response of the materials is strongly influenced by the relative amount of Fe in octahedral or tetrahedral sites of the spinel structure. Such ferrimagnetic behaviour has not been reported before LiMn2O4 doped with Fe or P separately. The potential applicability of this newly identified magnetic feature was demonstrated by a significant capacity gain when a lithium-ion cell is exposed to a static external magnetic field.

Multi-frequency and wide-angle nonreciprocity arising from non-uniform magnetic field

We investigate the effect of non-uniform external static magnetic field on the scattering nonreciprocity of a deep-subwavelength gyrotropic particle system. Based on a scattering matrix approach, we show analytically that asymmetrical extinction cross section of the scattering system for opposite illumination directions can be accessed at multi-frequency and wide-angle regimes, in the presence of magnetic field with weak spatial non-uniformity. A simplified dual-dipole model is further employed to capture the generic physics of nonreciprocal scattering, essentially attributed to the asymmetrical magneto-electric cross interactions. In addition, typical examples are provided with full-wave numerical verifications. Our finding may open a straightforward and efficient pathway to manipulate nonreciprocal scattering at the subwavelength scale.

Biomimetic Structural Protein Based Magnetic Responsive Scaffold for Enhancing Bone Regeneration by Physical Stimulation on Intracellular Calcium Homeostasis.

The bone matrix has distinct architecture and biochemistry which present a barrier to synthesizing bone-mimetic regenerative scaffolds. To mimic the natural structures and components of bone, biomimetic structural decellularized extracellular matrix (ECM)/regenerated silk fibroin (RSF) scaffolds incorporated with magnetic nanoparticles (MNP) are prepared using a facile synthetic methodology. The ECM/RSF/MNP scaffold is a hierarchically organized and interconnected porous structure with silk fibroin twined on the collagen nanofibers. The scaffold demonstrates saturation magnetization due to the presence of MNP, along with good cytocompatibility. Moreover, the β-sheet crystalline domain of RSF and the chelated MNP could mimic the deposition of hydroxyapatite and enhance compressive modulus of the scaffold by ≈20%. The results indicate that an external static magnetic field (SMF) with a magnetic responsive scaffold effectively promotes cell migration, osteogenic differentiation, neogenesis of endotheliocytes in vitro, and new bone formation in a critical-size femur defect rat model. RNA sequencing reveals that the molecular mechanisms underlying this osteogenic effect involve calsequestrin-2-mediated Ca2+ release from the endoplasmic reticulum to activate Ca2+ /calmodulin/calmodulin-dependent kinase II signaling axis. Collectively, bionic magnetic scaffolds with SMF stimulation provide a potent strategy for bone regeneration through internal structural cues, biochemical composition, and external physical stimulation on intracellular Ca2+ homeostasis.

A global spectral-Galerkin investigation of a Rayleigh–Taylor instability in plasma using an MHD–Boussinesq model

This paper presents a new efficient algorithm based on the spectral-Galerkin numerical approximations complemented by a magnetohydrodynamics–Boussinesq model and a new solver for studying the development of a Rayleigh–Taylor (RT) instability. We use the Shenfun computational framework in the Cartesian coordinates, which gives the spectral order and accuracy for the considered model based on the magnetohydrodynamics equations and the Boussinesq conjecture. The numerical simulations were conducted for each two- and three-dimensional case, both with and without an external static magnetic field. The validity of the numerical results was examined by comparing the calculated squared L2-norm of the density parameter with the linear stability analysis. We also examined the effects of a uniform tangential magnetic field on the onset and growth of an RT instability at different magnetic field strengths. The analysis of the effectiveness of the presented method suggests that it can be modified for further research on two-component plasma.

Control over magneto-optical plasmon rotation with Doppler broadening and cross-Kerr non-linearity

We investigate the impacts of cross-Kerr non-linearity and Doppler broadening on the magneto-optical rotation (MOR) induced in surface plasmon polaritons (SPPs) located at the interface of a metalic medium and a 4-level atomic system. In this paper, the external static magnetic field and a weak probe field under the cross-Kerr effect result in the birefringence enhancement of the system. Moreover, the incoherent effect of Doppler broadening can regulate the MOR of SPPs. Notably, the controlled MOR of SPPs can be leveraged for a variety of advantageous implementations in the fields of polarization spectroscopy, optical communication, nanoscale Faraday isolation, accurate metrology, as well as bio/chem sensing technologies.

Exceptional points and lines and Dirac points and lines in magnetoactive cholesteric liquid crystals

We investigated the properties of cholesteric liquid crystals (CLCs) being in external static magnetic field directed along the helix axis. We have shown that in the case of the wavelength dependence of magneto-optic activity parameter, and in the presence of absorption new features appear in the optics of CLCs. We have shown that in this case new photonic band gaps (PBGs) appear. This new PBG is sensitive to the polarization of the incident light. But if the chirality sign of the polarization of the incident diffracting light for the basic PBG (which exist also at the absence of external magnetic field) is determined only by the chirality sign of the CLC helix, then for the second one it is determined by the external magnetic field direction (i.e., on whether the directions of the external magnetic field and the incident light are parallel, or they are antiparallel). We have shown that in this case besides Dirac points there appear also Dirac lines as well as exceptional points and exceptional lines. And moreover, near some of these points and lines the narrow bands or wide bands of magnetically induced transparency, and magnetically induced absorption appear, and near the others a wide coherent perfect absorption band appears that is insensitive to incident light polarization. And finally at some wavelength the same reflection, transmission and absorption takes place for any polarization of incident light, although it is not Dirac point nor exceptional point. This system can apply as tunable narrow-band or broad-band filters and mirrors, a highly tunable broad/narrow-band coherent perfect absorber, transmitter, ideal optical diode, and other devices.

Synthesis, Characterization, and Second Harmonic Generation of Multiferroic Iron‐Doped Lithium Niobate Powders

AbstractRandom granular media can exhibit characteristics that are often related to ordered media. In the present work, this feature is observed in the polarized Second Harmonic Generation (SHG) response from reduced iron‐doped lithium niobate (LN:Fe) powders, which is an unexpected effect due to multiple scattering. In addition, the subsisting‐order properties of the powders can be further controlled by magnetic induction to tailor the SHG response. The samples are characterized by X‐ray Diffraction (XRD), X‐ray Photoelectron Spectroscopy (XPS), and confocal Raman Spectroscopy. The SHG response in the absence and presence of an external static magnetic field is then studied as the fundamental beam focus is translated from air into the powder. The SHG intensity polarization state is studied as a function of the linear polarization of the fundamental beam at the focus depth position, where the maximum SHG recorded intensity is observed. These results demonstrate that the SHG response of LN:Fe powders can be modified by post‐thermal treatment in a reducing atmosphere for photonic applications.

Magnetoelectric nanoparticles shape modulates their electrical output.

Core-shell magnetoelectric nanoparticles (MENPs) have recently gained popularity thanks to their capability in inducing a local electric polarization upon an applied magnetic field and vice versa. This work estimates the magnetoelectrical behavior, in terms of magnetoelectric coupling coefficient (αME), via finite element analysis of MENPs with different shapes under either static (DC bias) and time-variant (AC bias) external magnetic fields. With this approach, the dependence of the magnetoelectrical performance on the MENPs geometrical features can be directly derived. Results show that MENPs with a more elongated morphology exhibits a superior αME if compared with spherical nanoparticles of similar volume, under both stimulation conditions analyzed. This response is due to the presence of a larger surface area at the interface between the magnetostrictive core and piezoelectric shell, and to the MENP geometrical orientation along the direction of the magnetic field. These findings pave a new way for the design of novel high-aspect ratio magnetic nanostructures with an improved magnetoelectric behaviour.