External Magnetic Field Research Articles

3D Modelling of Electro Vortex Flow Inside Liquid Metal and Effect of External Magnetic Fields

Electrovortex flow emerges when the current inside conducting liquids interacts with its self-induced magnetic field. The flow structure and strength of the flow are dictated by the current value and the presence of an external magnetic field. We present here 3D simulations for the electrovortex flow inside a liquid metal cylinder. The results presented reveal a typical electrovortex structure for low currents. Higher currents induce turbulence inside the electrovortex flow without any presence of an external magnetic field. In presence of Earth’s magnetic field, the flow structure is affected significantly. Cyclone, tornado, and rope tornado are observed inside the domain due to the earth’s magnetic field depending on the ratio of current applied and the earth’s magnetic field.

Dead-zone-free atomic magnetometer based on hybrid Poincaré beams

In this paper, we present the experiment and the theory scheme of light-atom interaction in atomic magnetometers by using a hybrid Poincaré beam (HPB) to solve an annoying problem, named “dead zone.” This kind of magnetometer can be sensitive to arbitrary directions of external magnetic fields. The HPB has a complex polarization distribution, consisting of a vector radially polarized beam and a scalar circularly polarized beam in our experiment. These two kinds of beams have different directions of dead zones of external magnetic fields; thereby, the atomic magnetometer with an HPB can avoid the non-signal area when the direction of the external magnetic field is in the plane perpendicular to the light polarization plane. Furthermore, the optical magnetic resonance (OMR) signal using an HPB still has no dead zones even when the direction of the external magnetic field is in the plane parallel to the polarization plane in our scheme. Our work has the potential to simplify and optimize dead-zone-free atomic magnetometers.

Investigation of interfacial microstructure and connection mechanism of magnetic field-assisted magnesium/aluminum laser welding joint

Variable process experiments to prepare hybrid joints of AZ31 magnesium (Mg) and 6061 aluminum (Al) alloys by magnetic field-assisted laser welding were performed in an overlap Mg-on-Al configuration with the addition of titanium (Ti) foil. Temperature field and flow field of molten pool including chemical potential of each element were also calculated. It is shown that at the optimal welding parameters, the shear force of joint reaches 887.79 N, which is 83.4 % higher than that of no-added joint. In the case of external magnetic field, the improved mechanical properties of joints largely depend on the diffusional barrier effect of Ti foil, which benefits from the enhanced energy absorption and flow of molten pool leading to the enlargement of interface connection area and the formation of Ti-Al compounds such as TiAl3 at Mg/Al interface. Meanwhile, the grains refines due to the magnetic field, which reduces the strain at the joint and enhances the uniformity of the interface microstructure. However, under the condition of excessive magnetic field strength, the enhanced stirring effect of molten pool will cause Ti foil break and the direct interaction between Mg and Al, which deteriorates the joint properties.

On the influence of magnetic flux guide location to the out-of-plane magnetic field sensing of chip-scale AMR sensor

The anisotropic magneto-resistive (AMR) sensors could detect external magnetic fields through the change of magnetization and resistance. Typically made of thin films, the AMR sensors are generally only sensitive to the in-plane magnetic field. The AMR sensors with Ni pillar array structures as magnetic flux guides have been presented to enhance the detection of out-of-plane magnetic fields. However, the magnetic flux lines transmitted from adjacent pillars may interact with each other, so that their directions will be changed accordingly. Thus, the locations of pillar guides may influence the distribution of magnetic flux lines, and further change the out-of-plane magnetic field sensing performance of the AMR sensor. To gain insight on this design consideration, this study introduces a serpentine routing AMR film with flux guides distributed along each wire gaps. By varying the gap of the serpentine AMR wire and the distance between the pillar and the AMR wire, the influence of flux guide location on the out-of-plane magnetic field sensing is investigated. Through microfabrication processes, the flux guide array can be batch fabricated and defined at appropriate locations, and further monolithically integrated with AMR sensor. Measurements show that for a serpentine AMR sensor with a gap of 70μm, the sensitivity can be increased by 4.6-fold as the distance between flux guide and AMR film decreases from 20 μm to 0 μm. Moreover, when the flux guide fixed in the middle of gap of the serpentine AMR sensor, the sensitivity can be improved by 5.6-fold as the gap decreases from 70 μm to 50 μm.

Amorphous ribbons for GMI detection of stray fields FeOx magnetic filler of epoxicomposites

Magnetoimpedance (MI) effect in stress-annealed Co-based amorphous ribbon was studied in the states without and in presence of the magnetic epoxy composite of cylindrical shape. Iron oxide FeOx magnetic microparticles of different concentrations (0–70 wt%) were used as a magnetic filler. The condition of stress annealing (350 °C, 1 h and 250 MPa specific load) were selected in order to insure the high MI sensitivity with respect to external magnetic field in the field of a few Oersted. The MI responses were modified in the presence of the magnetic epoxy composites due to the contribution of the stray fields of embedded microparticles. It was experimentally found that degree of the MI curves modification depended on the microparticles concentration. The MI characteristics were also dependent on the length-to-width ratio of the MI element. The most sensitive MI element under study showed a linear dependence with a 1 %/weightpercent microparticle concentration slope. Mathematical modeling using finite elements (FEM) protocol for the properties of short MI elements confirmed the results and highlighted the non-monotonic contribution of high-concentration composites to the MI responses

Converging Hydrogen-Bonded Water Transport Channel with External Magnetic Field in a Janus Molecular Cobalt Phosphate for Enhanced Oxygen Evolution Reaction (OER) Activity

Converging Hydrogen-Bonded Water Transport Channel with External Magnetic Field in a Janus Molecular Cobalt Phosphate for Enhanced Oxygen Evolution Reaction (OER) Activity

Influence of ferromagnetic interlayer exchange coupling on current-induced magnetization switching and Dzyaloshinskii-Moriya interaction in Co/Pt/Co multilayer system.

This paper investigates the relationship among interlayer exchange coupling (IEC), Dzyaloshinskii-Moriya interaction (DMI), and multilevel magnetization switching within a Co/Pt/Co heterostructure, where varying Pt thicknesses enable control over the coupling strength. Employing Brillouin Light Scattering to quantify the effective DMI, we explore its potential role in magnetization dynamics and multilevel magnetization switching. Experimental findings show four distinct resistance states under an external magnetic field and spin Hall effect related spin current. We explain this phenomenon based on the asymmetry between Pt/Co and Co/Pt interfaces and the interlayer coupling, which, in turn, influences the DMI and subsequently impacts the magnetization dynamics. Numerical simulations, including macrospin, 1D domain wall, and simple spin wave models, further support the experimental observations of multilevel switching and help uncover the underlying mechanisms. Our proposed explanation, supported by magnetic domain observation using polar-magnetooptical Kerr microscopy, offers insights into both the spatial distribution of magnetization and its dynamics for different IECs, thereby shedding light on its interplay with DMI, which may lead to potential applications in storage devices.

Influence of a Magnetic Field on the Structure, Morphology and Gas Sensing Characteristics of ZnO: Al Thin Films Prepared by Pulsed Laser Ablation

In this work, aluminium-doped zinc oxide (AZO) nanostructure at 0.3 wt% and 0.5 wt% Al was synthesized using the pulse-laser ablation technique in liquid(PLAL) using pulsed Nd: YAG laser of a fundamental wavelength of (1064 nm). The process was done in the absence and presence of an external magnetic field. The deposited AZO nanostructures by drop-casting on etched-Si wafers were examined by different techniques. The XRD test illustrates enhancing the crystallinity of the prepared thin films by applying an external magnetic field. The FESEM images displayed the change of nanostructure to nano-sheets of high surface area after using a 77.2 mT permanent magnet placed behind the target during the ablation process. The gas sensor based on the AZO nanostructures has higher sensitivity against NO2 than H2S. Increasing the Al ratio from 0.3 wt% to 0.5 wt% changed the properties of the prepared samples to have small porosity and small surface area, which negatively affected the properties of the sensor

Mathematical model of weakly coupled spherical resonator chains under the influence of external magnetic field

Mathematical model of weakly coupled spherical resonator chains under the influence of external magnetic field

IMPACT ANALYSIS OF SURFACE ROUGHNESSOF THE PLATE-PLATE MEASURING SYSTEM ON RESISTANCETORQUE IN INTERACTION WITH MR FLUID

Magnetorheological (MR) fluids are complex suspensions of magnetic particles in a non-magnetic carrierfluid. They exhibit ‘smart’ properties that enable them to change their rheological parameters in responseto a change in the external magnetic field applied. This behavior is used in some engineering solutions, e.g.MR clutches or brakes. For such systems to work correctly, the resistance torque achieved by contact withthe MR fluid must be properly determined. This paper demonstrates how surface roughness of a contactsurface between the solid and the MR fluid affects the resistance torque value. Measurements were madeon a dedicated rotational rheometer using a shear mode fluid, most closely replicating the way MR clutchesand brakes work. Plate-plate geometry was used, in standard design, and modified by pasting sandpaper withdifferent grit levels. The tests have shown that the roughness of the mating surface affects the resistance torqueresults.

Photocatalytic degradation of methylene blue under visible light by cobalt ferrite nanoparticles/graphene quantum dots.

A simple approach was developed to synthesize cobalt ferrite nanoparticles/graphene quantum dots (CF/GQDs). The material was prepared from a homogeneous mixture of iron nitrate, cobalt nitrate, and starch at 140, 180 and 200 °C in a 24 h thermal hydrolysis process. The obtained materials were characterised by using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, ultraviolet-visible diffuse reflectance spectroscopy, Fourier-transform infrared spectroscopy, photoluminescence spectroscopy, vibrating-sample magnetometry, and nitrogen adsorption/desorption isotherms. Cobalt ferrite crystals of around 8-10 nm and graphene quantum dots formed directly at 200 °C. Stacking GQDs sheets onto the CF nanoparticles resulted in CF/GQDs nanoparticles. The nanocomposite exhibits satisfactory fluorescent and superparamagnetic properties, which are vital for catalytic applications. The CF/GQDs catalyse significantly the degradation of methylene blue (MB) under visible light. The catalyst can be recycled with an external magnetic field and displays suitable stability. Also, it was reused in three successive experiments with a loss of efficiency of about 5%. The CF/GQDs are considered as an efficient photocatalyst for MB degradation and other dyes.

Geometry-induced Bloch point domain wall in Permalloy conical frustum nanowires for advanced spintronics applications

In this study, we investigate the pseudo-static magnetic properties of Permalloy conical frustum nanowires using micromagnetic simulations. We thoroughly examine how both the major and minor radii influence the magnetic reversal mechanism when an external magnetic field is applied parallel to the nanowire axis. The obtained results show that under specific geometrical conditions, magnetization reverts though a Bloch point-type domain wall. In these cases, hysteresis curves exhibit two Barkhausen jumps during magnetization reversal, forming a plateau field range in which a Bloch point domain wall nucleates and propagates until its annihilation after the second Barkhausen jump. The nucleation of a Bloch point domain wall in a frustum conical nanowire geometry is reported. These findings highlight the significance of this geometry in nucleating these attractive topological defects for promising applications.

Terahertz Magnetic Moiré Grating for Enhanced Chirality Manipulation and Nonreciprocal Spin Isolation

AbstractMagneto‐optical activity is a significant way to achieve asymmetric transmission for spin photons. However, it is severely limited by the weak light‐matter interaction in the terahertz (THz) region. In this work, a magnetic Moiré grating (MMG) is constructed by sandwiching an Yttrium iron garnet (YIG) single crystal in a pair of twisted 2D subwavelength gratings. The twisted angle between two gratings introduces a strong geometric Moiré chirality related to the Moiré pattern. When an external magnetic field is applied to the YIG layer, three different symmetries of spacial mirror image, time reversal, and spin conjugation are broken simultaneously under the chiral coupling between magneto‐optical activity and Moiré chirality, leading to both the enhanced magneto‐optical chiral transmission and the nonreciprocal spin isolation. Under the magnetic field varying from −0.26 to +0.26 T in the experiment, the MMG achieves an active modulation of circular dichroism from 39 to −37.5 dB and optical activity from −35° to 30°. Moreover, the maximum spin isolation over 32.6 dB is also obtained near 0.5 THz. This mechanism provide a new way to realize independent manipulation and active modulation of THz spin photons more flexibly.

Design and Analysis of New Type of Magnetically Controlled Reactor

In recent years, various new types of magnetic materials have emerged, especially in the field of nanotechnology. The application of material composite technology has formed a new type of dual-phase composite magnetic material. Under the control of an external magnetic field, the material can achieve functional conversion between the hard magnetic phase and the soft magnetic phase, with magnetic permeability, non-magnetic permeability, and excitation ability. In this paper, it is proposed to use this material as the basic material for the magnetic state control of the reactor core, break through the bondage of the traditional reactor core to the performance of the controllable reactor, and innovatively form a new type of reactor structure. By adding a detection and control system, according to the working state of the power grid, the function conversion of the nano adjustable magnetic material is effectively adjusted to realize the automatic adjustment of the magnetic state of the reactor. Firstly, the preparation and material properties of dual-phase composite magnetic materials were studied. The design and preparation process from magnetic powder to bulk magnet were given, and the magnetic properties were measured. Secondly, a new 380 V/100 kVar magnetically controlled reactor was designed by using dual-phase composite magnetic material to form a composite core of magnetically controlled reactor on silicon steel sheet. The simulation analysis of electromagnetic characteristics and volt-ampere characteristics was carried out to verify the correctness of the proposed scheme.

Dust magnetoacoustic waves in an inhomogeneous cylindrical four-component dusty plasma in the presence of polarization force

Abstract Dust magnetoacoustic waves have been examined in an inhomogeneous, bounded, cylindrical dusty plasma containing oppositely polarized dust particles. Considering polarization force, dust dynamics in r − θ plane is studied in the presence of inhomogeneous external magnetic field along z axis. At equilibrium, the dusty plasma components are supposed to follow Gaussian density distribution. Using reductive perturbation method (RPM), a variable coefficient cylindrical Kadomtsev–Petviashvili (VCCKP) equation has been derived. For weak azimuthal perturbation, an analytical solution, obtained by Zhang (“Exact solutions of a kdv equation with variable coefficients via exp-function method,” Nonlinear Dynam., vol. 52, nos. 1–2, pp. 11–17, 2008) using Exp-function method, is chosen. Phase velocity of dust magnetoacoustic wave is found to be modified by the density inhomogeneities, polarization force, dust charge state ratio and ion-to-electron temperature ratio. Spatio-temporal evolution of the dust number densities has been noticed. Existence of the compressive electromagnetic solitary waves is observed numerically for the chosen dusty plasma parameter range. The impacts of the inhomogeneity, polarization force, dust charge state ratio and ion-to-electron temperature ratio on the relative amplitude of the dust magnetoacoustic wave are also discussed.

Design of magnetic photonic crystal microdroplet for sensitive detection of cationic organic pollutants by the coupled resonance effect

Photonic crystals (PCs), periodically arranged nanoparticles, have emerged with extraordinary optical properties for light manipulation owing to their photonic band gaps (PBGs). Here, a novel strategy and method was developed for efficient enrichment and sensitive detection of cationic organic pollutants in water. Size-controlled Fe3O4@poly (4-styrenesulfonic acid-co-maleic acid) (Fe3O4@PSSMA) was prepared, and high surface charge were formed with the coating of PSSMA layer on the surface of Fe3O4, which could be used for adsorption and removal of cationic organic pollutants. The Fe3O4@PSSMA after adsorbing cationic organic pollutant were assembled to magnetic photonic crystal microdroplet (MPCM) structure in an external magnetic field, which was used as surface-enhanced Raman scattering (SERS) substrate. By coupling the magnetically tuned PBGs with Raman laser wavelength, the light utilization efficiency can be improved and the coupled resonance effect was greatly enhanced. The enhancement factor (EF) of MB was more than 800 attributing to the dual function of enrichment and coupled resonance effect of MPCM. The developed analytical strategy is the first time to use MPCM as a SERS substrate to realize the sensitive detection of 10 nmol L−1 MB in real water, which greatly improves the application of MPCM in the field of contaminant analysis and detection in water.

Analytical determination of a quasi-stationary electromagnetic field created by magnetic moments and eddy currents in conducting half-space

Aim. Study of the distribution of a three-dimensional alternating quasi-stationary electromagnetic field at the surface of conducting half-space with strong skin-effect, the source of which is an arbitrarily oriented magnetic moment. Methodology. The expressions for non-uniform electromagnetic field with strong skin effect are used for the analysis, which is based on the found exact analytical solution of the general three-dimensional problem and the use of expansion into asymptotic series with respect to a small parameter that is proportional to the ratio of the field penetration depth to the distance between the sources of the external field and the surface of body. Specific expressions at the surface are completely determined by the known field of external sources. In this work, the external magnetic moment field is used. Results. For strong skin effect, expressions for the electric and magnetic field strength are obtained separately for the components of the magnetic moment oriented perpendicularly and parallel to the flat surface between the dielectric and conducting areas. The features of the electromagnetic field distribution are analyzed depending on the value of introduced small parameter. The results are presented for the module and phase shift of the field strength with respect to the phase of the external field source. Originality. The expressions found for the electromagnetic field appear to be more general than the use of closed contours with alternating current, since they extend types of external field sources and allow the use of the superposition method instead of integration over the entire contour. Practical value. The found specific analytical expressions of the electromagnetic field at the surface for the external field of magnetic moments significantly simplify the solution of the problems, since they do not require additional solution of the field equations. References 20, figures 8.

High-efficiency electromagnetic shielding based on multipolar effect in RGO/MXene aerogels decorated with ordered Fe3O4 cluster

With the widespread use of digital systems and electronic communication devices, there is an urgent need to develop lightweight and efficient electromagnetic interference (EMI) shielding materials to address the growing problem of radiation pollution. RGO/MXene/Fe3O4 aerogels were successfully designed and synthesised using a one-step hydrothermal process induced by an external magnetic field in this study. Reduced graphene RGO, MXene nanosheets and Fe3O4 nanoparticles were suitably assembled together to achieve the combined advantages. The aerogels exhibited large specific surface area and hierarchical porosity. The material not only achieves an effective synergy between magnetic loss and dielectric loss, but also exhibits satisfactory EMI shielding performance. Magnetic field induced RGO/MXene/Fe3O4 aerogels (MIRMFE-2) exhibits the best EMI shielding performance with an average SET value of 76.9 dB. The excellent shielding performance of MIRMFE is attributed to both its 3D porous structure and the high dielectric loss due to multiple polarization relaxation, magnetic loss due to eddy current loss and natural resonance. The synthesis of MIRMFE provides an effective method for, designing high-performance and lightweight EMI shielding materials.

Fabrication of magnetic field sensor based on a Co-based Schottky heterojunction

We have prepared a reliable magnetic field sensor based on a Co-based Schottky heterojunction with the possibility of finding practical application when the current–voltage (I–V) characteristics of the heterojunctions were modified by the external magnetic fields. For this purpose, the heterojunctions based on ferromagnetic thin films Co were deposited on Si (100) substrate via ultra-thin Pt films. The structural and magnetic properties of the heterojunctions were demonstrated, the crystal structure and the saturation magnetization of heterojunctions significantly increased with the increase of annealing temperatures. The electrical properties of the Co/Pt/Si heterojunction were investigated using temperature-dependent I–V characteristics, the rectifying properties were observed in the whole temperature ranging from 233 K to 283 K. Based on a simplified energy band structure, the magnetic field transport properties of Co/Pt/Si heterojunctions were investigated by taking into account the effects of spin and magnetic field on the potential barrier height of Co/Pt/Si heterojunctions. The results showed that the experimental ratio of current measured in a magnetic field B and in zero magnetic field (I(B)/I(0)) is linearly with the magnetic field B and almost independent of the applied voltage. The sensitivity and linearity of the magnetic field sensor were measured. The sensitivity of the sensor can reach 72.09 μA/T at an applied voltage frequency of 2000 Hz, which indicates that the linearity and sensitivity of the sensor are improved with the increase of the applied voltage frequency. The proposed sensors would be easy to integrate with current semiconductor processes with simple structure and they could be suitable for geological applications such as energy exploration.

Revealing hidden spin polarization in centrosymmetric van der Waals materials on ultrafast timescales

One of the key challenges for spintronic and quantum technologies is to achieve active control of the spin angular momentum of electrons in nanoscale materials on ultrafast, femtosecond timescales. While conventional ferromagnetic materials and materials supporting spin texture suffer both from conceptional limitations in miniaturization and inefficiency of optical and electronic manipulation, non-magnetic centrosymmetric layered materials with hidden spin polarization may offer an alternative pathway to manipulate the spin degree of freedom by external stimuli. Here we demonstrate an approach for generating transient spin polarization on a femtosecond timescale in the otherwise spin-unpolarized band structure of the centrosymmetric 2H-stacked group VI transition metal dichalcogenide WSe2. Using ultrafast optical excitation of a fullerene layer grown on top of WSe2, we trigger an ultrafast interlayer electron transfer from the fullerene layer into the WSe2 crystal. The resulting transient charging of the C60/WSe2 interface leads to a substantial interfacial electric field that by means of spin-layer-valley locking ultimately creates ultrafast spin polarization without the need of an external magnetic field. Our findings open a novel pathway for true optical engineering of spin functionalities such as the sub-picosecond generation and manipulation of ultrafast spin currents in 2D heterostructures.