Magnetic Effects Research Articles

Geomagnetic and ionospheric effects two consecutive strong earthquakes in Morocco on september 08, 2023

The geophysical effects of a strong seismic event in the form of two earthquakes of magnitude 6.8 and 4.9 that occurred on September 08, 2023 in Morocco at close times 22:11 and 22:30 UTC with an epicentral distance between the foci of ~ 4 km are considered. We used data from a number of observatories of the INTERMAGNET network and the results of magnetic registration at the Mikhnevo Geophysical Observatory of IDG RAS. It was shown that in the absence of significant global disturbances of the Earth’s magnetic field, earthquakes were accompanied by a series of three positive bay-shaped geomagnetic variations with maximum amplitudes from ~1 to ~10 nT, following each other after ~60 min. The maxima of the induced magnetic field variations were observed almost synchronously at distances from ~800 to ~10000 km. The delay time of the magnetic effect relative to the main shock of the first earthquake was ~70 min. Taking into account the almost planetary nature and high synchronicity of the magnetic field disturbances caused over a significant range of distances, as well as time delays corresponding in order of magnitude to the travel time of the seismic signal of a distance multiple of the size of the Earth, it is suggested that the magnetic effect of the seismic event in question was caused by a global source, which can serve as an excited geodynamo. The ionospheric effect of the seismic event under consideration is presented in the form of variations of the critical frequency f0F2 calculated from the data of the ground-based sounding station of the del Ebre Observatory.

Enhanced Magnetic Heating for Efficient Oxygen Evolution Reaction by Pinning Effect of Ferromagnetic/Antiferromagnetic Coupling.

The magnetic heating effect under alternating magnetic fields (AMFs) has recently gained attention in catalysis due to its potential to greatly boost catalytic activities by providing localized heating around magnetic nanoparticles. However, nanoparticles still suffer from low magnetic heating efficiency due to their low magnetic anisotropy and thermal fluctuation, which is a key barrier in the wide application of AMF-assisted catalysis. Herein, by introducing the pinning effect of ferromagnetic/antiferromagnetic (FM/AFM) coupling, NiO/NiOOH (AFM/FM) core-shell nanoparticles exhibit significantly enhanced oxygen evolution reaction activity and resistance to thermal fluctuations under AMF, compared to NiOOH nanoparticles. Notably, magnetized NiO/NiOOH nanoparticles provide an overpotential of 186 mV at 10 mA cm-2, outperforming unmagnetized ones (218 mV) under the same conditions, further emphasizing the prominent role of the pinning effect in enhanced magnetic heating efficiency. This work provides valuable inspiration to design advanced magnetic catalysts and meet the challenge of the development of AMF-assisted catalysis.

Proximity-induced ferromagnetism of platinum thin film on magnetic insulating CrI3 nanoflakes

The induced magnetization of Pt holds significant promise for the development of spintronic devices. In this study, we constructed a two-dimensional heterostructure consisting of a ferromagnetic insulating CrI3 nanoflake and metallic Pt thin films. The observation of anomalous Hall effect suggests the emergence of a ferromagnetic long-range order in the Pt thin film induced by the magnetic proximity effect. Density functional theory calculations were performed to investigate the underlying mechanisms. We propose that the spontaneous magnetization of Pt in Pt/CrI3 stems from an intensified exchange interaction between Pt 5d and Cr 3d electrons, which is facilitated by the interface coupling and the formation of interfacial hybrid orbitals. These results contribute to a deeper understanding of spin-based phenomena and have potential implications for advancements in the field of spintronics.

Features of MHD on Secant Curved Annular Circular Plate Lubricant as a Couple-Stress Fluid with Slip Velocity

The purpose of this study is to examine the magneto-hydrodynamic (MHD) and slip velocity effect on secant curved annular circular plates lubricated with couple stress fluid and to derive the modified Reynolds’s equation for non-Newtonian fluid under various operating conditions to obtain the optimum bearing parameters. Based upon the MHD theory and Stokes theory for couple stress fluid, the governing equations relevant to the problem under consideration are derived. This paper analyses the effect of slip velocity on secant curved annular circular plates with an electrically conducting fluid in the presence of a transverse magnetic field. It is found that there is an increase in squeeze film pressure, load carrying capacity and squeeze film time in secant curved annular circular plates due to the presence of magnetic effects with couple stress fluid and slip velocity.

Macapá, a Brazilian equatorial magnetometer station: installation, data availability, and methods for temperature correction

Abstract. In the last 60 years, the largest displacement of the magnetic equator (by about 1100 km northwards) occurred in the Brazilian longitudinal sector. The magnetic equator passed by Tatuoca magnetic observatory (TTB) in northern Brazil in 2012 and continues to move northward. Due to the horizontal geomagnetic field geometry at the magnetic equator, enhanced electric currents in the ionosphere are produced – the so-called equatorial electrojet (EEJ). The magnetic effect of the EEJ is observed in the range of ±3° from the magnetic equator, where magnetic observatories record an amplified daily variation of the H component. In order to track the spatial and temporal variation of this phenomena, a new magnetometer station was installed in Macapá (MAA), which is about 350 km northwest of TTB. In this paper, we present the setup and data analysis of MAA station from November 2019 until September 2021. Because of its special configuration, we develop a method for temperature correction of the vector magnetometer data.

An atomically controlled insulator-to-metal transition in iridate/manganite heterostructures.

All-insulator heterostructures with an emerging metallicity are at the forefront of material science, which typically contain at least one band insulator while it is not necessary to be. Here we show emergent phenomena in a series of all-correlated-insulator heterostructures that composed of insulating CaIrO3 and insulating La0.67Sr0.33MnO3. We observed an intriguing insulator-to-metal transition, that depends delicately on the thickness of the iridate component. The simultaneous enhancements of magnetization, electric conductivity, and magnetoresistance effect indicate a percolation-type nature of the insulator-to-metal transition, with the percolation threshold can be reached at an exceptionally low volume fraction of the iridate. Such a drastic transition is induced by an interfacial charge transfer, which interestingly alters the electronic and crystalline structures of the bulk region rather than the limited ultrathin interface. We further showcased the central role of effective correlation in modulating the insulator-to-metal transition, by demonstrating that the critical thickness of iridate for triggering the metallic state can be systematically reduced down to a single unit-cell layer.

Spatially-resolved spectroscopic investigation of the inhomogeneous magnetic field effects on a low-pressure capacitively-coupled nitrogen plasma

Although magnetized plasmas have been frequently used to enhance the process rate or improve the film quality via the control of ion flux as well as energy and plasma density in semiconductor processes, the inhomogeneous magnetic field—which leads to plasma non-uniformity—remains as a problem to be solved. To address this problem, it is essential to conduct a comprehensive assessment of the magnetic effect throughout the entire discharge. Therefore, in the present study, we investigated the magnetic field effects (B < 100 G) on a capacitively-coupled nitrogen plasma based on spectroscopic analyses. The spatially-resolved emission spectra were measured along the radial direction at various vertical positions under the pressures of 10 mTorr and 250 mTorr both with and without magnetic field. By analyzing emission spectra such as N2 FPS, N2 SPS, N2+ FNS, and N I, we were able to obtain the radial distributions of reactive species density, vibrational temperature, and excitation temperature. In low-pressure plasma, with the application of a magnetic field, maximum increases in vibrational temperature and excitation temperature of 462 K and 491 K, respectively, were observed within the bulk region beneath the magnet. This magnetic effect resulted in a significant increase in reactive species density along the radial direction. It was also found that the local enhancement of ion density by magnetic field was strongly related to the increase in excitation temperature and the density of the N2+(B) state. From this result, it is suggested that introducing an asymmetric magnetic field could modulate the spatial distributions of the physical and chemical properties of the plasma.

Aromaticity in Isoelectronic Analogues of Benzene, Carborazine and Borazine, from Electronic Structure and Magnetic Property.

Carborazine (B2C2N2H6) and borazine (B3N3H6) are isoelectronic analogues of benzene (C6H6). The aromatic character of borazine have basically reached a consensus after a long period of controversy, but the related properties of carborazine are even rarely reported. In this work, we systematically investigated the geometric structure, charge distribution, frontier molecular orbital characteristics, bonding, electronic delocalization, magnetic shielding effect, and induced ring current of carborazine and borazine, and compared the studied characteristics with those of benzene to determine the aromatic character of the two analogues. The combination of multiple properties shows that although they are isoelectronic, carborazine is evidently aromatic, while borazine only exhibits rather weak aromaticity. The C atom acting as a connecting bridge between B and N atoms in carborazine reduces the electronegativity difference on the molecular backbone and enhances the electronic delocalization over the conjugated path, which is the essence of the distinct disparity of aromaticity between carborazine and borazine.

Detecting axion dark matter with chiral magnetic effects

We show that dark matter axions or axionlike particles (ALP) induce spontaneously alternating electric currents in conductors along the external magnetic fields due to the (medium) axial anomaly, realizing the chiral magnetic effects (CME). We propose a new experiment to measure this current to detect the dark matter axions or ALP. These induced currents are the electron medium effects, directly proportional to the axion or ALP coupling to electrons, which depends on their microscopic physics. In the experimental setup, one measures the sum of the electric current due to CME and the vacuum current due to the anomalous axion-photon coupling. The CME current is, in general, subdominant by a factor of the Fermi velocity of electrons, compared to latter, unless the axion or ALP coupling to electrons is much bigger than its coupling to photons to compensate the Fermi velocity suppression. However, we find that repurposing the currently operating and planned axion haloscopes may have good sensitivity to probe the CME current. Published by the American Physical Society 2024

Chiral magnetic effect in heavy ion collisions: The present and future

Chiral magnetic effect in heavy ion collisions: The present and future

Mechanism of praseodymium yttrium regulating the absorption properties of M-type strontium ferrite: From single phase to multi phase mixed system

When Pr and Y ions are added to M-type strontium ferrite, a portion of the ions will enter the main phase lattice, while the excess ions will aggregate at the grain boundaries to form a secondary phase. The occupancy of rare earth ions in the main phase lattice and the formation of secondary phases are two key factors affecting the material's absorbing properties. The difference in ultimate solid solubility between rare earth ions Pr and Y in M-type strontium ferrite is significant, and they also form different secondary phases at grain boundaries. Consequently, the synthesized SrFe12-2xPrxYxO19 (0 < x ≤ 1.5) demonstrates its potential as a microwave absorbing material across a wide range of substitutions. Moreover, the performance changes have their own characteristics at different substitution levels. XRD results show that the samples include pure M phase and the coexistence of M phase and heterogeneous phases, with the heterogeneous phases being perovskite-type and garnet-type. SEM and EDS results indicate that Pr and Y co-substitution can refine grain size and reduce oxygen content. XPS results suggest that the valence change of Pr ions leads to the generation of Fe2+ ions and oxygen vacancies (Od). PPMS results reveal that saturation magnetization and coercivity are mainly affected by anisotropy field and particle size. Co-substitution of Pr and Y increases the dielectric and magnetic losses of the M phase, and the generated heterogeneous phases also enhance the dielectric and magnetic losses through interface polarization and magnetic exchange coupling effects, both cooperatively improving the wave-absorbing performance, with the minimum reflection loss (RLmin) reaching −51.57 dB (x = 0.1, d1 = 4.0 mm, EAB = 2.57 GHz).

Dual motion principal Au-Ni-PDA-CuS micromotors with NIR light and magnetic effect for detection of organic dye

Copper sulfide (CuS), despite some disadvantages such as rapid recombination, easy aggregation, photodegradation of oxidized CuS, and a limited ability to absorb light energy, is still a good photocatalyst. This semiconductor material with a narrow bandgap plays a significant role in the degradation of organic dyes. However, due to these mentioned drawbacks, it requires a linker. The polymer used as this intermediate binder is polydopamine (PDA). PDA not only eliminates the disadvantages of CuS but also facilitates its attachment to the carrier system, which is a micromotor. However, the purpose of using PDA here is not only to eliminate the disadvantages of CuS but also to enable light-triggered motion due to its sensitivity to near-infrared (NIR) radiation. Similarly, CuS, which is a good catalyst, has been used in the polymerization reaction to catalyze dopamine’s conversion to PDA. The micromotor used in the study, based on the dual-motion principle, exhibits high stability and good reusability. The synthesized Au-Ni-PDA-CuS composite micromotor demonstrates a good photocatalytic degradation performance under NIR irradiation. The degradation efficiency is 54.48% at the lowest concentration, while it is 17.72% at the highest concentration, indicating the effectiveness of the synthesized micromotors in achieving good photocatalytic degradation at low concentrations. As a result of the photocatalytic degradation reaction, cyclic voltammetry was performed for 100 cycles to demonstrate the stability of the micromotors.This study is based on the electrochemical method for the photocatalytic degradation of methyl red (MR), an azo dye, using micromotors with a dual-motion principle. Following the development on an azo dye, this study applied the same procedure on real samples, and through in vitro investigation, the photocatalytic degradation of the composite motor on real samples was observed electrochemically.

Inverse and conventional dual magnetocaloric effects in Ni substituted Y-type Sr2Zn2-xNixFe12O22 hexaferrites

The effects of Ni substitution on magnetic and magnetocaloric effect (MCE) are investigated in polycrystalline Y-type hexaferrites of Sr2Zn2-xNixFe12O22 (x = 0.0, 0.8, and 2.0). With the increasing of temperature, the M-T curves indicate successive magnetic structure transitions exist in Sr2Zn2-xNixFe12O22 (x = 0.0, 0.8, and 2.0), which play significant roles in MCE behaviors. As the Ni2+ doping ratio increases, the shape of −ΔSM−T curves near room temperature evolves gradually from a table-like to a peak-like form. Particularly, a significant contrast between CMCE and IMCE is observed below 100 K, whose behavior can be inherently exploited for heat sink in magnetic refrigeration applications. Among the samples in this series, Sr2Zn1.2Ni0.8Fe12O22 plays the best CMCE and IMCE performances, with the maximum magnetic entropy change (−ΔSMmax) values of 0.78 J/kg K at 354 K and −0.56 J/kg K at 16 K for ΔH=50kOe , respectively. Our work demonstrates that Sr2Zn2-xNixFe12O22 hexaferrites have great potential to be tailored for magnetic refrigeration with special needs such as different operating temperature zones, Ericsson cycle or heat sink at refrigeration.

Unsteady Two-Dimensional Drift of a Viscoelastic Fluid with Magnetic and Thermal Effects: A Perturbation Approach

This study explores the unsteady, two-dimensional flow of an electrically conductive, viscoelastic, and incompressible fluid past a uniformly moving, infinite, non-conducting vertical plate, in the presence of a uniform first-order chemical process involving mass and heat transfer. A uniform magnetic field is applied perpendicular to the flow, with the magnetic Reynolds number assumed small to neglect the induced magnetic field. The governing equations are solved using a regular perturbation method, yielding approximate solutions for concentration, velocity, temperature, and shear stress at the plate. Additionally, mass and heat transfer rates are determined, with the influence of viscoelasticity and other physical parameters emphasized. Where applicable, results are graphically represented.

An innovative approach to 2D localization using the magnetic shielding effect

The effect on an electromagnetic field when a low-cost magnetically permeable object such as copper or aluminum is placed within it can be observed to determine the object’s location. This approach offers a novel technique to achieve reliable localization, particularly in environments where line of sight sensing methods may be non-applicable. Shields up to a size of 30×30 mm and a thickness of 80 µm were investigated; copper shields of these dimensions reduced the signal strength to 91 %, and aluminum shields reduced the signal strength to 94 % of its initial strength. The distortions to the electromagnetic field were closely related to the location of the tag. By fitting an inverted Gaussian curve to each sensor’s data, the position of a shield along a line could be predicted. This method can be used to locate a tag within a 2D plane by creating a 2D array of sensors beneath the sensing plane.

Study of MHD on porous flat and curved circular plate lubricated with couple stress fluid-a slip velocity model

The current study achieved to explore novel of curved circular and porous flat plate under the existence of MHD and slip velocity. The gap between the plates is filled with conducting non-Newtonian lubricant as a couple stress fluids. We considered the phenomena of Darcy law is account for porous medium and Stokes theory is used to incorporate to couple stress effects. The effect of MHD slip velocity and couple stress lubricant is studied. By taking into account the couple stresses due to the microstructure additives and the magnetic effects due to the magnetization of the magnetic fluid modified Reynolds equation is obtained. The Reynolds equation is solved we obtain the derivation of non-dimensional pressure distribution, load carrying capacity and squeeze film time. Employing the Simpsons 1/3rd rule for numerical analysis in Mathematica tool and Origin Software to illustrate the behavior of pressure profile, load carrying capacity and squeeze film time in effect of Harmann number, couple stress parameter, slip velocity and permeability parameter. The results indicate that the influence of couple stresses and magnetic effects on the bearing characteristics are significantly apparent. It is concluded that fluids with couple stresses are better than Newtonian fluids. The improvement of the bearing characteristics is enhanced if the magnetic effects and slip velocity are present. But reverse effect due to upsurge of permeability parameter.

Main features of the geomagnetic effect of the October 14, 2023 annular solar eclipse in the Americas

The purpose of this paper is to investigate temporal variations in the northward, X, eastward, Y, and downward, Z, components of the geomagnetic field recorded during the October 14, 2023 annular solar eclipse, which main features include its annularity, the eclipse occurrence from local dawn to local dusk, its magnitude variation from 0.30 to 0.86, and the longest ever-observed path across the mainland of the Americas, covering latitudes from ∼65°N to 12°S. The analysis was made possible due to the data on temporal variations in the northward, X, eastward, Y, and downward, Z, components of the geomagnetic field collected at thirteen International Real-time Magnetic Observatory Network magnetometer stations (https://imag-data.bgs.ac.uk/GIN_V1/GINForms2). The solar eclipse acted to cause non-sinusoidal and quasi-sinusoidal perturbations having temporal durations of 180–240 min in all geomagnetic field components on a global scale (∼8000 km). The X-component experienced the largest perturbations attaining 10–20 nT, and the Z-component underwent the smallest disturbances. The quasi-sinusoidal perturbation amplitude did not exceed 5–6 nT, and the period most often showed variations within 15–40 min. The magnetic effect exhibited a tendency to increase with solar eclipse magnitude, while the magnitude of the effect has been shown to be significantly dependent on geographic coordinates, local time, ionospheric state, and the patterns of ionospheric currents as well. During the solar eclipse, the electron density depletion was estimated to be ∼0.10 to ∼0.40–0.60 when the eclipse obscuration Amax varied from 19% to 82%. The movement of the lunar shadow was accompanied by the generation of atmospheric gravity waves with period of ∼10–80 min and by electron density perturbations with amplitudes of the order of 0.01–0.03. The estimates made on the assumption that the magnetic effect is due to the ionospheric current disruptions show good agreement with the observations.

On the absence of the chiral magnetic effect in equilibrium QCD

In this paper we investigate the chiral magnetic effect (CME): the generation of an electric current due to a homogeneous background magnetic field and a homogeneous chiral imbalance in QCD. We demonstrate that the leading coefficient describing the CME vanishes in equilibrium, both for free fermions as well as in full QCD. Our full QCD results are based on continuum extrapolated lattice simulations using dynamical staggered quarks with physical masses as well as quenched Wilson quarks. We show that it is crucial that a gauge invariant ultraviolet regularization is used to compute the CME and elaborate on why some of the existing in-equilibrium calculations of this effect gave a nonzero result. We stress that our findings imply the absence of a time-independent CME current flowing in equilibrium QCD, but do not concern the CME as an out-of-equilibrium, time-dependent effect.

Proximity coupling induced two dimensional magnetic order in EuO-based synthetic ferrimagnets

Proximity effects allow for the adjustment of magnetic properties in a physically elegant way. If two thin ferromagnetic (FM) films are brought into contact, electronic coupling alters their magnetic exchange interaction at their interface. For a low-TC\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$T_C$$\\end{document} rare-earth FM coupled to a 3d transition metal FM, even room temperature magnetism is within reach. In addition, magnetic proximity coupling is particularly promising for increasing the magnetic order of metastable materials such as europium monoxide (EuO) beyond their bulk TC\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$T_C$$\\end{document}, since neither the stoichiometry nor the insulating properties are modified. We investigate the magnetic proximity effect at Fe/EuO and Co/EuO interfaces using hard X-ray photoelectron spectroscopy. By exciting the FM layers with circularly polarized light, magnetic dichroism is observed in angular dependence on the photoemission geometry. In this way, the depth-dependence of the magnetic signal is determined element-specifically for the EuO and 3d FM parts of the bilayers. In connection with atomistic spin dynamics simulations, the thickness of the EuO layer is found to be crucial, indicating that the observed antiferromagnetic proximity coupling is a short-ranged and genuine interface phenomenon. This fact turns the bilayer into a strong synthetic ferrimagnet. The increase in magnetic order in EuO occurs in a finite spatial range and is therefore particularly strong in the 2D limit—a counterintuitive but very useful phenomenon for spin-based device applications.

Circumferential multi-point corrosion status assessment of steel cables considering self-magnetic flux leakage superposition effect

With the advantages of convenient operation and efficient detection, the self-magnetic flux leakage (SMFL) has become an important technology for non-destructive testing of ferromagnetic materials. However, the multi-point corrosion status of steel cable structures is still difficult to precisely assess. In this study, the SMFL theoretical model for the circumferential distribution of steel cable corrosion was established, and the measurement experiment of circumferential multi-point corrosion status was carried out. The results show that the area of circumferential distribution region S, the accumulated magnetic field intensity A and ellipticity e are all positively and quadratically correlated with the corrosion ratio α and defect angle θ of steel cables. Moreover, the magnetic field superposition effect shows an exponential decay trend with the defect interval angle Δφ. The maximum deviation rate of A was less than 10 % under different multi-point corrosion distributions, verifying the principle of magnetic field superposition. Finally, the assessment method based on the effect was proposed, which could accurately and systematically diagnose the circumferential multi-point corrosion status in steel cables.