Magnetic Vector Research Articles

Jeans Gravitational Instability of a Rotating Collisionless Magnetized Plasma with Anisotropic Pressure

The problem of self-gravitational instability of an astrophysical rotating plasma in a strong magnetic field with an anisotropic pressure tensor is studied on the basis of the Chew–Goldberger–Low (CGL) quasi-hydrodynamic equations modified by generalized polytropic laws. Using the general form of a dispersion relation obtained by the normal-mode perturbation method, a discussion is provided of the propagation of small-amplitude perturbation waves in an infinite homogeneous plasma medium for transverse, longitudinal, and oblique directions with respect to the magnetic field vector. It is shown that different polytropic indices and anisotropic pressures not only change the classical Jeans instability condition but also cause the appearance of new unstable regions. Modified Jeans instability criteria are obtained for isotropic MHD equations and anisotropic CGL equations owing to the influence of the polytropic indices on gravitational and firehose instabilities for astrophysical plasma. It is shown that in the case of a longitudinal mode of perturbation wave propagation, the Jeans instability criterion does not depend on uniform rotation. In the case of the transverse propagation regime, the presence of rotation reduces the critical wave number and exerts a stabilizing effect on the growth rate of the unstable regime.

On Constructing Analytical Models of the Magnetic Field of Mercury from Satellite Data

Abstract—A new method is proposed for analytical description of the magnetic field of the Mercury from the data of satellite missions based on the local and regional versions of the linear integral representation method. The inverse problem on finding the sources of the field is reduced to solving ill-conditioned systems of linear algebraic equations with an approximately set right-hand part. The charts of the isolines of the z-component of the magnetic inductance vector in the Cartesian coordinate system rigidly connected with the planet, as well as the regional S-approximation of the field radial component are plotted. The results of the mathematical experiment on analytic continuation of the magnetic field towards the sources are presented.

Spin Orbit Torque Locally Controlling Exchange Bias to Realize High Detection Sensitivity of Two-dimensional Magnetic Field

Spin orbit torque (SOT) of spin current has provided an efficient manipulation of ferromagnet order, antiferromagnet order, and exchange bias field for various spintronic applications. Here, in contrast to the external magnetic field which is very hard to apply locally, we propose to utilize the local control characteristic of SOT on the macro-nano-meter scale to set four different directions of exchange bias field at the IrMn/CoFe interface on one chip simultaneously. Moreover, with this fully electrical control technology to replace the existing various complex processes based on magnetic field annealing, we fabricate monolithic dual-axis full Wheatstone-bridge magnetoresistance sensors to detect two-dimensional magnetic field vector, which exhibit very high detection sensitivity of 9.45 nT·Hz−1/2 and 12.3 nT·Hz−1/2 at 10 Hz for X-axis and Y-axis sensing, respectively. This work provides a paradigm to simultaneously implement function configurations of spintronic devices by using the local control characteristic of SOT.

A machine learning approach combined with wavelet analysis for automatic detection of Pc5 geomagnetic pulsations observed at geostationary orbits

Pc5 geomagnetic pulsations are ultra-low frequency (ULF) waves whose period lies within 150–600 s. Their detection is crucial for accurate space weather modelling, monitoring, and analysis. Identification of these pulsations using manual approaches is difficult and time-consuming because of the smaller magnitudes and the limited durations within which they occur. To overcome this challenge, we propose a robust Cascade Forward Neural Network (CFNN) model combined with the wavelet technique for automatically detecting Pc5 events from satellite datasets observed at geostationary orbits. The dataset used in this study is the magnetic field vector measurements retrieved from the Geostationary Operational Environmental Satellite-10 (GOES-10) from 2000 to 2009. Pc5 geomagnetic pulsations were extracted from the toroidal component of the field perturbation using a bandpass Butterworth filter. Continuous wavelet transform (CWT) analysis using the mother Morlet wavelet was utilized to validate the integrity of the extracted signal in the time–frequency domain. The extracted Pc5 signal was decomposed into details and approximations using Daubechies wavelet transform to separate the intelligible signal from the incoherent noise that left their trace on the magnetic field time series. The detail signal was subjected to denoising using the heuristic Stein Unbiased Risk Estimate (SURE) approach with soft thresholding to obtain the denoised Pc5 events. The denoised Pc5 events were utilized as the target in the machine learning whereas the inputs were obtained from 5-dimensional space transformation of the toroidal component of the time series. The developed algorithm performed well and demonstrated a detection accuracy of 80 % and a Root Mean Square Error (RMSE) of 0.13 nT indicating a high performance in detecting Pc5 events. For effective validation of the model, Pc5 events detected by our model were correlated with the Kp index and the amplitude of the Pc5 events observed at geostationary orbit. A good correlation was obtained in both cases, making our model a practical and preferred choice for Pc5 pulsation detection in contrast to conventional frequency analysis tools which take much time for signal processing on large data sets.

Assessment of magnetic field on body axis and orbit axis of RazakSAT in Near Equatorial Orbit using IGRF model

Magnetometer is reference sensor of satellite that function to measure the vector of magnetic field during satellite enter the orbit. The magnetic field measurement vector will be employed in the Attitude Determination System (ADS) to calculate the satellite’s orientation with respect to the Earth. However, any misalignments or disturbances on the ADS can affect the orientation of the satellite in terms of the orbital position. Therefore, in this paper assessment of magnetic field on body axis and orbit axis of RazakSAT by using The International Geomagnetic Reference Field (IGRF) model. RazakSAT as references to verify the IGRF model by using residual analysis that percentage error less than 5% requirement from Astronautic Technology Sdn Bhd (ATSB). The result show, Y-axis and Z-axis from orbit frame meet the requirement of ATSB is less than 5%.

Analytical Inverse Preisach Model and Its Comparison With Inverse Jiles–Atherton Model in Terms of Accuracy and Computational Speed

Inverse hysteresis model with magnetic flux density and magnetic field intensity as input and output respectively is more preferred, compared with the forward one, for resolving the electromagnetic issues of electrical equipment in terms of magnetic vector potential or with voltage sources. And an inverse hysteresis model with high accuracy and high computation speed both has broader range of applications. However, the well known classical Preisach hysteresis model is formulated with the forward form, and has the double integration of its distribution function, making it inconvenient and unpractical in the electrical engineering. In this paper, an analytical inverse Preisach model is proposed for the first time. Firstly, the analytical expressions of permeability of initial magnetization curve, descending and ascending branches of the hysteresis loop are derived using one closed form of Everett integral function. Subsequently the analytical inverse Preisach model is derived by the difference method, considering the reversible magnetization component that classical Preisach model cannot simulate with an odd function analytically. The experiment of one grain oriented silicon steel sample and one non-oriented silicon steel sample, under different magnetic excitation levels is conducted, and the accuracy and efficiency of the proposed analytical inverse Preisach model are confirmed by comparing its simulated hysteresis loops with the experimental ones and that computed with the widely used inverse Jiles-Atherton hysteresis model.

Physics-Informed Neural Networks for Solving 2-D Magnetostatic Fields

Physics-informed neural network (PINN) has shown great potential in the inverse and parametric designing problems in electrical engineering. Moreover, most existing works on PINN are dedicated to computational fluids, and very few attentions have been paid to static and low-frequency electromagnetic near fields with multiple media in electrical engineering applications. In this work, a PINN for solving two-dimensional (2D) magnetostatic fields in electromagnetic devices and systems is proposed. The magnetic field intensity and the magnetic vector potential are solved by training a neural network which encodes partial differential equations and boundary conditions as residuals. The computation of the spatial derivatives of media constitutive parameters, which negatively impacts the training of PINN, is eliminated. A mesh-assisted non-uniform sampling method for the selection of collocation points is proposed to further improve the performance of PINN. The proposed PINN is verified by comparing its results with those of the finite element method in two 2D magnetostatic case studies. It is expected that this work will promote further applications of PINN in the modelling, numerical analysis, and parametric design of electromagnetic devices and systems.

Magnetic structures and properties of new 1:1 MoB-type RCo0.6Ni0.4 and RCo0.5Ni0.5 (R = Tb, Dy, Ho): Structural transition induced by magnetic ordering

The magnetic properties, the crystal and the magnetic structures of the new 1: 1 RCo1−xNix phase formed by R = Tb, Dy and Ho, have been studied for x = 0.4 and 0.5 by means of physical property measurements, neutron and X-ray (from both laboratory and synchrotron) diffraction methods. These compounds crystallize in the tetragonal MoB structure type (tI16, I41/amd) at room temperature, with no ordered arrangement of Co/Ni atoms on the 8e Wyckoff site available for the transition element. Both the lattice parameters a and c (and unit cell volume, Vobs) decrease from Tb to Ho, with a and c following a linear and a quadratic trend, respectively. A magnetic phase transition is detected by heat capacity and magnetization data for TbCo0.6Ni0.4 at about 85 K. Similar transitions appear in DyCo0.6Ni0.4 and HoCo0.6Ni0.4 at 49 K and 27 K, respectively. These TC well follow the de Gennes factor along the lanthanide series. Neutron diffraction shows for the Tb- and Ho-compounds that strongly ferromagnetic structures characterized by a k = 0 magnetic propagation vector are formed on two different rare earth sublattices which are canted to each other. Only in the Tb-containing phases the magnetic transition leads to a symmetry reduction from tetragonal I41/amd to at least monoclinic I2/a. Magnetic symmetry analysis is used to argue that the presence of a magnetic moment component along the original tetragonal axis should be at the origin of this magneto-structural transition in the Tb-compounds with a possible further symmetry lowering.

A solution using only electromagnetic coils for relative pose control in satellite docking

This paper proposes an electromagnetic coil topology and its control strategy, which can be incorporated into the electromagnetic docking device to achieve relative pose control in satellite docking. The target satellite has a main coil; the chaser satellite possesses a main coil of the same size accompanied by six and four evenly arranged secondary coils inside and outside the main coil, respectively. The coil on the target satellite is DC energized, while the currents in the coils of the chaser satellite are regulated. To remove the coupling between the pitch/yaw torque and translational force, the internal and external secondary coils of the chaser satellite interact with the main coil of the target satellite to perform the control of relative pitch/yaw and relative translation, respectively, so relative pose control can be achieved. The torque and force vectors exerted by the secondary coils of the chaser satellite are synthesized onto the pitch and yaw axes of the body frame. According to their spatial composition relationship, the formulas are proposed, which obtain the magnetic moment vectors of the coils from the set torques and forces. The controllers regulating pitch/yaw, translation, and distance utilize a three-loop cascaded structure that consists of an outer position loop, a middle velocity loop and an inner current loop. The control strategy is verified by dynamics simulation.

Brushless Motor FOC Control Method for Robot Arm

With the development of modern industry, more stringent requirements are put forward for the servo control of the mechanical arm, especially the problems of insufficient precision, insufficient dynamic response and poor anti-interference ability. This paper takes the permanent magnet synchronous motor of permanent magnet synchronous motor (PMSM) as the research object, combines the RBF neural network with PID control to improve the traditional magnetic field vector control, improve the lag and dynamic response of traditional PI control, improve the stability of the control system; and introduces the online supervision mechanism to make the control system has good environmental adaptability and adaptive adjustment ability. The experimental results show that the magnetic field vector control algorithm based on RBF-PID has faster response time, higher accuracy and stronger anti-interference ability.

Evolution of MHD torus and mass outflow around spinning AGNs

ABSTRACT We perform axisymmetric, 2D magnetohydrodynamic simulations to investigate accretion flows around spinning active galactic nuclei. To mimic the space–time geometry of spinning black holes, we consider effective Kerr potential, and the mass of the black holes is 108 M⊙. We initialize the accretion disc with a magnetized torus by adopting the toroidal component of the magnetic vector potential. The initial magnetic field strength is set by using the plasma beta parameter (β0). We observe self-consistent turbulence generated by magneto rotational instability (MRI) in the disc. The MRI turbulence transports angular momentum in the disc, resulting in an angular momentum distribution that approaches a Keplerian distribution. We investigate the effect of the magnetic field on the dynamics of the torus and associated mass outflow from the disc around a maximally spinning black hole (ak = 0.99). For the purpose of our analysis, we investigate the magnetic state of our simulation model. The model β0 = 10 indicates the behaviour similar to the ‘magnetically arrested disc’ state, and all the other low magnetic model remains in the SANE state. We observe that mass outflow rates are significantly enhanced with the increased magnetic field in the disc. We find a positive correlation between the magnetic field and mass outflow rates. We also investigate the effect of black hole spin on the magnetized torus evolution. However, we have not found any significant effect of black hole spin on mass outflows in our model. Finally, we discuss the possible astrophysical applications of our simulation results.

High Efficiency and Flexible Modulation of Spintronic Terahertz Emitters in Synthetic Antiferromagnets.

Spintronic terahertz (THz) emitters based on synthetic antiferromagnets (SAFs) of FM1/Ru/FM2 (FM: ferromagnet) have shown great potential for achieving coherent superposition and significant THz power enhancement due to antiparallel magnetization alignment. However, key issues regarding the effects of interlayer exchange coupling and net magnetization on THz emissions remain unclear, which will inevitably hinder the performance improvement and practical application of THz devices. In this work, we have investigated the femtosecond laser-induced THz emission in Pt (3)/CoFe (3)/Ru (tRu = 0-3.5)/CoFe (tCoFe = 1.5-10)/Pt (3) (in units of nm) films with compensated and uncompensated magnetic moments. Antiferromagnetic (AF) coupling occurs in the Ru thickness ranges of 0.2-1.1 and 1.9-2.3 nm, with the first peak (tRu = 0.4 nm) of the AF coupling field (Hex) significantly higher than that of the second peak (2.0 nm). Rather high THz amplitude is found for the samples with strong AF coupling. Nevertheless, despite the same remanence ratio of zero, the THz amplitude for the symmetric SAF films declines significantly as the tRu decreases from 0.8 to 0.4 nm, which is mainly ascribed to the noncolinear magnetization vectors due to the increased biquadratic coupling term. Specifically, we demonstrate that an asymmetric SAF structure with a dominant FM layer is more favored than the completely compensated one, which could generate significantly enhanced THz electric field with well-controlled polarity and intensity. In addition, as the temperature decreases, the THz emission intensity increases for the SAF samples of tRu = 0.9 nm with negligible biquadratic coupling, which is contrary to the decreasing trend of the tRu = 0.4 nm sample and has been attributed to the greatly enhanced Hex.

Observation and formation mechanism of 360° domain wall rings in synthetic anti-ferromagnets with interlayer chiral interactions

The interlayer Dzyaloshinskii–Moriya interaction (IL-DMI) chirally couples spins in different ferromagnetic layers of multilayer heterostructures. So far, samples with IL-DMI have been investigated utilizing magnetometry and magnetotransport techniques, where the interaction manifests as a tunable chiral exchange bias field. Here, we investigate the nanoscale configuration of the magnetization vector in a synthetic anti-ferromagnet (SAF) with IL-DMI, after applying demagnetizing field sequences. We add different global magnetic field offsets to the demagnetizing sequence in order to investigate the states that form when the IL-DMI exchange bias field is fully or partially compensated. For magnetic imaging and vector reconstruction of the remanent magnetic states, we utilize x-ray magnetic circular dichroism photoemission electron microscopy, evidencing the formation of 360° domain wall rings of typically 0.5–3.0 μm in diameter. These spin textures are only observed when the exchange bias field due to the IL-DMI is not perfectly compensated by the magnetic field offset. From a combination of micromagnetic simulations, magnetic charge distribution, and topology arguments, we conclude that a non-zero remanent effective field with components both parallel and perpendicular to the anisotropy axis of the SAF is necessary to observe the rings. This work shows how the exchange bias field due to IL-DMI can lead to complex metastable spin states during reversal, important for the development of future spintronic devices.

Horizontal Magnetic Anomaly Accompanying the Co-Seismic Earthquake Light of the M7.3 Fukushima Earthquake of 16 March 2022: Phenomenon and Mechanism

A horizontal magnetic disturbance accompanying the co-seismic earthquake light (EQL) of the M7.3 Fukushima earthquake of 16 March 2022 was detected by a fluxgate magnetometer installed at the KAK station, which is 270 km south of the EQL and 210 km west of the epicenter. The instantaneous change of the declination component of the geomagnetic field reached about 1.7″, much exceeding the threshold of three-fold error (0.72″). Considering the direction information of the geomagnetic data, the horizontal magnetic disturbance vector was further analyzed, which manifested the normal of the horizontal magnetic disturbance vector passing through the position of the EQL. Combined with the experimental results of pressure-simulated rock current (PSRC), the mechanism of the EQL and the geomagnetic anomaly was proposed to interpret the spatiotemporal correlation between the EQL and the horizontal magnetic disturbance vector, which should be a manifest of the induced magnetic horizontal vector (IMHV), attributed to the upward seismic PSRC. Different from previous precursor studies on geomagnetic disturbance on the power spectrum, vertical component, or polarization, this paper focuses on the direction information of the horizontal magnetic disturbance vector, which could be further applied to locate potential seismogenic zones based on the IMHVs observed by multiple geomagnetic stations.

Serra Geral Group plumbing system and 3D geological framework in Morungava region, southern Paraná–Etendeka LIP (Brazil): Combining 3D geologic and magnetic models

A coupled 3D geophysical–geological model was constructed by integrating aeromagnetic data and a prior 3D geological model of the Morungava region (Araújo et al., 2023 [manuscript submitted for publication]), situated at the southeastern border of the Paraná–Etendeka large igneous province (LIP) in Brazil. Aeromagnetic data interpretation and modeling (qualitative and semi-quantitative interpretation, susceptibility inversion, forward modeling, and magnetic vector inversion (MVI)), along with magnetic susceptibility data, complemented understanding of the Serra Geral Group feeder system in the subsurface (spatial distribution, depth, and geometry) and illuminated the crustal framework at different depths. We recognized three major NE-elongated geophysical domains (NW, Central, and SE), which were interpreted as basement compartments: the Tijucas, Pelotas, and Jaguarão terranes. The final integrated 3D geophysical–geological model encompasses the stratigraphic framework and the Serra Geral Group plumbing system in the study area, that comprises: two dike systems, four subvolcanic complexes with associated nested sills, and two intrusive ring complexes. This is the first time that these aeromagnetic data have been combined with borehole and 3D geological models.

Artificial gauge fields in the t-z mapping for optical pulses: Spatiotemporal wave packet control and quantum Hall physics.

We extend the t-z mapping of time-dependent paraxial optics by engineering a synthetic magnetic vector potential, leading to a nontrivial band topology. We consider an inhomogeneous 1D array of coupled optical waveguides and show that the wave equation describing paraxial propagation of optical pulses can be recast as a Schrödinger equation, including a synthetic magnetic field whose strength can be controlled via the spatial gradient of the waveguide properties across the array. We use an experimentally motivated model of a laser-written array to demonstrate that this synthetic magnetic field can be engineered in realistic setups and can produce interesting physics such as cyclotron motion, a controllable Hall drift of the pulse in space or time, and propagation in chiral edge states. These results substantially extend the physics that can be explored within propagating geometries and pave the way for higher-dimensional topological physics and strongly correlated fluids of light.

Two-dimensional Axisymmetric Modeling of the Magnetic Field for High-voltage Gas Circuit Breakers

High fidelity numerical analyses of high-voltage gas circuit breakers have been conducted at Hitachi Energy Research with an in-house CFD-based arc simulation tool. The tool extends the capability of a commercial flow solver (ANSYS Fluent) to represent physical phenomena at play in a high voltage circuit breaker during a breaking operation, such as magnetostatics, polymeric and metal evaporation, and arc-network interaction. This work describes the implementation of the Biot-Savart law for computing the magnetic field generated by an electric arc under the magnetostatic approximation and in two--dimensional axisymmetric conditions. The implementation is compared to the reference one based on the magnetic vector potential formulation of the Amp`ere’s law in the Coulomb gauge. The limitations of the two formulations are discussed and their numerical accuracy compared.

Magnetic field patterns as a tool for stress estimation in steel samples

In this work, steel square samples were subjected to varying degrees of compression, resulting in a distribution of simultaneous compressive and tensile stresses within the samples. The tangential component of the surface magnetic flux density was mapped along both the direction of compression and perpendicular to it, using a magnetic sensor, for each level of compression. The results show that the maps of the relative difference of magnetic flux density for different levels of applied stress, with respect to the flux density at zero stress, exhibited a diagonal stripes pattern. This pattern was discovered thanks to the particular surface stress distribution in square samples. The formation of these patterns could be attributed to the re-orientation of magnetic domains due to stress and the magneto-elastic effect, which was confirmed by the change in orientation of the magnetic flux density vectors obtained from the measurement of two of their components. Additionally, the maps showed an increase in contrast between high and low values with an increase in applied stress. Finally, the maps of the module of the gradient of magnetic flux density displayed a distinct diagonal chessboard-like pattern, and the contrast between low and high values increased with an increase in applied stress.

Eigenvector Constraint-Based Method for Eliminating Dead Zone in Magnetic Target Localization

Magnetic target localization using the magnetic gradient tensor (MGT) plays a significant role in underwater localization. However, this method inherently has a localization dead zone, which presents challenges for real-world applications. This paper delves into the root cause of this dead zone, identifying the non-invertibility of the MGT when the magnetic moment vector is orthogonal to the position vector from the target to the observation point. To tackle this issue, a method based on the eigenvector constraints is proposed. By constructing an objective function with eigenvector constraints and leveraging the property that its gradient at the observation point is zero, we derive an equivalent expression for the inverse of MGT that always holds and further develop a dead-zone-free localization method. To validate the robustness and efficacy of the proposed localization method, a comparative analysis with other methods is conducted. Simulation results in a 10 m × 10 m area under Gaussian noise demonstrate the proposed method’s capability to eliminate the dead zone and achieve an average localization error of 0.032 m. Experimental results further demonstrate that the proposed method eliminates the localization dead zone and exhibits greater robustness than the dominant method in the normal region. In summation, this paper provides an effective method for eliminating localization dead zone, offering a more stable and reliable method for magnetic target localization in practice.

Dynamic physical-geological model of complex folding according to paleomagnetic data

The purpose of the study is to evaluate the possibility of using the mathematical apparatus of spatial rotations to solve the determination issues of the nature and age of natural remanent magnetization vectors under complex tectonic dislocations of rocks manifested in the areas of modern folded structures of platform framing. Dynamic physical-geological models are shown to be useful when forming complex tectonic-magmatic systems. Mathematical (computer) modeling in comparison with other methods of studying geological processes features higher accuracy, cost-effectiveness and unambiguity of data interpretation in achieving the set goal. On the basis of dynamic physical-geological model of complex folding, an algorithm is developed and the results of mathematical modeling of natural remanent magnetization vectors are given for solving direct and inverse problems on correct application of the fold test under complex rock deformations. The dynamic physical-geological model of complex folded structure formation shows that the characteristic natural remanent magnetization vectors identified in laboratory experiments on demagnetization can be used to determine their age relative to the folding stages, and, depending on this, fully or partially restore the number, sequence and direction of tectonic dislocations. This will enable us to solve the mineralogenic and geodynamic problems of folded region development more effectively on the basis of paleomagnetic data.