Direction Of Magnetic Vector Research Articles

Spontaneous volume magnetostriction in antiferromagnets and its manifestation in an Fe–Rh alloy

A formula for spontaneous volume magnetostriction of a two-sublattice antiferromagnet is obtained and discussed in detail in terms of an exchange striction model. The main feature of the formula is taking into account the dependence of volumetric strains on the directions of sublattice magnetization vectors. The calculation shows that this way it is possible to explain giant forced volume magnetostriction previously observed in the antiferromagnetic state of the Fe50Rh50 alloy. Besides, the temperature dependences of the specific volume and critical magnetic field of this alloy are calculated, and they are in a satisfactory agreement with the experiment.

The Hunt for Perpendicular Magnetic Field Measurements in Plasma

The one consistent technique for remotely estimating the magnetic field in plasma has been Faraday rotation. It is only sensitive to the portion of the vector parallel to the propagation path. We show how to remotely detect the portion of the vector that is perpendicular using a modified measurement. Isolating this electromagnetic propagation wave mode to measure the magnetic field enables us to (i) study more about the magnetic field vector in plasma, (ii) reduce error in total electron content measurements, and (iii) discover new magnetic field information from archived data sets. The Appleton–Hartree equation is used to verify a new approach to calculating the phase change to an electromagnetic wave propagating through a plasma at frequencies larger than the gyrofrequency, the cyclotron frequency, and the upper hybrid frequency. Focusing on the perpendicular propagation modes, the simplified equation for the integrated path effect from a perpendicular magnetic field is calculated. The direction of the perpendicular component is unknown, because the magnetic field is squared. Isolating the magnetic term in the equation with dual frequency waves is shown. We also show how to eliminate the magnetic field contribution to total electron content measurements with a similar approach. In combination with Faraday rotation, the degeneracy of the magnetic field vector direction is reduced to a cone configuration.

Magnetocaloric effect and phase transformation of LaFe11.0M0.5Si1.5 (M = Cu, Ni, Mg) alloys

La (Fe,Si)13 is a promising magnetic refrigerant material. In this paper, the effects of Cu, Ni and Mg substitution of Fe on the magnetocaloric effect and phase transition properties of LaFe11.5Si1.5 alloys were studied by first-principles calculations combined with experiments. Through scanning electron microscopy–energy-dispersive spectroscopy analysis, it was concluded that after Cu partially replaced Fe, the content of the 1:13 main phase significantly decreased to 61.49%, and the contents of the α-Fe and LaFeSi phases increased. Cu was not conducive to the formation of the main phase. After Mg partially replaced Fe, the content of the 1:13 main phase increased to 99.12%, and Mg promoted the formation of the main phase. The electronic structure of the alloy was reconstructed by density functional theory (DFT), and the effects of the doping atoms on the magnetic properties of the alloys were studied. The calculation results showed that Ni atoms had the same weak magnetism as that in the magnetic moment vector direction of Fe atoms, Cu and Mg atoms had magnetism opposite to that in the magnetic moment vector direction of Fe atoms, and all alloys showed a lower total magnetic moment. According to the Arrott curve and the field dependence method of the magnetocaloric effect (MCE), when Cu = 0.5 and Ni = 0.5, the alloy phase transition changed from a first-order phase transition to a second-order phase transition, and when Mg = 0.5, the alloy still had a first-order phase transition.

Electric current and magnetization distributions’ self-organization features in a magnetoresistive film nanoelement under the influence of an external magnetic field

The new generalized Laplace’s equation for an electric potential is presented, which in the general case, is nonlinear for media with resistance anisotropy caused by the anisotropic magnetoresistance (AMR) effect and determined by the orientation of the magnetization vector relative to the current density vector at an arbitrary point of the sample. The solution to this equation is obtained for an anisotropic medium with a non-uniform distribution of current density and magnetization in the case of an oblique-shaped plate of nanoscale thickness. In addition, the analytical solution was obtained for the current density distribution in such a medium using conformal mapping, which confirms the numerical solution in the case of an isotropic conductor. An analysis of the results showed that the presence of the AMR effect leads to a significant change in the current density distribution in the sample compared to the isotropic case, which is expressed in the deviation of the current density vector in perpendicular to the magnetization vector direction in the plate. It has been established that the presence of an external magnetic field in the film plane, which leads to the emergence of an inhomogeneous magnetization distribution, entails self-organization of the electric current distribution. The graphs of the plate resistance as a function of applied magnetic field demonstrate asymmetry for the cases of the direct and reverse directions of the external magnetic field, which cannot be obtained within the framework of simplified models of current flow in media with the AMR effect.

Particle Swarm Optimization for Magnetometer Calibration With Rotation Axis Fitting Using In-Orbit Data

This article demonstrates the performance of an improved particle swarm optimization (PSO) algorithm with scalar checking and rotation axis fitting objectives using in-orbit data, which is obtained from two CubeSats missions, Aalto-1 and ESTCube-1, as well as simulation as reference. The improved algorithm uses sequential objectives refinement process to combine the two optimization objectives. This improvement addresses some challenges of magnetometer calibration when using in-orbit data. First, the change in the magnetic field vector direction at different points in orbit which is uncorrelated to the rotation of the spacecraft itself. Second, the uncertainty of the rotation axis information used as the reference, e.g., from gyroscope noise. Third, the available data set is heavily affected by the rotation mode of the spacecraft, which imposes some limitation in the rotation axis information needed by the algorithm. The improved PSO algorithm is applied on simulated data in order to analyze the calibration performance under different spacecraft tumbling rates and noise levels. In ideal condition (varying rotation axis during measurements and sufficient sampling rate relative to the spin rate), the rotation axis fitting objective can reach ∼0.1° of correction accuracy.

Спектральные характеристики прецессии положения равновесия намагниченности в нормально намагниченной ферритовой пластине.

Спектральные характеристики прецессии положения равновесия намагниченности в нормально намагниченной ферритовой пластине.

Photoelectric Effect on a Hydrogen Atom in an Extremely Strong Magnetic Field

The photoelectric effect on a hydrogen atom located in an extremely strong magnetic field is considered. The dependence of the cross section on the angle between the photon momentum and the magnetic field strength vector (direction of free motion of the emitted electron) is investigated. It is shown that in the presence of a magnetic field the character of the dependence of the cross section on this angle is substantially altered. The dependence of the cross section on the photon energy is examined and it is shown that near the reaction threshold it is necessary to take into account the interaction of the electron with the nucleus of the hydrogen atom.

A Stable Adaptive Observer for Hard-Iron and Soft-Iron Bias Calibration and Compensation for Two-Axis Magnetometers: Theory and Experimental Evaluation

This letter addresses the problem of on-line estimation and compensation of the hard-iron and soft-iron biases of a 2-axis magnetometer under dynamic motion, utilizing only biased measurements from a 2-axis magnetometer. The proposed adaptive observer formulates the relation between the true magnetic field vector and the magnetometer measurements as an algebraic system where the unknown biases enter linearly. The observer is shown to be globally stable. When the magnetometer measurements are persistently exciting (PE), the system is shown to be globally asymptotically stable, and the biases are shown to converge to their true values. The estimated biases are used to provide a calibrated magnetic field direction vector which is utilized to estimate magnetic geodetic heading. The adaptive observer is evaluated in a numerical simulation and a full-scale vehicle trial. For the proposed observer: $(i)$ knowledge of the instrument attitude is not required for sensor bias estimation, $(ii)$ zero a priori knowledge of the local magnetic field vector magnitude or vector direction is needed, $(iii)$ the system is shown to be globally stable, $(iv)$ the error system is shown to be globally asymptotically stable when the measured magnetometer signal is PE. $(v)$ magnetometer hard-iron and soft-iron bias compensation is shown to dramatically improve dynamic heading estimation accuracy.

Highly Alfvénic slow solar wind at 0.3 au during a solar minimum: Helios insights for Parker Solar Probe and Solar Orbiter

Alfvénic fluctuations in solar wind are an intrinsic property of fast streams, while slow intervals typically have a very low degree of Alfvénicity, with much more variable parameters. However, sometimes a slow wind can be highly Alfvénic. Here we compare three different regimes of solar wind, in terms of Alfvénic content and spectral properties, during a minimum phase of the solar activity and at 0.3 au. We show that fast and Alfvénic slow intervals share some common characteristics. This would suggest a similar solar origin, with the latter coming from over-expanded magnetic field lines, in agreement with observations at 1 au and at the maximum of the solar cycle. Due to the Alfvénic nature of the fluctuations in both fast and Alfvénic slow winds, we observe a well-defined correlation between the flow speed and the angle between magnetic field vector and radial direction. The high level of Alfvénicity is also responsible of intermittent enhancements (i.e. spikes), in plasma speed. Moreover, only for the Alfvénic intervals do we observe a break between the inertial range and large scales, on about the timescale typical of the Alfvénic fluctuations and where the magnetic fluctuations saturate, limited by the magnitude of the local magnetic field. In agreement with this, we recover a characteristic low-frequency 1/f scaling, as expected for fluctuations that are scale-independent. This work is directly relevant for the next solar missions, Parker Solar Probe and Solar Orbiter. One of the goals of these two missions is to study the origin and evolution of slow solar wind. In particular, Parker Solar Probe will give information about the Alfvénic slow wind in the unexplored region much closer to the Sun and Solar Orbiter will allow us to connect the observed physics to the source of the plasma.

Micromagnetic simulation of magnetic domain structures evolution of FeGa alloys by phase-field method

The stabilization of magnetic domains and their temporal evolution in FeGa alloys are predicted by combining micromagnetic model with phase-field method in this paper. The total free energy includes magnetocrystalline anisotropy energy, exchange energy, magnetostatic energy, external field energy and elastic energy. Under the diverse magnetic fields, domain structures are various because of the different total free energy and magnetization processes. The results show that when magnetic field direction along [1 0 0], with different magnetic strength, the directions of magnetization vectors all parallel to the magnetic field direction and the magnetized area forms a single domain structure eventually. When the magnetic field along [1 1 1] direction, the magnetic domains form striped domains. The direction and strength of magnetic field can effectively control the structures of magnetic domains. The total free energy increases with the increase of magnetic field strength and evolutionary steps. The system is stable with the stabilization of total free energy.

Artificial intelligence techniques to the interpretation of geophysical measurements

SummaryIntegration of geology and geophysics thinking requires a common earth model, that accommodates, with errors, all the features from the geophysics interpretation products, topological rules from geology, field mapping and drill logs, and the link between the two via physical rock property estimates. Automation of intelligent search, inference engines to this problem involves 200+ individual processes, to yield a family of plausible models. The true limiting factor is managing technical complexity and communicating to the geoscience team, not compute power.All models are wrong and are destined to be replaced as further data or insights are gleaned. So, taking too much time trying to create the ultimate “correct” interpretation is wasteful, hence the need for automation.An example of a simple pattern recognition technique to locate kimberlite pipes that have a magnetic and/or gravity response is given. This uses a range of pipe diameters, depths, topography, density and susceptibility, and variable directions of remanent magnetization vectors, in an automated manner.

Stability analysis in three-terminal magnetic tunnel junction

Spin-transfer torque-based magnetic random access memory is becoming more and more attractive in industry due to its non-volatility, fast switching speed and infinite endurance. However, it suffers energy and speed bottlenecks, so the magnetic tunnel junction urgently needs a new write scheme. Compared with the spin-transfer torque, emerging spin-orbit torque will replace spin-transfer torque as a new write scheme of magnetic storage technology for its faster writing speed and avoiding the barrier breakdown. A three-terminal magnetic tunnel junction consists of magnetic tunnel junction/heavy metal structure offers a promising perspective from a technological point of view in the design of new generation of magnetic random access memory, for it is possible to control the magnetization dynamics through two current densities of spin-transfer torque and the spin-orbit torque. In this paper, the stability of magnetic states in the three-terminal magnetic tunnel junction is studied theoretically. Through linearizing the Landau-Lifshitz-Gilbert equation including the spin-transfer torque and the spin-orbit torque defined in the spherical coordinates, the new equilibrium directions and linear differential equations are obtained. Performing linear stability analysis of the new equilibrium directions, the phase diagrams defined by the direction of pinned-layer magnetization vector and the current density of spin-orbit torque are obtained. Several magnetic states are distinguished in the phase diagram, such as in-plane precessional and stable states, out-of-plane precessional and stable states. When the pinned-layer magnetization vector rotates out of the film plane, through adjusting the direction of pinned-layer magnetization vector, the switching from stable state to precessional one can be realized. Orientating the pinned-layer magnetization vector in the film plane, neither the out-of-plane precession nor stable states emerges for the current density of spin-orbit torque and spin-transfer torque are relatively small. The instability current takes a minimum value with the pinned-layer magnetization vector nearly parallel or antiparallel to the easy axis of free layer and increases with the direction of pinned-layer magnetization vector deviating from these two locations. The magnetization reversal can be realized through adjusting the current density of spin-transfer torque, and the reversal time can decrease greatly under the assisting of spin-orbit torque. By showing the dependence of magnetization vector on the time of different magnetic states, the validity of phase diagram is confirmed. The selecting of the different directions of the pinned-layer magnetization vector provides an alternative way to control the current-driven magnetization dynamics. This will provide useful guide for the application of three-terminal magnetic tunnel junction.

Numerical Experiment for Dipole-Dipole Interaction in Electro-Magnetism with Help of a Regular Tetrahedron

Aim of this work is to try to explain, on a Rational basis, some equations of Electro-Magnetism, which are based on Experimental data. Any Electric Field can produce a Field of many small Electric Dipoles, continuously distributed in space. In a region, where the Electric Field is constant, in direction and magnitude, all the small Dipoles are parallel to the Electric Field, and are represented by a single, long, parallel to them, fixed in space, Electric Dipole, which is here called Compass. An Alternating current, in a straight Conductor, is studied, by a simple, short computer program, for step-by-step nonlinear dynamic analysis. It is found that, only an Alternating current, not a direct current, can produce an Electric Dipole, in a straight Conductor. The two above Dipoles (Compass-Conductor) are assumed with equal lengths l, lying on two skew lines, perpendicular to each other, at a distance l√2, thus forming, by their four ends, a Regular Tetrahedron, with side length l. Repulsion, between Like Charges, obeys the simple Coulomb Electro-Static law. Whereas Interaction (Attraction or Repulsion), between Unlike Charges, obeys a more accurate Lennard-Jones law. The analysis of Dipole-Dipole (Compass-Conductor) Interaction is performed by hand calculator. The only out-of-balance forces, in the regular Tetrahedron, acting on the Rigid Conductor, are the so-called magnetic forces. Their direction is found, in a simple Rational way, with help of Regular Tetrahedron, without recoursing to a “right-hand-rule”. The proposed model is applied to 1) The force acting on an Electric Charge moving in a magnetic field. 2) The force acting on a Current carrying straight Conductor, due to a magnetic field. 3) The magnetic fields created around a Current carrying straight Conductor. In these applications, proposed model gives reasonable results. Particularly, in third application, results, obtained by proposed model, are found in satisfactory approximation with corresponding ones, obtained by an empirical formula, based on relevant Experimental observations of H.-C. Oersted and A.-M. Ampere. So, the reliability of proposed model is checked. Position and direction of magnetic field vector coincide with those of a corresponding fixed Compass of a constant Electric Field. Main point of present work is that, without introducing the concept of a magnetic field vector, by combining field of dipoles, produced by an electric field, with dipole of an alternating current carrying conductor, the magnetic forces can be determined.

New method for edges detection of magnetic sources using logistic function

The tilt angle of the analytic signal amplitude (TA) is defined as the arctangent of the ratio of the first vertical derivative to the total horizontal derivative of the analytic signal amplitude. It is commonly used as a useful tool to estimate edges of magnetic sources because its value is slightly dependence on the direction of magnetization vector, and it is more effective in estimating the edges of the bodies than the analytic signal amplitude and the standard tilt angle. Based on logistic function (L) that has the same shape with the shape of arctangent function, and the derivatives of the analytic signal amplitude, we introduce some new filters which also can reduce the effect of the magnetization direction. Other notable features of these filters are that they produce amplitude maxima over the edges of sources and that they balance anomalies from shallow and deep sources. The feasibility of the proposed filters is demonstrated on noise-free and noisy synthetic magnetic data from two 3D models where the obtained results coincide well with the actual edges. The effectiveness of the filters is also evaluated by comparing it with other edge detection methods. The results also show that our filters are less sensitive to variations in the depth of the source bodies and that a modified logistic function (Lk) can achieve better edge detection results than the analytic signal amplitude (AS), the analytic signal amplitude of the tilt angle (AT), the TA and L filters. The filters are also applied to real magnetic data from an area in south-central Vietnam, and the results demonstrate that the proposed filters is a useful tool for the qualitative interpretation of magnetic data.

Long-Term Changes in Mechanical and Electrical Characteristics of CdTe Crystals after Their Exposure to a Weak Pulsed Magnetic Field

Long-term changes in mechanical and electrical properties of p-type CdTe single crystals have been revealed after their exposure to a weak pulsed magnetic field (B = 1 T, ν = 12 Hz, texp = 10 min). A nonmonotonic increase in the hardness of crystals (presence of two peaks) and a nonmonotonic decrease in their specific dark conductivity (three peaks) have been observed. The peaks of changes in mechanical and electrical properties correlate on the time scale. It is shown that the intensity of observed effects depends on the crystal orientation with respect to the direction of magnetic induction vector B. In particular, the observed changes in properties for B || 〈111〉 are twice as large as those for B || 〈110〉. Possible mechanisms of the observed effect are discussed.

Orbital loop currents in iron-based superconductors

We show that the antiferromagnetic state commonly observed in the phase diagrams of the iron-based superconductors necessarily triggers loop currents characterized by charge transfer between different Fe $ 3d $ orbitals. This effect is rooted on the glide-plane symmetry of these materials and on the existence of an atomic spin-orbit coupling that couples states at the $X$ and $Y$ points of the 1-Fe Brillouin zone. In the particular case in which the magnetic moments are aligned parallel to the magnetic ordering vector direction which is the moment configuration most commonly found in the iron-based superconductors these loop currents involve the $d_{xy}$ orbital and either the $d_{yz}$ orbital (if the moments point along the $y$ axis) or the $d_{xz}$ orbitals (if the moments point along the $x$ axis). We show that the two main manifestations of the orbital loop currents are the emergence of magnetic moments in the pnictide/chalcogen site and an orbital-selective band splitting in the magnetically ordered state, both of which could be detected experimentally. Our results highlight the unique intertwining between orbital and spin degrees of freedom in the iron-based superconductors, and reveal the emergence of an unusual correlated phase that may impact the normal state and superconducting properties of these materials.

Velocity moment-based quasilinear theory and particle-in-cell simulation of parallel electron firehose instability

The present paper investigates the physics of electron firehose instability propagating parallel to the direction of ambient magnetic field vector, by means of particle-in-cell simulation and macroscopic quasilinear kinetic theory. The electron firehose instability is excited when parallel electron temperature exceeds perpendicular temperature, T∥e>T⊥e, under high beta conditions. A recent paper [Sarfraz et al., Phys. Plasmas 24, 012907 (2017)] formulated the quasilinear theory of parallel electron firehose instability by assuming that the electron and proton velocity distribution functions can be approximately described by bi-Maxwellian forms for all times but allowing for dynamical changes in perpendicular and parallel temperatures as well as the wave intensity. The present paper examines the validity of such an approach by making direct comparison against particle-in-cell simulation. It is shown that the macroscopic quasilinear approach provides a qualitative description of the nonlinear phase of the instability, but some quantitative discrepancies are also found. Possible causes for the discrepancies are discussed.

GENERATING OF ELECTRICITY FROM MAGNETOELECTRIC COMPOSITE WITH USE OF CHANGES IN DIRECTION OF MAGNETIC FIELD VECTOR

Paper shows study on the magnetoelectric composite material placed in an external magnetic field with changing magnetic field vecotr. An experimental setup for investigation of magnetoelectric properties of magnetostrictive-piezoelectric material was prepared. The hybrid structure is made of magnetostrictive composite (based on Terfenol-D) and piezoelectric material. Experimental results shown the response of prepared hybrid material to the rate of changes of direction of magnetic field vector. Investigation were mainly focused on possibility of generating of electric power from prepared material. It was found that the prepared hybrid material exhibits magnetoelectric effect in the case of work when direction of magnetic field vector was changing. This effect might be use in Energy Harvesting applications.

Influence of Axial Magnetic Field on Cathode Plasma Jets in High-Current Vaccum Arc

The cathode plasma jets in vacuum arc and the effect of magnetic field on them have been studied for several years and these studies are helpful to understand the arc characteristics and improve the controlling effect of magnetic field on arc plasma. In this paper, the experiments of the cup-shaped axial magnetic field (AMF) contacts were conducted in which a Helmholtz coil was introduced to generate different external imposed AMFs. It was found that the appearance of arc plasma was changed by variation of the external imposed AMF. If the composite AMF in arc column increased gradually, the obvious individual cathode plasma jets were detected, the arc constriction decreased, and the arc stability increased. Meanwhile, the inclination of cathode plasma jets was observed and the inclination direction was found to be consistent with the magnetic field vector direction which is closely related to the composite AMF. By variation of the external imposed AMF and its direction, the inclination direction of cathode plasma jets also changed. The criterion to detect obvious cathode jets in arc column is obtained that at the contact peripheral where R> 80.5% R0 (R0 is the contact radius), the AMF strength is no less than 4.5 mT/kA. It was also found that if the composite AMF in interelectrode gap points to different directions at a certain moment, it may lead to the transfer of arc column from the center to the edge of the interelectrode region and the arc instability until when the composite AMF in the interelectrode gap points to the same direction. It can be concluded that the appearance of individual cathode plasma jets can be manipulated by the variation of AMF, which is helpful to study the interaction between arc plasma and electrodes, especially the anode, and improve the interruption performance at higher current.

Primary physical mechanism of different magnetic fields action on roots of some plants

Background: Though the magnetic field action on biological object is proved now by many experiments it cannot be explained. The counterarguments are the small value of magnetic induction, that is effective for static magnetic field and the small value of ions free path length for ion cyclotron resonance presence. Objectives of the article were to generalize all the results that had been obtained before in static, alternative and combined magnetic fields and to explain all results by one and the same primary physical mechanism. Materials and methods that were used to obtain experimental results were based on the using of well reproducible magnetic conditions. For this purpose 3 lays µ-metal shield and superconductive shield with warm volume were used. The artificial magnetic field was created in the shield. The objects of the investigation were roots of cress, maize and pea. Their gravitropic reaction was studied. Results and discussion: All experimental results were compared with the theories and calculations maid before and following from the three mechanisms proposed below. It was shown that there were three physical primary mechanisms that could lead to effect of low frequency alternative and combined magnetic fields and permanent magnetic field on gravitropic reaction in plants. All of them depended on the relative location of roots, gravity and components of permanent and alternative magnetic fields between themselves. The first mechanism is based on the classic model of the rotation of ions in the plane that is perpendicular to the magnetic field direction or precession of magnetic moments round the direction of magnetic field vector. The second mechanism is connected with the piezoelectric properties of starch grain (porous piezoelectricity). This property of starch may create the change in the moving of starch grains in alternative and combined magnetic fields, and even in static one. The third mechanism is caused by the phase transition in water created by weak combined or alternative magnetic fields. Conclusions: The comparison of effects of these three mechanisms between themselves allowed choosing the most possible one. It was shown that the first mechanism was preferred. Only the first mechanism can explain the dependence of observed effects on magnetic field direction.