Inverse Magnetic Field Research Articles

Influence of Interlocking on Magnetic Properties of Electrical Steel Laminations

Interlocking is a suitable method to fix iron cores made of electrical steel sheets along the stack direction. However, this will increase iron loss of the core and, as a result, lower the efficiency and power density of electrical machines. In this paper, the influence of interlocking on the magnetic properties of ring cores is studied and evaluated by measurements. A linear increase of the inverse of magnetic field and iron loss with increasing number of interlocks shows that the influence of interlocking is local. This behavior coincides with the proposed model. Interlaminar eddy currents have no serious impact on the iron-loss properties. Averaged magnetic properties of the magnetically deteriorated regions are calculated according to the magnetic model. These data will be useful for accurate finite-element method calculations of iron losses in electrical machines.

Magnetoresistance oscillations in topological insulator microwires contacted with normal and superconducting leads

Recent efforts to detect and manipulate Majorana fermions in solid state devices have employed topological insulator (TI) nanowires proximity coupled to superconducting (SC) leads. This combination holds some promises for the fundamental physics and applications. We studied the transverse magnetoresistance (MR) of polycrystal Bi2Te2Se and single-crystal Bi0.83Sb0.17 TI microwires contacted with superconducting In2Bi leads. Bi2Te2Se has a simple band structure with a single Dirac cone on the surface and a large non-trivial bulk gap of 300meV. The semiconducting alloy Bi0.83Sb0.17 is a strong topological insulator due to the inversion symmetry of bulk crystalline Bi and Sb. To study the TI/SC interface, we prepared Bi2Te2Se and Bi0.83Sb0.17 glass-coated microwire samples using superconducting alloy In2Bi (Tc = 5.6K) to provide a contact of one side of the microwires with copper leads and gallium to provide a contact of the other side of microwires with copper leads. The MR oscillations equidistant in a transverse magnetic field (up to 1T) at the TI/SC interface were observed at various temperatures (4.2 K–1.5K) in both the Bi2Te2Se and Bi0.83Sb0.17 samples. In the Bi2Te3 sample with a diameter of d = 17µm, this oscillations exist with a period of ΔB = 18mT; in the Bi0.83Sb0.17 sample with d = 1.7µm MR oscillations are characterized by a period of ΔB = 46mT. The observed oscillations cannot be referred to the Shubnikov de Haas oscillations because they are not periodic in an inverse magnetic field and their amplitude decreases with increasing magnetic field. Most probably, transverse MR oscillations arise owing to the appearance of highly conducting edge states on the planar boundary of SC/TI.

Three-quarter Dirac points, Landau levels, and magnetization in α−(BEDT−TTF)2I3

The energies as a function of the magnetic field ($H$) and the pressure are studied theoretically in the tight-binding model for the two-dimensional organic conductor, $\alpha$-(BEDT-TTF)$_2$I$_3$, in which massless Dirac fermions are realized. The effects of the uniaxial pressure ($P$) are studied by using the pressure-dependent hopping parameters. The system is semi-metallic with the same area of an electron pocket and a hole pocket at $P < 3.0$~kbar, where the energies $(\varepsilon_{\rm D}^0$) at the Dirac points locate below the Fermi energy $(\varepsilon_{\rm F}^0$) when $H=0$. We find that at $P=2.3$~kbar the Dirac cones are critically tilted. In that case a new type of band crossing occurs at "three-quarter"-Dirac points, i.e., the dispersion is quadratic in one direction and linear in the other three directions. We obtain new magnetic-field-dependences of the Landau levels $(\varepsilon_n)$; $\varepsilon_n-\varepsilon^0_{\textrm{D}} \propto (n H)^{4/5}$ at $P=2.3$~kbar ("three-quarter"-Dirac points) and $|\varepsilon_n-\varepsilon_{\rm F}^0| \propto (n H)^2$ at $P=3.0$~kbar (the critical pressure for the semi-metallic state). We also study the magnetization as a function of the inverse magnetic field. We obtain two types of quantum oscillations. One is the usual de Haas van Alphen (dHvA) oscillation, and the other is the unusual dHvA-like oscillation which is seen even in the system without the Fermi surface.

Modelling and solving the position tracking problem of remote-controlled gastrointestinal drug-delivery capsules

Abstract A theoretical basis is presented to develop a real-time position tracking system for a remote-controlled drug-delivery capsule that would enable the targeted delivery of drugs to specific locations in the gastrointestinal tract. Tracking is accomplished by dual magnetic vector detection over time, using two separate sets of magnetic field sensing devices. One is used to detect the alternating magnetic field excited externally with certain frequencies, while the other is used to detect the geomagnetic field. A mathematical model of the magnetic flux density in space and time is constructed using the Biot–Savart law. Additionally, the earth’s magnetic field and quaternion rotation theory are also used in the model to compensate for the constantly changing spatial orientation of the capsule as it travels through the gastrointestinal tract. Based on the model, an improved artificial bee colony algorithm is used to solve the inverse magnetic field problem. Firstly, chaotic sequencing improves the initial solution diversity, and a ranked selection strategy is applied. At later stages, the Levenberg-Marquardt algorithm is introduced in order to accelerate convergence. To verify the theoretical basis presented above, a prototype of the tracking system is developed. Calculations verification results in a convergence rate of 100% with an average of 179 iterations. The prototype testing shows that the dual magnetic vector detection method simplifies the solution of the inverse magnetic field problem, shortens the tracking time for each round of data, and increases the solution accuracy.

Что ожидает человечество при инверсии магнитного поля Земли: угрозы мнимые и подлинные

Что ожидает человечество при инверсии магнитного поля Земли: угрозы мнимые и подлинные

Interplay of the Inverse Proximity Effect and Magnetic Field in Out-of-Equilibrium Single-Electron Devices

The magnetic field is shown to affect significantly non-equilibrium quasiparticle (QP) distributions under conditions of inverse proximity effect on the remarkable example of a single-electron hybrid turnstile. This effect suppresses the gap in the superconducting leads in the vicinity of turnstile junctions with a Coulomb blockaded island, thus, trapping hot QPs in this region. Applied magnetic field creates additional QP traps in the form of vortices or regions with reduced superconducting gap in the leads resulting in release of QPs away from junctions. We present clear experimental evidence of such interplay of the inverse proximity effect and a magnetic field revealing itself in the superconducting gap enhancement in a magnetic field as well as in significant improvement of the turnstile characteristics. The observed interplay of the inverse proximity effect and external magnetic field, and its theoretical explanation in the context of QP overheating are important for various superconducting and hybrid nanoelectronic devices, which find applications in quantum computation, photon detection and quantum metrology.

Numerical simulation of thermomagnetic convection of cold water near its density maximum in a square enclosure under a magnetic quadrupole field

Natural convection of cold water near its density maximum in a square enclosure is studied numerically under the influence of a magnetic quadrupole field without gravity. A generalized model which includes a non-Boussinesq parabolic density–temperature relationship is established. The governing equations in primitive variables are discretized using the finite-volume method and solved using the SIMPLE algorithm. The effects of magnetic force number, Rayleigh number and density inversion parameter on flow and heat transfer characteristics are analyzed. The results show that the primary flow pattern depends mainly on the density inversion parameter. Multi-cellular flow structures are observed for certain ranges of density inversion parameter independent of the value of Rayleigh number and magnetic force number. The heat transfer changes non-monotonically under combined actions of the quadrupole magnetic field and density inversion.

Robust ferromagnetism carried by antiferromagnetic domain walls

Ferroic materials, such as ferromagnetic or ferroelectric materials, have been utilized as recording media for memory devices. A recent trend for downsizing, however, requires an alternative, because ferroic orders tend to become unstable for miniaturization. The domain wall nanoelectronics is a new developing direction for next-generation devices, in which atomic domain walls, rather than conventional, large domains themselves, are the active elements. Here we show that atomically thin magnetic domain walls generated in the antiferromagnetic insulator Cd2Os2O7 carry unusual ferromagnetic moments perpendicular to the wall as well as electron conductivity: the ferromagnetic moments are easily polarized even by a tiny field of 1 mT at high temperature, while, once cooled down, they are surprisingly robust even in an inverse magnetic field of 7 T. Thus, the magnetic domain walls could serve as a new-type of microscopic, switchable and electrically readable magnetic medium which is potentially important for future applications in the domain wall nanoelectronics.

Using constrained inversion of gravity and magnetic field to produce a 3D litho‐prediction model

ABSTRACTGeologically constrained inversion of gravity and magnetic field data of the Victoria property (located in Sudbury, Canada) was undertaken in order to update the present three‐dimensional geological model. The initial and reference model was constructed based on geological information from over 950 drillholes to constrain the inversion. In addition, downhole density and magnetic susceptibility measured in six holes were statistically analysed to derive lower and upper bounds on the physical properties attributed to the lithological units in the reference model. Constrained inversion of the ground gravity and the airborne magnetic data collected at the Victoria property were performed using GRAV3D and MAG3D, respectively. A neural network was trained to predict lithological units from the physical properties measured in six holes. Then, the trained network was applied on the three‐dimensional distribution of physical properties derived from the inversion models to produce a three‐dimensional litho‐prediction model. Some of the features evident in the lithological model are remnants of the constraints, where the data did not demand a significant change in the model from the initial constraining model (e.g., the thin pair of diabase dykes). However, some important changes away from the initial model are evident; for example, a larger body was predicted for quartz diorite, which may be related to the prospective offset dykes; a new zone was predicted as sulfide, which may represent potential mineralisation; and a geophysical subcategory of metabasalt was identified with high magnetic susceptibility and high density. The litho‐prediction model agrees with the geological expectation for the three‐dimensional structure at Victoria and is consistent with the geophysical data, which results in a more holistic understanding of the subsurface lithology.

Inversion of magnetic fields inside pipelines: Modeling, validations, and applications

Spherical detector is a novel and promising approach for pipeline inspections with high signal-to-noise ratio and low risk of blockage. As the magnetic signals are recorded in a rotating frame by the rolling spherical detector, it is difficult to directly deploy the raw periodic signals for magnetic inspections, such as pipeline orientation calculations and the identifications of girth welds, turning points, and other pipe features. Against this backdrop, a magnetic inversion approach for transforming the measured magnetic signals from the rotating sensor frame into the stationary pipe frame is developed and demonstrated both analytically and experimentally. By comparing the transformed values with that measured by a sensor moving on a straight route, the inversion approach is proven to hold for an arbitrary fixed rotation axis, with the average and maximum errors mostly less than 1 and 2 µT, respectively. Field experiments demonstrate that the magnetic inversion can expose and enhance hidden or imperceptible magnetic anomalies and pipeline turning points and improve pipeline route calculation accuracy via secondary alignments. The results will promote the spherical detector to play a greater role in pipeline inspections.

Heisenberg's Uncertainty Principle, Intense Electric Field, Heavily Doped Optoelectronic Quantized Structures and the Electron Statistics.

In this paper we show that the direct application of Heisenberg’s uncertainty principle (HUP) leads to the expression of the electron statistics (ES) under extreme degeneracy and intense electric field in bulk, quantum wells, nano wires and in the presence of quantizing magnetic field in III–V, ternary and quaternary materials on the basis of a newly formulated electron dispersion laws without using the usual density-of-states (DOS) function approach for finding out the ES under different physical lattice matched to InP conditions. It appears taking HD InSb, InAs, Hg1−xCdxTe, In1−xGaxAsyP1−y as examples that the Fermi energy increases with increasing electron concentration and the surface electric field in all the cases. Besides the Fermi energy decreases with increasing alloy composition and film thickness in different manners which depend totally on the values of the energy band constants. The Fermi energy oscillates with inverse quantizing magnetic field due to SdH effect. We have also shown that under certain limiting conditions all our generalized results lead to the well known formulas as given in the literature.

Drifts, currents, and power scrape-off width in SOLPS-ITER modeling of DIII-D

The effects of drifts and associated flows and currents on the width of the parallel heat flux channel (λq) in the tokamak scrape-off layer (SOL) are analyzed using the SOLPS-ITER 2D fluid transport code. Motivation is supplied by Goldston’s heuristic drift (HD) model for λq, which yields the same approximately inverse poloidal magnetic field dependence seen in multi-machine regression. The analysis, focusing on a DIII-D H-mode discharge, reveals HD-like features, including comparable density and temperature fall-off lengths in the SOL, and up-down ion pressure asymmetry that allows net cross-separatrix ion magnetic drift flux to exceed net anomalous ion flux. In experimentally relevant high-recycling cases, scans of both toroidal and poloidal magnetic field (Btor and Bpol) are conducted, showing minimal λq dependence on either component of the field. Insensitivity to Btor is expected, and suggests that SOLPS-ITER is effectively capturing some aspects of HD physics. Absence of λq dependence on Bpol, however, is inconsistent with both the HD model and experimental results. The inconsistency is attributed to strong variation in the parallel Mach number, which violates one of the premises of the HD model.

Magnetic field inversions at 1 AU: Comparisons between mapping predictions and observations

AbstractLarge‐scale magnetic field configurations are important for the transport of solar wind strahl electrons, which are suprathermal and directed along the field outward from the Sun. Strahl electrons are routinely used to infer not only the field configurations between the Sun and Earth but also local field structures, i.e., field inversions, where the magnetic field is locally folded back or inverted. Using solar wind data from ACE observations and a 2‐D data‐driven solar wind model with nonzero azimuthal magnetic field at the solar wind source surface, magnetic field lines are mapped between the Sun and Earth and beyond, in the solar equatorial plane. Standard verification metrics are used to assess, for five solar rotations at different phases of solar cycle 23, the performance of the mapping predictions for observed inversions, which are inferred from solar wind suprathermal electrons and magnetic fields measured by ACE. The probability of detection is consistently ≈0.70 across the different phases. The success ratio, the Hanssen‐Kuipers skill score, and the Heidke skill score are ≈0.55–0.70 for the four rotations in the rising, solar maximum, and declining phases, but ≈0.35–0.60 for the rotation near solar minimum, during which almost half of the samples have undetermined field configurations. Our analyses confirm the persistence of inversions throughout solar cycle 23, suggest for most observed inversions a solar/coronal origin at the wind's source surface or below, and predict that inversions should be less common for larger heliocentric distance r ∼&gt; 3 AU than for smaller r.

High field magneto-transport in two-dimensional electron gas LaAlO3/SrTiO3

The transport properties of the complex oxide LaAlO3/SrTiO3 interface are investigated under a high magnetic field (55 T). Small oscillations of the magnetoresistance with altered periodicity are observed when plotted versus the inverse magnetic field. We attribute this effect to Rashba spin-orbit coupling which remains consistent with large negative magnetoresistance when the field is parallel to the sample plane. A large inconsistency between the carrier density extracted from Shubnikov-de Haas analysis and from the Hall effect is explained by the contribution to transport of at least two bands with different mobilities.

Quantum Hall conductance and de Haas–van Alphen oscillation in a tight-binding model with electron and hole pockets for(TMTSF)2NO3

Quantized Hall conductance and de Haas van Alphen (dHvA) oscillation are studied theoretically in the tight-binding model for (TMTSF)$_2$NO$_3$, in which there are small pockets of electron and hole due to the periodic potentials of anion ordering in the $a$-direction. The magnetic field is treated by hoppings as complex numbers due to the phase caused by the vector potential, i.e. Peierls substitution. In realistic values of parameters and the magnetic field, the energy as a function of a magnetic field (Hofstadter butterfly diagram) is obtained. It is shown that energy levels are broadened and the gaps are closed or almost closed periodically as a function of the inverse magnetic field, which are not seen in a semi-classical theory of the magnetic breakdown. Hall conductance is quantized with an integer obtained by Diophantine equation when the chemical potential lies in an energy gap. When electrons or holes are doped in this system, Hall conductance is quantized in some regions of a magnetic field but it is not quantized in other regions of a magnetic field due to the broadening of the Landau levels. The amplitude of the dHvA oscillation at zero temperature decreases as the magnetic field increases, while it is constant in the semi-classical Lifshitz Kosevich formula.

Specific features of quantum oscillations of magnetization in quasi-two-dimensional antiferromagnetic semimetals

The specific features of quantum oscillations of the magnetization in quasi-two-dimensional wide-band-gap antiferromagnetic semimetals with a low concentration of charge carriers have been considered theoretically. It has been shown that, in these systems, the Fermi energy determined from the analysis of the frequency of the de Haas–van Alphen oscillations according to the standard procedure can differ significantly from the true value. For the correct determination of the Fermi energy in the canted phase, it has been proposed to analyze quantum oscillations of the magnetization M not as a function of the inverse magnetic field 1/H, but as a function of 1/cosγ, where the angle γ characterizes the inclination angle of the magnetic field with respect to the plane of the quasi-two-dimensional semimetal.

JET SIGNATURES IN THE SPECTRA OF ACCRETING BLACK HOLES

ABSTRACT Jets are observed as radio emission in active galactic nuclei and during the low/hard state in X-ray binaries (XRBs), but their contribution at higher frequencies has been uncertain. We study the dynamics of jets in XRBs using the general-relativistic magnetohydrodynamic code HARM. We calculate the high-energy spectra and variability properties using a general-relativistic radiative transport code based on grmonty. We find the following signatures of jet emission: (i) a significant γ-ray peak above ∼1022 Hz, (ii) a break in the optical/UV spectrum, with a change from &ngr; L &ngr; &sim; &ngr; 0 ?> to &ngr; L &ngr; &sim; &ngr; ?> , followed by another break at higher frequencies where the spectrum roughly returns to &ngr; L &ngr; &sim; &ngr; 0 ?> , and (iii) a pronounced synchrotron peak near or below ∼1014 Hz indicates that a significant fraction of any observed X-ray emission originates in the jet. We investigate the variability during a large-scale magnetic field inversion in which the Blandford–Znajek (BZ) jet is quenched and a new transient hot reconnecting plasmoid is launched by the reconnecting field. The ratio of the γ-rays to X-rays changes from L &gamma; / L X &gt; 1 ?> in the BZ jet to L &gamma; / L X &lt; 1 ?> during the launching of the transient plasmoid.

State transitions triggered by inverse magnetic field: probably applied in high-mass X-ray binaries?

Previous works suggested that the state transitions in an X-ray binary can be triggered by accreting an inverse magnetic field from its companion star. A key point of this mechanism is the accretion and magnification of large-scale magnetic fields from the outer boundary of a thin disk. However, how such a process can be realized is still an open question. In this work, we check this issue in a realistic X-ray binary system. According to our calculations, a quite strong initial magnetic field, B ∼ 102 − 103 G, is required in order to assure that the large-scale magnetic field can be effectively dragged inward and magnified with the accretion of gas. Thus, such a picture probably can be present in high-mass X-ray binaries possessing a strong stellar magnetic field, e.g., Cyg X-1.

Fast control of topological vortex formation in Bose-Einstein condensates by counterdiabatic driving

Topological vortex formation has been known as the simplest method for vortex formation in BEC of alkali atoms. This scheme requires inversion of the bias magnetic field along the axis of the condensate, which leads to atom loss when the bias field crosses zero. In this Letter, we propose a scheme with which the atom loss is greatly suppressed by adding counter-diabatic magnetic field. A naive counter-diabatic field violates the Maxwell equations and we need to introduce an approximation to make it physically feasible. The resulting field requires an extra currents, which is experimentally challenging. Finally we solve this problem by applying a gauge transformation so that the counter-diabatic field is generated by controlling the original trap field with the additional control of the bias field.

Einstein's Photoemission from Quantum Confined Superlattices.

This paper is dedicated to the 83th Birthday of Late Professor B. R. Nag, D.Sc., formerly Head of the Departments of Radio Physics and Electronics and Electronic Science of the University of Calcutta, a firm believer of the concept of theoretical minimum of Landau and an internationally well known semiconductor physicist, to whom the second author remains ever grateful as a student and research worker from 1974-2004. In this paper, an attempt is made to study, the Einstein's photoemission (EP) from III-V, II-VI, IV-VI, HgTe/CdTe and strained layer quantum well heavily doped superlattices (QWHDSLs) with graded interfaces in the presence of quantizing magnetic field on the basis of newly formulated electron dispersion relations within the frame work of k · p formalism. The EP from III-V, II-VI, IV-VI, HgTe/CdTe and strained layer quantum wells of heavily doped effective mass superlattices respectively has been presented under magnetic quantization. Besides the said emissions, from the quantum dots of the aforementioned heavily doped SLs have further investigated for the purpose of comparison and complete investigation in the context of EP from quantum confined superlattices. Using appropriate SLs, it appears that the EP increases with increasing surface electron concentration and decreasing film thickness in spiky manners, which are the characteristic features of such quantized hetero structures. Under magnetic quantization, the EP oscillates with inverse quantizing magnetic field due to Shuvnikov-de Haas effect. The EP increases with increasing photo energy in a step-like manner and the numerical values of EP with all the physical variables are totally band structure dependent for all the cases. The most striking features are that the presence of poles in the dispersion relation of the materials in the absence of band tails create the complex energy spectra in the corresponding HD constituent materials of such quantum confined superlattices and effective electron mass exists within the band gap which is impossible without the concept of band tails. The well-known result of EP for bulk semiconductors having parabolic energy bands can be obtained as a special case of our generalized formulation and thus confirming the compatibility test. The content of this paper finds four important applications and we have suggested the methods of experimental determinations of important transport quantities in the field of quantum effect devices of nanoscience and nanotechnology.