Laboratory Magnetic Field Research Articles

Modeling of an Integrated Traction Motor Protection System

Purpose. The article is devoted to the creation of traction motor protection by modern methods and means based on a programmable logic controller (PLC). Methodology. To simulate motor fault monitoring in laboratory conditions, magnetic field and temperature sensors were installed on a small powerful induction motor, and then the data obtained from the sensors in normal and overloaded motor modes were analyzed. Based on the research, protection methods were developed. Findings. Previously used simple motor protection systems based on components such as timers, contactors, electromagnetic switches, voltage and current transformers were slow and inaccurate, and had low sensitivity. However, the production of PLCs and their application in this industry has eliminated these problems. The intensive operation of motors as the main executive equipment requires the creation of modern automated protection systems to ensure their reliable and stable operation. Originality. The paper improves the method of protection of traction motors based on the use of programmable logic controllers. In addition to the voltage and current parameters, the proposed method involves monitoring the magnetic field. It also provides for the possibility of adjusting the protection response time. As a result, in the event of overload, short circuit, and other non-standard situations, the improved method provides the system with the ability to make more accurate and reliable decisions. Practical value. The TIA Portal software package has modeled a traction motor protection system by temperature and current and considered its practical application. To make such systems more effective, in the future, comprehensive protection systems based on the diagnostic state of the traction motor can be developed. In addition, an effective system can be created by providing SCADA control of the engines of several vehicles simultaneously.

Light dark matter axion-wind detection with a static electric field

We explore the axionic dark matter search sensitivity with a narrow-band detection scheme aimed at the axion-photon conversion by a static electric field inside a cylindrical capacitor. An alternating magnetic field signal is induced by effective currents as the axion dark matter wind flows perpendicularly through the electric field. At low axion masses, such as in a KKLT scenario, front-end narrow band filtering is provided by using LC resonance with a high Q factor, which enhances the detectability of the tiny magnetic field signal and leads to thermal noise as the major background that can be reduced under cryogenic conditions. We demonstrate that high gaγ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$g_{a\\gamma }$$\\end{document} sensitivity can be achieved by using a strong electric field E∼\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$E\\sim $$\\end{document}MVm-1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{-1}$$\\end{document}. The QCD axion theoretical parameter space would require a high E∼\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$E\\sim $$\\end{document} GVm-1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{-1}$$\\end{document} field strength. Using the static electric field scheme essentially avoids exposing the sensitive superconducting pickup to an applied laboratory magnetic field.

Field-Tunable Berezinskii-Kosterlitz-Thouless Correlations in a Heisenberg Magnet.

We report the manifestation of field-induced Berezinskii-Kosterlitz-Thouless (BKT) correlations in the weakly coupled spin-1/2 Heisenberg layers of the molecular-based bulk material [Cu(pz)_{2}(2-HOpy)_{2}](PF_{6})_{2}. At zero field, a transition to long-range order occurs at 1.38K, caused by a weak intrinsic easy-plane anisotropy and an interlayer exchange of J^{'}/k_{B}≈1 mK. Because of the moderate intralayer exchange coupling of J/k_{B}=6.8 K, the application of laboratory magnetic fields induces a substantial XY anisotropy of the spin correlations. Crucially, this provides a significant BKT regime, as the tiny interlayer exchange J^{'} only induces 3D correlations upon close approach to the BKT transition with its exponential growth in the spin-correlation length. We employ nuclear magnetic resonance measurements to probe the spin correlations that determine the critical temperatures of the BKT transition as well as that of the onset of long-range order. Further, we perform stochastic series expansion quantum MonteCarlo simulations based on the experimentally determined model parameters. Finite-size scaling of the in-plane spin stiffness yields excellent agreement of critical temperatures between theory and experiment, providing clear evidence that the nonmonotonic magnetic phase diagram of [Cu(pz)_{2}(2-HOpy)_{2}](PF_{6})_{2} is determined by the field-tuned XY anisotropy and the concomitant BKT physics.

Anisotropic Gigahertz Antiferromagnetic Resonances of the Easy-Axis van der Waals Antiferromagnet CrSBr.

We report measurements of antiferromagnetic resonances in the van der Waals easy-axis antiferromagnet CrSBr. The interlayer exchange field and magnetocrystalline anisotropy fields are comparable to laboratory magnetic fields, allowing a rich variety of gigahertz-frequency dynamical modes to be accessed. By mapping the resonance frequencies as a function of the magnitude and angle of applied magnetic field, we identify the different regimes of antiferromagnetic dynamics. The spectra show good agreement with a Landau-Lifshitz model for two antiferromagnetically coupled sublattices, accounting for interlayer exchange and triaxial magnetic anisotropy. Fits allow us to quantify the parameters governing the magnetic dynamics: At 5 K, the interlayer exchange field is μ0HE = 0.395(2) T, and the hard and intermediate-axis anisotropy parameters are μ0Hc = 1.30(2) T and μ0Ha = 0.383(7) T. The existence of within-plane anisotropy makes it possible to control the degree of hybridization between the antiferromagnetic resonances using an in-plane magnetic field.

The Properties of Thermochemical Remanent Magnetization Acquired by Slow Laboratory Cooling of Titanomagnetite-Bearing Basalt Samples from Different Temperatures and the Results of the Thellier Method

—The experiments have been carried out on the acquisition of thermochemical remanent magnetization (TCRM) in basalt samples containing titanomagnetite (TM) with the Curie temperature Тс ~200°C by their rapid heating to maximum temperatures Т* from 450 to 530°C followed by slow cooling in the laboratory magnetic field Blab. At different stages of the preliminary thermal treatment of the initial samples, a set of magnetomineralogical studies including electron microscopy, X-ray diffraction and thermomagnetic analyzes, and measurements of magnetic hysteresis parameters were performed. It is shown that as early as the very beginning of the cooling process, all samples demonstrate explosive growth of TCRM corresponding to the stage of rapid single-phase oxidation of the initial titanomagnetite fraction of basalt, and that TCRM is acquired by the increase of Тс and volume of single-phase oxidized parts of TM grains as well as by the growth of the volume of Ti-depleted (relative to the initial TM) cells of microstructure of the subsequent oxidative exsolution. The Arai–Nagata diagrams for the samples carrying TCRM have a form of a broken line consisting of two linear segments. The low-temperature interval T < Т* corresponds to a mixture of thermochemical and thermoremanent (TRM) magnetizations and gives a slightly overestimated Blab because of the effect of a low cooling rate during the acquisition of TCRM and TRM. The high-temperature interval corresponds to pure TCRM and the Blab strength determined from this interval is underestimated by 20–27%. It is recommended to reject samples whose Araii–Nagata diagram has two or more linear segments against the background single-component NRM.

Hole spin echo envelope modulations

Hole spins in semiconductor quantum dots or bound to acceptor impurities show promise as potential qubits, partly because of their weak and anisotropic hyperfine couplings to proximal nuclear spins. Since the hyperfine coupling is weak, it can be difficult to measure. However, an anisotropic hyperfine coupling can give rise to a substantial spin-echo envelope modulation that can be Fourier-analyzed to accurately reveal the hyperfine tensor. Here, we give a general theoretical analysis for hole-spin-echo envelope modulation (HSEEM), and apply this analysis to the specific case of a boron-acceptor hole spin in silicon. For boron acceptor spins in unstrained silicon, both the hyperfine and Zeeman Hamiltonians are approximately isotropic leading to negligible envelope modulations. In contrast, in strained silicon, where light-hole spin qubits can be energetically isolated, we find the hyperfine Hamiltonian and $g$-tensor are sufficiently anisotropic to give spin-echo-envelope modulations. We show that there is an optimal magnetic-field orientation that maximizes the visibility of envelope modulations in this case. Based on microscopic estimates of the hyperfine coupling, we find that the maximum modulation depth can be substantial, reaching $\sim 10\%$, at a moderate laboratory magnetic field, $B\lesssim 200\,\mathrm{mT}$.

Surface plasmons modulated by ferromagnetic insulating layers on the surface of topological insulator

We study the spin-polarized surface plasmons on the surface of a three-dimensional topological insulator. The surface of the topological insulator is modulated by a pulsed exchange field provided by an array of ferromagnetic insulating (FI) stripes. A nonlinear quantum hydrodynamic model is adopted and solved self-consistently, in the presence of the quantum statistical effect and the spin effect. The exchange field can form and sustain the periodic polarization of the surface plasmons under a laboratory magnetic field condition. The nonlinear effect and increasing exchange field strength enhance the surface plasmon polarization. The quantum statistical effect inhibits the surface plasmon polarization. Different spin state leads to different sign of collective density polarization.

Achieving Ultrahigh Carrier Mobility in Two-Dimensional Hole Gas of Black Phosphorus.

We demonstrate that a field-effect transistor (FET) made of few-layer black phosphorus (BP) encapsulated in hexagonal boron nitride (h-BN) in vacuum exhibits a room-temperature hole mobility of 5200 cm2/(Vs), being limited just by the phonon scattering. At cryogenic temperatures, the FET mobility increases up to 45 000 cm2/(Vs), which is five times higher compared to the mobility obtained in earlier reports. The unprecedentedly clean h-BN-BP-h-BN heterostructure exhibits Shubnikov-de Haas oscillations and a quantum Hall effect with Landau level (LL) filling factors down to v = 2 in conventional laboratory magnetic fields. Moreover, carrier density independent effective mass of m* = 0.26 m0 is measured, and a Landé g-factor of g = 2.47 is reported. Furthermore, an indication for a distinct hole transport behavior with up- and down-spin orientations is found.

Type-controlled nanodevices based on encapsulated few-layer black phosphorus for quantum transport

We demonstrate that encapsulation of atomically thin black phosphorus (BP) by hexagonal boron nitride (h-BN) sheets is very effective for minimizing the interface impurities induced during fabrication of BP channel material for quantum transport nanodevices. Highly stable BP nanodevices with ultrahigh mobility and controllable types are realized through depositing appropriate metal electrodes after conducting a selective etching to the BP encapsulation structure. Chromium and titanium are suitable metal electrodes for BP channels to control the transition from a p-type unipolar property to ambipolar characteristic because of different work functions. Record-high mobilities of 6000 cm2 V−1 s−1 and 8400 cm2 V−1 s−1 are respectively obtained for electrons and holes at cryogenic temperatures. High-mobility BP devices enable the investigation of quantum oscillations with an indistinguishable Zeeman effect in laboratory magnetic field.

Interlayer Exchange Coupling: A General Scheme Turning Chiral Magnets into Magnetic Multilayers Carrying Atomic-Scale Skyrmions.

We report on a general principle using interlayer exchange coupling to extend the regime of chiral magnetic films in which stable or metastable magnetic Skyrmions can appear at a zero magnetic field. We verify this concept on the basis of a first-principles model for a Mn monolayer on a W(001) substrate, a prototype chiral magnet for which the atomic-scale magnetic texture is determined by the frustration of exchange interactions, impossible to unwind by laboratory magnetic fields. By means of abinitio calculations for the Mn/W_{m}/Co_{n}/Pt/W(001) multilayer system we show that for certain thicknesses m of the W spacer and n of the Co reference layer, the effective field of the reference layer fully substitutes the required magnetic field for Skyrmion formation.

Stopping power of two-dimensional spin quantum electron gases

Quantum effects can contribute significantly to the electronic stopping powers in the interactions between the fast moving beams and the degenerate electron gases. From the Pauli equation, the spin quantum hydrodynamic (SQHD) model is derived and used to calculate the stopping power and the induced electron density for protons moving above a two-dimensional (2D) electron gas with considering spin effect under an external in-plane magnetic field. In our calculation, the stopping power is not only modulated by the spin direction, but also varied with the strength of the spin effect. It is demonstrated that the spin effect can obviously enhance or reduce the stopping power of a 2D electron gas within a laboratory magnetic field condition (several tens of Tesla), thus a negative stopping power appears at some specific proton velocity, which implies the protons drain energy from the Pauli gas, showing another significant example of the low-dimensional physics.

Magnetic catalysis effect in the (2+1)-dimensional Gross–Neveu model with Zeeman interaction

Magnetic catalysis of the chiral symmetry breaking and other magnetic properties of the (2+1)-dimensional Gross–Neveu model are studied taking into account the Zeeman interaction of spin-1/2 quasi-particles (electrons) with tilted (with respect to a system plane) external magnetic field . The Zeeman interaction is proportional to magnetic moment μB of electrons. For simplicity, temperature and chemical potential are equal to zero throughout the paper. We compare in the framework of the model the above mentioned phenomena both at μB = 0 and μB ≠ 0. It is shown that at μB ≠ 0 the magnetic catalysis effect is drastically changed in comparison with the μB = 0 case. Namely, at μB ≠ 0 the chiral symmetry, being spontaneously broken by at subcritical coupling constants, is always restored at || → ∞ (even at = 0). Moreover, it is proved in this case that chiral symmetry can be restored simply by tilting to a system plane, and in the region B ⊥ → 0 the de Haas – van Alphen oscillations of the magnetization are observed. At supercritical values of coupling constant we have found two chirally non-invariant phases which respond differently on the action of . The first (at rather small values of ||) is a diamagnetic phase, in which there is an enhancement of chiral condensate, whereas the second is a paramagnetic chirally broken phase. Numerical estimates show that phase transitions described in the paper can be achieved at low enough laboratory magnetic fields.

Relevant magnetic and soil parameters as potential indicators of soil conservation status of Mediterranean agroecosystems

SUMMARY The main sources of magnetic minerals in soils unaffected by anthropogenic pollution are iron oxides and hydroxides derived from parent materials through soil formation processes. Soil magnetic minerals can be used as indicators of environmental factors including soil forming processes, degree of pedogenesis, weathering processes and biological activities. In this study measurements of magnetic susceptibility are used to detect the presence and the concentration of soil magnetic minerals in topsoil and bulk samples in a small cultivated field, which forms a hydrological unit that can be considered to be representative of the rainfed agroecosystems of Mediterranean mountain environments. Additionalmagneticstudiessuchasisothermalremanentmagnetization(IRM),anhysteretic remanent magnetization (ARM) and thermomagnetic measurements are used to identify and characterize the magnetic mineralogy of soil minerals. The objectives were to analyse the spatial variability of the magnetic parameters to assess whether topographic factors, soil redistribution processes, and soil properties such as soil texture, organic matter and carbonate contents analysed in this study, are related to the spatial distribution pattern of magnetic properties. The medians of mass specific magnetic susceptibility at low frequency (χlf )w ere 36.0 and 31.1 × 10 −8 m 3 kg −1 in bulk and topsoil samples respectively. High correlation coefficients were found between the χlf in topsoil and bulk core samples (r = 0.951, p < 0.01). Inaddition,volumetricmagneticsusceptibilitywasmeasuredinsituinthefield(κis)andvalues varied from 13.3 to 64.0 × 10 −5 SI. High correlation coefficients were found between χlf in topsoil measured in the laboratory and volumetric magnetic susceptibility field measurements (r = 0.894, p < 0.01). The results obtained from magnetic studies such as IRM, ARM and thermomagnetic measurements show the presence of magnetite, which is the predominant magnetic carrier, and hematite. The predominance of superparamagnetic minerals in upper soil layers suggests enrichment in pedogenic minerals. The finer soil particles, the organic matter content and the magnetic susceptibility values are statistically correlated and their spatial variability is related to similar physical processes. Runoff redistributes soil components including magnetic minerals and exports fine particles out the field. This research contributed tofurtherknowledgeontheapplicationofsoilmagneticpropertiestoderiveusefulinformation on soil processes in Mediterranean cultivated soils.

Berry phase and its sign in quantum superposition states of thermal87Rbatoms

We investigate the Berry phase in an ensemble of thermal ${}^{87}\mathrm{Rb}$ atoms which we prepare in a superposition state under conditions near and at electromagnetically induced transparency. The geometric phase is imprinted in the atoms by rotating the laboratory magnetic field. Phase-stabilized light fields permit us to monitor phase changes of the atomic sample in a Ramsey-type interferometer by instant probing of the absorptive response of the atoms as well as by monitoring the free-induction decay of the coherent superposition. The absolute sign of the phase is determined by reference to controllable phase shifts imposed by the experimenter. We prove that the geometric phase is independent of the rotational frequency of the magnetic field in the adiabatic regime, that the phase is additive in multiple rotations, and it is independent of the Land\'e factor of the atomic magnetic moment, as predicted in Berry's seminal paper. We show that the absolute sign of the phase encodes the sign of the observable angular momentum in relation to laboratory coordinates.

Low background x-ray detection with Micromegas for axion research

Axion helioscopes aim at the detection of solar axions through their conversion into x-rays in laboratory magnetic fields. The use of low background x-ray detectors is an essential component contributing to the sensitivity of these searches. Here we review the recent advances on Micromegas detectors used in the CERN Axion Solar Telescope (CAST) and proposed for the future International Axion Observatory (IAXO). The most recent Micromegas setups in CAST have achieved background levels of 1.5 × 10−6 keV−1 cm−2 s−1, a factor of more than 100 lower than the ones obtained by the first generation of CAST detectors. This improvement is due to the development of active and passive shielding techniques, offline discrimination techniques allowed by highly granular readout patterns, as well as the use of radiopure detector components. The status of the intensive R&D to reduce the background levels will be described, including the operation of replica detectors in test benches and the detailed Geant4 simulation of the detector setup and the detector response, which has allowed the progressive understanding of background origins. The best levels currently achieved in a test setup operating in the Canfranc Underground Laboratory (LSC) are as low as ∼ 10−7 keV−1 cm−2 s−1, showing the good prospects of this technology for application in the future IAXO.

Magnetic catalysis effect in the (2+1)-dimensional Gross-Neveu model with Zeeman interaction

Magnetic catalysis of the chiral symmetry breaking and other magnetic properties of the (2+1)-dimensional Gross--Neveu model are studied taking into account the Zeeman interaction of spin-1/2 quasi-particles (electrons) with tilted (with respect to a system plane) external magnetic field $\vec B=\vec B_\perp+\vec B_\parallel$. The Zeeman interaction is proportional to magnetic moment $\mu_B$ of electrons. For simplicity, temperature and chemical potential are equal to zero throughout the paper. We compare in the framework of the model the above mentioned phenomena both at $\mu_B=0$ and $\mu_B\ne 0$. It is shown that at $\mu_B\ne 0$ the magnetic catalysis effect is drastically changed in comparison with the $\mu_B= 0$ case. Namely, at $\mu_B\ne 0$ the chiral symmetry, being spontaneously broken by $\vec B$ at subcritical coupling constants, is always restored at $|\vec B|\to\infty$ (even at $\vec B_\parallel=0$). Moreover, it is proved in this case that chiral symmetry can be restored simply by tilting $\vec B$ to a system plane, and in the region $ B_\perp\to 0$ the de Haas -- van Alphen oscillations of the magnetization are observed. At supercritical values of coupling constant we have found two chirally non-invariant phases which respond differently on the action of $\vec B$. The first (at rather small values of $|\vec B|$) is a diamagnetic phase, in which there is an enhancement of chiral condensate, whereas the second is a paramagnetic chirally broken phase. Numerical estimates show that phase transitions described in the paper can be achieved at low enough laboratory magnetic fields.

On the feasibility of detecting an Aharonov-Bohm phase shift in neutral matter

It has been predicted that, in the presence of combined radial electric field and axial magnetic field, superfluid 4He in a torus will have a persistent current in its ground state. This surprising result arises from non-cancellation of the Aharonov-Bohm phase shifts associated with the opposite charges in the induced electric dipole moment of the neutral 4He atoms. We briefly review this prediction and describe our proposed experiment. In this feasibility study we show that by applying laboratory accessible electric and magnetic fields, a superfluid 4He interferometer (SHeQUID) will have sufficient sensitivity to conclusively determine whether or not the predicted physical phenomenon exists.

Quantum critical scaling in magnetic field near the Dirac point in graphene

Motivated by the recent measurement of the activation energy at the quantum Hall state at the filling factor f=1 in graphene we discuss the scaling of the interaction-induced gaps in vicinity of the Dirac point with the magnetic field. The gap at f=1 is shown to be bounded from above by E(1)/C, where E(n) are the Landau level energies and C = 5.985 + O(1/N) is a universal number. The universal scaling functions are computed exactly for a large number of Dirac fermions N. We find a sublinear dependence of the gap at the laboratory magnetic fields for realistic values of short-range repulsion between electrons, and in quantitative agreement with observation.

The Order Parameter Susceptibility and Collective Modes of Superconductors

The spectrum of order parameter fluctuations of superconductors can be determined through the measurement of the wave-vector and frequency-dependent generalized susceptibility, or pair-field susceptibility. The determination of the pair-field susceptibility is conceptually similar to other susceptibility measurements. In the case of paramagnets at temperatures above a ferromagnetic transition, the susceptibility is determined by the linear response to a magnetic field. Because the superconducting order parameter is off-diagonal in number space, for superconductors there is no classical field analogous to a laboratory magnetic field. However, an effective field can be applied to a fluctuating superconductor across a tunneling barrier through the Josephson coupling of the rigid order parameter of a second superconductor well below its transition temperature. This leads to an observable dc contribution to the tunneling current that is a higher order, “incoherent” Josephson current. The magnitude of this current determines the susceptibility. Its frequency and wave-vector dependence are determined by the dc voltage across the junction and the dc magnetic field applied in the plane of the junction, respectively. In conventional superconductors near, but above their transition temperatures, measurements of the pair-field susceptibility have revealed a diffusive dynamics that can be described by a simple time-dependent Ginzburg–Landau equation. Measurements of the pair-field susceptibility below the transition temperature have revealed the existence of a gapless, propagating order parameter collective mode that becomes quickly overdamped as the temperature is reduced below Tc. The physics of these phenomena and the existing experiments will be reviewed. Opportunities for the application of these techniques to contemporary problems of high-temperature superconductors will be presented. Of particular interest are the possibilities for characterizing the nature of the pseudogap regime.

Hydrogen atom in strong magnetic field: A high accurate calculation in spheroidal coordinates

A B-spline-type basis set method for the calculation of hydrogen atom in strong magnetic fields in the frame of spheroidal coordinates has been introduced. High accurate energy levels of hydrogen in the magnetic field, with strength ranging from 0 to 1000 a.u., have been obtained. For the ground state, 1s0, energies with at least 11 significant digits have been obtained. For the low-lying excited state, 2p−1, energies with at least 9 significant digits are obtained. The method has also been applied to the calculation of hydrogen Rydberg states in laboratory magnetic fields. Energy spectra with at least 10 significant digits are presented. A comparison with other results in the literatures has been performed. Our results are comparable to the most accurate one up to date. A possible extension to the cases of parallel and crossed electric and magnetic fields have been discussed.