Strong External Magnetic Field Research Articles

Эволюция квантования Ландау спектра спинонных пар в слабом мотовском диэлектрике La-=SUB=-0.15-=/SUB=-Sm-=SUB=-0.85-=/SUB=-MnO-=SUB=-3+delta-=/SUB=- со спинонной поверхностью Ферми с ростом температуры и напряженности магнитного поля

Measurements of the magnetization temperature dependences of La0.15Sm0.85MnO3+δ in the temperature range 4.2 - 100 K revealed a threshold magnetization feature near the temperature Td 50 K, associated with the existence of a small pseudogap Δe in the electron spectrum, which is characteristic of a weak Mott dielectric. An increase in the strength H of the external magnetic field leads to suppression of the dielectric pseudogap Δe, an increase in the density of states of free charge/ spin carriers at EF, and transformation of the charge/spin density waves fragments. A quantization of the pairs spectrum of the low-energy magnetic excitations of a Z2 quantum spin liquid in the form of spinon-gauge field composite quasiparticles was found in the temperature range 4.2 - 12 K. Formation of a continuous spectrum of the quantum spin liquid excitations in the regime of “weak magnetic fields” Н = 100 Oe, 350 Oe, 1 kOe is explained within the framework of the Landau quantization models of the spectrum of composite quasiparticles with fractional values of the factor ν filling of three overlapping Landau zones.. In the regime of a “strong external magnetic field” H = 3.5 kOe, the new quantum oscillations of the temperature dependences of the magnetization of an incompressible spinon liquid were founded in the form of three narrow steps (plateaus) corresponding to the complete filling of non-overlapping Landau zones with integer values of the filling factor by spinons.

Magnetic properties of directional textured dysprosium foils for cryogenic undulator

Directional textured dysprosium foils are fabricated by rapid solidification and sequential cold rolling, and the influences of their thickness values and magnetic structures on magnetic properties are analyzed and studied. The results show that magnetic properties of cold-rolled dysprosium foils are better than those of rapid solidification dysprosium foils, and the magnetization and permeability for each of the cold-rolled dysprosium foils are related to the thickness and temperature. Below Curie temperature, the cold-rolled dysprosium foils have obvious soft magnetic properties in a temperature range from 77 K to 4.2 K, the saturation magnetization for each of cold-rolled dysprosium foils increases by 5%－8%, and the saturation magnetization of 0.15-mm-thick cold-rolled dysprosium foil arrives at 2880 kA/m at 4.2 K, and the maximum permeability of cold-rolled 0.10-mm-thick dysprosium foil approaches to 30. The cryogenic magnetization of cold-rolled dysprosium foil with a strong external magnetic field is higher than that of conventional Co-V-Fe below 85 K. The cryogenic magnetic properties of textured dysprosium foils are related to the oxygen content and the orientation degree of (0001) crystal plane. The present study lays the foundation of technology and principle for preparing the chunky directional textured dysprosium soft magnet for cryogenic undulator.

Ground State, Isoelectronic Ions and Low-Lying Excited States of Lithium Atom in Strong Magnetic Field

In the framework of the variational Monte Carlo method, the ground states of the lithium atom and lithium like ions up to Z = 10 in an external strong magnetic field are evaluated. Furthermore, the two low-lying excited states , and of the lithium atom in strong magnetic field are also investigated. Simple trial wave functions for lithium are used.

Корреляция электрических, гальваномагнитных и магнитных характеристик нанокристаллических пленок железа, полученных методом ионно-ассистированного осаждения

Here we present the measurements of the temperature dependence of resistance, transverse and longitudinal magnetoresistance (MR) in nanocrystalline iron films in the temperature range 2-300 K and the sweep of the magnetic field up to 8 T. Thin nanocrystalline films of α- iron phase with 80 nm thickness were obtained by ion-beam assisted deposition on a silicon substrate. In addition to the shape anisotropy, the obtained iron films exhibited perpendicular magnetic anisotropy (PMA), which disappeared after annealing the films at a temperature of 450 oC in a vacuum. The effect of PMA on the sign and magnitude of the MR of iron films, as well as on the magnetic field dependences of the magnetoresistive effect, recorded at different orientations of the external magnetic field with respect to the film plane and current direction, is experimentally shown. The results obtained are discussed in the framework of modern views on the processes of charge transfer in a weakly disordered ferromagnetic films with different magnetic anisotropy and domain structure when a weak (less than the saturation field of magnetization) or strong (higher than the saturation field) external magnetic field is applied.

MHD mixed convection on an inclined stretching plate in Darcy porous medium with Soret effect and variable surface conditions

AbstractThis work is concerned with a steady 2D laminar MHD mixed convective flow of an electrically conducting Newtonian fluid with low electrical conductivity along with heat and mass transfer on an isothermal stretching semi-infinite inclined plate embedded in a Darcy porous medium. Along with a strong uniform transverse external magnetic field, the Soret effect is considered. The temperature and concentration at the wall are varying with distance from the edge along the plate, but it is uniform at far away from the plate. The governing equations with necessary flow conditions are formulated under boundary layer approximations. Then a continuous group of symmetry transformations are employed to the governing equations and boundary conditions which determine a set of self-similar equations with necessary scaling laws. These equations are solved numerically and similar velocity, concentration, and temperature for various values of involved parameters are obtained and presented through graphs. The momentum boundary layer thickness becomes larger with increasing thermal and concentration buoyancy forces. The flow boundary layer thickness decreases with the angle of inclination of the stretching plate. The concentration increases considerably for larger values of the Soret number and it decreases with Lewis number. The skin friction coefficient increases for increasing angle of inclination of the plate, magnetic and porosity parameters, however it decreases for rise of thermal and solutal buoyancy parameters. In this double diffusive boundary layer flow, Nusselt and Sherweed numbers increase for rise of thermal and solutal buoyancy parameters, Prandtl number, but they behave opposite nature in case of angle of inclination of the plate, magnetic and porosity parameters. The Sherwood number increases for increasing Lewis number but it decreases for increasing Soret number.

A Valleytronic Diamond Transistor: Electrostatic Control of Valley Currents and Charge-State Manipulation of NV Centers.

The valley degree of freedom in many-valley semiconductors provides a new paradigm for storing and processing information in valleytronic and quantum-computing applications. Achieving practical devices requires all-electric control of long-lived valley-polarized states, without the use of strong external magnetic fields. Because of the extreme strength of the carbon–carbon bond, diamond possesses exceptionally stable valley states that provide a useful platform for valleytronic devices. Using ultrapure single-crystalline diamond, we demonstrate electrostatic control of valley currents in a dual-gate field-effect transistor, where the electrons are generated with a short ultraviolet pulse. The charge current and the valley current measured at the receiving electrodes are controlled separately by varying the gate voltages. We propose a model to interpret experimental data, based on drift-diffusion equations coupled through rate terms, with the rates computed by microscopic Monte Carlo simulations. As an application, we demonstrate valley-current charge-state modulation of nitrogen-vacancy centers.

Isolated Dirac string induced by interaction between positive and negative monopoles

<sec>Based on the three-dimensional spinor Gross-Pitaevskii (GP) equation, the dynamic behavior of the Bose-Einstein condensate under the action of a time-dependent periodic external magnetic field is studied. The results show that the Bose-Einstein condensate with spin-1 in a ferromagnetic state will undergo topological deformation under the action of an external magnetic field periodically varying with time. When the two zero points of the magnetic field enter into the condensate, the density pattern of the spin-up state forms small convexities protruding upward and downward on the <i>z</i>-axis, respectively. As the two zero points of the magnetic field gradually coincide in the condensate, the upward and downward protruding convexities are elongated. Finally, the spin-up state in the shape of a line is distributed on the <i>z</i>-axis, which is consistent with the scenario of the isolated Dirac string predicted by theoretical analysis. </sec><sec>As far as we know, magnetic monopole can be divided into positive monopole and negative monopole. The positive magnetic monopole means that all magnetic induction lines are emitted from the center of the circle. And only the Dirac string points to the center of the circle. The negative monopole is that all the magnetic induction lines point from the outside to the center of the circle, and only the Dirac string emits from the center of the circle. Magnetic monopole is a topological defect in vector field, which accords with both quantum mechanics and gauge invariance of electromagnetic field. </sec><sec>Single magnetic monopole has been studied a lot in theory, and its analogues have been observed in experiment. But multiple monopoles and the interaction between them are still rarely studied. In this paper, multiple monopoles are produced based on the fact that the periodic magnetic field has multiple zeros. We use a new periodic magnetic field to generate a positive and negative magnetic monopole. Due to the strong external magnetic field, the vorticity in the condensate is consistent with the magnetic field of the monopole. Finally, by calculating the superfluid vorticity of the condensate, the characteristic diagram of the magnetic monopole is obtained. The results show that the condensate forms a pair of positive and negative magnetic monopoles at the two zero points of the magnetic field, corresponding to the two small convexities protruding upward and downward on the <i>z</i>-axis of the spin-up state, respectively. As the two zero points of the magnetic field coincide, the two Dirac strings in the positive and negative magnetic monopole gradually approach to each other, and after about 5 ms, they are completely connected, finally forming an isolated Dirac string. This result provides a new idea for further studying the isolated Dirac strings.</sec>

Seemingly anisotropic magnetodielectric effect in isotropic EuTiO3 ceramics

In the antiferromagnetic phase of $\mathrm{Eu}\mathrm{Ti}{\mathrm{O}}_{3}$ ceramics, a seemingly anisotropic magnetodielectric effect (up to 2.5%) was observed via the low-frequency dielectric permittivity measured in external magnetic field below 1.9 T. We explain the effect theoretically by taking into account the demagnetizing field which effectively reduces the internal magnetic flux density by 0.6 T when the external magnetic field is applied perpendicular to the plane of the disk-shaped sample. This finding is also confirmed experimentally by magnetization measurements. The refractive index between 0.2 and 0.5 THz exhibits a large anisotropy in an external magnetic field of up to 7 T. This anisotropy is due to a shift of the ferromagnetic resonance from the microwave to the sub-THz region with external magnetic field applied perpendicular to the magnetic component of the THz radiation. This magnon observation is performed in the strong external magnetic field (above 2 T) and in both paramagnetic and antiferromagnetic phases.

Nonlinear propagation of low‐frequency electromagnetic disturbances in plasmas

AbstractElectromagnetic (EM) waves/disturbances are typically the best means to understand and analyse an ionized medium like plasma. However, the propagation of EM waves with a frequency lower than the plasma frequency is prohibited by the freely moving charges of the plasma. In dense plasmas, though the plasma frequency can be typically quite high, EM sources at such higher frequency are not easily available. It is, therefore, of interest to seek possibilities wherein a low frequency (lower than the plasma frequency) EM disturbance propagates inside a plasma. This is possible in the context of magnetized plasmas. However, in order to have a magnetized plasma response in high‐density plasmas, one requires an extremely strong external magnetic field. In this manuscript, it is demonstrated that the nonlinearity of the plasma medium can aid the propagation of a slow (effective frequency lower than the plasma frequency) EM wave inside an overdense plasma. A possible mechanism of guiding, collimating, and trapping of the EM pulse or electron current pulses by appropriate tailoring of the local plasma density profile is also shown. Certain interesting applications of the propagation of such slow EM pulse through the inhomogeneous plasma is also discussed.

Research on the propagation properties of THz circularly polarized wave in BGK model inhomogeneous dusty plasma

When a hypersonic vehicle flies near space, a layer of complex dusty plasma will form around the vehicle under the influence of high temperature, which will cause radar signal attenuation (ATT) to different degrees and lead to communication barriers. Therefore, studying the interaction mechanism between electromagnetic waves and dusty plasma is important. In this paper, the Bhatnagar–Gross–Krook collision model of non-uniform dusty plasma is derived on the basis of Boltzmann's approximate equation. In addition, the modified expression of a dielectric coefficient of weakly ionized dusty plasma is obtained under the condition of magnetization. With the Wentzel–Kramers–Brillouin method, the ATT coefficients of terahertz wave with different external magnetic fields and dusty plasma parameters are calculated. Results show that a strong external magnetic field will cause the ATT of the right-hand circular polarized wave to produce a low absorption band, whereas the ATT of the left-hand circular polarized wave will evidently weaken. The electron concentration, dust concentration, dust particle radius, collision frequency, and charging frequency also influence the ATT under the external magnetic field. These studies provide theoretical references for the research on the blackouts of hypersonic vehicles.

Nuclear Reaction Screening, Weak Interactions, and r-process Nucleosynthesis in High Magnetic Fields

Abstract Coulomb screening and weak interactions in a hot, magnetized plasma are investigated. Coulomb screening is evaluated in a relativistic thermal plasma in which electrons and positrons are in equilibrium. In addition to temperature effects, effects on weak screening from a strong external magnetic field are evaluated. In high fields, the electron transverse momentum components are quantized into Landau levels. The characteristic plasma screening length at high temperatures and at high magnetic fields is explored. In addition to changes to the screening length, changes in weak interaction rates are estimated. It is found that high fields can result in increased β-decay rates as the electron and positron spectra are dominated by Landau levels. Finally, the effects studied here are evaluated in a simple r-process model. It is found that relativistic Coulomb screening has a small effect on the final abundance distribution. While changes in weak interaction rates in strong magnetic fields can have an effect on the r-process evolution and abundance distribution, the field strength required to have a significant effect may be larger than what is currently thought to be typical of the r-process environment in collapsar jets or neutron star mergers. If r-process sites exist in fields G, effects from fields on weak decays could be significant.

Asymptotics of the three-dimensional Vlasov equation in the large magnetic field limit

We study the asymptotic behavior of solutions to the Vlasov equation in the presence of a strong external magnetic field. In particular we provide a mathematically rigorous derivation of the guiding-center approximation in the general three dimensional setting under the action of large inhomogeneous magnetic fields. First order corrections are computed and justified as well, including electric cross field, magnetic gradient and magnetic curvature drifts. We also treat long time behaviors on two specific examples, the two dimensional case in carte-sian coordinates and a poloidal axi-symmetric geometry, the former for expository purposes. Algebraic manipulations that underlie concrete computations make the most of the linearity of the stiffest part of the system of characteristics instead of relying on any particular variational structure.

Chemical synthesis–free and facile preparation of magnetized polyethylene composite and its application as an efficient magnetic sorbent for some pesticides

In this study, a magnetized polyethylene composite has been prepared using ball milling procedure and employed as an efficient sorbent in magnetic dispersive solid phase extraction combined with dispersive liquid–liquid microextraction. This method has been utilized for the extraction and preconcentration of some pesticides from fruit juices prior to their quantification by gas chromatography–flame ionization detection. The prepared sorbent consisted of the natural iron oxide (obtained from sand) coated with polyethylene. In the present work, first a few mg of the magnetic composite is added into an aqueous solution containing the analytes and vortexed. After that the analytes are eluted with iso–propanol from the surface of the composite particles separated in the presence of a strong external magnetic field. For further enrichment of the analytes, 1,2–dibromoethane (at µL–level) as an extraction solvent is mixed with the obtained eluent and hastily injected into deionized water. The composite was characterized using techniques including vibrating sample magnetometry, X–ray diffraction, scanning electron microscopy, energy–dispersive X–ray spectroscopy, Brunauer–Emmett–Teller nitrogen sorption, and Fourier transform infrared spectrophotometry. Under optimal conditions, the method provided low limits of detection (0.94–1.9 μg L−1) and quantification (3.2–5.9 μg L−1), high enrichment factors (570–692), good linearity (r2 ≥ 0.994), and satisfactory repeatabilities (relative standard deviations ≤ 8% for intra– and inter–day precisions at a concentration of 15 μg L−1 of each analyte).

4009 Magneto-electric nanoparticles (MENs) cobalt ferrite-barrium titanate (CoFe2O4–BaTiO3) for non-invasive neuromodulation

OBJECTIVES/GOALS: Our goal is to develop a non-invasive stimulation technique using magneto-electric nanoparticles (MENs) for inducing and enhancing neuronal activity with high spatial and temporal resolutions and minimal toxicity, which can potentially be used as a more effective approach to brain stimulation. METHODS/STUDY POPULATION: MENs compose of core-shell structures that are attracted to strong external magnetic field (~5000 Gauss) but produces electric currents with weaker magnetic field (~450 Gauss). MENs were IV treated into mice and drawn to the brain cortex with a strong magnetic field. We then stimulate MENs with a weaker magnetic field via electro magnet. With two photon calcium imaging, we investigated both the temporal and spatial effects of MENs on neuronal activity both in vivo and in vitro. We performed mesoscopic whole brain calcium imaging on awake animal to assess the MENs effects. Furthermore, we investigated the temporal profile of MENs in the vasculatures post-treatment and its toxicities to CNS. RESULTS/ANTICIPATED RESULTS: MENs were successfully localized to target cortical regions within 30 minutes of magnetic application. After wirelessly applying ~450 G magnetic field between 10-20 Hz, we observed a dramatic increase of calcium signals (i.e. neuronal excitability) both in vitro cultured neurons and in vivo treated animals. Whole brain imaging of awake mice showed a focal increase in calcium signals at the area where MENs localized and the signals spread to regions further away. We also found MENs stimulatory effects lasted up to 24 hours post treatment. MEN stimulation increases c-Fos expression but resulted in no inflammatory changes, up to one week, by assessing microglial or astrocytes activations. DISCUSSION/SIGNIFICANCE OF IMPACT: Our study shows, through controlling the applied magnetic field, MENs can be focally delivered to specific cortical regions with high efficacy and wirelessly activated neurons with high spatial and temporal resolution. This method shows promising potential to be a new non-invasive brain modulation approach disease studies and treatments.

Particle trajectories in Weibel filaments: influence of external field obliquity and chaos

When two collisionless plasma shells collide, they interpenetrate and the overlapping region may turn Weibel unstable for some values of the collision parameters. This instability grows magnetic filaments which, at saturation, have to block the incoming flow if a Weibel shock is to form. In a recent paper (Bret, J. Plasma Phys., vol. 82, 2016b, 905820403), it was found by implementing a toy model for the incoming particle trajectories in the filaments, that a strong enough external magnetic field $\unicode[STIX]{x1D63D}_{0}$ can prevent the filaments blocking the flow if it is aligned with them. Denoting by $B_{f}$ the peak value of the field in the magnetic filaments, all test particles stream through them if $\unicode[STIX]{x1D6FC}=B_{0}/B_{f}>1/2$ . Here, this result is extended to the case of an oblique external field $B_{0}$ making an angle $\unicode[STIX]{x1D703}$ with the flow. The result, numerically found, is simply $\unicode[STIX]{x1D6FC}>\unicode[STIX]{x1D705}(\unicode[STIX]{x1D703})/\cos \unicode[STIX]{x1D703}$ , where $\unicode[STIX]{x1D705}(\unicode[STIX]{x1D703})$ is of order unity. Noteworthily, test particles exhibit chaotic trajectories.

Electromagnetic Hall current effect and fractional heat order for microtemperature photo-excited semiconductor medium with laser pulses

In this paper, the elastic semiconductor medium is exposed to outer laser pulses. The laser pulses cause vibrations in the inner structure of the medium with the time fractional heat order. Under the influence of strong external magnetic field, the effect of Hall current is appeared in this case the interaction between the strong magnetic field and microstructure (microelements) of the elastic medium is studied. The microtemperature states is generated due to photo-excited electrons in context of photothermal transport process. The one-dimensional (1D) deformation is used to describe the overlapping process between elastic-magneto-plasma-thermal distribution waves in case of semiconductor elastic rod. The governing equations are solved in Laplace integral transform domain in microelements field. Some external loads are applied at the outer free surface of the medium to obtain the physical quantities under investigation. To obtain the complete solutions of the physical quantities the numerical inversion technique of Laplace transform is used. The Hall current, fractional parameters and micro-temperature effect are presented graphically and discussed theoretically under the effect of laser pulses.

Microwave Measurement beyond the Quantum Limit with a Nonreciprocal Amplifier

The measurement of a quantum system is often performed by encoding its state in a single observable of a light field. The measurement efficiency of this observable can be reduced by loss or excess noise on the way to the detector. Even a \textit{quantum-limited} detector that simultaneously measures a second non-commuting observable would double the output noise, therefore limiting the efficiency to $50\%$. At microwave frequencies, an ideal measurement efficiency can be achieved by noiselessly amplifying the information-carrying quadrature of the light field, but this has remained an experimental challenge. Indeed, while state-of-the-art Josephson-junction based parametric amplifiers can perform an ideal single-quadrature measurement, they require lossy ferrite circulators in the signal path, drastically decreasing the overall efficiency. In this paper, we present a nonreciprocal parametric amplifier that combines single-quadrature measurement and directionality without the use of strong external magnetic fields. We extract a measurement efficiency of $62_{-9}^{+17} \%$ that exceeds the quantum limit and that is not limited by fundamental factors. The amplifier can be readily integrated with superconducting devices, creating a path for ideal measurements of quantum bits and mechanical oscillators.

Stochastic Magnetic Hydrodynamic Hierarchy in a Strong External Magnetic Field

Based on a stochastic microscopic collisional model of the motion of charged particles in a strong external magnetic field, a hierarchy of equations of magnetic hydrodynamics is constructed. The transition to increasingly rough approximations occurs in accordance with a decrease in the dimensioning parameter, similar to the Knudsen number in gas dynamics. The result is stochastic and nonrandom macroscopic equations that differ from the magnetic analog of the Navier–Stokes system of equations, as well as from the systems of magnetic quasi-hydrodynamics. The main feature of this derivation is more accurate velocity averaging due to the analytical solution of stochastic differential equations with respect to the Wiener measure, in the form of which the intermediate meso model is presented in the phase space. This approach differs significantly from the traditional one, which uses not the random process itself but its distribution function. Emphasis is placed on the clarity of assumptions when moving from one level of detail to another, and not on numerical experiments that contain additional approximation errors.

Magnetically induced/enhanced coarsening in thin films

External magnetic fields influence the microstructure of polycrystalline materials. We explore the influence of strong external magnetic fields on the long time scaling of grain size during coarsening in thin films with an extended phase-field-crystal model. Additionally, the change of various geometrical and topological properties is studied. In a situation which leads to stagnation, an applied external magnetic field can induce further grain growth. The induced driving force due to the magnetic anisotropy defines the magnetic influence of the external magnetic field. Different scaling regimes are identified dependent on the magnetization. At the beginning, the scaling exponent increases with the strength of the magnetization. Later, when the texture becomes dominated by grains preferably aligned with the external magnetic field, the scaling exponent becomes independent of the strength of the magnetization or stagnation occurs. We discuss how the magnetic influence change the effect of retarding or pinning forces, which are known to influence the scaling exponent. We further study the influence of the magnetic field on the grain size distribution (GSD), next neighbor distribution (NND) as well as grain shape and orientation. If possible, we compare our predictions with experimental findings.

MHD simulation of accretion processes in magnetic cataclysmic variable EX Hya

A hierarchical numerical model for investigation of the accretion processes in the magnetic cataclysmic variable EX Hya has been described. The coarsest level of the hierarchy corresponds to the accretion disk formation due to the mass transfer. The intermediate level describes the structure of the white dwarf magnetosphere. The finest level corresponds to the formation of the accretion curtain at the inner edge of the accretion disk. The model is based on the equations of the modified MHD, where a strong external magnetic field acts as an efficient fluid with which the plasma interacts. Results of simulations show that the accretion in EX Hya proceeds via accretion columns that have curtain-like shapes. These columns are very thin and the accretion regions cover a small fraction of the accretor surface. Numerical results agree with the parameters of the EX Hya system as determined by Semena et al. (2014).