External Magnetic Field Parallel Research Articles

Collisional Mechanism of Expanding Wavenumbers Range of Weibel-Type Instability in Magnetoactive Plasma

For plasma with anisotropic velocity distribution of particles in the form of two counter-propagating bi-Maxwellian beams, including bi-Maxwellian plasma, in the presence of external magnetic field parallel to the beams, it is shown that in a wide range of parameters, particle collisions lead to the expansion of the wavenumbers range, generally towards the long-wavelength region, and weaken the conditions for the occurrence of the Weibel-type instability. In the specified expanded range, its growth rate, found by means of solving the dispersion equation for the wave vectors orthogonal to the external magnetic field, turns out to be less than or on the order of the frequency of particle collisions. Thus, in this range of parameters, the instability development and formation of large-scale magnetic turbulence in a plasma with weak particle collisions require the long-term injection of particles with anisotropic velocity distribution.

Magnetically induced tunable exceptional and Dirac points

The photonic properties of cholesteric liquid crystals (CLCs) in an external magnetic field parallel to the helix axis are theoretically investigated for the first time in the short-wavelength band of the spectrum, where exceptional points (EPs) are found. It was shown that at the EP the real parts of two of four wave numbers touch each other or intersect at the absence of the dielectric anisotropy, and their imaginary parts intersect. At the EP the reflection, transmission and absorption show the same magnitudes for two eigenmodes of CLC layer. At anisotropic absorption near the EP there appear points where the magnetically induced transmittance/absorption are observed. The tunability of the EP was shown, i.e. we can change its wavelength by changing the magnitude of the external magnetic field. It was demonstrated the resonant enhancement of the chirality near the EP. Then it was shown that near the EP the two eigenmodes of CLC layer become strongly non-orthogonal.

Magnetic Field Induction ZnFe2O4@Carbon for Construction of a PVDF‐HFP‐Based 3D Dielectric Network

AbstractFunctional fillers in the polymerization system cannot be arranged in an orderly manner when exposed to natural conditions. The application of magnetic fields in the material preparation process has been shown to greatly enhance the distribution of functional fillers, leading to the organized alignment of functional fillers and the production of polymer matrix composites with remarkable characteristics. In this experiment, rod‐like ZnFe2O4 was synthesized by reverse microemulsion method, and amorphous carbon was coated on the surface of ZnFe2O4 by freeze‐drying method to obtain ZnFe2O4@Carbon core‐shell particles. The composite films were prepared by dispersing ZnFe2O4 with different volume contents into P(VDF‐HFP) matrix. The external parallel magnetic field was used to manipulate the ZnFe2O4@C/P(VDF‐HFP) composite film during the hot‐pressing process, resulting in an oriented ZnFe2O4@C/P(VDF‐HFP) composite film. The experiment revealed that when ZnFe2O4@C is aligned with the film orientation, the dielectric constant of the composite film is 50(50 Hz), which is 130 % higher than that of the unoriented composite film and 290 % higher than that of pure P(VDF‐HFP). When the filling amount is 40 Vol.%, the energy storage density of ZnFe2O4@C/P(VDF‐HFP) composite film is 1.18 times higher than that of unoriented composite material and 1.32 times higher than that of pure P(VDF‐HFP).

Dirac materials in parallel non-uniform electromagnetic fields generated by SUSY: a chiral Planar Hall Effect

Within a Supersymmetric Quantum Mechanics (SUSY-QM) framework, the (3+1) Dirac equation describing a Dirac material in the presence of external parallel electric and magnetic fields is solved. Considering static but non-uniform electric and magnetic profiles with translational symmetry along the y-direction, the Dirac equation is transformed into two decoupled pairs of Schrödinger equations, one for each chirality of the fermion fields. Taking trigonometric and hyperbolic profiles for the vector and scalar potentials, respectively, we arrive at SUSY partner Pöschl-Teller-like quantum potentials. Restricting to the conditions of the potentials that support an analytic zero-mode solution, we obtain a nontrivial current density perpendicular to the electric and magnetic fields, thus, defining a plane where these three vectors become coplanar, indicating the possibility of realizing the Planar Hall Effect. Furthermore, this non-vanishing current density is the sum of current densities for the left- and right-chiralities, suggesting that the net current is a consequence of chiral symmetry. Possible application in current steering of solitonic nature through a Type-I Weyl semimetal is discussed.

Numerical study of the effect of a magnetic field on Rayleigh-Taylor instability with different density disturbances

Rayleigh-Taylor instability (RTI) is a fundamental physical process in fluids and plasmas. RTI is ubiquitous and must be considered in the field of high-energy-density physics, such as in space physics, astrophysics, and inertial confinement fusion. In this work, two-dimensional numerical simulations of laser-driven RTI with different density perturbations are performed using a radiation magnetohydrodynamic simulation program (FLASH). The effect of the applied magnetic field on the evolution of RTI at different Atwood numbers is systematically discussed. The results show that RTI evolves freely without an external magnetic field, and it is accompanied by the generation of secondary Kelvin–Helmholtz instability. Reducing the Atwood number weakens the mixing of fluids and has a strong stabilizing effect on the RTI. Introducing an external magnetic field parallel to the perturbation wave vector further inhibits the development of RTI and Kelvin–Helmholtz instability, with magnetic pressure playing a dominant role. The study results are important to gaining an in-depth understanding of the mixing of magnetic fluids and the magnetic field evolution at the instability interface and provide a reference for subsequent experimental studies on the related magnetization RTI.

Magnetic field caused enhanced absorption and circular dichroism of an achiral plasmonic nanostructure.

In this paper, modulation of light-matter interactions by a magnetic field is used to generate circular dichroism (CD) from an achiral plasmonic nanostructure. Theoretical investigations show an increase in light absorption by the nanostructure in the presence of a magnetic field. The achiral nanostructure exhibits CD in external magnetic field parallel to circularly polarized light (CPL) incidence. The CD emergence is caused by modulation of electron motion to reduced/enhanced frequencies under CPL incidence. Compared to previous studies, in this paper the mechanism of CD emergence, and the physical reasoning behind the change in CD due to change in magnetic field direction and intensity, are explained. CD intensity increases with increasing magnetic field intensity, while CD sign changes on magnetic field direction reversal. Varying structural parameters significantly influences CD intensity. This study can be helpful in magneto-optics and in magneto-chiral applications.

Effect of magnetic field on electroconvection in a thin layer of magnetic nanofluid

It is shown that the external magnetic field (of the strength < 10 kA/m) parallel to the electric field (DC and AC) reduces the electroconvection development threshold voltage and the time of electroconvection development (up to 50 %), and creates a more branched pattern of electroconvective flows in a layer of magnetic nanofluid. The magnetic field perpendicular to the electric field increases the electroconvection development threshold (up to 15 %) and leads to electroconvective pattern degeneracy into a system of strips parallel to the magnetic field. It is demonstrated that the critical voltage increases with increasing magnetic nanofluid layer thickness and voltage frequency.

Irreversibility analysis of an unsteady micropolar CNT-blood nanofluid flow through a squeezing channel with activation energy-Application in drug delivery

Background and objectiveDue to the low toxicity, unique physiochemical properties, and appropriate surface modifications, Carbon Nanotubes (CNTs) are used as target carriers in drug delivery systems. In the present problem, we have considered both single-walled and multi-walled CNTs to study the impact of irreversibility on the micropolar nanofluid flow through a squeezing channel with the base fluid blood. The blood is considered a micropolar fluid in the presence of different blood cells and their rotational nature. Further, blood is influenced by the external magnetic field parallel to the microrotation along with viscous and Joule dissipations. MethodHighly coupled and nonlinear partial differential equations are solved with Homotopy Analysis Method (HAM) after simplified equations using similarity transformation. Further, we have concluded the minimum squared residual errors to show the method's accuracy. A comparison made with the existing literature and shows a good agreement. ResultsThe angular velocity of the fluid particles is enhanced by increasing the squeezing number. In the case of the squeezing, volume fraction has improved the viscous drag and is found high for MWCNT embedded nanofluid. The heat transfer rate is higher for the MWCNT embedded nanofluid than the SWCNT embedded nanofluid. A descent found in entropy generation boosts up with the Brinkman parameter while opposite phenomena appear for radiation and Hartman number and vortex viscosity. Both Bejan number and entropy generation profiles are restricted with an increase in vortex viscosity. ConclusionSWCNTs are showed to be more effective and efficient than the MWCNTs in elevating velocity, temperature and irreversibility of the system. Outcomes of this problem will help to understand the implementation of the drug carrier and irreversibility phenomena during drug delivery.

Multiscale magnetic field structures in an expanding elongated plasma cloud with hot electrons subject to an external magnetic field

We carry out three-dimensional and two-dimensional particle-in-cell simulations of the expansion of a magnetized plasma that initially uniformly fills a half-space and contains a semicylindrical region of heated electrons elongated along the surface of the plasma boundary. This geometry is related, for instance, to ablation of a plane target by a femtosecond laser beam under quasi-cylindrical focusing. We find that a decay of the inhomogeneous plasma–vacuum discontinuity is strongly affected by an external magnetic field parallel to its boundary. We observe various transient phenomena, including an anisotropic scattering of electrons and an accompanying Weibel instability, and reveal various spatial structures of the arising magnetic field and current, including multiple flying-apart filaments of a Z-pinch type and slowly evolving current sheets with different orientations. The magnitude of the self-generated magnetic field can be of the order of, or significantly exceed that of, the external one. Such phenomena are expected in the laser and cosmic plasmas, including the explosive processes in the planetary magnetospheres and stellar coronal arches.

Rashba effect in a quantum dot subject to a parabolic confining potential and external fields

The Rashba effect has been investigated in a spherical quantum dot confined by a radial parabolic potential. Also, external parallel magnetic and electric fields have been applied. The solution of the Schrödinger equation in the presence of the Rashba interactions has been derived by applying an approach that differs from the one used in an earlier treatment. The wave function in the presence of these interactions has been expanded in terms of the eigenfunctions of the Hamiltonian in their absence. In our opinion, the form introduced for the wave function presents the exact solution in a more accurate manner. The coefficients of expansion have been chosen either to depend on the three quantum numbers involved or on the principal quantum number only. The results have shown that the Rashba interactions have a considerable effect on the electron energy levels and on their splitting. The variation of this effect with the applied fields and the Rashba coupling strength has been investigated.Graphical abstract

Numerical simulation of unsteady ethylene glycol/CNTs micropolar nanofluid flow through a squeezing channel: An approach to industrial applications

AbstractThe impressive high thermal conductivity and low weight allow the carbon nanotubes (CNTs) to improve heat dissipation and cooling. In the present problem, we aim to analyze the CNTs embedded micropolar nanofluid flow between two parallel stretching sheets with the base fluid ethylene glycol (EG) which is effectively used as antifreeze and coolant. Both single‐walled carbon nanotubes and multiwalled carbon nanotubes (MWCNTs) are considered. The fluid is influenced by the external magnetic field parallel to the microrotation along with viscous and Joule dissipations. The flow and heat equations are converted to a set of coupled ordinary differential equations with the aid of similarity transformations. Due to the nonexistence of the closed‐form solution, we have developed the analytical approximate solution by homotopy analysis method using the polynomial base function. Furthermore, we have used the most efficient Runge–Kutta integration scheme of the fourth order associated with shooting technique to solve the system of equations. Results are exhibited graphically for various physical parameters and also found a good agreement with earlier work. From the results, we noticed that squeezing increases the angular velocity of the fluid particles. Also, in the case of squeezing, the volume fraction has enhanced the viscous drag and was found high for MWCNT–EG nanofluid.

Magnetic order and magnetic properties of the oxygen deficient SmBaMn2O5 layered perovskite

Magnetism in SmBaMn2O5 was investigated on a single crystal by magnetic and neutron diffraction measurements. This is an oxygen deficient perovskite with a layered ordering of Sm and Ba cations. Mn atoms are coordinated with five oxygens forming a square pyramid and they are ordered in a checkerboard pattern of expanded-compressed pyramids in the ab-plane. The neutron diffraction study revealed a ferrimagnetic ordering of Mn moments below TN=134 K. Macroscopic measurements reveal a very anisotropic behavior. Measurements with the external magnetic field parallel (M||c) and perpendicular (M⊥c) to the c-axis confirm that this is the easy axis above 10 K. Below this temperature, the Sm sublattice begins to polarize and the magnetization M||c decreases while M⊥c experiences a huge increase. This indicates that Sm moments begin to order around 10 K in the ab-plane with a minor component on the c-axis that opposes the overall magnetization from Mn sublattices.

Wake formation behind Langmuir probes in ionospheric plasmas

• A significant wake is formed behind thin cylindrical Langmuir probes. • Thin Langmuir probes ought to be at least ∼15 Debye lengths apart to not interfere. • An external magnetic field enhances and skews the wake behind a thin probe. This paper presents a simulation study of the wake formation behind a Langmuir probe thinner than the Debye Length in the space environments such as the ionosphere’s F region. We find that the wakes formed in plasma density and electric potential behind the positively biased probe can extend up to 15 Debye lengths in the subsonic plasma flow. Higher electric bias and flow velocity can further enhance the plasma wake perturbations. With an external magnetic field parallel to the object’s axis, the plasma wake becomes asymmetric and more extensive than for the unmagnetized case. The wing structures in the electron and ion densities are also observed along the background magnetic field in the case of subsonic plasma flow. The quantitative results in this paper may provide a practical reference for data processing and the future design of the Langmuir probe instrument flying in the F region on such as sounding rockets and low Earth orbit (LEO) satellite missions. In particular, since the Langmuir probe instrument may comprise two or more biased Debye-scale Langmuir probes, the plasma wake formed behind a single probe may influence the measurements from other instruments onboard.

Magnetic properties of chiral EuIr2P2

We present a minimal model that provides a description of the magnetic and thermodynamic properties of \Eu. The model contains two exchange coupling parameters, which are calculated using Density Functional Theory, and a local easy axis magnetic anisotropy term. The classical ground state of the system is a generalization of the well known 120$^\circ$ structure observed in triangular antiferromagnets. Monte Carlo simulations show two phase transitions as a function of the temperature. With increasing temperature, the system transitions from the ground state into a high-entropy collinear antiferromagnet, which in turn at higher temperatures presents a second order transition to a paramagnetic state. A high enough external magnetic field parallel to the anisotropy axis produces a spin-flop transition at low temperatures. The field also reduces the temperature range of stability of the collinear antiferromagnet phase and leads to a single phase transition as a function of the temperature. The reported behavior of the specific heat, the magnetization, and the magnetic susceptibility is in agreement with the available experimental data. Finally, we present the magnetic phase diagrams for magnetic fields parallel and perpendicular to the easy axis.

Thermo-Magneto-Electric Transport through a Torsion Dislocation in a Type I Weyl Semimetal

Herein, we study electronic and thermoelectric transport in a type I Weyl semimetal nanojunction, with a torsional dislocation defect, in the presence of an external magnetic field parallel to the dislocation axis. The defect is modeled in a cylindrical geometry, as a combination of a gauge field accounting for torsional strain and a delta-potential barrier for the lattice mismatch effect. In the Landauer formalism, we find that due to the combination of strain and magnetic field, the electric current exhibits chiral valley-polarization, and the conductance displays the signature of Landau levels. We also compute the thermal transport coefficients, where a high thermopower and a large figure of merit are predicted for the junction.

Enhanced Spin Accumulation in Semiconductor at Room Temperature Using Ni0.65Zn0.35Fe2O4(NZFO) as Spin Injector in NZFO/MgO/p-Si Device

In this article, the fabrication of a Ni0.65Zn0.35Fe2O4/MgO/p-Si heterostructure device has been optimized using the pulsed laser deposition (PLD) technique, and a detailed investigation of its structural, electrical, and magnetic features has been performed experimentally. The electronic and magneto-transport characteristics have been explored in the temperature range of 100–300 K. The current-voltage (I-V) characteristics of the heterojunction have been recorded, which displayed an excellent rectifying magnetic tunnel diode-like behavior throughout that temperature regime. The application of an external magnetic field parallel to the plane of the NZFO film causes the current (I) across the junction to decrease, clearly indicating positive junction magnetoresistance (JMR) of the heterostructure. The root of displaying positive magnetoresistance in our heterojunction has been well justified using the standard spin injection model. The electrical injection of spin-polarized carriers and its accumulation and detection in a p-Si channel have been demonstrated using the NZFO/MgO tunnel contact using a three-terminal (3-T) Hanle device. The parameters such as spin lifetime (99 ps), spin diffusion length (276 nm), and spin polarization (0.44) have been estimated from the Hanle curve detected in our heterostructure at room temperature, making the Ni0.65Zn0.35Fe2O4/MgO/p-Si device a very favorable promising junction structure in the field of spintronics for several device appliances in the future.

Spin-transfer torque driven localized spin excitations in the presence of field-like torque

We study the existence of localized one-spin excitation in the Heisenberg one- dimensional ferromagnetic spin chain in the presence of perpendicular and parallel external magnetic fields and current with spin-transfer torque and field-like torque. The Landau–Lifshitz–Gilbert–Slonczewski (LLGS) equation is exactly solved for the one spin excitation in the absence of onsite anisotropy for the excitations of spin with fields perpendicular and parallel to the chain. We show the removal of damping in the spin excitations by appropriately introducing current and also the enhancement of angular frequency of the oscillations due to field-like torque in the case of both perpendicular and parallel field. The exactness of the analytical results is verified by matching with numerical counterparts. Further, we numerically confirm the existence of in-phase and anti-phase stable synchronized oscillations for two spin-excitations in the presence of current with perpendicular field and field-like torque. We also show that the one-spin excitation is stable against thermal noise and gets only slightly modified against thermal fluctuations.

Chiral symmetry restoration and deconfinement in the contact interaction model of quarks with parallel electric and magnetic fields

We study the impact of steady, homogeneous, and external parallel electric and magnetic field strengths ( ) on the chiral symmetry breaking-restoration and confinement-deconfinement phase transition. We also sketch the phase diagram of quantum chromodynamics (QCD) at a finite temperature T and in the presence of background fields. The unified formalism for this study is based on the Schwinger-Dyson equations, symmetry preserving vector-vector contact interaction model of quarks, and an optimal time regularization scheme. At , in the purely magnetic case (i.e., ), we observe the well-known magnetic catalysis effect. However, in a pure electric field background ( ), the electric field tends to restore the chiral symmetry and deconfinement above the pseudo-critical electric field . In the presence of both and , we determine the magnetic catalysis effect in the particular region where dominates over , whereas we observe the chiral inhibition (or electric chiral rotation) effect when overshadows eB. At finite T, in the pure electric field case, the phenomenon of inverse electric catalysis appears to exist in the proposed model. Conversely, for a pure magnetic field background, we observe the magnetic catalysis effect in the mean-field approximation and inverse magnetic catalysis with -dependent coupling. The combined effects of and on the pseudo-critical yields an inverse electromagnetic catalysis, with and without an -dependent effective coupling of the model. The findings of this study agree well with the already predicted results obtained via lattice simulations and other reliable effective models of QCD.

Oscillating Magnetohydrodynamic Stokes Flow between Porous Plates with Spatiotemporally Periodic Reabsorption

The study addresses the oscillating magnetohydrodynamic (MHD) Stokes flow between two parallel plates with periodic reabsorption both spatially and temporally. Two cases are distinguished by applying either (1) transverse or (2) parallel external magnetic field. Analytical solutions of velocity and pressure are derived for both cases and the effect of Womersley and Hartmann number, and the absorption coefficient is examined. The study generalizes existing literature on analytic MHD Stokes flow solutions accounting for periodic boundary conditions both in time and space. The non-oscillating non-MHD Stokes flow in a porous channel (available in the literature) is proven to be a limit of the analytic solution introduced here. The MHD effects are noticeable in flows oscillating with low or moderate frequency but are barely detectable in high-frequency flows even in the presence of strong magnetic fields.

Effects of parallel electric and magnetic fields on Rydberg excitons in buckled two-dimensional materials

We study direct and indirect magnetoexcitons in Rydberg states in monolayers and double-layer heterostructures of Xenes (silicene, germanene, and stanene) in external parallel electric and magnetic fields, applied perpendicular to the monolayer and heterostructure. We calculate binding energies of magnetoexcitons for the Rydberg states 1$s$, 2$s$, 3$s$, and 4$s$, by numerical integration of the Schr\"{o}dinger equation using the Rytova-Keldysh potential for direct magnetoexciton and both the Rytova-Keldysh and Coulomb potentials for indirect excitons. Latter allows understanding a role of screening in Xenes. In the external perpendicular electric field, the buckled structure of the Xene monolayers leads to appearance of potential difference between sublattices allowing to tune electron and hole masses and, therefore, the binding energies and diamagnetic coefficients (DMCs) of magnetoexcitons. We report the energy contribution from electric and magnetic fields to the binding energies and DMCs. The tunability of the energy contribution of direct and indirect magnetoexcitons by electric and magnetic fields is demonstrated. It is also shown that DMCs of direct excitons can be tuned by the electric field, and the DMCs of indirect magnetoexcitons can be tuned by the electric field and manipulated by the number of h-BN layers. Therefore, these allowing the possibility of electronic devices design that can be controlled by external electric and magnetic fields and the number of h-BN layers. The calculations of the binding energies and DMCs of magnetoexcitons in Xenes monolayers and heterostructures are novel and can be compared with the experimental results when they will be available.