Presence Of External Magnetic Field Research Articles

Theoretical study of a tunable optical device on the base of magnetoactive cholesteric liquid crystals

We investigated the light reflection from half-space of cholesteric liquid crystal (CLC) being in external static magnetic field directed along the helix axis at normal light incidence. In this case there appear three photonic band gaps (PBGs) and these bands can be tuned in large intervals. We found the eigenpolarizations (EPs) at reflection of light from half-space and investigated their peculiarities. We have shown that in the absence both of absorption and of external magnetic field and at minimal influence of dielectric boundary (when the dielectric permittivity of isotropic half-space which borders with CLC half-space is equal to the CLC's mean dielectric permittivity) these polarizations are orthogonal. While, in the presence of external magnetic field they become quasi-orthogonal everywhere outside the main PBG (which exist also at the absence of external magnetic field), and they are significantly non-orthogonal within the main PBG. At some values of helix pitch they become significantly non-orthogonal practically everywhere. Moreover, in this case there exist some special points where the EPs degenerate. This system can apply as tunable narrow-band or broad-band filter and mirror, a highly tunable broad/narrow-band optical diode, and other devices.

Field-Induced Slow Magnetization Relaxation of a Tetrahedral S=2 FeIIS4-Containing Complex.

In the work described herein, the spin relaxation properties of the mononuclear tetrahedral S = 2 [Fe{(SPiPr2)2N}2] complex (1) were studied by employing static and dynamic magnetic measurements al liquid helium temperatures. In the absence of an external direct current (DC) magnetic field, 1 exhibits fast magnetization relaxation. However, in the presence of external magnetic fields of a few kOe, slow relaxation is induced as monitored by alternating current (AC) magnetic susceptibility measurements up to 10 kHz, in the temperature range 2-5 K. Analysis of the temperature dependence of the corresponding relaxation time reveals contributions by Quantum Tunnelling of Magnetization, and the Direct and Orbach processes in the magnetization relaxation mechanism of 1. The energy barrier, Ueff, of the Orbach process, as determined by this analysis, is compared with that related to the zero field splitting parameters of 1 which were previously determined by high- frequency and -field electron paramagnetic resonance and Mössbauer spectroscopies.

Geant4 simulation of secondary photons generated by laser–solid interaction in the presence of external magnetic field

A parametric study of the average energy and scattering angle distribution of Bremsstrahlung x-ray photons generated in over-dense fuel were investigated using the Geant4 simulation toolkit in fast ignition concept. In our simulation, over-dense fuel with the mass ρc∼(300−1000)g.cm−3, and fast ignitor with the intensity I=(1021,1023)W.cm−2 and wavelength λ=(0.35,0.53)μm were considered in the presence of an external magnetic field with the strength Bext=(0−10)kT. Further, for the produced MeV electrons in pre-plasma, two types of energy distribution functions, i.e., exponential and quasi two-temperature, were considered. The simulation results show that by applying an external magnetic field strength Bext∼(1−2)kT, a smooth increase was observed in the x-ray photon average energy and a considerable increase in scattering angle and photon counts in over-dense plasma obtained, so that the peak values mostly obtained for Bext∼1kT. Meanwhile, between the two energy distribution functions for electrons, the optimal average energy and scattering angle values were obtained by considering the quasi-two-temperature energy distribution function and for the fast igniter intensity and wavelength, I=1021W.cm−2,λ=0.35μm respectively, and the fuel density ρc∼300g.cm−3. Finally, regarding to the obtained optimal average photon energy (i.e., Ebph<0.4MeV), which could be considered as minimum photon energy loss and maximum electron penetration toward the fuel, the minimum thickness of lead and concrete shields required to reduce the flux of photons to its one-tenth value were found to be 1.5 cm and 30.7 cm, respectively.

A Numerical Study on the Influence of External Magnetic field on Hydrogen Electric Arc Flow

We present a 3D numerical model capable of simulating hydrogen electric arc. The numerical model couples the electromagnetic field with hydrogen plasma arc dynamics (flow and heat transfer). Electric arc operates under the conditions of atmospheric pressure using direct current (DC) in the presence of external magnetic field. It is found that arc instabilities emerge spontaneously near the cathode before propagating downwards along the arc jet. Also, spontaneous splitting into several arcs is observed before merging again into one arc. The horizontal magnetic field induces arc skewing and directional flow perpendicular to the applied magnetic field. However, the axial magnetic field induces a rotational flow and arc swirling.

Effect of the magnetic field on the conductance and spin polarization in phosphorene superlattice

The spin-dependent conductance and spin polarization are investigated theoretically in a phosphorene superlattice in the presence of external magnetic field and Rashba interaction. It is demonstrate that, the spin-dependent conductance with and without spin-flip as well as spin polarization can be effectively controlled by changing the magnetic field strength and the number of the superlattice barriers. For small magnetic field strength, the conductance for with and without spin-flip shows an oscillating behavior as increasing the strength of the Rashba interaction, and by increasing the number of barriers, the oscillating behavior becomes prominent. Further, when the magnetic field is greater than a limit value, the spin conductance will be zero. The size of the spin-dependent transmission window in the phosphorene superlattice under external magnetic field decreases drastically. The magnitude, sign and behavior of the spin polarization can be tuned by the amount of the external magnetic field.

The pool boiling heat transfer of ammonia/Fe3O4 nano-refrigerant in the presence of external magnetic field and heat flux: A molecular dynamics approach

Pool boiling is distinguished by its capacity to eliminate excessive heat fluxes (HFs) at low temperatures. In recent decades, the optimal design of flooded evaporators elevated the significance of pool boiling HT with refrigerant to conserve natural resources and energy. The industry highly regards this process on account of its superior heat transfer (HT) coefficient in comparison to other HT mechanisms. Among the types of boiling, pool boiling has a special place due to its ability to remove HFs at low temperatures. This study was the first to investigate the boiling characteristics of the ammonia/Fe3O4 nano-refrigerant in a copper (Cu) nanochannel (NC) through molecular dynamics (MD) simulations. The primary goal was to investigate the effect of external HF (EHF) and external magnetic field amplitude (EMFA) on nanostructures' atomic behavior (AB) and thermal behavior (TB). The research findings indicate that increasing the applied EHF led to increased particle movement and the HT rate. By changing the EHF, boiling behavior in the nano-refrigerant may also be seen. Maximum (Max) velocity (Vel.) increased to 8.970 Å/ps when the EHF increases to 0.5 W/m2. Atomic collisions and particle mobility both increase when the EHF increases. Therefore, the maximum temperature value increases to 359.46 K. When the EMFA applied to the nano-refrigerant reaches to 0.5 T, the maximum values of the parameters, such as the Temp. and the velocity, reach to 410.07 K, and 11.802 Å/ps, respectively.

Quantum transport of massless Dirac fermions through wormhole-shaped curved graphene in presence of constant axial magnetic flux

In this work, we have studied the spin-dependent quantum transport of charged fermion on (2+1)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$(2+1)$$\\end{document}-dimensional spacetime, whose spatial part is described by a wormhole-type geometry in the presence of constant axial magnetic flux. Choosing the solutions of the Dirac equation associated with real energy and momentum, we explored the spin-dependent transmission probabilities and giant magnetoresistance (GMR) through a single layer of wormhole graphene with an external magnetic field, using the transition matrix (T-Matrix) approach. The spin-up and spin-down components within the A and B sublattices of graphene in the matrix of 4×1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$4\ imes 1$$\\end{document} wave function are coupled to each other due to the wormhole structure and the magnetic field. We have found that transport properties strongly depend on the magnetic field, incident energy, and geometric parameters of the system. We observed that the transmission probability increases as the radius of the wormhole increases, and the length of the wormhole decreases. The higher energies lead to a decrease in the transmission probabilities of particles. Furthermore, we observed that the probability of the spin-flip effect is almost larger than that of the non-spin-flip effect, illustrating that electrons lose their spins during transmission. These findings highlight the complex and interesting behavior of wormhole graphene in the presence of external magnetic fields and suggest that these nano structures can have potential applications in electronic and spintronic devices.

Effect of dense plasma environment and external magnetic field on atomic structure and radiative properties of Ar XVII

Atomic structures and radiative properties of He like Ar XVII in the presence of dense plasma environments and external magnetic field have been presented within the framework of the relativistic theory. For this purpose, the relativistic configuration interaction method by incorporating the generalized b-potential and external magnetic field has been implemented. Plasma screening effect on 1s2 1S0 → 1s2p 3P1 transitions of Ar XVII ion in the presence of an external magnetic field has been investigated. We also studied the Zeeman splitted energies and predicted the excitation energies of Ar XVII ion for the magnetic sublevels 1s2p 3P0 (MJ = 0), 3P1 (MJ = 0, ±1), 3P2 (MJ = 0, ±1, ±2), 1P1 (MJ =0, ±1). Our calculated results are in excellent agreement with National Institute of Science and Technology (NIST) database and other theoretical available data.

A comparative study of extraordinary and ordinary modes in the presence of external magnetic field in self-focusing of higher-order mode TEM$$_{m,n}$$ of elegant Hermite–cosh-Gaussian laser beams in collisionless plasma medium

A comparative study of extraordinary and ordinary modes in the presence of external magnetic field in self-focusing of higher-order mode TEM$$_{m,n}$$ of elegant Hermite–cosh-Gaussian laser beams in collisionless plasma medium

Spatially structured optical effects via composite vortex light in a dielectric medium

In this letter, we have proposed a model for spatially structured transmitted and reflected lights from dielectric medium consists of four-level coherent system. An elliptically polarized probe field and a composite vortex light in the presence of external magnetic field are interacted by this medium. We have shown that by controlling the external magnetic field, ellipticity of the probe light and orbital angular momentum (OAM) of the composite vortex light, the transmitted and reflected lights can be controlled. We have also found that due to the spatial pattern of the composite vortex light, the spatially pattern light amplification can be obtained by adjusting the spatial control of the transmitted and reflected lights. In other word, by tuning the OAM number of the composite vortex light and external magnetic field, the spatial controlling of the transmitted and reflected lights are possible and this leads to controlling the high-gain spatially pattern regions.

Collisions and dynamics of particles with magnetic dipole moment and electric charge near magnetized rotating Kerr black holes

Analysis of test magnetized and charged particles around black holes immersed in external magnetic fields may help to explain the observed astrophysical phenomena related to black holes, such as the acceleration of particles up to high energies. In this sense, we studied the circular motion of test-charged particles with magnetic dipole orbiting around magnetized rotating Kerr black holes. First, we derive the effective potential for the circular motion of such particles, including interactions between the external magnetic field and the electric charge, and the magnetic interaction between the magnetic dipole. In addition, we analyze the angular momentum and energy of particles corresponding to circular orbits. The effects of magnetic interaction and coupling parameters on the position of innermost stable circular orbits (ISCOs), the energy and angular momentum of the particles at ISCO, and the energy efficiency from the Novikov-Thorne accretion disc have been investigated. We also find cases of degeneracy between magnetic dipole interaction and magnetic coupling parameters, giving the same ISCO radius. Finally, we studied various cases of collisions of neutral, magnetized, and electrically charged particles near rotating Kerr black holes in the presence of external magnetic fields. The critical angular momentum of spinning charged particles is found in which the particles can collide. We also analyze the effects of both magnetic interactions on the center-of-mass energy of the colliding particles.

Recent advances in magnetic nanomaterials in wastewater treatment: a review

Considering the scarcity of potable water, the search for an effective and easy purification technology has been of utmost importance. Conventional methods have not been able to match demands, which triggered the search for an advanced method based on nanotechnology that can fulfill the desired conditions. Magnetic nanomaterials are among the top runners owing to their unique ability to respond in the presence of an external magnetic field. Due to their small size, they can be easily functionalized and surface tuned for targeting specific ions and dyes. One of the biggest advantages of these materials is that they can be easily separated posttreatment. This review summarizes the latest developments in the field of magnetic nanomaterials in wastewater treatment.

Analytical calculation of beam profile and orbital angular momentum spectrum of Laguerre Gaussian beams reflected from a graphene plasmonic structure.

In this paper, Laguerre Gaussian (LG) beams with different topological charges are used for excitation of surface plasmon polaritons (SPPs) through a graphene layer inserted in the Otto-configuration. By utilizing the angular spectrum representation (ASR) and Lorenz-gauge vector potential, an explicit analytical expression is derived for the electromagnetic fields of the reflected beam. At the optimal excitation state of graphene SPPs, the reflected beam exhibits a distinctive field profile characterized by two identical crescent-shaped lobes separated by a vertical strip with null intensity. Furthermore, in the absence of external magnetic field, the orbital angular momentum (OAM) spectrum of the reflected beam at the optimal excitation of SPPs reveals the annihilation of central OAM mode and the generation of two equal OAM sidebands, regardless of the incident OAM topological charge. Furthermore, the phase distributions of electric field of the reflected beam confirm the existence of OAM sidebands in the vicinity of optimal SPPs excitation. As the system is taken away from the optimal excitation of SPPs by introduction of an external magnetic field or increasing the chemical potential or increasing the incident angle, both central and sideband modes appear in the OAM spectrum of the reflected beam. In this case, when the topological charge of the incident wave increases, the weight of central OAM mode decreases while the weight of sidebands increases. In contrast, in the presence of external magnetic field, at the optimal excitation of SPPs, both central OAM and sidebands modes exist in the reflected beam such that the weight of central modes increases with the external magnetic field. This effect is also confirmed by plotting the phase distributions of the reflected beam at different external magnetic fields and for different incident topological charges. Therefore, the manipulation of graphene plasmons characteristics leads to the control of OAM sideband generation.

Effects of velocity, thermal and concentration slips on the entropy generation of nanofluid over an inclined sheet

PurposeThis paper aims at studying numerically the entropy generation of nanofluid flowing over an inclined sheet in the presence of external magnetic field, heat source/sink, chemical reaction along with slip boundary conditions imposed on an impermeable wall.Design/methodology/approachA suitable similarity transformation technique has been used to convert the coupled nonlinear partial differential equations to ordinary differential equations (ODEs). The ODEs are then solved simultaneously using the finite difference method implemented through an in-house computer program. The effects of different controlling parameters such as magnetic parameter, radiation parameter, Brownian motion parameter, thermophoresis parameter, chemical reaction parameter, Reynolds number, Brinkmann number, Prandtl number, velocity slip parameter, temperature slip parameter and the concentration slip parameter on the entropy generation and Bejan number have been discussed comprehensively through the relevant physical insights for the first time.FindingsThe relative strengths of the irreversibilities due to heat transfer, fluid friction and the mass diffusion arising due to the change in each of the controlling variables have been delineated both in the near-wall and far-away-wall regions, which may be helpful for a better understanding of the thermo-fluid dynamics of nanofluid in boundary layer flows. The numerical results obtained from the present study have also been validated with results published in open literature.Originality/valueThe effects of different controlling parameters such as magnetic parameter, radiation parameter, Brownian motion parameter, thermophoresis parameter, chemical reaction parameter, Reynolds number, Brinkmann number, Prandtl number, velocity slip parameter, temperature slip parameter and the concentration slip parameter on the entropy generation and Bejan number have been discussed comprehensively through the relevant physical insights for the first time.

Electrophoretic propulsion of matchstick-shaped magnetodielectric particles in the presence of external magnetic fields in a nematic liquid crystal.

Synthesis of micro- and nanoparticles of pre-designed shape and surface properties is an integral part of soft and synthetic active matter. We report synthesis of matchstick-shaped (MS) magnetodielectric particles and demonstrate their potential as active agents with field-controllable trajectories in a nematic liquid crystal (NLC). The MS particles with homeotropic anchoring in NLCs align either parallel or perpendicular to the director depending on the dipolar or quadrupolar director distortions. When subjected to transverse electric and magnetic fields, the particles experience electric and magnetic torques trying to align them in the respective field directions. At equilibrium, the long axis is tilted at an angle with respect to the director. The change in orientation alters the surrounding elastic distortion, which results in unbalanced electroosmotic flows. These flows provide the necessary impetus for propelling the particles in various directions with different velocities depending on their orientations.

Quantum steering vs entanglement and extracting work in an anisotropic two-qubit Heisenberg model in presence of external magnetic fields with DM and KSEA interactions

We examine the Dzyaloshinski-Moriya (DM) and Kaplan-Shekhtman-Entin-Wohlman-Aharony (KSEA) interactions in thermal equilibrium submitted to the anisotropic Heisenberg two-qubit model in an inhomogeneous magnetic field. The steerability between the two qubits is evaluated using quantum steering. The concurrence serves as a witness to quantum entanglement. Both the extracted work and the ideal efficiency of the two qubits are quantified. We discuss how quantum correlations behave in relation to the bath's temperature, the Kaplan-Shekhtman-Entin-Wohlman-Aharony coupling parameter and DM coupling. We find that the nonclassical correlations in a two-qubit Heisenberg XYZ Model are fragile under thermal effects. Nevertheless, the results indicate that the concurrence is stronger than quantum steering under thermal effects in the presence of DM and KSEA. We obtained that an extraction of work is comparable with the bare energies.

External magnetic field: Enhancing electrochromic efficiency of magnetic metals composited WO3 films prepared by sparking method

This study investigated the impact of magnetic metals (Fe, Ni, and Co) composited WO3 films on the enhancement of electrochromic (EC) performance. These films were fabricated using a one-step sparking method with and without the presence of external magnetic fields (B). The FE-SEM images show that the fluffy morphology (without B) gradually shifts to form a denser surface (with B). This shift is most likely ascribed to the rearrangement of the deposited particles under the magnetic field, leading to an improvement in film reversibility. The Co/W nanocomposite films, among the tested films, exhibited the most significant enhancement, as demonstrated by their reversibility, which increased from 14.4 % (without B) to 73.3 % (with B), and coloration efficiency, which improved from 27.1 cm2/C (without B) to 131.3 cm2/C (with B). These improvements are crucial in the practical application of these materials. Moreover, a minimum resistivity of 0.45 × 10-3 Ωcm and a maximum mobility of 183.12 cm2/Vs were observed in this sample.Subsequently, the cobalt-composited tungsten oxide (CoW) films were deeply investigated in term of their morphological, structural, optical, and electrochromic properties under the influence of various magnetic fields at 0–500 mT, labeled as CoW without B, CoW-200, CoW-300, CoW-400, and CoW-500, respectively. Raman spectroscopy confirmed that the Co3O4 crystalline structure in the CoW-300 sample underwent transformation into a robust WO3 monoclinic phase in the CoW-400 sample. In addition, the XPS analysis of the CoW-400 sample revealed an oxygen vacancy peak, which facilitated electron transport and improved the conductivity. Finally, an excellent 176.0 cm2/C coloration efficiency and 87.2 % reversibility was obtained for the Co/W composite film prepared by the sparking method under a magnetic field of 400 mT, which is a potential material for electrochromic devices.

Charged particles motion and quasiperiodic oscillation in Simpson–Visser spacetime in the presence of external magnetic fields

The present work is devoted to the study of the dynamics of charged particles around Simpson–Visser black holes (with the length parameter lle 2) and wormholes (l>2) immersed in an external asymptotically uniform magnetic field. To do this, first, we solve the Maxwell equation for 4-potentials of the electromagnetic field and show that the difference between the numerical solution and Wald’s solution is small enough to neglect it, which may allow us to use the solution obtained by Wald. We also study fundamental frequencies of in the vertical and radial oscillations of charged particles around circular stable orbits around the magnetized black hole. The effects of the magnetic interaction and length parameters on the fundamental frequencies. We investigate the quasiperiodic oscillations (QPOs) around the black hole in relativistic precession and epicyclic resonance models. It is also shown that the combined effects of magnetic interaction for negatively charged particles and length parameters can mimic the spacetime effects of the Schwarzschild black hole compensating for their effects, as well as the spin of rotating Kerr black holes. The distance between an orbit where a QPO is generated with the ratio of upper and lower frequencies 3: 2 and innermost stable circular orbits is also studied. It is found that the QPO orbits are very close to ISCO in the RP model at l<2. This implies that the obtained result helps to determine the ISCO around black holes. We also study the applications of observed QPOs around stellar-mass black holes in microquasars and supermassive black holes.

Investigations on low temperature magnetic and magnetoelectric properties of multiferroic-NiO nanocomposites

Multiferroic BiFeO3-NiO (BFO-NiO) nanocomposites have been synthesized using sol-gel route and investigated via. the first principle DFT calculations, multiferroic-magnetoelectric response, and extremely low-temperature magnetic analysis. Powder X-ray diffraction (XRD) patterns along with Rietveld refinement data confirmed the phase purity viz. rhombohedral distorted perovskite BiFeO3- rock salt type NiO crystal structure and composite formation. Temperature dependent magnetic measurements confirmed the enhancement in the magnetism and the exchange bias effect due to the antiferromagnetic (AFM) and ferromagnetic (FM) exchange coupling interactions. Zero field cooled (ZFC) and field cooled (FC) magnetic results demonstrate the observation of typical superparamagnetic (SP) behavior for all the samples at room temperature whereas at low temperature a transition is reported from SP to quantum superparamagnetic (QSP) state through quantum tunneling of magnetic moment for all samples. Maximum polarization of 5.7μC/cm2 is observed for BFO-20% NiO composition. The noticeable change in the ferroelectric P vs E loops in the presence of external magnetic field confirm the evidence of multiferroic and magnetoelectric coupling behavior in the BFO-NiO nanocomposites. The DFT calculations have been done using WIEN2k software and found in well agreement with the reported experimental results. Further, the suitable temperature dependent magnetic squareness, evidence of considerable magnetoelectric coupling, exchange bias effect and SP nature make the BFO-NiO nanocomposites considerable suitable for various device applications such as information storage, magnetic random access memory, targeted drug delivery, magnetic resonance imaging (MRI), bio-sensing and tailoring other photocatalytic applications.

Anomalous absorption of p-polarised laser on metallic surface ingrained with noble-metal nanotubes in the presence of external magnetic field

Anomalous absorption of p-polarised laser on metallic surface ingrained with noble-metal nanotubes in the presence of external magnetic field