Moderate Magnetic Field Research Articles

Magnetic segregation behaviors of a binary mixture in fluidized beds

In industrial processes, external energy fields are used to efficiently regulate the segregation behaviors of fluidized beds containing binary mixtures. We added a magnetic field force model to the discrete element method used to numerically investigate the segregation behaviors of binary component particles in magnetic field-fluidized beds. We explored the effects of magnetic field intensity, gradient, and superficial gas velocity on the extent of segregation. Bi-dispersed particles were separated under moderate magnetic field intensities, and segregation increased as the field intensity rose. However, if the field intensity became excessive, magnetic particles tended to agglomerate, reducing segregation. Thus, control of the magnetic field gradient within a certain range is key for effective particle segregation.

Robust Quantum Oscillation of Dirac Fermions in a Single-Defect Resonant Transistor.

The massless nature of Dirac Fermions produces large energy gaps between Landau levels (LLs), which is promising for topological devices. While the energy gap between the zeroth and first LLs reaches 36 meV in a magnetic field of 1 T in graphene, exploiting the quantum Hall effect at room temperature requires large magnetic fields (∼30 T) to overcome the energy level broadening induced by charge inhomogeneities in the device. Here, we report a way to use the robust quantum oscillations of Dirac Fermions in a single-defect resonant transistor, which is based on local tunneling through a thin (∼1.4 nm) hexagonal boron nitride (h-BN) between lattice-orientation-aligned graphene layers. A single point defect in the h-BN, selected by the orientation-tuned graphene layers, probes local LLs in its proximity, minimizing the energy broadening of the LLs by charge inhomogeneity at a moderate magnetic field and ambient conditions. Thus, the resonant tunneling between lattice-orientation-aligned graphene layers highlights the potential to spectroscopically locate the atomic defects in the h-BN, which contributes to the study on electrically tunable single photon source via defect states in h-BN.

Magnetic-field tuning of the spin dynamics in the magnetic topological insulators(MnBi2Te4)(Bi2Te3)n

We report a high frequency/high magnetic field electron spin resonance (HF-ESR) spectroscopy study in the sub-THz frequency domain of the two representatives of the family of magnetic topological insulators (MnBi$_{2}$Te$_{4}$)(Bi$_{2}$Te$_{3}$)$_{n}$ with $n = 0$ and 1. The HF-ESR measurements in the magnetically ordered state at a low temperature of $T = 4$ K combined with the calculations of the resonance modes showed that the spin dynamics in MnBi$_{\text{4}}$Te$_{\text{7}}$ is typical for an anisotropic easy-axis type ferromagnet (FM) whereas MnBi$_{\text{2}}$Te$_{\text{4}}$ demonstrates excitations of an anisotropic easy-axis type antiferromagnet (AFM). However, by applying the field stronger than a threshold value $\sim 6$ T we observed in MnBi$_{\text{2}}$Te$_{\text{4}}$ a crossover from the AFM resonance modes to the FM modes which properties are very similar to the ferromagnetic response of MnBi$_{\text{4}}$Te$_{\text{7}}$. We attribute this remarkably unusual effect unexpected for a canonical easy-axis AFM, which, additionally, can be accurately reproduced by numerical calculations of the excitation modes, to the closeness of the strength of the AFM exchange and magnetic anisotropy energies which appears to be a very specific feature of this compound. Our experimental data evidences that the spin dynamics of the magnetic building blocks of these compounds, the Mn-based septuple layers (SLs), is inherently ferromagnetic featuring persisting short-range FM correlations far above the magnetic ordering temperature as soon as the SLs get decoupled either by introducing a nonmagnetic quintuple interlayer, as in MnBi$_{\text{4}}$Te$_{\text{7}}$, or by applying a moderate magnetic field, as in MnBi$_{\text{2}}$Te$_{\text{4}}$, which may have an effect on the surface topological band structure of these compounds.

Sample formulations for dissolution dynamic nuclear polarization

Hyperpolarization by dissolution dynamic nuclear polarization (dDNP) can boost magnetic resonance sensitivity by several orders of magnitude. The method relies on the transfer of electron spin polarization to the surrounding nuclear spins in the solid-state at low temperatures and moderate magnetic fields. One critical aspect for the success of a dDNP experiment is the sample formulation. Sample formulations have continually evolved, from frozen glassy solutions to complex hybrid polarizing solids, enabling faster and more repeatable DNP, as well as new applications to molecular systems that could not have be addressed before. In this review, we present some of the most important scientific advances related to sample formulations with a historical perspective, from the invention of DNP until today.

Pemetaan batuan penyusun candi di bawah permukaan berdasarkan metode geomagnetik studi kasus: cagar budaya candi Songgiriti desa Songgokerto kecamatan Batu kota Batu

The geomagnetic method is often used in petroleum, geothermal and mineral exploration and can be applied to searching prospect archaeological objects (Siahaan, 2009). Several studies has been used the geomagnetic method to seek for archaeological objects by Ariani (2012) in Losari Temples and Sismanto et al (1997) in Kedulan Temple. In Batu City there is one of the cultural heritage that have not been intact called Songgoriti Temple. So, in this research we expected the existence of temple’s rocks using geomagnetic method. The de sign of the research using geomagnetic methods begins with the study of litera ture. This research was conducted with two methods there is calculating the val ue of the magnetic susceptibility of samples Temple’s rock using Bartington Susceptibility Meter MS2B and retrieving data field using the Proton magneto meter type ENVI SCINTREX. In the end of this research, we accepted the re sults of the two methods were compared to find out the site rock of temple. In magnetometer data analysis, data is processed using Magpick software, surfer 9.0 software and Mag2dc software. The results of the research show that a local magnetic field patterns of rocks in the area of cultural heritage Songgoriti Tem ple is divided into three parts namely high local magnetic field (yellow to red), the moderate local magnetic field (green to yellow) and low local magnetic field (blue). Furthermore based on five cross-sectional modeling using Mag2dc, we obtained the prediction the site of temple Songgoriti that is the sample number 1 found on the 2 position i.e at coordinates 49S 664547.5m 9130115m and coor dinate 49S 664585m 9130105m; sample number 3 found on the 2 position i.e at coordinates 49S 664583m 9130100m and coordinate 49S 664585m 9130100m; sample number 4 found on the 2 position i.e. at coordinates 49S 664577.5m 9130115m and coordinate 49S 664577.5m 9130110m; sample number 5 found on the 3 position i.e. at coordinates 49S 664566m 9130095m, coordinates 49S 664573m 9130095m and coordinate 49S 664582.5 m 9130095m; sample num ber 6 is found in 5 position i.e. at coordinates 49S 664545.5 m 9130110m, coordinates 49S 664550m 9130110m, coordinates 49S 664546m 9130105m, coordinates 49S 664565m 9130105m and coordinates 49S 664562.5 m 9130100m. For sample number 2 that is not found at all in the five models cross section. This may be caused by the value of the magnetic susceptibility sample number 2 is minor when compared to another samples that is 0.86 x 10-6 m3/kg

On the opportunity of Laser Plasma simulation of Plasma Jets formation in moderate magnetic fields ∼ kGs

Today a number of various experiments with Laser-Produced Plasmas (LPP), done at very-high Magnetic Fields (up to B0 > MG) are using to model the physics of Astrophysical and Space Jets, a various processes of their formation and possible long-range propagation at various angles S to magnetic fields. We discuss the opportunity and present the first results of new-type experiments on simulation of Jets with LPP at KI-1 facility of ILP, at moderate magnetic field ∼ kGs, oriented quasi-transverse (S ≍ 600) of LPP-blob expansion (with velocity V 0) relative to B 0. They were done on the base of all our preliminary studies, both at large-scale, high-vacuum chamber (0120 cm of KI-1) and others devices with LPP (oriented earlier at V0 transverse to B0, with $ = 900).

Spin polarized quantum oscillations in monolayer InSe induced by magnetic field

We study the quantum capacitance and the Landau levels (LLs) in n-type monolayer InSe subjected to a vertical magnetic field. Starting from a single band k⋅p Hamiltonian, we analytically obtain the LLs by solving the Hamiltonian and find that the LLs have a uniform distribution on the LL index and magnetic field, i.e., the equal LL spacings. Further, the LLs are fully spin polarized under moderate magnetic fields originating from the spin–orbit coupling and Zeeman splitting. The magneto-capacitance peaks show one-to-one correspondence to the LLs, resulting in a perfect square-wave-shaped spin polarization. Our results is useful to detect the effective mass and spin–orbit coupling parameters of n-type monolayer InSe and design spintronics devices based on it.

A 3D magnetohydrodynamic simulation of the propagation of a plasma plume transverse to applied magnetic field

We have carried out a 3D ideal-MHD (magnetohydrodynamic) simulation to study the evolution of a laser-generated plasma plume in a moderate external magnetic field (0.13 T) oriented perpendicular to the flow direction of the plasma plume. The simulation shows that the plasma plume pushes the external magnetic field lines outward in the direction of the expansion. This leads to the compression and bending of the magnetic field lines. The force resulting from the change in shape and the density of the magnetic field lines opposes the expansion of the plume. An elliptic layer of shocked plasma is formed at the plasma/external field interface leaving a cavity in the plume core due to the outward expansion and the inertia of the plume. As the plasma pressure drops due to expansion, the imbalance between the magnetic energy and the internal energy results in the collapse of the cavity. These observations have striking similarities with the observations of the experiments (Behera et al 2017 Phys. Plasmas 24 033511) performed recently to study the plasma plume expansion in the presence of an external transverse magnetic field. This similarity indicates that the physical mechanisms dominantly governing the plasma plume expansion in the moderate magnetic field are aptly described in the ideal MHD regime. The studies thus show that the laser-generated plasma plume can be utilized to carry out interesting experiments on MHD phenomena in a simple laboratory setup.

Novel static magnetic field effects on green chemistry biosynthesis of silver nanoparticles in Saccharomyces cerevisiae

The bacteriocidal properties of silver nanoparticles (AgNPs) depend on their average diameter (toxicity increases with decreasing diameter). In the present work, we describe novel green chemistry biosynthesis of AgNPs from AgNO3 added to cell-free culture medium of baker’s yeast, Saccharomyces cerevisiae, yielding nanoparticles in the range 11–25 nm. However, when yeast was grown in a moderate static magnetic field, AgNPs obtained from the resulting cell-free culture medium, were significantly smaller (2–12 nm) than those obtained without magnetic field. These latter nanoparticles were highly crystalline, stable and near-uniform shape. Furthermore, the antibacterial activity of AgNPs obtained from static magnetic fields were greater than those from control cultures. Static magnetic fields show a promising ability to generate biocidal nanoparticles via this novel green chemistry approach.

Collimated Bidirectional Propagating Spin Wave Generated by a Nonlocal Spin-Current Nano-oscillator

Pure spin currents, generated by nonlocal spin injection and spin-orbit effects, have been widely used to control magnetization reversal and dynamics by current without charge transfer and its side effects in the device's actual working region. Here we experimentally demonstrate that a single coherent spin-wave mode can be excited by the pure spin current in a nonlocal spin-injection spin-valve device. The microwave spectra show that the observed spin-wave frequency is higher than the ferromagnetic resonance frequency, and almost does not change with the excitation current at moderate magnetic fields, indicating that the observed dynamical mode is a linear propagating spin-wave mode. Furthermore, micromagnetic simulations based on our device geometry generally reproduce the experimentally observed field-dependent and current-dependent oscillation characteristics, and provide us with the additional spatial information that the spin-wave mode exhibits collimated and bidirectional propagation paths in the direction perpendicular to the applied magnetic field. Our simulation results also show that the current-local Oersted field in our nonlocal device is much smaller than in conventional nanocontact magnetic oscillators, and has a minimal impact on the spin-wave dynamics. A near-symmetrically-collimated and bidirectional propagating spin-wave beam with magnetic field--controllable beam direction and current-independent frequency, achieved in our demonstrated nonlocal spin-current nano-oscillator, can be used as a local spin-wave source for magnonic logic devices and can be used to build daisy-chaining oscillatory neural networks with mutual synchronization.

Mechanical design and analytic solution for unfolding deformation of locomotive ferromagnetic robots

Magnetically actuated robots are attracting much interest due to the advantages of fast response, remote manipulation and enabling operations in enclosed spaces. Recent advances in fabricating ferromagnetic polymeric matrices embedded with hard magnetic fillers provide routes to multimodal locomotion for soft-bodied robots. One limitation of these matrix-based robot designs is that it requires low volume fraction of hard magnetic fillers to achieve soft and compliant robot body such that moderate magnetic fields are sufficient for actuation. However, low volume fraction of functional magnetic fillers leads to magnetically weak soft robots that are difficult to actuate. Here, we propose a compliant and high-performance robot design operating at magnetic fields down to 1 mT by utilizing a high-quality ferromagnetic film and mechanics-guided three-dimensional (3D) assembly technique. A parylene coating is deposited to keep the assembled arch shape, allowing releasing and actuating the structure as a freestanding robot. The robot would unfold and fold periodically under cyclic magnetic fields, driving the robot in a desired direction. To illustrate the versatile applicability of this approach, robots in two different representative geometries are presented, one in traditional straight configuration and the other in serpentine configuration. Through theoretical analysis and finite element analysis, fundamental results are offered for the proposed robot design, including concise solutions to the unfolding deformation, the effects of coating thickness on spring back, the maximum strain in the hard ferromagnetic film and a comparison of unfolding deformation of both designs. The results clearly show the effect of geometry/material parameters, external magnetic field and prestrain in assembly process, providing essential design guidelines to compliant and fast-moving magnetic robots via the proposed method.

Magnetocatalysis: The Interplay between the Magnetic Field and Electrocatalysis

Magnetocatalysis: The Interplay between the Magnetic Field and Electrocatalysis

The ensemble of immobilized superparamagnetic nanoparticles: the role of the spatial distribution in the sample

ABSTRACT In this work, static, thermodynamic and magnetic properties of interacting superparamagnetic nanoparticles have been studied using theory and computer simulation. Two types of particles’ distributions in the sample have been considered: (a) at the nodes of the simple cubic lattice and (b) by the random way. It was assumed that the directions of the easy axes for all particles were parallel to each other and directed at an angle to the external magnetic field. The theoretical approach is based on the expanding of the Helmholtz free energy into the classical virial series up to the second virial coefficient. The analytical expressions of the Helmholtz free energy for both textures allow us to obtain theoretical predictions for the static magnetization and the isochoric heat capacity. These characteristics turned out in a good agreement with the Monte-Carlo simulation data in the broad range of considered system parameters. In a zero and moderate external magnetic fields, the new theory allows to describe the numerical calculations much more efficient than the ideal approximations, for which the interparticle dipole-dipole interactions were neglected.

Magnetized wake driven anomalous diffusion in complex plasma

Diffusion of a three-dimensional dust ensemble embedded in a flowing plasma in the presence of a moderate magnetic field is investigated using Langevin dynamics simulation. It is found that the asymmetric wake potential created due to streaming ions drive the dusty plasma from the subdiffusive to the superdiffusive regime. A novel wake dominant regime is identified that shows superdiffusive behavior for suitable adjustment of the magnetic field. The dependence of the cross field diffusion coefficient on the magnetic field exhibits three distinct behaviors characterized by (a) B2−3 for an ultra-low magnetic field and strongly correlated state, (b) B≃0.1 for a moderate magnetic field, and (c) classical B−2 for a relatively large magnetic field. Our analysis shows that the magnetic field is mediated via the streaming ions in regimes (a) and (b) of relatively low magnetic field where the dependence of the diffusion coefficient on the magnetic field is faster than the usual classical regime.

Collapse of turbulent massive cores with ambipolar diffusion and hybrid radiative transfer

Context.Massive stars form in magnetized and turbulent environments and are often located in stellar clusters. The accretion and outflows mechanisms associated with forming massive stars and the origin of the stellar multiplicity of their system are poorly understood.Aims.We study the effect of magnetic fields and turbulence on the accretion mechanism of massive protostars and their multiplicity. We also focus on disk formation as a prerequisite for outflow launching.Methods.We present a series of four radiation-magnetohydrodynamical simulations of the collapse of a massive magnetized, turbulent core of 100M⊙with the adaptive-mesh-refinement code RAMSES, including a hybrid radiative transfer method for stellar irradiation and ambipolar diffusion. We varied the Mach and Alfvénic Mach numbers to probe sub- and super-Alfvénic turbulence and sub- and supersonic turbulence regimes.Results.Sub-Alfvénic turbulence leads to single stellar systems, and super-Alfvénic turbulence leads to binary formation from disk fragmentation following the collision of spiral arms, with mass ratios of 1.1–1.6 and a separation of several hundred AU that increases with initial turbulent support and with time. In these runs, infalling gas reaches the individual disks through a transient circumbinary structure. Magnetically regulated, thermally dominated (plasma betaβ> 1) Keplerian disks form in all runs, with sizes 100–200 AU and masses 1–8M⊙. The disks around primary and secondary sink particles have similar properties. We obtain mass accretion rates of ~10−4M⊙yr−1onto the protostars and observe higher accretion rates onto the secondary stars than onto their primary star companion. The primary disk orientation is found to be set by the initial angular momentum carried by turbulence rather than by magnetic fields. Even without turbulence, axisymmetry and north–south symmetry with respect to the disk plane are broken by the interchange instability and thermally dominated streamers, respectively.Conclusions.Small (≲300 AU) massive protostellar disks such as those that are frequently observed today can so far only be reproduced in the presence of (moderate) magnetic fields with ambipolar diffusion, even in a turbulent medium. The interplay between magnetic fields and turbulence sets the multiplicity of stellar clusters. A plasma betaβ> 1 is a good indicator for distinguishing streamers and individual disks from their surroundings.

Modulation of uniform magnetic field on electron dynamics in low‐pressure capacitively coupled plasmas

AbstractThe electron dynamics in uniform magnetized capacitively coupled plasmas are investigated by using a one‐dimensional particle‐in‐cell simulation with a Monte Carlo collision model. It is found that the nonlinear dynamic behaviors of electrons are slightly modulated at weak magnetic fields, with more electron beams appearing during one sheath expansion. The electron beams are reversed before reaching the opposite electrode at moderate magnetic fields under the effect of Lorentz force. The discharge becomes very localized at very high magnetic fields, as the energetic electrons are confined in the vicinity of the sheath edge. The nonlocal to local transition of discharge characteristics is induced at different magnetic fields for various discharge frequencies. Generally, the discharge transition happens at stronger magnetic fields for high‐discharge frequencies. A quantitative relation between the discharge frequency and cyclotron frequency is given for the discharge transition.

Electrically driven cylindrical free shear flows under an axial uniform magnetic field

We consider a mathematical model of two-dimensional electrically driven laminar axisymmetric circular free shear flows in a cylindrical vessel under the action of an applied axial uniform magnetic field. The mathematical approach is based on the studies by J.C.R. Hunt and W.E. Williams (J. Fluid. Mech., 31, 705, 1968). We solve a system of stationary partial differential equations with two unknown functions of velocity and induced magnetic field. The flows are generated as a result of the interaction of the electric current injected into the liquid and the applied field using one or two pairs of concentric annular electrodes located apart on the end walls. Two lateral free shear layers and two Hartmann layers on the end walls and a quasi-potential flow core between them emerge when the Hartmann number Ha >> 1. As a result, almost all injected current passes through these layers. Depending on the direction of the current injection, coinciding or two counter flows between the end walls are realized. The Hartmann number varies in a range from 2 to 300. When a moderate magnetic field (Ha = 50) is reached, the flow rate and the induced magnetic field flux cease to depend on the magnitude of the applied field but depend on the injected electric current value. Increasing magnetic field leads only to inner restructuring of the flows. Redistributions of velocities and induced magnetic fields, electric current density versus Hartmann number are analyzed. Figs 18, Refs 21.

Expansion Tube Experiments of Magnetohydrodynamic Aerobraking for Superorbital Earth Reentry

A set of magnetohydrodynamic (MHD) aerobraking experiments was conducted with the aim of simulating the Earth reentry environment for Mars return trajectories, and to study the effects of MHD flow control on the ionizing shock layer surrounding a planetary entry vehicle. The X2 expansion tube of the University of Queensland was used, which could provide realistic flowfield boundary conditions, where ionization is spontaneously generated within the shock layer as in true flight and the freestream is nonconducting. Suitable flow conditions providing strong MHD interaction at superorbital Earth reentry velocities were developed. Steel ball and neodymium permanent magnet models were tested, both uncoated and coated with electrically insulating high-temperature epoxy. Shock-layer high-speed imaging showed a significant increase in shock standoff distance for the magnetic models. The experimental shock standoff results generally agreed well with analytical and numerical shock standoff predictions. These experiments demonstrate that a strong MHD interaction can be generated for a Mars return trajectory with moderate magnetic field strengths. Furthermore, they provide a promising framework for future MHD aerobraking experiments to investigate MHD drag force and heat-flux mitigation.

Effect of magnetic graphene oxide on cellular behaviors and osteogenesis under a moderate static magnetic field

The biological behaviors of magnetic graphene oxide (MGO) in a static magnetic field (SMF) are unknown. The current study is to investigate the cellular behaviors, osteogenesis and the mechanism in BMSCs treated with MGO combined with an SMF. Results showed that the synthetic MGO particles were bio-compatible and could significantly improve the osteogenesis of BMSCs under SMFs, as verified by elevated alkaline phosphatase activity, mineralized nodule formation, and expressions of mRNA and protein levels. Under SMF at the same intensity, the addition of graphene oxide to Fe3O4 could increase the osteogenic ability of BMSCs. The Wnt/β-catenin pathway was indicated to be related to the MGO-driven osteogenic behavior of the BMSCs under SMF. Taken together, our findings suggested that MGO under an SMF could promote osteogenesis in BMSCs through the Wnt/β-catenin pathway and hence should attract more attention for practical applications in bone tissue regeneration.

Mean-field theory of superradiant phase transition in complex networks.

In this work we consider a superradiant phase transition problem for the Dicke-Ising model, which generalizes the Dicke and Ising models for annealed complex networks presuming spin-spin interaction. The model accounts for the interaction between a spin-1/2 (two-level) system and external classical (magnetic) and quantized (transverse) fields. We examine regular, random, and scale-free network structures characterized by the δ function, random (Poisson), and power-law exponent [p(k)∝k^{-γ}] degree distributions, respectively. To describe paramagnetic (PM)-ferromagrenic (FM) and superradiant (SR) phase transitions we introduce two order parameters: the total weighted spin z component and the normalized transverse field amplitude, which correspond to the spontaneous magnetization in z and x directions, respectively. For the regular networks and vanishing external field we demonstrate that these phase transitions generally represent prerequisites for the crossover from a disordered spin state to the ordered one inherent to the FM and/or SR phase. Due to the interplay between the spin interaction and the finite-size effects in networks we elucidate novel features of the SR state in the presence of the PM-FM phase transition. In particular, we show that the critical temperature may be high enough and essentially depends on parameters which characterize statistical properties of the network structure. For the scale-free networks we demonstrate that the network architecture, characterized by the particular value of γ, plays a key role in the SR phase transition problem. Within the anomalous regime scale-free networks possess a strong effective spin-spin interaction supporting fully ordered FM state, which is practically nonsensitive to variations of the quantum transverse field or moderate classical magnetic field. In a scale-free regime the networks exhibit vanishing of the collective spin component in z direction with increasing γ accompanied by establishing spontaneous magnetization in the transverse field. The SR phase transition occurs in the presence of some FM state. We establish the conditions for the network parameters, classical and quantum field features to obtain a quantum phase transition in the spin system when the critical temperature approaches zero.