Presence Of High Magnetic Field Research Articles

Pronounced modification of the wetting and spreading behavior of molten Ag-Cu alloy on TC4 substrate in response to high magnetic fields

This study investigated the wetting of TC4 substrate by molten Ag-Cu alloy under various high magnetic fields (HMFs) during the heating process. By examining changes in melt morphology, variations in contact angle, and characterizing the interface microstructure, we elucidated the underlying mechanism through which HMFs affected wetting behavior. The findings suggest that higher magnetic flux density resulted in smaller contact angles and more extensive spreading at the same temperature, culminating in a greater final spreading diameter. However, there was no significant difference in the final contact angle under various HMFs. Moreover, higher magnetic flux density resulted in a longer precursor zone and thicker reaction layer. The composition of precursor zones and reaction layers remained consistent with and without an HMF. The spreading process was divided into two stages regardless of the presence or absence of an HMF. In the absence of an HMF, the sluggish formation and spreading of precursor zone led to a lower spreading rate in the first spreading stage. Subsequently, as temperature rose, interface reactions drove rapid melt spreading, accelerating the spreading rate during the second spreading stage. In the presence of HMFs, the strong thermo-electromagnetic convection within melt and at liquid/solid interface notably promoted interface reactions and rapid formation of precursor zones, leading to a substantially heightened spreading rate in the first spreading stage. The slowing reaction rate and the limited volume of the melt collectively resulted in a slower spreading rate in the second spreading stage. This study provides new insights into modifying reactive wetting, with potential applications in advanced brazing techniques.

Transport theory and the founding of condensed matter physics

In 1966, Woon Siong Gan coined and invented the name transport theory in condensed matter physics. Today, transport theory is the backbone theory of condensed matter physics and the whole condensed matter physics can be represented by transport theory. His PhD thesis pioneered the application of statistical mechanics to ultrasound propagation in semiconductor in the presence of high magnetic fields and low temperatures with the phase transition from the spherical energy surface of metal to the warped energy surface of semiconductor. The usual treatment is using the many-body theory of quantum field theory. Phase transition is an important topic in condensed matter physics. Thus, his PhD thesis also played a role in the founding of condensed matter physics. In this paper, transport theory is applied to phase transition, an important topic in condensed matter physics. The advantages of using transport theory is its broad coverage of both particles interaction and description of the singularity characteristics of phase transition. An example for illustration is that of magnetization which has Ising model describing spins interaction and the Lee Yang theory describing the singularity behavior of the partition function at the critical point of phase transition.

Hydromagnetic Non-Newtonian Fluid Flow in a Convergent Conduit

In the present study, a hydromagnetic non-Newtonian (dilatant) fluid flow in a convergent conduit, in the presence of a variable transverse magnetic field, has been investigated. The governing nonlinear partial differential equations are reduced to system of ordinary differential equations. These equations are solved numerically by the collocation method and implemented in MATLAB. The study determines the flow profiles and the impact of the flow parameters on the flow variables. Joule heating, variable viscosity, viscous dissipation, skin friction, the rate of heat transfer, and the induced magnetic field are taken into account. The obtained results are presented graphically and the impact of varying flow parameters on the skin friction coefficient and the Nusselt number is presented in tabular form. These results indicate that an increase in the Reynolds number, Eckert’s number, and the Joule heating parameter increases the fluid’s velocity, while an increase in the Hartmann number and the unsteadiness parameter decreases the convective heat transfer and the fluid’s velocity. Further, the skin friction coefficient decreases with increase in the Reynolds number, the Hartmann number, and the Joule heating parameter. Therefore, a less viscous fluid is appropriate to facilitate the fluid’s motion, but the presence of high magnetic field reduces the fluid’s motion.

Effects of Gradient Magnetic Field on Charge Behavior and Electrical Tree Growth in Epoxy Resin

In this paper, a high-field magnet experimental system is setup to investigate the dielectric properties of epoxy resin in the presence of high magnetic field. An asymmetric ferromagnetic electrode system is used to build gradient magnetic field and investigate its effect on tree characteristics of epoxy resin. Influence mechanisms of gradient magnetic field on dielectric properties and tree characteristics of epoxy resin are discussed through combining experimental results and simulation calculation. Experimental results show that electrical trees are more easily to be initiated and spread more rapidly in gradient magnetic field. The conductivity of the epoxy resin increases with the increase of magnetic field strength due to energy level splitting, which is analyzed through electrodynamics calculation. The relative permittivity decreases, and the dielectric loss tangents increase when high magnetic field is applied. Changes of conductivity and relative permittivity affect the charge behavior and electric field distribution in epoxy resin, resulting in the particular electrical tree.

Magneto-Optical Properties of Tri-Layer Graphene Measured via Terahertz Time Domain Spectroscopy

We present an experimental study on terahertz (THz) magneto-optical (MO) properties of tri-layer graphene on quartz substrate, grown by chemical vapor deposition. The MO conductivities are measured in the Faraday geometry by applying optical polarization and using THz time domain spectroscopy (TDS) in high magnetic fields at liquid nitrogen temperature. We find that the real and imaginary parts of the longitudinal and transverse MO conductivities fit well to the classic MO Drude formula for tri-layer graphene. Thus, we are able to determine optically the key sample parameters such as the electron density, the electron effective mass and the relaxation time for tri-layer graphene. The dependence of the relaxation time on magnetic field is examined. This work indicates that THz TDS can be employed as a powerful tool to measure MO properties of tri-layer graphene and other 2D electronic materials in the presence of high magnetic fields.

Masses and decay widths of charmonium states in the presence of strong magnetic fields

The masses and decay widths of charmonium states are studied in the presence of strong magnetic fields. The mixing between the pseudoscalar and vector charmonium states at rest is observed to lead to appreciable negative (positive) shifts in the masses of the pseudoscalar (longitudinal component of the vector) charmonium states in vacuum/hadronic medium in the presence of high magnetic fields. The pseudoscalar and vector charmonium masses in the hadronic medium, calculated in an effective chiral model from the medium changes of a scalar dilaton field, have additional significant modifications due to the mixing effects. The masses of the $D$ and $\bar D$ mesons in the magnetized hadronic matter are calculated within the chiral effective model. The partial decay widths of the vector charmonium state to $D\bar D$ are computed using a field theoretical model for composite hadrons with quark/antiquark constituents, and are compared to the decay widths calculated using an effective hadronic Lagrangian. The effects of the mixing are observed to lead to significant contributions to the masses of the pseusoscalar and vector charmonium states, and an appreciable increase in the decay width $\psi(3770) \rightarrow D\bar D$ at large values of the magnetic fields. These studies of the charmonium states in strong magnetic fields should have observable consequences on the dilepton spectra, as well as on the production of the open charm mesons and the charmonium states in ultra relativistic heavy ion collision experiments.

The accelerating nanoscale Kirkendall effect in Co films–native oxide Si (100) system induced by high magnetic fields

The morphology evolution and magnetic properties of Co films–native oxide Si (100) were investigated at 873, 973, and 1073 K in a high magnetic field of 11.5 T. Formation of Kirkendall voids in the Co films was found to cause morphology evolution due to the difference in diffusion flux of Co and Si atoms through the native oxide layer. The high magnetic fields had considerable effect on the morphology evolution by accelerating nanoscale Kirkendall effect. The diffusion mechanism in the presence of high magnetic fields was given to explain the increase of diffusion coefficient. The morphology evolution of Co films on native oxide Si (100) under high magnetic fields during annealing resulted in the magnetic properties variation.

Scanning tunneling microscopy study of the quasicrystalline 30° twisted bilayer graphene

Twisted bilayer graphene with a twist angle of exactly 30° (30°-TBG) is a unique two-dimensional (2D) van der Waals (vdW) system because of its quasicrystalline nature. Here we report, for the first time, scanning tunneling microscopy (STM) measurements of the quasicrystalline 30°-TBG that was obtained in a controllable way by using transfer-assisted fabrication of a pair of graphene sheets. The quasicrystalline order of the 30°-TBG, showing a 12-fold rotational symmetry, was directly visualized in atomic-resolved STM images. In the presence of high magnetic fields, we observed Landau quantization of massless Dirac fermions, demonstrating that the studied 30°-TBG is a relativistic Dirac fermion quasicrystal. Because of a finite interlayer coupling between the adjacent two layers of the 30°-TBG, a suppression of density-of-state (DOS) at the crossing point between the original and mirrored Dirac cones was observed. Moreover, our measurements also observe strong intervalley scattering in the defect-free quasicrystal, indicating that the electronic properties of the 30°-TBG should be quite different from that of its component: the graphene monolayer.

MHD and heat transfer analyses of a fluid flow through scraped surface heat exchanger by analytical solver

Scraped surface heat exchangers (SSHEs) diversely used in various industries for different settings when continuous processing of fluid and related material is required. In this work, heat transfer for steady incompressible flow of a Newtonian fluid in the presence of high magnetic field with temperature variant viscosity in a small gap of SSHE is studied for a fixed temperature difference narrow gaps between rotor and stator. The fluidic system is modeled mathematically in terms of PDEs for non-isothermal megnetohydrodynamic (MHD) flow with temperature dependent viscosity for linear blade shape. The solution of modeled PDEs are obtained analytically by exploiting the strength of Adomian decomposition method (ADM). The effects of different flow parameters of the systems are studied and their results are presented with analytical expressions and graphical illustrations.

High-Magnetic-Field Tunneling Spectra of ABC-Stacked Trilayer Graphene on Graphite.

ABC-stacked trilayer graphene (TLG) was predicted to exhibit novel many-body phenomena due to the existence of almost dispersionless flat bands near the charge neutrality point. Here, using high-magnetic-field scanning tunneling microscopy, we present Landau Level (LL) spectroscopy measurements of high-quality ABC-stacked TLG on graphite. We observe an approximately linear magnetic-field scaling of valley splitting and spin splitting in the ABC-stacked TLG. Our experiment indicates that the spin splitting decreases dramatically with increasing the LL index. When the lowest LL is partially filled, we find an obvious enhancement of the spin splitting, attributing to strong many-body effects. Moreover, we observe linear energy scaling of the inverse lifetime of quasiparticles, providing an additional evidence for the strong electron-electron interactions in the ABC-stacked TLG. These results imply that interesting broken-symmetry states and novel electron correlated effects could emerge in the ABC-stacked TLG in the presence of high magnetic fields.

Effect of magnetic polarity on surface roughness during magnetic field assisted EDM of tool steel

Electrical discharge machining (EDM) is one of the non-traditional machining techniques where the process offers wide range of parameters manipulation and machining applications. However, surface roughness, material removal rate, electrode wear and operation costs were among the topmost issue within this technique. Alteration of magnetic device around machining area offers exciting output to be investigated and the effects of magnetic polarity on EDM remain unacquainted. The aim of this research is to investigate the effect of magnetic polarity on surface roughness during magnetic field assisted electrical discharge machining (MFAEDM) on tool steel material (AISI 420 mod.) using graphite electrode. A Magnet with a force of 18 Tesla was applied to the EDM process at selected parameters. The sparks under magnetic field assisted EDM produced better surface finish than the normal conventional EDM process. At the presence of high magnetic field, the spark produced was squeezed and discharge craters generated on the machined surface was tiny and shallow. Correct magnetic polarity combination of MFAEDM process is highly useful to attain a high efficiency machining and improved quality of surface finish to meet the demand of modern industrial applications.

GEM detector performance with innovative micro-TPC readout in high magnetic field

Gas detector development is one of the pillars of the research in fundamental physics. Since several years, a new concept of detectors, called Micro Pattern Gas Detector (MPGD), allowed to overcome several problems related to other types of commonly used detectors, like drift chamber and micro strips detectors, reducing the rate of discharges and providing better radiation tolerance. Among the most used MPGDs are the Gas Electron Multipliers (GEMs). Invented by Sauli in 1997, nowadays GEMs have become an important reality for particle detectors in high energy physics. Commonly deployed as fast timing detectors and triggers, their fast response, high rate capability and high radiation hardness make them also suitable as tracking detectors. The readout scheme is one of the most important features in tracking technology. Analog readout based on the calculation of the center of gravity technique allows to overcome the limit imposed by digital pads, whose spatial resolution is limited by the pitch dimensions. However, the presence of high external magnetic fields can distort the electronic cloud and affect the performance. The development of the micro-TPC reconstruction method brings GEM detectors into a new prospective, improving significantly the spatial resolutionin presence of high magnetic fields. This innovative technique allows to reconstruct the 3-dimensional particle position, as Time Projection Chamber, but within a drift gap of a few millimeters. In these report, the charge centroid and micro-TPC methods are described in details. We discuss the results of several test beams performed with planar chambers in magnetic field. These results are one of the first developments of micro-TPC technique for GEM detectors, which allows to reach unprecedented performance in a high magnetic field of 1 T.

Supercurrent Interference in Few-Mode Nanowire Josephson Junctions.

Junctions created by coupling two superconductors via a semiconductor nanowire in the presence of high magnetic fields are the basis for the potential detection, fusion, and braiding of Majorana bound states. We study NbTiN/InSb nanowire/NbTiN Josephson junctions and find that the dependence of the critical current on the magnetic field exhibits gate-tunable nodes. This is in contrast with a well-known Fraunhofer effect, under which critical current nodes form a regular pattern with a period fixed by the junction area. Based on a realistic numerical model we conclude that the Zeeman effect induced by the magnetic field and the spin-orbit interaction in the nanowire are insufficient to explain the observed evolution of the Josephson effect. We find the interference between the few occupied one-dimensional modes in the nanowire to be the dominant mechanism responsible for the critical current behavior. We also report a strong suppression of critical currents at finite magnetic fields that should be taken into account when designing circuits based on Majorana bound states.

The swimming polarity of multicellular magnetotactic prokaryotes can change during an isolation process employing magnets: evidence of a relation between swimming polarity and magnetic moment intensity.

Magnetotactic microorganisms are characterized by swimming in the direction of an applied magnetic field. In nature, two types of swimming polarity have been observed: north-seeking microorganisms that swim in the same direction as the magnetic field, and south-seeking microorganisms that swim in the opposite direction. The present work studies the reversal in the swimming polarity of the multicellular magnetotactic prokaryote Candidatus Magnetoglobus multicellularis following an isolation process using high magnetic fields from magnets. The proportion of north- and south-seeking organisms was counted as a function of the magnetic field intensity used during the isolation of the organisms from sediment. It was observed that the proportion of north-seeking organisms increased when the magnetic field was increased. The magnetic moment for north- and south-seeking populations was estimated using the U-turn method. The average magnetic moment was higher for north- than south-seeking organisms. The results suggest that the reversal of swimming polarity must occur during the isolation process in the presence of high magnetic fields and magnetic field gradients. It is shown for the first time that the swimming polarity reversal depends on the magnetic moment intensity of multicellular magnetotactic prokaryotes, and new studies must be undertaken to understand the role of magnetic moment polarity and oxygen gradients in determination of swimming polarity.

Enhanced magnetodielectric response in Dy modified NiCr2O4

The chemically synthesized high purity spinel NiCr2−xDyxO4 (x=0, 0.1) samples have been characterized using magnetic and dielectric measurements in presence of high magnetic field. Crystal and magnetic structure of the samples have been determined by analyzing neutron diffraction data recorded between temperature of 6K and 300K. NiCr2O4 crystallizes in tetragonal phase with the space group of I41/amd whereas NiCr1.9Dy0.1O4 crystallizes in the mixed phase of cubic (space group of Fd3¯m) and tetragonal phases at room temperature. An additional phase of DyCrO3 with orthorhombic structure has been found in the Dy doped compound. The lattice parameter a increases and the c decreases in tetragonal structure with the substitution of Dy in Cr site. Both the samples show superlattice reflection peak indicating the presence of long range AFM ordering (transverse component) below 40K. But the saturation magnetization slightly increases after Dy doping. An anomaly observed near Curie temperature in ε′ (T) of NiCr2O4 and NiCr1.9Dy0.1O4 demonstrates the contribution of coupling between ferroelectricity and ferrimagnetism in the compounds. A linear correlation between the difference in dielectric constant and the field dependent squared magnetization for both the samples has been observed. The spin–spin interactions are most likely responsible for the observed magnetodielectric (MD) effect due to the magnetodielectric hysteresis in both parent and doped samples. Interestingly the MD% is found to increase with Dy doping.

Interdiffusion and magnetic properties of Co/Cu/Co trilayers produced by high magnetic field annealing

The influence of interdiffusion on the magnetic properties of Co/Cu/Co trilayers after annealing in the presence of a strong magnetic field was investigated. The interdiffusion zone of films that were annealed at temperatures of 573 K and 773 K in the presence of high magnetic fields were not affected. However, the interdiffusion zone of films annealed at 673 K in the presence of a high magnetic field increased significantly due to phase transformation. Meanwhile, the high magnetic field has an influence on alloying process by affects the concentration distribution of Co and Cu across the interface because of magnetic force. The change in the interdiffusion, caused by high magnetic field annealing, decreased the content of the magnetic phase. This decreasing in the magnetic phase reduced the saturation magnetization. The coercivity decreases in the sample annealed at 673 K with a high magnetic field can result from not completely alloying compared with non-field case.

Effect of Fe on the Martensitic Transition, Magnetic and Magnetocaloric Properties in Ni-Mn-In Melt-spun Ribbons

The effect of Fe on the martensitic transitions, magnetic and inverse magnetocaloric effect in Ni47Mn40-xFexIn13 ribbons (x = 1, 2, 3 and 5) has been investigated. All the ribbon compositions under study have shown the presence of austenite phase at room temperature. The variation of martensitic transition with the increase in Fe-content is non-monotonic. The thermal hysteresis of the martensitic transition increased with the increase in Fe-content. The martensitic transitions shifted to lower temperatures in the presence of high magnetic fields. A maximum magnetic entropy change (∆SM) of 50 Jkg-1K-1 has been achieved in the Ni47Mn38Fe2In13 (x = 1) ribbon at 282 K for an applied field of 5 T.

Direct imaging of topological edge states at a bilayer graphene domain wall.

The AB–BA domain wall in gapped graphene bilayers is a rare naked structure hosting topological electronic states. Although it has been extensively studied in theory, a direct imaging of its topological edge states is still missing. Here we image the topological edge states at the graphene bilayer domain wall by using scanning tunnelling microscope. The simultaneously obtained atomic-resolution images of the domain wall provide us unprecedented opportunities to measure the spatially varying edge states within it. The one-dimensional conducting channels are observed to be mainly located around the two edges of the domain wall, which is reproduced quite well by our theoretical calculations. Our experiment further demonstrates that the one-dimensional topological states are quite robust even in the presence of high magnetic fields. The result reported here may raise hopes of graphene-based electronics with ultra-low dissipation.

The space velocities of radio pulsars

Known models proposed to explain the high space velocities of pulsars based on asymmetry of the transport coefficients of different sorts of neutrinos or electromagnetic radiation can be efficient only in the presence of high magnetic fields (to 1016 G) or short rotation periods for the neutron stars (of the order of 1 ms). This current study shows that the observed velocities are not correlated with either the pulsar periods or their surface magnetic fields. The initial rotation periods are estimated in a model for the magnetedipolar deceleration of their spin, assuming that the pulsar ages are equal to their kinematic ages. The initial period distribution is bimodal, with peaks at 5 ms and 0.5 s, and similar to the current distribution of periods. It is shown that asymmetry of the pulsar electromagnetic radiation is insufficient to give rise to additional acceleration of pulsars during their evolution after the supernova explosion that gave birth to them. The observations testify to deceleration of the motion, most likely due to the influence of the interstellar medium and interactions with nearby objects. The time scale for the exponential decrease in the magnetic field τD and in the angle between the rotation axis and magnetic moment τs are estimated, yielding τβ = 1.4 million years. The derived dependence of the transverse velocity of a pulsar on the angle between the line of sight and the rotation axis of the neutron star corresponds to the expected dependence for acceleration mechanisms associated with asymmetry of the radiation emitted by the two poles of the star.

Power distribution for the ATLAS LAr Trigger Digitizer Board

The R&D activity for the design of the power distribution section of the ATLAS Liquid Argon (LAr) Calorimeter Trigger Digitizer Board board (LTDB) is presented. Many aspects concerning the radiation hardness and the ability to operate Point-of-load converters also in presence of high magnetic fields are covered. Devices designed by CERN for experiments at LHC have been used and their capability for implementation in the LTDB has been exploited with the aim to have a power distribution section with the required performances.