Pulsed Magnetic Field Research Articles

Изучение влияния слабых импульсов магнитного поля на локальные свойства ленточных аморфных сплавов Fe(Ni, Cu)(SiB)

Atomic force microscopy and magnetic force microscopy have been used to study the influence of weak magnetic field pulses on the local properties of ribbon amorphous Fe(Ni, Cu)(SiB) alloys about 100 µm thick, 10 mm wide, and 50 mm long, which were obtained by ultrafast cooling of the melt on a rotating copper drum. On the surface of the tape adjacent to the copper drum, there were practically no areas with low rough-ness, which did not allow subsequent studies of this side of the tape by magnetic force microscopy. This method was used to investigate another, free surface of the foil, which was not adjacent to the copper drum and did not have significant roughness. Prior to the impact of magnetic field pulses on the foil, no magnetic contrast was observed on the free side of the ribbon. After magnetic pulse processing, a magnetic contrast was registered on this side of the foil: stripe domains 0.6–0.8 μm wide became visible, and closing domains, became visible on structural defects, wedge-shaped Neel domains, from 1 µm to 1.6 µm wide. The results of the study allow us to say that the magnetization reversal losses are to a large extent associated with losses due to eddy currents and are associated with the domain width, which depends slightly on the modes of magnetic pulse processing. The obtained results of the research can be used to refine the method for relieving stresses arising in the process of manufacturing amorphous ribbons.

Enhanced Mechanical Properties of QAl9-4 Aluminum Bronze for High-Speed-Rail Brake Systems with a Pulsed Magnetic Field.

To improve the mechanical properties and wear resistance of QAl9-4 aluminum bronze alloy parts of high-speed rail brake calipers, the solid aluminum bronze alloy was treated with a pulsed magnetic field in which the magnetic induction intensity was 3T at room temperature. After that, a tensile test and a friction and wear test were carried out on the alloy. The results indicate that the magnetic field promotes the movement of low-angle grain boundaries less than 2° and splices to form subcrystals or fine crystals, which reduces the mean grain size of the alloy. The disordered dislocation changed into a locally ordered dislocation line, the dislocation distribution became uniform, and the dislocation density increased, which simultaneously improved the alloy's tensile strength and elongation. The elongation increased by 10.2% compared with that without the magnetic field. The increase in strength can provide strong support for the wear-resistant hard phase, and the enhancement of plasticity can increase the alloy's ability to absorb frictional vibration. Therefore, it was hard for cracks to form and extend, and the specimen's average friction coefficient was reduced by 22.05%. The grinding crack width and depth decreased, the wear debris became more uniform and fine, and the alloy's wear resistance increased.

A proposal for leaky integrate-and-fire neurons by domain walls in antiferromagnetic insulators

Brain-inspired neuromorphic computing is a promising path towards next generation analogue computers that are fundamentally different compared to the conventional von Neumann architecture. One model for neuromorphic computing that can mimic the human brain behavior are spiking neural networks (SNNs), of which one of the most successful is the leaky integrate-and-fire (LIF) model. Since conventional complementary metal-oxide-semiconductor (CMOS) devices are not meant for modelling neural networks and are energy inefficient in network applications, recently the focus shifted towards spintronic-based neural networks. In this work, using the advantage of antiferromagnetic insulators, we propose a non-volatile magnonic neuron that could be the building block of a LIF spiking neuronal network. In our proposal, an antiferromagnetic domain wall in the presence of a magnetic anisotropy gradient mimics a biological neuron with leaky, integrating, and firing properties. This single neuron is controlled by polarized antiferromagnetic magnons, activated by either a magnetic field pulse or a spin transfer torque mechanism, and has properties similar to biological neurons, namely latency, refraction, bursting and inhibition. We argue that this proposed single neuron, based on antiferromagnetic domain walls, is faster and has more functionalities compared to previously proposed neurons based on ferromagnetic systems.

Transient Magnetoelectric Coupling Induced by the Dynamic Intertwinement between Exchange Striction and Compensation in GdFeO3.

In this study, we investigate the dynamic magnetoelectric (ME) coupling behaviors of GdFeO3 under pulsed magnetic fields. When a magnetic field is applied along the c-axis, and the temperature is near the compensation temperature (Tcomp = 3.5 K), we observe a subtle transition involving the reversal of Fe3+ moments at approximately 0.8 T in magnetization (M) measurements. This transition induces a corresponding jump in electrical polarization (P), which is not present in the static field measurements. The dynamic intertwining between M and P signifies a competition between antiferromagnetic (AFM) coupling between Gd3+ and Fe3+ moments and their Zeeman energies. The robust AFM coupling leads to the reversal of Fe3+ moments near Tcomp, triggering the abrupt change in P. Based on the exchange striction mechanism in the ferrimagnetic GdFeO3, we propose the possibility of achieving highly magnetic field sensitive ME coupling near the compensation temperature in ferrimagnetic multiferroic orthoferrites.

Huge magnetostriction in superconducting single-crystalline BaFe1.908Ni0.092As2

The performance of iron-based superconductors in high magnetic fields plays an important role for their practical application. In this work, we measured the magnetostriction and magnetization of BaFe1.908Ni0.092As2 single crystals using pulsed magnetic fields up to 60 T and static magnetic fields up to 33 T, respectively. A huge longitudinal magnetostriction (of the order of 10–4) was observed in the direction of twin boundaries. The magnetization measurements evidence a high critical-current density due to strong bulk pinning. By using magnetization data with an exponential flux-pinning model, we can reproduce the magnetostriction curves qualitatively. This result shows that the magnetostriction of BaFe1.908Ni0.092As2 can be well explained by a flux-pinning-induced mechanism.

Reversible magnetic domain reorientation induced by magnetic field pulses of fixed direction

Reversible magnetic domain reorientation induced by magnetic field pulses of fixed direction

Pulse Field Magnetization (PFM) With Sectioned HTS Stacked Tape Structures for Electrical Machine

High temperature superconducting (HTS) stacks of superconducting tapes provide a solution for all-superconducting electrical machines since they could work as trapped-field magnets. Most experiments with these stacks use pieces of tapes with relatively small areas as wider tapes are more difficult to acquire, therefore in this paper we investigate substitutions for these wider tapes to be implemented in superconducting electrical machines. With different stack architectures and substrate materials made by SuperOx, AMSC and THEVA, the magnetizing effect using pulse field magnetization (PFM) would be different. To explore the differences of this effect, sectioned stacks are tested in a modified synchronous machine designed by ASuMED under liquid nitrogen conditions. By changing different sectioned stacks of tape and testing them under the same condition, the characteristics of the trapped flux, magnetization and demagnetization could be affected, different stacks are simulated with COMSOL finite element models using an electromagnetic-thermal coupled model, and different stacks are tested with different charging voltages.

Pulsed Field Magnetizing Behavior of Gd-Ba-Cu-O Bulk Superconductor With a Superconducting Joint

In this study, conditions for obtaining high-quality superconducting joint to a Gd-Ba-Cu-O bulk superconductor to investigate for the first time the effect of pulse field magnetization (PFM) properties of the joined bulk and to study an effective pulse magnetization method. We fabricated a good superconducting joint using the local melting method with sintered Er-Ba-Cu-O and applied the PFM method to the joined bulk. As a result, a high magnetic field of 1.2 T was trapped in the joined part when the magnetic field strength more than 5 T was applied at 50 K. From the evaluation results of the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> - <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</i> characteristics of each region cut from the joined sample confirmed that the joined sample was efficiently magnetized due to the preferential field penetration path and the dispersion of heat generation from the joined part. This is a finding that could lead to the future use of PFM in the bulk using superconducting joint with minimal reduction of the trapped magnetic field, and could simplify the magnetization method, which has been a drawback of PFM.

A Numerical Analysis of Pulsed-Field Magnetization Characteristics of REBCO Bulk Magnets When Using Various Soft-Iron Yokes

We aim to improve the magnetizing efficiency while maintaining the trapped magnetic field of REBCO bulk magnets activated by pulsed-field magnetization (PFM). Recently, we performed numerical analysis using a 3D simulation model based on our bulk PFM system and estimated the magnetizing characteristics when using disk-, ring-, and cross-shaped yokes. In this paper, a detailed analysis model that accounts for the inhomogeneity of the REBCO bulk is created, and the magnetizing properties are evaluated at different temperatures and applied fields. Comparison of the experimental and numerical results for the dependence of the total magnetic flux on the applied magnetic field shows a similar trend of change. From the results of the time variation of the one-dimensional magnetic field distribution in the ascent and descent processes of the applied field, we can reproduce the experimentally confirmed fact that the magnetic flux enters from the GSR and is trapped in the GSR by considering the difference in the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J_c</i> of the GSB and the GSR in the analysis. Furthermore, it was confirmed not only in the previous experiment but also in the present analysis that the GSB arrangement of the cross-type yoke enables efficient magnetization.

Superconducting Magnetic Energy Storage for Pulsed Power Magnet Applications

As part of the exploration of energy efficient and versatile power sources for future pulsed field magnets of the National High Magnetic Field Laboratory-Pulsed Field Facility (NHMFL-PFF) at Los Alamos National Laboratory (LANL), the feasibility of superconducting magnetic energy storage (SMES) for pulsed-field magnets and other pulsed power loads is examined. Basic SMES parameters needed to power one of the coil groups of the large 100 T magnet were determined. A circuit topology for the power transfer between the SMES and the magnet was devised, and the basic performance of the topology was simulated to reproduce the pulse shape currently used in the 100 T magnet. The Finite element analysis (FEA) method was used to calculate the magnetic field distribution of several preferred coil configurations for effective SMES design. Magnetic field distribution and the field dependent critical current density of commercial high temperature superconducting (HTS) tapes were used to understand the conductor/cable requirements for the SMES.

Liquid helium-cooled high-purity copper coil for generation of long pulsed magnetic fields

To generate long-duration pulsed magnetic fields with low energy consumption, we present a practical setup that implements an electromagnet made of high-purity copper (99.9999%). The resistance of the high-purity copper coil decreases from 171 mΩ (300 K) to 19.3 mΩ (77.3 K) and to below ∼0.15 mΩ (4.2 K), indicating a high residual resistance ratio of 1140 and a substantial reduction in Joule loss at low temperature. Using a 157.5 F electric-double-layer-capacitor bank with a charged voltage of 100 V, a pulsed magnetic field of 19.8 T with a total field duration of more than 1 s is generated. The field strength of the liquid helium-cooled high-purity copper coil is approximately double that of a liquid nitrogen-cooled one. The low resistance of the coil and the resultant low Joule heating effect explain the improvements in accessible field strength. The low electric energy used for field generation warrants further investigation on low-impedance pulsed magnets consisting of high-purity metals.

Yoke geometry study using pulsed field magnetization on superconducting joined bulk Gd-Ba-Cu-O

Conditions for obtaining high-quality superconducting joint in Gd-Ba-Cu-O bulk superconductors were investigated, and the effects of PFM properties of the joined bulk and the change of yoke geometry in magnetization were examined. For a good superconducting joint fabricated by the local melting method using sintered Er-Ba-Cu-O, the J c-B property and multiple Hall sensors indicates that the joined part is the preferential field penetration path. PFM was performed using a changed geometry of yoke in which concentrated long pulse to the joined part, but the result was equivalent to the trapped field before the changing yoke because the volume of the yoke was reduced. This is the first attempt to approach an effective PFM method for the joined bulk from the viewpoint of a changed geometry of yoke.

Pulsed magnetic fields of over 100 T produced by relativistic intensity laser pulse irradiating no-hole capacitor-coil target

A relativistic intensity laser pulse with energy from 25 to 130 J was used to produce strong magnetic fields in interactions with the designed no-hole capacitor-coil target. The magnetic field was estimated by the proton deflectometry method ignoring the potential influences of electric field. The proton deflection profiles in experiments are in good agreement with that by particle-track simulation with only the effect of coil magnetic field. The maximum magnetic field obtained in the experiment in the center of the coil is 117 ± 4 T. The experimental results with different laser energies are consistent with the previously found magnetic field production model in magnetic field amplitude and time sequence. It shows that the model has good prediction ability for magnetic field results. The results are beneficial to establish the experimental platform for generating a controllable pulsed magnetic field by relativistic intensity laser interaction. It potentially opens new frontiers in basic physics which require strong magnetic field environments.

Static and dynamic magnetic characteristics in concentric permalloy nanorings

Magnetic nanodisks and nanorings have been focus of attention for quite some time due to their applicability in magnetic memory devices. In this paper, static and dynamic magnetic properties of Permalloy concentric thin ring nanostructures are reported as a function of the number of rings by using micromagnetic simulations. The maximum outer radius (R) and thickness (t) of the concentric rings are fixed at 100 nm and 20 nm respectively. The distance between any two neighbouring rings is always maintained equal to the width of each ring while the number of nanorings is increased starting from one to five. In-plane magnetic hysteresis loops show that in all cases, the remanence and coercivity values are found to be almost zero while vortex state is exhibited with opposite helicity in adjacent nanorings. When the number of nanorings reach five, the narrowest hysteresis loop is observed with almost no hysteresis at all. Dynamic susceptibility spectra was computed by relaxing the system from a out of plane saturated state followed by an in-plane excitation using a small field pulse. In most of the cases, the in plane magnetic field pulse excites azimuthal spin wave modes. The resonance frequency corresponding to these excitation modes depends on the remanent configuration and the number of peaks increase with increment in the number of rings. The ferromagnetic resonance mode that is common for all the samples considered, moves towards lower frequency with increase in number of concentric rings.

Combined Pulsed Magnetic Field and Radiofrequency Electromagnetic Field Enhances MMP-9, Collagen-4, VEGF Synthesis to Improve Wound Healing Via Hif-1α/eNOS Pathway.

The blood supply of the tissue is very important in the acceleration of wound healing. Radiofrequency electromagnetic field (RF) and the pulsed magnetic field (PMF) increase vasodilation to contribute wound healing. The aim of this study was to evaluate the effects of RF and PMF on wound healing via hypoxia-inducible factor-1 alpha (Hif-1α)/endothelial nitric oxide synthase (eNOS) pathway. Forty-eight rats were divided into 4 groups as sham (wound created only), PMF (27.12MHz, 12 times a day at 30-min intervals), RF (0.5 mT, continuously) and PMF + RF groups. Wounds were created at 1.5 × 1.5cm size to the dorsal region, and animals were put into unit. Six animals were killed on days 4 and 7; wound tissues were collected for histopathological, immunohistochemical as collagen-4, cytokeratin, matrix metalloproteinase-9 (MMP-9), vascular endothelial growth factor (VEGF) staining and Hif-1α/eNOS/VEGF expressions. On day 4, in addition to increasing VEGF and MMP-9 stainings, connection between intact tissue and scar tissue which was stronger in the RF- and PMF-applied groups was observed. On day 7, epithelization started; inflammatory reaction decreased; collagen production, cytokeratin, VEGF and MMP-9 expression enhanced, especially in the RF + PMF applied group. eNOS, Hif-1α and VEGF expression levels were found to be significantly highest in both days of RF + PMF-applied group. This study revealed that both in vitro RF and PMF applications can cause notable changes in factors that are required for tissue repair on wound healing such as epithelization, connective tissue formation, collagen production and angiogenesis via vasodilatory Hif-1α/eNOS pathway and VEGF signaling. This journal requires that authors assign a level of evidence to each submission to which Evidence-Based Medicine rankings are applicable. This excludes Review Articles, Book Reviews, and manuscripts that concern Basic Science, Animal Studies, Cadaver Studies, and Experimental Studies. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Study on condition prediction and influencing factors of manganese carbonate recovery by high gradient pulse magnetic separation

Manganese carbonate ore belongs to weakly magnetic minerals, and its co-associated minerals are mainly non-magnetic minerals, which can be separated from gangue minerals at high magnetic field intensity. However, manganese grade and recovery of magnetic separation concentrate of manganese carbonate ore are low in actual production. Therefore, the influences of manganese carbonate particle size, magnetic field intensity, volume susceptibility, pulse stroke, pH, and other factors were studied. The optimal test conditions for manganese carbonate ore recovery by high-gradient magnetic separation were predicted through the calculation results. The results show that the particle radius of manganese carbonate is 0.020 mm, the pulse impulse time is 200 r/min, and the magnetic field intensity is 0.9 T. The optimum condition test was carried out with Qianbei manganese carbonate ore as the material. The test results show that the optimum conditions are the particle radius of 0.074-0.019 mm, pulse impulse time of 200 r/min, and magnetic field intensity of 1.2 T. The reason for the deviation is that the actual ore has a fine distribution particle size, many associative bodies, complex composition, and serious agglomeration, resulting in variable particle volume susceptibility. The capture yield increases with the increase of magnetic field intensity and volume susceptibility but decreases with the increase of pulse. The lower the surface potential of manganese carbonate, the higher the recovery of manganese carbonate. The grade of manganese concentrate was 19.06% and the recovery was 76.85%. Mixed manganese concentrate with a grade of 18.04% and recovery of 87.14% was obtained by adding drugs and changing the grinding method.

Strong magnetoelastic coupling in MnCoSi compounds studied in pulsed magnetic fields

The orthorhombic MnCoSi compounds have been found to present a large magnetoelastic coupling, which is regarded as the source for the magnetocaloric effect (MCE) and the magnetostrictive effect. As a result, these compounds are potential materials for caloric applications such as solid-state refrigeration. In the present study, we offer fundamental insights in the magnetoelastic coupling in these compounds based on their structural, metamagnetic, and MCE behavior. The directly measured adiabatic temperature change ($\mathrm{\ensuremath{\Delta}}{T}_{\mathrm{ad}}$) in different initial temperatures (down to 18 K) and pulsed magnetic fields (up to 40 T) presents a moderate MCE performance (the maximum $\mathrm{\ensuremath{\Delta}}{T}_{\mathrm{ad}}=--3.1\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ for a field change of 13 T), which results from the metamagnetic behavior of these compounds. Furthermore, the magnetization measurements in pulsed (and static) magnetic fields indicate that the magnetoelastic coupling is significantly enhanced for increasing fields resulting in an improved saturation magnetization. The metamagnetic transition is continuously pushed to lower temperatures in higher fields. The phase diagram constructed from the experimental transition temperatures ${T}_{t}$ and the critical magnetic fields ${\ensuremath{\mu}}_{0}{H}_{\mathrm{cr}}$ indicate that the transition is terminated below 18 K and that ferromagnetism is stabilized for fields above 22.3 T. Our results provide unique insights into the strong magnetoelastic coupling under high pulsed magnetic fields, providing guidelines for the design of giant magnetocaloric materials for future caloric applications.

Runaway electron mitigation with pulsed localized vertical magnetic field perturbation in ADITYA tokamak

To reduce the risk of severe damage to the vessel and inner peripherals of any tokamak and its safe operation, a robust technique for the mitigation of runaway electrons (REs) is required. The REs in ADITYA tokamak are effectively mitigated by an application of local vertical magnetic field (LVF) perturbation. The LVF perturbation is applied using a pair of electromagnetic coils placed at the top and bottom of the ADITYA vacuum vessel in a Helmholtz configuration at one toroidal location. Powered by a capacitor bank power supply, these coils can produce a localized vertical magnetic field at the plasma center in the range of ∼150 G–260 G for a variable duration of 5–20 ms. The LVF pulse is first applied at the breakdown/current-ramp phase, where the REs are generated in the discharges initiated by the conventional ohmic breakdown in ADITYA. With the application of LVF pulse the REs are significantly reduced as indicated by the reduction in the REs generated hard x-ray flux. It has been observed that to extract the REs efficiently, an LVF pulse of magnitude at least ∼1% of the toroidal magnetic field with a minimum duration of ∼5 ms should be applied. The LVF perturbation is applied at different times into the discharge, i.e. during the breakdown/current ramp-up phase and current flat-top phase. The REs are significantly reduced in all the phases and improved discharge consistency. The LVF acts as an error field and a short-pulse of the LVF influences the REs more in comparison to the thermal electrons due to the faster velocities of the REs.

Migration Behavior of Inclusions at the Solidification Front in Oxide Metallurgy.

Distribution of inclusions plays an essential role in inducing intracrystalline ferrite, and the migration behavior of inclusions during solidification has a significant influence on their distribution. The solidification process of DH36 (ASTMA36) steel and the migration behavior of inclusions at the solidification front were observed in situ using high-temperature laser confocal microscopy. The annexation, rejection, and drift behavior of inclusions in the solid-liquid two-phase region were analyzed, providing a theoretical basis for regulating the distribution of inclusions. Analysis of inclusion trajectories showed that the velocity of inclusions decreases significantly as they near the solidification front. Further study of the force on inclusions at the solidification frontier shows three situations: attraction, repulsion, and no influence. Additionally, a pulsed magnetic field was applied during the solidification process. The original dendritic growth mode changed to that of equiaxed crystals. The compelling attraction distance for inclusion particles with a diameter of 6 μm at the solidification interface front increased from 46 μm to 89 μm, i.e., the effective length for the solidification front engulfing inclusions can be increased by controlling the flow of molten steel.

Multi-instrument study of a spread-F event at Arecibo linked to solar wind variations

Using five diverse data sets, we demonstrate that apparently local ionospheric spread-F activity, observed with an HF radar and the Arecibo Observatory (AO) Incoherent Scatter Radars (ISR) under geomagnetically quiet conditions, is likely the local manifestation of a mesoscale or larger ionospheric response to relatively weak solar wind activity. The solar wind activity included a weak pressure pulse and Interplanetary Magnetic Field (IMF) realignment events. The mid-latitude spread-F activity was observed with a 4.42 MHz radar located near AO and the dual-beam 430 MHz AO ISRs. Additionally, the Coupling, Energetics and Dynamics of Atmospheric Regions (CEDAR) Madrigal Global Navigation Satellite System-Total Electron Content (GNSS-TEC), the NASA OMNI, and the SuperMAG datasets were used to establish the (mesoscale/global) wide-context of the local, deep-context radar results. While the ISR event appears to be “classical” local spread-F, often attributed to Perkins-like plasma instabilities, the HF radar reveals large ionospheric structures coincident with the ISR event. However, that the apparently AO-local event was part of a very dynamic mesoscale event that lasted for over ten hours, is shown via independent AO-sector and AO-conjugate sector keograms constructed using detrended vertical TEC (delta-vTEC) data. The keograms reveal a prominent F-region feature that appears to propagate from west-to-east and then back to the west passing over AO twice. The ISR manifestation of this mesoscale event is indistinguishable from decades of similar ISR results which were assumed to be strictly “local”. The strong non-local (mesoscale) properties revealed by the delta-vTEC keograms suggest a possible space weather influence. Study of the relevant NASA OMNI solar wind and superMAG magnetometer data points to modest solar wind features including IMF realignment that may have electrodynamically launched, with little time delay, the observed mesoscale ionospheric events. Given the apparent rapid ionospheric response to the solar wind features, we suggest that limited latitudinal scale, prompt penetration electric fields (PPEF), associated with highly-localized partial ring current activity, be considered in the system-of-systems context of our observations. In any case, the need to examine magnetospheric/ionospheric electrodynamics across a wide range of instruments and data sets is demonstrated.