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At least 757 records · Page 42

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DOE OSTI2016

Long-time variation in magnetic structure of CeIr 3 Si 2 : Observation of a nucleation-and-growth process of magnetic domains

CeIr 3 Si 2 is the first three-dimensional uniform magnet in which the long-time variation in magnetic structure was observed. To clarify the microscopic mechanism of this magnetic structural change, time-resolved neutron scattering measurements have been reinvestigated. Clear time variations in the line widths as well as the amplitudes of magnetic Bragg diffractions have been observed in this improved instrumentation. On the notion of this observation, a nucleation-and-growth model of magnetic structural change has been presented. The numerical calculation with this model reproduces well the observation.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2018

Ion heating and magnetic flux pile-up in a magnetic reconnection experiment with super-Alfvénic plasma inflows

This work presents a magnetic reconnection experiment in which the kinetic, magnetic and thermal properties of the plasma each play an important role in the overall energy balance and structure of the generated reconnection layer. Magnetic reconnection occurs during the interaction of continuous and steady flows of super-Alfvénic, magnetized, aluminum plasma, which collide in a geometry with two-dimensional symmetry, producing a stable and long-lasting reconnection layer. Optical Thomson scattering measurements show that when the layer forms, ions inside the layer are more strongly heated than electrons, reaching temperatures of $T_i \sim \bar Z_e > \sim 300 eV$ – much greater than can be expected from strong shock and viscous heating alone. Later in time, as the plasma density in the layer increases, the electron and ion temperatures are found to equilibrate, and a constant plasma temperature is achieved through a balance of the heating mechanisms and radiative losses of the plasma. Measurements from Faraday rotation polarimetry also indicate the presence of significant magnetic field pile-up occurring at the boundary of the reconnection region, which is consistent with the super-Alfvénic velocity of the inflows.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2018

Analysis of the short-to-ground event in the LARP-AUP MQXFAP1 magnet, and its implication on the production and tests of the series magnets

Starting from 2022, the Large Hadron Collider (LHC) at CERN will be shut down to increase the luminosity of the machine. One of the main interventions will be inserting more performing low-β quadrupoles, called MQXF, in the interaction points. The US is involved in this activity with the US HL-LHC Accelerator Upgrade Project (AUP), and is responsible of the production and test of the Q1 and Q3 cryo-assemblies (each one containing two 4.2-m magnets in a single cold mass) of the triplet. After completing the US short model phase, the prototyping phase has started with MQXFAP1 (1st prototype, 4m long) test at the Brookhaven National Laboratory vertical test facility. However, after the magnet reached nominal current, a short-to-ground event stopped the test when the magnet was at 97.5% of acceptance current. In this paper, an analysis of this event is presented. We present how the short event can be modeled, and we base our conclusions on simulations and experimental evidence, trying to explain the mechanism that led to the short-to-ground formation. The short-to-ground has occurred in a coil that was known to have a previous coil-to-heater short. Therefore, we explain the connection between these two events, the possible risks for the future magnets, and how to prevent this issue from happening again in the series magnets.

43 PARTICLE ACCELERATORS↗

DOE OSTI2018

Analysis of the short to-ground event in the LARP-AUP MQXFAP1 magnet, and its implication on the production and tests of the series magnets

Starting from 2022, the Large Hadron Collider (LHC) at CERN will be shut down to increase the luminosity of the machine. One of the main interventions will be inserting more performing low-β quadrupoles, called MQXF, in the interaction points. The US is involved in this activity with the US HL-LHC Accelerator Upgrade Project (AUP), and is responsible of the production and test of the Q1 and Q3 cryo-assemblies (each one containing two 4.2-m magnets in a single cold mass) of the triplet. After completing the US short model phase, the prototyping phase has started with MQXFAP1 (1st prototype, 4m long) test at the Brookhaven National Laboratory vertical test facility. However, after the magnet reached nominal current, a short-to-ground event stopped the test when the magnet was at 97.5% of acceptance current. In this paper, an analysis of this event is presented. We present how the short event can be modeled, and we base our conclusions on simulations and experimental evidence, trying to explain the mechanism that led to the shortto- ground formation. The short-to-ground has occurred in a coil that was known to have a previous coil-to-heater short. Therefore, we explain the connection between these two events, the possible risks for the future magnets, and how to prevent this issue from happening again in the series magnets.

43 PARTICLE ACCELERATORS↗

DOE OSTI2017

Iron nitride permanent magnet and technique for forming iron nitride permanent magnet

A bulk permanent magnetic material may include between about 5 volume percent and about 40 volume percent Fe16N2 phase domains, a plurality of nonmagnetic atoms or molecules forming domain wall pinning sites, and a balance soft magnetic material, wherein at least some of the soft magnetic material is magnetically coupled to the Fe16N2 phase domains via exchange spring coupling. In some examples, a bulk permanent magnetic material may be formed by implanting N+ ions in an iron workpiece using ion implantation to form an iron nitride workpiece, pre-annealing the iron nitride workpiece to attach the iron nitride workpiece to a substrate, and post-annealing the iron nitride workpiece to form Fe16N2 phase domains within the iron nitride workpiece.

36 MATERIALS SCIENCE↗

DOE OSTI2020

System and method for measuring fluid properties using magnetic field techniques via magnetic tracer

A method and apparatus for determining a property of a fluid in a vessel. The method uses magnetic tracer particles and an externally applied magnetic field which orients the particles. When the fluid moves, it changes the orientation of the tracer particles, thus changing the magnetic fields. These changes are detected by external magnetic field sensors. By using mathematical models, the property of the fluid in the vessel is determined from the detected magnetic field. In this manner, fluid vorticity, velocity, strain and stress may be estimated.

42 ENGINEERING↗

DOE OSTI2020

Iron nitride permanent magnet and technique for forming iron nitride permanent magnet

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2022

Iron nitride permanent magnet and technique for forming iron nitride permanent magnet

Wang, Jian-Ping↗

DOE OSTI2022

Applied magnetic field synthesis and processing of iron nitride magnetic materials

Techniques are disclosed concerning applied magnetic field synthesis and processing of iron nitride magnetic materials. Some methods concern casting a material including iron in the presence of an applied magnetic field to form a workpiece including at least one ironbased phase domain including uniaxial magnetic anisotropy, wherein the applied magnetic field has a strength of at least about 0.01 Tesla (T). Also disclosed are workpieces made by such methods, apparatus for making such workpieces and bulk materials made by such methods.

Wang, Jian-Ping↗

DOE OSTI2021

Manipulation of Magnetic Skyrmion in a 2D van der Waals Heterostructure via Both Electric and Magnetic Fields

As a promising candidate for the much-desired low power consumption spintronic devices, 2D magnetic van der Waals material also provides a versatile platform for the design and control of topological spin textures. In this work on WTe 2 /CrCl 3 bilayer van der Waals heterostructures, a complete Néel-type skyrmion–bimeron–ferromagnet phase transition is demonstrated, accompanied by the evolution of the topological number. This cyclic transition, mediated by a perpendicular magnetic field, is largely driven by the competition between the out-of-plane magnetocrystalline anisotropy and magnetic dipole–dipole interaction. In the presence of a driving current, the Néel-type skyrmion gains a higher velocity yet larger skyrmion Hall angle, in comparison to the bimeron. By incorporating a ferroelectric CuInP 2 S 6 monolayer as a substrate, writing and erasing of skyrmions may be regulated using a ferroelectric polarization. Here this work sheds light on a novel approach to the design and control of magnetic skyrmions on 2D van der Waals materials.

multiferroic↗

DOE OSTI2018

161 Dy Time-Domain Synchrotron Mössbauer Spectroscopy for Investigating Single-Molecule Magnets Incorporating Dy Ions [ 161 Dy time-domain synchrotron Mössbauer spectroscopy as a new way forward for investigating single molecule magnets incorporating Dy ions]

Time–domain synchrotron Mössbauer spectroscopy (SMS) based on the Mössbauer effect of 161 Dy has been used to investigate the magnetic properties of a Dy III –based single–molecule magnet (SMM). The magnetic hyperfine field of [Dy(Cy 3 PO) 2 (H 2 O) 5 ]Br 3 •2 (Cy 3 PO)•2 H 2 O•2 EtOH is with B 0 =582.3(5) T significantly larger than that of the free–ion Dy III with a 6 H 15/2 ground state. This difference is attributed to the influence of the coordinating ligands on the Fermi contact interaction between the s and 4f electrons of the Dy III ion. Furthermore this study demonstrates that 161 Dy SMS is an effective local probe of the influence of the coordinating ligands on the magnetic structure of Dy–containing compounds.

74 ATOMIC AND MOLECULAR PHYSICS↗

DOE OSTI2015

Low-temperature magnetization dynamics of magnetic molecular solids in a swept field

The swept-field experiments on magnetic molecular solids such as Fe{sub 8} are studied using Monte Carlo simulations, and a kinetic equation developed to understand collective magnetization phenomena in such solids, where the collective aspects arise from dipole–dipole interactions between different molecules. Because of these interactions, the classic Landau–Zener–Stückelberg theory proves inadequate, as does another widely used model constructed by Kayanuma. It is found that the simulations provide a quantitatively accurate account of the experiments. The kinetic equation provides a similarly accurate account except at very low sweep velocities, where it fails modestly. This failure is attributed to the neglect of short-range correlations between the dipolar magnetic fields seen by the molecular spins. The simulations and the kinetic equation both provide a good understanding of the distribution of these dipolar fields, although analytic expressions for the final magnetization remain elusive.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2021

On the missing magnetic flux and topological effects of a screw dislocation on a charged particle in an inhomogeneous magnetic field

Highlights: • Aharonov–Bohm-type effect associated with the missing magnetic flux. • Persistent currents associated with the missing magnetic flux. • Aharonov–Bohm-type effect associated with the screw dislocation topology. We study the interaction of an electron/hole with inhomogeneous magnetic field in the presence of a screw dislocation. We consider the internal structure of the defect, i.e., we consider the core that gives rise to a finite size to the defect. In addition, we assume that this core determines a forbidden region for the electron/hole. Then, we solve the Schrödinger equation and show that an Aharonov–Bohm-type effect arises from the influence of the topological defect and the missing magnetic flux on the eigenvalues of energy.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2014

Magnetic-field-induced synthesis of Fe{sub 3}O{sub 4} nanorods by a gas–liquid interfacial process: Microstructure control, magnetic and photocatalytic properties

Highlights: • Fe{sub 3}O{sub 4} nanorods were synthesized via a MFI gas–liquid interfacial route. • The morphology of the Fe{sub 3}O{sub 4} nanoparticle can be changed during its growth process. • MF render Fe{sub 3}O{sub 4} nanorods higher degree of crystallinity and better magnetic property. - Abstract: In this paper, we designed a magnetic field (MF) induced gas–liquid interface route to synthesize magnetic Fe{sub 3}O{sub 4} nanorods (NRs). The results showed that the MF can significantly affect the morphology of the particles. In this original method, only relatively inexpensive and environmental chemicals were used. The structure and morphology of the Fe{sub 3}O{sub 4} NRs were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and vibrating sample magnetometry technique. The crystal growth mechanisms in the magnetic field induced process were expounded in detail. The as-synthesized Fe{sub 3}O{sub 4} NRs were successfully used as a catalytic carrier for the photo degradation of phenol.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Self-Consistent Field Methods for Excited States in Strong Magnetic Fields: A Comparison Between Energy - and Variance-based Approaches

An efficient implementation of geometrical derivatives at the Hartree–Fock (HF) and current-density functional theory (CDFT) levels is presented for the study of molecular structure in strong magnetic fields. The required integral derivatives are constructed using a hybrid McMurchie–Davidson and Rys quadrature approach, which combines the amenability of the former to the evaluation of derivative integrals with the efficiency of the latter for basis sets with high angular momentum. In addition to its application to evaluating derivatives of four-center integrals, this approach is also applied to gradients using the resolution-of-the-identity approximation, enabling efficient optimization of molecular structure for many-electron systems under a strong magnetic field. The CDFT contributions have been implemented for a wide range of density functionals up to and including the meta-GGA level with current-density dependent contributions and (range-separated) hybrids for the first time. Illustrative applications are presented to the OH and benzene molecules, revealing the rich and complex chemistry induced by the presence of an external magnetic field. Challenges for geometry optimization in strong fields are highlighted, along with the requirement for careful analysis of the resulting electronic structure at each stationary point. The importance of correlation effects is examined by comparison of results at the HF and CDFT levels. The present implementation of molecular gradients at the CDFT level provides a cost-effective approach to the study of molecular structure under strong magnetic fields, opening up many new possibilities for the study of chemistry in this regime.

Comparison↗

DOE OSTI2023

Ultra-Low Viscosity and High Magnetic Susceptibility Magnetic Ionic Liquids Featuring Functionalized Diglycolic Acid Ester Rare-Earth and Transition Metal Chelates

Magnetic ionic liquids (MILs) comprise a subcategory of ionic liquids (ILs) and contain a paramagnetic metal center allowing them to be readily manipulated by an external magnetic field. While MILs are popularly employed as solvents in catalysis, separations, and organic synthesis, most low viscosity combinations possess a hydrophilic character that limits their use in aqueous matrices. To date, no study has reported the synthesis and characterization of hydrophobic MILs with viscosities similar to those of hydrophilic MILs and organic solvents while simultaneously exhibiting enhanced magnetic and thermal properties. In this study, diglycolic acid esters are employed as ligands to chelate with paramagnetic metals to produce cations that are paired with metal chelates composed of hexafluoroacetylacetonate ligands to form MILs incorporating multiple metal centers in the cation and anion. Viscosity values below 31.6 cP were obtained for these solvents, the lowest ever reported for hydrophobic MILs. Solubilities in nonpolar solvents such as benzene were observed to be as high as 50% (w/v) MIL-to-solvent ratio while being insoluble in water at concentrations as low as 0.01% (w/v). Effective paramagnetic moment values for these solvents ranged from 5.33 to 15.56 Bohr magnetons (μB), with mixed metal MILs containing multiple lanthanides in the anion generally offering higher magnetic susceptibilities. MILs composed of ligands containing octyl substituents were found to possess thermal stabilities up to 190 °C. The synthetic strategies explored in this study exploit the highly tunable nature of the employed cation and anion pairs to design versatile ultra-low viscosity magnetoactive solvents that possess tremendous potential and applicability in liquid–liquid separation systems, catalysis, and microfluidics where the mechanical movement of the solvent can be easily facilitated using electromagnets.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2014

Studies on the effect of the axial magnetic field on the x-ray bremsstrahlung in a 2.45 GHz permanent magnet microwave ion source

A compact microwave ion source has been designed and developed for operation at a frequency of 2.45 GHz. The axial magnetic field is based on two permanent magnet rings, operating in the “off-resonance” mode and is tunable by moving the permanent magnets. In order to understand the electron energy distribution function, x-ray bremsstrahlung has been measured in the axial direction. Simulation studies on the x-ray bremsstrahlung have been carried out to compare with the experimental results. The effect of the axial magnetic field with respect to the microwave launching position and the position of the extraction electrode on the x-ray bremsstrahlung have been studied.

43 PARTICLE ACCELERATORS↗

DOE OSTI2014

Do dispersive waves play a role in collisionless magnetic reconnection?

Using fully kinetic simulations, we demonstrate that the properly normalized reconnection rate is fast ∼0.1 for guide fields up to 80× larger than the reconnecting field and is insensitive to both the system size and the ion to electron mass ratio. These results challenge conventional explanations of reconnection based on fast dispersive waves, which are completely absent for sufficiently strong guide fields. In this regime, the thickness of the diffusion layer is set predominantly by the electron inertial length with an inner sublayer that is controlled by finite gyro-radius effects. As the Alfvén velocity becomes relativistic for very strong guide fields, the displacement current becomes important and strong deviations from charge neutrality occur, resulting in the build-up of intense electric fields which absorb a portion of the magnetic energy release. Over longer time scales, secondary magnetic islands are generated near the active x-line while an electron inertial scale Kelvin-Helmholtz instability is driven within the outflow. These secondary instabilities give rise to time variations in the reconnection rate but do not alter the average value.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗