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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 505 records · Page 28
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Magnetic design of the commutational magnet and quadrupoles for PERLE accelerator

PERLE (Powerful Energy Recovery LINAC for Experiment) is a high-power Energy Recovery LINAC (ERL) facility with 20 mA beam current and beam energy from 250 MeV to 500 MeV featuring three passes through two cryomodules. It is a hub for validation of the ERL technology development towards future energy and intensity frontier machines. Design challenges of PERLE and its beam parameters make it a test-bed to validate multi-turn high current ERL operation for the LHeC. It will be the first ERL for some pioneering experiment of the eN interaction with radioactive nuclei. In this work, design and optimization of the commutational magnet (B-com) used to spread/combine the three beams and one series of the quadrupole magnet is discussed. It gives the design parameters including: yoke geometry, pole profile, and material, and calculation of the excitation current needed to drive the magnet, the coil parameters and the number of turns. The B-com magnet is optimized for a 30° bending angle with magnetic field of 0.88 T along the magnet length and a harmonic content of 0.036%. The quadrupole magnet is designed for a gradient field of 34.15 T/m and experiences saturation above this value. Further studies to avoid saturation and achieve the maximum gradient of 44.1 T/m required by the beam dynamics is undergoing.

Abukeshek, R.↗
DOE OSTI2023

Emergent orbital magnetization in Kitaev quantum magnets

Unambiguous identification of the Kitaev quantum spin liquid (QSL) in materials remains a huge challenge despite many encouraging signs from various measurements. To facilitate the experimental detection of the Kiteav QSL, here we propose to use remnant charge response in Mott insulators hosting QSL to identify the key signatures of QSL. We predict an emergent orbital magnetization in a Kitaev system in an external magnetic field. The direction of the orbital magnetization can be flipped by rotating the external magnetic field in the honeycomb plane. The orbital magnetization is demonstrated explicitly through a detailed microscopic analysis of the multiorbital Hubbard-Kanamori Hamiltonian and also supported by a phenomenological picture. We first derive the localized electrical loop current operator in terms of the spin degrees of freedom. Thereafter, utilizing the Majorana representation, we estimate the loop currents in the ground state of the chiral Kitaev QSL state, and obtain the consequent current textures, which are responsible for the emergent orbital magnetization. Finally, we discuss the possible experimental techniques to visualize the orbital magnetization which can be considered as the signatures of the underlying excitations.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Magnetic Energy Release, Plasma Dynamics, and Particle Acceleration in Relativistic Turbulent Magnetic Reconnection

In strongly magnetized astrophysical plasma systems, magnetic reconnection is believed to be the primary process during which explosive energy release and particle acceleration occur, leading to significant high-energy emission. Past years have witnessed active development of kinetic modeling of relativistic magnetic reconnection, supporting this magnetically dominated scenario. A much less explored issue in studies of relativistic reconnection is the consequence of three-dimensional dynamics, where turbulent structures are naturally generated as various types of instabilities develop. This paper presents a series of three-dimensional, fully kinetic simulations of relativistic turbulent magnetic reconnection (RTMR) in positron–electron plasmas with system domains much larger than kinetic scales. Our simulations start from a force-free current sheet with several different modes of long-wavelength magnetic field perturbations, which drive additional turbulence in the reconnection region. Because of this, the current layer breaks up and the reconnection region quickly evolves into a turbulent layer filled with coherent structures such as flux ropes and current sheets. Additionally, we find that plasma dynamics in RTMR is vastly different from its 2D counterpart in many aspects. The flux ropes evolve rapidly after their generation, and can be completely disrupted by the secondary kink instability. This turbulent evolution leads to superdiffusive behavior of magnetic field lines as seen in MHD studies of turbulent reconnection. Meanwhile, nonthermal particle acceleration and the timescale for energy release can be very fast and do not depend strongly on the turbulence amplitude. Additionally, the main acceleration mechanism is a Fermi-like acceleration process supported by the motional electric field, whereas the nonideal electric field acceleration plays a subdominant role. We also discuss possible observational implications of three-dimensional RTMR in high-energy astrophysics.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Sub-Alfvénic Turbulence: Magnetic-to-kinetic Energy Ratio, Modification of Weak Cascade, and Implications for Magnetic Field Strength Measurements

Abstract We study the properties of sub-Alfvénic magnetohydrodynamic (MHD) turbulence, i.e., turbulence with Alfvén mach number M A = V L / V A < 1, where V L is the velocity at the injection scale and V A is the Alfvén velocity. We demonstrate that MHD turbulence can have different properties, depending on whether it is driven by velocity or magnetic fluctuations. If the turbulence is driven by isotropic bulk forces acting upon the fluid, i.e., is velocity driven, in an incompressible conducting fluid we predict that the kinetic energy is M A − 2 times larger than the energy of magnetic fluctuations. This effect arises from the long parallel wavelength tail of the forcing, which excites modes with k ∥ / k ⊥ < M A . We also predict that as the MHD turbulent cascade reaches the strong regime, the energy of slow modes exceeds the energy of Alfvén modes by a factor M A − 1 . These effects are absent if the turbulence is driven through magnetic fluctuations at the injection scale. We confirm our predictions with numerical simulations. Since the assumption of magnetic and kinetic energy equipartition is at the core of the Davis–Chandrasekhar–Fermi (DCF) approach to measuring magnetic field strength in sub-Alfvénic turbulence, we conclude that the DCF technique is not universally applicable. In particular, we suggest that the dynamical excitation of long azimuthal wavelength modes in the galactic disk may compromise the use of the DCF technique. We discuss alternative expressions that can be used to obtain magnetic field strength from observations and consider ways of distinguishing the cases of velocity and magnetically driven turbulence using observational data.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Magnetic design of the commutational magnet and quadrupoles for PERLE accelerator

PERLE (Powerful Energy Recovery LINAC for Experiment) is a high-power Energy Recovery LINAC (ERL) facility with 20 mA beam current and beam energy from 250 MeV to 500 MeV featuring three passes through two cryomodules. It is a hub for validation of the ERL technology development towards future energy and intensity frontier machines. Design challenges of PERLE and its beam parameters make it a test-bed to validate multi-turn high current ERL operation for the LHeC. It will be the first ERL for some pioneering experiment of the eN interaction with radioactive nuclei. In this work, design and optimization of the commutational magnet (B-com) used to spread/combine the three beams and one series of the quadrupole magnet is discussed. It gives the design parameters including: yoke geometry, pole profile, and material, and calculation of the excitation current needed to drive the magnet, the coil parameters and the number of turns. The B-com magnet is optimized for a 30° bending angle with magnetic field of 0.88 T along the magnet length and a harmonic content of 0.036%. The quadrupole magnet is designed for a gradient field of 34.15 T/m and experiences saturation above this value. Further studies to avoid saturation and achieve the maximum gradient of 44.1 T/m required by the beam dynamics is undergoing.

Abukeshek, R.↗
DOE OSTI2024

Fabrication method for a component having magnetic and non-magnetic dual phases

Methods for forming a dual-phase magnetic component from an initial component comprising a non-magnetic austenite composition are provided. The method may include: forming a coating on a portion of the surface of the initial component to form a masked area while leaving an unmasked area thereon. Thereafter the initial component may be heated to a treatment temperature such that nitrogen diffuses out of the unmasked area of the initial component to transform the non-magnetic austenite composition to a magnetic phase in the unmasked area. Thereafter, the initial component may be cooled from the treatment temperature to form a dual-phase magnetic component having a magnetic region corresponding to the unmasked area and a non-magnetic region corresponding to the masked area.

Huang, Shenyan↗
DOE OSTI2023

Role of Magnetic Defects in Tuning Ground States of Magnetic Topological Insulators

Abstract Magnetic defects play an important, but poorly understood, role in magnetic topological insulators (TIs). For example, topological surface transport and bulk magnetic properties are controlled by magnetic defects in Bi 2 Se 3 ‐based dilute ferromagnetic (FM) TIs and MnBi 2 Te 4 (MBT)‐based antiferromagnetic (AFM) TIs. Despite its nascent ferromagnetism, the inelastic neutron scattering data show that a fraction of the Mn defects in Sb 2 Te 3 form strong AFM dimer singlets within a quintuple block. The AFM superexchange coupling occurs via Mn–Te–Mn linear bonds and is identical to the AFM coupling between antisite defects and the FM Mn layer in MBT, establishing common interactions in the two materials classes. It is also found that the FM correlations in (Sb 1− x Mn x ) 2 Te 3 are likely driven by magnetic defects in adjacent quintuple blocks across the van der Waals gap. In addition to providing answers to long‐standing questions about the evolution of FM order in dilute TI, these results also show that the evolution of global magnetic order from AFM to FM in Sb‐substituted MBT is controlled by defect engineering of the intrablock and interblock coupling.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Magnetic Field Angular Dependence of Magnetization Loss in ReBCO Superconducting Tapes

In the applications of high-temperature superconductors (HTS), the HTS tapes are usually exposed to the external magnetic field with different orientations. The critical current and AC loss are affected by both the field amplitude and field angles due to the anisotropy of HTS tapes. In this work, we first introduce the experimental system to measure the magnetization loss in HTS tapes based on the calibration-free method. Then, we present the magnetization loss results in 4.8-mm-wide AMSC wire, 4-mm-wide SuperPower wire, 4-mm-wide SuNam wire, and 10-mm-wide Fujikura wire in a perpendicular applied field at 77 K. The field amplitude is up to 100 mT, and the frequency varies from 44.2 to 87.1 Hz. We also present the magnetization loss in AMSC wire, SuperPower wire, SuNam wire, and Fujikura wire at different field angles. The field angle varies from 10 to 90 {sup ∘} in 10 {sup ∘} steps. The loss reduction with the decreasing of the field angle shows the anisotropic property of HTS tapes. We finally plot the measured magnetization loss of the samples as a function of the magnetic field amplitude normalized by the field angle to verify an empirical formula.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Dispersion Characteristics and Phase Index of One-Dimensional Magnetized Ferrite Photonic Crystals in Transverse Magnetization Configuration for TE Modes

The dispersion characteristics and phase index of magnetized one-dimensional ferrite photonic crystals in transverse magnetization for transverse electric modes are investigated. The dispersion relation and expression for phase index are derived by using transfer matrix method. The effects of structural parameters such as external magnetic fields, filling factor, and β on dispersion properties and phase index are investigated. The dielectric nature of the considered magnetized ferrite photonic crystal structure is demonstrated. Also, the band structure for ω < 1.5 × 10{sup 10} rad s{sup − 1} is strongly affected by external magnetic fields. It is observed that phase index occurs in the form of lobes and is found to be controlled by external magnetic field, β, and filling factor.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Valley Hall Effect and Magnetic Moment in Magnetized Silicene

We investigate the physical properties of silicene with both staggered sublattice potential and magnetization by using Kubo formalism, the latter arises from the magnetic proximity effect by depositing Fe atoms to silicene or depositing silicene on an appropriate ferromagnetic insulator. Based on the low-energy continuum model of the system where inversion symmetry is broken, we show that the system exhibits spin half metal state when staggered sublattice potential is in the same magnitude with mean and staggered magnetization. Besides, Hall conductivity and magnetic moment are all valley dependent, so we investigate the valley Hall effect of the system further by considering magnetization exclusively. This means carriers in different valleys turning into opposite directions transverse to an in-plane electric field. At last, we prove these results by investigating Berry curvature that characterizing Hall transport, which is also valley dependent. These effects can be used to generate valley-polarized currents solely by magnetization, forming the basis for the valley-based electronics applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Geometry Dependence of Magnetization Reversal in Nanocomposite Alloys

The geometrical optimization of aligned hard-soft permanent-magnet nanocomposites is investigated by model calculations. Considered criteria are the shapes of the soft and c-axis-aligned hard phases, the packing fraction of the soft phase, and magnetostatic interactions. Taking into account that the energy product is enhanced via the volume fraction of the soft phase, subject to maintaining coercivity, we find that the best structures are soft-magnetic cubes as well as long rods with a square cross section. Comparing embedded soft cubes with embedded soft spheres of the same size, our nucleation-field analysis shows that the volume fraction of the soft phase is enhanced by 91%, with a coercivity reduction of only 25%. Magnetostatic interactions often but not always deteriorate the permanent-magnet performance, as exemplified by the example of MnBi:FeCo bilayers and multilayers.

magnetization reversal↗
DOE OSTI2018

Effects of Magnetic and Electric Field Uniformity on Coded Aperture Imaging Quality in a Cycloidal Mass Analyzer

Cycloidal mass analyzers are unique sector mass analyzers as they exhibit perfect double focusing, making them ideal for incorporating spatial aperture coding, which can increase the throughput of a mass analyzer without affecting the resolving power. However, the focusing properties of the cycloidal mass analyzer depend on the uniformity of the electric and magnetic fields. In this paper, finite element simulation and charged particle tracing were used to investigate the effect of field uniformity on imaging performance of a cycloidal mass analyzer. For the magnetic field, we evaluate a new permanent magnet geometry by comparing it to a traditional geometry. Results indicate that creating an aperture image in a cycloidal mass spectrometer with the same FWHM as the slit requires less than 1% variation in magnetic field strength along the ion trajectories. The new magnet design, called the opposed dipole magnet, has less than 1% field variation over an area approximately 62 × 65 mm; nearly twice the area available in a traditional design of similar size and weight. This allows ion imaging across larger detector arrays without loss of resolving power. In addition, we compare the aperture imaging quality of a traditionally used cycloidal mass spectrometer electric design with a new optimized design with improved field uniformity. .

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2013

Nonequilibrium spin transport through a diluted magnetic semiconductor quantum dot system with noncollinear magnetization

The spin-dependent transport through a diluted magnetic semiconductor quantum dot (QD) which is coupled via magnetic tunnel junctions to two ferromagnetic leads is studied theoretically. A noncollinear system is considered, where the QD is magnetized at an arbitrary angle with respect to the leads' magnetization. The tunneling current is calculated in the coherent regime via the Keldysh nonequilibrium Green's function (NEGF) formalism, incorporating the electron-electron interaction in the QD. We provide the first analytical solution for the Green's function of the noncollinear DMS quantum dot system, solved via the equation of motion method under Hartree-Fock approximation. The transport characteristics (charge and spin currents, and tunnel magnetoresistance (TMR)) are evaluated for different voltage regimes. The interplay between spin-dependent tunneling and single-charge effects results in three distinct voltage regimes in the spin and charge current characteristics. The voltage range in which the QD is singly occupied corresponds to the maximum spin current and greatest sensitivity of the spin current to the QD magnetization orientation. The QD device also shows transport features suitable for sensor applications, i.e., a large charge current coupled with a high TMR ratio. - Highlights: Black-Right-Pointing-Pointer The spin polarized transport through a diluted magnetic quantum dot is studied. Black-Right-Pointing-Pointer The model is based on the Green's function and the equation of motion method. Black-Right-Pointing-Pointer The charge and spin currents and tunnel magnetoresistance (TMR) are investigated. Black-Right-Pointing-Pointer The system is suitable for current-induced spin-transfer torque application. Black-Right-Pointing-Pointer A large tunneling current and a high TMR are possible for sensor application.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2024

Unconventional pressure-induced magnetic transitions and mechanical properties in non-magnetic LaFeSi

Here, this work demonstrates that two consecutive magnetic transitions occur in non-magnetic LaFeSi compound under negative hydrostatic pressure (small volume expansion). Electronic structure properties of LaFeSi were calculated using density functional theory (DFT) to understand the origin of these magnetic transitions. Mechanical properties of LaFeSi, especially elastic properties (shear and Young’s modulus, and Poisson’s ratio), were determined by DFT distortion calculations to elucidate lattice anisotropy and stability. The antiferromagnetic transition at –7.52 GPa, predicted in our work for LaFeSi, is consistent with the reported experimentally observed antiferromagnetic ground states in CeMnSi and LaMnSi compounds having similar crystal geometry. This finding of unexpected magnetic ordering predicts that layered non-magnetic materials, like LaFeSi, may become magnetically active with lattice expansion.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Synthesis, crystal structure and magnetic properties of Li{sub 2}InMo{sub 3}O{sub 8}: A novel reduced molybdenum oxide containing magnetic Mo{sub 3} clusters

Powder samples and single crystals of Li{sub 2}InMo{sub 3}O{sub 8} were obtained by solid state reaction. The structure was determined by single-crystal X-ray diffraction (771 independent reflections for 33 refinable, R1=0.0158 and wR2=0.0354). Li{sub 2}InMo{sub 3}O{sub 8} is isomorphous with Li{sub 2}SnMo{sub 3}O{sub 8} and crystallizes in the hexagonal space group P6{sub 3}mc with unit-cell parameters a=5.7931(2) Å, c=10.4681(4) Å and Z=2. The crystal structure consists of distorted hexagonal-close-packed oxygen layers with stacking sequence abac along [0 0 1] and that are held together by alternating lithium–indium and molybdenum layers. The Li{sup +} and In{sup 3+} ions occupy, respectively, tetrahedral and octahedral sites in the ratio 2:1. The Mo atoms occupy octahedral sites and form strongly bonded triangular clusters involving three MoO{sub 6} octahedra that are each shared along two edges, constituting a Mo{sub 3}O{sub 13} unit. The variations of the Mo–Mo and Mo–O bond lengths according to the number of electrons per Mo{sub 3} cluster are discussed. The trivalent oxidation state of the indium leads to one unpaired electron per Mo{sub 3} and thus gives rise to a paramagnetic spin behavior with an effective magnetic moment of 1.5 μ{sub B} per Mo{sub 3} cluster. The magnetic susceptibility vs. temperature curve also shows a maximum at 25 K arising probably from an antiferromagnetic ordering between the Mo{sub 3} clusters. - Graphical abstract: We present here the synthesis, the crystal structure, and the magnetic properties of the new quaternary compound Li{sub 2}InMo{sub 3}O{sub 8} containing magnetic Mo{sub 3}O{sub 13} units with one unpaired electron. - Highlights: • The new quaternary reduced molybdenum oxide containing Mo{sub 3} clusters, Li{sub 2}InMo{sub 3}O{sub 8}, was synthesized by solid state reaction. • Single-crystal X-ray study. • One unpaired electron per Mo{sub 3} cluster leading to a paramagnetic spin behavior with an effective magnetic moment of 1.5 μ{sub B} per Mo{sub 3} cluster. • Magnetic susceptibility measurements show a maximum at 25 K arising probably from an antiferromagnetic ordering between the Mo{sub 3} clusters.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Structural, magnetic and optical properties of a dilute magnetic semiconductor based on Ce{sub 1−x}Co{sub x}O{sub 2} thin film grown on LaAlO{sub 3}

Highlights: • Co doped CeO{sub 2} was grown on LaAlO{sub 3} (0 0 1) via a modified sol–gel spin-coating technique. • The concentration of the Co ions was varied from 1 to 15 at.%. • The incorporation of 5 at.% of Mn ions was found to provide formation of exceptionally magnetic moment. • This amount demonstrated a giant magnetic moment of 1.09 μ{sub B}/Co. • This amount reduced the optical band gap and enhanced the optical performance. - Abstract: The enhancement of the room temperature ferromagnetism and optical properties of the dilute magnetic metal oxides is a crucial clue to construct spin-based optoelectronic devices. In this work, Ce{sub 1−x}Co{sub x}O{sub 2} (0.01 ≤ x ≤0.15) thin films were prepared via ethylene glycol modified sol–gel spin coating technique on the LaAlO{sub 3} (0 0 1) substrate to enhance their room temperature ferromagnetism and optical properties. The structures, magnetic and optical properties of the prepared films were characterized by X-ray diffraction, atomic force microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, SQUID magnetometer, X-ray photoelectron spectroscopy and UV–vis spectrophotometer. The results demonstrated that a single phase cubic structure was formed, implying the substitution of Co ions into the Ce ions sites. The prepared films showed room temperature ferromagnetism with saturation magnetic moment of 1.09 μ{sub B}/Co was achieved for 5 at.% Co-doped CeO{sub 2}. This film exhibited high optical transparency of 85% and low optical band energy gap of 3.39 eV. The improved magnetic and optical properties are argued to the increase of the density of the oxygen vacancies into the cerium oxide crystal structure due to the incorporation of Co ions.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Layer-Dependent Magnetism and Spin Fluctuations in Atomically Thin van der Waals Magnet CrPS 4

van der Waals (vdW) magnets, an emerging family of two-dimensional (2D) materials, have received tremendous attention due to their rich fundamental physics and significant potential for cutting-edge technological applications. In contrast to the conventional bulk counterparts, vdW magnets exhibit significant tunability of local material properties, such as stacking engineered interlayer coupling and layer-number dependent magnetic and electronic interactions, which promise to deliver previously unavailable merits to develop multifunctional microelectronic devices. As a further ingredient of this emerging topic, here we report nanoscale quantum sensing and imaging of atomically thin vdW magnet chromium thiophosphate CrPS 4 , revealing its characteristic layer-dependent 2D static magnetism and dynamic spin fluctuations. We also show a large tunneling magnetoresistance in CrPS 4 -based spin filter vdW heterostructures. Here, the excellent material stability, robust strategy against environmental degradation, in combination with tailored magnetic properties highlight the potential of CrPS 4 in developing state-of-the-art 2D spintronic devices for next-generation information technologies.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗