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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 829 records · Page 46
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Tuning the Magnetic Exchange via a Control of Orbital Hybridization in Cr 2 ( Te 1 - x W x ) O 6

Here, we report the complex magnetic phase diagram and electronic structure of Cr 2 ( Te 1-x W x ) O 6 systems. While compounds with different x values possess the same crystal structure, they display different magnetic structures below and above x c = 0.7 , where both the transition temperature T N and sublattice magnetization (M s ) reach a minimum. Unlike many known cases where magnetic interactions are controlled either by injection of charge carriers or by structural distortion induced via chemical doping, in the present case it is achieved by tuning the orbital hybridization between Cr 3d and O 2p orbitals through W 5d states. The result is supported by ab initio electronic structure calculations. Through this concept, we introduce a new approach to tune magnetic and electronic properties via chemical doping.

Zhu, M.↗
DOE OSTI2015

Avoiding Tokamak Disruptions by Applying Static Magnetic Fields That Align Locked Modes with Stabilizing Wave-Driven Currents [Avoiding Tokamak Disruptions by Magnetically Aligning Locked Modes with Stabilizing Wave-Driven Currents]

The international ITER tokamak has the objective of demonstrating the scientific feasibility of magnetic confinement fusion as a source of energy. A concern towards the achievement of this goal is represented by major disruptions: complete losses of confinement often initiated by a non-rotating ('locked') magnetic island created by magnetic reconnection. During disruptions, energy and particles accumulated in the plasma volume over many seconds are lost in a few milliseconds and released on the plasma-facing materials. In addition, multi-MA level currents flowing in the tokamak plasma for its sustainment and confinement are lost, also in milliseconds, thus terminating the plasma discharge and causing electromagnetic stresses that, if unmitigated, could lead to excessive device wear. Moreover it is shown that magnetic perturbations can be used to avoid disruptions by "guiding" the magnetic island to lock in a position where it is accessible to millimetre wave beams that fully stabilize it.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

Quantized Chiral Magnetic Current from Reconnections of Magnetic Flux

We introduce a new mechanism for the chiral magnetic e ect that does not require an initial chirality imbalance. The chiral magnetic current is generated by reconnections of magnetic ux that change the magnetic helicity of the system. The resulting current is entirely determined by the change of magnetic helicity, and it is quantized.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Revealing the Nature of the Ultrafast Magnetic Phase Transition in Ni by Correlating Extreme Ultraviolet Magneto-Optic and Photoemission Spectroscopies

By correlating time- and angle-resolved photoemission and time-resolved transverse- magnetooptical Kerr effect measurements, both at extreme ultraviolet wavelengths, we uncover the universal nature of the ultrafast photoinduced magnetic phase transition in Ni. This allows us to explain the ultrafast magnetic response of Ni at all laser fluences - from a small reduction of the magnetization at low laser fluences, to complete quenching at high laser fluences. In this work, both probe methods exhibit the same demagnetization and recovery timescales. The spin system absorbs the energy required to proceed through a magnetic phase transition within 20 fs after the peak of the pump pulse. However, the spectroscopic signatures of demagnetization of the material appear only after ≈ 200 fs, and subsequent recovery of the magnetization on timescales ranging from 500 fs to >70 ps. We also provide evidence of two competing channels with two distinct timescales in the recovery process, that suggest the presence of coexisting phases in the material.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Changes of Magnetism in a Magnetic Insulator due to Proximity to a Topological Insulator

We report here the modification of magnetism in a magnetic insulator Y 3 Fe 5 O 12 thin film by topological surface states (TSS) in an adjacent topological insulator Bi 2 Se 3 thin film. Ferromagnetic resonance measurements show that the TSS in Bi2Se3 produces a perpendicular magnetic anisotropy, results in a decrease in the gyromagnetic ratio, and enhances the damping in Y 3 Fe 5 O 12 . Such TSS-induced changes become more pronounced as the temperature decreases from 300 to 50 K. These results suggest a completely new approach for control of magnetism in magnetic thin films.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Effect of Ge substitution on magnetic properties in the itinerant chiral magnet MnSi

We have investigated the effect of Ge substitution on the magnetic ordering in the B20 itinerant chiral magnet MnSi prepared by melting and annealing under ambient pressure. From a metallurgical survey, the solubility limit of Ge was found to be x = 0.144(5) with annealing temperature T an = 1073 K. Magnetization measurements on MnSi 1–x Ge x samples show that the helical ordering temperature T c increases rapidly in the low-x range, whereas it becomes saturated at higher concentration x > 0.1. Here, the Ge substitution also increases both the saturation magnetization M s and the critical field to the fully polarized state H c2 . In contrast to the saturation behavior of T c , those parameters increase linearly up to the highest Ge concentration investigated. In the temperature-magnetic field phase diagram, we found enlargement of the skyrmion phase region for large x samples. We, furthermore, observed the nonlinear behavior of helical modulation vector k as a function of Ge concentration, which can be described qualitatively using the mean field approximation.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Hybridized kagome bands and induced Ti magnetism in RTi3Bi4 (R = Nd, Sm, Gd) kagome metals studied using angle-resolved photoemission spectroscopy and x-ray magnetic circular dichroism

Kagome materials are known for hosting emergent quantum phenomena driven by the interaction between different lattice, charge and spin orders. Here, we present a detailed angle resolved photoemission (ARPES), density functional theory (DFT) and x-ray magnetic circular dichroism (XMCD) study of the electronic and magnetic structure of RTi3Bi4 (R = Nd, Sm, Gd). ARPES and DFT demonstrate that the bulk electronic band structure is dominated by the hybridization of the Ti bands, and the weak electron-like pocket at Γ is identified as a surface state. The isotropic XAS profile of the M 4,5-edge of the rare earth is consistent with the presence of R 3+ oxidation state. Using the XMCD sum rules, backed by the atomic multiplet theory calculations, we obtain the spin and orbital magnetic moments. The Ti L2,3-edge XMCD reveals the presence of a small magnetic moment in GdTi3Bi4, presumably driven by the proximity of the Ti kagome layers to the zigzag chains of Gd, while the total magnetic moment of Gd is shared by the f and d electrons. Our combined XMCD, ARPES and DFT study brings an important piece of information to understand the spin flip transitions and anomalous Hall effect observed in the RTi3Bi4 kagome metals.

Lim, C.↗
DOE OSTI2013

Magnetic Separation Dynamics of Colloidal Magnetic Nanoparticles

Surface functionalized magnetic nanoparticles (MNPs) are appealing candidates for analytical separation of heavy metal ions from waste water and separation of actinides from spent nuclear fuel. This work studies the separation dynamics and investigates the appropriate magnetic-field gradients. A dynamic study of colloidal MNPs was performed for steady-state flow. Measurements were conducted to record the separation time of particles as a function of magnetic field gradient. The drag and magnetic forces play a significant role on the separation time. A drop in saturation magnetization and variation of particle size occurs after surface functionalization of the MNPs; these are the primary factors that affect the separation time and velocity of the MNPs. The experimental results are correlated to a theoretical one-dimensional model.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

From one to three, exploring the rungs of Jacob’s ladder in magnetic alloys

Magnetic systems represent an important challenge for electronic structure methods, in particular Density Functional Theory (DFT), which uses a single determinant wavefunction. To assess the predictions obtained by DFT in this type of materials, we benchmark different exchange correlation functionals with respect to each other, and with respect to available experimental data, on two families of binary iron alloys which are metallic and magnetic. We climb three rungs in Jacob’s ladder of DFT (i) the local density approximation, (ii) the industry standard approximation due to Perdew, Burke and Ernzerhof, and the revised version for solids, PBEsol (iii) and finally a very accurate meta-GGA functional SCAN, which corresponds to the third rung. More than 350 structures in ferromagnetic and antiferromagnetic configurations were considered. We compare the Convex Hull, the calculated magnetic moment, crystal structure, formation energy and electronic gap if present. We conclude that none of the functionals work in all conditions: whereas PBE and PBEsol can give a fair description of the crystal structure and the energetics, SCAN strongly overestimates the formation energy – giving values which are at least twice as large as PBE (and experiment). Magnetic moments are better predicted by PBE as well. Finally, our results show that magnetic and strongly correlated materials are a tough litmus test for DFT, and that they represent the next frontier in the development of a truly universal exchange correlation functionals.

Romero, Aldo H.↗
DOE OSTI2019

Collaborative Research: The evolution of magnetic skeletons during 3D magnetic reconnection. Final Technical Report

The goals of this project were to investigate magnetic field evolution during 3D magnetic reconnection; begin development of an open source Python package for plasma research and education; advise students on research projects related to magnetic reconnection; and organize a conference session on diversity, equity, and inclusion in plasma physics. The principal investigator advanced an analytical theory to describe the ideal and non-ideal motion of the magnetic field lines that connect two magnetic null points; led development of the PlasmaPy package through version 0.2.0; directly advised two students; and is co-organizing a town hall on diversity, equity, and inclusion at a major plasma physics conference.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

The Interplay of Magnetically Dominated Turbulence and Magnetic Reconnection in Producing Nonthermal Particles

Magnetized turbulence and magnetic reconnection are often invoked to explain the nonthermal emission observed from a wide variety of astrophysical sources. By means of fully kinetic 2D and 3D particle-in-cell simulations, we investigate the interplay between turbulence and reconnection in generating nonthermal particles in magnetically dominated (or, equivalently, “relativistic”) pair plasmas. A generic by-product of the turbulence evolution is the generation of a nonthermal particle spectrum with a power-law energy range. The power-law slope p is harder for larger magnetizations and stronger turbulence fluctuations, and it can be as hard as p ≲ 2. The Larmor radius of particles at the high-energy cutoff is comparable to the size l of the largest turbulent eddies. Plasmoid-mediated reconnection, which self-consistently occurs in the turbulent plasma, controls the physics of particle injection. Then, particles are further accelerated by stochastic scattering off turbulent fluctuations. The work done by parallel electric fields—naturally expected in reconnection layers—is responsible for most of the initial energy increase and is proportional to the magnetization σ of the system, while the subsequent energy gain, which dominates the overall energization of high-energy particles, is powered by the perpendicular electric fields of turbulent fluctuations. The two-stage acceleration process leaves an imprint in the particle pitch-angle distribution: lowenergy particles are aligned with the field, while the highest-energy particles move preferentially orthogonal to it. The energy diffusion coefficient of stochastic acceleration scales as Dγ ~ 0.1σ( c/l ) γ 2 , where γ is the particle Lorentz factor. This results in fast cceleration timescales t acc ~ (3 /σ)l/c . Our findings have important implications for understanding the generation of nonthermal particles in high-energy astrophysical sources.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

Demonstrating magnetic field robustness and reducing temporal T1 noise in transmon qubits through magnetic field engineering

The coherence of superconducting transmon qubits is often disrupted by fluctuations in the energy relaxation time (T1), limiting their performance for quantum computing. While background magnetic fields can be harmful to superconducting devices, we demonstrate that both trapped magnetic flux and externally applied static magnetic fields can suppress temporal fluctuations in T1 without significantly degrading its average value or qubit frequency. Using a three-axis Helmholtz coil system, we applied calibrated magnetic fields perpendicular to the qubit plane during cooldown and operation. Remarkably, transmon qubits based on tantalum-capped niobium (Nb/Ta) capacitive pads and aluminum-based Josephson junctions (JJs) maintained T1 lifetimes near 300 μs even when cooled in fields as high as 600 mG. Both trapped flux up to 600 mG and applied fields up to 400 mG reduced T1 fluctuations by more than a factor of two, while higher field strengths caused rapid coherence degradation. We attribute this stabilization to the polarization of paramagnetic impurities, the role of trapped flux as a sink for non-equilibrium quasiparticles (QPs), and partial saturation of fluctuating two-level systems (TLSs). These findings challenge the conventional view that magnetic fields are inherently detrimental and introduce a strategy for mitigating noise in superconducting qubits, offering a practical path toward more stable and scalable quantum systems.

Abdisatarov, Bektur [Fermilab; Jefferson Lab]↗
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↗