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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 991 records · Page 55
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Three-Dimensional Charge Density Wave Order in YBa2Cu3O6.67 at High Magnetic Fields

Charge density wave (CDW) correlations have been shown to universally exist in cuprate superconductors. However, their nature at high fields inferred from nuclear magnetic resonance is distinct from that measured by x-ray scattering at zero and low fields. Here we combine a pulsed magnet with an x-ray free electron laser to characterize the CDW in YBa2Cu3O6.67 via x-ray scattering in fields up to 28 Tesla. While the zero-field CDW order, which develops below T ~ 150 K, is essentially two-dimensional, at lower temperature and beyond 15 Tesla, another three-dimensionally ordered CDW emerges. The field-induced CDW onsets around the zero-field superconducting transition temperature, yet the incommensurate inplane ordering vector is field-independent. This implies that the two forms of CDW and hightemperature superconductivity are intimately linked.

Gerber, S.↗
DOE OSTI2016

Quasi-static and dynamic magnetic tension forces in arched, line-tied magnetic flux ropes

Solar eruptions are often driven by magnetohydrodynamic instabilities such as the torus and kink instabilities that act on line-tied magnetic flux ropes. Recent laboratory experiments designed to study these eruptive instabilities have demonstrated the key role of both dynamic (Myers et al 2015 Nature 528, 526) and quasi-static (Myers et al 2016 Phys. Plasmas, in press) magnetic tension forces in contributing to the equilibrium and stability of line-tied magnetic flux ropes. In this paper, we synthesize these laboratory results and explore the relationship between the dynamic and quasi-static tension forces. While the quasi-static tension force is found to contribute to the flux rope equilibrium in a number of regimes, the dynamic tension force is substantial mostly in the so-called failed torus regime where magnetic self-organization events prevent the flux rope from erupting.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

Enhanced Energy Density in Permanent Magnets using Controlled High Magnetic Field during Processing

This ORNL Manufacturing Demonstraction Facility (MDF) technical collaboration focused on the use of high magnetic field processing (>2Tesla) using energy efficient large bore superconducting magnet technology and high frequency electromagnetics to improve magnet performance and reduce the energy budget associated with Alnico thermal processing. Alnico, alloys containing Al, Ni, Co and Fe, represent a class of functional nanostructured alloys, and show the greatest potential for supplementing or replacing commercial Nd-based rare-earth alloy magnets.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Microscopic subsurface characterization of layered magnetic materials using magnetic resonance force microscopy

This project resulted in the following accomplishments: 1) The invention of scanned probe ferromagnetic resonance microscopy. Upon implementation and refinement this approach was used to measure static and dynamic magnetic resonance properties of ferromagnets with an unprecedented combination of spectral and spatial resolution. 2) Demonstration and study of spin pumping in a pristine ferromagnet across a boundary defined entirely by a magnetic field gradient, and so free of materials discontinuities. 3) First demonstrated highly efficient dynamic spin injection from Y 3 Fe 5 O 12 (YIG) into NiO, an antiferromagnetic (AF) insulator and robust spin propagation in AF NiO over distances up to 100-nm thickness; both spin injection and spin transport are mediated by the AF spin correlations. 4) Demonstration of exceptionally high efficiency conversion of spin current to charge current achieved in spin pumping from the dynamic magnetization of a ferromagnetic insulator into a variety of adjacent metal films. 5) Seminal study of the nature of spin-orbit coupling in d-electron metals that revealed the dominant sensitivity of the d-orbital moment to the d-electron count and revealing the important roles of both d-electron configuration and atomic number in the physics of the spin Hall effect. 6) Demonstration of observation of FMR by means of optically-detected NV diamond relaxometry that provided a highly sensitive, spatially resolved FMR detection method and revealed spin pumping across 100-nm length scales by means of dipolar coupling. 7) Using magnetic field localization, developed for FMR imaging, demonstrated a novel approach to discretizing spin wave modes to improve the characteristics of auto-oscillators driven by pure spin currents produced by the spin Hall effect. 8) We demonstrated large spin pumping signals from propagating high wavevector spinwaves in thin film YIG find that the spin pumping efficiency was insensitive to wavevector thus emphasizing the promise of thin YIG films for spinwave-based spintronics by allowing for predictable down-scaling of device dimensions and enabling a broad range of operational frequencies.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

The application of macroscopic flakes for Fe-6.5%Si bulk magnetics with superior magnetic properties

Inductors are used in power electronics to convert current to different frequency and voltage. They are used extensively from where power is generated all the way to electric vehicles and portable electronic devices. The soft magnetic materials used in the inductors is critical for the performance of the inductors. Currently, a majority of the inductor uses powder core. The use of powder is not ideal as the 3D granule powders generate large demagnetization field working against the applied field, resulting in reduced permeability and efficiency. In this paper, 2D flakes were used to replace the 3D granules as the feedstock for fabricating inductor core. The crystalline Fe-Si based crystalline soft magnetic material in the form of flakes approximately 0.1mm thick, 1mm long and 2mm wide were prepared via melt spinning. The flakes were then coated with insulating materials before compacted into a toroid. The effect of coating thickness and concentration on magnetic properties of the toroidal sample are studied. It was also found that the magnetic cores made by flakes surpass the cores made by same size powder with larger permeability and lower iron losses.

Fe-6.5%Si Steel↗
DOE OSTI2023

Magnetic properties of Lu and Y doped Ce-Fe-B magnets

The growing demand for Nd2Fe14B magnets is exacerbating the current critical materials shortage. To reduce the amount of critical material in Nd2Fe14B magnets, chemical substitutions have been used and shown to improve the magnetic behavior, such as the Curie Temperature TC, anisotropy field Ha, and saturation magnetization MS.

Bretana, Alex↗
DOE OSTI2026

The Dependence of Electron-only Magnetic Reconnection on Plasma Beta and Magnetic Shear: Theory and Observations

We investigate the onset conditions for electron-only magnetic reconnection through an analysis of 86 reconnection events observed by the Magnetospheric Multiscale mission in magnetosheath and magnetospheric current sheets. Our study presents the first observational evidence that the occurrence of electron-only reconnection depends on both the magnetic-field shear angle (θ) across the current sheet and the cross-sheet electron beta jump, quantified either by the inflow electron beta difference (Δβ e ) or by a modified electron beta jump (Δβ$^*_e$) defined by the cross-sheet electron pressure difference normalized by the average of the inflow magnetic pressure in the two inflow regions. We extend the diamagnetic-drift suppression mechanism from standard reconnection to electron-only reconnection by deriving relations applicable to electron-scale current sheets. Using scaling estimates, the electron-only reconnection suppression relation is derived as Δβ$^*_e$ ≳ 2(L/d e ) tan (θ/2), while a natural extension of the ion-coupled reconnection suppression criterion is Δβ e ≳ 2(L/d e ) tan (θ/2). At low Δβ e and Δβ$^*_e$ values, reconnection is detected across a large range of magnetic shear (from low to high), whereas high Δβ e and Δβ$^*_e$ conditions restrict reconnection to large shear configurations: shear angles as small as θ ≈ 5° occur when Δβ e (or Δβ$^*_e$) ≲0.1. However, only events exceeding θ ≳ 70° are found when Δβ e ≳ 1.0; this apparent restriction weakens when employing Δβ$^*_e$, as the corresponding data points shift toward smaller values of the modified electron beta jump. These findings quantitatively support theoretical predictions of reconnection suppression in high-β e plasmas at low shears, attributed to X-line drift induced by pressure gradients across electron-scale current sheets.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Long-Time Variation of Magnetic Structure in (Pr x La 1-x )Co 2 Si 2 : Coexistence of Slow and Fast Processes in Magnetic Phase Transition

In this paper, long-time variations of the magnetic structure in PrCo 2 Si 2 and (Pr 0.98 La 0.02 )Co 2 Si 2 were studied by magnetization and time-resolved neutron scattering measurements. The amplitudes of magnetic Bragg peaks showed marked time variations after cooling or heating across the magnetic transition temperature T 1 between two different antiferromagnetic phases. However, the amplitude of the time variation decreased rapidly with increasing distance from T 1 . Finally, we analyzed the results on the basis of a phase transition model that includes the coexistence of fast and slow processes.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Dual-stage trapped-flux magnet cryostat for measurements at high magnetic fields

A method and a dual-stage trapped-flux magnet cryostat apparatus are provided for implementing enhanced measurements at high magnetic fields. The dual-stage trapped-flux magnet cryostat system includes a trapped-flux magnet (TFM). A sample, for example, a single crystal, is adjustably positioned proximate to the surface of the TFM, using a translation stage such that the distance between the sample and the surface is selectively adjusted. A cryostat is provided with a first separate thermal stage provided for cooling the TFM and with a second separate thermal stage provided for cooling sample.

42 ENGINEERING↗
DOE OSTI2019

Magnetic diode in artificial magnetic honeycomb lattice

A magnetic artificial honeycomb lattice comprising a multiplicity of connecting elements separated by hexagonal cylindrical pores, wherein: (a) the hexagonal cylindrical pores: (i) have widths that are substantially uniform and an average width that is in a range of about 15 nm to about 20 nm; and (ii) are substantially equispaced and have an average center-to-center distance that is in a range of about 25 nm to about 35 nm; and (b) the connecting elements comprise a magnetic material layer, and the connecting elements have: (i) lengths that are substantially uniform and an average length that is in a range of about 10 nm to about 15 nm; (ii) widths that are substantially uniform and an average width that is in a range of about 4 nm to 8 nm; and (iii) a thickness of the magnetic material layer that is substantially uniform and an average thickness that is in a range of about 2 nm to about 8 nm; and (c) the magnetic artificial honeycomb lattice has a surface area, disregarding the presence of the hexagonal cylindrical pores, that is in a range of about 100 mm.sup.2 to about 900 mm.sup.2.

Singh, Deepak Kumar↗
DOE OSTI2023

Permanent magnet alloys for gap magnets

Provided are Ce/Co/Cu permanent magnet alloys containing certain refractory metals, such as Ta and/or Hf, and optionally Fe which represent economically more favorable alternative to Sm-based magnets with respect to both material and processing costs and which retain and/or improve magnetic characteristics useful for GAP MAGNET applications.

Palasyuk, Andriy↗
DOE OSTI2018

Spin-Dependent Thermoelectric Effects in Double-Barrier Magnetic Tunnel Junctions with a Non-magnetic Metal Spacer

Spin-dependent thermoelectric (TE) effects are studied in MgO-based double-barrier magnetic tunnel junctions with a non-magnetic metal spacer (DBMTJs-NM) in the linear response regime. Using non-equilibrium Green’s function (NEGF) formalism, the results show resonant peaks at specific thicknesses of the NM spacer because of the resonant tunneling effect through the DBMTJs-NM. Effects of average temperature and magnetization alignment are also described. Therefore, thermally charge and spin voltage lead to large spin-dependent TE effects by the DBMTJs-NM structures.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Annealing Effects on Microstructure and Magnetic Properties of (NdPr){sub 9.5}(FeNbCoCu){sub 79.5}(BC){sub 11} Nanocomposite Magnets

Annealing effects on microstructure and magnetic properties of (NdPr){sub 9.5}(FeNbCo){sub 79.5}(BC){sub 11} ribbons were investigated. It was observed that Nd{sub 2}Fe{sub 14}B and Fe{sub 3}B phases were directly formed at low spinning speed. Then, the alloys transformed to an amorphous state at a speed of 20 m/s. Annealed at 700 {sup ∘}C for 10 min, the amorphous alloys as-quenched at 20 m/s crystallized into a nanocomposite composed of Nd{sub 2}Fe{sub 14}B and α-Fe phases. The formation of Fe{sub 3}B phases was inhibited. The magnetic properties firstly increased and then decreased with the increasing of annealing time. The optimum magnetic properties were achieved in the alloys annealed at 700 {sup ∘}C for 10 min. The corresponding coercivity, remanence, and the maximum energy product was 427.5 kA/m, 0.94 T, and 101.2 kJ/m{sup 3}, respectively. In addition, fine and uniform grains were formed. The average grain size was 10 nm.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Characteristics of a Degenerate Neutron Gas in a Magnetic Field with Allowance for the Anomalous Magnetic Moment of the Neutron

General expressions for the dependence of the Fermi energy, pressure, and total energy of a degenerate neutron gas in a magnetic field on the magnitude of the field and the neutron concentration with allowance for the anomalous magnetic moment of the neutron have been obtained in implicit form, and the dependence of these quantities on the field is presented in graphical form for the neutron concentration C = 10{sup 38} cm{sup –3}, which is typical for neutron stars. Analytical estimates of the pressure have been made for the magnitude of the fields possible in neutron stars ~10{sup 17}–10{sup 19} G and this neutron concentration ~10{sup 38} cm{sup –3}, including when the neutron gas is close to its saturated state with preferred orientation of the anomalous magnetic moment of all the neutrons in alignment with the field. It is found that even such fields ~10{sup 17} G have practically no effect on the pressure in comparison with the case when the field is absent, an effect being possible only for В ~ 10{sup 18}–10{sup 19} G. The analytical dependence on the neutron concentration of the corresponding field B{sub S} at which the neutron gas transitions to the saturated state has been found in explicit form. It is established that for B > B{sub S} the indicated characteristics of the neutron gas, and likewise its state, no longer change.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Synthesis, structure, and magnetic characterization of Cr{sub 4}US{sub 8}

The compound Cr{sub 4}US{sub 8} has been synthesized at 1073 K and its crystal structure has been determined at 100 K. The structure is modulated with a two-fold commensurate supercell. The subcell may be indexed in an orthorhombic cell but weak supercell reflections lead to the monoclinic superspace group P2{sub 1}/c(α0γ)0s with two Cr sites, one U site, and four S sites. The structure comprises a three-dimensional framework of CrS{sub 6} octahedra with channels that are partially occupied by U atoms. Each U atom in these channels is coordinated by eight S atoms in a bicapped trigonal-prismatic arrangement. The magnetic behavior of Cr{sub 4}US{sub 8} is complex. At temperatures above ~120 K at all measured fields, there is little difference between field-cooled and zero field-cooled data and χ(T) decreases monotonously with temperature, which is reminiscent of the Curie–Weiss law. At lower temperatures, the temperature dependence of χ(T) is complex and strongly dependent on the magnetic field strength. - Graphical abstract: Structure of Cr{sub 4}US{sub 8} viewed down the a axis. - Highlights: • At 1073 K Cr{sub 4}US{sub 8} was synthesized and at 100 K its crystal structure was determined. • The 3D structure comprises CrS{sub 6} octahedra with channels partially occupied by U. • The magnetic behavior of Cr{sub 4}US{sub 8} is complex.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Deep generative learning of magnetic frustration in artificial spin ice from magnetic force microscopy images

Increasingly large datasets of microscopic images with nanoscale resolution facilitate the development of machine learning methods to identify and analyze subtle physical phenomena embedded within the images. In this work, microscopic images of honeycomb lattice spin-ice samples serve as datasets from which we automate the calculation of net magnetic moments and directional orientations of spin-ice configurations. In the first stage of our workflow, machine learning models are trained to accurately predict magnetic moments and directions within spin-ice structures. Variational Autoencoders (VAEs), an emergent unsupervised deep learning technique, are employed to generate high-quality synthetic magnetic force microscopy (MFM) images and extract latent feature representations, thereby reducing experimental and segmentation errors. The second stage of proposed methodology enables precise identification and prediction of frustrated vertices and nanomagnetic segments, effectively correlating structural and functional aspects of microscopic images. This facilitates the design of optimized spin-ice configurations with controlled frustration patterns, enabling potential on-demand synthesis.

36 MATERIALS SCIENCE↗
DOE OSTI2013

On the structure of guide magnetic field in the inertia-driven magnetic reconnection with the presence of shear flow

The effect of equilibrium shear flow on the structure of out-of-plane magnetic field is analytically investigated in the two-fluid magnetohydrodynamic (MHD) regimes of the collisionless tearing instability, where the electron inertia breaks the frozen-in condition. Our scaling analysis reveals that the Alfvénic and sub-Alfvénic shear flows cannot significantly modify the linear regimes of applicability. In addition, we show that the structure of out-of-plane magnetic field can either be quadrupolar or non-quadrupolar in Hall-MHD regimes. In particular, both types of structures can dominate at β < 1 (β is the ratio of plasma kinetic pressure to the pressure in the magnetic field) depending on the value of the normalized ion inertial skin depth. This conclusion, however, is in contradiction to the claim presented by Rogers et al. [J. Geophys. Res. 108, A3 (2003)], which states that the quadrupolar structure cannot appear at β < 1. The reasons of this disagreement are discussed in our study.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Interaction of magnetic resonators studied by the magnetic field enhancement

It is the first time that the magnetic field enhancement (MFE) is used to study the interaction of magnetic resonators (MRs), which is more sensitive than previous parameters–shift and damping of resonance frequency. To avoid the coherence of lattice and the effect of Bloch wave, the interaction is simulated between two MRs with same primary phase when the distance is changed in the range of several resonance wavelengths, which is also compared with periodic structure. The calculated MFE oscillating and decaying with distance with the period equal to resonance wavelength directly shows the retardation effect. Simulation also shows that the interaction at normal incidence is sensitive to the phase correlation which is related with retardation effect and is ultra-long-distance interaction when the two MRs are strongly localized. When the distance is very short, the amplitude of magnetic resonance is oppressed by the strong interaction and thus the MFE can be much lower than that of single MR. This study provides the design rules of metamaterials for engineering resonant properties of MRs.

36 MATERIALS SCIENCE↗