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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 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Contribution of Electron Pressure to Ring Current and Ground Magnetic Depression Using RAM-SCB Simulations and Arase Observations During 7–8 November 2017 Magnetic Storm

Understanding the physical processes that control the dynamics of energetic particles in the inner magnetosphere is important for both space-borne and ground-based assets essential to the modern society. The storm time distribution of ring current particles in the inner magnetosphere depends strongly on their transport in the evolving electric and magnetic fields along with particle acceleration and loss. Here, we investigated the ring current particle variations using observations and simulations. We compared the ion (H + , He + , and O + ) and electron flux and plasma pressure variations from Arase observations with the self-consistent inner magnetosphere model: Ring current Atmosphere interactions Model with Self Consistent magnetic field (RAM-SCB) during the 7–8 November 2017 geomagnetic storm. We investigated the contribution of the different species (ions and electrons) to the magnetic field deformation observed at ground magnetic stations (09°–45° MLat) using RAM-SCB simulations. The results show that the ions are the major contributor with ~88% and electrons contribute ~12% to the total ring current pressure. It is also found that the electron contribution is non-negligible (~18%) to the ring current in dawn-side during the main phase of the storm. Thus, the electron contribution to the storm time ring current is important and should not be neglected.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Strong 3D and 1D magnetism in hexagonal Fe-chalcogenides FeS and FeSe vs. weak magnetism in hexagonal FeTe

We present a comparative theoretical study of the hexagonal forms of the Fe-chalcogenides FeS, FeSe and FeTe with their better known tetragonal forms. While the tetragonal forms exhibit only an incipient antiferromagnetism and experimentally show superconductivity when doped, the hexagonal forms of FeS and FeSe display a robust magnetism. We show that this strong magnetism arises from a van Hove singularity associated with the direct Fe-Fe c-axis chains in the generally more three-dimensional NiAs structure. We also find that hexagonal FeTe is much less magnetic than the other two hexagonal materials, so that unconventional magnetically-mediated superconductivity is possible, although a large T c value is unlikely.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Self-healing magnetic nanocomposites with robust mechanical properties and high magnetic actuation potential prepared from commodity monomers via graft-from approach

Herein, we report the design, synthesis and characterization of self-healing magnetic nanocomposites prepared from readily available commodity monomers. These multi-functional materials demonstrate robust mechanical properties, with a Young's modulus of 70 MPa and over 500% extensibility. The magnetic nanocomposites also show self-healing ability, achieving 46% recovery of extensibility in 5 hours in ambient conditions while retaining high magnetic actuation with a commodity magnet.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Emergent kink stability of a magnetized plasma jet injected into a transverse background magnetic field

In this paper, we report experimental results on the injection of a magnetized plasma jet into a transverse background magnetic field in the HelCat linear plasma device at the University of New Mexico [M. Gilmore et al., J. Plasma Phys. 81(1), 345810104 (2015)]. After the plasma jet leaves the plasma-gun muzzle, a tension force arising from an increasing curvature of the background magnetic field induces in the jet a sheared axial-flow gradient above the theoretical kink-stabilization threshold. Finally, we observe that this emergent sheared axial flow stabilizes the n = 1 kink mode in the jet, whereas a kink instability is observed in the jet when there is no background magnetic field present.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Soft x-ray absorption spectroscopy and magnetic circular dichroism as operando probes of complex oxide electrolyte gate transistors

Electrolyte-based transistors utilizing ionic liquids/gels have been highly successful in the study of charge-density-controlled phenomena, particularly in oxides. Experimental probes beyond transport have played a significant role, despite challenges in their application in electric double-layer transistors. Here, we demonstrate the application of synchrotron soft x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) as operando probes of the charge state and magnetism in ion-gel-gated ferromagnetic perovskite films. Electrochemical response via oxygen vacancies at positive gate bias in LaAlO 3 (001)/La 0.5 Sr 0.5 CoO 3-δ is used as a test case. XAS/XMCD measurements of 4–25 unit-cell-thick films first probe the evolution of hole doping (from the O K-edge pre-peak) and ferromagnetism (at the Co L-edges), to establish a baseline. Operando soft XAS/XMCD of electrolyte-gated films is then demonstrated, using optimized spin-coated gels with a thickness of ~1 μm and a specific composition. The application of gate voltages up to +4 V is shown to dramatically suppress the O K-edge XAS pre-peak intensity and Co L-edge XMCD, thus enabling the Co valence and ferromagnetism to be tracked upon gate-induced reduction. Soft XAS and XMCD, with appropriate electrolyte design, are thus established to be viable for the operando characterization of electrolyte-gated oxides.

Yu, Biqiong↗
DOE OSTI2018

Cubic phase stability, optical and magnetic properties of Cu-stabilized zirconia nanocrystals

By means of experimental and ab initio investigations, in this article we report on the cubic phase stability of Cu doped zirconia (ZrO 2 ) at room temperature, and further characterize its structural, optical and magnetic properties. Various compositions of Zr 1– x Cu x O 2 (0.01 ≤ x ≤ 0.25) nanocrystallites of average size ~16 nm were synthesized using co-precipitation technique. Thermal analysis and kinetics of crystallization revealed that the cubic phase at ambient temperature can be stabilized by using a critical calcination temperature of 500 °C for 8 h in air and a critical composition of $x_c$ = 0.10 ± 0.05. For $x < x_c$, some undigested monoclinic phase of ZrO 2 exists together with the cubic structure. However, for $x > x_c$, the monoclinic CuO emerges as a secondary phase with shrinkage of unit-cell volume with increasing the Cu content. At x = 0.05 and 500 °C calcination temperature, we observe a high degree of cubic crystallinity which breaks down into monoclinic phase with increasing calcination temperature beyond 550 °C. Electron magnetic resonance studies provide evidence for the substitution of Cu 2+ ( 2 D 5/9 ,3d 9 ) ions at Zr 4+ sites with g ∥ = 2.250, g ⊥ = 2.018 and average g a = (g ∥ + 2g ⊥ )/3 ~ 2.1. The temperature dependence of magnetic susceptibility measurements from 2 K to 300 K exhibits Curie–Weiss behaviour whose analysis using g a = 2.1 and spin S = 1/2 yields x = 0.028 and x = 0.068 for the nominal x = 0.05 and x = 0.20 samples, respectively. This magnetic analysis confirms the findings from x-ray diffraction that only a part of Cu is successfully doped into cubic phase of Cu-doped ZrO 2 . The optical bandgap decreases with increasing x, which is due to the emergence of Cu-d states at Fermi-level near the valence bands, thus making Cu-doped zirconia a hole doped (p-type) semiconductor.

electron spin resonance↗
DOE OSTI2020

Effect of geometric and magnetic boundary conditions on magnetic islands in 3D force-free ideal MHD equilibria

Three-dimensional boundary features and magnetic perturbations affect the magnetic topology of the force-free ideal MHD equilibria formed within a given volume. The use of the PSI-Tet 3D finite-element equilibrium code reveals the existence of magnetic islands inside such equilibria within boundaries with three-dimensional features in configurations that directly depend on the natures of those features. Here, the nature and limits of the influence of such features are explored, as is the influence of flux boundary conditions to qualitatively identify the structure of magnetic islands in Taylor state equilibria with three-dimensional boundary conditions.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2026

Incommensurate Magnetism Drives Singular Angular Magnetoresistance in the Magnetic Weyl Semimetal CeAlGe

Here, we demonstrate that a multi-𝐤 incommensurate magnetic state in the Weyl semimetal CeAlGe gives rise to a singular angular magnetoresistance (SAMR), which is an electrical transport signature capable of detecting magnetic field direction with exceptional precision. In contrast, its sister compound CeAlSi is devoid of both multi-𝐤 order and SAMR. We reveal that both phenomena appear upon 57% Ge substitution in CeAlSi 1−𝑥⁢ Ge 𝑥 and coincide with electronic structure changes that soften the single-ion in-plane anisotropy and enhance Weyl-mediated magnetic interactions. These results unveil a remarkable connection between band topology, electronic transport, and collective magnetism in Weyl semimetals.

Yao, Xiaohan [Boston College, Chestnut Hill, MA (U↗
DOE OSTI2020

Magnetic detwinning and biquadratic magnetic interaction in EuFe 2 As 2 revealed by 153 Eu NMR

In the nematic state of iron-based superconductors, twin formation often obscures the intrinsic, anisotropic, in-plane physical properties. Relatively high in-plane external magnetic fields H ext greater than the typical laboratory-scale magnetic fields 10–15 T are usually required to completely detwin a sample. However, recently a very small in-plane H ext ~ 0.1 T was found to be sufficient for detwinning the nematic domains in EuFe 2 As 2 . To explain this behavior, a microscopic theory based on biquadratic magnetic interactions between the Eu and Fe spins has been proposed. In this paper, using 153 Eu nuclear magnetic resonance (NMR) measurements below the Eu 2+ ordering temperature, we show experimental evidence of the detwinning under small in-plane H ext . Our NMR study also reveals the evolution of the angles between the Eu and Fe spins during the detwinning process, which provides experimental evidence for the existence of biquadratic coupling in the system.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Topological and magnetic properties of a noncollinear spin state on a honeycomb lattice in a magnetic field

Here, this paper studies the topological and magnetic properties of a noncollinear spin state on a honeycomb lattice that evolves from coplanar to ferromagnetic with a magnetic field applied along the z axis. The coplanar state is stabilized by nearest-neighbor ferromagnetic interactions, single-ion anisotropy along z, and DzyaloshinskiiMoriya interactions between next-nearest-neighbor sites. Below the critical field H$_c$ that aligns the spins, the magnetic unit cell contains six sites and the spin dynamics contains six magnon modes. Although the classical energy is degenerate with respect to the twist angle φ between nearest-neighbor spins, the dependence of the free energy on φ at low temperatures is dominated by the magnon zero-point energy, which contains extremum at φ = πl/3 for integer l. The only unique ground states GS(φ) have l = 0 or 1. For H < H$'_c$, the zero-point energy has minima at even l and the ground state is GS(0); for H$'_c$ < H < H$'_c$, the zero-point energy has minima at odd l and the ground state is GS(π/3). In GS(0), the magnon density of states exhibits five distinct topological phases with increasing field associated with the opening and closing of energy gaps between two or three magnonic bands. While the Berry curvature vanishes for the coplanar φ = 0 phase in zero field, the Berry curvature and Chern numbers exhibit signatures of the five topological phases below H$'_c$. Whereas the Berry curvature and Chern number are sensitive to changes in the magnon density of states within GS(π/3), the inelastic spectrum S(k,ω) is sensitive to changes in the intensity of the magnon modes in the different magnetic phases GS(0) and GS(π/3) rather than the five topological phases within GS(π/3).

Fishman, Randy S. [Oak Ridge National Laboratory (↗
DOE OSTI2025

Magnetic glassiness in noncentrosymmetric Sm 7 Pd 3 : Interplay of magnetic frustration, long-range order, and frozen domains

Here, we present a comprehensive investigation of the intricate spin dynamics in the noncentrosymmetric compound Sm 7 ⁢Pd 3 , revealing the coexistence of spin-glass, domain-glass, and ferromagnetic (FM) behaviors. Magnetic field-dependent measurements indicate large coercivity, suggesting ferromagnetic domain formation below the Curie temperature (𝑇 C ≈ 173 K), while temperature-dependent magnetization data point to antiferromagnetic (AFM) coupling, highlighting the competition between FM and AFM interactions. Detailed ac susceptibility, isothermal remanent magnetization, and aging effect measurements demonstrate the presence of two distinct types of glassiness in the sample, and their possible origins are discussed extensively. Magnetization measurements reveal the mixing of the 𝐽 = 5/2 ground state of Sm 3+ with the excited 𝐽 = 7/2 multiplet, lying 965 K above. The specific heat data show further crystalline electric field splitting of the 𝐽 = 5/2 state into a ground-state doublet and a fourfold-degenerate excited state.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Tipping the magnetic instability in paramagnetic S r 3 R u 2 O 7 by Fe impurities [Tipping the magnetic instability in paramagnetic S r 3 R u 2 O 7 by modest Fe substitution]

We report the magnetic and electronic properties of the bilayer ruthenate Sr 3 Ru 2 O 7 upon Fe substitution for Ru. We find that Sr 3 (Ru 1-x Fe x ) 2 O 7 shows spin-glass-like phase below 4 K for x = 0.01 and commensurate E-type antiferromagnetically ordered insulating ground state characterized by the propagation vector q c = (0.25 0.25 0) for x ≥ 0.03, in contrast to the paramagnetic metallic state in the parent compound with strong spin fluctuations occurring at wave vectors q = (0.09 0 0) and (0.25 0 0). The observed antiferromagnetic ordering is quasitwo-dimensional with very short correlation length along the c axis, a feature similar to the Mndoped Sr 3 Ru 2 O 7 . Lastly, our results suggest that this ordered ground state is associated with the intrinsic magnetic instability in the pristine compound, which can be readily tipped by the local magnetic coupling between the 3d orbitals of the magnetic dopants and Ru 4d orbitals.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Magnetic interactions in PdCrO 2 and their effects on its magnetic structure

We report a neutron scattering study of the metallic triangular lattice antiferromagnet PdCrO 2 . Powder neutron diffraction measurements confirm that the crystalline space group symmetry remains R$\bar{3}$m below T N . This implies that magnetic interactions consistent with the crystal symmetry do not stabilize the noncoplanar magnetic structure, which was one of two structures previously proposed on the basis of single crystal neutron diffraction measurements. Inelastic neutron scattering measurements find two gaps at low energies, which can be explained as arising from a dipolar-type exchange interaction. This symmetric anisotropic interaction also stabilizes a magnetic structure very similar to the coplanar magnetic structure, which was also suggested by the single crystal diffraction study. In conclusion, the higher-energy magnon dispersion can be modelled by linear spin-wave theory with exchange interactions up to sixth nearest neighbors, but discrepancies remain which hint at additional effects unexplained by the linear theory.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Pair Invariant Mass to Isolate Background in the Search for the Chiral Magnetic Effect in Au+Au Collisions at √sNN = 200 GeV

Quark interactions with topological gluon configurations can induce local chirality imbalance and parity violation in quantum chromodynamics, which can lead to the chiral magnetic effect (CME)-an electric charge separation along the strong magnetic field in relativistic heavy-ion collisions. The CME-sensitive azimuthal correlator observable (Delta gamma) is contaminated by background arising, in part, from resonance decays coupled with elliptic anisotropy (v(2)). We report here differential measurements of the correlator as a function of the pair invariant mass (m(inv)) in 20-50% centrality Au + Au collisions at root s(NN) = 200 GeV by the STAR experiment at the BNL Relativistic Heavy Ion Collider. Strong resonance background contributions to Delta gamma. are observed. At large m(inv) where this background is significantly reduced, the Delta gamma. value is found to be significantly smaller. An event-shape-engineering technique is deployed to determine the v(2) background shape as a function of m(inv). We extract a v(2)-independent and m(inv)-averaged signal Delta gamma(sig) = (0.03 +/- 0.06 +/- 0.08) x 10(-4), or (2 +/- 4 +/- 5)% of the inclusive Delta gamma (m(inv) > 0.4 GeV/c(2)) = (1.58 +/- 0.02 +/- 0.02) x 10(-4), within pion p(T) = 0.2-0.8 GeV/c and averaged over pseudorapidity ranges of -1 < eta < -0.05 and 0.05 < eta < 1. This represents an upper limit of 0.23 x 10(-4), or 15% of the inclusive result, at 95% confidence level for the m(inv)-integrated CME contribution.

Adam, J.↗
DOE OSTI2017

Tuning Perpendicular Magnetic Anisotropy by Oxygen Octahedral Rotations in ( La 1 – x Sr x MnO 3 ) / ( SrIrO 3 ) Superlattices

Here, perpendicular magnetic anisotropy (PMA) plays a critical role in the development of spintronics, thereby demanding new strategies to control PMA. Here we demonstrate a conceptually new type of interface induced PMA that is controlled by oxygen octahedral rotation. In superlattices comprised of La 1–x Sr x MnO 3 and SrIrO 3 , we find that all superlattices (0 ≤ x ≤ 1) exhibit ferromagnetism despite the fact that La 1–x Sr x MnO 3 is antiferromagnetic for x > 0.5. PMA as high as 4 × 10 6 erg/cm 3 is observed by increasing x and attributed to a decrease of oxygen octahedral rotation at interfaces. We also demonstrate that oxygen octahedral deformation cannot explain the trend in PMA. These results reveal a new degree of freedom to control PMA, enabling discovery of emergent magnetic textures and topological phenomena.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Magnetic Excitations across the Metal-Insulator Transition in the Pyrochlore Iridate Eu 2 Ir 2 O 7 [Evolution of Magnetic Excitations across the Metal-Insulator Transition in the Pyrochlore Iridate Eu 2 Ir 2 O 7 ]

Here, we report a resonant inelastic x-ray scattering study of the magnetic excitation spectrum in a highly insulating Eu 2 Ir 2 O 7 single crystal that exhibits a metal-insulator transition at T MI = 111(7) K. A propagating magnon mode with a 20 meV bandwidth and a 28 meV magnon gap is found in the excitation spectrum at 7 K, which is expected in the all-in-all-out magnetically ordered state. This magnetic excitation exhibits substantial softening as the temperature is raised towards T MI and turns into a highly damped excitation in the paramagnetic phase. Remarkably, the softening occurs throughout the whole Brillouin zone including the zone boundary. This observation is inconsistent with the magnon renormalization expected in a local moment system and indicates that the strength of the electron correlation in Eu 2 Ir 2 O 7 is only moderate, so that electron itinerancy should be taken into account in describing its magnetism.

74 ATOMIC AND MOLECULAR PHYSICS↗