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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 595 records · Page 33
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Manipulation of the Electronic State of Mott Iridate Superlattice through Protonation Induced Electron-Filling

Spin-orbit-coupled Mott iridates show great similarity with parent compounds of superconducting cuprates, attracting extensive research interest especially for their electron-doped states. However, previous experiments have been largely limited within a small doping range due to the absence of effective dopants, and therefore the electron-doped phase diagram remains elusive. Here, an ionic-liquid-gating-induced protonation method is utilized to achieve electron-doping into a 5d Mott-insulator built with a SrIrO 3 /SrTiO 3 superlattice (SL), and a systematic mapping of its electron-doped phase diagram is achieved with the evolution of the iridium valence state from 4+ to 3+, equivalent to doping of one electron per iridium ion. Along increasing doping level, the parent Mott-insulator is first turned into a localized metallic state with gradually suppressed magnetic ordering, and then further evolves into a nonmagnetic band insulating state. This work forms an important step forward for the study of electron-doped Mott iridate systems, and the strategy of manipulating the band filling in an artificially designed SL structure can be readily extended into other systems with more exotic states to explore.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Equilibrium spin polarization arising from chirality

Chirality-induced spin selectivity (CISS) describes how chiral molecules and materials generate spin polarization even at thermal equilibrium. This observation has challenged established principles of microscopic reversibility and Onsager reciprocity. We resolve this paradox by formulating a pseudo-Hermitian quantum framework that separates thermodynamic equilibrium from time-reversal symmetry. Within this approach, structural chirality and electron correlations, irrespective of their microscopic origin, are sufficient to produce CISS observables. Chirality enters through a non-local metric η that couples spin and spatial motion, leading to real spectra, unitary evolution, and thermodynamic consistency. The framework predicts a chirality-induced spin magnetic ordering characterized by a spin-displacement order, which reconciles equilibrium spin polarization with detailed balance and explains the persistence of CISS in materials composed of light elements. We derive generalized Onsager-Casimir relations that respect the observed CISS symmetry, i.e., parity $(\mathscr{P})$-odd and time-reversal $(\mathscr{T})$-odd, but exhibiting $\mathscr{PT}$-even symmetry. This approach establishes a coherent foundation for equilibrium CISS and provides a route to link chemical chirality with measurable spin-to-charge conversion effects.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Machine learning study of magnetism in uranium-based compounds

Actinide and lanthanide-based materials display exotic properties that originate from the presence of itinerant or localized f electrons and include unconventional superconductivity and magnetism, hidden order, and heavy-fermion behavior. Due to the strongly correlated nature of the 5f electrons, magnetic properties of these compounds depend sensitively on applied magnetic field and pressure, as well as on chemical doping. However, precise connection between the structure and magnetism in actinide-based materials is currently unclear. In this investigation, we established such structure-property links by assembling and mining two datasets that aggregate, respectively, the results of high-throughput density functional theory simulations and experimental measurements for the families of uranium- and neptunium-based binary compounds. Various regression algorithms were utilized to identify correlations among accessible attributes (features or descriptors) of the material systems and predict their cation magnetic moments and general forms of magnetic ordering. Descriptors representing compound structural parameters and cation f-subshell occupation numbers were identified as most important for accurate predictions. The best machine learning model developed employs the random forest regression algorithm. It can predict both spin and orbit moment size with root-mean-square error of 0.17 μ B and 0.19 μ B , respectively. Lastly, the random forest classification algorithm is used to predict the ordering (paramagnetic, ferromagnetic, and antiferromagnetic) of such systems with 76% accuracy.

36 MATERIALS SCIENCE↗
NASA NTRS1990

DE-2 observations of filamentary currents at ionospheric altitudes

Conjunctive measurements made by the Dynamics Explorer 1 and 2 spacecraft on October 22, 1981, under conditions of southward IMF, suggest the existence of a cusp ion injection from a region at the magnetopause with a scale size of about 1/2 to 1 earth radii. Current signatures observed by the LAPI and MAGB instruments on board DE-2 indicate the existence of a rotation in the magnetic field that is consistent with a filamentary current system. The observed current structure can be interpreted as the ionospheric signature of a flux transfer event (FTE). In addition to this large-scale current structure there exist three small-scale filamentary current pairs. These current pairs close locally and thus, if the present interpretation of this event as an FTE is correct, represent the first reported observations of FTE interior structure at low-altitudes.

Smith, M. F.↗
NASA NTRS2012

DC and Structured Electric Fields Observed on the C/NOFS Satellite and Their Association with Longitude, Plasma Density, and Solar Activity

Observations of DC electric fields and associated E x B plasma drifts gathered by the Vector Electric Field Investigation (VEFI) on the Air Force Communication/Navigation Outage Forecasting System (C/NOFS) satellite are presented. We show statistical averages of the vector fields and resulting E x B plasma flows for the first three years of operations as a function of season, longitude, local time, and Fl 0.7 conditions. Magnetic field data from the VEFI science magnetometer are used to compute the plasma flows. Although typically displaying eastward and outward-directed fields during the day and westward and downward-directed fields at night, the data from DC electric field detector often reveal variations from this pattern that depend on longitude, solar activity, and plasma density. Clear "wave-4" tidal effects in both electric field components have been detected and will be presented. Zonal plasma drifts show a marked variation with solar activity and may be used as a proxy for neutral winds at night. Evidence for pre-reversal enhancements in the meridional drifts that depend on solar activity is present for some longitudes, and are corroborated by clear evidence in the plasma density data that the spacecraft journeyed below the F-peak during evenings when the rise in the ionosphere is most pronounced. In addition to DC electric fields, the data reveal considerable electric field structures at large scales (approx 100's of km) that are usually confined to the nightside. Although such electric field structures are typically associated with plasma density depletions and structures, what is surprising is the number of cases in which large amplitude, structured DC electric fields are observed without a significant plasma density counterpart structure, including their appearance at times when the ambient plasma density appears relatively quiescent. We investigate the mapping of structured electric fields along magnetic field lines from distant locations and consider tropospheric thunderstorm sources to explain some of the observations. The dependence of the structuring on season and solar activity will be reported and discussed.

Pfaff, Robert↗
DOE OSTI2025

Bounce-averaged theory in arbitrary multi-well plasmas: solution domains and the graph structure of their connections

Bounce-averaged theories provide a framework for simulating relatively slow processes, such as collisional transport and quasilinear diffusion, by averaging these processes over the fast periodic motions of a particle on a closed orbit. This procedure dramatically increases the characteristic time scale and reduces the dimensionality of the modelled system. The natural coordinates for such calculations are the constants of motion (COM) of the fast particle motion, which by definition do not change during an orbit. However, for sufficiently complicated fields – particularly in the presence of local maxima of the electric potential and magnetic field – the COM are not sufficient to specify the particle trajectory. In such cases, multiple domains in COM space must be used to solve the problem, with boundary conditions enforced between the domains to ensure continuity and particle conservation. Previously, these domains have been imposed by hand, or by recognising local maxima in the fields, limiting the flexibility of bounce-averaged simulations. Here, we present a general set of conditions for identifying consistent domains and the boundary condition connections between the domains, allowing the application of bounce-averaged theories in arbitrarily complicated and dynamically evolving electromagnetic field geometries. We also show how the connections between the domains can be represented by a directed graph, which can help to succinctly represent the trajectory bifurcation structure.

fusion plasma↗
DOE OSTI2023

Quasi-one-dimensional Ising-like antiferromagnetism in the rare-earth perovskite oxide TbScO 3

The rare-earth perovskite TbScO 3 has been widely used as a substrate for the growth of epitaxial ferroelectric and multiferroic thin films, while its detailed low-temperature magnetic properties were rarely reported. In this paper, we performed detailed magnetization, specific heat, and single crystal neutron scattering measurements, along with the crystalline electric field calculations to study the low-temperature magnetic properties of TbScO 3. All our results suggest the magnetic Tb 3+ has an Ising-like pseudo-doublet ground state at low temperatures. Due to the constrain of local point symmetry, these Tb 3+ Ising moments are confined in the ab plane with a tilt angle of φ=±48° to the a axis. In zero field, the system undergoes an antiferromagnetic phase transition at T N =2.53 K, and forms a G x A y noncollinear magnetic structure below T N . Here, we find the dipole-dipole interactions play an important role to determine the magnetic ground state, which are also responsible for the quasi-one-dimensional magnetism in TbScO 3 . The significant anisotropic diffuse scatterings further confirm the quasi-one-dimensional magnetism along the c axis. The magnetic phase diagram with the field along the easy b axis is well established. In addition to the G x A y antiferromagnetic state, there is an exotic field-induced phase emerged near the critical field B c ≃0.7 T, where three-dimensional magnetic order is suppressed but strong one-dimensional correlations may still exist.

36 MATERIALS SCIENCE↗
NASA NTRS1990

Magnetic flux ropes in 3-dimensional MHD simulations

The interaction of the solar wind and the earth's magnetosphere is presently simulated by a 3D, time-dependent, global MHD method in order to model the magnetopause and magnetotail generation of magnetic flux ropes. It is noted that strongly twisted and localized magnetic flux tubes simular to magnetic flux ropes appear at the subpolar magnetopause when the IMF has a large azimuthal component, as well as a southward component. Plasmoids are generated in the magnetotail after the formation of a near-earth magnetic neutral line; the magnetic field lines have a helical structure that is connected from dawn to dusk.

Ogino, Tatsuki↗
NASA NTRS1993

Comment on 'Observations of reconnection of interplanetary and lobe magnetic field lines at the high-latitude magnetopause' by J.T. Gosling, M.F. Thomsen, S.J. Bame, R.C. Elphic, and C.T. Russell

Comment is presented on the results of measurements, reported by Gosling et al. (1991), that were made on ISEE in the vicinity of the high-latitude dusk magnetopause near the terminator plane, at a time when the local magnetosheath and tail lobe magnetic fields were nearly oppositely directed. The character of the observed plasma flowing both tailward and sunward within the high-latitude magnetopause current layer presented real evidence for the local reconnection process. Gosling et al. argued that this process may be a manifestation of different global magnetospheric topology structures. In the comment, a global magnetospheric convection pattern is constructed for the northward IMF and for the case of a large azimuthal component of the IMF with small Bz, irrespective of its sign. The suggested scheme provides a simple explanation for the observed sunward convection in the polar caps both for the northward and for strong By with small Bz. According to the present model, for the magnetosheath field at 2300 UT on June 11, 1978, the reconnection between the open field lines appears at the northern neutral point.

Belen'kaia, Elena↗
NASA NTRS1994

Equilibrium structure of solar magnetic flux tubes: Energy transport with multistream radiative transfer

We examine the equilibrium structure of vertical intense magnetic flux tubes on the Sun. Assuming cylindrical geometry, we solve the magnetohydrostatic equations in the thin flux-tube approximation, allowing for energy transport by radiation and convection. The radiative transfer equation is solved in the six-stream approximation, assuming gray opacity and local thermodynamic equilibrium. This constitutes a significant improvement over a previous study, in which the transfer was solved using the multidimensional generalization of the Eddington approximation. Convection in the flux tube is treated using mixing-length theory, with an additional parameter alpha, characterizing the suppression of convective energy transport in the tube by the strong magnetic field. The equations are solved using the method of partial linearization. We present results for tubes with different values of the magnetic field strength and radius at a fixed depth in the atmosphere. In general, we find that, at equal geometric heights, the temperature on the tube axis, compared to the ambient medium, is higher in the photosphere and lower in the convection zone, with the difference becoming larger for thicker tubes. At equal optical depths the tubes are generally hotter than their surroundings. The results are comparatively insensitive to alpha but depend upon whether radiative and convective energy transport operate simultaneously or in separate layers. A comparison of our results with semiempirical models shows that the temperature and intensity contrast are in broad agreement. However, the field strengths of the flux-tube models are somewhat lower than the values inferred from observations.

Hasan, S. S.↗
NASA NTRS2003

Turbulent Simulation of the Dynamics of the Magnetotail

In situ observations indicate that the dynamical processes in the geoplasma environment generally entail localized intermittent processes and anomalous global transports. It was suggested by T. Chang that instead of considering the turbulence as a mixture of interacting waves, such type of patchy intermittency could be more easily understood in terms of the development, interaction, merging, preferential acceleration and evolution of coherent magnetic structures. In this three-year project, we have used direct numerical MHD simulations to study some aspects of the MHD dynamics in Chang's model. Our large-scale numerical calculations and simulations have been supplemented by and coordinated with theoretical studies conducted by Chang and his colleagues.

Wu, Cheng-Chin↗
DOE OSTI2024

Filling-enforced obstructed atomic insulators

Topological band theory has achieved great success in the high-throughput search for topological band structures both in paramagnetic and magnetic crystal materials. However, a significant proportion of materials are topologically trivial insulators at the Fermi level. In this paper, we show that, remarkably, for a subset of the topologically trivial insulators, knowing only their electron number and the Wyckoff positions of the atoms we can separate them into two groups: the obstructed atomic insulator (OAI) and the atomic insulator (AI). The interesting group, the OAI, have a center of charge not localized on the atoms. Using the theory of topological quantum chemistry, in this work we first derive the necessary and sufficient conditions for a topologically trivial insulator to be a filling enforced obstructed atomic insulator (feOAI) in the 1651 Shubnikov space groups. Remarkably, the filling enforced criteria enable the identification of obstructed atomic bands without knowing the representations of the band structures. Hence, no calculations are needed for the filling enforced criteria, although they are needed to obtain the band gaps. With the help of the Topological Quantum Chemistry website, we have performed a high-throughput search for feOAIs and have found that 957 ICSD entries (638 unique materials) are paramagnetic feOAIs, among which 738 (475) materials have an indirect gap. The metallic obstructed surface states of feOAIs are also showcased by several material examples. Published by the American Physical Society 2024

Materials Science↗
NASA NTRS1997

UVI Auroral Observations During the January 10, 1997 Magnetic Cloud Event

Solar wind IMF and plasma conditions surrounding the January 10-11 magnetic cloud event provided very interesting observations relating to magnetospheric and ionospheric processes. Prior to the arrival of the magnetic cloud a shock front followed by abrupt swings in the IMF orientation were observed by the Wind spacecraft at about 100 Re upstream. The Polar Ultraviolet Imager (UVI) near apogee over the northern hemisphere recorded the encounter of the shock with the magnetosphere. Enhancement of dayside precipitation around noon MLT and progression of the enhancement along dawn and dusk flanks of the oval culminating in a very localized pseudo onset near midnight MLT were observed. During the following mainly northward IMF the polar cap region was the site of multiple sunward aligned arcs and curled arc structures that persisted until the IMF turned rapidly southward. While the IMF remained southward the polar cap cleared of arc structures and expanded, and the auroral oval became very thin. No substorms were observed for at least 25 minutes after the following northward turning contrary to what might be expected on the basis of recent reports of substorm initiation by northward turning of the IMF. These observations and others during the magnetic cloud event provide a clear case study of the effect of the solar wind on dayside precipitation, thickness of the boundary layer, magnetosphere-polar cap magnetic topology and sources of the polar cap precipitation, and triggering of substorms. These issues will be discussed along with the presentation of the UVI auroral observations and solar wind measurements.

Brittnacher, M. J.↗
DOE OSTI2022

Epitaxial intergrowths and local oxide relaxations in natural bixbyite Fe 2– x Mn x O 3

The scattering pattern of a crystal obeys the symmetry of the crystal structure through the corresponding Laue group. This is usually also true for the diffuse scattering, containing information about disorder, but here a case is reported where the diffuse scattering is of lower symmetry than the parent crystal structure. The mineral bixbyite has been studied by X-ray and neutron scattering techniques since 1928 with some of the most recent studies characterizing the low-temperature transition to a magnetically disordered spin-glass state. However, bixbyite also exhibits structural disorder, and here single-crystal X-ray and neutron scattering is used to characterize the different modes of disorder present. One-dimensional rods of diffuse scattering are observed in the cubic mineral bixbyite, which break the expected symmetry of the scattering pattern. It is shown that this scattering arises from epitaxial intergrowths of the related mineral, braunite. The presence of this disorder mode is found to be directly observable as well-defined residuals in the average structure refined against the Bragg diffraction. An additional three-dimensional diffuse scattering component is observed in neutron scattering data, which is shown to originate from the substitutional disorder on the Fe/Mn sites. This occupational disorder gives rise to local relaxations of the oxide sublattice, and the pattern of oxide displacements can be rationalized based on crystal-field theory. The combined use of neutron and X-ray single-crystal scattering techniques highlights their great complementarity. In particular, the large sample requirements for neutron scattering experiments prove to be an obstacle in solving the intergrowth disorder due to several growth orientations, whereas for X-ray scattering the one-dimensional nature of the intergrowth disorder renders solving this a more tractable task. On the other hand, the oxide relaxations cannot be resolved using X-rays due to the low Mn/Fe contrast. By combining the two approaches both types of disorder have been characterized.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Exchange field enhanced upper critical field of the superconductivity in compressed antiferromagnetic EuTe2

Abstract Understanding the interplay between superconductivity and magnetism has been a longstanding challenge in condensed matter physics. Here we report high pressure studies on the C -type antiferromagnetic semiconductor EuTe 2 up to 36.0 GPa. A structural transition from the I4/mcm to the C2/m space group is identified at ~16 GPa. Superconductivity is observed above ~5 GPa in both structures. In the low-pressure phase, magnetoresistance measurements reveal strong couplings between the local moments of Eu 2+ and the conduction electrons of Te 5 p orbits. The upper critical field of superconductivity is well above the Pauli limit. While EuTe 2 becomes nonmagnetic in the high-pressure phase and the upper critical field drops below the Pauli limit. Our results demonstrate that the high upper critical field of EuTe 2 in the low-pressure phase is due to the exchange field compensation effect of Eu 2+ and the superconductivity in both structures may arise in the framework of the Bardeen-Cooper-Schrieffer theory.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRSDate not supplied

Decoding the energy inputs that drive the upper atmosphere with NASA’s Geospace Dynamics Constellation (GDC)

NASA’s Geospace Dynamics Constellation (GDC) mission will study the effect of space weather phenomena on Earth’s upper atmosphere ion and neutral gases and, in turn, their impact on human assets. GDC will provide multi-point observations to determine how the Earth’s upper atmosphere is driven to dynamic changes and extremes by the solar wind. Magnetospheric energy input, both kinetic and electromagnetic, will be captured by the Comprehensive Auroral Precipitation Experiment (CAPE), the Thermal Plasma Sensor (TPS), and the Near Earth Magnetometer Instrument in a Small Integrated System (NEMISIS). CAPE captures the complete kinetic energy inputs with observations of the precipitating and upgoing electrons and precipitating ions. TPS captures part of the electromagnetic energy inputs with observations of the thermal plasma velocity that map E-field inputs, and NEMISIS captures the other part of the electromagnetic energy input with measurements of magnetic field variations due to field aligned currents. We use similar observations from the Defense Meteorological Space Platform (DMSP) satellites to demonstrate the balance between the different energy inputs (electron and ion Joule heating and Poynting flux) during the different phases of storms. We explore the local time and spatial structure and the impact they have on atmospheric density and winds with simulations of the Global Ionosphere and Thermosphere Model (GITM) and demonstrate how GDC will enable us to reconstruct those energy inputs locally and regionally

Eftyhia Zesta↗
DOE OSTI2020

Bulk and Nanocrystalline Cesium Lead-Halide Perovskites as Seen by Halide Magnetic Resonance

Lead-halide perovskites increasingly mesmerize researchers because they exhibit a high degree of structural defects and dynamics yet nonetheless offer an outstanding (opto)electronic performance on par with the best examples of structurally stable and defect-free semiconductors. This highly unusual feature necessitates the adoption of an experimental and theoretical mindset and the reexamination of techniques that may be uniquely suited to understand these materials. Surprisingly, the suite of methods for the structural characterization of these materials does not commonly include nuclear magnetic resonance (NMR) spectroscopy. The present study showcases both the utility and versatility of halide NMR and NQR (nuclear quadrupole resonance) for probing the structure and structural dynamics of CsPbX 3 (X = Cl, Br, I), in both bulk and nanocrystalline forms. The strong quadrupole couplings, which originate from the interaction between the large quadrupole moments of, e.g., the 35 Cl, 79 Br, and 127 I nuclei, and the local electric-field gradients, are highly sensitive to subtle structural variations, both static and dynamic. The quadrupole interaction can resolve structural changes with accuracies commensurate with synchrotron X-ray diffraction and scattering. It is shown that space-averaged site-disorder is greatly enhanced in the nanocrystals compared to the bulk, while the dynamics of nuclear spin relaxation indicates enhanced structural dynamics in the nanocrystals. The findings from NMR and NQR were corroborated by ab initio molecular dynamics, which point to the role of the surface in causing the radial strain distribution and disorder. These findings showcase a great synergy between solid-state NMR or NQR and molecular dynamics simulations in shedding light on the structure of soft lead-halide semiconductors.

36 MATERIALS SCIENCE↗
NASA NTRS1989

The structure of the microwave emission from sunspot magnetic fields

Theoretical microwave intensity and polarization maps have been obtained for a sunspot model which incorporates a point dipole buried below the photosphere, a 2000-km thick transition region separating the chromosphere from the corona, a coronal temperature of 2.5 x 10 to the 6th K, and a coronal density of about 10 to the 9th/cu cm. The present code includes both thermal bremsstrahlung and thermal gyroemission at the 1st-5th harmonics of the local electron gyrofrequency. The maps are shown to accurately reproduce many of the observed sunspot features. Significant changes in the I and V maps are found over closely spaced frequencies in the 5-GHz band which would be detectable with the VLA.

Brosius, Jeffrey W.↗