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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 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Giant Orbital Anisotropy with Strong Spin–Orbit Coupling Established at the Pseudomorphic Interface of the Co/Pd Superlattice

Orbital anisotropy at interfaces in magnetic heterostructures has been key to pioneering spin–orbit-related phenomena. However, modulating the interface’s electronic structure to make it abnormally asymmetric has been challenging because of lack of appropriate methods. Here, the authors report that low-energy proton irradiation achieves a strong level of inversion asymmetry and unusual strain at interfaces in [Co/Pd] superlattices through nondestructive, selective removal of oxygen from Co3O4/Pd superlattices during irradiation. Structural investigations corroborate that progressive reduction of Co3O4into Co establishes pseudomorphic growth with sharp interfaces and atypically large tensile stress. The normal component of orbital to spin magnetic moment at the interface is the largest among those observed in layered Co systems, which is associated with giant orbital anisotropy theoretically confirmed, and resulting very large interfacial magnetic anisotropy is observed. All results attribute not only to giant orbital anisotropy but to enhanced interfacial spin–orbit coupling owing to the pseudomorphic nature at the interface. They are strongly supported by the observation of reversal of polarity of temperature-dependent Anomalous Hall signal, a signature of Berry phase. This work suggests that establishing both giant orbital anisotropy and strong spin–orbit coupling at the interface is key to exploring spintronic devices with new functionalities.

42 ENGINEERING↗
DOE OSTI2023

Effect of Co/SiO 2 Single-Site Heterogeneity on Small Alkane Dehydrogenation Kinetics

Atomically dispersed, high-spin Co(II) atoms in distorted tetrahedral coordination to an amorphous silica (am-SiO 2 ) support, and more recently in zeolite frameworks, are active and selective for light alkane dehydrogenation. This paper investigates how variations in the geometry of the active sites affect the ethane dehydrogenation activity of atomically dispersed Co(II) on an am-SiO 2 support. We generate a distribution of sites and determine the geometric parameters that exhibit the strongest correlation with the coordination geometry and activity of the metal atom by means of linear dimensionality reduction techniques. We perform electronic structure calculations and microkinetic modeling and deduce the mechanism and kinetics for a representative sample of sites. Irrespective of the active site geometry, the rate of ethane dehydrogenation is governed by the β-hydride elimination, which involves quartet-doublet spin-crossing and proceeds adiabatically due to strong spin-orbit coupling. Informed by the complete microkinetic analysis of the sites, we derive the reduced rate expression as a function of three site-dependent quantities. We show that these site-dependent quantities correlate with the energy of formation of the ethyl intermediate that forms via C-H bond activation. This correlation allows us to derive the site-averaged rate for the entire distribution of sites. Among various sites, the tri-coordinate and planar tetra-coordinate Co sites exhibit higher Lewis acidity than the tetrahedral sites, and consequently, higher initial rates. Finally, we discuss the implications for more active catalysts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Antiferromagnetic fluctuations and orbital-selective Mott transition in the van der Waals ferromagnet Fe 3–x GeTe 2

Fe 3–x GeTe 2 is a layered magnetic van der Waals material of interest for both fundamental and applied research. Despite the observation of intriguing physical properties, open questions exist even on the basic features related to magnetism: is it a simple ferromagnet or are there antiferromagnetic regimes, and are the moments local or itinerant. In this work, we demonstrate that antiferromagnetic spin fluctuations coexist with the ferromagnetism through comprehensive elastic and inelastic neutron scattering and thermodynamic measurements. Our realistic dynamical mean-field theory calculations reveal that the competing magnetic fluctuations are driven by an orbital selective Mott transition (OSMT), where only the plane-perpendicular a 1g orbital of the Fe(3d) manifold remains itinerant. Our results highlight the multi-orbital character in Fe 3–x GeTe 2 that supports a rare coexistence of local and itinerant physics within this material.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Combination of searches for heavy spin-1 resonances using 139 fb -1 of proton-proton collision data at $\sqrt{s}$ = 13 TeV with the ATLAS detector

A combination of searches for new heavy spin-1 resonances decaying into different pairings of W, Z, or Higgs bosons, as well as directly into leptons or quarks, is presented. The data sample used corresponds to 139 fb -1 of proton-proton collisions at $\sqrt{s}$ = 13 TeV collected during 2015–2018 with the ATLAS detector at the CERN Large Hadron Collider. Analyses selecting quark pairs (qq, bb, $t\overline{t}$, and tb) or third-generation leptons (τν and ττ) are included in this kind of combination for the first time. A simplified model predicting a spin-1 heavy vector-boson triplet is used. Cross-section limits are set at the 95% confidence level and are compared with predictions for the benchmark model. These limits are also expressed in terms of constraints on couplings of the heavy vector-boson triplet to quarks, leptons, and the Higgs boson. The complementarity of the various analyses increases the sensitivity to new physics, and the resulting constraints are stronger than those from any individual analysis considered. The data exclude a heavy vector-boson triplet with mass below 5.8 TeV in a weakly coupled scenario, below 4.4 TeV in a strongly coupled scenario, and up to 1.5 TeV in the case of production via vector-boson fusion.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

Cation- and lattice-site-selective magnetic depth profiles of ultrathin Fe 3 O 4 (001) films

A detailed understanding of ultrathin film surface properties is crucial for the proper interpretation of spectroscopic, catalytic, and spin-transport data. We present x-ray magnetic circular dichroism (XMCD) and x-ray resonant magnetic reflectivity (XRMR) measurements on ultrathin Fe 3 O 4 films to obtain magnetic depth profiles for the three resonant energies corresponding to the different cation species F e o c t 2 + , F e t e t 3 + , and F e o c t 3 + located on octahedral and tetrahedral sites of the inverse spinel structure of Fe 3 O 4 . By analyzing the XMCD spectrum of Fe 3 O 4 using multiplet calculations, the resonance energy of each cation species can be isolated. Performing XRMR on these three resonant energies yields magnetic depth profiles that each correspond to one specific cation species. The depth profiles of both kinds of Fe 3+ cations reveal a (3.9 ± 1.0) -Å -thick surface layer of enhanced magnetization, which is likely due to an excess of these ions at the expense of the F e o c t 2 + species in the surface region. The magnetically enhanced F e t e t 3 + layer is additionally shifted about 2.9 ± 0.4 Å farther from the surface than the F e o c t 3 + layer.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1980

The influence of orbit selection on the accuracy of the Stanford Relativity gyroscope experiment

This paper discusses an error analysis for the Stanford Relativity experiment, designed to measure the precession of a gyroscope's spin-axis predicted by general relativity. Measurements will be made of the spin-axis orientations of 4 superconducting spherical gyroscopes carried by an earth-satellite. Two relativistic precessions are predicted: a 'geodetic' precession associated with the satellite's orbital motion and a 'motional' precession due to the earth's rotation. Using a Kalman filter covariance analysis with a realistic error model we have computed the error in determining the relativistic precession rates. Studies show that a slightly off-polar orbit is better than a polar orbit for determining the 'motional' drift.

Vassar, R.↗
DOE OSTI2020

Direct Demonstration of Topological Stability of Magnetic Skyrmions via Topology Manipulation

Topological protection precludes a continuous deformation between topologically inequivalent configurations in a continuum. Motivated by this concept, magnetic skyrmions, topologically nontrivial spin textures, are expected to exhibit topological stability, thereby offering a prospect as a nanometer-scale nonvolatile information carrier. In real materials, however, atomic spins are configured as not continuous but discrete distributions, which raises a fundamental question if the topological stability is indeed preserved for real magnetic skyrmions. Answering this question necessitates a direct comparison between topologically nontrivial and trivial spin textures, but the direct comparison in one sample under the same magnetic fields has been challenging. Here we report how to selectively achieve either a skyrmion state or a topologically trivial bubble state in a single specimen and thereby experimentally show how robust the skyrmion structure is in comparison with the bubbles. We demonstrate that topologically nontrivial magnetic skyrmions show longer lifetimes than trivial bubble structures, evidencing the topological stability in a real discrete system. Our work corroborates the physical importance of the topology in the magnetic materials, which has hitherto been suggested by mathematical arguments, providing an important step toward ever-dense and more-stable magnetic devices.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Catalytic 1,3-Proton Transfer in Alkenes Enabled by Fe=NR Bond Cooperativity: A Strategy for p K a -Dictated Regioselective Transposition of C=C Double Bonds

Transition metal catalyzed alkene double bond transposition usually involves metal hydride intermediates. Despite significant advances in the design of catalysts that dictate product selectivity, control over substrate selectivity is less advanced and transition metal catalysts that selectively transpose double bonds in substrates containing multiple 1-alkene functionalities are rare. Herein, we report that the three-coordinate high spin (S = 2) Fe(II) imido complex [Ph 2 B( t BuIm) 2 Fe=NDipp][K(18-C-6)THF 2 ] (1-K(18-C-6)) catalyzes 1,3-proton transfer from 1-alkene substrates to afford 2-alkene transposition products. Mechanistic investigations involving kinetics, competition, and isotope labeling studies, supported by experimentally calibrated DFT computations, strongly support an unusual nonhydridic mechanism for alkene transposition that is enabled by the cooperative action of the iron center and basic imido ligand. As dictated by the pK a of the allylic protons, this catalyst enables the regioselective transposition of C=C double bonds in substrates containing multiple 1-alkenes. The high spin (S = 2) state of the complex allows a wide scope of functional groups to be tolerated, including those that are typical catalyst poisons, such as amines, N-heterocycles, and phosphines. Furthermore, these results demonstrate a new strategy for metal-catalyzed alkene transposition with predictable substrate regioselectivity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Outgassing measurements of bare and magnetite-coated low-carbon steel vacuum chambers

The outgassing properties of bare and magnetite-coated AISI 1020 low-carbon steel vacuum chambers were evaluated to establish material selection criteria for extreme high vacuum applications, namely, to explore the possibility of using these materials to build next-generation spin-polarized photoelectron guns. Water outgassing measurements using the throughput method revealed that the magnetite-coated chamber exhibited five times lower outgassing at room temperature prior to baking, but this advantage disappears after 80 °C baking. Hydrogen outgassing measurements demonstrated significant differences after intensive heat treatment: the bare low-carbon steel vacuum chamber achieved a specific outgassing rate of 9.6 × 10 −16 Torr L s −1 cm −2 after 400 °C/50 h bake plus additional heat treatment at lower temperatures, 25 times lower than the magnetite-coated low-carbon steel chamber. Residual gas analysis showed >99% hydrogen composition after heat treatment for both materials, with carbon species below detection limits for bare low-carbon steel versus 0.8% for magnetite-coated surfaces. These measurements indicate that properly conditioned bare low-carbon steel can achieve the <10 −12 Torr pressures required for next-generation spin-polarized photogun applications. In conclusion, the paper includes various analysis techniques intended to explain observed behaviors: isotherm analysis of pump-down plots, Arrhenius analysis of hydrogen outgassing rate data, and residual gas composition tracking.

Adsorption isotherm↗
NASA NTRS1974

A feasibility study of developing toroidal tanks for a spinning spacecraft

The use of toroidal tanks in an advanced Pioneer, spin-stabilized Jupiter orbiter was investigated. Fluid behavior in spinning toroids was evaluated and the need for a propellant acquisition system was established. A common surface tension acquisition system design was selected from four candidates for gas-free liquid feed to a single outlet in both MMH and N2O4 tanks. Fabrication of toroidal tanks using either titanium or aluminum alloys is feasible. Integration of two toroidal tanks with surface tension systems in place of four spherical tanks provides spacecraft weight, packaging, structural mounting, thermal control and stability advantages.

Anderson, J. E.↗
NASA NTRS2009

Examining the Impacts of High-Resolution Land Surface Initialization on Model Predictions of Convection in the Southeastern U.S.

One of the most challenging weather forecast problems in the southeastern U.S. is daily summertime pulse convection. During the summer, atmospheric flow and forcing are generally weak in this region; thus, convection typically initiates in response to local forcing along sea/lake breezes, and other discontinuities often related to horizontal gradients in surface heating rates. Numerical simulations of pulse convection usually have low skill, even in local predictions at high resolution, due to the inherent chaotic nature of these precipitation systems. Forecast errors can arise from assumptions within physics parameterizations, model resolution limitations, as well as uncertainties in both the initial state of the atmosphere and land surface variables such as soil moisture and temperature. For this study, it is hypothesized that high-resolution, consistent representations of surface properties such as soil moisture and temperature, ground fluxes, and vegetation are necessary to better simulate the interactions between the land surface and atmosphere, and ultimately improve predictions of local circulations and summertime pulse convection. The NASA Short-term Prediction Research and Transition (SPORT) Center has been conducting studies to examine the impacts of high-resolution land surface initialization data generated by offline simulations of the NASA Land Informatiot~ System (LIS) on subsequent numerical forecasts using the Weather Research and Forecasting (WRF) model (Case et al. 2008, to appear in the Journal of Hydrometeorology). Case et al. presents improvements to simulated sea breezes and surface verification statistics over Florida by initializing WRF with land surface variables from an offline LIS spin-up run, conducted on the exact WRF domain and resolution. The current project extends the previous work over Florida, focusing on selected case studies of typical pulse convection over the southeastern U.S., with an emphasis on improving local short-term WRF simulations over the Mobile, AL and Miami, FL NWS county warning areas. Future efforts may involve examining the impacts of assimilating remotely-sensed soil moisture data, and/or introducing weekly greenness vegetation fraction composites (as opposed to monthly climatologies) into ol'fline NASA LIS runs. Based on positive impacts, the offline LIS runs could be transitioned into an operational mode, providing land surface initialization data to NWS forecast offices in real time.

Case, Jonathan L.↗
NASA NTRS2014

NASA's Optical Measurement Program 2014

The Optical Measurements Group (OMG) within the NASA Orbital Debris Program Office (ODPO) addresses U.S. National Space Policy goals by monitoring and characterizing debris. Since 2001, the OMG has used the Michigan Orbital Debris Survey Telescope (MODEST) at Cerro Tololo Inter-American Observatory (CTIO) in Chile for general orbital debris survey. The 0.6-m Schmidt MODEST provides calibrated astronomical data of GEO targets, both catalogued and uncatalogued debris, with excellent image quality. The data are utilized by the ODPO modeling group and are included in the Orbital Debris Engineering Model (ORDEM) v. 3.0. MODEST and the CTIO/SMARTS (Small and Moderate Aperture Research Telescope System) 0.9 m both acquire filter photometric data, as well as synchronously observing targets in selected optical filters. This information provides data used in material composition studies as well as longer orbital arc data on the same target, without time delay or bias from a rotating, tumbling, or spinning target. NASA, in collaboration with the University of Michigan, began using the twin 6.5-m Magellan telescopes at Las Campanas Observatory in Chile for deep imaging (Baade) and spectroscopic data (Clay) in 2011. Through the data acquired on Baade, debris have been detected that are ~3 magnitudes fainter than detections with MODEST, while the data from Clay provide better resolved information used in material characterization analyses via selected bandpasses. To better characterize and model optical data, the Optical Measurements Center (OMC) at NASA/JSC has been in operation since 2005, resulting in a database of comparison laboratory data. The OMC is designed to emulate illumination conditions in space using equipment and techniques that parallel telescopic observations and source-target-sensor orientations. Lastly, the OMG is building the Meter Class Autonomous Telescope (MCAT) at Ascension Island. The 1.3-m telescope is designed to observe GEO and LEO targets, using a modified Ritchey-Chrétien configuration on a double horseshoe equatorial mount to allow tracking objects at LEO rates through the dome's keyhole at zenith. Through the data collection techniques employed at these unique facilities, NASA's ODPO has developed a multi-faceted approach to characterize the orbital debris risk to satellites in various altitudes and provide material characterization of debris via photometric and spectroscopic measurements. Ultimately, the data are used in conjunction with in-situ and radar measurements to provide accurate data for models of our space environment and service spacecraft risk assessment.

Cowardin, H.↗
DOE OSTI2021

Quantum magnetism of iron-based ladders: Blocks, spirals, and spin flux

Motivated by increasing experimental evidence of exotic magnetism in low-dimensional iron-based materials, we present a comprehensive theoretical analysis of magnetic states of the multiorbital Hubbard ladder in the orbital-selective Mott phase (OSMP). Here, the model we used is relevant for iron-based compounds of the AFe 2 X 3 family (where A=Cs, Rb, Ba, K are alkali metals and X=S, Se are chalcogenides). To reduce computational effort, and obtain almost exact numerical results in the ladder geometry, we utilize a low-energy description of the Hubbard model in the OSMP—the generalized Kondo-Heisenberg Hamiltonian. Our main result is the doping vs interaction magnetic phase diagram. We reproduce the experimental findings on the AFe 2 X 3 materials, especially the exotic block magnetism of BaFe 2 Se 3 (antiferromagnetically coupled 2×2 ferromagnetic islands of the ↑↑↓↓ form). As in recent studies of the chain geometry, we also unveil block magnetism beyond the 2×2 pattern (with block sizes varying as a function of the electron doping) and also an interaction-induced frustrated block-spiral state (a spiral order of rigidly rotating ferromagnetic islands). Moreover, we predict new phases beyond the one-dimensional system: a robust regime of phase separation close to half filling, incommensurate antiferromagnetism for weak interaction, and a quantum spin-flux phase of staggered plaquette spin currents at intermediate doping. Finally, exploiting the bonding/antibonding band occupations, we provide an intuitive physical picture giving insight into the structure of the phase diagram.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1992

Spacecraft flight control system design selection process for a geostationary communication satellite

The Earth's first artificial satellite, Sputnik 1, slowly tumbled in orbit. The first U.S. satellite, Explorer 1, also tumbled out of control. Now, as we launch the Mars observer and the Cassini spacecraft, stability and control have become higher priorities. The flight control system design selection process is reviewed using as an example a geostationary communication satellite which is to have a life expectancy of 10 to 14 years. Disturbance torques including aerodynamic, magnetic, gravity gradient, solar, micrometeorite, debris, collision, and internal torques are assessed to quantify the disturbance environment so that the required compensating torque can be determined. Then control torque options, including passive versus active, momentum control, bias momentum, spin stabilization, dual spin, gravity gradient, magnetic, reaction wheels, control moment gyros, nutation dampers, inertia augmentation techniques, three-axis control, reactions control system (RCS), and RCS sizing, are considered. A flight control system design is then selected and preliminary stability criteria are met by the control gains selection.

Barret, C.↗
DOE OSTI2021

Voltage-controlled spin–orbit torque switching in W/CoFeB/MgO

Voltage control of magnetism and spintronics have been highly desirable but rarely realized. In this work, we show voltage-controlled spin–orbit torque (SOT) switching in W/CoFeB/MgO films with perpendicular magnetic anisotropy (PMA) with voltage administered through SrTiO 3 with a high dielectric constant. We show that a DC voltage can significantly lower PMA by 45%, reduce switching current by 23%, and increase the damping-like torque as revealed by the first- and second-harmonic measurements. These are characteristics that are prerequisites for voltage-controlled and voltage-select SOT switching spintronic devices.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2026

Out-of-time-order correlators bridge classical transport and quantum dynamics

The out-of-time-order correlator (OTOC) has emerged as a central tool for quantifying decoherence across wide-ranging physical platforms. Here, we demonstrate its direct measurement in a classical ensemble using nuclear magnetic resonance with a modulated gradient spin echo sequence and extend the method into a multidimensional correlation to track exchange phenomena. Position is encoded through magnetic field gradients and momentum through the velocity autocorrelation function, enabling experimental access to OTOCs for proton motion confined within the self-similar lattice of the metal–organic framework MOF-808. Here, water confined to specified geometries within the MOF pores gives rise to spatially distinct diffusive eigenmodes with characteristic relative entropies. We demonstrate that periodic radio frequency driving combined with gradient modulation yields entropy evolution through the selection of distinct diffusion modes. Frequency-resolved diffusion spectra connect these entropy dynamics to classical heat exchange laws, revealing how operational features of quantum systems are mirrored in confined, macroscopic spin ensembles.

Fricke, Sophia N. [University of California, Berke↗
DOE OSTI2021

Dynamics in Flexible Pillar[ n ]arenes Probed by Solid-State NMR

Pillar[n]arenes are supramolecular assemblies that can perform a range of technologically important molecular separations which are enabled by their molecular flexibility. Here, we probe dynamical behavior by performing a range of variable-temperature solid-state NMR experiments on microcrystalline perethylated pillar[n]arene (n = 5, 6) and the corresponding three pillar[6]arene xylene adducts in the 100–350 K range. This was achieved either by measuring site-selective motional averaged 13 C 1 H heteronuclear dipolar couplings and subsequently accessing order parameters or by determining 1 H and 13 C spin–lattice relaxation times and extracting correlation times based on dipolar and/or chemical shift anisotropy relaxation mechanisms. We demonstrate fast motional regimes at room temperature and highlight a significant difference in dynamics between the core of the pillar[n]arenes, the protruding flexible ethoxy groups, and the adsorbed xylene guest. Additionally, unexpected and sizable 13 C 1 H heteronuclear dipolar couplings for a quaternary carbon were observed for p-xylene adsorbed in pillar[6]arene only, indicating a strong host–guest interaction and establishing the p-xylene location inside the host, confirming structural refinements.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Calculation of ion–ion mutual neutralization rate constants using Landau–Zener theory coupled with trajectory simulations for Ar + –Cl − , Br − , I −

In this computational study, we self-consistently calculate the rate constants of mutual neutralization reactions by incorporating the electron transfer probability, using Landau–Zener state transition theory with inputs derived from ab initio quantum chemistry calculations, into classical trajectory simulations. Electronic structure calculations are done using correlation consistent basis sets with multi-reference configuration interaction to map all the molecular electronic states below the ion-dissociation limit as a function of the distance between the reacting species. Our electronic structure calculations have been significantly improved from our previous work through improved selection of molecular electronic configurations maintaining a fine grid of 1a 0 over a wide range of bond lengths and accurate treatment of spin–orbit couplings. Non-adiabatic coupling matrix elements are calculated with the three-point central difference method near each avoided crossing to estimate the exact crossing point R x and coupling parameter H if , which are inputs to the multi-channel Landau–Zener theory to calculate the electron transition probability. Our approach is applied to estimate the mutual neutralization rate constants for the following ion pairs: Ar + –Cl − , Ar + –Br − , Ar + –I − at ∼133 Pa. Furthermore, our predictions are compared against the experimental data reported. It is seen that the improvement in the electronic structure calculation results in excellent agreement between the simulation results and the available experimental data to within a factor of ∼2 or ∼±50%.

Complete-active space self-consistent field↗