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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 1,045 records · Page 58
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Presence of Induced Weak Ferromagnetism in Fe-Substituted YFe x Cr 1–x O 3 Crystalline Compounds

Fe-substituted YFe x Cr 1–x O 3 crystalline compounds show promising magnetic and multiferroic properties. Here we report the synthesis and characterization of several compositions from this series. Using the autocombustion route, various compositions (x = 0.25, 0.50, 0.6, 0.75, 0.9, and 1) were synthesized as high-quality crystalline powders. In order to obtain microscopic and atomic information about their structure and magnetism, characterization was performed using room temperature X-ray diffraction and energy dispersion analysis as well as temperature-dependent neutron diffraction, magnetometry, and 57 Fe Mössbauer spectrometry. Rietveld analysis of the diffraction data revealed a crystallite size of 84 (8) nm for YFeO 3 , while energy dispersion analysis indicated compositions close to the nominal compositions. The magnetic results suggested an enhancement of the weak ferromagnetism for the YFeO 3 phase due to two contributions. First, a high magnetocrystalline anisotropy was associated with the crystalline character that favored a unique high canting angle of the antiferromagnetic phase (13°), as indicated by the neutron diffraction analysis. This was also evidenced by the high magnetic hysteresis curves up to 90 kOe by a remarkable high critical coercivity value of 46.7 kOe at room temperature. Second, the Dzyaloshinskii–Moriya interactions between homogenous and heterogeneous magnetic pairs resulted from the inhomogeneous distribution of Fe 3+ and Cr 3+ ions, as indicated by 57 Fe Mössbauer studies. Together, these results point to new methods of controlling the magnetic properties of these materials.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Effect of Ionic Core on the Properties of Non-Isothermal Plasmas

This study investigates the effects of ionic cores on non-isothermal plasmas using a novel ion-ion interaction potential that incorporates screening effects from both ion cores and exchange-correlation interactions. Our findings indicate that with increasing distance, the effective potential approaches a Yukawa-like screening potential, while at shorter distances, strong electron binding weakens screening. The different values of the cutoff radius ' cut and core edge steepness α significantly influence the potential behavior and radial distribution functions (RDFs). Higher coupling parameters (Γ i ) strengthen the electron-ion interactions, leading to deeper potential wells and more pronounced non-ideality corrections. Increasing Θ decreases the absolute values of non-ideality corrections, indicating fewer interactions in the system. A larger cutoff radius r cut due to weaker screening effects. As Γ i at a fixed parameter also reduces corrections increases, non-ideality corrections grow, reflecting stronger coupling. The results show the importance of taking into account the ion core effects in dense non-isothermal plasma research.

dense plasmas↗
DOE OSTI2021

Superstructured Biomaterials Formed by Exchange Dynamics and Host–Guest Interactions in Supramolecular Polymers

Dynamic and reversible assembly of molecules is ubiquitous in the hierarchical superstructures of living systems and plays a key role in cellular functions. Recent work from the laboratory reported on the reversible formation of such superstructures in systems of peptide amphiphiles conjugated to oligonucleotides and electrostatically complimentary peptide sequences. Here, a supramolecular system is reported upon where exchange dynamics and host–guest interactions between β-cyclodextrin and adamantane on peptide amphiphiles lead to superstructure formation. Superstructure formation with bundled nanoribbons generates a mechanically robust hydrogel with a highly porous architecture that can be 3D printed. Functionalization of the porous superstructured material with a biological signal results in a matrix with significant in vitro bioactivity toward neurons that could be used as a supramolecular model to design novel biomaterials.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Synthesis and Magnetic Properties of Nanocrystalline FeTiO{sub 3} Materials

Ilmenite (FeTiO{sub 3}) nanoparticles with different size distributions were prepared through a sol-gel auto-ignition method. As-prepared powder is annealed at moderate temperatures to get nanocrystalline FeTiO{sub 3}, and structural, micro-structural, and magnetization characterizations are carried out. Magnetization vs temperature shows antiferromagnetic ordering around 52 K and below 15 K a weak ferromagnetic order develops. The Curie-Weiss law is well obeyed above the Néel temperature (T{sub N}) for all samples. Hysteresis curves show finite coercivity below the peak temperature and none at room temperature. M-H curves for all the samples cooled with a bias magnetic field show exchange bias below T{sub N} which is interpreted due to the finite size and surface effects. The exchange bias is attributed to weak ferromagnetism due to surface spin disorder (Dzyaloshinskii-Moriya interaction) and ferromagnetic interaction (double exchange) due to mixed valence states of Fe ions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Programming Metabolite Exchange to Understand and Control Plant-Microbe Interactions

Many aspects of plant growth and survival are dependent upon beneficial interactions between plant tissues and bacterial species of the endophyte and rhizosphere. These associated microorganisms can contribute positively to plant growth, stress tolerance, metabolism and protection against plant pathogens. For example, an endosymbiotic bacterium Burkholderia phytofirmans PsJN was shown to colonize and promote growth of switchgrass under controlled conditions, suggesting it may be a promising candidate for improving bioenergy crop production (Kim et al., 2012). Despite the documented benefits of endophytic and rhizosphere microbes on plant fitness and photosynthetic productivity, there is still a gap in our understanding of specific molecular -and cellular-level processes that guide the development of beneficial plant-microbe interactions. As these interactions involve physical contact/metabolite exchange we also posit that directed co-localization of beneficial bacteria and plant cells will enhance these benefits. We propose to engineer bacterial species that co-localize with the plant tissue and then to measure cell growth as well as carry out –omics analysis to obtain information regarding the specifics of these beneficial interactions as well as their extent. This report describes our progress with these goals and the results.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS1971

Thermal conductivity and resonant multipole interactions

The influence of multipole interactions on exchanges of rotational energy in molecular collisions was investigated by means of a simple two-state impact parameter approximation. The calculations are restricted to linear molecules and to dipole and quadrupole fields. The effects of such exchanges on the thermal conductivity of gases and of gaseous mixtures was investigated, after correcting the kinetic theory of mixtures to include exchanges between unlike molecules. It was found that dipole-quadrupole and quadrupole-quadrupole interactions may have a significant effect for molecules with low moments of inertia. In particular, quadrupole interactions are important in the hydrogen isotopes, and the calculated corrections for H2 are consistent with recent experimental work by Harris. The theory seems capable of accounting for the anomalies observed in HF + DF and HCl + DCl mixtures in terms of multipolar accidental resonances.

Nyeland, C.↗
DOE OSTI2017

Searching for new spin-dependent interactions with SmCo 5 spin sources and a spin-exchange-relaxation-free comagnetometer

We propose a novel method to search for possible new macroscale spin- and/or velocity-dependent forces (SVDFs) based on specially designed SmCo 5 spin sources and a spin exchange relaxation-free (SERF) comagnetometer. A simulation shows that, by covering a SmCo 5 permanent magnet with a layer of pure iron, a high net spin density source of about $1×10^{22}/cm^3$ could be obtained. Taking advantages of the high spin density of this iron-shielded SmCo 5 and the high sensitivity of the SERF, the proposed method could set up new limits of greater than 10 orders of magnitude more sensitive than those from previous experiments or proposals in exploring SVDFs in force ranges larger than 1 cm.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Helium-4 gravitational form factors: Exchange currents

We evaluate the leading exchange corrections to the helium-4 gravitational form factors (GFFs) to momenta of the order of the nucleon mass. We use both the K-harmonic method with simple pair nucleon potential, and a Jastrow trial function using the Argonne 𝑣 14 potential, to evaluate the helium-4 GFFs. The exchange current contributions include the pair interaction, plus the seagull and the pion exchange interactions, modulo the recoil corrections. To estimate the off-shellness of the pion nucleon coupling in this momenta range, we discuss the results using either the pseudoscalar (PS) or pseudovector (PV) pion-nucleon couplings. When the PV coupling is used, the pair diagram contribution is higher order in the nonrelativistic expansion. The results for the helium-4 A-GFF are comparable to those given by the impulse approximation, especially for the PS coupling using both the K-harmonic method and variational method. The exchange current contributions with the PS coupling for the charge form factor of helium-4, yield better agreement with the existing data over a broad range of momenta, especially when the Argonne 𝑣 14 potential including the D-wave admixture is used.

A ≤ 5↗
DOE OSTI2019

Multiscale Feature-feature Interactions Control Patterns of Hyporheic Exchange in a Simulated Headwater Mountain Stream

Recent predictions of hyporheic exchange at the basin-scale assume individual features control exchange independently of each other, which has been demonstrated in relatively uniform, low-gradient rivers. However, this assumption may not hold in steep catchments where both the type and size of individual features may vary over short distances, leading to irregular patterns of feature dominance on hyporheic exchange flows. Also, steep longitudinal gradients support substantial downvalley flows in the subsurface, which may create feedbacks between adjacent features. In this study, we test the extent to which features interact with one another and whether they can be aggregated to make reach-scale predictions in a headwater mountain stream. Using systematic manipulations of a 2-D stream centerline model and spectral analyses, we test for the presence of both feature-feature and multiscale interactions. Our results show that changing the height of individual step-pool features can alter hyporheic flow fields in neighboring, and sometimes distant, features. Spectral analyses revealed two scales of streambed topography—a local scale of single features and an intermediate scale that spanned multiple local-scale features. All features produced hyporheic exchange, but turnover of deeper hyporheic water only occurred at a few key locations where local- and intermediate-scale features amplified each other. Further, shallow bedrock increases the ratio of local- and intermediate-scale flowpaths to regional-scale flowpaths. Conceptual models portraying hyporheic exchange as a series of nested flowpaths should include the interactions among streambed topographic features in mountain streams. These results have implications for upscaling, field experiments, and stream restoration in steep catchments.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2014

Highly frustrated spin-lattice models of magnetism and their quantum phase transitions: A microscopic treatment via the coupled cluster method

We outline how the coupled cluster method of microscopic quantum many-body theory can be utilized in practice to give highly accurate results for the ground-state properties of a wide variety of highly frustrated and strongly correlated spin-lattice models of interest in quantum magnetism, including their quantum phase transitions. The method itself is described, and it is shown how it may be implemented in practice to high orders in a systematically improvable hierarchy of (so-called LSUBm) approximations, by the use of computer-algebraic techniques. The method works from the outset in the thermodynamic limit of an infinite lattice at all levels of approximation, and it is shown both how the 'raw' LSUBm results are themselves generally excellent in the sense that they converge rapidly, and how they may accurately be extrapolated to the exact limit, m → ∞, of the truncation index m, which denotes the only approximation made. All of this is illustrated via a specific application to a two-dimensional, frustrated, spin-half J{sub 1}{sup XXZ}−J{sub 2}{sup XXZ} model on a honeycomb lattice with nearest-neighbor and next-nearest-neighbor interactions with exchange couplings J{sub 1} > 0 and J{sub 2} ≡ κJ{sub 1} > 0, respectively, where both interactions are of the same anisotropic XXZ type. We show how the method can be used to determine the entire zero-temperature ground-state phase diagram of the model in the range 0 ≤ κ ≤ 1 of the frustration parameter and 0 ≤ Δ ≤ 1 of the spin-space anisotropy parameter. In particular, we identify a candidate quantum spin-liquid region in the phase space.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Data, figures, animations, and scripts associated with the manuscript "Integrated Effects of Site Hydrology and Vegetation on Exchange Fluxes and Carbon Cycling at the Coastal Terrestrial Aquatic Interface"

This package contains the data, figures, animations, and scripts used in "Integrated Effects of Site Hydrology and Vegetation on Exchange Fluxes and Carbon Cycling at the Coastal Terrestrial Aquatic Interface" (Li et al., 2023). This study examines the interactions between soil, vegetation and hydrologic conditions in coastal areas, with a focus on the Chesapeake Bay region. The researchers used a mechanistic model called ATS-PFLOTRAN to explore how these interactions affect exchange process in different regions and the carbon/nitrogen cycle across the terrestrial-aquatic interface (TAI). Simulation scenarios isolate the effects of control factors and reaction constants derived from laboratory experiments. The results show a carbon cycle "hot zone" in coastal wetlands and in the transition zone between wetlands and uplands. Transpiration enhances fluxes between the surface and subsurface domains and increases dissolved oxygen in TAI. The decomposition of leaf-derived organic carbon provides an additional source of carbon for aerobic respiration and denitrification in the TAI. Microbial activity plays a key role in controlling redox conditions and their variability. This modeling study improves the understanding of complex TAI interactions and facilitates the representation of coastal ecosystems in larger-scale Earth system models.Several files can be found from this data package.1. Readme,md: This file describe the Title, Target Journal, Target submission date, Co-author, Science Questions, Hypotheses, Key words, Key message, Model and Data, Repo Structure. The user can read this file first and then go to details.2. mesh.zip: This file contains the mesh file for simulation cases. 3. Figure.zip: This file contains figures used in the manuscript . 4. animation.zip: This file contains animations used in the manuscript . 5. Data.zip: This file contains all required input data, such as concentration and flow boundaries. Also, it contains the DEM and processes results on area fraction. 6. Simulation_setup_and_results.zip: This file contains setup of cases used in the manuscript . The result files are too large, if you need that data, please contact to the Author. 7. notebooks.zip: This file contains the Jupyter notebooks for performing sensitivity analysis and other pre-process and post-process analyses.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2015

Cross-correlation spin noise spectroscopy of heterogeneous interacting spin systems

Interacting multi-component spin systems are ubiquitous in nature and in the laboratory. As such, investigations of inter-species spin interactions are of vital importance. Traditionally, they are studied by experimental methods that are necessarily perturbative: e.g., by intentionally polarizing or depolarizing one spin species while detecting the response of the other(s). Here, we describe and demonstrate an alternative approach based on multi-probe spin noise spectroscopy , which can reveal inter-species spin interactions - under conditions of strict thermal equilibrium - by detecting and cross-correlating the stochastic fluctuation signals exhibited by each of the constituent spin species. Specifically, we consider a two-component spin ensemble that interacts via exchange coupling, and we determine cross-correlations between their intrinsic spin fluctuations. The model is experimentally confirmed using “two-color” optical spin noise spectroscopy on a mixture of interacting Rb and Cs vapors. Noise correlations directly reveal the presence of inter-species spin exchange, without ever perturbing the system away from thermal equilibrium. These non-invasive and noise-based techniques should be generally applicable to any heterogeneous spin system in which the fluctuations of the constituent components are detectable.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2015

Magnetic properties of manganites doped with gallium, iron, and chromium ions

The magnetization and the crystal structure of the La{sub 0.7}Sr{sub 0.3}Mn{sub 1−x}M{sub x}O{sub 3} (M = Ga, Fe, Cr; x ≤ 0.3) systems are studied. The substitution of gallium and chromium is shown to cause phase separation into antiferromagnetic and ferromagnetic phases, whereas the substitution of iron for manganese stabilizes a spinglass state. The ferromagnetic phase in the chromium-substituted compositions is much more stable than that in the case of substitution by iron ions or diamagnetic gallium ions. The magnetic properties are explained in terms of the model of superexchange interactions and the localization of most e{sub g} electrons of manganese. The stabilization of ferromagnetism in the chromium-substituted compositions can be caused by the fact that the positive and negative contributions to the superexchange interaction between Mn{sup 3+} and Cr{sup 3+} ions are close to each other but the antiferromagnetic part of the exchange is predominant. Moreover, some chromium ions are in the tetravalent state, which maintains the optimum doping conditions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Extend NdJ relationship with the size, multiple exchanges and Dzyaloshinskii-Moriya interaction for Néel skyrmions in hexagonal magnetic interfaces

For the integration with other parts of spintronic devices, it is desired to minimize the size of skyrmions to a nanometer scale. To provide a theoretical guidance for this endeavour, we established an extended NdJ relationship between the skyrmion size and fundamental magnetic properties of two-dimensional hexagonal ferromagnetic lattices, including multiple exchanges between different neighbors (J 1 -J 4 ), Dzyaloshinskii-Moriya interactions (d 1 and d 2 ) and on-site magnetic anisotropy energy. We demonstrated the applicability of this approach through density functional theory and spin spiral calculations for several interface, e.g., Co/Gra, Rh/Gra, Co/Pt 3 and MgO/Co/Pt 3 , and showed that the size of Néel skyrmions can be effectively reduced by either enhancing d or more conveniently reducing J through cancelation of J i s.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Intrinsic Role of Cationic Substitution in Tuning Li/Ni Mixing in High-Ni Layered Oxides

Nickel-rich transition metal (TM) layered oxides, particularly those ones with high Ni content, attract world-wide interest for potential use as high-capacity cathodes in next-generation Li-ion batteries. However, as Ni loading increases, Li and Ni sitting at octahedra tend to mix, resulting in reduced electrochemical activity, which has been one major obstacle to their practical applications. We investigate the kinetic and thermodynamic aspects of Li/Ni mixing in LiNi 0.7 MnxCo 0.3-x O 2 (0≤x≤0.3) as they are being synthesized, through a multimodal approach for quantitative determination of structural ordering and com-parison to ab initio calculations. Results from this study elucidate the role of Mn/Co substitution at Ni sites in tuning Li/Ni ordering, intrinsically through local magnetic interaction. Specifically, Co substitution facilitates Li/Ni ordering by relieving the intra-plane magnetic frustration and reducing the inter-plane super-exchange (SE) interaction; in contrast, Mn exacerbates mag-netic frustration, strengthens SE, thereby aggravating Li/Ni mixing. These findings highlight the interplay between local magnetic interactions and cationic ordering, which has yet to be fully investigated for the needs of designing high-Ni layered cathodes and, broadly, TM-based oxides for various applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Exchange bias and antiferromagnetic interfacial exchange coupling in the mixed-spin oxide Li{sub 2/7}Ni{sub 5/7}O

We present a detailed study on magnetic properties of mixed spin oxide Li{sub 2/7}Ni{sub 5/7}O, where small ferromagnetic (FM) clusters (with averaged diameter of ∼18 Å) immersed with an antiferromagnetic (AFM) host. The exchange bias (EB) with shifts of the hysteresis loop along both the field and magnetization axes is found, which is due to the interfacial interaction between the FM clusters and the AFM host. An AFM interfacial exchange coupling is deduced from the exchange interactions between Ni ions. The type and strength of this interfacial exchange interaction are discussed in terms of the EB at low temperature.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Evidence of exchange bias effect originating from the interaction between antiferromagnetic core and spin glass shell

Spin glass behavior and exchange bias effect have been observed in antiferromagnetic SrMn{sub 3}O{sub 6−x} nanoribbons synthesized via a self-sacrificing template process. The magnetic field dependence of thermoremanent magnetization and isothermal remanent magnetization shows that the sample is good correspondence to spin glass and diluted antiferromagnetic system for the applied field H < 2 T and H > 2 T, respectively. By detailed analysis of training effect using Binek's model, we argue that the observed exchange bias effect in SrMn{sub 3}O{sub 6−x} nanoribbons arises entirely from an interface exchange coupling between the antiferromagnetic core and spin glass shell. The present study is useful for understanding the nature of shell layer and the origin of exchange bias effect in other antiferromagnetic nanosystems as well.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Resistivity Minimum in Highly Frustrated Itinerant Magnets

We study here the transport properties of frustrated itinerant magnets comprising localized classical moments, which interact via exchange with the conduction electrons. Strong frustration stabilizes a liquidlike spin state, which extends down to temperatures well below the effective Ruderman-Kittel-Kasuya-Yosida interaction scale. The crossover into this state is characterized by spin structure factor enhancement at wave vectors smaller than twice the Fermi wave vector magnitude. Finally, the corresponding enhancement of electron scattering generates a resistivity upturn at decreasing temperatures.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗