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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 1,585 records · Page 88
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Quantitative investigation of surface structure and interatomic potential with impact-collision ion scattering spectroscopy

Helium ion beam interactions with materials have important implications for magnetic confinement fusion, material modification, and helium ion microscopy. These interactions depend on the precise physics of how helium ions channel into the materials, which can vary greatly based on the local crystalline orientation. Here, we performed a dedicated experiment to investigate helium ion channeling in a well-characterized tungsten single crystal. Time-of-flight impact-collision ion scattering spectroscopy was used to obtain multi-angle maps of the backscattering intensity for 3 keV He + → W(111). We found that the backscattering intensity profile arising from helium ion channeling could be well described by a shadow cone analysis. This analysis revealed that subsurface W atoms as deep as the ninth monolayer contributed to the backscattering intensity profile. Binary collision approximation simulations were performed with MARLOWE to model the experimental maps with sufficient accuracy to allow for quantitative comparisons using reliability factors. These quantitative comparisons were applied to investigate how the W lattice structure and He–W interatomic potential affect the multi-angle maps.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Hopf Solitons in Helical and Conical Backgrounds of Chiral Magnetic Solids

Three-dimensional topological solitons attract a great deal of interest in fields ranging from particle physics to cosmology, but remain experimentally elusive in solid-state magnets. Here we numerically predict magnetic heliknotons, an embodiment of such nonzero-Hopf-index solitons localized in all spatial dimensions while embedded in a helical or conical background of chiral magnets. In this work we describe conditions under which heliknotons emerge as metastable or ground-state localized nonsingular structures with fascinating knots of magnetization field in widely studied materials. We demonstrate magnetic control of three-dimensional spatial positions of such solitons, as well as show how they interact to form moleculelike clusters and possibly even crystalline phases comprising three-dimensional lattices of such solitons with both orientational and positional order. Finally, we discuss both fundamental importance and potential technological utility of magnetic heliknotons.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2026

Cooperative spin coupling in PrFeO3

A transition from crystal-field to spin wave excitations has been experimentally observed in PrFeO3 using inelastic neutron scattering. Theoretical modeling with density functional theory and the mean field random phase approximation successfully reproduces the experimental observations and allows extraction of the values for the various exchange interactions. The study reveals that the strong coupling between the two magnetic sublattices of Pr and Fe is the fundamental mechanism underlying the low-temperature Pr magnetism. This coupling, analogous to the Dicke cooperative interaction between atoms and photons, polarizes the Pr moments, enhances the Pr-Pr interactions, and contributes to the formation of a quasidoublet, leading to the transition from single-particle to collective excitations within the Pr sublattice. Furthermore, this coupling induces spin reorientation on the Fe sublattice. The manipulation of magnetic moments via spin waves is achievable through the coupling between different magnetic sublattices in a bulk material containing multiple magnetic ions.

Garlea, Vasile [ORNL] (ORCID:0000000253227271)↗
NASA NTRS2002

Characterization of electrochemically deposited polypyrrole using magnetoelastic material transduction elements

Magnetoelastic alloy films have been used as a working electrode in an electrochemical cell. This material allows magnetic interrogation of electrochemical deposition. This technique was used to monitor the electrochemical deposition of polypyrrole by multisweep (CV) and potentiostatic methods. Since the determination of the mass-sensitive magnetoelastic film's resonance frequency is based on magnetic transduction, an inherent advantage of this method is that it requires no electrical connections other than the working lead of the potentiostat. Increases in pyrrole deposition correlated with a decrease in the peak resonance frequency of the magnetoelastic alloy. This technique provides a novel approach by which one can monitor electrochemical processes.

NASA Discipline Life Sciences Technologies↗
DOE OSTI2020

Creation of skyrmions in van der Waals ferromagnet Fe 3 GeTe 2 on (Co/Pd) n superlattice

Magnetic skyrmions are topological spin textures, which usually exist in noncentrosymmetric materials where the crystal inversion symmetry breaking generates the so-called Dzyaloshinskii-Moriya interaction. This requirement unfortunately excludes many important magnetic material classes, including the recently found two-dimensional van der Waals (vdW) magnetic materials, which offer unprecedented opportunities for spintronic technology. Using photoemission electron microscopy and Lorentz transmission electron microscopy, we investigated and stabilized Néel-type magnetic skyrmion in vdW ferromagnetic Fe 3 GeTe 2 on top of (Co/Pd) n in which the Fe 3 GeTe 2 has a centrosymmetric crystal structure. We demonstrate that the magnetic coupling between the Fe 3 GeTe 2 and the (Co/Pd) n could create skyrmions in Fe 3 GeTe 2 without the need of an external magnetic field. Our results open exciting opportunities in spintronic research and the engineering of topologically protected nanoscale features by expanding the group of skyrmion host materials to include these previously unknown vdW magnets.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

A Mössbauer Spectroscopy Investigation of Nickel‐Zinc Ferrites Synthesized by a Self‐Combustion Method for Soft Magnetic Core Applications

Soft ferrites are materials of interest for magnetic cores, as used for wireless charging transformers. Their low permeabilities, high resistivity, and magnetic polarization make them interesting for high-power electric vehicle charging and drive systems. The nickel-zinc-doped ferrites are of particular interest; however, the compositional space is quite large with respect to dopant concentrations, stoichiometric ratios and synthesis technique. Nickel-zinc spinel ferrites with varying nickel-zinc ratios prepared by a self-combustion reaction followed by heat treatment exhibit good crystallinity, and their low-temperature Mössbauer spectra show local magnetism and site occupation in agreement with materials prepared by solid-state reaction. Thus, the combustion synthesis method offers a facile tunability of compositions, which, combined with the possibility of rapid characterization of atomic-scale magnetism by Mössbauer spectroscopy, enables advances in the compositional and processing space at a fast pace. Low-temperature Mössbauer spectroscopy data for samples with increasing nickel content reveals a systematic increase in average hyperfine field (2.8 T/Ni) and decrease in average isomer shift (−0.036 mm/s/Ni) that can determine the nickel/zinc content, even in the absence of applied magnetic field data. Furthermore, a gradual evolution of color is also observed with increasing nickel content, albeit trends in color depend on sintering conditions.

Mössbauer spectroscopy↗
DOE OSTI2013

Structural and magnetic properties of Sm{sub 2−x}Mn{sub x}O{sub 3} nanoparticles

Graphical abstract: - Highlights: • C-type Sm{sub 2−x}Mn{sub x}O{sub 3} (0.0 ≤ x ≤0.20) is prepared by sol–gel method. • A maximum solubility of x = 0.15 is confirmed by X-ray diffraction, Raman and infrared techniques. • Samples with x > 0.05 exhibit weak ferromagnetic properties; for x ≤ 0.05 antiferromagnetic behaviors is obtained. • Correlation between magnetic behaviors and structural and microstructural parameters is discussed. - Abstract: Mixed oxide Sm{sub 2−x}Mn{sub x}O{sub 3} (SMO), x = 0.0, 0.05, 0.10, 0.15 and 0.20 were synthesized by a sol–gel process. A single phase solid solution is formed up to x = 0.15 which confirmed by using X-ray diffraction, Raman spectroscopy and infrared techniques. Crystal structure and microstructure analyses were performed by Rietveld refinement. Preferential cationic distribution, over the two crystallographic sites 8b and 24d of space group Ia3{sup ¯}, is found for doped samples but with different extent. The r.m.s. microstrain 〈ε{sub L}{sup 2}〉{sup 1/2} depends on composition x in a systematic way emphasizing the preferential distribution. Magnetization measurements show that samples with x ≤ 0.05 have antiferromagnetic behavior, while samples with x > 0.05 exhibit a weak ferromagnetic behavior with magnetic phase transformation at 15 and 16 K for x = 0.1 and x = 0.15, respectively.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Magnetic origin of dielectric transition in BiFeO{sub 3}

Magnetic relaxation measurements at 5K, 50K and 120K on BiFeO{sub 3} prepared by sol-gel auto combustion method shows stretched -exponential decay. These results shows the two factors viz, cooperative dynamics and rate of dynamics of spin, may be responsible for the low temperature magnetic-glassy behavior, concluded from bifurcation of zero field cooled (ZFC) and field cooled (FC) data of dc magnetization. Temperature dependent dielectric measurement shows a possible phase transition, seen in the dielectric-relaxation time and dielectric constant in the range 200 – 240K. Comparison of dielectric and magnetization data indicates a possibility of magneto-electric coupling.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Growth and characterization of diammonium copper disulphate hexahydrate single crystal

Graphical abstract: Diammonium copper disulphate hexahydrate (DACS) is one of the most promising inorganic dielectric crystals with exceptional mechanical properties. Good quality crystals of DACS were grown by using solution method in a period of 30 days. The grown crystals were subjected to single crystal X-ray diffraction analysis in order to establish their crystalline nature. Thermo gravimetric, differential thermal analysis, FTIR, and UV–vis–NIR analysis were performed for the crystal. Several solid state physical parameters have been determined for the grown crystals. The dielectric constant and the dielectric loss and AC conductivity of the grown crystal were studied as a function of frequency and temperature has been calculated and plotted. - Highlights: • Diammonium copper disulphate is grown for the first time and CCDC number obtained. • Thermal analysis is done to see the stability range of the crystals. • Band gap and UV cut off wavelength of the crystal are determined to be 2.4 eV and 472.86 nm, respectively. • Dielectric constant, dielectric loss and AC conductivity are plotted as a function of applied field. - Abstract: Diammonium copper disulphate hexahydrate is one of the most promising inorganic crystals with exceptional dielectric properties. A good quality crystal was harvested in a 30-day period using solution growth method. The grown crystal was subjected to various characterization techniques like single crystal X-ray diffraction analysis, thermo gravimetric, differential thermal analysis, FTIR, and UV–vis–NIR analysis. Unit cell dimensions of the grown crystal have been identified from XRD studies. Functional groups of the title compounds have been identified from FTIR studies. Thermal stability of the samples was checked by TG/DTA studies. Band gap of the crystal was calculated. The dielectric constant and dielectric loss were studied as a function of frequency of the applied field. AC conductivity was plotted as a function of temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Preparation and adsorption properties of nano magnetite chitosan films for heavy metal ions from aqueous solution

Highlights: • Nano magnetite–chitosan films were prepared by casting method. • The efficiency of the prepared films for removing heavy metals was investigated. • The adsorption mechanism was studied using different isotherm and kinetic models. • Films reuse and metals recovery were studied. - Abstract: Nano magnetite chitosan (NMag–CS) film was prepared and characterized with different analytical methods. X-ray diffraction (XRD) patterns confirmed the formation of a pure magnetite structure and NMag–CS nanocomposite. TEM image of the film, revealed the uniform dispersion of magnetite nanoparticles inside chitosan matrix. The adsorption properties of the prepared film for copper, lead, cadmium, chromium and nickel metal ions were evaluated. Different factors affecting the uptake behavior by the composite films such as time, initial pH and film dose were investigated. The adsorption equilibrium attained using 2 g/L of the film after 120 min of reaction. The equilibrium data were analyzed using Langmuir and Freundlich models. The adsorption kinetics followed the mechanism of the pseudo-second-order equation for all metals. The metals regenerated from films with an efficiency greater than 95% using 0.1 M ethylene diamine tetra acetic acid (EDTA) and films were successfully reused for adsorption.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Enhancing MnBi 2 Te 4 Stability by Doping

MnBi 2 Te 4 (MBT) is an intrinsically magnetic topological material that possesses unique properties due to the quantum Hall effect. However, the low Mn–Bi mixed antisite formation energy is detrimental to these properties as it alters the long-range magnetic ordering in the Mn layer. Therefore, it is crucial to destabilize the antisite defects in MBT while preserving the favorable electronic properties. Here, to this end, we utilized a screening approach to understand the role of dopants in the Mn and Bi sites. We find that Sc, Y, and La dopings prefer substitutions on the Bi site and significantly increase the Mn–Bi antisite defect formation energy. We find that the contribution from the empty s and d states of Sc, Y, and La around the Fermi level is insignificant. However, at the high concentration limit, the Bi–Te octahedra are significantly modified with doping, leading to important changes in the band structure.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2011

Neutron Scattering Studies of spin excitations in hole-doped Ba0.67K0.33Fe2As2 superconductor

We report inelastic neutron scattering experiments on single crystals of superconducting Ba0.67K0.33Fe2As2 (Tc5 38 K). In addition to confirming the resonance previously found in powder samples, we find that spin excitations in the normal state form longitudinally elongated ellipses along the QAFM direction in momentum space, consistent with density functional theory predictions. On cooling below Tc, while the resonance preserves its momentum anisotropy as expected, spin excitations at energies below the resonance become essentially isotropic in the in-plane momentum space and dramatically increase their correlation length. These results suggest that the superconducting gap structures in Ba0.67Ka0.33Fe2As2 are more complicated than those suggested from angle resolved photoemission experiments.

ELECTRONIC MATERIALS AND DEVICES↗
DOE OSTI2019

Polarimetry of Regular and Stochastic Signals in Magnetooptics

A brief review is presented of application of the high-sensitive laser polarimetry for detecting small changes—either regular, or stochastic—of the medium magnetization. Principles and results of application of the spectroscopy of spin fluctuations to atomic and semiconductor systems are described. New possibilities of studying the radiospectroscopic and optical properties of spin systems using the methods of noise spectroscopy are considered. Prospects for expanding the circle of objects of the spin noise spectroscopy at the expense of impurity dielectrics are discussed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Tunable topological Dirac surface states and van Hove singularities in kagome metal GdV 6 Sn 6

Transition-metal-based kagome materials at van Hove filling are a rich frontier for the investigation of novel topological electronic states and correlated phenomena. To date, in the idealized two-dimensional kagome lattice, topologically Dirac surface states (TDSSs) have not been unambiguously observed, and the manipulation of TDSSs and van Hove singularities (VHSs) remains largely unexplored. Here, we reveal TDSSs originating from a $\mathbb{Z}_2$ bulk topology and identify multiple VHSs near the Fermi level (E F ) in magnetic kagome material GdV 6 Sn 6 . Using in situ surface potassium deposition, we successfully realize manipulation of the TDSSs and VHSs. The Dirac point of the TDSSs can be tuned from above to below E F , which reverses the chirality of the spin texture at the Fermi surface. These results establish GdV 6 Sn 6 as a fascinating platform for studying the nontrivial topology, magnetism, and correlation effects native to kagome lattices. They also suggest potential application of spintronic devices based on kagome materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

In-situ fabrication of graded material with the application of a horizontal magnetic field during directional solidification

Highlights: • The horizontal magnetic field caused the migration of primary grains and the formation of graded material. • TEMF play a major effect on the formation of graded material. • The magnitude of TEMF increases with the increase of magnetic field intensity. • This work initiates a new method to prepare the “graded material” via an applied horizontal magnetic field. - Abstract: The present paper proposes a method of graded materials preparation under a low horizontal magnetic field during directional solidification. The external horizontal magnetic field was applied to the mushy zone of the directionally solidified Al-10 wt% Cu and Al-18 wt% Si samples, which was perpendicular to the growth direction. Experimental results demonstrate that the applied horizontal magnetic field produces a gradient size distribution of the primary α(Al) grains in Al-10 wt% Cu alloys and a gradient fraction distribution of primary Si particles in Al-18 wt% Si alloys. 3D numerical simulations indicate that the formation of graded structure should be attributed to the migration of primary phase driven by the thermoelectric magnetic force (TEMF). The formation of segregation channel should be attributed to the TEM convection (TEMC) in the mushy zone. Further, in situ synchrotron X-ray radiography observations of the initial transient of directional solidification show that the primary α(Al) phases were migrated approximately along the direction perpendicular to the magnetic field. These results suggest that the TEM effects can greatly change the growth of primary grains and the solidification structure, and the application of an external horizontal magnetic field would be beneficial to fabricate the graded material during directional solidification.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Quantum Corrections and Magnetotransport in 3D Dirac Semimetal Cd{sub 3 –x}Mn{sub x}As{sub 2} Films

Thin films of solid solutions based on the three-dimensional Dirac semimetal Cd{sub 3}As{sub 2} with the addition of manganese are investigated. Cd{sub 3 –x}Mn{sub x}As{sub 2} films (x = 0, 0.05, and 0.1) 50–70 nm in thickness are formed on a glassceramic substrate using vacuum-thermal deposition from cadmium arsenide ingots doped by Mn and fabricated by direct alloying elements by the vacuum-cell method. The temperature and magnetic-field dependences of the resistance are measured and the transport parameters of the films under study are determined. Positive magnetoresistance of the characteristic shape corresponding to the contribution of the weak antilocalization effect is observed for films with x = 0 and 0.05. The contribution from the weak localization effect is observed at a higher Mn content (x = 0.1). This change in the quantum correction type as applied to topological semimetals points to reconstruction of the band structure and transition from the Dirac semimetal state into a trivial semiconductor phase, which corresponds to the critical Mn content x{sub c} ~ 0.07 in this case.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗