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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 1,765 records · Page 98
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Crystal structure and magnetic properties of Gd 8 Mn 3 Sb 19

Here, in this study, a novel magnetic semimetal compound, Gd 8 Mn 3 Sb 19 , was synthesized successfully via high-temperature solid-state reaction. The crystal structure of Gd 8 Mn 3 Sb 19 was determined using both single crystal and powder X-ray diffraction techniques, revealing a non-centrosymmetric orthorhombic space group, Pmn2 1 (No. 31). The Sb atoms in Gd 8 Mn 3 Sb 19 form five-atom-wide Sb 5 7− ribbons, narrower three-atom-wide Sb 3 5− ribbons, and single Sb 3− anions. On the other hand, both Gd 3+ and Mn 2+ ions form the distorted Gd 3 and Mn 3 triangular lattices, respectively. The magnetic measurements suggest the complex magnetic interactions contributed by both Gd 3+ and Mn 2+ ions. A sharp peak observed in the magnetic susceptibility plot at approximately 25 K corresponds to the antiferromagnetic-type transition in Gd 8 Mn 3 Sb 19 . Furthermore, the magnetic measurements along different directions indicate the strong magnetic anisotropy present in Gd 8 Mn 3 Sb 19 , which is likely due to the complex magnetic interactions arising from the existence of Gd and Mn ions. Finally, the electrical resistivity measurements of Gd 8 Mn 3 Sb 19 indicate semimetallic behavior with a positive magnetoresistance.

Chemistry↗
DOE OSTI2011

Phase composition and magnetic properties of niobium-iron codoped TiO{sub 2} nanoparticles synthesized in Ar/O{sub 2} radio-frequency thermal plasma

Nanoparticles of Nb{sup 5+}-Fe{sup 3+} codoped TiO{sub 2} with various Nb{sup 5+} concentrations (Nb/(Ti+Fe+Nb)=0-10.0 at%) and Fe{sup 3+} (Fe/(Ti+Fe+Nb)=0-2.0 at%) were synthesized using Ar/O{sub 2} thermal plasma. Dopant content, chemical valence, phase identification, morphology and magnetic properties were determined using several characterization techniques, including inductively coupled plasma-optical emission spectrometer, X-ray photoelectron spectroscopy, X-ray diffraction, UV-vis diffuse reflectance spectrometer, field-emission scanning electron microscopy, transmission electron microscopy and SQUID commercial instrument. The XRD revealed that all the plasma-synthesized powders were exclusively composed of anatase as major phase and rutile. The rutile weight fraction was increased by the substitution of Fe{sup 3+} for Ti{sup 4+} whereas it was reduced by the Nb{sup 5+} doping. The plasma-synthesized Nb{sup 5+}-Fe{sup 3+} codoped TiO{sub 2} powders had intrinsic magnetic properties of strongly paramagnetic and feebly ferromagnetic at room temperature. The ferromagnetic properties gradually deteriorated as the Fe{sup 3+} concentration was decreased, suggesting that the ferromagnetism was predominated by the phase composition as a carrier-mediated exchange. - Graphical Abstract: Spherical nanoparticles of Nb{sup 5+}-Fe{sup 3+} codoped TiO{sub 2} were synthesized using Ar/O{sub 2} thermal plasma. The plasma-synthesized powders were composed of anatase as major phase and rutile. Rutile weight fraction was increased by Fe{sup 3+} addition but was reduced by Nb{sup 5+} doping. Strongly paramagnetic and feebly ferromagnetic properties are of intrinsic nature. Ferromagnetic properties gradually deteriorated as Fe{sup 3+} concentration was increased. Highlights: > Nanoparticles of Nb{sup 5+}-Fe{sup 3+} codoped TiO{sub 2} were synthesized using Ar/O{sub 2} thermal plasma. > The plasma-synthesized powders were composed of anatase as major phase and rutile. > Rutile weight fraction was increased by Fe{sup 3+} addition but was reduced by Nb{sup 5+} doping. > Strongly paramagnetic and feebly ferromagnetic properties are of intrinsic nature. > Ferromagnetic properties gradually deteriorated as Fe{sup 3+} concentration was increased.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

Origin of room temperature d{sup 0} ferromagnetism and characteristic photoluminescence in pristine SnO{sub 2} nanowires: A correlation

Arrays of SnO{sub 2} nanowires are fabricated by employing a wet chemical template assisted sol-gel route using ordered nanoporous anodic aluminium oxide as the host. The origin of room temperature d{sup 0} ferromagnetism in pristine polycrystalline SnO{sub 2} nanowires is investigated by correlating photoluminescence and electron paramagnetic resonance (EPR) studies. It has been found that the naturally grown structural defects of oxygen vacancies namely singly ionised oxygen vacancy (V{sub O}{sup {center_dot}}) clusters induce the characteristic photoluminescence and contribute in ferromagnetism of pristine SnO{sub 2} nanowires at room temperature. The presence of the V{sub O}{sup {center_dot}} structural defects in the pure SnO{sub 2} nanowires is also assured by the EPR spectroscopy. Present study will help understand the puzzle about the unexpected magnetic phenomenon in these undoped wide band gap oxide semiconductors. Highlights: Black-Right-Pointing-Pointer SnO{sub 2} NWs are fabricated by wet chemical AAO template assisted route. Black-Right-Pointing-Pointer SnO{sub 2} NWs exhibit d{sup 0} ferromagnetism at room temperature. Black-Right-Pointing-Pointer Origin of ferromagnetism is correlated with photoluminescence and EPR studies. Black-Right-Pointing-Pointer Oxygen vacancy clusters are attributed to boost ferromagnetism in SnO{sub 2} NWs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Thermodynamic studies of CaLaFe₁₁O₁₉(s)

Thermodynamic studies on CaLaFe₁₁O₁₉(s) were carried out using Knudsen effusion mass spectrometry and calorimetry, viz. differential scanning calorimetry and high temperature oxide melt solution calorimetry. Standard molar Gibbs free energy of formation (Δ{sub f}G⁰{sub m}), enthalpy of formation and heat capacity (C⁰{sub ₚ,m}) of the compound were calculated as a function of temperature for the first time. C⁰{sub ₚ,m}(CaLaFe₁₁O₁₉) was determined and used for second law analysis, from which enthalpy and entropy of formation of the compound were calculated and the respective values are: Δ{sub f}H⁰{sub m}(298.15 K)/kJ mol⁻¹=-6057(±8) and S⁰{sub m}(298.15 K)/J K⁻¹ mol⁻¹=427(±5). Δ{sub f}H⁰{sub m}(298.15 K)/kJ mol⁻¹: -6055(±6) was also calculated using oxide melt solution calorimetry, which is in close agreement with the second law value. A heat capacity anomaly was also observed at T=684 K. A table of thermodynamic data from 298.15 K to 1000 K for CaLaFe₁₁O₁₉(s) was also constructed to represent an optimized set of data. - graphical abstract: Variation of standard molar heat capacities of CaLaF₁₁O₁₉(s) and MFe₁₂O₁₉(s) (M=Sr, Ba and Pb) as a function of temperature. Highlights: • Thermodynamic studies on CaLaFe₁₁O₁₉(s) were performed using KEQMS and solution calorimetry. • It was synthesized using gel combustion route and characterized by XRD technique. • The compound is magnetic in nature and shows a heat capacity anomaly at 684 K. • Thermodynamic table was constructed from 298 K to 1000 K.

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

Reducing waste of the hydride-dehydride process for U-6 wt% Nb spherical powders through lower impact and targeted milling

The breakdown of solid metal into powder during the hydride-dehydride process is commercially important for the formation of titanium and other metal powders. Typically, the milling of the brittle hydride powder occurs in a ball mill, where milling media impacts powder particles to break them down. The milling media can impact particles that are larger than desired, as desired, or smaller than desired, indiscriminately making all particles smaller. In this work, we investigate how to minimize waste powder production during milling using two different milling methods, planetary ball milling and milling in a sieve shaker (sieve-milling). Both processes yielded similar amounts of 20–75 μm diameter powder (the target size range); however, sieve-milling generated a significantly smaller amount of undersized waste powder. The powders were characterized by X-ray diffraction, SEM/STEM, and magnetic susceptibility. Several differences between ball milling and sieve-milling processes are discussed. We then conclude that the decreased yield of undersized powder in sieve-milling was due to a combination of lower impact energy in sieve-milling, unreacted metallic cores in the hydride flakes, and the ability to mill target particle sizes during sieve-milling. While these results are from the milling of brittle hydride powder, similar methods may be applicable to other brittle powders, including ceramics or salts.

Chemistry↗
DOE OSTI2025

Detecting Magnon-phonon coupling in yttrium iron garnet with variable temperature STEM-EELS

Magnons, quanta of spin wave excitations in magnetically ordered materials, have been identified as candidates for several potentially transformative technologies in recent years. Macroscopic techniques, such as neutron scattering or Raman spectroscopy, can be used to identify and analyze magnons, but provide relatively delocalized information about the sample. Understanding how the bonding and local structure of a material interacts with, and influences, the magnon population in a material is a crucial step toward the ability to produce any real-world application utilizing magnons. By leveraging the combined spatial resolution of scanning transmission electron microscopy (STEM) and the energy resolution of monochromated electron energy-loss spectroscopy (EELS) nanoscale analysis of magnons can be performed. While the weak interaction of magnons with the electron beam makes magnon EELS challenging on reasonable timescales, magnon-phonon coupling can be leveraged to understand magnons through their effect on the more easily measured phonons. Here, we examine yttrium iron garnet (YIG) flakes, and demonstrate non-linear, temperature-dependent shifts in the phonon frequencies, consistent with previously described magnon-phonon coupling effects. The ability to measure the temperature-dependence of vibrational frequencies with high precision in individual nanoscale flakes, demonstrates the ability to study magnon-phonon coupling in the STEM with unprecedented spatial resolution.

Reifsnyder, Alexander [ORNL]↗
DOE OSTI2016

Structural and Electronic Effects on the Properties of Fe 2 (dobdc) upon Oxidation with N 2 O

Here, we report electronic, vibrational, and magnetic properties, together with their structural dependences, for the metal–organic framework Fe 2 (dobdc) (dobdc 4 – = 2,5-dioxido-1,4-benzenedicarboxylate) and its derivatives, Fe 2 (O) 2 (dobdc) and Fe 2 (OH) 2 (dobdc)—species arising in the previously proposed mechanism for the oxidation of ethane to ethanol using N 2 O as an oxidant. Magnetic susceptibility measurements reported for Fe 2 (dobdc) in an earlier study and reported in the current study for Fe II 0.26 [Fe III (OH)] 1.74 (dobdc)(DMF) 0.15 (THF) 0.22 , which is more simply referred to as Fe 2 (OH) 2 (dobdc), were used to confirm the computational results. Theory was also compared to experiment for infrared spectra and X-ray powder diffraction structures. Structural and magnetic properties were computed by using Kohn-Sham density functional theory both with periodic boundary conditions and with cluster models. In addition, we studied the effects of different treatments of the exchange interactions on the magnetic coupling parameters by comparing several approaches to the exchange-correlation functional: generalized gradient approximation (GGA), GGA with empirical Coulomb and exchange integrals for 3d electrons (the GGA+U method), nonseparable gradient approximation with empirical Coulomb and exchange integrals for 3d electrons (GAM+U), hybrid GGA, meta-GGA, and hybrid meta- GGA. We found the coupling between the metal centers to be ferromagnetic in the case of Fe 2 (dobdc) and antiferromagnetic in the cases of Fe 2 (O) 2 (dobdc) and Fe 2 (OH) 2 (dobdc). The shift in magnetic coupling behavior correlates with the changing electronic structure of the framework, which derives from both structural and electronic changes that occur upon metal oxidation and addition of the charge-balancing oxo and hydroxo ligands.

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

Dipolar Heteronuclear Correlation Solid-State NMR Experiments between Half-Integer Quadrupolar Nuclei: The Case of 11 B– 17 O

With 73% of all NMR-active nuclei being quadrupolar, there is great interest in the development of NMR experiments that can probe the proximity of quadrupolar spins. Here, pulse sequences for magic-angle spinning (MAS) 11 B– 17 O resonance-echo saturation-pulse double-resonance (RESPDOR) and dipolar heteronuclear multiple quantum correlation (D-HMQC) solid-state NMR experiments were investigated. In these pulse sequences, rotational-echo double-resonance (REDOR) recoupling was used with central transition (CT)-selective π-pulses applied to either the 11 B or 17 O spins to recouple 11 B– 17 O dipolar interactions. 11 B{ 17 O} RESPDOR experiments on 17 O-enriched boric acid and benzene diboronic acid showed that application of dipolar recoupling on the 11 B channel yielded more signal dephasing than when recoupling is applied on the 17 O channel; however, short effective 11 B transverse relaxation time constants (T 2 ') hinder the acquisition of dephasing curves out to long recoupling durations. Application of REDOR recoupling to 17 O spins was found to produce significant dephasing without compromising the 11 B T 2 '. Comparison of experimental 11 B{ 17 O} RESPDOR curves to those of numerical simulations enabled the 17 O isotopic enrichment to be estimated. 2D 11 B{ 17 O} D-HMQC spectra were recorded with either 11 B or 17 O REDOR recoupling under a variety of radio frequency field conditions. Lastly, 2D 11 B{ 17 O} and 23 Na{ 17 O} D-HMQC spectra of an 17 O-enriched sodium borate glass were acquired to demonstrate the practical application of these heteronuclear correlation experiments to probe structural connectivity between two quadrupolar spins. Importantly, the high-field 2D 11 B– 17 O D-HMQC NMR spectrum revealed two unique 17 O sites correlating to 4-coordinate BO 4 ( [4] B), which were attributed to the [3] B–O– [4] B and [4] B–O– [4] B bridging O atoms. Furthermore, the heteronuclear correlation experiments outlined here should be applicable to a variety of quadrupolar spin pairs.

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

Superconducting Fourfold Fe(Te,Se) Film on Sixfold Magnetic MnTe via Hybrid Symmetry Epitaxy

Epitaxial Fe(Te,Se) thin films have been grown on various substrates but never been grown on magnetic layers. In this work, we report the epitaxial growth of fourfold Fe(Te,Se) film on a sixfold antiferromagnetic insulator, MnTe. The Fe(Te,Se)/MnTe heterostructure shows a clear superconducting transition at around 11 K, and the critical magnetic field measurement suggests the origin of the superconductivity to be bulk-like. Structural characterizations suggest that the uniaxial lattice match between Fe(Te,Se) and MnTe allows a hybrid symmetry epitaxy mode, which was recently discovered between Fe(Te,Se) and Bi 2 Te 3 . Furthermore, the Te/Fe flux ratio during deposition of the Fe(Te,Se) layer is found to be critical for its superconductivity. Now that superconducting Fe(Te,Se) can be grown on two related hexagonal platforms, Bi 2 Te 3 and MnTe, this result opens a new possibility of combining topological superconductivity of Fe(Te,Se) with the rich physics in the intrinsic magnetic topological materials (MnTe) n (Bi 2 Te 3 ) m family.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2026

i -Wave Symmetry Altermagnetism and Anomalous Hall Conductivity in Monolayer FeCl 3

In this work, the FeCl 3 monolayer is proposed to host a rare and exotic i -wave symmetry altermagnetism. Using first-principles calculations, we performed a detailed investigation of the structural stability and electronic, magnetic, and spintronic properties of monolayer FeCl 3 . Our results suggest the system is semiconducting in nature and exhibits i-wave symmetry nonrelativistic spin splitting (NRSS), originating from its hexagonal crystal structure with roto-inversion symmetries and anisotropic crystal field. The momentum-resolved spin-splitting further supports the presence of spin-dependent topological features. Further, the monolayer exhibits sizable conventional spin-Hall and anomalous Hall conductivities, highlighting its promise as a versatile platform for next-generation flexo-spintronic applications.

altermagnetism↗
DOE OSTI2018

Valley Manipulation by Optically Tuning the Magnetic Proximity Effect in WSe 2 /CrI 3 Heterostructures

Monolayer valley semiconductors, such as tungsten diselenide (WSe 2 ), possess valley pseudospin degrees of freedom that are optically addressable but degenerate in energy. Lifting the energy degeneracy by breaking time-reversal symmetry is vital for valley manipulation. This has been realized by directly applying magnetic fields or via pseudomagnetic fields generated by intense circularly polarized optical pulses. However, sweeping large magnetic fields is impractical for devices, and the pseudomagnetic fields are only effective in the presence of ultrafast laser pulses. The recent rise of two-dimensional (2D) magnets unlocks new approaches to controlling valley physics via van der Waals heterostructure engineering. Here, we demonstrate the wide continuous tuning of the valley polarization and valley Zeeman splitting with small changes in the laser-excitation power in heterostructures formed by monolayer WSe 2 and 2D magnetic chromium triiodide (CrI 3 ). The valley manipulation is realized via the optical control of the CrI 3 magnetization, which tunes the magnetic exchange field over a range of 20 T. Lastly, our results reveal a convenient new path toward the optical control of valley pseudospins and van der Waals magnetic heterostructures.

2D magnets↗
DOE OSTI2019

Disorder-to-Order Transition Mediated by Size Refocusing: A Route toward Monodisperse Intermetallic Nanoparticles

Intermetallic nanoparticles are remarkable because of their often enhanced catalytic, magnetic, and optical properties, which arise from their ordered crystal structures and high structural stability. Typical syntheses of intermetallic nanoparticles include thermal annealing of the disordered counterpart in atmosphere (or vacuum) or colloidal syntheses, where the phase transformation is achieved in solution. Although both methods can produce intermetallic nanoparticles, there is difficulty in achieving monodisperse nanoparticles, which is critical to exploiting their properties for various applications. In this work, we demonstrate that overgrowth on random alloy AuCu nanoparticles mediated by size refocusing yields monodisperse intermetallic AuCu nanoparticles. Size refocusing has been used in syntheses of semiconductor and upconverting nanocrystals to achieve monodisperse samples, but now we demonstrate size refocusing as a mechanism to achieve the disorder-to-order phase transformation in multimetallic nanoparticles. The phase transformation was monitored by time evolution experiments, where analysis of reaction aliquots with transmission electron microscopy and powder X-ray diffraction revealed the generation and dissolution of small nanoparticles coupled with an increase in the average size of the nanoparticles and conversion to the ordered phase. This demonstration advances the understanding of intermetallic nanoparticle formation in colloidal syntheses, which can expedite the development of electrocatalysts and magnetic storage materials.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2011

High pressure route to generate magnetic monopole dimers in spin ice

The gas of magnetic monopoles in spin ice is governed by one key parameter: the monopole chemical potential. A significant variation of this parameter could access hitherto undiscovered magnetic phenomena arising from monopole correlations, as observed in the analogous electrical Coulomb gas, like monopole dimerization, critical phase separation, or charge ordering. However, all known spin ices have values of chemical potential imposed by their structure and chemistry that place them deeply within the weakly correlated regime, where none of these interesting phenomena occur. Here we use high-pressure synthesis to create a new monopole host, Dy 2 Ge 2 O 7 , with a radically altered chemical potential that stabilizes a large fraction of monopole dimers. The system is found to be ideally described by the classic Debye–Huckel–Bjerrum theory of charge correlations. We thus show how to tune the monopole chemical potential in spin ice and how to access the diverse collective properties of magnetic monopoles.

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

Spin dynamics and orbital-antiphase pairing symmetry in iron-based superconductors

The symmetry of the wave function describing the Cooper pairs is one of the most basic quantities in a superconductor yet its measurement in the iron-based superconductors has proved to be very difficult. The complex multi-band nature of these materials makes the interplay of superconductivity with spin and orbital dynamics very intriguing, leading to very material dependent magnetic excitations, and pairing symmetries. In this work we use first-principles many-body method, including ab initio determined two-particle vertex function, to study the spin dynamics and superconducting pairing symmetry in a large number of iron-based superconductors. In iron compounds with high transition temperature, we find both the dispersive high-energy spin excitations, and very strong low energy commensurate or nearly commensurate spin response, suggesting that these low energy spin excitations play the dominate role in cooper pairing. We discover three closely competing types of pairing symmetries, which take a very simple form in the space of active iron 3d orbitals, and differ only in the relative quantum mechanical phase of the xz, yz and xy orbital contributions. The extensively discussed s +- symmetry appears when contributions from all orbitals have equal sign, while the opposite sign in xz and yz orbitals leads to the d wave symmetry. A novel orbital antiphase s +- symmetry emerges when xy orbital has opposite sign to xz and yz orbitals. We propose that this orbital-antiphase pairing symmetry explains the puzzling variation of the experimentally observed superconducting gaps on all the Fermi surfaces of LiFeAs. This novel symmetry of the order parameter may be realized in other iron superconductors.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Giant coercivity and high magnetic blocking temperatures for N 2 3- radical-bridged dilanthanide complexes upon ligand dissociation

Increasing the operating temperatures of single-molecule magnets—molecules that can retain magnetic polarization in the absence of an applied field—has potential implications toward information storage and computing, and may also inform the development of new bulk magnets. Progress toward these goals relies upon the development of synthetic chemistry enabling enhancement of the thermal barrier to reversal of the magnetic moment, while suppressing alternative relaxation processes. Here in this paper, we show that pairing the axial magnetic anisotropy enforced by tetramethylcyclopentadienyl (Cp Me4H ) capping ligands with strong magnetic exchange coupling provided by an N 2 3- radical bridging ligand results in a series of dilanthanide complexes exhibiting exceptionally large magnetic hysteresis loops that persist to high temperatures. Significantly, reducing the coordination number of the metal centers appears to increase axial magnetic anisotropy, giving rise to larger magnetic relaxation barriers and 100-s magnetic blocking temperatures of up to 20 K, as observed for the complex [K(crypt-222)][(Cp Me4H 2 Tb) 2 (μ-N∙ 2</sub)].

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗