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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 559 records · Page 31
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

On the synthesis, characterization and magnetic properties of two new phases discovered in the PbO–Fe{sub 2}O{sub 3}–P{sub 2}O{sub 5} system

The PbFe{sub 3}O(PO{sub 4}){sub 3} powder compound was studied by means of X-ray diffraction (XRD) from 300 to 6 K, electron-probe microanalysis (EPMA) coupled with wavelength dispersion spectroscopy (WDS), calorimetric (DSC and specific heat) and magnetic properties measurements. Magnetization, magnetic susceptibility and specific heat measurements carried out on PbFe{sub 3}O(PO{sub 4}){sub 3} powders firmly establish a series of three ferromagnetic (FM)-like second order phase transitions spanned over the 32–8 K temperature range. Discrepancies between magnetization and specific heat data obtained in PbFe{sub 3}O(PO{sub 4}){sub 3} powders and single crystals are highlighted. A first extraction of the critical exponents (β,γ,δ) was performed by ac magnetic susceptibility in both PbFe{sub 3}O(PO{sub 4}){sub 3} powders and single crystals and the values were found to be consistent with mean-field theory. Further exploration of the PbO–Fe{sub 2}O{sub 3}–P{sub 2}O{sub 5} system led to the discovery of a new langbeinite phase, Pb{sub 1.5}Fe{sub 2}(PO{sub 4}){sub 3}, the crystal structure of which was solved by room temperature single crystal XRD (P2{sub 1}3, Z=4, a=9.7831(2) Å). This phase does not undergo any structural phase transition down to 6 K nor any kind of long range ordering down to 2 K. - Graphical abstract: Three ferromagnetic-like phase transitions discovered in the new compound PbFe{sub 3}O(PO{sub 4}){sub 3} by specific heat and ZFC/FC magnetization measurements. - Highlights: • Three FM-like second order phase transitions in PbFe{sub 3}O(PO{sub 4}){sub 3} powders. • Critical exponents (β,γ,δ) in PbFe{sub 3}O(PO{sub 4}){sub 3} consistent with mean-field behavior. • Discovery of a new langbeinite phase, Pb{sub 1.5}Fe{sub 2}(PO{sub 4}){sub 3}.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Spin Berry curvature-enhanced orbital Zeeman effect in a kagome metal

Berry phases and the related concept of Berry curvature can give rise to many unconventional phenomena in solids. Here, we discover a colossal orbital Zeeman effect of topological origin in a bilayer kagome metal, TbV 6 Sn 6 . Using spectroscopic imaging scanning tunnelling microscopy, we reveal that the magnetic field leads to a splitting of the gapped Dirac dispersion into two branches with enhanced momentum-dependent g factors, resulting in a substantial renormalization of the Dirac band. These measurements provide a direct observation of a magnetic field-controlled orbital Zeeman coupling to the orbital magnetic moments of up to 200 Bohr magnetons near the gapped Dirac points. Our work provides direct insight into the momentum-dependent nature of topological orbital moments and their tunability via the magnetic field, concomitant with the evolution of the spin Berry curvature. Furthermore, these results can be extended to explore large orbital magnetic moments driven by the Berry curvature governed by other quantum numbers beyond spin, such as the valley in certain graphene-based structures.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Propagation of electro-kinetic waves in magnetized GaN semiconductor with nano-sized ion colloids

Based on hydrodynamic model of multi-component plasma, an analytical study on propagation of longitudinal electro-kinetic (LEK) waves in wurtzite and zincblende structures of GaN is carried out. Nano-sized ion colloids (NICs) are embedded in the sample by the technique of ion-implantation. The implanted NICs are considered massive by an order as compared to the host lattice points and do not participate in Based LEK perturbations. Though, the NICs are continuously bombarded by the electrons as well as the holes yet, the former acquires a net negative charge owing to relatively higher mobility of electrons and consequently results into depletion of electron density in the medium. It i s found that the presence of charged NICs significantly modifies the dispersion and amplification characteristics of LEK waves in magnetized GaN semiconductor plasma and their role becomes increasingly effective as the fraction of charge on them increases.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Perspectives on spin hydrodynamics in ferromagnetic materials

The field of spin hydrodynamics aims to describe magnetization dynamics from a fluid perspective. For ferromagnetic materials, there is an exact mapping between the Landau-Lifshitz equation and a set of dispersive hydrodynamic equations. This analogy provides ample opportunities to explore novel magnetization dynamics and magnetization states that can lead to potential applications that rely entirely on magnetic materials, for example, long-distance transport of information. Additionally, this article provides an overview of the theoretical foundations of spin hydrodynamics and their physical interpretation in the context of spin transport. We discuss other proposed applications for spin hydrodynamics as well as our view on challenges and future research directions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Competition of lattice and spin excitations in the temperature dependence of spin-wave properties

The interplay of magnons and phonons can induce strong temperature variations in the magnetic exchange interactions, leading to changes in the magnetothermal response. This is a central mechanism in many magnetic phenomena, and in the new field of Spin Caloritronics, which focuses on the combination of heat and spin currents. Boson model systems have previously been developed to describe the magnon-phonon coupling but, until recently, studies rely on empirical parameters. In this paper, we propose a first-principles approach to describe the dependence of the magnetic exchange integrals on phonon renormalization, leading to changes in the magnon dispersion as a function of temperature. The temperature enters into the spin dynamics (by introducing fluctuations) as well as in the magnetic exchange itself. Depending on the strength of the coupling, these two temperatures may or may not be equilibrated, yielding different regimes. We test our approach in typical and well-known ferromagnetic materials: Ni, Fe, and Permalloy. Finally, we compare our results to recent experiments on the spin-wave stiffness, and discuss departures from Bloch’s law and parabolic dispersion.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Propagation of surface waves on a semi-bounded quantum magnetized collisional plasma

The propagation of surface waves on a semi-bounded quantum plasma in the presence of the external magnetic field and collisional effects is investigated by using quantum magnetohydrodynamics model. A general analytical expression for the dispersion relation of surface waves is obtained by considering the boundary conditions. It is shown that, in some special cases, the obtained dispersion relation reduces to the results reported in previous works. It is also indicated that the quantum, external magnetic field and collisional effects can facilitate the propagation of surface waves on a semi-bounded plasma. In addition, it is found that the growth rate of the surface wave instability is enhanced by increasing the collision frequency and plasmonic parameter.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Effect of trapping in a degenerate plasma in the presence of a quantizing magnetic field

Effect of trapping as a microscopic phenomenon in a degenerate plasma is investigated in the presence of a quantizing magnetic field. The plasma comprises degenerate electrons and non-degenerate ions. The presence of the quantizing magnetic field is discussed briefly and the effect of trapping is investigated by using the Fermi-Dirac distribution function. The linear dispersion relation for ion acoustic wave is derived in the presence of the quantizing magnetic field and its influence on the propagation characteristics of the linear ion acoustic wave is discussed. Subsequently, fully nonlinear equations for ion acoustic waves are used to obtain the Sagdeev potential and the investigation of solitary structures. The formation of solitary structures is studied both for fully and partially degenerate plasmas in the presence of a quantizing magnetic field. Both compressive and rarefactive solitons are obtained for different conditions of temperature and magnetic field.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1973

Ion streaming instabilities with application to collisionless shock wave structure

The electromagnetic dispersion relation for two counterstreaming ion beams of arbitrary relative strength flowing parallel to a dc magnetic field is derived. The beams flow through a stationary electron background and the dispersion relation in the fluid approximation is unaffected by the electron thermal pressure. The dispersion relation is solved with a zero net current condition applied and the regions of instability in the k-U space (U is the relative velocity between the two ion beams) are presented. The parameters are then chosen to be applicable for parallel shocks. It was found that unstable waves with zero group velocity in the shock frame can exist near the leading edge of the shock for upstream Alfven Mach numbers greater than 5.5. It is suggested that this mechanism could generate sufficient turbulence within the shock layer to scatter the incoming ions and create the required dissipation for intermediate strength shocks.

Golden, K. I.↗
DOE OSTI2014

Electronic band structure of magnetic bilayer graphene superlattices

Electronic band structure of the bilayer graphene superlattices with δ-function magnetic barriers and zero average magnetic flux is studied within the four-band continuum model, using the transfer matrix method. The periodic magnetic potential effects on the zero-energy touching point between the lowest conduction and the highest valence minibands of pristine bilayer graphene are exactly analyzed. Magnetic potential is shown also to generate the finite-energy touching points between higher minibands at the edges of Brillouin zone. The positions of these points and the related dispersions are determined in the case of symmetric potentials.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
NASA NTRS2021

The Dispersion of the Modified Two-Stream and Lower Hybrid Drift Instabilities in the Near-pole Plume of a Magnetically Shielded Hall Thruster

Recent analytical and numerical investigations have shown that instabilities in the lower hybrid frequency range can grow in the plume region downstream of the front magnet pole pieces of a magnetically shielded Hall thruster. Growth of the Modified Two-Stream (MTSI) and Lower Hybrid Drift (LHDI) instabilities was found with wave propagation in the r-z (or in-) plane and azimuthal (or out-of-plane) directions, respectively. In the analysis of the LHDI electron collisions were found to be insufficient to quench the instability in a region contained by the thruster ion beam and hollow cathode plume. The implication of the findings is that ions may be heated anomalously by these instabilities, in both the out-of-plane and in-plane directions, thereby altering the velocity field and enhancing the energy of those ions that strike nearby thruster surfaces. In this article we summarize the solution of the dispersion relation for each of these instabilities and provide additional results that can be compared directly with data from future plasma diagnostics, including with direct measurements of the wave dispersion.

Ortega, A. Lopez↗
DOE OSTI2023

Magnon Dispersion in CeIn3

This dataset contains measurements of the low-energetic magnetic excitations in the heavy-fermion material CeIn3. Neutron spectroscopy data were recorded on a single-crystal mosaic of around 2 g total mass at the spectrometer CNCS. In a first row of measurements with incident neutron energy 12 meV the excitations were mapped out in major parts of the first Brillouin zone. In a second row of measurements with 3.315 meV incident neutron energy, the gapless and relatively steep dispersion in the vicinity of the R-point, corresponding to (1/2,1/2,1/2) in reciprocal space, was investigated.

excitations↗
DOE OSTI2024

Fermi Surface Nesting Driving the RKKY Interaction in the Centrosymmetric Skyrmion Magnet Gd 2 PdSi 3

The magnetic skyrmions generated in a centrosymmetric crystal were recently first discovered in Gd 2 PdSi 3 . In light of this, we observe the electronic structure by angle-resolved photoemission spectroscopy (ARPES) and unveil its direct relationship with the magnetism in this compound. The Fermi surface and band dispersions are demonstrated to have a good agreement with the density functional theory (DFT) calculations carried out with careful consideration of the crystal superstructure. Most importantly, we find that the three-dimensional Fermi surface has extended nesting which matches well the q vector of the magnetic order detected by recent scattering measurements. Finally, the consistency we find among ARPES, DFT, and the scattering measurements suggests the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction involving itinerant electrons to be the formation mechanism of skyrmions in Gd 2 PdSi 3 .

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2012

Alfven waves in dusty plasmas with plasma particles described by anisotropic kappa distributions

We utilize a kinetic description to study the dispersion relation of Alfven waves propagating parallelly to the ambient magnetic field in a dusty plasma, taking into account the fluctuation of the charge of the dust particles, which is due to inelastic collisions with electrons and ions. We consider a plasma in which the velocity distribution functions of the plasma particles are modelled as anisotropic kappa distributions, study the dispersion relation for several combinations of the parameters {kappa}{sub Parallel-To} and {kappa}{sub Up-Tack }, and emphasize the effect of the anisotropy of the distributions on the mode coupling which occurs in a dusty plasma, between waves in the branch of circularly polarized waves and waves in the whistler branch.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Scanning systems for particle cancer therapy

A particle beam to treat malignant tissue is delivered to a patient by a gantry. The gantry includes a plurality of small magnets sequentially arranged along a beam tube to transfer the particle beam with strong focusing and a small dispersion function, whereby a beam size is very small, allowing for the small magnet size. Magnets arranged along the beam tube uses combined function magnets where the magnetic field is a combination of a bending dipole field with a focusing or defocusing quadrupole field. A triplet set of combined function magnets defines the beam size at the patient. A scanning system of magnets arranged along the beam tube after the bending system delivers the particle beam in a direction normal to the patient, to minimize healthy skin and tissue exposure to the particle beam.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2014

Atomic-Scale Chemical Imaging and Quantification of Metallic Alloy Structures by Energy-Dispersive X-Ray Spectroscopy

Determination of atomic-scale crystal structure for nanostructured intermetallic alloys, such as magnetic alloys containing Al, Ni, Co (alnico) and Fe, is crucial for understanding physical properties such as magnetism, but technically challenging due to the small interatomic distances and the similar atomic numbers. By applying energy-dispersive X-ray spectroscopy (EDS) mapping to the study of two intermetallic phases of an alnico alloy resulting from spinodal decomposition, we have determined atomic-scale chemical composition at individual lattice sites for the two phases: one is the B2 phase with Fe0.76Co0.24 -Fe0.40Co0.60 ordering and the other is the L21 phase with Ni0.48Co0.52 at A-sites, Al at BΙ-sites and Fe0.20Ti0.80 at BΙΙ-sites, respectively. The technique developed through this study represents a powerful real-space approach to investigate structure chemically at the atomic scale for a wide range of materials systems.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Synthesis and characterization of barium ferrite–silica nanocomposites

In this work, we prepared barium ferrite-silica (BaM-SiO{sub 2}) nanocomposites of different molar ratios by high-energy ball milling, followed by heat-treatment at different temperatures. The microstructure, morphology and magnetic properties were characterized for different synthesis conditions by using X-ray diffraction (XRD), scanning electron microscopy (SEM) and vibrating sample magnetometry (VSM). The results indicate that 15 h of milling was enough to avoid the generation of hematite phase and to get a good dispersion of barium ferrite particles in the ceramic matrix. For milling periods beyond 15 h and heat treatment above 900 °C, the XRD patterns showed the presence of hematite phase caused by the decomposition of BaM. The agglomerate size observed through SEM analysis was around 150 nm with a good BaM dispersion into the SiO{sub 2} matrix. The highest saturation magnetization (Ms) value obtained was 43 emu/g and the corresponding coercivity (Hc) value of 3.4 kOe for the composition 60BaM-40SiO{sub 2} milled for 15 h and heat treated at 900 °C. This coercivity value is acceptable for the application in magnetic recording media. Highlights: • Barium ferrite–silica nanocomposites were prepared by high energy ball milling. • Optimal processing time is 15 h milling and heat treatment at 900 °C. • This is enough to avoid the generation of hematite phase. • Obtain good dispersion of barium ferrite particles in the ceramic matrix • Above this processing time shows the presence of increased amount of hematite.

36 MATERIALS SCIENCE↗
NASA NTRS1983

A perpendicular ion beam instability - Solutions to the linear dispersion relation

A 200-eV Xe(+) ion beam directed perpendicular to the terrestrial magnetic field in the F region ionosphere produced very narrow band electrostatic emissions just above multiples of the hydrogen cyclotron frequency. Although the plasma conditions associated with the ion beam were undoubtedly very complex, a simple ion beam in a background ionosphere is considered first. The dispersion relation for flute mode waves and an unmagnetized perpendicular ion beam is solved for a diffuse H(+) plasma and then for a combination of dense O(+) and diffuse H(+). These solutions account for most of the wave properties, including the observation of narrow spectral peaks separated by the hydrogen cyclotron frequency and the observation of no spectral peaks below 2000 Hz. We cannot dismiss field-aligned currents associated with the Xe(+) beam as an alternate source of free energy for the narrow band emissions. However, our intention here is to examine closely the Xe(+) beam as a source for directly exciting the plasma waves.

Kintner, P. M.↗
DOE OSTI2013

TEST FOR WAVEVECTOR ANISOTROPIES IN PLASMA TURBULENCE CASCADES

The frequency and wavevector matching conditions in nonlinear three-wave coupling are used to test whether the forward cascade of plasma turbulence may lead to wavevector anisotropies in a homogeneous, collisionless, magnetized plasma. Linear kinetic theory at {beta}{sub p} = 0.01, 0.10, and 1.0 is used to determine the frequency-wavenumber dispersion of three normal modes: long-wavelength Alfven-cyclotron waves, long-wavelength magnetosonic waves, and intermediate-wavelength magnetosonic-whistler waves. Using linear dispersion in the nonlinear matching conditions, the test predicts with one exception that forward cascades are favored by fluctuations propagating nearly perpendicular to the background magnetic field B{sub o}. This is consistent with the typical development of wavevector anisotropies with k >> k{sub Parallel-To} (subscripts refer to directions perpendicular and parallel to B{sub o}, respectively) in computer simulations of the forward cascade of various types of plasma turbulence. The exception is that, at {beta}{sub p} = 1.0, the test predicts that the cascade of long-wavelength magnetosonic waves should be favored by modes at k {approx} k{sub Parallel-To }.

79 ASTRONOMY AND ASTROPHYSICS↗