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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 595 records · Page 33
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Mild hydrothermal crystal growth of new uranium(IV) fluorides, Na{sub 3.13}Mg{sub 1.43}U{sub 6}F{sub 30} and Na{sub 2.50}Mn{sub 1.75}U{sub 6}F{sub 30}: Structures, optical and magnetic properties

Two new uranium(IV) fluorides, Na{sub 3.13}Mg{sub 1.43}U{sub 6}F{sub 30} (1) and Na{sub 2.50}Mn{sub 1.75}U{sub 6}F{sub 30} (2), were synthesized through an in situ mild hydrothermal route, and were structurally characterized by single crystal X-ray diffraction. The compounds exhibit complex crystal structures composed of corner- or edge-shared UF{sub 9} and MF{sub 6} (M=Mg, Mn) polyhedra, forming hexagonal channels in the three-dimensional framework, in which ordered or disordered divalent metal and sodium atoms reside. The large hexagonal voids contain the nearly regular M(II)F{sub 6} octahedra and sodium ions, whereas the small hexagonal cavities include M(II) and sodium ions on a mixed-occupied site. Magnetic susceptibility measurements yielded effective magnetic moments of 8.36 and 11.6 µ{sub B} for 1 and 2, respectively, confirming the presence and oxidation states of U(IV) and Mn(II). The large negative Weiss constants indicate the spin gap between a triplet and a singlet state in the U(IV). Magnetization data as a function of applied fields revealed that 2 exhibits paramagnetic behavior due to the nonmagnetic singlet ground state of U(IV) at low temperature. UV–vis diffuse reflectance and X-ray photoelectron spectroscopy data were also analyzed. - Graphical abstract: Two new quaternary U(IV) fluorides, Na{sub 3.13}Mg{sub 1.43}U{sub 6}F{sub 30} and Na{sub 2.50}Mn{sub 1.75}U{sub 6}F{sub 30}, were crystallized via an in situ reduction step of U(VI) to U(IV) under mild hydrothermal conditions. The compounds show complex crystal structures based on the 3-D building block of U{sub 6}F{sub 30}. Magnetic property measurements revealed that the U(IV) exhibits a nonmagnetic singlet ground state at low temperature with a spin gap. - Highlights: • Na{sub 3.13}Mg{sub 1.43}U{sub 6}F{sub 30} and Na{sub 2.50}Mn{sub 1.75}U{sub 6}F{sub 30} have been synthesized and characterized. • The U(IV) fluorides exhibit complex three-dimensional crystal structures. • The optical properties were investigated. • Magnetic susceptibility data were collected.

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

A family of rare earth uranium oxides, RE{sub 6}UO{sub 12-δ}, (RE = Rare Earth). Synthesis, structure and magnetic behavior

Highlights: • A series of rare earth urinates, RE{sub 6}UO{sub 12}, were synthesized using the solid state method. • The crystal structures of RE{sub 6}UO{sub 12} were refined using the Rietveld method. • Magnetic properties were measured and AF ordering was observed in RE = Gd, Tb, Dy. - Abstract: A series of rare earth uranates, RE{sub 6}UO{sub 12-δ} (RE = La, Nd, Sm – Dy, Er and Yb), were synthesized via the solid state method and their structures were determined using the Rietveld method. These compounds crystallize in the rhombohedral space group R-3H with the lattice parameters a = 10.47005(3) Å and c = 9.98034(3) Å for the La analogue. The temperature and field dependent magnetization are reported for each analogue. Antiferromagnetic ordering is observed for RE = Gd, Tb, and Dy with Néel temperatures of 2.1 K, 5.8 K, and 2.8 K, respectively. Magnetic measurements on the La{sub 6}UO{sub 12} analogue indicate the presence of some U{sup 5+}, and therefore, oxygen vacancies in the structure. The variability of the U valence is examined.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Magnetic properties of Co-Zr-B magnets produced by spark plasma sintering method

Magnets of Co-Zr-B, one of the permanent magnetic compounds without rare-earth elements, were successfully produced by the spark plasma sintering method. The resultant Co-Zr-B magnets had high densities of 92%–96% and consisted mainly of the Co{sub x}Zr (x ≈ 5) phase. The coercivity of the Co-Zr-B magnets was highly dependent on the consolidation temperature and the boron content. The highest maximum energy product of 6.0 MGOe, with a remanence of 6.4 kG and the coercivity of 4.0 kOe, was achieved by the Co{sub 80}Zr{sub 18}B{sub 2} magnets consolidated at 873 K.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Post magnetic field annealing effect on magnetic and structural properties of Co{sub 80}Pt{sub 20} nanowires and nanotubes fabricated by electrochemical method

Highly ordered Co{sub 80}Pt{sub 20} nanowires (NWs) and nanotubes (NTs) have been synthesized by low cost DC electrochemical deposition method with constant stirring during the fabrication process in anodic aluminum oxide nano-templates with average pore diameter of about 200 nm. The structural and magnetic properties of nanostructures have been investigated before and after simple and magnetic field annealing. Magnetic field of 1 T has been applied during annealing process in the direction perpendicular to NWs and NTs axis. X-Ray Diffraction analysis shows face centered cubic (fcc) as the dominant phase for Co{sub 80}Pt{sub 20} NWs and post annealing led to better crystallinity with retained fcc phase. Furthermore, magnetic properties, including saturation magnetization (M{sub s}), squareness ratio (M{sub r}/M{sub s}), and coercivity (H{sub c}), have been investigated as a function of annealing temperature by Vibrating Sample Magnetometer.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2014

Simulation of magnetic island dynamics under resonant magnetic perturbation with the TEAR code and validation of the results on T-10 tokamak data

Simulation of the magnetic island evolution under Resonant Magnetic Perturbation (RMP) in rotating T-10 tokamak plasma is presented with intent of TEAR code experimental validation. In the T-10 experiment chosen for simulation, the RMP consists of a stationary error field, a magnetic field of the eddy current in the resistive vacuum vessel and magnetic field of the externally applied controlled halo current in the plasma scrape-off layer (SOL). The halo-current loop consists of a rail limiter, plasma SOL, vacuum vessel, and external part of the circuit. Effects of plasma resistivity, viscosity, and RMP are taken into account in the TEAR code based on the two-fluid MHD approximation. Radial distribution of the magnetic flux perturbation is calculated with account of the externally applied RMP. A good agreement is obtained between the simulation results and experimental data for the cases of preprogrammed and feedback-controlled halo current in the plasma SOL.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Slew-rate dependence of tracer magnetization response in magnetic particle imaging

Magnetic Particle Imaging (MPI) is a new biomedical imaging technique that produces real-time, high-resolution tomographic images of superparamagnetic iron oxide nanoparticle tracers. Currently, 25 kHz and 20 mT/μ{sub 0} excitation fields are common in MPI, but lower field amplitudes may be necessary for patient safety in future designs. Here, we address fundamental questions about MPI tracer magnetization dynamics and predict tracer performance in future scanners that employ new combinations of excitation field amplitude (H{sub o}) and frequency (ω). Using an optimized, monodisperse MPI tracer, we studied how several combinations of drive field frequencies and amplitudes affect the tracer's response, using Magnetic Particle Spectrometry and AC hysteresis, for drive field conditions at 15.5, 26, and 40.2 kHz, with field amplitudes ranging from 7 to 52 mT/μ{sub 0}. For both fluid and immobilized nanoparticle samples, we determined that magnetic response was dominated by Néel reversal. Furthermore, we observed that the peak slew-rate (ωH{sub o}) determined the tracer magnetic response. Smaller amplitudes provided correspondingly smaller field of view, sometimes resulting in excitation of minor hysteresis loops. Changing the drive field conditions but keeping the peak slew-rate constant kept the tracer response almost the same. Higher peak slew-rates led to reduced maximum signal intensity and greater coercivity in the tracer response. Our experimental results were in reasonable agreement with Stoner-Wohlfarth model based theories.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Fast magnetic reconnection with large guide fields

In this letter, it is demonstrated using two-fluid simulations that low-β magnetic reconnection remains fast, regardless of the presence of fast dispersive waves, which have been previously suggested to play a critical role. To understand these results, a discrete model is constructed that offers scaling relationships for the reconnection rate and dissipation region (DR) thickness in terms of the upstream magnetic field and DR length. We verify these scalings numerically and show how the DR self-adjusts to process magnetic flux at the same rate that it is supplied to a larger region where two-fluid effects become important. The rate is therefore independent of the DR physics and is in good agreement with kinetic results.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Separation of the contributions to the magnetization of Tm{sub 1-x}Yb{sub x}B{sub 12} solid solutions in steady and pulsed magnetic fields

The magnetization of substitutional Tm{sub 1-x}Yb{sub x}B{sub 12} solid solutions is studied in the composition range 0 < x {<=} 0.81. The measurements are performed at low temperatures (1.9-300 K) in steady (up to 11 T) and pulsed (up to 50 T, pulse duration of 20-100 ms) magnetic fields. An analysis of the experimental data allowed the contributions to the magnetization of the paramagnetic phase of the Tm{sub 1-x}Yb{sub x}B{sub 12} compounds to be separated. These contributions include a Pauli component, which corresponds to the response of the heavy-fermion manybody states that appears in the energy gap in the vicinity of the Fermi level (density of states (3-4) Multiplication-Sign 10{sup 21} cm{sup -3} meV{sup -1}), and a contribution with saturation in high magnetic fields attributed to the localized magnetic moments ((0.8-3.7){mu}{sub B} per unit cell) of the nanoclusters formed by rare-earth ions with an antiferromagnetic interaction.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Ultra-high quality factors in superconducting niobium cavities in ambient magnetic fields up to 190 mG

Ambient magnetic field, if trapped in the penetration depth, leads to the residual resistance and therefore sets the limit for the achievable quality factors in superconducting niobium resonators for particle accelerators. Here, we show that a complete expulsion of the magnetic flux can be performed and leads to: (1) record quality factors Q > 2 × 10{sup 11} up to accelerating gradient of 22 MV/m; (2) Q ∼ 3 × 10{sup 10} at 2 K and 16 MV/m in up to 190 mG magnetic fields. This is achieved by large thermal gradients at the normal/superconducting phase front during the cooldown. Our findings open up a way to ultra-high quality factors at low temperatures and show an alternative to the sophisticated magnetic shielding implemented in modern superconducting accelerators.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗