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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 937 records · Page 52
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Synthesis and characterizations of (In{sub 0.90}Sn{sub 0.05}Ni{sub 0.05}){sub 2}O{sub 3} nanoparticles using solid state reaction method

ITO (In{sub 0.95}Sn{sub 0.05}){sub 2}O{sub 3} and Ni doped ITO (In{sub 0.90}Sn{sub 0.05}Ni{sub 0.05}){sub 2}O{sub 3} nanoparticles (NPs) were synthesized by solid state reaction method and subjected to study their structural, optical and magnetic properties. The NPs had a size distribution in the range of 40 nm and were identified as the bcc cubic In{sub 2}O{sub 3} by X-ray diffraction (XRD). Optical properties of the samples were studies using UV-Vis-NIR spectrophotometer. Magnetic measurements were carried out at room temperature and at 100 K using vibrating sample magnetometer and found that the ITO nanoparticles were ferromagnetic in nature at room temperature. The strength of the magnetization decreased in ITO nanoparticles when the magnetic measurements carried out at 100 K.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2016

Effect of synthesis conditions on the photocatalytic property of multiferroic BiFeO{sub 3} towards the degradation of phenol red

Multiferroic BiFeO{sub 3} has been synthesized through hydrothermal route under different reaction conditions. From the basic characterization such as of X-Ray diffraction analysis (XRD), the synthesized Nps were found to having rhombohedral structure with R3c space group. Photodegradation studies of toxic dye phenol red have been investigated under visible light irradiation. Vibrating sample magnetometer (VSM) analysis has been carried out to identify the magnetic properties and recycle ability photocatalysts.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Effect of air annealing on structure and magnetic properties of Sn{sub 1-x}Fe{sub x}O{sub 2} thin films

Sn{sub 1-x}Fe{sub x}O{sub 2} (x = 0.07) thin films were prepared on to glass substrates using flash evaporation technique and annealed in air at different temperatures. The X-ray diffraction study showsed that all the thin films annealed at different temperatures were in tetragonal rutile structure of SnO{sub 2}. The Elemental analysis confirms the presence of Fe and Sn and O in the films. The magnetic measurements were carried out using vibrating sample magnetometer and found that the strength of magnetization decreased with increase of annealing temperature.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Coherent population trapping with polarization modulation

Coherent population trapping (CPT) is extensively studied for future vapor cell clocks of high frequency stability. In the constructive polarization modulation CPT scheme, a bichromatic laser field with polarization and phase synchronously modulated is applied on an atomic medium. A high contrast CPT signal is observed in this so-called double-modulation configuration, due to the fact that the atomic population does not leak to the extreme Zeeman states, and that the two CPT dark states, which are produced successively by the alternate polarizations, add constructively. Here, we experimentally investigate CPT signal dynamics first in the usual configuration, a single circular polarization. The double-modulation scheme is then addressed in both cases: one pulse Rabi interaction and two pulses Ramsey interaction. The impact and the optimization of the experimental parameters involved in the time sequence are reviewed. We show that a simple seven-level model explains the experimental observations. The double-modulation scheme yields a high contrast similar to the one of other high contrast configurations like push-pull optical pumping or crossed linear polarization scheme, with a setup allowing a higher compactness. The constructive polarization modulation is attractive for atomic clock, atomic magnetometer, and high precision spectroscopy applications.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Cation distribution in CuFe{sub 2}O{sub 4} nanoparticles: Effects of Ni doping on magnetic properties

The Cu{sub 1−x}Ni{sub x}Fe{sub 2}O{sub 4} nanoparticles (with x = 0, 0.3, 0.5, 0.7, and 1) were synthesized by using spray co-precipitation method at annealing temperature T{sub a} = 900 °C in air for 5 h. The crystal structure, microstructure, oxidation state, and magnetic properties of the samples were characterized by using X-ray diffraction, synchrotron X-ray diffraction, scanning electron microscopy, X-ray absorption spectroscopy, and vibrating sample magnetometer. It was shown that all the samples have cubic structure. Lattice constant and grain size decrease, while the Curie temperature T{sub C} increases with increasing of Ni{sup 2+} content. A small amount of Fe{sup 2+} was found in all the samples. Cation distribution was determined by using a combination of magnetization measurements, extended X-ray absorption fine structure analysis, and Rietveld refinement from synchrotron X-ray diffraction data. It was indicated that Ni{sup 2+} ions occupy in octahedral site only, while Cu{sup 2+} ions distribute in both tetrahedral and octahedral sites. The variation of magnetic parameters is discussed based on Ni{sup 2+} concentration, grain size, the cation distribution, surface effect, and the presence of Fe{sup 2+} ion in the samples.

36 MATERIALS SCIENCE↗
DOE OSTI2013

SCALING OF THE ELECTRON DISSIPATION RANGE OF SOLAR WIND TURBULENCE

Electron scale solar wind (SW) turbulence has attracted great interest in recent years. Considerable evidence exists that the turbulence is not fully dissipated near the proton scale, but continues cascading down to electron scales. However, the scaling of the magnetic energy spectra as well as the nature of the plasma modes involved at those small scales are still not fully determined. Here we survey 10 yr of the Cluster STAFF search-coil magnetometer waveforms measured in the SW and perform a statistical study of the magnetic energy spectra in the frequency range [1, 180] Hz. We found that 75% of the analyzed spectra exhibit breakpoints near the electron gyroscale ρ{sub e}, followed by steeper power-law-like spectra. We show that the scaling below the electron breakpoint cannot be determined unambiguously due to instrumental limitations that we discuss in detail. We compare our results to those reported in other studies and discuss their implications for the physical mechanisms involved and for theoretical modeling of energy dissipation in the SW.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Comet 1P/Halley multifluid MHD model for the Giotto fly-by

The interaction of comets with the solar wind has been the focus of many studies including numerical modeling. We compare the results of our multifluid MHD simulation of comet 1P/Halley to data obtained during the flyby of the European Space Agency's Giotto spacecraft in 1986. The model solves the full set of MHD equations for the individual fluids representing the solar wind protons, the cometary light and heavy ions, and the electrons. The mass loading, charge-exchange, dissociative ion-electron recombination, and collisional interactions between the fluids are taken into account. The computational domain spans over several million kilometers, and the close vicinity of the comet is resolved to the details of the magnetic cavity. The model is validated by comparison to the corresponding Giotto observations obtained by the Ion Mass Spectrometer, the Neutral Mass Spectrometer, the Giotto magnetometer experiment, and the Johnstone Plasma Analyzer instrument. The model shows the formation of the bow shock, the ion pile-up, and the diamagnetic cavity and is able to reproduce the observed temperature differences between the pick-up ion populations and the solar wind protons. We give an overview of the global interaction of the comet with the solar wind and then show the effects of the Lorentz force interaction between the different plasma populations.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

A STATISTICAL STUDY OF THE SOLAR WIND TURBULENCE AT ION KINETIC SCALES USING THE K-FILTERING TECHNIQUE AND CLUSTER DATA

Plasma turbulence at ion kinetic scales in the solar wind is investigated using the multi-point magnetometer data from the Cluster spacecraft. By applying the k-filtering method, we are able to estimate the full three-dimensional power spectral density P(ω{sub sc}, k) at a certain spacecraft frequency ω{sub sc} in wavevector (k) space. By using the wavevector at the maximum power in P(ω{sub sc}, k) at each sampling frequency ω{sub sc} and the Doppler shifted frequency ω{sub pla} in the solar wind frame, the dispersion plot ω{sub pla} = ω{sub pla}(k) is found. Previous studies have been limited to very few intervals and have been hampered by large errors, which motivates a statistical study of 52 intervals of solar wind. We find that the turbulence is predominantly highly oblique to the magnetic field k >> k {sub ∥}, and propagates slowly in the plasma frame with most points having frequencies smaller than the proton gyrofrequency ω{sub pla} < Ω{sub p}. Weak agreement is found that turbulence at the ion kinetic scales consists of kinetic Alfvén waves and coherent structures advected with plasma bulk velocity plus some minor more compressible components. The results suggest that anti-sunward and sunward propagating magnetic fluctuations are of similar nature in both the fast and slow solar wind at ion kinetic scales. The fast wind has significantly more anti-sunward flux than sunward flux and the slow wind appears to be more balanced.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

KINETIC TURBULENCE IN THE TERRESTRIAL MAGNETOSHEATH: CLUSTER OBSERVATIONS

We present a first statistical study of subproton- and electron-scale turbulence in the terrestrial magnetosheath using waveform data measured by the Cluster/STAFF search coil magnetometer in the frequency range [1, 180] Hz. It is found that clear spectral breaks exist near the electron scale, which separate two power-law-like frequency bands referred to as the dispersive and the electron dissipation ranges. The frequencies of the breaks f{sub b} are shown to be well correlated with the electron gyroscale ρ {sub e} rather than with the electron inertial length d{sub e} . The distribution of the slopes below f{sub b} is found to be narrow and peaks near –2.9, while that of the slopes above f{sub b} is found to be broader, peaking near –5.2, with values as low as –7.5. This is the first time that such steep power-law spectra are reported in space plasma turbulence. These observations provide new constraints on theoretical modeling of kinetic turbulence and dissipation in collisionless magnetized plasmas.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Magnetization curves of sintered heavy tungsten alloys for applications in MRI-guided radiotherapy

Purpose: Due to the current interest in MRI-guided radiotherapy, the magnetic properties of the materials commonly used in radiotherapy are becoming increasingly important. In this paper, measurement results for the magnetization (BH) curves of a range of sintered heavy tungsten alloys used in radiation shielding and collimation are presented. Methods: Sintered heavy tungsten alloys typically contain >90 % tungsten and <10 % of a combination of iron, nickel, and copper binders. Samples of eight different grades of sintered heavy tungsten alloys with varying binder content were investigated. Using a superconducting quantum interference detector magnetometer, the induced magnetic momentm was measured for each sample as a function of applied external field H{sub 0} and the BH curve derived. Results: The iron content of the alloys was found to play a dominant role, directly influencing the magnetizationM and thus the nonlinearity of the BH curve. Generally, the saturation magnetization increased with increasing iron content of the alloy. Furthermore, no measurable magnetization was found for all alloys without iron content, despite containing up to 6% of nickel. For two samples from different manufacturers but with identical quoted nominal elemental composition (95% W, 3.5% Ni, 1.5% Fe), a relative difference in the magnetization of 11%–16% was measured. Conclusions: The measured curves show that the magnetic properties of sintered heavy tungsten alloys strongly depend on the iron content, whereas the addition of nickel in the absence of iron led to no measurable effect. Since a difference in the BH curves for two samples with identical quoted nominal composition from different manufacturers was observed, measuring of the BH curve for each individual batch of heavy tungsten alloys is advisable whenever accurate knowledge of the magnetic properties is crucial. The obtained BH curves can be used in FEM simulations to predict the magnetic impact of sintered heavy tungsten alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Double resonance fequency light shift compensation in optically oriented laser-pumped alkali atoms

The contributions of the vector and scalar components to the magnetically dependent microwave transition frequency light shift are analyzed and the compensation of these components is experimentally demonstrated for the {sup 87}Rb atoms optically oriented by a laser tuned to the D{sub 2} line of the head doublet. The Allan variance is studied as a function of the averaging time for a tandem of optically pumped quantum magnetometers (OPQMs), one of which is based on a low-frequency spin oscillator while another is based on a quantum microwave discriminator with a resonance frequency that corresponds to magnetically dependent transitions between HFS sublevels with the extremal value of the magnetic quantum number. It is shown that the compensation of the scalar and vector components of the light shift in OPQMs reduces the Allan variance at averaging times that exceed hundreds of seconds compared to a quantum discriminator based on the magnetically independent 0–0 transition. In this case, the minimal Allan variance in OPQMs at the end resonance is achieved at considerably longer averaging times than in the case of the quantum discriminator that is tuned to the 0–0 transition frequency.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Magnetic and absorbing properties of M-type substituted hexaferrites BaFe{sub 12–x}Ga{sub x}O{sub 19} (0.1 < x < 1.2)

X-ray powder diffraction is used to determine the unit cell parameters and to refine the crystal structure of the solid solutions of M-type hexagonal barium ferrite BaFe{sub 12–x}Ga{sub x}O{sub 19} (x = 0.1–1.2) with isostructural diamagnetic cation Ga{sup 3+} substitution at T = 300 K. As the level of substitution increases, the unit cell parameters are shown to decrease monotonically. The temperature (300 K ≤ T ≤ 750 K, H = 8.6 kOe) and field (T = 300 K,–20 kOe ≤ H ≤ 20 kOe) dependences of the saturation magnetization of these solid solutions are studied with a vibrating-sample magnetometer. The concentration dependences of the Curie temperature T{sub C}, the specific spontaneous magnetization, and the coercive force are plotted. The magnetic parameters are found to decrease with increasing substitution. The microwave properties of the solid solutions are analyzed in an external magnetic field (0 ≤ H ≤ 4 kOe). As the cation Ga{sup 3+} concentration increases from x = 0.1 to 0.6, the natural ferromagnetic resonance (NFMR) frequency decreases; as the concentration increases further to x = 1.2, this frequency again increases. As the cation Ga{sup 3+} concentration increases, the NFMR line width increases, which indicates a widening of the frequency range where electromagnetic radiation is intensely absorbed. Here, the resonance curve peak amplitude changes insignificantly. The shift of the NFMR frequency in an applied magnetic field is more pronounced for samples with low cation Ga{sup 3+} concentrations. The role of diamagnetic substitution is revealed, and the prospects and advantages of Ga-substituted beryllium hexaferrite as the material absorbing high-frequency electromagnetic radiation are demonstrated.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Heat-Treatment Induced Magnetic Anisotropy of GaMnSb Films

Conditions and mechanisms of controlled variation of the magnetic anisotropy of GaMnSb films containing magnetic MnSb nanoinclusions by means of heat treatment have been determined. For this purpose, the temperature and magnetic-field dependences of the magnetic moments of samples before and after thermal annealing were measured using a SQUID magnetometer. It is established that the heat treatment of GaMnSb films leads to a significant increase in the values of characteristics determined by the magnetic anisotropy, including the growth of blocking temperature (from 95 to 390 K) and the magnetic anisotropy field (from 330 to 630 Oe). Results of transmission electron microscopy investigation indicate that a change in the magnetic anisotropy of GaMnSb films as a result of their thermal annealing can be related to a transition of the crystalline structure of magnetic MnSb nanoinclusions from hexagonal (space group P6{sub 2}/mmc) to cubic (space group F-43m).

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Preparation and Characterization of Mn Doped ZnO Nanorods

Mn doped ZnO nanorods were prepared by chemical precipitation method. The micro-structural and structural properties of the nanorods were calculated from the X-ray diffraction technique. The formed nanorods was seen in the scanning electron microscopy. The purity of the sample was confirmed by the energy dispersive X-ray analysis (EDX). The optical properties were studied using UV-Vis spectroscopy and photoluminescence. In the photoluminescence spectrum, the peaks due to recombination of free electrons, oxygen vacancy and intrinsic defects were observed. The magnetic properties were studied using vibrating sample magnetometer (VSM) and the paramagnetic nature of the material was confirmed.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Pulsed Field-Induced Magnetization Switching in Antiferromagnetic Ferrihydrite Nanoparticles

The dynamic magnetization switching of ferrihydrite nanoparticles has been investigated by a pulsed magnetometer technique in maximum fields H{sub max} of up to 130 kOe with pulse lengths of 4, 8, and 16 ms. Ferrihydrite exhibits antiferromagnetic ordering and defects cause the uncompensated magnetic moment in nanoparticles; therefore, the behavior typical of magnetic nanoparticles is observed. The dynamic hysteresis loops measured under the above-mentioned conditions show that the use of pulsed fields significantly broadens the temperature region of existence of the magnetic hysteresis and the coercivity can be governed by varying the maximum field and pulse length. This behavior is resulted from the relaxation effects typical of conventional ferro- and ferrimagnetic nanoparticles and the features typical of antiferromagnetic nanoparticles.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Effect of Heat Treatment on the Dispersion of the Magnetic Anisotropy of MnSb Nanoinclusions Embedded in Thin GaMnSb Films

We observed a temperature-controlled increase in the magnetic anisotropy and its dispersion in thin GaMnSb films with MnSb nanoinclusions obtained by pulsed laser deposition. The data of transmission electron microscopy indicate that in the samples, a transition of the crystalline structure of magnetic MnSb nanoinclusions from hexagonal (spatial group (sp. gr.) P6{sub 3}/mmc) to cubic (sp. gr. F-43m) takes place. Analysis of the temperature dependences of the magnetic moment m(T), measured using a SQUID magnetometer, obtained for both unannealed and annealed samples cooled in a zero magnetic field and a magnetic field of 10 kOe, indicates that this mechanism is not unique. In unannealed samples, the distribution of the magnetic anisotropy of MnSb nanoinclusions, determined from the dependences of m(T), is unimodal. In the annealed samples, the same dependence becomes multimodal. This means that several thermally activated processes occur in the samples during annealing, resulting in several “populations” of nanoinclusions present in the annealed thin films. The contribution to the increase in the magnetic anisotropy during annealing can result in the structural phase transition, the mismatch of the crystal lattices between MnSb and GaSb, an increase in the average volume of MnSb nanoinclusions, and a change in their stoichiometry.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

The Effect of the Polarization Characteristics of Probe Light on the Signal of Optically Detected Magnetic Resonance in Magnetometric and Gyroscopic Quantum Sensors

We consider the effect of the polarization characteristics of probe light on the signal of optically detected magnetic resonance in quantum sensors, including quantum magnetometers based on the phenomenon of electron paramagnetic resonance and quantum gyroscopes employing both the electron and nuclear magnetic resonance. Relationships between the magnetic resonance signal magnitude and parameters of the optical system elements, which are based on the Stokes–Mueller formalism, are derived and verified. It is found that the main destructive influence in the signal in a standard two-beam scheme is produced by phase delays introduced by both metallic and dielectric mirrors. Methods for compensation of this destructive influence are proposed and verified.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Modeling magnetic fields from a DC power cable buried beneath San Francisco Bay based on empirical measurements

Here, the Trans Bay Cable (TBC) is a ±200-kilovolt (kV), 400 MW 85-km long High Voltage Direct Current (DC) buried transmission line linking Pittsburg, CA with San Francisco, CA (SF) beneath the San Francisco Estuary. The TBC runs parallel to the migratory route of various marine species, including green sturgeon, Chinook salmon, and steelhead trout. In July and August 2014, an extensive series of magnetic field measurements were taken using a pair of submerged Geometrics magnetometers towed behind a survey vessel in four locations in the San Francisco estuary along profiles that cross the cable’s path; these included the San Francisco-Oakland Bay Bridge (BB), the Richmond-San Rafael Bridge (RSR), the Benicia- Martinez Bridge (Ben) and an area in San Pablo Bay (SP) in which a bridge is not present. In this paper, we apply basic formulas that ideally describe the magnetic field from a DC cable summed vectorially with the background geomagnetic field (in the absence of other sources that would perturb the ambient field) to derive characteristics of the cable that are otherwise not immediately observable. Magnetic field profiles from measurements taken along 170 survey lines were inspected visually for evidence of a distinct pattern representing the presence of the cable. Many profiles were dominated by field distortions unrelated to the cable caused by bridge structures or other submerged objects, and the cable’s contribution to the field was not detectable. BB, with 40 of the survey lines, did not yield usable data for these reasons. The unrelated anomalies could be up to 100 times greater than those from the cable. In total, discernible magnetic field profiles measured from 76 survey lines were regressed against the equations, representing eight days of measurement. The modeled field anomalies due to the cable (the difference between the maximum and minimum field along the survey line at the cable crossing) were virtually identical to the measured values. The modeling yielded a pooled cable depth below the bay floor of 2.06 m (±1.46 std dev), and estimated the angle to the horizontal of the imaginary line connecting the crosssectional center of the cable’s two conductors (0.1143 m apart) as 178.9° ±61.9° (std dev) for Ben, 78.6°±37.0° (std dev) for RSR, and 139.9°±27.4° (std dev) for SP. The mean of the eight daily average currents derived from the regressions was 986 ±185 amperes (A) (std dev), as compared to 722 ±95 A (std dev) provided by Trans Bay Cable LLC. Overall, the regressions based on fundamental principles (Biot Savart law) and the vectorial summation of cable and geomagnetic fields provide estimates of cable characteristics consistent with plausible expectations.

54 ENVIRONMENTAL SCIENCES↗