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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 829 records · Page 46
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Magnetic and electrical properties of Martian particles

The only determinations of the magnetic properties of Martian materials come from experiments on the two Viking Landers. The results suggest Martian soil containing 1 to 10 percent of a highly magnetic phase. Though the magnetic phase mineral was not conclusively identified, the predominate interpretation is that the magnetic phase is probably maghemite. The electrical properties of the surface of Mars were only measured remotely by observations with Earth based radar, microwave radiometry, and inference from radio-occultation of Mars orbiting spacecraft. No direct measurements of electrical properties on Martian materials have been performed.

Olhoeft, G. R.↗
DOE OSTI2018

The Effect of Oxygen Adsorption for Vacancy-Induced d{sup 0} Magnetism in HfO{sub 2} (110) Surface

Based on the density functional theory, we investigated the electronic structures and magnetic properties of the oxygen adsorption on the defective cubic HfO{sub 2} (110) surface. The adsorption capacities of the perfect and defective surfaces follow in the sequence as: oxygen-deficient model >perfect surface >hafnium-deficient model. When the oxygen molecules adsorb on the nonmagnetic perfect HfO{sub 2} surface, the system has a local magnetic moment and the antiferromagnetic coupling is more stable. For the defective cubic HfO{sub 2} (110) surface, it is found that the oxygen vacancy is more easy to form than the hafnium vacancy by comparing the vacancy formation energy. And the hafnium vacancy could induce a large magnetic moment while the oxygen vacancy alone could not. After adsorption of the oxygen molecule, the nonmagnetic oxygen-deficient HfO{sub 2} model is transformed into the magnetic surface. On the contrary, the introduction of adsorbed oxygen molecule causes the magnetic moment of hafnium-deficient HfO{sub 2} surface to reduce. Additionally, if the oxygen molecules adsorb on the defective HfO{sub 2} (110) surface, the ferromagnetic coupling is energetically favorable.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

High-Temperature Ferrofluids Based on Molten Salts

Molten metal chloride salts are promising candidates for advanced heat transfer fluids in generation IV nuclear reactors and beyond. However, research on the magnetic properties of suspended metallic nanoparticles at elevated temperatures is scarce, and there have been no attempts to develop a high-temperature, molten salt based ferrofluid. Such a ferrofluid would enable in situ manipulation of both the physical and thermal properties of the fluid via an external magnetic field. This study examines molten salt based ferrofluids comprised of metallic cobalt nanoparticles dispersed in molten metal chloride salts. High-temperature magnetometry and magneto-thermogalvometric measurements were conducted to evaluate the magnetic characteristics of the ferrofluid. Further analysis was conducted through a combination of microscopy, spectroscopy, solubility tests, and diffraction measurements. Furthermore, the metallic cobalt nanoparticles exhibited a notable degree of chemical stability and sustained magnetism from 25 to 800 °C when suspended in NaCl–MgCl 2 and KCl–ZnCl 2 mixtures.

Cobalt↗
DOE OSTI2019

A study of defect structures in Fe-alloyed ZnO: Morphology, magnetism, and hyperfine interactions

In order to study the effect of Fe cation substitution on the local structure, defect formation, and hyperfine interactions in ZnO, Mössbauer spectroscopy measurements of the microwave processed Zn 1 - x Fe x O (x = 0.05, 0.10, 0.15, and 0.20) nanoparticles, together with ab initio calculations, were performed. Complementary information on the distribution of particle size and morphology, as well as magnetic properties, were obtained by X-ray diffraction, transmission electron microscopy, and squid-magnetometry. The selected model for analyzing the Mössbauer spectra of our samples is a distribution of quadrupole splittings. The fitting model with two Lorentz doublets was rejected due to its failure to include larger doublets. The Fe 3 + ions do not yield magnetic ordering in the samples at room temperature. The results from first-principles calculations confirm that the major component of the Mössbauer spectra corresponds to the Fe-alloyed ZnO with Zn vacancy in the next nearest neighbor environment. The magnetic measurements are consistent with the description of the distribution of iron ions over the randomly formed clusters in the ZnO host lattice. While at room temperature all the samples are paramagnetic, magnetic interactions cause a transition into a cluster spin-glass state at low temperatures. © 2019 Author(s).

60 APPLIED LIFE SCIENCES↗
DOE OSTI2019

Electromagnetic Wave-Absorbing Properties of Steel Slag

This research explores the electromagnetic radiation protection function of steel slag for use as a building material. Scanning electron microscopy, x-ray diffraction, x-ray photoelectron spectroscopy and Mössbauer spectroscopy were used to analyze the chemical composition and mineralogical phase of steel slag powder. Electromagnetic parameters of the samples were analyzed and discussed in detail for the frequency range of 1-18 GHz. We found that steel slag had the electromagnetic wave-absorbing property due to electric components (such as FeO and carbon powder) and magnetic components [such as magnetite (Fe{sub 3}O{sub 4}) and hematite (α-Fe{sub 2}O{sub 3})]; electric loss was far greater than magnetic loss. With the increasing milling time, the electric and magnetic properties were increased. The calculated reflectivity curve of steel slag powder epoxide resin–matrix composite at a thickness of 10 mm had several interference peaks, and the absorbing properties increased gradually with increasing frequency. Moreover, the minimum reflectivity was − 21 dB (Decibel) at 13 GHz (Gigahertz). The steel slag powder cement-based composite showed electromagnetic wave-absorbing properties at 10-18 GHz, and the greatest absorption of the 25 mm sample reached 11.5 dB; therefore, the steel slag shows promise as a building material for electromagnetic protection.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Electronic and Magnetic Investigations on Fe{sub 2}NiTe Alloy with High Curie Temperature

Full-potential local-orbital minimum-basis and spin-polarized relativistic Korringa-Kohn-Rostoker along with Monte Carlo simulations are applied to study the electronic and magnetic properties of Fe{sub 2}NiTe with Hg{sub 2}CuTi structure. The analysis of orbital population shows the electrons of 4s, 3d, 4d, and 4p from transition metal and 5s, 5d, and 5p from Te atom participating in bonding. It is demonstrated by the density of states of d-d and p-d hybridizations. Calculations show the magnetic moment is carried mainly by Fe atoms. Accordingly, the exchanges of Fe constituents play a leading role in interactions. By using the calculated Heisenberg exchange coupling parameters, the Curie temperature is estimated to be 761.38 K within mean-field approximation. In order to obtain more accurate value of the Curie temperature, Monte Carlo method is adopted to model the normalized magnetization as functions of the temperature, the obtained 507.93 K value is noticeably higher than the room temperature, which is favorable in realistic spintronics application. Finally, the magnetic moments, exchange interactions, and Curie temperatures in the range of 5.4 to 6.5 Å are calculated; the results implies the Curie temperatures are still above room temperature between given lattice intervals.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

First-principles Study of Strain-Induced Magnetism in Defective Arsenene

By using first-principles calculations, we explore the influences of tensile strain on the magnetic properties of a defective arsenene monolayer with mono-vacancy and di-vacancy. Calculation results show that unstrained defective arsenene monolayers both are intrinsically nonmagnetic. However, appropriate tensile strains can induce a ferromagnetic coupling in mono-vacancy- (8%) and di-vacancy-doped systems (7%), respectively. In addition, we also discussed the physical mechanism of strain-induced magnetism emergence and predicted a possibility of magnetism appearance in the experiment. Our study may provide insight for the design of memory-switching spintronic devices with metal-free magnetism by using arsenene.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS2012

Axisymmetric Flow Properties for Magnetic Elements of Differing Strength

Aspects of the structure and dynamics of the flows in the Sun's surface shear layer remain uncertain and yet are critically important for understanding the observed magnetic behavior. In our previous studies of the axisymmetric transport of magnetic elements we found systematic changes in both the differential rotation and the meridional flow over the course of Solar Cycle 23. Here we examine how those flows depend upon the strength (and presumably anchoring depth) of the magnetic elements. Line of sight magnetograms obtained by the HMI instrument aboard SDO over the course of Carrington Rotation 2097 were mapped to heliographic coordinates and averaged over 12 minutes to remove the 5-min oscillations. Data masks were constructed based on the field strength of each mapped pixel to isolate magnetic elements of differing field strength. We used Local Correlation Tracking of the unmasked data (separated in time by 1- to 8-hours) to determine the longitudinal and latitudinal motions of the magnetic elements. We then calculated average flow velocities as functions of latitude and longitude from the central meridian for approx 600 image pairs over the 27-day rotation. Variations with longitude indicate and characterize systematic errors in the flow measurements associated with changes in the signal from disk center to limb. Removing these systematic errors reveals changes in the axisymmetric flow properties that reflect changes in flow properties with depth in the surface shear layer.

Rightmire-Upton, Lisa↗
DOE OSTI2022

Magnetic structure and spin dynamics of the quasi-two-dimensional antiferromagnet Zn-doped copper pyrovanadate

We report magnetic properties of the antiferromagnet Zn x Cu 2-x V 2 O 7 (ZnCVO) with x ≈ 0.06 have been thoroughly investigated on powder and single-crystal samples. The crystal structure determination using powder x-ray and neutron diffraction confirms that our ZnCVO samples are isostructural with β-Cu 2 V 2 O 7 (β-CVO) with a small deviation in the lattice parameters. Macroscopic magnetic property measurements also confirm the similarity between the two compounds. The Cu 2+ spins were found to align along the crystallographic c axis, antiparallel to their nearest neighbors connected by the leading exchange interaction J 1 . Spin dynamics reveals a typical symmetric spin-wave dispersion with strong interactions in the bc plane and weak interplane coupling. The exchange interaction analysis indicates that the spin network of ZnCVO is topologically consistent with the previous DFT prediction but the values of leading exchange interactions are contradictory. Furthermore, rather than the predicted 2D honeycomb structure, the spin network in ZnCVO could be better described by the anisotropic 2D spin network composed of J 1 , J 5 , and J 6 interactions, four bonds per one spin site, coupled by weak interplane interactions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Ferromagnetism and Carrier Transport in n-type Diluted Magnetic Semiconductors Ge{sub 0.96−x}Bi{sub x}Fe{sub 0.04}Te Thin Film

The structural, Hall effect, electronic transport, and magnetic properties of Ge{sub 0.96−x}Bi{sub x}Fe{sub 0.04}Te epitaxial thin film as prepared by pulsed laser deposition technique were reported. X-ray diffraction patterns including linear scans and phi scans confirmed that all films are high quality epitaxy and crystallinity. With the substitution of high valence Bi for Ge element, we found that the previous carriers of hole were changed to electron, which was testified by the negative slopes obtained from the measurements of Hall effect under different temperatures. The electronic transports show a typical semiconductor behavior and can be understood by the small polaron hopping model because the lattice distortions increase the electron-phonon interaction. An obvious ferromagnetic properties occur in the high Bi-doping Ge{sub 0.64}Bi{sub 0.32}Fe{sub 0.04}Te rather than in that with low Bi-doping concentration, indicating that the ferromagnetic establishment is entirely dependent on carrier’s transmissions. The first-principles calculation performed on this system also reveals that the ferromagnetic state exactly exists in the present n-type diluted magnetic semiconductors with Bi co-dopants.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

The Effects of an Applied Transverse Field in a Graphene-Like Ising Bilayer Film with Nonequivalent Planes

Using the effective field theory with correlations, we have studied the phase diagrams and the thermal variations of total magnetization (m{sub T}) in a graphene-like Ising bilayer film with nonequivalent planes, consisting of two A (spin-1/2) and B (spin-1) planes with an applied transverse field in the B plane. We have investigated the effects of an applied transverse field and the interplane exchange interaction on the magnetic properties. Many interesting behaviors, such as various types of m{sub T} curves and the re-entrant phenomena, have been obtained, depending on the selections of physical parameters.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
NASA NTRS1982

Influence of gravity driven convection on the directional solidification of Bi/MnBi eutectic composites

The role of gravity on Bridgman-Stockharger directional solidification of eutectic Bi/MnBi has been studied in reduced gravity aboard NASA sounding rocket SPAR flight experiments and contrasted with normal gravity investigations. The directional solidification of eutectic Bi/MnBi results in a low volume fraction, faceted/nonfaceted aligned rod eutectic whose MnBi rod size, interrod spacing, thermal and magnetic properties are sensitive functions of solidification processing conditions. The morphology of the low-gravity samples showed striking differences compared with identically processed, normal gravity samples grown in the same apparatus. The MnBi rod diameter and interrod spacing distributions were significantly smaller, approximately 50 percent, for the low gravity samples compared with identically processed one gravity samples. Accompanying the smaller MnBi rod diameters observed in the flight samples, was an increase in permanent magnet properties which reached greater than 97 percent of the theoretical maximum. Gravitationally induced thermal instabilities in one-gravity which result in irregular interface movement and associated difficulty of the faceted MnBi phase to branch are suggested to explain the morphological differences between one and low gravity solidification.

Pirich, R. G.↗
DOE OSTI2022

Anisotropic magnetic and transport properties of orthorhombic o-Pr 2 Co 3 Ge 5

Abstract The crystal structure, electron energy-loss spectroscopy (EELS), heat capacity, and anisotropic magnetic and resistivity measurements are reported for Sn flux grown single crystals of orthorhombic Pr 2 Co 3 Ge 5 (U 2 Co 3 Si 5 -type, Ibam ). Our findings show that o -Pr 2 Co 3 Ge 5 hosts nearly trivalent Pr ions, as evidenced by EELS and fits to temperature dependent magnetic susceptibility measurements. Complex magnetic ordering with a partially spin-polarized state emerges near T sp = 32 K, with a spin reconfiguration transition near T M = 15 K. Heat capacity measurements show that the phase transitions appear as broad peaks in the vicinity of T sp and T M . The magnetic entropy further reveals that crystal electric field splitting lifts the Hund’s rule degeneracy at low temperatures. Taken together, these measurements show that Pr 2 Co 3 Ge 5 is an environment for complex f state magnetism with potential strongly correlated electron states.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Modulating above-room-temperature magnetism in Ga-implanted Fe 5 GeTe 2 van der Waals magnets

The creation of van der Waals (vdW) ferromagnets with tunable Curie temperature (T C ) and magnetic anisotropy is essential in developing vdW magnet-based devices. Here, we report an effective and reliable method for modulating the magnetic properties of vdW Fe 5 GeTe 2 by site-specific Ga + implantation. In this study, we report an easy axis in the ab-plane for bulk Fe 5 GeTe 2 (T C = 310 K) and an axis out of the plane for thin Fe 5 GeTe 2 flakes (T C = 290 K). Combining element-resolved photoemission electron microscopy and spatially resolved magneto-optic Kerr microscopy, we find that the implantation of a tiny amount of 10 –3 Ga + ·Å –3 in Fe 5 GeTe 2 greatly enhances the T C from 290 to 360 K and switches the magnetic easy axis from the out-of-plane c axis to the ab-plane. The room-temperature x-ray magnetic circular dichroism signal is enhanced from 0% to 9% at an implantation level of 10 –2 Ga + ·Å –3 . These results provide new opportunities for tailoring the magnetic properties of vdW materials beyond room temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Single-ion magnetism in the extended solid-state: insights from X-ray absorption and emission spectroscopy

Large single-ion magnetic anisotropy is observed in lithium nitride doped with iron. The iron sites are two-coordinate, putting iron doped lithium nitride amongst a growing number of two coordinate transition metal single-ion magnets (SIMs). Uniquely, the relaxation times to magnetisation reversal are over two orders of magnitude longer in iron doped lithium nitride than other 3d-metal SIMs, and comparable with high-performance lanthanide-based SIMs. To understand the origin of these enhanced magnetic properties a detailed characterisation of electronic structure is presented. Access to dopant electronic structure calls for atomic specific techniques, hence a combination of detailed single-crystal X-ray absorption and emission spectroscopies are applied. Together K-edge, L 2,3 -edge and Kβ X-ray spectroscopies probe local geometry and electronic structure, identifying iron doped lithium nitride to be a prototype, solid-state SIM, clean of stoichiometric vacancies where Fe lattice sites are geometrically equivalent. Extended X-ray absorption fine structure and angular dependent single-crystal X-ray absorption near edge spectroscopy measurements determine Fe I dopant ions to be linearly coordinated, occupying a D 6h symmetry pocket. The dopant engages in strong 3dπ-bonding, resulting in an exceptionally short Fe–N bond length (1.873(7) Å) and rigorous linearity. It is proposed that this structure protects dopant sites from Renner–Teller vibronic coupling and pseudo Jahn–Teller distortions, enhancing magnetic properties with respect to molecular-based linear complexes. The Fe ligand field is quantified by L 2,3 -edge XAS from which the energy reduction of 3d z 2 due to strong 4s mixing is deduced. Quantification of magnetic anisotropy barriers in low concentration dopant sites is inhibited by many established methods, including far-infrared and neutron scattering. We deduce variable temperature L 3 -edge XAS can be applied to quantify the J = 7/2 magnetic anisotropy barrier, 34.80 meV (~280 cm –1 ), that corresponds with Orbach relaxation via the first excited, M J = ±5/2 doublet. The results demonstrate that dopant sites within solid-state host lattices could offer a viable alternative to rare-earth bulk magnets and high-performance SIMs, where the host matrix can be tailored to impose high symmetry and control lattice induced relaxation effects.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

High-temperature 2D ferromagnetism in conjugated microporous porphyrin-type polymers

The need for magnetic 2D materials that are stable to the enviroment and have high Curie temperatures is very important for various electronic and spintronic applications. We have found that two-dimensional porphyrin-type aza-conjugated microporous polymer crystals are such a material (Fe-aza-CMPs). Fe-aza-CMPs are stable to CO, CO 2 , and O 2 atmospheres and show unusual adsorption, electronic, and magnetic properties. Indeed, they are semiconductors with small energy band gaps ranging from 0.27 eV to 0.626 eV. CO, CO 2 , and O 2 molecules can be attached in three different ways where single, double, or triple molecules are bound to iron atoms in Fe-aza-CMPs. For different attachment configurations we find that for CO and CO 2 a uniform distribution of the molecules is most energetically favorable while for O 2 molecules aggregation is most energetically preferable. The magnetic moments decrease from 4 to 2 to 0 for singly, doubly, triply occupied configurations for all gasses respectively. The most interesting magnetic properties are found for O 2 molecules attached to the Fe-aza-CMP. For a single attachment configuration we find that an antiferromagnetic state is favorable. When two O 2 molecules are attached, the calculations show the highest exchange integral with a value of J = 1071 μeV. This value has been verified by two independent methods where in the first method J is calculated by the energy difference between ferromagnetic and anitferromagnetic configurations. The second method is based on the frozen magnon approach where the magnon dispersion curve has been fitted by the Ising model. Finally, for the second method J has been estimated at J = 1100 μeV in excellent agreement with the first method.

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

Room temperature magnetic ordering and analysis by bound magnetic polaron model of Yb3+ doped nanocrystalline zinc oxide (Zn0.98Yb0.02O)

Highlights: • ZnO and Yb doped ZnO are synthesized by co-precipitation method. • Rietvelt anlysis of XRD patterns confirms the complete substitution of Yb{sup 3+} in ZnO. • Vacancy and defect mediated RTFM is introduced in doped ZnO. • BMP model successfully analyze the magnetic property of Zn{sub 0.98}Yb{sub 0.02}O. - Abstract: Nanocrystalline ZnO and Yb-doped ZnO (Zn{sub 0.98}Yb{sub 0.02}O) are prepared by simple co-precipitation method. The pure crystallographic phases of ZnO and Zn{sub 0.98}Yb{sub 0.02}O are confirmed by Rietveld analyses of XRD patterns. Raman and photoluminescence spectra recorded at room temperature (RT) indicates that lattice defects and oxygen vacancy in Zn{sub 0.98}Yb{sub 0.02}O is more than that of ZnO. Magnetic measurements of ZnO and Zn{sub 0.98}Yb{sub 0.02}O are carried out from 300 to 5 K. Ferromagnetic ordering is observed in Zn{sub 0.98}Yb{sub 0.02}O at RT and the strength of the ordering increases with the lowering of temperature. Ferromagnetism of Zn{sub 0.98}Yb{sub 0.02}O is attributed to the oxygen vacancy introduced by annealing in vacuum. Magnetization vs. temperature curve is well fitted by the combination of 3D spin wave and Curie-Weiss law, which suggest simultaneous presence of para- and ferro-magnetic phases in Zn{sub 0.98}Yb{sub 0.02}O. Ferromagnetic ordering is successfully explained by vacancy mediated bound-magnetic polaron model.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Role of Ho Doping in Magnetization Mechanism of BiFeO{sub 3} Thin Films

BiFeO{sub 3} (BFO) as one of the considerable interesting multiferroic materials has been widely investigated for its fantastic science and potential application. Herein, effects of Ho doping on the structure, morphology, and magnetic properties of BFO thin films were systematically studied. X-ray diffraction (XRD) indicates a successful substitution of Ho at Bi site and a transition in crystal structure of Bi{sub 0.9}Ho{sub 0.1}FeO{sub 3} (BHFO) thin film. Raman scattering spectrum is further evidence of XRD analysis results. The Ho-doped BFO thin films possess uniform morphology. X-ray photoelectron spectroscopy (XPS) confirms that the substitution of Bi{sup 3+} ions with Ho{sup 3+} ions is beneficial. The remanent magnetization of BHFO thin films is about three times than that of the BFO thin films under a maximum magnetic field of 15,000 Oe. And we systematically discussed several possible reasons for the enhancement of magnetization.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗