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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 901 records · Page 50
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Property and microstructural nonuniformity in the yttrium-barium-copper-oxide superconductor determined from electrical, magnetic, and ultrasonic measurements

The purpose of this dissertation was the following: (1) to characterize the effect of pore fraction on a comprehensive set of electrical and magnetic properties for the yttrium-barium-copper-oxide (YBCO) high temperature ceramic superconductor; and (2) to determine the viability of using a room-temperature, nondestructive characterization method to aid in the prediction of superconducting (cryogenic) properties. The latter involved correlating ultrasonic velocity measurements at room temperature with property-affecting pore fraction and oxygen content variations. The use of ultrasonic velocity for estimating pore fraction in YBCO is presented, and other polycrystalline materials are reviewed, modeled, and statistically analyzed. This provides the basis for using ultrasonic velocity to interrogate microstructure. The effect of pore fraction (0.10-0.25) on superconductor properties of YBCO samples was characterized. Spatial (within-sample) variations in microstructure and superconductor properties were investigated, and the effect of oxygen content on elastic behavior was examined. Experimental methods used included a.c. susceptibility, electrical, and ultrasonic velocity measurements. Superconductor properties measured included transition temperature, magnetic transition width, transport and magnetic critical current density, magnetic shielding, a.c. loss, and sharpness of the voltage-current characteristics. An ultrasonic velocity image constructed from measurements at 1mm increments across a YBCO sample revealed microstructural variations that correlated with variations in magnetic shielding and a.c. loss behavior. Destructive examination using quantitative image analysis revealed pore fraction to be the varying microstructural feature.

Roth, Don J.↗
DOE OSTI2020

Magnetic oxygen in transition metal oxides: A case study of Ba 2 CoO 4

Transition metal oxides (TMOs) exhibit exotic magnetic properties in both naturally formed and artificially structured materials, often difficult to understand in conventional wisdom. Magnetic insulator Ba 2 CoO 4 has mystified the community, because the CoO 4 tetrahedron is completely isolated with the nearest Co atoms far apart (~5 Å), making it impossible to account for long-range magnetic ordering seen experimentally using only Co. By theoretically investigating magnetism and relating our findings to experimental observations in bulk Ba 2 CoO 4 , we illustrate for the first time that the magnetic moment on oxygen atoms are the origin of the unexpected long-range magnetic ordering and low magnetic dimensionality. We find that the magnetic moment is not only localized on Co atoms, as assumed in all conventional data analysis, but also distributed on its tetrahedrally-coordinated O atoms. The total magnetic moment of the CoO 4 building block is 4.63μ B with the magnetic moment on Co being only 3.08μ B . Therefore, the magnetic building block is CoO 4 not Co. Furthermore, our first principles calculations are capable of explaining the origin of the unique magnetic response, including the presence of long-range magnetic ordering with two-dimensional character, and a one-dimensional magnetoelastic behavior. Having oxygen contribute to the magnetic moment will undoubtedly be identified as a universal property of magnetic TMOs, which will require a fresh look at conventional models of magnetism in TMOs.

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

Multifunctional Prussian blue analogue magnets: Emerging opportunities

There is a surge of interest to expand the search for entirely new classes of molecular magnets as the emergence of information storage and quantum computing devices. Prussian blue analogues as a family of molecular magnets are especially attracting wide attention due to their large number of derivatives with a range of magnetic ordering temperature from cryogenic to high temperature. Furthermore, this review presents Prussian blue analogues as multifunctional molecular magnets, which involves the development of molecular magnet syntheses and crystal structures, and magnetic properties under external stimuli. In addition, the porous network structures and vacancy order of Prussian blue analogues present a wide capability to interact with water molecules and gas adsorption. External stimuli, such as thermal, pressure, electric and magnetic field and photoexcitation, play an important role in controlling the hidden states and cooperative phenomena of high temperature molecular magnets based on Prussian blue analogues.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effects of Fe and Co Co-doping on Structural, Magnetic, and Optical Properties of Ti{sub 0.9}Fe{sub 0.1−x}Co{sub x}O{sub 2} Magnetic Semiconductors

A series of six samples with a general formula Ti{sub 0.9}Fe{sub 0.1−x}Co{sub x}O{sub 2} (x = 0.0, 0.02, 0.04, 0.06, 0.08, and 0.1) has been synthesized by solid-state reaction method at annealing temperature of 1150 {sup ∘}C for 2 hours. The synthesized samples have been characterized by X-ray diffractometer, Raman spectroscopy, scanning electron microscopy, EDX, vibrating sample magnetometer, and ultraviolet-visible spectroscopy to investigate structural, defective, morphological, elemental, magnetic, and optical properties. Structural analysis revealed dominant structure of rutile with a minor peak of hematite and anatase. An intensity loss and peak broadening of TiO{sub 2} (rutile) vibration lines has been observed from Raman analysis. Magnetic characterization showed ferromagnetic behavior at room temperature. Optical characterization revealed blue shift in band gap energy with increasing amount of Co concentration.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Magnetic and Electrical Properties of Hg{sub 1–x–}Mn{sub x}Fe{sub y}Te{sub 1–z}S{sub z} Crystals

Electrical and magnetic properties of the semimagnetic semiconductor Hg{sub 1–x–y}Mn{sub x}Fe{sub y}Te{sub 1–z}S{sub z} solid solutions were studied in the ranges of temperatures 77–320 K and magnetic fields 0.25–6 kOe. In the crystals under study, the effect of giant magnetoresistance was observed that reached 75% at low temperatures. This is due to the fact that charge carriers that participate in the current transfer interact with a magnetized ferromagnetic cluster subsystem (Fe–Fe–Fe) and become spin-polarized. It is these spin-polarized charge carriers that are strongly scattered on antiferromagnetic Mn–S–Mn–S and Mn–Te–Mn–Te clusters, since the magnetic moments inside the clusters and the resulting magnetic moments of these clusters are randomly oriented.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Temperature-dependent Structural and Spectroscopic Studies of (Bi 1– x Fe x )FeO 3

We report on temperature-dependent structural and spectroscopic features of (Bi 1–x Fe x )FeO 3 perovskite for x = 0.15 and 0.25. Samples were synthesized by heating quantum crystalline precursors obtained by the polyol method. Crystal structures of each composition were obtained from in-house X-ray, synchrotron X-ray, and time-of-flight neutron powder diffraction data Rietveld refinements. Partial replacement of the Bi site by the Fe 3+ cation significantly changes the crystal physicochemical properties, such as thermal expansion, polyhedral distortion, Debye temperature, and vibrational and magnetic properties. Whereas BiFeO 3 is multiferroic, both Bi 0.85 Fe 0.15 FeO 3 and Bi 0.75 Fe 0.25 FeO 3 are found to be superparamagnetic, as observed by temperature-dependent Mössbauer and SQUID measurements. Lattice thermal expansion was modeled using the Debye–Einstein-anharmonicity approach. Debye temperatures obtained from the mean-squared atomic displacement parameter and lattice thermal expansion are compared. Furthermore, temperature dependence of selective Raman modes is also analyzed.

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

A Comparative Study of Physical Properties of Er and Yb Nanophase Ferrite for Industrial Application

Nano ferrites CuCr{sub 0.3}Er{sub 0.03}Fe{sub 1.67}O{sub 4} and CuCr{sub 0.3}Yb{sub 0.03}Fe{sub 1.67}O{sub 4} were synthesized using standard ceramic technique. X-ray diffraction (XRD) patterns confirmed that the samples had cubic spinel structures. The average crystallite sizes of Er and Yb samples were in the range of 104.2–100 nm. The morphology analyses using field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM) and atomic force microscopy (AFM) confirmed that the samples were in the nanoscale range. The compositional analyses using energy-dispersive x-ray (EDX) showed the atomic percentage (at.%) and weight percentage (wt%) of the investigated samples. The magnetic properties were carried out at room (300 K) and at low (100 K) temperatures magnetic hysteresis loop. The data showed that Er sample had higher saturation magnetization (M{sub s}) and lower coercivity (H{sub c}) than that of Yb sample suggesting that Er sample can be applied in magnetic applications. Moreover, Er sample had higher dielectric constant (ε’), dielectric loss (ε”) and dielectric loss tangent (tan δ) than that of Yb sample. However, Yb sample had higher resistivity than that of Er sample suggesting that Yb sample can be applied in electrical applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Fe(III) and Cu(II) coordination polymers assembled from di/tris-phosphonic acid and auxiliary ligands: Structure, SOD-like activity and magnetic behavior

Hydrothermal reactions of (benzylazanediyl)bis(methylene)-diphosphonic acid (H{sub 4}L{sup 1}) or (benzene-1,3,5-triyltris(methylene))triphosphonic acid (H{sub 6}L{sup 2}) with Fe(III)/Cu(II) nitrate and 4, 4′-bipy or 2, 2′-bipy result in five new phosphonates, namely, [FeHL{sup 1}(H{sub 2}O)]{sub n} (1), {[Cu_2L"1(4, 4′-bipy)_0_._5(H_2O)]·0.25H_2O}{sub n} (2), [Cu{sub 2}H{sub 2}L{sup 2}(4, 4′-bipy)(H{sub 2}O){sub 2}]{sub n} (3), [CuH{sub 4}L{sup 2}(2, 2′-bipy)]{sub n} (4) and [Cu{sub 2}(H{sub 4}L{sup 2}){sub 2}(2, 2′-bipy){sub 2}(H{sub 2}O){sub 4}] (5), respectively. X-ray structural analysis indicates that 2 and 3 feature 3D framework structures with 3, 3, 3, 4-connected and 4, 5-connected topology; 1 and 4 display 1D chain structures, while 5 has a dimer structure. The di- or trisphosphonate ligands (H{sub 4}L{sup 1} and H{sub 6}L{sup 2}) in the five complexes adopt different coordination modes and auxiliary ligands (4, 4′-bipy and 2, 2′-bipy) control the dimensionality of the final complexes. The superoxide dismutase (SOD) activities of 2–5 were assessed by modified nitrobluetetrazolium (NBT) assay. The IC{sub 50} values required to yield 50% inhibition of the reduction of NBT are 1.84, 2.02, 6.95 and 1.70 μM for 2–5, respectively, demonstrating better SOD-like activity than most of the Cu-SOD mimic enzymes reported in literatures. Among them, 2 and 3 have good stability and reusability under the simulative physiological conditions. The dismutation of 4 and 5 toward superoxide anion radicals can be attributed to the synergistic effect of the decomposition products of 4 and 5 containing Cu(II) and [H{sub 4}L{sup 2}]{sup 2-} with or without 2, 2′-bipy or Cu(II) and 2, 2′-bipy, which were identified by liquid mass spectrometry (LC/MS). The magnetic properties of complexes 1–4 were also investigated, indicating the presence of magnetic exchange between metal ions. The results show that 1 and 3 exhibit antiferromagnetic interactions, while 2 and 4 show ferromagnetic interactions between metal centres.

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

Non-heme High-Spin {FeNO} 6–8 Complexes: One Ligand Platform Can Do It All

Heme and non-heme iron-nitrosyl complexes are important intermediates in biology. While there are numerous examples of low-spin heme iron-nitrosyl complexes in different oxidation states, much less is known about high-spin (hs) non-heme iron-nitrosyls in oxidation states other than the formally ferrous NO adducts ({FeNO} 7 in the Enemark-Feltham notation). In this study, we present a complete series of hs-{Fe-NO} 6-8 complexes using the TMG 3 tren coligand. Redox transformations from the hs-{FeNO} 7 complex [Fe(TMG 3 tren)(NO)] 2+ to its {FeNO} 6 and {FeNO} 8 analogs do not alter the coordination environment of the iron center, allowing for detailed comparisons between these species. Here, we present new MCD, NRVS, XANES/EXAFS and Mössbauer data, demonstrating that these redox transformations are metal based, which allows us to access hs-Fe(II)-NO¯, Fe(III)-NO¯ and Fe(IV)-NO¯ complexes. Vibrational data, analyzed by NCA, directly quantify changes in Fe-NO bonding along this series. Optical data allow for the identification of a “spectator” charge-transfer transition that, together with Mössbauer and XAS data, directly monitors electronic changes of the Fe center. Using EXAFS, we are also now able to provide structural data for all complexes. The magnetic properties of the complexes are further analyzed (from magnetic Mössbauer). The properties of our hs-{FeNO} 6-8 complexes are then contrasted to corresponding, low-spin iron-nitrosyl complexes, where redox transformations are generally NO-centered. The hs-{FeNO} 8 complex can further be protonated by weak acids, and the product of this reaction is characterized. Altogether, these results provide unprecedented insight into the properties of biologically relevant non-heme iron-nitrosyl complexes in three relevant oxidation states.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Structural and Hysteretic Properties of La{sub 0.7}Ca{sub 0.3−x}Sr{sub x}MnO{sub 3} Manganites Using the Hydrothermal Route

Manganitesof La{sub 0.7}Ca{sub 0.3−x}Sr{sub x}MnO{sub 3} have been produced using the hydrothermal method. The influence of the concentration of La, Ca, and Sr on the structural, morphological, and magnetic properties was studied and analyzed. The x-ray diffraction studies showed the occurrence of orthorombic and trigonal symmetries in the crystalline structure, depending on the stoichiometry. X-ray photoelectron spectroscopy studies were performed, showing the presence of the elements La3d, Ca2p, Sr3d, Mn2p, and O1s. In all samples, a deficiency of oxygen was observed and ascribed to hydroxide formation. The FTIR spectra shows the Mn–O–Mn bonds in the stretching vibration mode; on the other hand, a great relative amount of Mn{sup 4+} ions that are not included in the manganite phase was observed. Furthermore, morphology analyses developed using scanning electron microscopy showed cauliflower-type microstructures in all samples. The dependence of magnetization on magnetic field was also studied where a low coercivity and a high-saturation magnetization were evidenced. Values of the squareness ratio coefficient ranged between 0.0587 and 0.0867, indicating that the individual particles exhibit a strong random anisotropy.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Effect of Nd Substitution on Properties of Multiferroic Bismuth Ferrite Synthesized by Sol-Gel Auto-combustion Method

In this work, pure and Nd-doped bismuth ferrite nanocrystals with the general formula of Bi{sub 1−x}Nd{sub x}FeO{sub 3} (x = 0, 0.05, 0.1, 0.15, 0.2) were synthesized via the sol-gel auto-combustion method at two different calcination temperatures (550 and 650{sup ∘}C). Phase analysis and investigating structural, thermal, and magnetic properties and measuring the size of nanoparticles have been done by using X-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric and differential thermal analysis (TG/DTA), and vibrating sample magnetometry (VSM). For undoped BiFeO{sub 3} (BFO), increasing calcination temperature will increase the average size of nanocrystals. On the other hand, the average size of nanoparticles is decreased by increasing the concentration of neodymium in the structure of BFO. By entering neodymium to the structure of bismuth ferrite at the calcination temperature of 550{sup ∘}C, the ferromagnetic properties decline. However, at 650{sup ∘}C, ferromagnetic properties are improved which is due to a fall in the number of Fe{sup 2+} ions. In this case, by decreasing the Fe{sup 2+} ions, remanent and saturation magnetization increase.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Spin Glass Behavior and Giant Magnetoresistance via Aliovalent Fe/Ni Alloying in Amorphous Tetrathiafulvalene-Tetrathiolate Coordination Polymers

The discovery of materials with programmable combinations of charge transport and magnetic properties is a major goal in synthetic chemistry. Molecular materials, such as coordination polymers (CPs), are emerging candidates in this field due to their synthetic modularity. While there are many conductive or magnetic CPs, single-component examples with both properties are still emerging. Here, in this work, we demonstrate how alloying paramagnetic Fe(III) centers into a highly conductive Ni-based CP results in novel amorphous materials with high conductivity and giant magnetoresistance. Aliovalent doping with paramagnetic Fe centers engenders spin-glass transitions, while Ni and the strong π-stacking interactions of tetrathiafulvalene-2,3,6,7-tetrathiolate (TTFtt) ligands support conductivity. Ni 0.69 Fe 0.31 TTFtt has σ ≈ 200 S/cm and a 1.8 K magnetoresistance of −52% at 5 T, among the largest for any coordination solid. This work demonstrates not only how magnetic properties can be rationally incorporated into conductive CPs, but also an unexpected potential for amorphous materials in spintronic applications.

amorphous materials↗
DOE OSTI2023

The role of electron correlations in the electronic structure of putative Chern magnet TbMn6Sn6

Abstract A member of the RMn 6 Sn 6 rare-earth family materials, TbMn 6 Sn 6 , recently showed experimental signatures of the realization of a quantum-limit Chern magnet. In this work, we use quantum Monte Carlo (QMC) and density functional theory with Hubbard U (DFT + U ) calculations to examine the electronic structure of TbMn 6 Sn 6 . To do so, we optimize accurate, correlation-consistent pseudopotentials for Tb and Sn using coupled-cluster and configuration–interaction (CI) methods. We find that DFT + U and single-reference QMC calculations suffer from the same overestimation of the magnetic moments as meta-GGA and hybrid density functional approximations. Our findings point to the need for improved orbitals/wavefunctions for this class of materials, such as natural orbitals from CI, or for the inclusion of multi-reference effects that capture the static correlations for an accurate prediction of magnetic properties. DFT + U with Mn magnetic moments adjusted to the experiment predict the Dirac crossing in bulk to be close to the Fermi level, within ~120 meV, in agreement with the experiments. Our non-stoichiometric slab calculations show that the Dirac crossing approaches even closer to the Fermi level, suggesting the possible realization of Chern magnetism in this limit.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Magnetic and structural properties of Mn X NiSn ( X = Mn, Fe, Co)

Crystal structure and magnetic properties of Heusler alloys MnXNiSn (X = Mn, Fe, Co) are investigated using density functional theory and compared with experimental results. The parent alloy Mn 2 NiSn, which crystallizes in the inverse Heusler structure, is found to be ferrimagnetic, in agreement with previous experimental and theoretical work. The Fe and Co substitutions cause the alloys to assume a fairly well-ordered Y structure and enhance the magnetization substantially. We find that the strong nearest neighbour Mn-X exchange changes from antiferromagnetic (X = Mn) to ferromagnetic (X = Fe, Co), which explains and actually overestimates the experimental changes. A striking feature of the system is that Fe and Co have opposite effects on the Curie temperature T c : they reduce and enhance T c , respectively. We qualitatively explain this behaviour in terms of two-sublattice model based on the nearest-neighbour exchange.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Perspective: Ferromagnetic Liquids

Mechanical jamming of nanoparticles at liquid–liquid interfaces has evolved into a versatile approach to structure liquids with solid-state properties. Ferromagnetic liquids obtain their physical and magnetic properties, including a remanent magnetization that distinguishes them from ferrofluids, from the jamming of magnetic nanoparticles assembled at the interface between two distinct liquids to minimize surface tension. This perspective provides an overview of recent progress and discusses future directions, challenges and potential applications of jamming magnetic nanoparticles with regard to 3D nano-magnetism. We address the formation and characterization of curved magnetic geometries, and spin frustration between dipole-coupled nanostructures, and advance our understanding of particle jamming at liquid–liquid interfaces.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Local Magnetic Fields in Diamagnetic BiSbO{sub 4} and Bi{sub 4}Si{sub 3}O{sub 12}: {sup 209}Bi NQR

Local magnetic fields H{sub loc} exceeding significantly the magnetic fields produced by nuclear magnetic moments (a few gauss) have been detected in bismuth compounds with valence s and p electrons, which are generally believed to be diamagnetic, by the methods based on measuring the parameters of nuclear quadrupole interactions. Anomalies in the magnetic properties of BiSbO{sub 4} and Bi{sub 4}Si{sub 3}O{sub 12} were clearly manifested when analyzing the line shapes in their {sup 209}Bi NQR spectra. The quartet of lines for the lower transition ν{sub 1} (Δm = 1/2–3/2) in the spectrum of Bi{sub 4}Si{sub 3}O{sub 12} in zero external magnetic field and the doublets for the lines of all other transitions in the spectrum of BiSbO{sub 4} at unique crystallographic positions of bismuth atoms in the crystal lattices of the compounds suggest a magnetic nature of the splittings. The most probable values of H{sub loc} in these compounds are those in the range from 40 to 100 G.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Competing incommensurate spin fluctuations and magnetic excitations in infinite-layer nickelate superconductors

The recently discovered infinite-layer nickelates show great promise in helping to disentangle the various cooperative mechanisms responsible for high-temperature superconductivity. However, lack of antiferromagnetic order in the pristine nickelates presents a challenge for connecting the physics of the cuprates and nickelates. Here, by using a quantum many-body Green’s function-based approach to treat the electronic and magnetic structures, we unveil the presence of many two- and three-dimensional magnetic stripe instabilities that are shown to persist across the phase diagram of LaNiO 2 . Our analysis indicates that the magnetic properties of the infinite-layer nickelates are closer to those of the doped cuprates, which host a stripe ground state, rather than the undoped cuprates. The computed longitudinal-spin, transverse-spin, and charge spectra of LaNiO 2 are found to contain an admixture of contributions from localized and itinerant carriers. Theoretically obtained dispersion of magnetic excitations (spin-flip) is found to be in good accord with the results of recent resonant inelastic X-ray scattering experiments. Our study gives insight into the origin of strong magnetic competition in the infinite-layer nickelates and their relationship with the cuprates.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Superparamagnetic Properties and Significant Applications of Iron Oxide Nanoparticles for Astonishing Efficacy—a Review

This paper reviewed the comprehensive literature survey on the physical, chemical, and the catalytic properties and applications of iron oxide nanoparticles. In recent years, iron oxide has made a versatile progress due to its outstanding magnetic property. The average crystallite size was reported in previous literatures in the range of 10–45 nm using Scherrer’s formula. The powder morphology was found to deliberate quasi-spherical and predominantly spherical shape. The specific surface area as measured by N{sub 2} adsorption BET isotherm was reported in the range of 17.6–26.21 m{sup 2}/g. Depending on the synthesis pathway there was, an inverse or normal spinel structure could be achieved. X-ray diffraction analysis revealed the crystallite size in the range between 8 and 42 nm. Fourier transform infrared spectroscopy reported the changes in functional group, stretching vibrations in the iron oxide nanoparticles. Scanning electron microscopy analysis showed most of Fe{sub 3}O{sub 4} nanoparticles were in spherical morphology with the particle size range between 10 and 26 nm. Vibrating sample magnetometer reported the magnetization value for Fe{sub 3}O{sub 4} nanoparticles.

77 NANOSCIENCE AND NANOTECHNOLOGY↗