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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 1,333 records · Page 74
All sourcesNASA NTRSDOE OSTI
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 OSTI2017

Mo-Terminated Edge Reconstructions in Nanoporous Molybdenum Disulfide Film

The catalytic and magnetic properties of molybdenum disulfide (MoS 2 ) are significantly enhanced by the presence of edge sites. One method to obtain a high density of edge sites in a two-dimensional (2D) film is by introducing porosity. Yet, the large-scale bottom-up synthesis of a porous 2D MoS 2 film remains challenging and the correlation of growth conditions to the atomic structures of the edges is not well understood. In this work, using molecular beam epitaxy, we prepare wafer-scale nanoporous MoS 2 films under conditions of high Mo flux and study their catalytic and magnetic properties. Atomic-resolution electron microscopy imaging of the pores reveals two new types of reconstructed Mo-terminated edges, namely, a distorted 1T (DT) edge and the Mo-Klein edge. Nanoporous MoS 2 films are magnetic up to 400 K, which is attributed to the presence of Mo-terminated edges with unpaired electrons, as confirmed by density functional theory calculation. The small hydrogen adsorption free energy at these Mo-terminated edges leads to excellent activity for the hydrogen evolution reaction.

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↗
DOE OSTI2018

Causes of the Metamagnetism in a Disordered EuMn{sub 0.5}Co{sub 0.5}O{sub 3} Perovskite

The magnetic properties of the EuMn{sub 0.5}Co{sub 0.5}O{sub 3} perovskite synthesized under various conditions are studied in fields up to 140 kOe. The sample synthesized at T = 1500°C is shown to exhibit a metamagnetic phase transition, which is irreversible below T = 40 K, and the sample synthesized at T = 1200°C demonstrates the field dependence of magnetization that is typical of a ferromagnet. Both samples have T{sub C} = 123 K and approximately the same magnetization in high magnetic fields. The metamagnetism is assumed to be related to a transition from a noncollinear ferromagnetic phase to a collinear phase, and the presence of clusters with ordered Co{sup 2+} and Mn{sup 4+} ions leads to ferromagnetism. The noncollinear phase is formed due to the competition between positive Co{sup 2+}–Mn{sup 4+} and negative Mn{sup 4+}–Mn{sup 4+} and Co{sup 2+}–Co{sup 2+} interactions, which make almost the same contributions, and to the existence of a high magnetic anisotropy.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Spin reorientation in multiferroic spinel Co{sub 0.5}Fe{sub 0.5}Cr{sub 2}O{sub 4} with Mössbauer spectroscopy

We studied the magnetic properties of multiferroic spinel Co{sub 0.5}Fe{sub 0.5}Cr{sub 2}O{sub 4}, especially focusing on the spin-ordering, spin-reorientation, and charge re-distribution effects. From the Rietveld refinement analysis, the crystal structure was identified to be a normal cubic spinel of Fd-3m. Based on the temperature-dependent measurements of the magnetization and magnetic hyperfine field (H{sub hf}), Curie temperature (T{sub C}) of Co{sub 0.5}Fe{sub 0.5}Cr{sub 2}O{sub 4} was determined to be around 86 K where H{sub hf} ≅ 0. From the change of slope in the M-T curve, the conical-spiral magnetic ordering temperature was determined to be 20 K, which coincides with H{sub hf} measurement. Also, we have observed the decrease in the slope of the electric quadrupole splitting (ΔE{sub Q}) curve above 20 K, suggesting that the change in ΔE{sub Q} around T{sub S} is originated from charge redistribution due to the spin-relocation associated with the distortion of each tetrahedral site around Fe{sup 2+} ion above T{sub S}. This indicates that Co{sub 0.5}Fe{sub 0.5}Cr{sub 2}O{sub 4} has the noncollinear conical-spiral spin ordering with incommensurate spin structure below T{sub S}, while above T{sub S}, it has ferrimagnetic spin ordering with commensuration in the collinear state. In addition, the Jahn-teller distortion temperature is measured to be around 155 K, since both ΔE{sub Q} and Δ{sub 1} of {sup 5}T{sub 2g} band decrease rapidly with increasing temperature and disappear around 155 K.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Induce magnetism into silicene by embedding transition-metal atoms

Embedding transition-metal (TM) atoms into nonmagnetic nanomaterials is an efficient way to induce magnetism. Using first-principles calculations, we systematically investigated the structural stability and magnetic properties of TM atoms from Sc to Zn embedded into silicene with single vacancy (SV) and double vacancies (DV). The binding energies for different TM atoms correlate with the TM d-shell electrons. Sc, Ti, and Co show the largest binding energies of as high as 6 eV, while Zn has the lowest binding energy of about 2 eV. The magnetic moment of silicene can be modulated by embedding TM atoms from V to Co, which mainly comes from the 3d orbitals of TM along with partly contributions from the neighboring Si atoms. Fe atom on SV and Mn atom on DV have the largest magnetic moment of more than 3 μB. In addition, we find that doping of N or C atoms on the vacancy site could greatly enhance the magnetism of the systems. Our results provide a promising approach to design silicene-based nanoelectronics and spintronics device.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Synthesis and characterization of Fe{sub 3}O{sub 4}: Porous carbon nanocomposites for biosensor application

Fe{sub 3}O{sub 4}:Porous carbon (Fe{sub 3}O{sub 4}:PC) nano-magnetic composites were prepared by using different weight fractions of acid treated PC by the chemical co-precipitation route and annealed at 573 K, 773 K and 973 K temperatures in inert N{sub 2} gas atmosphere for 2 hrs to obtain desired stoichiometry of nanocomposites. The structural, morphological and magnetic properties of these composites were characterized by powder XRD, TEM, EPR and VSM analytical techniques. The crystallinity of the composites, g-value and spin concentration increases with increasing annealing temperature. TEM images confirmed the formation of nanosized ferrite nanoprticles whose size increases from 23 nm to 54 nm on increasing annealing temperature. Porous carbon increases porosity, coercivity and reduces saturation magnetization of these prepared nanocomposites.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Interplay between crystal and magnetic structures in YFe{sub 2}(H{sub α}D{sub 1−α}){sub 4.2} compounds studied by neutron diffraction

We report a detailed magnetic structure investigation of YFe{sub 2}(H{sub α}D{sub 1−α}){sub 4.2} (α=0, 0.64, 1) compounds presenting a strong (H,D) isotope effect by neutron diffraction and Mössbauer spectroscopy analysis. They crystallize in the same monoclinic structure (Pc space group) with 8 inequivalent Fe sites having different H(D) environment. At low temperature, the compounds are ferromagnetic (FM) and show an easy magnetization axis perpendicular to the b axis and only slightly tilted away from the c axis. Upon heating, they display a first order transition from a ferromagnetic towards an antiferromagnetic (AFM) structure at T{sub M0} which is sensitive to the H/D isotope nature. The AFM cell is described by doubling the crystal cell along the monoclinic b axis. It presents an unusual coexistence of non magnetic Fe layer sandwiched by two thicker ferromagnetic Fe layers which are antiparallel to each other. This FM-AFM transition is driven by the loss of ordered moment on one Fe site (Fe7) through an itinerant electron metamagnetic (IEM) behaviour. The key role of the Fe7 position is assigned to both its hydrogen rich atomic environment and its geometric position. Above T{sub M0} a field induced metamagnetic transition is observed from the AFM towards the FM structure accompanied by a cell volume increase. Both thermal and magnetic field dependence of the magnetic structure are found strongly related to the anisotropic cell distortion induced by (H,D) order in interstitial sites. - Graphical abstract: Representation of the FM-AFM magnetic structures of YFe{sub 2}D{sub 4.2} deuteride. - Highlights: • YFe{sub 2}(H,D){sub 4.2} compounds undergoes a isotope sensitive FM-AFM transition at T{sub M0}. • The FM structure is formed of Fe moments perpendicular to the monoclinic b axis. • AFM structure is formed by antiparallel Fe layers separated by non-magnetic Fe layer. • One Fe site among eight loses its moment at T{sub M0} due to larger Fe–H bonding. • Magnetic properties are driven by the monoclinic distortion induced by D order.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Magnetic studies of nickel ferrite nanoparticles prepared by sol-gel technique

Ni-ferrite nanoparticles were synthesized by sol–gel technique by varying the solvent concentration. X-ray diffraction studies confirmed the phase purity in the samples. The lattice constant and grain size were found to be in the range of 0.833-0.834 nm and 14-26 nm respectively. There was no systematic variation in magnetization value with the solvent concentration and grain size. The highest magnetization, remanence and coercivity values of 60 emu/g, 12 emu/g and 180 Oe respectively were observed at 300K in the present study for the sample prepared in 75ml of solvent. The observed magnetization value is 20% higher than the bulk value of 50 emu/g. The magnetization, coercivity and remanence values were enhanced at 60K compared to those at 300K. The observed high magnetization value in the nanoparticles can be explained on the basis of modified cation distribution in the lattice sites. The enhanced magnetic properties at 60K may be understood due to the reduced thermal fluctuation and increased anisotropy at low temperature.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
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 OSTI2018

Influence of Chromium Doping on Electrical and Magnetic Behavior of Nd{sub 0.5}Sr{sub 0.5}MnO{sub 3} System

With a view to understand the influence of chromium doping at the Mn site on the electrical and magnetic behavior of the Nd{sub 0.5}Sr{sub 0.5}MnO{sub 3} manganite system, a series of samples were prepared by the citrate sol–gel route method. The samples were characterized structurally by XRD. A systematic investigation of electrical resistivity over a temperature range 5–300 K was carried out mainly to understand the magneto-transport behavior in these materials. Studies on the variation of magnetization with temperature over a temperature range 80–330 K were undertaken. Investigation of magnetization at different magnetic fields at two different temperatures, viz. 80 and 300 K, was also carried out. The results show that chromium doping gave typical electrical and magnetic properties. It has been concluded that the coexistence of charge ordered and ferromagnetic phases induced by chromium doping plays an important role in the low-temperature behavior of the system.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Mapping the magnetic and crystal structure in cobalt nanowires

Using off-axis electron holography under Lorentz microscopy conditions to experimentally determine the magnetization distribution in individual cobalt (Co) nanowires, and scanning precession-electron diffraction to obtain their crystalline orientation phase map, allowed us to directly visualize with high accuracy the effect of crystallographic texture on the magnetization of nanowires. The influence of grain boundaries and disorientations on the magnetic structure is correlated on the basis of micromagnetic analysis in order to establish the detailed relationship between magnetic and crystalline structure. This approach demonstrates the applicability of the method employed and provides further understanding on the effect of crystalline structure on magnetic properties at the nanometric scale.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Mössbauer Analysis and Cation Distribution of Zn Substituted BaFe{sub 12}O{sub 19} Hexaferrites

Barium hexaferrite is a well-known hard magnetic material. Doping using nonmagnetic cation such as Zn{sup 2+} were found to enhance magnetization owing to preferential tetrahedral site (4 f{sub 1}) occupancy of the zinc. However, the distribution of cations in hexaferrites depends on many factors such as the method of preparation, nature of the cation, and chemical composition. Here, Zn-doped barium hexaferrites (Ba{sub 1−x}Zn{sub x}Fe{sub 12}O{sub 19}) were synthesized by sol-gel method. In this study, we summarized the magnetic properties of Ba{sub 1−x}Zn{sub x}Fe{sub 12}O{sub 19} (x = 0, 0.1, 0.2, 0.3) BaM, investigated by Mössbauer spectroscopy. Moreover, cation distribution was also calculated for all the products. Mössbauer parameters were determined from 57Fe Mössbauer spectroscopy and according to it, the replacement of Ba-Zn affects all parameters such as isomer shift, the variation in line width, hyperfine magnetic field, and quadrupole splitting. Cation distribution revealed the relative area of undoped BaM, 12k, 2a, and 4 f{sub 2} positions which are close to theoretical values.

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↗
DOE OSTI2016

Thermally stimulated iron oxide transformations and magnetic behaviour of cerium dioxide/iron oxide reactive sorbents

The present paper is devoted to detailed study of the magnetically separable sorbents based on a cerium dioxide/iron oxide composite annealed at temperatures T{sub a} = 773 K, 873 K, and 973 K. The X-ray diffraction and high resolution transmission electron microscopy are used to determine the phase composition and microstructure morphology. Mössbauer spectroscopy at room (300 K) and low (5 K) temperatures has contributed to more exact identification of iron oxides and their transformations Fe{sub 3}O{sub 4} → γ-Fe{sub 2}O{sub 3} (ε-Fe{sub 2}O{sub 3}) → α-Fe{sub 2}O{sub 3} in dependence on calcination temperature. Different iron oxide phase compositions and grain size distributions influence the magnetic characteristics determined from the room- and low-temperature hysteresis loop measurements. The results are supported by zero-field-cooled and field-cooled magnetization measurements allowing a quantitative estimation of the grain size distribution and its effect on the iron oxide transformations. - Highlights: •Magnetically separable sorbents based on a CeO{sub 2}/Fe{sub 2}O{sub 3} composite were investigated. •Microstructure of sorbents was determined by XRD, TEM and Mössbauer spectroscopy. •Magnetic properties were studied by hysteresis loops at room- and low-temperatures. •Phase transitions of iron oxides with increasing annealing temperature are observed.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Magnetic studies of cobalt doped barium hexaferrite nanoparticles prepared by modified sol-gel method

M-type barium hexaferrite (BaFe{sub 12}O{sub 19}) and cobalt doped barium hexaferrite (BaFe{sub 11}CoO{sub 19}) nanopowders were synthesized by modified sol-gel auto-combustion technique and were annealed at 900°C in air for 4 hours. The annealed powders were studied in the present work and X-ray diffraction studies showed pure phase formation after annealing. The average grain size in the nanopowder sample was decreased after doping. Magnetization value of 60 emu/g was observed at 300 K for the barium hexaferrite and was reduced to 54 emu/g after doping. The coercivity of 5586 Oe was observed at 300 K for the undoped sample and was found to be decreased in the doped sample. As the measurement temperature was decreased from 300 K to 60 K, magnetization value was increased in both the samples compared to those at 300 K. The coercivity of the undoped sample was found to decrease whereas it was increased for the doped sample at 60 K. The observed magnetic properties may be understood on the basis of modified exchange interaction and anisotropy in the doped sample compared to that of pure barium hexaferrite.

77 NANOSCIENCE AND NANOTECHNOLOGY↗