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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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Effect of Preparation Conditions on the Structure and Magnetic Properties of Metal-Doped Magnesium Ferrites Synthesized From Laterite Leaching Solutions

In this paper, metal-doped magnesium ferrites (MgFe{sub 2}O{sub 4}) were synthesized from laterite leaching solutions using a coprecipitation-calcination method. The as-synthesized samples were characterized by x-ray diffraction (XRD), Fourier transform infrared spectrometer (FTIR), and physical property measurement system (PPMS) to determine the structure and magnetic properties. The effects of preparation conditions including precipitant reagents and metal ion concentrations in the laterite leaching solutions on the as-prepared spinel ferrites were investigated systematically. It is indicated that Ni–Co–Mn-doped MgFe{sub 2}O{sub 4} and Mn–Al–Cr-doped MgFe{sub 2}O{sub 4} could be synthesized from laterite leaching solutions by using sodium hydroxide (NaOH) and ammonia solution (NH{sub 3}⋅H{sub 2}O) as precipitant reagent, respectively. By adjusting the metal ion concentrations in the laterite leaching solutions, Ni–Co–Mn-doped MgFe{sub 2}O{sub 4} with different substitution contents were obtained. With the Ni and Mn substitution content increasing, the lattice constant and average grain size decreased, while x-ray density increased correspondingly. Magnetic property tests indicated that all the as-prepared samples exhibited typical ferrimagnetic behavior at room temperature, and the saturation magnetization (Ms) depended on the Ni, Co, and Mn substitution content. Specifically, the Ms and Hc values of the as-prepared metal-doped MgFe{sub 2}O{sub 4} sample with optimum substitution content of 0.185 could reach 33.22 emu g{sup −1} and 53 Oe, respectively.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Microstructural evolutions, phase transformations and hard magnetic properties in polycrystalline Ce–Co–Fe–Cu alloys

This work focuses on systematic studies of Ce–Co based 1:5 permanent magnet alloys of CeCo 4.4-x Fe x Cu 0.6 and CeCo 3.9-x Fe x Cu 1.2 (x = 0, 0.3, 0.6, 0.9, 1.2, 1.8) by varying Co:Fe. The overarching aim of this manuscript is to elucidate the hard-magnetic properties through a better understanding of phase formation by the structural, microstructural, and magnetic properties in these materials. Improved mutual solubility of Fe in the 1:5 phase has been observed with an extended homogeneity range by Cu substitution. For both composition series, Fe contents of x ≤ 0.6 show a homogeneous microstructure with a single 1:5 phase and good magnetic properties. The composition region 0.6 < x ≤ 0.9 appears to be near the boundary of solubility and evolution of other phases. At x = 1.8, it is found that the homogeneous 1:5 phase and magnetic hardness deteriorated due to the evolution of secondary phases such as 2:17, 2:7, and Fe–Co. Furthermore, the addition of Fe improved both the magnetization and Curie temperature via increased effective exchange interactions, while an increase in Cu content enhanced coercivity.

33 ADVANCED PROPULSION SYSTEMS↗
DOE OSTI2018

Quantum Magnetic Properties in Perovskite with Anderson Localized Artificial Spin‐1/2

Abstract Quantum magnetic properties in a geometrically frustrated lattice of spin‐1/2 magnet, such as quantum spin liquid or solid and the associated spin fractionalization, are considered key in developing a new phase of matter. The feasibility of observing the quantum magnetic properties, usually found in geometrically frustrated lattice of spin‐1/2 magnet, in a perovskite material with controlled disorder is demonstrated. It is found that the controlled chemical disorder, due to the chemical substitution of Ru ions by Co‐ions, in a simple perovskite CaRuO 3 creates a random prototype configuration of artificial spin‐1/2 that forms dimer pairs between the nearest and further away ions. The localization of the Co impurity in the Ru matrix is analyzed using the Anderson localization formulation. The dimers of artificial spin‐1/2, due to the localization of Co impurities, exhibit singlet‐to‐triplet excitation at low temperature without any ordered spin correlation. The localized gapped excitation evolves into a gapless quasi‐continuum as dimer pairs break and create freely fluctuating fractionalized spins at high temperature. Together, these properties hint at a new quantum magnetic state with strong resemblance to the resonance valence bond system.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2015

Magnetic properties of the spin-3/2 Blume-Capel model on a hexagonal Ising nanowire

Magnetic properties, such as magnetizations, internal energy, specific heat, entropy, Helmholtz free energy, and phase diagrams of the spin-3/2 Blume-Capel model on a hexagonal Ising nanowire with core-shell structure are studied by using the effective-field theory with correlations. The hysteresis behaviors of the system are also investigated and the effects of Hamiltonian parameters on hysteresis behaviors are discussed in detail. The obtained results are compared with some theoretical results and a qualitatively good agreement is found.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Tuning the Magnetic Properties and Structural Stabilities of the 2-17-3 Magnets Sm 2 Fe 17 X 3 (X=C, N) by Substituting La or Ce for Sm

Designing a permanent magnet with reduced critical rare-earth content is of paramount importance in the development of cost-effective modern technologies. By performing comprehensive first-principles calculations, we investigate the potential avenues for reducing the critical rare-earth content in Sm 2 Fe 17 N 3 and Sm 2 Fe 17 C 3 by making a La or Ce substitution for Sm. The calculated magnetic properties of base compounds are in good agreement with the previous low-temperature (4.2-K) experimental measurements, and they show a large axial anisotropy. Although La or Ce substitution results in a slight reduction of magnetic anisotropy, the magnetic moments of Fe atoms mostly remain unchanged. Specifically, large axial anisotropies of 7.2 and 4.1 MJ/m 3 are obtained for SmCeFe 17 N 3 and SmLaFe 17 N 3 , respectively. These values of anisotropies are comparable to the state-of-the-art permanent magnet Nd 2 Fe 14 B. The foremost limitation of Sm 2 Fe 17 X 3 magnets for practical application is the formation nitrogen or carbon vacancies at high temperatures. By calculating the N- (C)- vacancy formation energy, we show that La or Ce substitution enhances the vacancy formation energy. Here, this enhanced vacancy formation energy will likely improve the thermodynamic stability of these alloys at high temperatures. Therefore, La- or Ce-substituted Sm 2 Fe 17 C 3 and Sm 2 Fe 17 N 3 compounds are promising candidates for high-performance permanent magnets with substantially reduced rare-earth content.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Size effects in the magnetic properties of ε-Fe{sub 2}O{sub 3} nanoparticles

We report the results of comparative analysis of magnetic properties of the systems based on ε-Fe{sub 2}O{sub 3}, nanoparticles with different average sizes (from ∼3 to 9 nm) and dispersions. The experimental data for nanoparticles higher than 6–8 nm in size are consistent with the available data, specifically, the transition to the magnetically ordered state occurs at a temperature of ∼500 K and the anomalies of magnetic properties observed in the range of 80–150 K correspond to the magnetic transition. At the same time, Mőssbauer and ferromagnetic resonance spectroscopy data as well as the results of static magnetic measurements show that at room temperature all the investigated samples contain ε-Fe{sub 2}O{sub 3} particles that exhibit the superparamagnetic behavior. It was established that the magnetic properties of nanoparticles significantly change with a decrease in their size to ∼6 nm. According to high-resolution electron microscopy and Mőssbauer spectroscopy data, the particle structure can be attributed to the ε–modification of trivalent iron oxide; meanwhile, the temperature of the magnetic order onset in these particles is increased, the well-known magnetic transition in the range of 80–150 K does not occur, the crystallographic magnetic anisotropy constant is significantly reduced, and the surface magnetic anisotropy plays a decisive role. This is apparently due to redistribution of cations over crystallographic positions with decreasing particle size, which was established using Mössbauer spectra. As the particle size is decreased and the fraction of surface atoms is increased, the contribution of an additional magnetic subsystem formed in a shell of particles smaller than ∼4 nm becomes significant, which manifests itself in the static magnetic measurements as paramagnetic contribution.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

First principles calculation of the structural, electronic, and magnetic properties of Au-Pd atomic chains

The structural, electronic and magnetic properties of free standing Au-Pd bimetallic atomic chain is studied using ab-initio method. It is found that electronic and magnetic properties of chains depend on position of atoms and number of atoms. Spin polarization factor for different atomic configuration of atomic chain is calculated predicting a half metallic behavior. It suggests a total spin polarised transport in these chains.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Ab Initio Study of Structural, Electronic, and Magnetic Properties of A{sub 1−x}{sup III}Mn{sub x}B{sup VI}: In{sub 1−x}Mn{sub x}S-Diluted Magnetic Semiconductor

First-principles density functional calculations on the new class of diluted magnetic semiconductor A{sub 1−x}{sup III}Mn{sub x}B{sup VI} In{sub 1−x}Mn{sub x}S for x = 0.25 and 0.5 are investigated to study the structural, electronic, and magnetic properties, employing the full-potential linearized augmented plane wave method. Electronic band structures and density of states revealed a half-metallic character of In{sub 1−x}Mn{sub x}S and show the stability of anti-ferromagnetic states as compared with ferromagnetic states. The calculated exchange constants J{sub dd} are in good agreement with experimental and theoretical results on magnetic properties of single crystalline A{sub 1−x}{sup III}Mn{sub x}B{sup VI} in the anti-ferromagnetic case. Our predicated calculations on the s,p-d exchange constants N{sub 0}α and N{sub 0}β show that they are lower than in A{sub 1−x}{sup II}Mn{sub x}B{sup VI} DMS. The local environment is found tetrahedral as in the II–VI DMS and other (III,Mn) VI compounds. The total magnetic moment for In{sub 1−x}Mn{sub x}S for different concentrations is in accordance with the exact value 5 μ{sub B} and comes mainly from impurity Mn. The local magnetic moments of Mn ions are reduced from their free space charges values due to the p-d hybridization which produces small magnetic moments on the nonmagnetic In and S sites. The Curie temperature of In{sub 1−x}Mn{sub x}S is calculated within the mean field approximation and compared with other DMS systems.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Effect of gamma irradiation on the structural and magnetic properties of Co–Zn spinel ferrite nanoparticles

Highlights: • Co–Zn ferrite nanoparticles were examined before and after γ-irradiation. • Single phase cubic spinel structure of Co–Zn was confirmed by XRD data. • The grain size was reported in the range of 52–62 nm after γ-irradiation. • Ms, Hc, n{sub B} were reported to be increased after gamma irradiation. - Abstract: In this work, the structural and magnetic properties of Co{sub 1−x}Zn{sub x}Fe{sub 2}O{sub 4} (0.0 ≤ x ≤ 1.0) ferrite nanoparticles were studied before and after gamma irradiation. The as-synthesized samples of Co–Zn ferrite nanoparticles prepared by sol–gel auto-combustion technique were analysed by XRD which suggested the single phase; cubic spinel structure of the material. Crystal defects produced in the spinel lattice were studied before and after Co{sup 60} γ-irradiation in a gamma cell with a dose rate of 0.1 Mrad/h in order to report the changes in structural and magnetic properties of the Co–Zn ferrite nanoparticles. The average crystallite size (t), lattice parameter (α) and other structural parameters of gamma-irradiated and un-irradiated Co{sub 1−x}Zn{sub x}Fe{sub 2}O{sub 4} spinel ferrite system was calculated from XRD data. The morphological characterizations were performed using scanning electron microscopy (SEM). The magnetic properties were measured using pulse field hysteresis loop tracer by applying magnetic field of 1000 Oe, and the analysis of data obtained revealed that the magnetic property such as saturation magnetization (Ms), coecivity (Hc), magneton number (n{sub B}) etc. magnetic parameters were increased after irradiation.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Electronic and Magnetic Properties of Mn-doped and (Mn,C)-codoped w-AlN with the Presence of N Vacancy

In this paper, we discover the structural, electronic, and magnetic properties of Mn-doped (6.25 and 12.5%) and Mn-C-codoped wurtzite AlN with the presence of nitrogen vacancy. These properties have been investigated using density functional theory implemented in Quantum ESPRESSO package. AlN doped and codoped were optimized by using Broyden-Fletcher-Goldfarb-Shanno (BFGS) approximation. The electronic and magnetic properties are determined by the total and partial density of states. The presence of impurities and nitrogen vacancy induces magnetic properties, indicating that these materials are good candidates for electromagnetic and spintronics applications. Our results are in good agreement with experimental and other theoretical studies. We can conclude from this study that this material can be used as diluted magnetic semiconductors.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Effect of microstrain on the magnetic properties of BiFeO{sub 3} nanoparticles

We report on size induced microstrain-dependent magnetic properties of BiFeO{sub 3} nanoparticles. The microstrain is found to be high (ε > 0.3%) for smaller crystallite sizes (d < 30 nm), and shows a sharp decrease as the particle size increases. The presence of pseudo-cubic symmetry is evidenced for these nanoparticles. Raman spectral studies suggest straightening of the Fe-O-Fe bond angle accompanied by a decrease in FeO{sub 6} octahedral rotation for d < 65 nm. The magnetization shows a dip around 30 nm, half the size of spin cycloid length for BiFeO{sub 3}, due to a decrease in rhombohedral distortion with crystallite size. We also observe a similar trend in the T{sub N} with respect to size indicating that the microstrain plays a significant role in controlling the magnetic property of BiFeO{sub 3}.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Electronic and Magnetic Properties of Os-Doped Rhodium Clusters: a Theoretical Study

The stability and electronic and magnetic properties of Rh{sub n}Os (n= 2–12) clusters in their most stable configurations were systematically studied by using density functional theory (DFT) at M06L/aug-cc-pVDZ level. Calculation of the second-order difference of energies and fragmentation energies exhibited that Rh{sub 3}Os, Rh{sub 5}Os, Rh{sub 7}Os, and Rh{sub 9}Os clusters are more stable than any other clusters. The calculated HOMO-LUMO energy gaps of the Rh{sub n}Os clusters are found to be in the range of 0.018 to 0.299 eV, implying that the metallic behavior can appear in these clusters. Accordingly, the Rh{sub n}Os clusters can be employed as heterogeneous nanocatalysts in many chemical reactions. The local Fukui function (f{sub k}{sup −}) has also been calculated, and the obtained results reveal that the highest f{sub k}{sup −} values are predicted for the Rh atoms. Therefore, the Rh atoms in the clusters are considered the most reactive sites that undergo reactions with electrophilic reagents. The analysis of the magnetic properties of the Rh{sub n}Os clusters shows that the total magnetic moment per atom of these clusters varies from 0.67 to 1.75 µ{sub B}/atom. And, the PDOS analysis reveals that the d orbitals play a crucial role for the magnetism of the Rh{sub n}Os clusters, and the contribution of the s and p orbitals is small.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Magnetic properties in MnBi alloy of small crystallites for permanent magnet devices

A rare-earth free alloy like MnBi is a potential candidate for developing small magnets and devices. In a commercially viable method, a MnBi alloy was prepared by arc melting Mn and Bi metals in a 1:1 ratio. In terms of the X-ray diffraction a single crystalline MnBi phase is formed of the as prepared alloy. FESEM images delineate thin MnBi layers (25 – 40 nm thickness) of average EDX composition throughout the specimen. A large coercivity 5.501 kOe (6.5 emu/g magnetization) observed in an M-H at 300 K is decreased to 0.171 (9.0 emu/g magnetization) at 100 K in decreasing upon cooling.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Size-dependent structure and magnetic properties of DyMnO{sub 3} nanoparticles

The structure and magnetic properties of orthorhombic DyMnO{sub 3} nanoparticles with different particle sizes are investigated in this paper. With decreasing particle size, all the lattice parameters a, b, and c gradually decrease, whereas the orthorhombic distortion increases. Magnetic measurements reveal that the antiferromagnetic interaction of Mn ions is weakened due to the decrease in Mn-O-Mn bond angle. Above a critical field H*, DyMnO{sub 3} undergoes a field-induced metamagnetic transition at 4 K, which is related to the spin reversal of Dy moments. The critical field H* increases monotonically with size reduction, indicating an enhancement of the antiferromagnetic interaction of Dy ions due to the decreased distance between rare earth ions. The magnetization at 4 K and 5 T, i.e., M(4 K, 5 T) shows a non-monotonic variation with particle size d, i.e., M(4 K, 5 T) initially increases with size reduction but decreases again for d < 68 nm. A modified core-shell model, in which the ferromagnetic ordering (Dy magnetic structure) and antiferromagnetic ordering (Mn magnetic structure) coexist in the core, is proposed to explain this behavior.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Magnetic Properties of Fullerene–Thermally Exfoliated Graphite Composites Doped with Sodium

The magnetic properties (field range H = 0–50 kOe, temperature range T = 3–300 K), and structural features of a sodium-doped carbon composite material based on fullerene C{sub 60} and thermally exfoliated graphite (TEG) are studied. The material is obtained with different ratios of the components by sintering at a pressure of 7 GPa and T = 600°C, at which it is found that significant amorphization of the crystal lattice of the initial C{sub 60} occurs. The dia-, para-, and ferromagnetic components (M{sub D}, M{sub PM}, and M{sub FM}) were separated from the total magnetic moment of the samples under study. It is found that a sodium dopant has no effect on the magnetic properties of the composite. Analysis of the M{sub PM}(H) field dependences by using the Brillouin function for the fullerene-containing sample (i.e., without TEG) makes it possible to determine the quantum number of the total angular momentum of paramagnetic (PM) centers. Its value is found to be J = 1, which corresponds to elementary magnetic moment μ{sub PM} = 2μ{sub B} of a PM center. The concentration of PM centers is estimated at the level of N{sub PM} ≈ (2–5) × 10{sup 18} g{sup –1} for most samples, including the material without TEG. The introduction of TEG into the initial composition and an increase in its proportion in the composite leads to a strong increase in the magnetic moment, which is explained by an increase in both the J value and the concentration of PM centers.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Strain- and thickness-dependent magnetic properties of epitaxial La 0.67 Sr 0.33 CoO 3 /La 0.67 Sr 0.33 MnO 3 bilayers

Magnetic properties and interfacial phenomena of epitaxial perovskite oxides depend sensitively on parameters such as film thickness and strain state. In this work, epitaxial La0 .67 Sr 0.33 CoO 3 (LSCO)/La 0.67 Sr 0.33 MnO 3 (LSMO) bilayers were grown on NdGaO 3 (NGO) and LaAlO 3 (LAO) substrates with a fixed LSMO thickness of 6 nm, and LSCO thickness (t LSCO ) varying from 2 to 10 nm. Soft x-ray magnetic spectroscopy revealed that magnetically active Co 2+ ions that strongly coupled to the LSMO layer were observed below a critical t LSCO for bilayers grown on both substrates. On LAO substrates, this critical thickness was 2 nm, above which the formation of Co 2+ ions was quickly suppressed leaving only a soft LSCO layer with mixed valence Co 3+ /Co 4+ ions. The magnetic properties of both LSCO and LSMO layers displayed strong t LSCO dependence. This critical t LSCO increased to 4 nm on NGO substrates, and the magnetic properties of only the LSCO layer displayed t LSCO dependence. A non-magnetic layer characterized by Co 3+ ions and with a thickness below 2 nm exists at the LSCO/substrate interface for both substrates. Therefore, the results contribute to the understanding of interfacial exchange spring behavior needed for applications in next generation spintronic and magnetic memory devices.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Structural and magnetic properties of Mg substituted Co nanoferrites

The structural and magnetic properties of magnesium substituted cobalt nano ferrites Co{sub x}Mg{sub 1-x}Fe{sub 2}O{sub 4} (x= 0.2, 0.4 and 1.0) have been investigated. The structural characterization has been done by X-ray diffraction (XRD) technique and transmission electron microscopy (TEM). The magnetic studies indicate that the samples show ferromagnetic behaviour at room temperature as well as at low temperature. The magnetization decreases with Mg content in both the cases due to the less magnetic nature of Mg ions than that of the Co ions.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

Synthesis, structural characterization and magnetic properties of Fe/Pt core-shell nanoparticles

Structural and magnetic properties of Fe/Pt core-shell nanostructure prepared by a sequential reduction process are reported. Transmission electron microscopy shows nearly spherical particles fitting a lognormal size distribution with D{sub o} = 3.0 nm and distribution width λ{sub D} = 0.31. In x-ray diffraction, Bragg lines only from the Pt shell are clearly identified with line-widths yielding crystallite size = 3.1 nm. Measurements of magnetization M vs. T (2 K–350 K) in magnetic fields up to 90 kOe show a blocking temperature T{sub B} = 13 K below which hysteresis loops are observed with coercivity H{sub C} increasing with decreasing T reaching H{sub C} = 750 Oe at 2 K. Temperature dependence of the ac susceptibilities at frequencies f{sub m} = 10 Hz–5 kHz is measured to determine the change in T{sub B} with f{sub m} using the Vogel-Fulcher law. This analysis shows the presence of significant interparticle interaction, the Neel-Brown relaxation frequency f{sub o} = 5.3 × 10{sup 10 }Hz and anisotropy constant K{sub a} = 3.6 × 10{sup 6 }ergs/cm{sup 3}. A fit of the M vs. H data up to H = 90 kOe for T > T{sub B} to the modified Langevin function taking particle size distribution into account yields magnetic moment per particle consistent with the proposed core-shell structure; Fe core of 2.2 nm diameter and Pt shell of 0.4 nm thickness.

77 NANOSCIENCE AND NANOTECHNOLOGY↗