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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 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Synthesis and Magnetic Properties of New Pyrochlore Fe{sub 2}Mn{sub 2}O{sub 7} Compound

The compound Fe{sub 2}Mn{sub 2}O{sub 7} was prepared using ceramic method Fe{sub 2}O{sub 3} and MnO{sub 2} as a precursor. It was crystallized in pyrochlore oxides type monoclinic structure in the P2/M space group. Concerning the magnetic study, they showed that the compound undergoes a ferromagnetic (FM) transition near 68 K. As for the Arrott’s plots, they revealed a second-order phase transition. The variation of the applied magnetic field revealed a magnetocaloric effect that is manifested by a maximum variation of the magnetic entropy of 1 J/kgK for a field change of 5 T, with a cooling power of 63J/kg.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Magnetic Properties of a Nano-graphene Monolayer with Higher-Order Exchange Interaction Coupling

Using the Monte Carlo simulation, we have studied the phase diagrams and the hysteresis behaviors of a single layer Ising nanographene with next-nearest neighbors coupling J{sub 2} and four-spin interaction J{sub 4} in the presence of a crystal field D and applied magnetic field h. It can emphasize that, for appropriate system parameters, the nanographene can exhibit a new phenomenon manifested in the emergence of an antiferromagnetic phase sandwiched between two ferromagnetic ones. Concerning the hysteresis behavior, the system can present a multiple hysteresis loops.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Investigation to the Structural, Optical, and Magnetic Properties of Synthesized Ni-Doped Anatase Nanoparticles: Essential Role of Treatment in Hydrogen on Long-Range Ferromagnetic Order

Nanocomposite powders of anatase TiO{sub 2} doped with Ni ions (TiO{sub 2}:Ni) were synthesized by facile thermal co-decomposition of a mixture of metals complexes. The X-ray diffraction (XRD) analyses using the Rietveld method confirm the formation of almost single nanocrystalline anatase structure. Anatase TiO{sub 2} incorporated with Ni ions (TiO{sub 2}:Ni) illustrated the formation of a substitutional solid solutions (SSS). The diffuse reflection spectroscopy (DRS) method used to study the optical properties of the prepared samples revealed a redshift associated with Ni doping and hydrogenation, which is explained by the creation of point defects including O-vacancies. This study showed the essential importance of hydrogenation process in order to create or boost room-temperature ferromagnetism (RT-FM). The magnetic measurements indicated that anatase TiO{sub 2} doped with 4.8 mol% Ni produce a magnetic saturation of 0.84 emu/g, which is a remarkable result compared with that related to the similar studies on doped TiO{sub 2}.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2020

Low-temperature MnBi alloys: Electronic and magnetic properties, constitution, morphology and fabrication (Review article)

The article reviews the rich phenomena of physical properties of MnBi. The diverse phenomena include strong spin-orbit interaction, anomalous temperature dependence of the coercivity and the magneto-crystalline anisotropy field, unique magneto-optical properties. Issues addressed include the nature of the electronic ground states of MnBi, the electronic and magnetic structures, Fermi surface, magneto-crystalline anisotropy, x-ray magnetic dichroism. The discussion includes key experiments, such as optical and magneto-optical spectroscopic measurements, de Haas-van Alphen (dHvA) measurements, x-ray photoemission and x-ray absorption spectroscopy measurements as well as x-ray magnetic circular dichroism. The effect of the spin-orbit (SO) interaction and Coulomb repulsion U were found to be crucial for the Fermi surface, cyclotron masses, magneto-optical properties, and x-ray magnetic circular dichroism. The microscopic origin of unique magneto-crystalline anisotropy and giant Kerr effect in MnBi is analyzed in detail. The huge Kerr effect in MnBi is caused by the combination of a sizable magnetic moment on manganese, the large spin-orbit coupling of bismuth, and a strong hybridization between the manganese 3d and the bismuth 6p states. The magneto-optically active states are mainly the 6p states of Bi. We show that the observed temperature dependence of the magneto-crystalline anisotropy can be explained taking into account the spin-orbit interaction together with strong Coulomb electron-electron interaction. The SO coupling of Bi is equally responsible for the large magneto-crystalline anisotropy energy as is the exchange splitting of Mn. The fabrication, morphology, and constitution of low-temperature MnBi alloys in bulk, thin films, and nanoparticles are discussed. The nanocomposite permanent magnetic materials based on MnBi, (Co, Fe) and Nd 2 Fe 14 B are also discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Electrical and Magnetic Properties of Ultrathin Polycrystalline Fe Films Grown on SiO{sub 2}/Si(001)

Ultrathin polycrystalline Fe films have been grown on the oxidized surface of a Si(001) substrate. The resistivity and magnetic hysteresis of Fe films have been measured in the range of thickness from 2.5 to 10 nm. Based on the analysis of the data obtained, it is suggested that there is a transition to the structurally continuous film at a thickness of ~6 nm. It is found that Fe grains in this film acquire the preferred (111) orientation during this transition.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2018

Characteristics of Co3O4 and cobalt nanostructured microspheres: Morphology, structure, reduction process, and magnetic properties

Highlights: • The metal cobalt samples consist in both α-Co with a hexagonal close-packed lattice and β-Co face-centered cubic crystal at reduction temperatures 220, 240, 300 and 350 °C. • Co{sub 3}O{sub 4} reduction proceeded in successive stages: water removal, residual salt removal, Co{sub 3}O{sub 4} → CoO and CoO → Co transitions. • Inheritance of morphology may have droplet–Co{sub 3}O{sub 4}–Co association. - Abstract: Nanostructured magnetic cobalt microspheres were synthesized using a two-stage method. First, nanostructured cobalt oxide Co{sub 3}O{sub 4} microspheres were produced by ultrasonic spray pyrolysis at different temperatures from 800 to 1100C. Second, the nanostructured powders obtained were reduced to metal cobalt in an hydrogen atmosphere at different temperatures from 220 to 350C. In this study the evolution of the morphology from Co{sub 3}O{sub 4} nanostructured microspheres to nanostructured Co, resulting from the Co{sub 3}O{sub 4} reduction process, and the structure of metal cobalt, were investigated. It was found that the metal cobalt agglomerates have the same shape and mean diameter (∼ 1,5 μm) as those of the cobalt oxide, Co{sub 3}O{sub 4}. The amount of Co microspheres with smaller diameters decreased with increasing reduction temperature. Also, the β-Co content increased with increasing reduction temperature.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Construction of three lanthanide metal-organic frameworks: Synthesis, structure, magnetic properties and highly selective sensing of metal ions

Three lanthanide metal-organic frameworks (Ln-MOFs), [Ln(TZI)(H{sub 2}O){sub 4}]·3H{sub 2}O (Ln=Gd (1) and Tb (2) and Dy (3), H{sub 3}TZI=5-(1H-tetrazol-5-yl)isophthalic acid), have been synthesized under hydrothermal conditions. Single crystal X-ray diffraction reveals that 1–3 are isostructural and display a 1D double chain based on dinuclear motifs with (μ-COO){sub 2} double bridges. Magnetic studies indicate antiferromagnetic interactions in 1, ferromagnetic interactions in 2 and 3. Furthermore, compound 3 displays a slow relaxation behavior. Compound 2 exhibits intense characteristic green emission of Tb(III) ions in the solid state, which can be observed by the naked eye under UV light. Interestingly, 2 can selectively sense Pb{sup 2+} and Fe{sup 3+} ions through luminescence enhancement and quenching, respectively. The luminescence quenching mechanisms have been investigated in detail. The study on luminescence Ln-MOFs as a probe for sensing Pb{sup 2+} and Fe{sup 3+} ions is exceedingly rare example. - Graphical abstract: Three Ln-MOFs were successfully synthesized using a 5-(1H-tetrazol-5-yl)isophthalic acid ligand. They displays different magnetic behavior. Especially, the Dy(III) compound slow relaxation behavior. Interestingly, the Tb(III) compound can selectively sense Pb{sup 2+} and Fe{sup 3+} ions through luminescence enhancement and quenching, respectively. - Highlights: • Three Ln-MOFs with tetrazolate dicarboxylate ligand. • Dy(III) compound displays slow relaxation behavior. • The Tb(III) compound shows highly selective luminescence sensing of the Fe{sup 3+} and Pb{sup 2+} ions.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Size Dependences of the Magnetic Properties of Superconducting Lead–Porous Glass Nanostructures

Superconducting structures Pb–PG formed by filling a porous glass matrix with the lead from melt under pressure have been investigated. Samples with characteristic pore structure diameters of d ≈ 7, 3, and 2 nm have been studied. It has been found that the critical temperature of the superconducting transition in the samples under study is similar to the corresponding value T{sub c} ≈ 7.2 K for bulk lead. At the same time, it has been observed that the critical magnetic field of the nanocomposites, which attains H{sub c}(T = 0 K) ≈ 165 kOe for Pb–PG (3 nm), exceeds several times the value H{sub c}(0) = 803 Oe for bulk lead. The low-temperature magnetic- field dependences of magnetic moment M(H) contain quasi-periodic flux jumps, which vanish with a decrease in the lead nanostructure diameter. A qualitative model of the observed effects is considered.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2023

Synthesis, crystal structure, and magnetic properties of CoMoFeAl and related compounds

We have carried out joint theoretical and experimental investigations of three Heusler compounds CoMoFeAl, CoMo 0.5 Fe 1.5 Al, and Co 1.5 Mo 0.5 FeAl. Our first-principle calculations show that all three compounds show either ferro- or ferrimagnetic order with CoMoFeAl and CoMo 0.5 Fe 1.5 Al exhibiting high spin polarization of almost 80%. The investigated samples were prepared using arc melting and high vacuum annealing. All the samples show cubic crystal structure with disorder. The parent compound CoMoFeAl shows a small saturation magnetization of 12 emu/g, and a Curie temperature of 440 K. The other two compounds, namely, Co 1.5 Mo 0.5 FeAl and CoMo 0.5 Fe 1.5 Al, show much higher saturation magnetizations of 62 emu/g and 59 emu/g, and substantially higher Curie temperatures of 950 K and 780 K, respectively.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Synthesis, Structural, Electronic, and Magnetic Properties of Cubic Perovskite La{sub 1−x}Ba{sub x}MnO{sub 3} (0.125 ≤ x ≤ 0.875) for Spintronic Devices

In this study, La{sub 0.5}Ba{sub 0.5}MnO{sub 3} has been synthesized by hydrothermal method. Crystal structure and morphology are determined by x-ray diffraction and scanning electron microscopy. It is observed that Ba-doped LaMnO{sub 3} (LMO) has the same cubic crystal structure as the host material with space group Pm3̄m. Half of the La atoms are replaced by Ba in the composition. Further, the electronic and magnetic structures are investigated by solving the Kohn-Sham equation with the full-potential linearized augmented plane wave method (FP-LAPW), with GGA+U approximation for exchange and correlation, for Ba concentration from 12.5 to 87.5%. The system is half-metallic ferromagnetic (FM) up to 55% and then converts into anti-ferromagnetic (AFM). This happens due to the onset of super exchange on increasing Ba concentrations. It is suggested that Ba-doped LMO is the best material for the fabrication of an exchange-biased spin valve. The spacer material can be any non-magnetic cubic perovskite such as BaTiO{sub 3} while the FM and AFM layers can be made of Ba-doped LMO with different concentrations of Ba. .

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Structural, electronic, and magnetic properties of nearly ideal J eff = 1/2 iridium halides

Heavy transition metal magnets with J e f f = 1 2 electronic ground states have attracted recent interest due to their penchant for hosting new classes of quantum spin liquids and superconductors. Unfortunately, model systems with ideal J e f f = 1 2 states are scarce due to the importance of noncubic local distortions in most candidate materials. In this work, we identify a family of iridium halide systems [i.e., K 2 Ir Cl 6 , K 2 Ir Br 6 , ( NH 4 ) 2 Ir Cl 6 , and Na 2 Ir Cl 6 · 6 ( H 2 O ) ] with Ir 4 + electronic ground states exhibiting extremely small deviations from the ideal J e f f = 1 2 limit. We also find ordered magnetic ground states for the three anhydrous systems, with single-crystal neutron diffraction on K 2 Ir Br 6 revealing type-I antiferromagnetism. This spin configuration is consistent with expectations for significant Kitaev exchange in a face-centered-cubic magnet. This work establishes that incorporating isolated Ir X 6 octahedra in materials, where X is a halogen ion with a low electronegativity, is an effective design principle for realizing unprecedented proximity to the pure J e f f = 1 2 state. However, at the same time, we highlight undeniable deviations from this ideal state, even in clean materials with ideal Ir X 6 octahedra as inferred from the global cubic crystal structures.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Structural, Optical, and Magnetic Properties of Gd-Doped TiO{sub 2} Nanoparticles

Polycrystalline pure and (1, 3 and 5%) Gd-doped TiO{sub 2} nanoparticles were synthesised by simple sol-gel method. The structure, morphology and physico-chemical properties of samples were characterised by X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectra, transmission electron microscopy and N{sub 2} absorption and desorption isotherms. Photoluminescence (PL) measurements revealed that the samples exhibit extended light absorption frequencies in visible light region. The visible emission of TiO{sub 2} is found to be largely dependent on the defects and which were found to be tailored by varying Gd doping concentration. Room temperature magnetic studies reveal the transition from ferromagnetic to paramagnetic nature which occurs due to the high magnetic moment of Gd ions and its interaction with host lattice.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

CTAB-Assisted Synthesis of N-Doped Fe{sub 3}C Nanowires and Their Magnetic Properties

N-doped iron carbide (N-doped Fe{sub 3}C) nanomaterials have a wide range of applications. In this study, a hexadecyltrimethylammonium bromide (CTAB)-assisted two-step process was used to prepare N-doped Fe{sub 3}C nanomaterials. The effect of CTAB addition on the phase, structure, and morphologies of the products has been investigated in detail based on the characterization results of X-ray diffraction (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), Raman spectra (Raman), N{sub 2} adsorption–desorption, and elemental analysis. By tuning the amount of CTAB, N-doped Fe{sub 3}C nanowires were prepared. The magnetic hysteresis loops at room temperature of the N-doped Fe{sub 3}C nanomaterials show ferromagnetic characteristics.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2026

Crystal Structures, Optical Behavior, and Magnetic Properties in Hydrated Lanthanide Iron Sulfates

Single crystals of LnFe(SO 4 ) 3 (H 2 O) 2 (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm; compounds 1–11) and LnFe(SO 4 ) 3 (H 2 O) (Ln = Tm, Yb, Lu; compounds 12–14) were synthesized under hydrothermal conditions. Single-crystal X-ray diffraction (SCXRD) analysis revealed that the dihydrated compounds (1–11) crystallize in centrosymmetric (CS) structures, with the lanthanide ions adopting eight-coordinate geometries. In contrast, the monohydrated compounds (12–14) exhibit noncentrosymmetric (NCS) structures, where the lanthanide ions are seven-coordinated. Vibrating sample magnetometry (VSM) confirmed that compounds 2, 4, and 7–11 are paramagnetic below 400 K, with compound 8 displaying the highest magnetic susceptibility. Compounds 1, 5, 6, 13, and 14 show a sharp increase in magnetic susceptibility at Néel temperatures ( T N ) of approximately 72, 76, 70, 58, and 56 K, respectively, indicating antiferromagnetic ordering. High-temperature magnetic susceptibility measurements further support the presence of antiferromagnetic transitions in these compounds. Second harmonic generation (SHG) measurements showed that the noncentrosymmetric Yb (compound 13) and Lu (compound 14) compounds exhibit SHG intensities of 0.3× and 1.6× that of potassium dihydrogen phosphate (KDP), respectively.

anions↗
DOE OSTI2018

The Geometrical Structures and Magnetic Properties of Charged Aluminum-Doped Platinum Clusters: Aluminum Occupied High Coordination Site

The most stable states of neutral and charged Pt{sub n}Al (n = 1 − 8) clusters have been performed using DFT methods. All the most stable structures of neutral and charged Pt{sub n}Al clusters can be obtained by substituting a Pt atom with an Al atom except Pt{sub 7}Al and the Al atom occupies the vertex position with lager coordination number. The Pt{sub 5}, Pt{sub 4,6}Al, Pt{sub 3}Al{sup +}, and Pt{sub 6}Al{sup −} clusters have higher local relative stability and can be seen as “magic clusters.” The fragmentation energy is the largest when a Pt atom is bonded with an Al atom. The average magnetic moments of Pt{sub n+ 1} cluster reduce due to the addition of Al atoms. The static polarizability has been studied in this paper.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Quaternary M{sub 0.25}Cu{sub 0.25}Mg{sub 0.5}Fe{sub 2}O{sub 4} (M = Ni, Zn, Co, Mn) ferrite oxides: Synthesis, characterization and magnetic properties

Highlights: • Superparamagnetic quaternary nanoferrite (M{sub 0.25}Cu{sub 0.25}Mg{sub 0.5}Fe{sub 2}O{sub 4,} where M = Mn, Zn, Co, Ni) were obtained. • C, O, H and metals were observed by XPS analysis. • Phases purity were confirmed by XRD diffraction and crystallite size (3–10 nm) were determind. - Abstract: We report the synthesis of M{sub 0.25}Cu{sub 0.25}Mg{sub 0.5}Fe{sub 2}O{sub 4} (where M = Mn, Zn, Co, Ni) nanoparticles using the coprecipitation method in the presence of carboxymethyl cellulose (CMC) as the in-situ surfactant. The crystalline structure and surface morphology were examined by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM) and it was established that the average diameter of the magnetic nanoparticles (MNPs) is in the range of 3–10 nm. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) show that the MNPs are activated by the hydrophilic groups of the surfactant, which coat them and enhance their stability. The vibrating sample magnetometry measurements show the superparamagnetic behavior of the nanoparticles. Due to their small crystallite size, which implies large surface area, and their functionalization with organic groups, the obtained nanoparticles could have medical and catalytic applications.

36 MATERIALS SCIENCE↗
DOE OSTI2018

The synthesis of CuO and NiO nanoparticles by facile thermal decomposition of metal-Schiff base complexes and an examination of their electric, thermoelectric and magnetic Properties

Highlights: • Thermal decomposition of Schiff base complexes provides a convenient and effective pathway to fabricate CuO and NiO NPs. • The electrical conduction in CuO NPs and NiO NPs is governed by intrinsic band-to-band type and large polarons conduction mechanism, respectively. • The thermoelectric measurements confirm that the NPs are P-type degenerate semiconductors. • The NPs show weak ferromagnetic ordering at room temperature and antiferromagnetic to paramagnetic transition with high dipolar interaction. - Abstract: In this study, CuO and NiO NPs have been synthesized by facile thermal decomposition of Schiff base complexes and their physical properties have been examined. The synthesized CuO and NiO NPs are crystallized in polycrystalline monoclinic and cubic structures with average particle size 17 ± 0.4 and 62 ± 1 nm, respectively. The electrical conductivity measurements confirm that the conduction in the CuO NPs is a band-to-band type while the conduction in the NiO NPs is governed by the large polaron conduction mechanism. The thermoelectric measurements confirm that the CuO and NiO NPs are P-type degenerate semiconductors with room temperature Seebeck coefficients equal to 89.9 and 12.1 mV/K, respectively. The magnetic measurements exhibit that the NPs have weak ferromagnetic ordering and antiferromagnetic to paramagnetic transition with high dipolar interaction.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗