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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 1,657 records · Page 92
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

9 T high magnetic field annealing effects on FeN bulk sample

α″-Fe{sub 16}N{sub 2} has been suggested as a promising candidate for future rare-earth-free magnets. In this paper, we report to use high magnetic field (9 T) assisted post-annealing process to enhance the Fe{sub 16}N{sub 2} phase formation in FeN bulk rod samples during the α′ → α″ phase transformation and thus improve its magnetic properties. It was found by X-ray Diffraction measurement that the volume ratio of Fe{sub 16}N{sub 2} phase was increased up to 22%, which corresponds to an increase in the amount of transformation from α′ → α″ up to 78%. Also, the saturation magnetization (M{sub s}) of the prepared FeN rod sample was increased to 227 emu/g with its coercivity up to 376 Oe at room temperature. A working mechanism for the high field assisted post-annealing process was presented.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Magnetic and structural investigations on La{sub 0.6}Sr{sub 0.4}MnO{sub 3} nanostructured manganite: Evidence of a ferrimagnetic shell

This paper presents the structural and magnetic properties of La{sub 0.6}Sr{sub 0.4}MnO{sub 3} nanoparticles with sizes from 21 to 106 nm, which have been prepared using the sol–gel method. The reduction of the nanoparticles' size tends to broaden the paramagnetic to ferromagnetic transition, as well as to promote magnetic hysteresis and a remarkable change on the magnetic saturation. In order to better understand the magnetic behavior of those nanoparticles, a simple model based on a ferromagnetic core and a ferrimagnetic shell was considered, where the magnetization was described in terms of the standard mean-field Brillouin function. This model matches the experimental data, leading to conclusion the nanoparticles with size <40nm are single magnetic domain. In addition, the output fitting parameters give information on the Landé factor of the core and shell. - Graphical abstract: Core–shell model: The core has a ferromagnetic character, while the shell is ferrimagnetic. Each one has two sub-lattices (Mn{sup 3+} and Mn{sup 4+}) that interact through a mean-field (see Eq. (6)). Interactions strength and signals are also represented in this figure. In this figure the arrows (or vectors) represent the magnetic moment of ions Mn{sup 3+} (s=2) and Mn{sup 4+} (s=3/2). βλ's describe the ferromagnetic interaction between Mn{sup 4+} ions into the core (βλ{sub co}) and into the shell (βλ{sub sh}), while αλ's represent ferromagnetic interaction between Mn{sup 3+} ions into the core (αλ{sub co}) and into the shell (αλ{sub sh}). The −λ{sub sh} and +λ{sub co}co are associated to the mean field parameter of interaction between Mn{sup 3+} and Mn{sup 4+} sub-lattices in the shell (ferrimagnetic, negative sign) and core (ferromagnetic, positive sign), respectively. - Highlights: • Evidences of ferromagnetic shell in La{sub 0.6}Sr{sub 0.4}MnO{sub 3} ferromagnetic nanoparticles. • Core(ferromagnetic)–shell(ferromagnetic) model for nanostructured manganite. • Sol–gel method was successfully used to obtain nanostructured manganite.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Magnetic and structural properties of Ni film deposited on Si substrate

The structural and magnetic properties of as deposited and annealed Au capped Ni (20 nm) thin films on Si substrate are reported here. In the as prepared condition, the material does not show intermixing but annealing induces clusterization of mobile Ni atoms resulting in an increase in average crystallite size from ∼12 nm to ∼25 nm as revealed from X-ray diffraction measurements. Also, there is significant intermixing at the Ni/Si interface, which leads to the increase in coercivity and M{sub r}/M{sub s} ratio from 14 Oe to 93 Oe and 0.073 to 0.49 respectively. These polycrystalline samples were also subjected to low temperature (5 K) magnetic measurements in order to look for their compatibility for making magnetic recording structures. At low temperature, the as prepared sample shows coercivity of ∼283 Oe which increases to ∼300 Oe in annealed sample. The results are explained in terms of annealing induced intermixing, increase in grain size and release of stresses at Ni/Si interface.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

The Effect of Hf Substituting for Cu on the Glass-Forming Ability, Crystallization Behavior, and Saturation Magnetization in Fe{sub 85}Si{sub 2}B{sub 8}P{sub 4}Cu{sub 1−x}Hf{sub x} Alloys

The effect of Hf substituting for Cu on the glass-forming ability (GFA), crystallization behavior, and saturation magnetization (M{sub s}) in Fe-rich Fe{sub 85}Si{sub 2}B{sub 8}P{sub 4}Cu{sub 1−x}Hf{sub x} alloys has been investigated. The result shows that the addition of Hf plays a positive role in improving GFA, and the Fe{sub 85}Si{sub 2}B{sub 8}P{sub 4}Cu{sub 0.5}Hf{sub 0.5} alloy ribbon shows an entirely amorphous structure. Both the ribbons of Fe{sub 85}Si{sub 2}B{sub 8}P{sub 4}Cu{sub 1} and Fe{sub 85}Si{sub 2}B{sub 8}P{sub 4}Cu{sub 0.5}Hf{sub 0.5} have two obviously exothermic crystallization peaks, and the addition of Hf improves the onset temperatures of both first and second crystallization peaks, and leads to the improvement of the thermal stability of the amorphous alloys. For the Fe{sub 85}Si{sub 2}B{sub 8}P{sub 4}Cu{sub 0.5}Hf{sub 0.5} ribbon, after annealing at 623 K, crystallization seeds with sizes of 2–4 nm are found and the initial crystallization has occurred; as the annealing temperature is increased to 723 and 823 K, the size distribution of most of the grains is about 20 nm and bigger than 20 nm, respectively. The M{sub s} of the Fe{sub 85}Si{sub 2}B{sub 8}P{sub 4}Cu{sub 0.5}Hf{sub 0.5} ribbon is about 154 emu/g, which is obviously lower than 205 emu/g of the Fe{sub 85}Si{sub 2}B{sub 8}P{sub 4}Cu{sub 1} ribbon. However, after annealing at 723 K, the M{sub s} increases to 212 emu/g for the former alloy. The newly developed amorphous/nanocrystalline Fe-Si-B-P-Cu-Hf alloy with excellent soft magnetic properties shows a potential application for substituting partial Si steels.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Atomic layer deposition of superparamagnetic and ferrimagnetic magnetite thin films

One of the key challenges in realizing superparamagnetism in magnetic thin films lies in finding a low-energy growth way to create sufficiently small grains and magnetic domains which allow the magnetization to randomly and rapidly reverse. In this work, well-defined superparamagnetic and ferrimagnetic Fe{sub 3}O{sub 4} thin films are successfully prepared using atomic layer deposition technique by finely controlling the growth condition and post-annealing process. As-grown Fe{sub 3}O{sub 4} thin films exhibit a conformal surface and poly-crystalline nature with an average grain size of 7 nm, resulting in a superparamagnetic behavior with a blocking temperature of 210 K. After post-annealing in H{sub 2}/Ar at 400 °C, the as-grown α−Fe{sub 2}O{sub 3} sample is reduced to Fe{sub 3}O{sub 4} phase, exhibiting a ferrimagnetic ordering and distinct magnetic shape anisotropy. Atomic layer deposition of magnetite thin films with well-controlled morphology and magnetic properties provides great opportunities for integrating with other order parameters to realize magnetic nano-devices with potential applications in spintronics, electronics, and bio-applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Effect of adatom deposition on surface magnetism and exchange coupling parameter in (0001) SmCo{sub 5} slabs

First principles calculations are performed on 3d-transition metal atom deposited (0001) surface of SmCo{sub 5} to understand the magnetic properties and the improvement of Curie temperature (T{sub c}). Various atomic sites are examined to identify the energetically feasible adsorption of adatom and it is found that the void site of Co-rich (0001) SmCo{sub 5} surface is the most favourable one to deposit. The surface magnetic moments of various adatom deposited SmCo{sub 5} surfaces are larger than the clean surface except for Cu and Zn. Eventually, the surface exchange coupling of clean and adatom deposited surface is found to increase for Mn, Fe, Co, Ni, and Cu deposited surfaces and this improvement results in the increase in T{sub c} of SmCo{sub 5} slab.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Influence of carbon chain length on the synthesis and yield of fatty amine-coated iron-platinum nanoparticles

Iron oxide nanoparticles are among the most widely used and characterized magnetic nanoparticles. However, metal alloys such as superparamagnetic iron-platinum particles (SIPPs), which have better magnetic properties, are receiving increased attention. Scalable techniques to routinely synthesize SIPPs in bulk need further study. Here, we focus on the role played by the fatty amine ligand in the formation of the bimetallic FePt nanocrystal. More specifically, we compare the effect of varying lengths of fatty amine ligands on the shape, structure, uniformity, composition, and magnetic properties of the SIPPs. We synthesized SIPPs by employing a ‘green’ thermal decomposition reaction using fatty amine ligands containing 12 to 18 carbons in length. Greater fatty amine chain length increased the polydispersity, particle concentration, iron concentration, and the stability of the SIPPs. Additionally, longer reflux times increased the diameter of the particles, but decreased the iron concentration, suggesting that shorter reaction times are preferable. Fourier transform infrared spectroscopy of the SIPPs indicates that the ligands are successfully bound to the FePt cores through the amine group. Superconducting quantum interference device magnetometry measurements suggest that all of the SIPPs were superparamagnetic at room temperature and that SIPPs synthesized using tetradecylamine had the highest saturation magnetization. Our findings indicate that the octadecylamine ligand, which is currently used for the routine synthesis of SIPPs, may not be optimal. Overall, we found that using tetradecylamine and a 30-min reflux reaction resulted in optimal particles with the highest degree of monodispersity, iron content, stability, and saturation magnetization.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Electronic structure and magnetism in g-C{sub 4}N{sub 3} controlled by strain engineering

Regulation of magnetism and half-metallicity has attracted much attention because of its potential in spintronics. The magnetic properties and electronic structure of graphitic carbon nitride (g-C{sub 4}N{sub 3}) with external strain are determined theoretically based on the density function theory and many-body perturbation theory (G{sub 0}W{sub 0}). Asymmetric deformation induced by uniaxial strain not only regulates the magnetic characteristics but also leads to a transformation from half-metallicity to metallicity. However, this transition cannot occur in the structure with symmetric deformation induced by biaxial strain. Our results suggest the use of strain engineering in metal-free spintronics applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Characterization of Magnetic NiFe Nanoparticles with Controlled Bimetallic Composition

The exploration of the magnetic properties of bimetallic alloy nanoparticles for various technological applications requires the ability to control the morphology, composition, and surface properties. In this report, we describe new findings of an investigation of the morphology and composition of NiFe alloy nanoparticles synthesized under controlled conditions. The controllability over the bimetallic composition has been demonstrated by the observation of an approximate linear relationship between the composition in the nanoparticles and in the synthetic feeding. The morphology of the NiFe nanoparticles is consistent with an fcc-type alloy, with the lattice strain increasing linearly with the iron content in the nanoparticles. The alloy nanoparticles exhibit remarkable resistance to air oxidation in comparison with Ni or Fe particles. The thermal stability and the magnetic properties of the as-synthesized alloy nanoparticles are shown to depend on the composition. The alloy nanoparticles have also be sown to display low saturation magnetization and coercivity values in comparison with the Ni nanoparticles, in line with the superparamagnetic characteristic. These findings have important implications for the design of stable and controllable magnetic nanoparticles for various technological applications.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2023

Solution combustion synthesis of iron-based alumina catalysts for dehydrogenation of fossil fuels

Microwave-assisted thermocatalytic dehydrogenation of fossil fuels has been proposed as a method for hydrogen production with no CO2 emissions. The byproduct is carbon, which has a commercial value. Iron-based alumina nanocomposites are promising catalysts for this process as they both absorb microwave radiation and catalyze the dehydrogenation. In addition, they may have magnetic properties, which could be used for their separation from the carbon byproduct. Solution combustion synthesis (SCS) is an attractive technique for the fabrication of iron-based alumina nanocomposites because it can produce high specific surface area oxides in a facile manner. However, the effects of the heating mode, the fuel, and the iron/aluminum ratio on the combustion synthesis behavior and the product properties have not been studied yet. In the present work, the iron-based alumina nanocomposites were obtained by SCS using a hotplate, a muffle furnace, and a microwave oven. The initial mixtures were aqueous solutions of iron nitrate, aluminum nitrate, and an organic fuel. The concentrations of the two nitrates were varied in proportion to Fe:Al molar ratios of 1:2, 1:1, and 2:1. Two fuels were tested: citric acid and glycine. The combustion was less vigorous when citric acid was used as the fuel, which is explained by the lower exothermicity of the reaction. X-ray diffraction analysis of the products confirmed the formation of complex oxides of Fe and Al, specifically it detected hercynite and magnetite phases. Brunauer-Emmett-Teller surface area analysis has shown that the powders obtained using citric acid have specific surface areas as high as 276 m2/g, significantly higher than those obtained using glycine. Muffle furnace and hotplate heating led to comparable specific surface areas, while microwave heating resulted in significantly lower specific surface areas. The magnetic properties of the products increase with increasing the Fe/Al molar ratio from 1:2 (no response to a magnetic field) to 1:1 (weak response) and 2:1 (strong response).

solution combustion synthesis, nanoscale oxides, f↗
DOE OSTI2018

Antiferromagnetic Ordering at Room Temperature in Co-Doped Sb{sub 2}Te{sub 3} Topological Insulators

Structural and magnetic properties of Co-doped Sb{sub 2}Te{sub 3} topological insulators have been investigated. Surface morphology was studied using scanning electron microscope (SEM) and atomic force microscope (AFM). X-ray photo electron spectroscopy (XPS) study reveals the mixed states of Co in Co{sup 2+} and Co{sup 3+}. Magnetic study indicates that the substitution of Co in Sb{sub 2}Te{sub 3} not only tune the materials from diamagnetic to antiferromagnetic (even at room temperature) but also propose a promising materials for antiferromagnetic TI which may be useful even for room temperature applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

High spin polarization in CoFeMnGe equiatomic quaternary Heusler alloy

We report the structure, magnetic property, and spin polarization of CoFeMnGe equiatomic quaternary Heusler alloy. The alloy was found to crystallize in the cubic Heusler structure (prototype LiMgPdSn) with considerable amount of DO{sub 3} disorder. Thermal analysis result indicated the Curie temperature is about 750 K without any other phase transformation up to melting temperature. The magnetization value was close to that predicted by the Slater-Pauling curve. Current spin polarization of P = 0.70 ± 0.01 was deduced using point contact andreev reflection measurements. The temperature dependence of electrical resistivity has been fitted in the temperature range of 5–300 K in order to check for the half metallic behavior. Considering the high spin polarization and Curie temperature, this material appears to be promising for spintronic applications.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Permanent magnet electron beam ion source/trap systems with bakeable magnets for improved operation conditions

The magnetic system of a Dresden electron beam ion source (EBIS) generating the necessary magnetic field with a new type of permanent magnet made of high energy density NdFeB-type material operable at temperatures above 100 °C has been investigated and tested. The employment of such kind of magnets provides simplified operation without the time-consuming installation and de-installation procedures of the magnets for the necessary baking of the ion source after commissioning and maintenance work. Furthermore, with the use of a new magnetization technique the geometrical filling factor of the magnetic Dresden EBIS design could be increased to a filling factor of 100% leading to an axial magnetic field strength of approximately 0.5 T exceeding the old design by 20%. Simulations using the finite element method software Field Precision and their results compared with measurements are presented as well. It could be shown that several baking cycles at temperatures higher than 100 °C did not change the magnetic properties of the setup.

43 PARTICLE ACCELERATORS↗
DOE OSTI2014

Structural and thermodynamic properties of Fe{sub 1.12}Te with multiple phase transitions

The parent compound of iron chalcogenide superconductors, Fe{sub 1+y}Te, with a range of excess Fe concentrations exhibits intriguing structural and magnetic properties. Here, the interplay of magnetic and structural properties of Fe{sub 1.12}Te single crystals have been probed by low-temperature synchrotron X-ray powder diffraction, magnetization, and specific heat measurements. Thermodynamic measurements reveal two distinct phase transitions, considered unique to samples possessing excess Fe content in the range of 0.11≤y≤0.13. On cooling, an antiferromagnetic transition, T{sub N}≈57 K is observed. A closer examination of powder diffraction data suggests that the transition at T{sub N} is not purely magnetic, but accompanied by the commencement of a structural phase transition from tetragonal to orthorhombic symmetry. This is followed by a second prominent first-order structural transition at T{sub S} with T{sub S}<T{sub N}, where an onset of monoclinic distortion is observed. The results point to a strong magneto-structural coupling in this material.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Ab Initio and Monte Carlo Approaches for the Magnetocaloric Effect in BaMnO{sub 3} Oxide Perovskite

The self-consistent ab initio calculations, based on density functional theory approach (DFT) and using full potential linearised augmented plane wave (FLAPW) method, have been used to investigate both electronic and magnetic properties of the BaMnO{sub 3} perovskite. Spin-polarised calculations, including the spin-orbit interaction, are used to determine the energy of the ferromagnetic (FM) and antiferromagnetic (AFM) states of BaMnO{sub 3} perovskite. Obtained data from ab initio calculations are used as input for the Monte Carlo simulations to compute other magnetic parameters. Magnetisation, specific heat and magnetic entropy change have been given using the Monte Carlo simulations. The adiabatic temperature change, transition temperature and relative cooling power have been established.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Synthesis and characterization of intrinsically radiolabeled lanthanide phosphate nanoparticles toward biomedical and environmental applications

Lanthanide phosphate nanomaterials are appealing as multifunctional platforms for biomedical applications because of their low toxicity, radiation resistance, and unique luminescence and magnetic properties. Lanthanide phosphate nanoparticles (NPs) radiolabeled with 156 Eu were synthesized by an aqueous route using sodium tripolyphosphate as a phosphate source and complexing agent. GdPO 4 was used as a host matrix, while synthetic concentrations of Ce 3+ /Tb 3+ and Eu 3+ were varied between 5–40% and 10–30%, respectively, and yielded spherical NPs with hexagonal crystal system and particle size < 5 nm. Luminescence emission and magnetic susceptibility were influenced by lanthanide concentrations where characteristic 5 D 0 - 7 F J and 5 D 4 - 7 F J transitions were observed for Eu 3+ - and Tb 3+ -doped NPs, respectively. Chemical yield of > 90% was achieved for GdPO 4 and Gd 0.6 Ce 0.3 Tb 0.1 PO 4 NPs intrinsically radiolabeled with 156 Eu. Lastly, in vitro retention of 156 Eu within LnPO 4 NPs was > 97% over 3 weeks. Intrinsically radiolabeled LnPO 4 NPs have the potential to combine the luminescence and magnetic properties of Ln 3+ ions with lanthanide radioisotopes for biomedical and environmental applications.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Observation of the large magnetocaloric effect and suppression of orbital entropy change in Fe-doped MnV{sub 2}O{sub 4}

We present the structural and magnetic properties of Mn{sub 1−x}Fe{sub x}V{sub 2}O{sub 4} (x = 0.1, 0.2, and 0.3), and investigate the magnetocaloric effect in those compounds. The ferrimagnetic spin ordering is enhanced with the Fe doping at Mn site of MnV{sub 2}O{sub 4}, while the orbital ordering is suppressed. Large magnetic entropy changes up to 3.8 J/kg K as well as the relative cooling power up to 110 J/kg at the field change of 0-2 T for Mn{sub 1−x}Fe{sub x}V{sub 2}O{sub 4} are calculated from the isothermal magnetization measurements. The large orbital entropy change of MnV{sub 2}O{sub 4} is suppressed by the Fe doping, while the spin entropy contribution arising from the strong spin-orbit coupling remains. Moreover, the doping of Fe broadens the temperature span of the large magnetic entropy change and increases the relative cooling power of MnV{sub 2}O{sub 4} by 2.4 times.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Critical analysis on nanostructured CoFeB synthetic orthogonal ferrimagnet

Critical analysis on the magnetic properties of synthetic ferrimagnet (SyF), Ta/MgO/CoFeB/Ru/CoFeB/MgO/Ta, is demonstrated via both static and dynamic techniques. With the Ru thickness being 2.3 nm, the coupling between two CoFeB layers becomes orthogonal, which can be used for spin-transfer-torque nano-oscillator (STNO). The fitting of angular dependent ferromagnetic resonance (FMR) allows the precise determination of magnetic anisotropy of each CoFeB layer, the relative magnetizations and the exchange field near the frequency of STNO applications. In addition, the mechanism of resonance broadening at out-of-plane direction is identified to be magnetic inhomogeneity by fitting the angular dependent linewidth of FMR spectra, which provides indispensable information for the future design of STNO devices.

77 NANOSCIENCE AND NANOTECHNOLOGY↗