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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 1,117 records · Page 62
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Half-metallic Ferromagnetism in Novel Rh{sub 2}-based Full-Heusler Alloys Rh{sub 2}FeZ (Z = Ga and In)

In this approach, we have employed the ab initio method of full-potential linearized plane waves plus local orbital based on the framework of density functional theory, within the spin generalized gradient approximation plus U (GGA+U), where U is the Hubbard correlation term for exchange-correlation potential. This method is used to predict the equilibrium structural parameters, the electronic structure, and the magnetic properties of Rh{sub 2}FeGa and Rh{sub 2}FeIn full-Heusler alloys. The structural properties result show that both Rh{sub 2}FeGa and Rh{sub 2}FeIn compounds are stable in ferromagnetic states. The spin-polarized electronic structure demonstrate that both full-Heusler compounds are half-metals with half-metallic band gap (E{sub HM}) of 0.326 eV for Rh{sub 2}FeGa alloy and 0.245 eV for Rh{sub 2}FeIn alloy, where the apparition of an indirect gap from Γ to X in minority spin is shown by these Heusler alloys. Furthermore, calculations of total magnetic moment give the value of 5 µ{sub B}, which agrees with Slater-Pauling rule; also, the atomic magnetic moment of both Rh and Fe transition metals have the same sign which depicts the ferromagnetic behavior.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Half-Metallic Ferromagnetism in V-Doped FmP Binary Monopnictide Compounds: an Ab Initio Calculations

The ab initio calculations of the structural phase stability, magnetic phase stability, and electronic and magnetic properties of the FmP binary monopnictides and the half-metallic ferromagnetic properties of their Fm{sub 1−x}V{sub x}P (for x = 0.25, 0.50, 0.75, and 1)-doped alloys have been assured through the spin-polarized density functional theory (DFT), and they are performed by employing the full-potential linearized augmented plane waves plus local orbitals (FP-L/APW + lo) method that is implemented in the WIEN2k package. The exchange and correlation potential is parameterized by the generated gradient approximation (GGA) of Perdew-Burke-Ernzerhof (PBE) scheme. According to the studies of the magnetic phase stability, the fermium monopnictides (FmP) have a paramagnetic regime, while the ferromagnetic behavior appears when we dope this compound with vanadium. Through the ferromagnetic character of all Fm{sub 1−x}V{sub x}P alloys, the spin-polarized band structures and densities of states exhibit a nearly half-metallic character of Fm{sub 0.75}V{sub 0.25}P alloy, whereas Fm{sub 0.50}V{sub 0.50}P, Fm{sub 0.25}V{sub 0.75}P, and VP compounds showed metallic character. Moreover, the total magnetic moment of the three ternary alloys is mainly contributed by Fm and V elements, where the p-d hybridization reduces the atomic magnetic moment of V element from its free space charge and produces feeble magnetic moments on the nonmagnetic P sites.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Magnetic Interactions on Oxide Ferromagnet/Ferromagnetic Intermetallide Interface

The magnetic properties of heterostructures consisting of two films are studied. The upper layer involves rare-earth intermetallic nanostructured superlattices consisting of exchange-coupled layers (TbCo{sub 2}/FeCo){sub n} (TCFC), and the lower layer includes either epitaxial manganite La{sub 0.7}Sr{sub 0.3}MnO{sub 3} (LSMO) with optimum strontium doping or an epitaxial film of an yttrium–iron garnet Y{sub 3}Fe{sub 5}O{sub 12} (YIG) with a Bi additive. TCFC is a ferromagnet having high Curie temperature and provides controllable induced magnetic anisotropy. Experimental studies showed that the interlayer interaction of the TCFC/LSMO heterostructure is antiferromagnetic. There was an increase in the FMR line width in the structures due to the flow of a spin current through the interface between two films. There was electric voltage in the TCFC/YIG heterostructure induced in the TCFC intermetallide film, due to an inverse spin Hall effect under ferromagnetic resonance conditions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Synthesis and Characterization of NiFe{sub 2}O{sub 4} Nanoparticles for the Enhancement of Direct Sunlight Photocatalytic Degradation of Methyl Orange

The current investigation shows the simple and direct sunlight-mediated photocatalytic degradation of methyl orange dye by quasi globular NiFe{sub 2}O{sub 4} nanocrystals synthesized from the high-temperature chemical co-precipitation method. The experiment was carried out under direct sunlight which shows significant degradation results lead to the practical possibility of heterogeneous photocatalysis towards environmental remediation. The as-synthesized quasi globular NiFe{sub 2}O{sub 4} nanocrystals also were characterized by well-known analytical measurements of their structural, morphological, bonding, surface area, band gap and magnetic properties prior to the photocatalytic experiments. The presence of active free radicals formed during the photocatalytic reaction was confirmed from the EPR signals recorded for the solution containing the photocatalyst and dye solution, and accordingly, the photocatalytic degradation mechanism was discussed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Superconducting Performance, Structure, Microstructure, and Trapped Field of Top-Seeded Melt-Processed Bulk Y{sub 3}Ba{sub 5}Cu{sub 8}O{sub x}

The sintering temperature for the production of Y{sub 3}Ba{sub 5}Cu{sub 8}O{sub 18} (Y-358) preform powders synthesized in sol-gel spontaneous combustion technique was optimized. A large single-grain bulk Y-358 crystal was fabricated employing a top-seeded melt-growth technique utilizing the optimally sintered preform powders (i.e., at 900 {sup ∘}C for 12 h). Structural, microstructural, elemental, and magnetic properties were investigated by means of X-ray diffraction, scanning electron microscopy, and SQUID, respectively. The structural characterization indicated that the sample is highly textured in (00l) direction. The Y-358 phase fractions were estimated in both preform powders and bulk sample using Rietveld refinement. The onset of superconducting transition is observed at 92.5 K, and the curve is very sharp indicative of the high quality of the produced bulk sample. The field dependence of critical current density (J{sub c}) was determined at 77 K, and the self-field J{sub c} was found to be ∼26 kA/cm{sup 2}. A magnetic field of 0.27 T was trapped by the sample at 77 K.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Spin Reorientation in Antiferromagnetic MnPd 5 Se with an Anti-CeCoIn 5 Structure Type

MnPd 5 Se, a derivative of the anti-CeCoIn 5 -type phase, was synthesized from a high-temperature solid-state reaction, structurally determined by X-ray diffraction, and magnetically characterized with a combined magnetic measurement and neutron powder diffraction (NPD). According to the X-ray diffraction results, MnPd 5 Se crystallizes in a layered tetragonal structure with the same space group as CeCoIn 5 , P4/mmm (No. 123). MnPd5Se shows antiferromagnetic ordering around 80 K on the basis of the magnetic property measurements. An A-type antiferromagnetic structure was revealed from the analysis of neutron powder diffraction results at 300, 50, and 6 K. Moreover, a spin orientation rotation was observed as the temperature decreased. Pd L 3 X-ray absorption near edge spectroscopy results for MnPd5Se semiqualitatively correlate with the calculated density of states supporting a nominal 0.2 electron transfer into the Pd d orbital from either Se or Mn in the compound. The discovery of MnPd 5 Se, along with our previously reported MnT 5 Pn (T = Pd or Pt; Pn = P or As), provides a tunable system for studying the magnetic ordering from ferromagnetism to antiferromagnetism with the strong spin–orbit coupling effect.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Type-II Weyl nodes, flat bands, and evidence for a topological Hall-effect in the new ferromagnet FeCr 3 Te 6

The interplay between linearly dispersing, or Dirac-like, and flat electronic bands, for instance, in the kagome ferromagnets, has attracted attention due to a possible interplay between topology and electronic correlations. Here, we report the synthesis, structural, electrical, and magnetic properties of a single-crystalline ferromagnetic compound, namely Fe 1/3 ⁢CrTe 2 or FeCr 3 ⁢Te 6 , which crystallizes in the 𝑃$\overline{3}$⁢𝑚⁢1 space group instead of the 𝐼⁢2/𝑚 previously reported for FeCr 2 ⁢Te 4 . Electronic band structure calculations reveal type-II Dirac nodes and relatively flat bands near the Fermi level (ε 𝐹 ). This compound shows onset Curie temperature 𝑇 c ≃ 120K, followed by an additional ferromagnetic transition near 𝑇 c2 ∼ 92.5K. Below 𝑇 c , FeCr 3 ⁢Te 6 displays a pronounced anomalous Hall effect, as well as sizable coercive fields that exceed 𝜇 0 ⁢𝐻=1 T at low 𝑇⁢s. However, a scaling analysis indicates that the anomalous Hall effect results from a significant intrinsic contribution, as expected from the calculations, and also from the extrinsic mechanism, i.e., scattering. The extrinsic contribution probably results from occupational disorder at the 1b Fe-site within the van der Waals gap of the CrTe 2 host. We also observe evidence for a topological Hall component superimposed onto the overall Hall response, suggesting the presence of chiral spin textures akin to skyrmions in this centrosymmetric system. Their possible presence will require experimental confirmation.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Ferromagnetic Cr 4 PtGa 17 : A Half-Heusler-Type Compound with a Breathing Pyrochlore Lattice

Here, we describe the crystal structure and elementary magnetic properties of a previously unreported ternary intermetallic compound, Cr 4 PtGa 17 , which crystallizes in a rhombohedral unit cell in the noncentrosymmetric space group R3m. The crystal structure is closely related to those of XYZ half-Heusler compounds, where X, Y, and Z are reported to be single elements only, occupying three different face-centered-cubic sublattices. The new material, Cr 4 PtGa 17 , can be most straightforwardly illustrated by writing the formula as (PtGa 2 )(Cr 4 Ga 14 )Ga (X = PtGa 2 , Y = Cr 4 Ga 14 , Z = Ga); that is, the X and Y sites are occupied by clusters instead of single elements. The magnetic Cr occupies a breathing pyrochlore lattice. Ferromagnetic ordering is found below T C ~ 61 K, by both neutron diffraction and magnetometer studies, with a small, saturated moment of ~0.25 μ B /Cr observed at 2 K, making Cr 4 PtGa 17 the first ferromagnetically ordered material with a breathing pyrochlore lattice. A magnetoresistance of ~140% was observed at 2 K. DFT calculations suggest that the material has a nearly half-metallic electronic structure. The new material, Cr 4 PtGa 17 , the first realization of both a half-Heusler-type structure and a breathing pyrochlore lattice, might pave a new way to achieve novel types of half-Heusler compounds.

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

Giant Exchange Bias of Hysteresis Loops on Cr{sup 3+}-doped Ag Nanoparticles

In this study, we fabricate Cr-doped Ag nanoparticles (AgCrO{sub 2} and Ag{sub 0.5}Cr{sub 2.5}O{sub 4}) by flash autocombustion method. XRD confirmed that the samples have a single-phase spinel structure. The morphology is studied using high-resolution transmission electron microscopy (HRTEM) to confirm that the samples are on nanoscale. The magnetic properties are studied using a vibrating sample magnetometer (VSM) at room temperature (300 K) and at low temperatures (200 and 100 K). Exchange bias has occurred for the investigated samples below room temperatures. The shifts have occurred in the horizontal directions which may be ascribed to the frozen spins in the samples.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Magnetic Exchange Interactions in Geometrically Frustrated Antiferromagnet of ZnCr{sub 2−x}Ga{sub x}O{sub 4}

In this work, the structural and magnetic properties in ZnCr{sub 2−x}Ga{sub x}O{sub 4} were investigated. In ZnCr{sub 2−x}Ga{sub x}O{sub 4}, Ga{sup 3+} ions substitute partial Cr{sup 3+} ions and occupy the B sites. ZnCr{sub 2}O{sub 4} undergoes a paramagnetic-antiferromagnetic transition at 12 K. In ZnCr{sub 2−x}Ga{sub x}O{sub 4}, the antiferromagnetic short-range correlation occurs below 60 K above T{sub N}. The Ga{sup 3+} doping weakens the antiferromagnetic nearest-neighbor exchange interaction (J{sub 1}) and induces ferromagnetic next-nearest-neighbor exchange interaction (J{sub 2}) among the B site magnetic ions. The generation of the ferromagnetic J{sub 2} is ascribed to structure distortion induced by the Ga{sup 3+} doping.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Sample Dependence of Magnetism in the Next-Generation Cathode Material LiNi 0.8 Mn 0.1 Co 0.1 O 2

We present a structural and magnetic study of two batches of polycrystalline LiNi 0.8 Mn 0.1 Co 0.1 O 2 (commonly known as Li NMC 811), a Ni-rich Li ion battery cathode material, using elemental analysis, X-ray and neutron diffraction, magnetometry, and polarized neutron scattering measurements. We find that the samples, labeled S1 and S2, have the composition Li 1–x Ni 0.9+x–y Mn y Co 0.1 O 2 , with x = 0.025(2), y = 0.120(2) for S1 and x = 0.002(2), y = 0.094(2) for S2, corresponding to different concentrations of magnetic ions and excess Ni 2+ in the Li + layers. Both samples show a peak in the zero-field-cooled (ZFC) dc susceptibility at 8.0(2) K, but the temperature at which the ZFC and FC (field-cooled) curves deviate is substantially different: 64(2) K for S1 and 122(2) K for S2. The ac susceptibility measurements show that the transition for S1 shifts with frequency whereas no such shift is observed for S2 within the resolution of our measurements. Our results demonstrate the sample dependence of magnetic properties in Li NMC 811, consistent with previous reports on the parent material LiNiO 2 . Here, we further establish that a combination of experimental techniques is necessary to accurately determine the chemical composition of next-generation battery materials with multiple cations.

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

Preparation and Characterization of Nanocopper Ferrite and Its Green Catalytic Activity in Alcohol Oxidation Reaction

A new type of magnetic material copper ferrite (CuFe{sub 2}O{sub 4}) is successfully manufactured through microwave combustion method. Starch has been tested as a single fuel in this combustion-based synthesis of copper ferrite by using different fuel compositions and equivalence ratios (fuel/oxidant). The formed copper ferrite is characterized by X-ray diffraction analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM), diffuse reflectance spectroscopy (DRS), and photoluminescence (PL) spectroscopy. Magnetic properties of the prepared copper ferrite are analyzed by vibrating sample magnetometer (VSM). Surface area is measured by the nitrogen adsorption/desorption isotherms. A detailed examination of the morphology of the material in various microwave method-catalyzed processes shows that they provide an optimum catalytic activity due to a combination of lower crystal size and higher activity.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2022

Hard Ferromagnetism Down to the Thinnest Limit of Iron-Intercalated Tantalum Disulfide

Two-dimensional (2D) magnetic crystals hold promise for miniaturized and ultralow power electronic devices that exploit spin manipulation. In these materials, large, controllable magnetocrystalline anisotropy (MCA) is a prerequisite for the stabilization and manipulation of long-range magnetic order. In known 2D magnetic crystals, relatively weak MCA typically results in soft ferromagnetism. Furthermore, we demonstrate that ferromagnetic order persists down to the thinnest limit of Fe x TaS 2 (Fe-intercalated bilayer 2H-TaS 2 ) with giant coercivities up to 3 T. We prepare Fe-intercalated TaS 2 by chemical intercalation of van der Waals-layered 2H-TaS 2 crystals and perform variable-temperature transport, transmission electron microscopy, and confocal Raman spectroscopy measurements to shed new light on the coupled effects of dimensionality, degree of intercalation, and intercalant order/disorder on the hard ferromagnetic behavior of Fe x TaS 2 . More generally, we show that chemical intercalation gives access to a rich synthetic parameter space for low-dimensional magnets, in which magnetic properties can be tailored by the choice of the host material and intercalant identity/amount, in addition to the manifold distinctive degrees of freedom available in atomically thin, van der Waals crystals.

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

First-Principles Study in New Hf{sub 2}CoZ (Z = B, C, Al, Si, Ga, Ge, In, Sn, Tl, and Pb) Heusler Alloys

The full-potential linearized augmented plane wave method within density functional theory was used to investigate the electronic structures, magnetic properties, and half-metallicity in Hf{sub 2}CoZ (Z = B,C, Al, Si, Ga, Ge, In, Sn, Tl, and Pb) alloys with AlCu{sub 2}Mn- and CuHg{sub 2}Ti-type structures. The AlCu{sub 2}Mn-type structure is energetically favorable than the CuHg{sub 2}Ti-type structure for all compounds. Hf{sub 2}CoGa, Hf{sub 2}CoAl, Hf{sub 2}CoIn, Hf{sub 2}CoTl, and Hf{sub 2}CoSn compounds in the CuHg{sub 2}Ti-type structure were half-metallic ferromagnets. The d-d and covalent hybridizations between transition metals Hf and Co were effective in the formation of minority band gap. The total magnetic moments of half-metallic Hf{sub 2}CoZ (Z = Al, Ga, In, Sn, and Tl) compounds in the CuHg{sub 2}Ti-type structure obeyed the Slater–Pauling rule (M{sub tot} = Z{sub tot} − 18). Hf{sub 2}CoIn and Hf{sub 2}CoTl compounds were half-metals in relatively wide ranges of lattice constants which indicates that they can be promising and interesting candidates for spintronic devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Direct-Write Printing Copper–Nickel (Cu/Ni) Alloy with Controlled Composition from a Single Electrolyte Using Co-Electrodeposition

Although various processes for metal printing at the micro- and mesoscale have been demonstrated, printing functional devices such as thermocouples, thermopiles, and heat flux sensors that function based on interfaces between an alloy and another alloy/metal demands processes for printing alloys. Furthermore, a high-quality and crystalline alloy is required for acceptable function of these devices. This article reports for the first time co-electrodeposition-based printing of single-phase solid solution nanocrystalline copper/nickel (Cu/Ni) alloy with various controllable compositions (Cu100Ni0 to Cu19Ni81) from a single electrolyte. Additionally, the printed alloy is nanocrystalline (<35 nm), continuous, and dense with no apparent porosity, with remarkable mechanical and magnetic properties, without any postprocessing annealing such as heat treatment. In addition, a functional thermocouple fabricated using this process is demonstrated. Such a process can not only be used for fabrication of functional devices, it may also facilitate fundamental studies on alloys by printing a continuous library of alloy composition for material characterization.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Magnetic Behaviors of 3d Transition Metal-Doped Silicane: a First-Principle Study

We perform a first-principle computation on the magnetic properties of 3d transition metal (TM)-doped silicane. All the substituted systems are energetically stable. Robust half-metallic properties are found in Ti-, V- and Mn-substituted silicane. At the dopant concentration of 12.5%, we evaluate that the Curie temperature of Ti- and Mn-substituted silicane is at 340 and 666 K respectively in the mean-field approximation. Consequently, room-temperature ferromagnetism is easily achievable in Ti- and Mn-substituted silicane. Our work demonstrates potential application of Ti and Mn-substituted silicane for room-temperature spintronic devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Decreased Energy Gap and Enhanced Conductivity in Zn-Doped Sr{sub 2}IrO{sub 4}

The 5d transition metal oxide Sr{sub 2}IrO{sub 4} has attracted much interest in the high-temperature superconductivity community since it highly resembles the cuprate superconductor in crystal and electronic structures. Here, we report on the transport and magnetic properties of Zn-doped Sr{sub 2}IrO{sub 4}. It is found that the energy gap of Sr{sub 2}IrO{sub 4} is rapidly decreased with a small amount of Zn doping. Consequently, the electrical conductivity is significantly enhanced. The present work could serve as the prerequisite stage in exploring the possible superconductivity of the Sr{sub 2}IrO{sub 4} compound.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Electronic Structure and Ferromagnetism in Zincblende Zn{sub 1−x}Co{sub x}S Nanoparticles

We have prepared Zn{sub 1−x}Co{sub x}S nanoparticles (NPs) and studied their local-geometric, electronic, and magnetic properties. X-ray diffraction analyses have indicated that NPs with average crystallite sizes of 2.2 ∼ 2.9 nm are single phase and crystallize in the zincblende-type structure. Cobalt ions with oxidation state + 2 (Co{sup 2+}) replaced for Zn{sup 2+} and almost unchanged the zincblende-type structure of the ZnS host lattice. Interestingly, all samples show room-temperature ferromagnetism and ferromagnetic order increases with increasing Co content (x) in Zn{sub 1−x}Co{sub x}S NPs. With the results obtained from analyzing the local-geometric structures at Zn and Co K-edges and photoluminescence spectra, we believe that ferromagnetism in Zn{sub 1−x}Co{sub x}S NPs is related to intrinsic defects and exchange interactions between Co{sup 2+} ions. We have also reviewed the recent studies on ZnS-based dilute-magnetic materials.

77 NANOSCIENCE AND NANOTECHNOLOGY↗