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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 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Template Synthesis, Structure, and Magnetic Properties of Layered Nanowires

Nanowires (NWs) consisting of Ni/Cu and Co/Cu alternating layers with a diameter of 100 nm and layer thicknesses varying between 10 and 500 nm are prepared by template synthesis in pores of polymer track-etched membranes. Bath compositions and different regimes for pulsed electrodeposition of NWs are explored. A procedure for electrodeposition of NWs using pulses of equal charge is developed. By diminishing the amount of charge per pulse, initially we manage to lower the layer thickness to 10–15 nm, but further diminishing of charge in pulses leads to the blending of elemental composition of adjacent layers and/or formation of rod–shell nanostructures within the NWs. The coercive force (15–30 mT) and residual magnetization of our layered NWs are determined from magnetization measurements. For NWs with a layer thickness of 50–100 nm, the magnetization curves recorded in the out-of-plane and in-plane geometries are similar in shape and have similar parameters. For NWs with thicker layers (250 and 500 nm), magnetization curves are markedly different due to magnetic anisotropy (an easy magnetization axis emerges longitudinally to NWs) and interference between neighboring NWs. Magnetic force microscopy of isolated NWs identifies that the NWs comprise magnetic regions extending over ~100–150 nm. The NW can be partially remagnetized by applying an external magnetic field (+16 mT) longitudinally.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Magnetic Properties of MFeCrO{sub 4} (M = Co/Ni) Prepared by Solution Combustion Method

Single phase MFeCrO{sub 4} (M = Co/Ni) nanosized samples are prepared by solution combustion method using glycine as fuel. Lattice parameter obtained after Rietveld refinement of the powder x-ray diffraction pattern of CoCrFeO{sub 4} and NiCrFeO{sub 4} samples are 8.374 and 8.325 Å and corresponding crystallite sizes are 40 and 27 nm, respectively. FTIR spectra of both samples show tetrahedral and octahedral metal oxygen bond stretching peaks at 596 and 488 cm{sup −1}, indicating spinel phase formation. DC magnetisation study indicates that both samples are ferrimagnetic at room temperature, with CoCrFeO{sub 4} having a higher value of saturation magnetisation. Mössbauer spectra indicate the presence of magnetic relaxation in the samples. Also, the strength of interaction with nearest neighbour Fe{sup 3+} cations is higher in NiCrFeO{sub 4}.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Structural, Optical and Magnetic Properties of PANI/Se{sub 0.95}Fe{sub 0.05} Nanocomposites

Polyaniline (PANI) coupled with Se{sub 0.95}Fe{sub 0.05} in various weight percentage (5 and 10 wt%) were formed by in situ polymerization method of PANI in the presence of Se{sub 0.95}Fe{sub 0.05}. The functionality of the investigated nanocomposites was investigated by X-ray diffraction (XRD), Fourier transform infrared (FTIR), vibrating sample magnetometer (VSM), and photoluminescence (PL) analyses. The structural characteristics of PANI and the existence of Se{sub 0.95}Fe{sub 0.05} together with PANI were confirmed using XRD. The different functional groups of nanocomposite were studied using FTIR. PANI/Se{sub 0.95}Fe{sub 0.05} nanocomposites exhibited a weak ferromagnetic behavior. Law of Approach to saturation was used to determine the saturation magnetization of nanocomposites samples. The PL of PANI and nanocomposites emitted five emissions in violet and blue ranges. The PL intensity of the emission peaks is significantly reduced when Se{sub 0.95}Fe{sub 0.05} is introduced to PANI matrix.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Solvothermal Synthesis of Mesoporous Fe{sub 3}O{sub 4} Nanoparticles in Mixed Solvent of Ethylene Glycol and Water: Structure and Magnetic Properties

Mesoporous Fe{sub 3}O{sub 4} nanoparticles were synthesized by a solvothermal method, via a mixed solvent of ethylene glycol (EG) and deionized water, using iron chloride and urea as the precursors. The phase, morphology, and pore structure are investigated by the characterization of X-ray diffraction (XRD), transmission electron microscopy (TEM), and N{sub 2} isotherm adsorption–desorption. The results show that the amount of water in the mixed solvent plays vital role in controlling the size of Fe{sub 3}O{sub 4} nanoparticles, specific surface area, and pore size. Additionally, solid Fe{sub 3}O{sub 4} nanospheres were prepared using only EG as solvent, while α-Fe{sub 2}O{sub 3} nanosized polyhedrals were obtained with only water as solvent. The mesoporous Fe{sub 3}O{sub 4} nanoparticles show a ferromagnetic behavior, with saturation magnetizations (Ms) of 78–82 emu g{sup − 1} and coercivities (Hc) ranging from 13–58 Oe. The α-Fe{sub 2}O{sub 3} nanoparticles also exhibit a weak-ferrimagnetic character, with a remanent magnetization (Mr) of 0.24 emu g{sup − 1}, and Hc of 558 Oe.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Effect of Sb substitution on crystal structure, texture and hard magnetic properties of melt-spun MnBi alloys

Melt-spun Mn 50 Bi 50-x Sb x alloys with x ≤ 5 were prepared at different solidification rates and characterized both in the as-spun state and after annealing. In the as-spun alloys, the Sb substitution leads to the formation of a metastable phase, similar to the binary "quenched high-temperature phase" but without the superstructure of the latter and exhibiting a different – increasing – temperature dependence of coercivity. The new nanocrystalline metastable phase is not only itself characterized by a high room-temperature coercivity (in excess of 20 kOe), but upon annealing it transforms into a high-coercivity (up to 13.5 kOe) "low-temperature" α phase. However, the advantage of obtaining a high coercivity without the otherwise required milling made possible by the Sb substitution is undermined by the absence of a local crystallographic texture in the melt-spun alloys. The best combination of the isotropic hard magnetic properties realized for the Mn 55 Bi 43.5 Sb 1.5 composition is a remanence of 35.5 emu/g and a coercivity of 8.1 kOe. The annealed Sb-free Mn 50 Bi 50 alloys did possess a local crystallographic alignment and, for high solidification rates, a moderate coercivity up to 5.6 kOe; however, they had an inadequate "rectangularity" in the demagnetization curve. The orthorhombic compound known as MnBi 0.9 Sb 0.1 and described earlier as antiferromagnetic was obtained in the annealed ribbons with x ≈ 5. The compound was found to order ferromagnetically between 200 K and ≈250 K and to exhibit a significant coercivity, 14.3 kOe at 50 K. Here, it is suggested that the MnBi 0.9 Sb 0.1 may actually be a Sb-stabilized "new phase" observed earlier as metastable in the Bi–MnBi eutectic alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Chemical, Morphological, Structural, Optical, and Magnetic Properties of Transition Metal Titanium (Ti)-Doped LaFeO{sub 3} Nanoparticles

In the present work, pure and transition metal titanium (Ti)-doped LaFe{sub 1−x}Ti{sub x}O{sub 3}(x = 0.0, 0.2, 0.4, and 0.6) nanoparticles have been successfully synthesized by hydrothermal synthesis technique for various molar ratios of 0.2, 0.4, and 0.6. The prepared samples were grinned and annealed in furnace at 600 {sup ∘}C/4 h. The X-ray diffraction (XRD) analysis confirms the phase orthorhombic formation of LaFeO{sub 3} and Ti-doped LaFeO{sub 3}. The stoichiometric analysis was performed through energy-dispersive X-ray studies (EDX). The micro-structural features of surface morphology were examined by field emission scanning electron microscopy (FESEM). Further, surface nanocrystalline of the titanium (Ti)-doped LaFe{sub 1−x}Ti{sub x}O{sub 3} was also investigated through high-resolution transmission electron microscopic (TEM) analysis. The enhancement of room temperature magnetization value has been observed from the M–H curve which is measured using vibrating sample magnetometer (VSM).The weak ferromagnetic behavior was observed from hysteresis loop. From hysteresis loop, saturation takes place when the applied magnetic field intensity is 15 kO{sub e}.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2025

Tuning the magnetic properties of the spin-split antiferromagnet MnTe through pressure

The hexagonal antiferromagnet MnTe has attracted enormous interest as a prototypical example of a spin-compensated magnet in which the combination of crystal and spin symmetries lifts the spin degeneracy of the electron bands without the need for spin-orbit coupling, a phenomenon called nonrelativistic spin splitting (NRSS). Subgroups of NRSS are determined by the specific spin-interconverting symmetry that connects the two opposite-spin sublattices. In MnTe, this symmetry is rotation, leading to the subgroup with spin splitting away from the Brillouin zone center, often called altermagnetism. MnTe also has the largest spontaneous magnetovolume effect of any known antiferromagnet, implying strong coupling between the magnetic moment and volume. This magnetostructural coupling offers a potential knob for tuning the spin-splitting properties of MnTe. Here, we use neutron diffraction with in situ applied pressure to determine the effects of pressure on the magnetic properties of MnTe and further explore this magnetostructural coupling. We find that applying pressure significantly increases the Néel temperature, but decreases the ordered magnetic moment. We explain this as a consequence of strengthened magnetic exchange interactions under pressure, resulting in higher 𝑇 N , with a simultaneous reduction of the local moment of individual Mn atoms, described here via density functional theory. This reflects the increased orbital hybridization and electron delocalization with pressure. In conclusion, these results shed light on the competition between magnetic exchange interactions and the strength of individual magnetic moments and show that the magnetic properties of MnTe can be controlled by pressure, opening the door to improved properties for spintronic applications through tuning via physical or chemical pressure.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Quantum Magnetic Properties and Metal‐to‐Insulator Transition in Chemically Doped Calcium Ruthenate Perovskite

Ruthenates provide a comprehensive platform to study a plethora of novel properties, such as quantum magnetism, superconductivity, and magnetic fluctuation mediated metal–insulator transition (MIT). Herein, an overview of quantum mechanical phenomenology in calcium ruthenium oxide with varying compositions is provided. While the stoichiometric composition of exhibits non‐fermi liquid (FL) behavior with quasi‐criticality, chemically doped compounds depict prominent signatures of quantum magnetic fluctuations at low temperature that in some cases are argued to mediate in metal–insulator transition. In the case of cobalt‐doped , an unusual continuum fluctuation is found to persist deep inside the glassy phase of the material. These observations reflect the richness of the ruthenate research platform in the study of quantum magnetic phenomena of fundamental importance.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Magnetic properties of Lu and Y doped Ce-Fe-B magnets

The growing demand for Nd2Fe14B magnets is exacerbating the current critical materials shortage. To reduce the amount of critical material in Nd2Fe14B magnets, chemical substitutions have been used and shown to improve the magnetic behavior, such as the Curie Temperature TC, anisotropy field Ha, and saturation magnetization MS.

Bretana, Alex↗
DOE OSTI2019

Stability, Electronic and Magnetic Properties of Rare Earth (Eu, Tm) Implanted InGaN

The electronic structure and magnetic behavior of InGaN:RE (RE = Eu, Tm) have been studied by using scalar relativistic full-potential linear augmented-plane-wave plus local orbital (FPLAPW + lo) calculations with LSDA+U approximation. Band structure and density of states are analyzed. It appears that the In-site is the preferred site for doping InGaN alloy with rares earth (Eu, Tm) from the formation energy. Our study reveals that these materials are semiconductors with a direct band gap of 1.2345 eV and 1.3657 eV for InGaN:Eu and InGaN:Tm respectively. The total energy of the FM phase is lower than the AFM total energy; this confirms the fact that the ground state at zero temperature is ferromagnetic. A small-induced magnetic moment on other nonmagnetic atoms (Ga, In, and N) and the total magnetic moment of these compounds is mainly due to RE-4f states.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Unusual electrical and magnetic properties in layered EuZn 2 As 2

Eu-based compounds often exhibit unusual magnetism, which is critical for nontrivial topological properties seen in materials such as EuCd 2 As 2 . The authors investigate the structure and physical properties of EuZn 2 As 2 through measurements of the electrical resistivity, Hall effect, magnetization, and neutron diffraction. Their data show that EuZn 2 As 2 orders antiferromagnetically with an A-type spin configuration below T N = 19 K. Surprisingly, there is strong evidence for dominant ferromagnetic fluctuations above T N , as reflected by positive Curie–Weiss temperature and extremely large negative magnetoresistance (MR) between T N and T fl ≈200 K. Furthermore, the angle dependence of the MRab indicates field-induced spin reorientation from the ab-plane to a direction ≈45° from the ab plane. Compared to EuCd 2 As 2 , the doubled T N and T fl make EuZn 2 As 2 a better platform for exploring nontrivial magnetic and electronic properties in both magnetic fluctuation (T N < T < T fl ) and ordered (T < T N ) regimes.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Magnetic properties of Lutetium and Yttrium doped Ce 2 Fe 14 B magnets

The increasing demand for Nd-Dy and Sm-Co based permanent magnets is exacerbating the current critical materials shortage, therefore improving and optimizing current candidate critical element free permanent magnets is necessary to develop future clean energy technologies. In this work, we aim to increase the thermal stability and magnetic performance of Ce 2 Fe 14 B based permanent magnets through the substitution of Ce ions with noncritical rare earth elements Lu and Y. The substitution of Lu (x=0; 0.05; 0.1; 0.15) for Ce ions in (LuxCe 2-x )Fe 14 B was unsuccessful, likely due to disparities in ionic size and valencies, and failed to exhibit improved thermal stability or magnetic performance. In contrast, Y substitution for Ce ions in (Y x Ce 2-x )Fe14B (x= 0.1; 0.2; 0.3; 0.4; 0.5) alloys was successful. Notably, these alloys demonstrated enhanced thermal stability, as evidenced by an increase in the Curie temperature, reaching a peak of 443 K at x= 0.5. Y substitution also helped to suppress the CeFe2 Laves phase. Without loss of the anisotropy field Y substitution increased the saturation magnetization, MS, peaking at MS = 125 emu/g for a Y concentration of x= 0:4, demonstrating (Y 0.4 Ce 1.6 )Fe 14 B as a potential critical element free permanent magnet with an energy product as high as 29 MGOe. This work is advantageous in developing low cost high performance permanent magnets with reduced or little to no critical rare earth elements.

Rai, Binod K.↗
DOE OSTI2020

Modeling of Magnetic Properties of Magnetorheological Elastomers Using JA Hysteresis Model

Magnetorheological elastomers (MREs) are composite materials that consist of magnetically permeable particles in a nonmagnetic polymeric matrix. Under the influence of an external magnetic field, a reversible deformation change occurs in the mechanical properties of these materials. Due to their coupled magnetomechanical response, these materials have been found suitable for a range of applications including tunable vibration absorbers, sensors, and actuators. Notably, improvement of such devices are prerequisites to efficient energy conversion systems, hence the need to understand further the MRE technology. The Jiles-Atherton (JA) theory takes into consideration the magneto-coupling experienced by effective domains in a magnetic material. Algorithm based on the theory yields five model parameters; saturation magnetization (M s ), domain density (a), domain coupling (α), loss coefficient (k), and reversibility (c). Using JA theory, model parameters were calculated and linked to the physical attributes of Fe powder and isotropic MRE. The results show that the calculated Ms for the MRE is reasonably related to that of the Fe powder by a factor of the particle's volume fraction used in the MRE. Further, the calculated k, a, and α provided support for the reduced pinning factor, domain density, and increased domain coupling in the MRE due to the changes in the domain structure between the two materials. From the calculated JA parameters, finite-element modeling (FEM) of the MRE hysteresis loop was performed. The analysis showed that the modeled magnetic properties including coercivity, remanence, and coordinates of the hysteresis loop tip vary with geometric position.

42 ENGINEERING↗
DOE OSTI2019

Influence of Ce{sup 3+} Ion Doping on Structural and Magnetic Properties of Magnesium Nanoferrite

Pure and rare earth ion Ce{sup 3+}-doped magnesium nanoferrite magnetic particles, i.e., MgFe{sub 2}O{sub 4} and MgCe{sub x}Fe{sub 2−x}O{sub 4} (x = 0.0, 0.025, 0.05, 0.075, and 0.1) were successfully fabricated using sol-gel technique, and qualitative studies were carried out using X-ray diffractometer (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), high-resolution field-emission scanning electron microscopy (HRFESEM) equipped with energy-dispersive spectroscopy (EDS), vibrating sample magnetometer (VSM), and electron paramagnetic resonance (EPR) techniques. X-ray diffraction analysis confirmed the crystalline phase of the synthesized samples with no extra phase. The crystallite size obtained from W-H plots follow the same trend as calculated using Scherrer method, and the strain decreases with increasing Ce{sup 3+} ion concentration indicating a lesser number of deformities. FTIR spectra revealed the shifting of lower-frequency band to the higher side with the larger radii Ce{sup 3+} ions. HRFESEM images reveal the reduction in stress on doping. No additional impurities are observed in synthesized samples as is confirmed by EDS analysis. The average particle size obtained by TEM are in agreement with XRD analysis. EPR studies showed an increase in g value and line width with doping. Magnetic measurements carried out at room temperature reveals the value of magnetization initially decreases up to x = 0.05 and afterwards increases with the addition of Ce{sup 3+} ions. These properties reveal superparamagnetic nature of cerium-doped magnesium nanoparticles and can be suitable for catalyst and humidity sensors.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2020

Li 4 Ru 2 OCl 10 ·10H 2 O: crystal structure, magnetic properties and bonding interactions in ruthenium-oxo complexes

The results of the structural determination, magnetic characterization, and theoretical calculations of a new ruthenium-oxo complex, Li 4 [Ru 2 OCl 10 ]·10H 2 O, are presented. Single crystals were grown using solvent methods and the crystal structure was characterized by single crystal X-ray diffraction. Li 4 [Ru 2 OCl 10 ]·10H 2 O crystallizes into a low-symmetry triclinic structure ($P\bar1$) due to the much smaller Li + cation compared to K + cation in the tetragonal complex K 4 [Ru 2 OCl 10 ]·H 2 O. The X-ray photoelectron spectra confirm only the single valent Ru 4+ in Li 4 [Ru 2 OCl 10 ]·10H 2 O even though two distinct Ru sites exist in the crystal structure. Magnetic measurements reveal the diamagnetic property of Li 4 [Ru 2 OCl 10 ]·10H 2 O with unpaired electrons existing on Ru 4+ . Furthermore, the molecular orbital analysis matches well with the observed UV and magnetic measurements.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Tuning the Magnetic Properties of CrI 3 Using Ni Thin Film Deposition for Applications in Spintronic Devices

Chromium triiodide (CrI 3 ), a van der Waals magnet, has recently been shown to host Ising ferromagnetism down to the monolayer limit. It is a potentially important material in 2D magnet-based applications, such as magnetic sensors and spintronic devices. Prior studies have revealed the coexistence of two different types of interlayer magnetic coupling, the antiferromagnetic (AFM) coupling near the surface and ferromagnetic (FM) coupling in the deep bulk layers, in pristine CrI 3 crystals below the Curie temperature. In this study, we used Ni thin film deposition to tune the surface magnetic states in bulk CrI 3 . A nanometer thickness (4 nm thick) of Ni was deposited on the surface of CrI 3 using electron-beam evaporation to form a Ni/CrI 3 heterostructure. The deposited Ni thin layer forms nanoclusters that completely cover the CrI 3 surface. Magnetic states of CrI 3 before and after Ni deposition are probed by ultralow-frequency magneto-Raman spectroscopy. Instead of seeing three spin wave branches in Raman scattering below 2 T, as in pristine bulk CrI 3 , in Ni/CrI 3 , we observe only a single spin wave branch, which is softened compared to that in pristine CrI 3 and displays a Zeeman shift under an out-of-plane magnetic field up to 7 T. This observation reveals that the AFM layers on pristine CrI 3 crystal surfaces transit into FM layers, so the entire CrI 3 crystal is in the FM state after Ni deposition. First-principles calculations show that Ni atoms tend to diffuse into the CrI 3 lattice, and the FM interlayer coupling has a much lower energy than AFM coupling in the presence of Ni atoms. As a result, our studies show that the magnetic state of CrI 3 can be modified through deposition of a thin metal layer on the surface, offering a route for controlling the spin degree of freedom in van der Waals magnets.

36 MATERIALS SCIENCE↗