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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 973 records · Page 54
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Critical Behavior and Size Dependence of Magnetic Entropy Changes on La{sub 0.6}Sr{sub 0.4}MnO{sub 3} Manganite

In this work, nano and micro scales of La{sub 0.6}Sr{sub 0.4}MnO{sub 3} ceramics are prepared by sol-gel and solid-state reaction methods. In order to investigate the dependency of the magnetic properties on the size variation of as-prepared samples, their magnetic entropy change (ΔS{sub M}) at different magnetic fields and temperatures are fitted by Lorentz universal function. The obtained results confirmed the size impression on magneto-caloric properties, in spite of proving significant influence on some parameters related to the refrigeration system.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Enhanced Magneto-optical and Photocatalytic Properties of Ferromagnetic Mg{sub 1−y}Ni{sub y}Fe{sub 2}O{sub 4} (0.0 ≤ y ≤ 1.0) Spinel Nano-ferrites

Spinel Mg{sub 1−y}Ni{sub y}Fe{sub 2}O{sub 4} (0.0 ≤ y ≤ 1.0) ferrite magnetic nanoparticles (MNPs) were synthesized by a sol-gel combustion method using urea as the reducing agent/fuel. Powder X-ray diffraction (XRD) analysis revealed the formation of cubic spinel Mg{sub 1−y}Ni{sub y}Fe{sub 2}O{sub 4} powders and confirmed pure crystalline phase and the average crystalline size of 21.25 to 17.04 nm. Functional group bonds between metal and oxygen (M–O) were confirmed by Fourier transform infrared (FT-IR) spectra. The microstructure of the powders was recorded by high-resolution scanning electron microscope (HR-SEM) and confirmed the particle-like surface morphology with smaller agglomeration, due to the magnetic interaction of the particles. Energy-dispersive X-ray (EDX) results showed the composition of the expected elements and confirmed the phase purity of the products. Vibrating sample magnetometer (VSM) technique recorded at room temperature was used to analyse the magnetic properties of the samples and the hysteresis loops showed the ferromagnetic behaviour. Moreover, the samples Mg{sub 1−y}Ni{sub y}Fe{sub 2}O{sub 4} NPs were tested for the photocatalytic degradation (PCD) of methylene blue (MB) dye and the sample y = 0.6 showed maximum degradation efficiency (96.83 %), due to the smaller particle size with higher surface area than other compositions. Furthermore, spinel Mg{sub 1−y}Ni{sub y}Fe{sub 2}O{sub 4} nano-photocatalysts can be reused several times without change of its catalytic activity.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2026

Paramagnetic Properties of Rare Earth Hydroxides, Oxalates, and Dibutyl Phosphates

Magnetic separations present a promising approach for the recovery of rare earth (RE) elements from mixtures, particularly when coupled with precipitation techniques that enhance process efficiency and selectivity. However, the magnetic properties of RE materials typically encountered in the separations industry are not well characterized. Here, we synthesized a series of RE materials, combining four REs – praseodymium (Pr), neodymium (Nd), terbium (Tb), and dysprosium (Dy) – with three precipitating agents – hydroxide, oxalate, and dibutyl phosphate. All materials showed typical paramagnetic behavior consistent with the Curie-Weiss law. At low temperatures, we observed weak antiferromagnetic correlations, which were more pronounced for the lighter RE ions (Pr, Nd). Particle morphology and crystallography analyses showed that the dibutyl phosphates were well-ordered metal-organic frameworks, the oxalates were crystals with mixed hydration states, and the hydroxides were mostly amorphous. Regardless of the degree of crystallinity, the effective magnetic moments aligned well with theoretical estimates based on Hund's rules and 4f electron configurations of the corresponding RE ions. For a given RE ion, the magnetophoretic response was thus determined by the size of the particles rather than specific metal-ligand coupling, with dibutyl phosphate promoting the formation of larger crystals that were the most strongly attracted to magnets.

Wang, Qingpu (ORCID:0000000156041571)↗
NASA NTRS1977

Electrical, magnetic, and optical properties of the tetrathiafulvalene /TTF/ pseudohalides, /TTF/12/SCN/7 and /TTF/12/SeCN/7

The electrical, magnetic, and optical properties of charge-transfer salts containing tetrathiafulvalene (TTF) and the pseudohalides, thiocyanate (SCN) and selenocyanate (SeCN), have been investigated. These salts are quasi-one-dimensional compounds containing cation radicals only, in contrast to a cation-radical-anion-radical system, such as tetrathiafulvalene tetracyanoquinodimethane (TTF) (TCNQ). Measurements of electrical conductivity, thermoelectric power, and optical reflectivity of single crystals of the nonstoichiometric salts (TTF)12(SCN)7 and (TTF)12(SeCN)7 show metal-like characteristics above 200 K (high-temperature region). The conductivities at room temperature are approximately 750 mho/cm comparable to those found in (TTF) (TCNQ), and increase with decreasing temperature down to approximately 200 K. The thermoelectric power at room temperature is small and positive (approximately 9 microvolts/deg K), and decreases linearly with decreasing temperature in this region (as expected for metal-like hole conduction along the TTF chains). The ESR intensity, however, decreases with decreasing temperature above 200 K. At 170 K a metal-nonmetal transition occurs, and the transport and magnetic properties below this temperature are characteristic of a semiconducting state.

Somoano, R. B.↗
DOE OSTI2018

Superconducting Properties of Indium Nanostructured in Pores of Thin Films of SiO{sub 2} Microspheres

Samples of a superconducting indium nanocomposite based on a thin-film porous dielectric matrix prepared by the Langmuir–Blodgett method are obtained for the first time, and their low-temperature electrophysical and magnetic properties are studied. Films with thickness b ≤ 5 μm were made from silicon dioxide spheres with diameter D = 200 and 250 nm; indium was introduced into the pores of the films from the melt at a pressure of P ≤ 5 kbar. Thus, a three-dimensional weakly ordered structure of indium nanogranules was created in the pores, forming a continuous current-conducting grid. Measurements of the temperature and magnetic field dependences of the resistance and magnetic moment of the samples showed an increase in the critical parameters of the superconductivity state of nanostructured indium (critical temperature T{sub c} ≤ 3.62 K and critical magnetic field H{sub c} at T = 0 K H{sub c}(0) ≤ 1700 Oe) with respect to the massive material (T{sub c} = 3.41 K, H{sub c}(0) = 280 Oe). In the dependence of the resistance on temperature and the magnetic field, a step transition to the superconductivity state associated with the nanocomposite structure was observed. A pronounced hysteresis M(H) is observed in the dependence of the magnetic moment M of the nanocomposite on the magnetic field at T < T{sub c}, caused by the multiply connected structure of the current-conducting indium grid. The results obtained are interpreted taking into account the dimensional dependence of the superconducting characteristics of the nanocomposite.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2022

Ultrafast optical control of surface and bulk magnetism in magnetic topological insulator/antiferromagnet heterostructure

Abstract Optical control of the magnetic properties in topological insulator systems is an important step in applying these materials in ultrafast optoelectronic and spintronic schemes. In this work, we report the experimental observation of photo-induced magnetization dynamics in the magnetically doped topological insulator (MTI)/antiferromagnet (AFM) heterostructure composed of Cr-(Bi,Sb) 2 Te 3 /CrSb. Through proximity coupling to the AFM layer, the MTI displays a dramatically enhanced magnetism, with robust perpendicular magnetic anisotropy. When subjected to intense laser irradiation, both surface and bulk magnetism of the MTI are weakened by laser-induced heating of the lattice, however, at the surface, the deleterious heat effect is compensated by the strengthening of Dirac-hole-mediated exchange coupling as demonstrated by an unconventional pump-fluence-dependent exchange-bias effect. Through theoretical analyses, the sizes of exchange coupling energies are estimated in the MTI/AFM bilayer structure. The fundamentally different mechanisms supporting the surface and bulk magnetic order in MTIs allow a novel and distinctive photo-induced transient magnetic state with antiparallel spin configuration, which broadens the understanding of the magnetization dynamics of MTIs under ultrashort and intense optical excitation.

42 ENGINEERING↗
DOE OSTI2022

Spin structure and dynamics of the topological semimetal Co 3 Sn 2-x In x S 2

The anomalous Hall effect (AHE), typically observed in ferromagnetic (FM) metals with broken time-reversal symmetry, depends on electronic and magnetic properties. In Co 3 Sn 2-x In x S 2 , a giant AHE has been attributed to Berry curvature associated with the FM Weyl semimetal phase, yet recent studies report complicated magnetism. We use neutron scattering to determine the spin dynamics and structures as a function of x and provide a microscopic understanding of the AHE and magnetism interplay. Spin gap and stiffness indicate a contribution from Weyl fermions consistent with the AHE. The magnetic structure evolves from c-axis ferromagnetism at x = 0 to a canted antiferromagnetic (AFM) structure with reduced c-axis moment and in-plane AFM order at x = 0.12 and further reduced c-axis FM moment at x = 0.3. Since noncollinear spins can induce non-zero Berry curvature in real space acting as a fictitious magnetic field, our results revealed another AHE contribution, establishing the impact of magnetism on transport.

36 MATERIALS SCIENCE↗
DOE OSTI2019

First-Principles Calculations to Investigate the Structural, Electronic, and Half-Metallic Properties of Ti{sub 2}RhSn{sub 1-x}Si{sub x}, Ti{sub 2}RhSn{sub 1-x}Ge{sub x}, and Ti{sub 2}RhGe{sub 1-x}Si{sub x} (x = 0, 0.25, 0.5, 0.75, and 1) Quaternary Heusler Alloys

The structural, electronic, and magnetic properties of Ti{sub 2}RhSn{sub 1-x}Si{sub x}, Ti{sub 2}RhSn{sub 1-x}Ge{sub x}, and Ti{sub 2}RhGe{sub 1-x}Si{sub x} (x = 0, 0.25, 0.5, 0.75, and 1) quaternary Heusler alloys have been investigated using first-principles density functional theory within generalized gradient approximation (GGA) and local spin-density approximation with Hubbard-U corrections (LSDA+U). The calculations have been performed using the full-potential linearized augmented Plane wave plus local orbitals method. The crystal structures of Ti{sub 2}RhSn{sub 1-x}Si{sub x}, Ti{sub 2}RhSn{sub 1-x}Ge{sub x}, and Ti{sub 2}RhGe{sub 1-x}Si{sub x} were found to be cubic in (F-43m) symmetry for x = 0, 1 and cubic in (P-43m) symmetry for x = 0.25, 0.75, while tetragonal in (P-4m2) symmetry for x = 0.5. The results show that all Ti{sub 2}RhSn1-xSix, Ti{sub 2}RhGe{sub 0.75}Si{sub 0.25}, and Ti{sub 2}RhGe alloys are half-metallic ferrimagnetic. These new materials are good candidates for potential applications in spintronic.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Binder-free cold spray deposition of NdFeB permanent magnets

Cold spray deposition is employed to manufacture binder-free Nd 2 Fe 14 B permanent magnets. Millimeter thick deposits can be fabricated in seconds on substrates such as glass or copper. The Nd 2 Fe 14 B particles appear to partially embed in the substrate and interlock with one another, building up a dense layer that is consolidated by subsequent impacts. The impact and subsequent heating of the particles leads to formation of a magnetically soft phase that significantly reduces coercivity, X-ray diffraction identifies it as Fe. Furthermore, this can be mitigated by reducing gas velocity and temperature, leading to a partial retention of magnetic properties.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Self-Assembled TiN-Metal Nanocomposites Integrated on Flexible Mica Substrates towards Flexible Devices

The integration of nanocomposite thin films with combined multifunctionalities on flexible substrates is desired for flexible device design and applications. For example, combined plasmonic and magnetic properties could lead to unique optical switchable magnetic devices and sensors. In this work, a multiphase TiN-Au-Ni nanocomposite system with core–shell-like Au-Ni nanopillars embedded in a TiN matrix has been demonstrated on flexible mica substrates. The three-phase nanocomposite film has been compared with its single metal nanocomposite counterparts, i.e., TiN-Au and TiN-Ni. Magnetic measurement results suggest that both TiN-Au-Ni/mica and TiN-Ni/mica present room-temperature ferromagnetic property. Tunable plasmonic property has been achieved by varying the metallic component of the nanocomposite films. The cyclic bending test was performed to verify the property reliability of the flexible nanocomposite thin films upon bending. This work opens a new path for integrating complex nitride-based nanocomposite designs on mica towards multifunctional flexible nanodevice applications.

42 ENGINEERING↗
DOE OSTI2021

Tuning the room temperature ferromagnetism in Fe 5 GeTe 2 by arsenic substitution

In order to tune the magnetic properties of the cleavable high-Curie temperature ferromagnet Fe$_{5-x}$GeTe 2 , the effect of increasing the electron count through arsenic substitution has been investigated. Small additions of arsenic (2.5% and 5%) seemingly enhance ferromagnetic order in polycrystalline samples by quenching fluctuations on one of the three magnetic sublattices, whereas larger As concentrations decrease the ferromagnetic Curie temperature (T C ) and saturation magnetization. Furthermore, this work also describes the growth and characterization of Fe 4.8 AsTe 2 single crystals that are structurally analogous to Fe$_{5-x}$GeTe 2 but with some phase stability complications. Magnetization measurements reveal dominant antiferromagnetic behavior in Fe 4.8 AsTe 2 with a Néel temperature of $T_{\textrm{N}} \approx$ 42 K. A field-induced spin-flop below T N results in a switch from negative to positive magnetoresistance, with significant hysteresis causing butterfly-shaped resistance loops. In addition to reporting the properties of Fe 4.8 AsTe 2 , this work shows the importance of manipulating the individual magnetic sublattices in Fe$_{5-x}$GeTe 2 and motivates further efforts to control the magnetic properties in related materials by fine tuning of the Fermi energy or crystal chemistry.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Magnetic and photocatalytic properties of bismuth doped KNbO3 microrods

Highlights: • K{sub 1-x}Bi{sub x}NbO{sub 3} microrods were prepared by solid state reaction method. • Structural information confirms orthorhombic structure of K{sub 1-x}Bi{sub x}NbO{sub 3}. • Band gap of KNbO{sub 3} was varied between 3.13 and 2.95 eV by Bi doping. • Magnetic property of KNbO{sub 3} microrods effectively modified by Bi doping. • Bi doping considerably enhances the degradation of methyl orange dye. - Abstract: The effect of bismuth doping on the structural, magnetic and photocatalytic properties of K{sub 1-x}Bi{sub x}NbO{sub 3} (x = 0.0, 0.01, 0.03, 0.05 and 0.07 mol.%) microrods were studied. X-ray diffraction, Fourier transform infrared and Raman studies revealed the orthorhombic system of KNbO{sub 3}. The scanning electron microscopy images display the nearly rod shape crystallites of K{sub 1-x}Bi{sub x}NbO{sub 3.} The UV–vis diffuse reflectance spectral result showed that the band gap varying between 3.13 and 2.95 eV. Photoluminescence spectra showed that the emission peaks in the visible region between 459 and 544 nm, which are mainly attributed to the oxygen vacancy present in the K{sub 1-x}Bi{sub x}NbO{sub 3} sample. Vibrating sample magnetometer analysis revealed diamagnetic behavior of Bi doped KNbO{sub 3} samples. The BET surface area of K{sub 1-x}Bi{sub x}NbO{sub 3} microrods varies between 9.54 and 14.48 m{sup 2}g{sup −1}. The rate constant of methyl orange degradation with Bi doped samples is about 2 (x = 0.05) and 2.25 (x = 0.07) times faster when compared with that of undoped KNbO{sub 3}.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Element-Specific Study of Magnetic Anisotropy and Hardening in SmCo 5– x Cu x Thin Films

This work investigates the effect of copper substitution on the magnetic properties of SmCo 5 thin films synthesized by molecular beam epitaxy. A series of thin films with varying concentrations of Cu were grown under otherwise identical conditions to disentangle structural and compositional effects on the magnetic behavior. The combined experimental and theoretical studies show that Cu substitution at the Co 3g sites not only stabilizes the formation of the SmCo 5 structure but also enhances magnetic anisotropy and coercivity. Density functional theory calculations indicate that Sm(Co 4 Cu 3g ) 5 possesses a higher single-ion anisotropy as compared to pure SmCo 5 . In addition, X-ray magnetic circular dichroism reveals that Cu substitution causes an increasing decoupling of the Sm 4f and Co 3d moments. Scanning transmission electron microscopy confirms predominantly SmCo 5 phase formation and reveals nanoscale inhomogeneities in the Cu and Co distribution. Our study based on thin film model systems and advanced characterization as well as modeling reveals novel aspects of the complex interplay of intrinsic and extrinsic contributions to magnetic hysteresis in rare-earth-based magnets, i.e., the combination of increased intrinsic anisotropy due to Cu substitution and the extrinsic effect of inhomogeneous elemental distribution of Cu and Co.

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

The northeast materials database for magnetic materials

The discovery of magnetic materials with high operating temperature ranges and optimized performance is essential for advanced applications. Current data-driven approaches are limited by the lack of accurate, comprehensive, and feature-rich databases. This study aims to address this challenge by using Large Language Models (LLMs) to create a comprehensive, experiment-based, magnetic materials database named the Northeast Materials Database (NEMAD), which consists of 67,573 magnetic materials entries (www.nemad.org). The database incorporates chemical composition, magnetic phase transition temperatures, structural details, and magnetic properties. Enabled by NEMAD, we trained machine learning models to classify materials and predict transition temperatures. Our classification model achieved an accuracy of 90% in categorizing materials as ferromagnetic (FM), antiferromagnetic (AFM), and non-magnetic (NM). The regression models predict Curie (Néel) temperature with a coefficient of determination (R 2 ) of 0.87 (0.83) and a mean absolute error (MAE) of 56K (38K). These models identified 25 (13) FM (AFM) candidates with a predicted Curie (Néel) temperature above 500K (100K) from the Materials Project. This work shows the feasibility of combining LLMs for automated data extraction and machine learning models to accelerate the discovery of magnetic materials.

Ferromagnetism↗
DOE OSTI2023

Nonvolatile Memristive Effect in Few-Layer CrI 3 Driven by Electrostatic Gating

The potential of memristive devices for applications in nonvolatile memory and neuromorphic computing has sparked considerable interest, particularly in exploring memristive effects in two-dimensional (2D) magnetic materials. However, the progress in developing nonvolatile, magnetic field-free memristive devices using 2D magnets has been limited. In this work, we report an electrostatic-gating-induced nonvolatile memristive effect in CrI 3 -based tunnel junctions. The few-layer CrI 3 -based tunnel junction manifests notable hysteresis in its tunneling resistance as a function of gate voltage. We further engineered a nonvolatile memristor using the CrI 3 tunneling junction with low writing power and at zero magnetic field. We show that the hysteretic transport observed is not a result of trivial effects or inherent magnetic properties of CrI 3 . We propose a potential association between the memristive effect and the newly predicted ferroelectricity in CrI 3 via gating-induced Jahn–Teller distortion. Furthermore, our work illuminates the potential of 2D magnets in developing next-generation advanced computing technologies.

2D magnet↗
DOE OSTI2019

Confinement of magnetism in atomically thin La0.7Sr0.3CrO3/La0.7Sr0.3MnO3 heterostructures

Abstract At crystalline interfaces where a valence-mismatch exists, electronic, and structural interactions may occur to relieve the polar mismatch, leading to the stabilization of non-bulk-like phases. We show that spontaneous reconstructions at polar La 0.7 Sr 0.3 MnO 3 interfaces are correlated with suppressed ferromagnetism for film thicknesses on the order of a unit cell. We investigate the structural and magnetic properties of valence-matched La 0.7 Sr 0.3 CrO 3 /La 0.7 Sr 0.3 MnO 3 interfaces using a combination of high-resolution electron microscopy, first principles theory, synchrotron X-ray scattering and magnetic spectroscopy and temperature-dependent magnetometry. A combination of an antiferromagnetic coupling between the La 0.7 Sr 0.3 CrO 3 and La 0.7 Sr 0.3 MnO 3 layers and a suppression of interfacial polar distortions are found to result in robust long-range ferromagnetic ordering for ultrathin La 0.7 Sr 0.3 MnO 3 . These results underscore the critical importance of interfacial structural and magnetic interactions in the design of devices based on two-dimensional oxide magnetic systems.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Thermal stability of anisotropic bonded magnets prepared by additive manufacturing

Abstract In this research, anisotropic NdFeB + SmFeN hybrid and NdFeB bonded magnets are additively printed in a polyphenylene sulfide (PPS) polymer binder. Printed NdFeB + SmFeN PPS bonded magnets displayed excellent magnetic properties ( B r [remanence] = 6.9 kG [0.69 T], H cj [coercivity] = 8.3 kOe [660 kA/m], and BH max [energy product] = 9.9 MGOe [79 kJ/m 3 ]) with superior corrosion resistance and thermal stability. The anisotropic NdFeB bonded magnet shows a high coercivity of 14.6 kOe (1162 kA/m) with a BH max of 8.7 MGOe (69 kJ/m 3 ). The coercivity and remanence temperature coefficients for NdFeB + SmFeN hybrid bonded magnets are −0.10%/K and −0.46%/K, and for NdFeB bonded magnets are −0.14%/K and −0.53%/K in the range of 300–400 K, indicating that the hybrid bonded magnets are thermally stable. The average flux aging loss for hybrid magnets was also determined to be very stable over 2000 h at 448 K (175°C) in air with 2.04% compared to that of NdFeB magnets with 3.62%.

thermal stability↗
DOE OSTI2019

Preparation of RE(DBM){sub 3}·Phen (RE=Eu{sup 3+},Tb{sup 3+}) Plate-Loading Fe{sub 3}O{sub 4} Nanospheres and their Magnetic-Optic Bifunctional Property

A facile wet chemical method has been used to synthesize bifunctional core-shell nanoparticles of Fe{sub 3}O{sub 4}@RE(DBM){sub 3}·Phen (RE=Eu{sup 3+},Tb{sup 3+}) showing an interesting combination of magnetic and luminescent properties. This method is convenient, cheap, and efficient. The morphology, structure, luminescent, and magnetic properties of the nanoparticles were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-vis absorption, fluorescence emission, and superconducting quantum interference device magnetometer (SQUID-VSM). The maximum emission peaks of novel Eu{sup 3+} and Tb{sup 3+} nanocomposites are at 618 nm and at 514 nm, respectively. And their corresponding special saturation magnetization Ms. are 25.853 emu/g and 24.015 emu/g, respectively. For the nanoparticles, it is shown that there have better magnetic behavior and they may act as red- and green-emitting material with potential application for fluorescent magnetic particle testing. Moreover, this chemical route could be used to obtain the development of several bifunctional systems of other rare earth ions for practical application.

77 NANOSCIENCE AND NANOTECHNOLOGY↗