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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 1,423 records · Page 79
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Magnetic control over the fundamental structure of atomic wires

When reducing the size of materials towards the nanoscale, magnetic properties can emerge due to structural variations. Here, we show the reverse effect, where the structure of nanomaterials is controlled by magnetic manipulations. Using the break-junction technique, we find that the interatomic distance in platinum atomic wires is shorter or longer by up to ~20%, when a magnetic field is applied parallel or perpendicular to the wires during their formation, respectively. The magnetic field direction also affects the wire length, where longer (shorter) wires are formed under a parallel (perpendicular) field. Our experimental analysis, supported by calculations, indicates that the direction of the applied magnetic field promotes the formation of suspended atomic wires with a specific magnetization orientation associated with typical orbital characteristics, interatomic distance, and stability. A similar effect is found for various metal and metal-oxide atomic wires, demonstrating that magnetic fields can control the atomistic structure of different nanomaterials when applied during their formation stage.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Magnetic and Transport Properties of Co{sub 1+δ}Sb Single Crystals

For some 3d transition-metal monopnictides, their physical properties are strongly affected by interstitial 3d transition-metal atoms, such as Fe{sub 1+δ}Sb, in which the electrical transport, magnetic properties and carrier concentrations have strong dependence on the composition of interstitial Fe (Shiomi et al. Phys. Rev. Lett. 108(5), 056601 2012), Therefore, it is important to study the influence of interstitial Co on the physical properties of Co{sub 1+δ}Sb. Here, the magnetic and transport properties have been studied on Co{sub 1.05}Sb single crystals. The magnetic and electrical transport measurements reveal that stoichiometric CoSb is a nonmagnetic metal. The interstitial Co in this compound exhibits a paramagnetic behaviour and weak antiferromagetic correlations. However, it has no effect on transport properties. A very low magnetoresistance (≤ 0.2%) was observed under the magnetic field up to 14 T, which suggests that Co{sub 1+δ}Sb could be a potential material of electronic devices for the application at a high magnetic field.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Unusual magnetic and transport properties in HoMn 6 Sn 6 kagome magnet

Here, with intricate lattice structures, kagome materials are an excellent platform to study various fascinating topological quantum states. In particular, kagome materials, revealing large responses to external stimuli such as pressure or magnetic field, are subject to special investigation. Here we study the kagome-net HoMn 6 Sn 6 magnet that undergoes paramagnetic to ferrimagnetic transition (below 376 K) and reveals spin-reorientation transition below 200 K. In this compound, we observe the topological Hall effect and substantial contribution of anomalous Hall effect above 100 K. We unveil the pressure effects on magnetic ordering at a low magnetic field from the pressure tunable magnetization measurement. By utilizing high-resolution angle-resolved photoemission spectroscopy, Dirac-like dispersion at the high-symmetry point K is revealed in the vicinity of the Fermi level, which is well supported by the first-principles calculations. Our investigation will pave the way to understanding the magnetotransport and electronic properties of various rare-earth-based kagome magnets.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Peculiarities of Magnetic States of Iron-Cobalt Coatings Formed on Aluminum by Plasma Electrolytic Oxidation

Ferromagnetic oxide coatings were formed on aluminum alloy by the plasma-electrolytic oxidation technique in an electrolyte with colloidal particles of iron and cobalt hydroxides. Iron and cobalt are concentrated in the coating pores as a part of nanosized crystallites. The size of individual crystallites in the pores was ∼50–100 nm. The deficit of oxygen to form oxides in crystallites shows that the metals in the crystallites are predominantly in a reduced state. It is also possible that the metal or oxide nuclei are surrounded by oxide-hydroxide shells. The coatings obtained within 5 min have a high coercive force H{sub c} = 1300 Oe. A theoretical analysis of the magnetic properties of Fe-, Co-containing coatings has been performed using the model of clusters consisting of magnetostatically interacting particles. The theoretical value of the saturation magnetization and the experimental values of the coercive force can be explained with the presence of two phases in the nanoparticles: a large antiferromagnetic or ferromagnetic (hydroxides and/or oxides of iron and cobalt) and a small superparamagnetic (iron, cobalt, magnetite, maghemite).

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Evidence of Room Temperature Ferromagnetism in Zn{sub 1−x}Sn{sub x}S Thin Films

Tin (Sn)-doped zinc sulfide (Zn{sub 1−x}Sn{sub x}S) thin films at different tin (Sn) concentrations (= 0.00, 0.02, 0.05, and 0.08) were coated onto Corning 7059 glass substrates using the electron beam evaporation technique. The films were subjected to different characterization techniques to study the physical properties of the thin films. The structural properties of the films were studied using a powder X-ray diffractometer (XRD), and it was found that the films were cubic in structure without any impurity phases. The crystallite size increased with an increase of Sn concentration, and the mean crystallite size was 21 nm. The chemical composition and surface morphology of the films were studied using scanning electron microscopy (FE-SEM) with energy-dispersive analysis of X-rays (EDAX). Optical properties such as transmittance and absorbance were recorded using a diffuse reflectance spectroscope (UV–vis–NIR). All the films exhibited high optical transmittance of 85% in the visible region of the solar spectrum. The band gap of the films was calculated using Tauc’s relation, and it was found that it increased from 3.53 to 3.57 eV with an increase in the Sn doping concentration from x = 0.02 to x = 0.08. The room temperature photoluminescence studies of the films were recorded using a fluorescence spectrophotometer, and it was found that the films exhibited a prominent emission peak at 420 nm. The magnetic properties of the films and glass substrates at room temperature were studied using a vibrating sample magnetometer. From this, it was found that the films were weakly ferromagnetic at room temperature and the strength of magnetization increased with an increase of doping concentration from x = 0.02 to x = 0.05 and decreased at higher doping concentrations (x = 0.08). The films showed high magnetization at x = 0.05. The films at x = 0.05 exhibited the magnetization (M{sub s}), retentivity (M{sub r}), and coercive fields (H{sub c}) 18 × 10{sup − 6} emu/cm{sup 3}, 1.6 × 10{sup − 6} emu/cm{sup 3}, and 91.80 Oe, respectively.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Magnetic and Electronic Properties of BN Nanosheets with Different Nonmagnetic Metal Dopants: a First-Principles Study

The structural, electronic, and magnetic properties of monolayer boron nitride (BN) doped with a series of nonmagnetic metal atoms, including Ga, Li, Mg, and Na, are systematically investigated by the first-principles method. Both different dopants and doping sites are considered. Magnetic behavior is observed in the systems doped with Li, Mg, and Na atoms. On the other hand, owing to the stable structures of the BN monolayers with Li and Mg dopants among the three magnetic systems, we study the magnetic interaction in these two systems. Interestingly, a long-range ferromagnetic (FM) coupling is observed in the BN monolayer with two Li atoms doped as the Li–Li distance increases. Our results show that the FM interaction originates from a p–d exchange-like s–p coupling interaction. Moreover, nonmagnetic state appears in the system with two Mg dopants.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Stability, Magnetism and Hardness of Iron Carbides from First-Principles Calculations

The stability, electronic structure, magnetism and hardness of iron carbides in eight different space groups were investigated by the first-principles calculations. The electron-ion interactions were modelled using the Vanderbilt ultra-soft pseudopotentials (USPP) and norm-conserving pseudopotentials (NCPP). Generalized gradient approximation (GGA) in the Perdew-Burke-Ernzerhof (PBE) formulation was used to describe the exchange-correlation energy. The calculated lattice parameters for USPP were in good agreement with experimental results. The formation enthalpy, cohesive energy and elastic constants revealed that with the exception of hex-Fe{sub 2}C, all Fe-C compounds were both thermodynamically and mechanically stable. Meanwhile, the iron carbides’ bulk and shear moduli were also calculated and compared. Furthermore, magnetic properties were studied and it was found that the average magnetic moment of Fe{sub 23}C{sub 6} (2.123 μ{sub B}) was the largest among these compounds, with a value close to that of pure α-Fe (2.24 μ{sub B}μ. As expected, hex-Fe{sub 2}C is a paramagnetic metal based on the obtained densities of states and partial densities of states. Furthermore, the magnetic behaviour of iron carbides with polymorphic transformation was almost identical. Finally, several semi-empirical methods were used for estimating the hardness of the iron carbides.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Structural, dielectric and magnetic studies on BiPbSr{sub 2}MnO{sub 6}

We have investigated structural, room temperature dielectric and magnetic properties of BiPbSr{sub 2}MnO{sub 6} as a potential candidate to show magnetoelectric coupling. The X-ray diffraction study shows the crystal structure is noncentrosymmetrical with orthorhombic space group A2aa while neutron diffraction study demonstrates the above structure is centrosymmetrical with orthorhombic space group Amaa. The DC susceptibility measurement performed on polycrystalline powders exhibits antiferromagnetic ordering below transition temperature ∼ 190K. The frequency dependent dielectric measurement at room temperature displays the normal polar dielectric behavior.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Theoretical study of Coulomb correlations and spin-orbit coupling in SrIrO{sub 3}

Given that energy scales associated with crystal field splitting, spin orbit coupling and coulomb correlations in iridates are comparable, hence leading to exotic properties, we investigate the physical properties of orthorhombic SrIrO{sub 3} using density functional theory. Our calculations, however, show that SrIrO{sub 3} is a bad metal with no long range magnetic ordering, unlike its sister compounds Sr{sub 2}IrO{sub 4} and Sr{sub 3}Ir{sub 2}O{sub 7}. Moreover, despite having large band width, it appears conclusive that the larger resistivity in SrIrO{sub 3} is due to spin orbit interactions. Besides, the effects of electron-electron correlations on its electronic structure and magnetic properties are also discussed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Structural, Optical, Magnetic, and Dielectric Properties of Cr{sup 3+} Substituted Cobalt Aluminate Nanoparticles

The present study investigates the influence of Cr{sup 3+} substitution on structural, optical, dielectric, and magnetic properties of cobalt aluminates in the aluminates series CoAl{sub 2-x}Cr{sub x}O{sub 4}, 0.00 ≤ x ≤ 0.20. These series of nanoparticles are effectively synthesized using the co-precipitation method. The cubic spinel aluminate structure is confirmed by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopic measurements. Transmission electron microscopy (TEM) analysis shows the formation of spherical nanoparticles, which are homogeneous in shape and size. The optical properties of the prepared samples have been investigated by means of optical absorbance spectra. The optical band gap E{sub opt}{sup i} and Urbach energy E{sub u} are estimated. At room temperature, the magnetization of undoped CoAl{sub 2}O{sub 4} reveals a weak ferromagnetic behavior. This ferromagnetism is increased for the sample with x = 0.05, and the samples with higher Cr{sup 3+} content have a tendency to be superparamagnetic on account of the formation of single-domain particles as a consequence of small particle size. Real part of dielectric constant (ε{sup ′}), dielectric loss (tanδ), ac conductivity (σ{sub ac}), real part of impedance (Z{sup ′}), and imaginary part of impedance (Z{sup ″}) are analyzed as a function of frequency and Cr{sup 3+} content. The results show that the dielectric loss (tanδ), dielectric permittivity (ε{sup ′}), and ac conductivity (σ{sub ac}) decrease with the increase in Cr{sup 3+} content, x = 0.05, and then increase with a further increase in Cr{sup 3+} content. The increase in these parameters has been explained on the basis of the hopping mechanism. From the Cole–Cole diagram, the value of the relaxation time τ can be calculated and it has been found to increase with increasing the Cr{sup 3+} content. Actually, a high dielectric constant makes these materials good for energy storage at high frequencies.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Simulation of the Magnetocaloric Effect in Sr{sub 2−x}Gd{sub x}FeMoO{sub 6} (0 ≤ x ≤ 0.25)

The magnetocaloric properties for double perovskite oxides Sr{sub 2−x}Gd{sub x}FeMoO{sub 6} with x = 0, 0.06, 0.1, 0.15, 0.2, and 0.25 under 0.05 T magnetic field have been theoretically investigated by using a phenomenological model. It has been noted that the Gd doping in this system decreases the magnetocaloric effect. However, magnetic properties in these systems are tunable for manipulating magnetocaloric refrigeration that occurs in various temperature ranges. This stimulates the Sr{sub 2−x}Gd{sub x}FeMoO{sub 6} samples as recommended for practical applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Understanding the Electronic Behavior of f-Element Intermetallics

Due to their partially filled f-orbitals, lanthanide and actinide intermetallic materials exhibit intriguing electronic, structural, and magnetic properties. These materials provide a unique platform to explore exotic magnetic and quantum phenomena that arise from their strongly correlated f-electrons, offering insights into f-electron behavior. Incorporating light elements such as boron and carbon can significantly impact the electronic, chemical, and physical properties of these materials, with varying influence between lanthanides and actinides due to the more localized f-electrons in lanthanides. In this work, lanthanide-based intermetallic single crystals containing light atoms were synthesized using the molten metal flux growth method. In this method, one or more low-melting metals such as aluminum, gallium, tin, and bismuth are used in excess as the reaction medium. This solution-state approach allows for lower reaction temperatures compared to solid-state reactions and enables the isolation of kinetic products rather than thermodynamically stable compounds. The synthesized crystals were analyzed using an extensive array of analytical and computational characterization techniques, including single crystal X-ray diffraction, scanning electron microscopy, energy-dispersive spectroscopy, magnetization measurements, and density functional theory calculations. These analyses provided detailed insights into the structural and magnetic properties of the synthesized materials.

37 - INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL C↗
DOE OSTI2015

Improvement of thermal stability of amorphous CoFeSiB thin films

The excellent soft magnetic properties of amorphous (a-) CoFeSiB films make it suited for use in the yoke of granular-in-gap sensors, but only if their thermal stability can be improved. To this end, this study investigated the effects of adding small amounts of other metals on the magnetic and structural properties of a-CoFeSiB films. It was found that adding metals with relatively large atomic radii is an effective way to increase thermal stability, with both Ta and Hf showing good thermal stability after annealing at temperatures of 473 to 573 K. Indeed, a -(CoFeSiB){sub 96.2}Hf{sub 3.8} film was found to maintain its initial coercivity of 0.2 Oe without very little decrease in magnetization after annealing at 623 K. Furthermore, even after annealing at 673 K a -(CoFeSiB){sub 93.0}Hf{sub 7.0} film still had a relatively low coercivity of approximately 0.5 Oe.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Magnetoelectric polymer nanocomposite for flexible electronics

This paper reports the fabrication and characterization of a new type of magnetoelectric polymer nanocomposite that exhibits excellent ferromagnetism and ferroelectricity simultaneously at room temperature. The multiferroic nanocomposite consists of high aspect ratio ferromagnetic iron nanowires embedded inside a ferroelectric co-polymer poly(vinylindene fluoride-trifluoroethylene), P(VDF-TrFE). The nanocomposite has been fabricated via a simple low temperature spin coating technique. Structural, ferromagnetic, ferroelectric, and magnetoelectric properties of the developed nanocomposite have been characterized. The nanocomposite films showed isotropic magnetic properties due to the random orientation of the iron nanowires inside the film. In addition, the embedded nanowires did not hinder the ferroelectric phase development of the nanocomposite. The developed nanocomposite showed a high magnetoelectric coupling response of 156 mV/cmOe measured at 3.1 kOe DC bias field. This value is among the highest reported magnetoelectric coupling in two phase particulate polymer nanocomposites.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Atomic-scale determination of spontaneous magnetic reversal in oxide heterostructures

Interfaces between transition metal oxides are known to exhibit emerging electronic and magnetic properties. Here we report intriguing magnetic phenomena for La 2/3 Sr 1/3 MnO 3 films on an SrTiO 3 (001) substrate (LSMO/STO), where the interface governs the macroscopic properties of the entire monolithic thin film. The interface is characterized on the atomic level utilizing scanning transmission electron microscopy and electron energy loss spectroscopy (STEM-EELS), and density functional theory (DFT) is employed to elucidate the physics. STEM-EELS reveals mixed interfacial stoichiometry, subtle lattice distortions, and oxidation-state changes. Magnetic measurements combined with DFT calculations demonstrate that a unique form of antiferromagnetic exchange coupling appears at the interface, generating a novel exchange spring-type interaction that results in a remarkable spontaneous magnetic reversal of the entire ferromagnetic film, and an inverted magnetic hysteresis, persisting above room temperature. Formal oxidation states derived from electron spectroscopy data expose the fact that interfacial oxidation states are not consistent with nominal charge counting. The present work demonstrates the necessity of atomically resolved electron microscopy and spectroscopy for interface studies. Theory demonstrates that interfacial nonstoichiometry is an essential ingredient, responsible for the observed physical properties. The DFT-calculated electrostatic potential is flat in both the LSMO and STO sides (no internal electric field) for both Sr-rich and stoichiometric interfaces, while the DFT-calculated charge density reveals no charge transfer/accumulation at the interface, indicating that oxidation-state changes do not necessarily reflect charge transfer and that the concept of polar mismatch is not applicable in metal−insulator polar−nonpolar interfaces.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Magnetic oxygen in transition metal oxides: A case study of Ba 2 CoO 4

Transition metal oxides (TMOs) exhibit exotic magnetic properties in both naturally formed and artificially structured materials, often difficult to understand in conventional wisdom. Magnetic insulator Ba 2 CoO 4 has mystified the community, because the CoO 4 tetrahedron is completely isolated with the nearest Co atoms far apart (~5 Å), making it impossible to account for long-range magnetic ordering seen experimentally using only Co. By theoretically investigating magnetism and relating our findings to experimental observations in bulk Ba 2 CoO 4 , we illustrate for the first time that the magnetic moment on oxygen atoms are the origin of the unexpected long-range magnetic ordering and low magnetic dimensionality. We find that the magnetic moment is not only localized on Co atoms, as assumed in all conventional data analysis, but also distributed on its tetrahedrally-coordinated O atoms. The total magnetic moment of the CoO 4 building block is 4.63μ B with the magnetic moment on Co being only 3.08μ B . Therefore, the magnetic building block is CoO 4 not Co. Furthermore, our first principles calculations are capable of explaining the origin of the unique magnetic response, including the presence of long-range magnetic ordering with two-dimensional character, and a one-dimensional magnetoelastic behavior. Having oxygen contribute to the magnetic moment will undoubtedly be identified as a universal property of magnetic TMOs, which will require a fresh look at conventional models of magnetism in TMOs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Multifunctional Prussian blue analogue magnets: Emerging opportunities

There is a surge of interest to expand the search for entirely new classes of molecular magnets as the emergence of information storage and quantum computing devices. Prussian blue analogues as a family of molecular magnets are especially attracting wide attention due to their large number of derivatives with a range of magnetic ordering temperature from cryogenic to high temperature. Furthermore, this review presents Prussian blue analogues as multifunctional molecular magnets, which involves the development of molecular magnet syntheses and crystal structures, and magnetic properties under external stimuli. In addition, the porous network structures and vacancy order of Prussian blue analogues present a wide capability to interact with water molecules and gas adsorption. External stimuli, such as thermal, pressure, electric and magnetic field and photoexcitation, play an important role in controlling the hidden states and cooperative phenomena of high temperature molecular magnets based on Prussian blue analogues.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effects of Fe and Co Co-doping on Structural, Magnetic, and Optical Properties of Ti{sub 0.9}Fe{sub 0.1−x}Co{sub x}O{sub 2} Magnetic Semiconductors

A series of six samples with a general formula Ti{sub 0.9}Fe{sub 0.1−x}Co{sub x}O{sub 2} (x = 0.0, 0.02, 0.04, 0.06, 0.08, and 0.1) has been synthesized by solid-state reaction method at annealing temperature of 1150 {sup ∘}C for 2 hours. The synthesized samples have been characterized by X-ray diffractometer, Raman spectroscopy, scanning electron microscopy, EDX, vibrating sample magnetometer, and ultraviolet-visible spectroscopy to investigate structural, defective, morphological, elemental, magnetic, and optical properties. Structural analysis revealed dominant structure of rutile with a minor peak of hematite and anatase. An intensity loss and peak broadening of TiO{sub 2} (rutile) vibration lines has been observed from Raman analysis. Magnetic characterization showed ferromagnetic behavior at room temperature. Optical characterization revealed blue shift in band gap energy with increasing amount of Co concentration.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗