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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 469 records · Page 26
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Low temperature superconductor and aligned high temperature superconductor magnetic dipole system and method for producing high magnetic fields

A dipole-magnet system and method for producing high-magnetic-fields, including an open-region located in a radially-central-region to allow particle-beam transport and other uses, low-temperature-superconducting-coils comprised of low-temperature-superconducting-wire located in radially-outward-regions to generate high magnetic-fields, high-temperature-superconducting-coils comprised of high-temperature-superconducting-tape located in radially-inward-regions to generate even higher magnetic-fields and to reduce erroneous fields, support-structures to support the coils against large Lorentz-forces, a liquid-helium-system to cool the coils, and electrical-contacts to allow electric-current into and out of the coils. The high-temperature-superconducting-tape may be comprised of bismuth-strontium-calcium-copper-oxide or rare-earth-metal, barium-copper-oxide (ReBCO) where the rare-earth-metal may be yttrium, samarium, neodymium, or gadolinium. Advantageously, alignment of the large-dimension of the rectangular-cross-section or curved-cross-section of the high-temperature-superconducting-tape with the high-magnetic-field minimizes unwanted erroneous magnetic fields. Alignment may be accomplished by proper positioning, tilting the high-temperature-superconducting-coils, forming the high-temperature-superconducting-coils into a curved-cross-section, placing nonconducting wedge-shaped-material between windings, placing nonconducting curved-and-wedge-shaped-material between windings, or by a combination of these techniques.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Heat treatable magnets having improved alignment through application of external magnetic field during binder-assisted molding

Improved manufacturing processes and resulting anisotropic permanent magnets, such as for example alnico permanent magnets, having highly controlled and aligned microstructure in the solid state are provided. A certain process embodiment involves applying a particular orientation and strength of magnetic field to loose, binder-coated magnet alloy powder particles in a compact-forming device as they are being formed into a compact in order to preferentially align the magnet alloy powder particles in the compact. The preferential alignment of the magnet alloy powder particle is locked in place in the compact by the binder after compact forming is complete. After removal from the device, the compact can be subjected to a subsequent sintering or other heat treating operation.

Kassen, Aaron G.↗
DOE OSTI2018

The Role of Wheel Surface Quality on Structural and Hard Magnetic Properties of Nd–Fe–B Permanent Magnet Powders

Rapidly solidified Nd{sub 15}Fe{sub 77}B{sub 8} magnetic alloy powders have been produced by using melt-spinning method. Different wheel surface structures such as smooth and textured were tested to investigate the effect of wheel surface morphology on powder shape, microstructure, Curie temperature, and magnetic properties. Produced powders were subjected to surfactant-active ball-milling process for powder size reduction and to enhance magnetic and thermal properties. Generally, flaky-shaped powders were obtained with smooth surface wheels and spherical-shaped powders were produced with textured surface wheel. Microstructure of flaky-shaped powders consisted of polygonal fine equiaxed grains with an average grain size of 0.45 µm. Spherical-shaped powders had dendritic microstructure regardless of their sizes. Both flaky and spherical powders involved hard magnetic Nd{sub 2}Fe{sub 14}B phase located in the grain interior and a fine network of Nd-rich phase at the grain boundaries. Surfactant-active ball-milling process significantly contributed to magnetic and thermal properties of powders. The coercivity values of flaky-shaped powders milled for 90, 150, 210, 270, 330, and 390 min milling times were substantially higher than that of spherical-shaped powders milled for the same period of times. The Curie temperatures of Nd{sub 15}Fe{sub 77}B{sub 8} ingot alloy and spherical- and flaky-shaped powders were found as 279, 305, and 321 {sup ∘}C, respectively. On the other hand, the Curie temperatures of flaky- and spherical-shaped powders milled for 390 min were measured as 331 and 311 {sup ∘}C, respectively.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Magnetic Relaxation Experiments in CNT-Based Magnetic Nanocomposite

In this work, we discuss the relaxation of the magnetic moments in a novel carbon nanotube (CNT)-based nanocomposite synthesized by using chemical vapor deposition process. The material consists of a matrix of CNT filled by Fe-based nanoparticles. This structure is seen clearly by scanning and transmission. X-ray diffraction and Raman spectroscopy are used to detect the predominant Fe{sub 3}C phase and the CNT presence in the sample, respectively. The results obtained from both hysteresis cycles, M(H), and zero field cooled-field cooled (ZFC-FC) measurements confirm that the material is characterized by both a strong ferromagnetic exchange and random magnetic anisotropy. For the first time, we have been able to fit the magnetic relaxation data, M(t), by using both the two distributions of nanoparticles data deduced from the ZFC-FC data and the temperature dependence of the magnetic anisotropy obtained from the law of approach to saturation in random magnets. .

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2021

Active magnetic regenerative cooling with smaller magnets

Magnetocaloric heat pumping near room temperature, a.k.a. magnetic cooling, relies on the active regenerator cycle to achieve functional temperature spans and realize economic and societal benefits promised by this emerging solid-state cooling technology. The cycle itself depends upon synchronizing oscillating flow of a heat transfer fluid through a solid porous active material matrix, or the refrigerant, with periods when the refrigerant is in the highest available (field-on) and in nearly zero (field-off) magnetic fields to accomplish heat transfer. With this in mind, in this work we analyze varying flow and magnetic field wave forms and the timing between when the fluid is pumped and when the magnetic field is turned on and off. We demonstrate that the volume and the cost of permanent magnet generating the field changes can be cut nearly in half with little to no effect on the device temperature span and cooling power normalized by the refrigerant mass.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Influence of crystallographic orientation and applied magnetic field on domain structure in duplex stainless steel studied using magnetic force microscopy

Highlights: • Ferrite phase in a duplex stainless steel consists of stripe type domains. • Domain contrast decreases with deviation of plane normal from <100>. • Domain width increases with deviation of plane normal from <100>. • Domain alignment with applied field observed along <100> directions. • Grain boundary stray field is a function of misorientation between grains. - Abstract: The paper investigates the local micro-magnetization behavior in duplex stainless steel (DSS) using magnetic force microscopy (MFM). DSS has equal amount of austenite phase in ferrite matrix. The MFM imaging clearly differentiates ferrite phase (ferromagnetic) from the austenite phase (paramagnetic) due to the maze type magnetic domains present in the ferrite phase. The magneto crystalline anisotropic effect on the domain structure is discussed with the support of electron backscatter diffraction (EBSD) measurements. The MFM phase contrast and domain width are correlated with the orientation of surface normal with respect to the easy axis of magnetization (<100>). The influence of external magnetic field (±127 kA/m) application on the domain structure is studied as a function of the grain orientation and the leakage field at the grain boundaries is analyzed based on the mis-orientation between the grains.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Room temperature magnetic ordering and analysis by bound magnetic polaron model of Yb3+ doped nanocrystalline zinc oxide (Zn0.98Yb0.02O)

Highlights: • ZnO and Yb doped ZnO are synthesized by co-precipitation method. • Rietvelt anlysis of XRD patterns confirms the complete substitution of Yb{sup 3+} in ZnO. • Vacancy and defect mediated RTFM is introduced in doped ZnO. • BMP model successfully analyze the magnetic property of Zn{sub 0.98}Yb{sub 0.02}O. - Abstract: Nanocrystalline ZnO and Yb-doped ZnO (Zn{sub 0.98}Yb{sub 0.02}O) are prepared by simple co-precipitation method. The pure crystallographic phases of ZnO and Zn{sub 0.98}Yb{sub 0.02}O are confirmed by Rietveld analyses of XRD patterns. Raman and photoluminescence spectra recorded at room temperature (RT) indicates that lattice defects and oxygen vacancy in Zn{sub 0.98}Yb{sub 0.02}O is more than that of ZnO. Magnetic measurements of ZnO and Zn{sub 0.98}Yb{sub 0.02}O are carried out from 300 to 5 K. Ferromagnetic ordering is observed in Zn{sub 0.98}Yb{sub 0.02}O at RT and the strength of the ordering increases with the lowering of temperature. Ferromagnetism of Zn{sub 0.98}Yb{sub 0.02}O is attributed to the oxygen vacancy introduced by annealing in vacuum. Magnetization vs. temperature curve is well fitted by the combination of 3D spin wave and Curie-Weiss law, which suggest simultaneous presence of para- and ferro-magnetic phases in Zn{sub 0.98}Yb{sub 0.02}O. Ferromagnetic ordering is successfully explained by vacancy mediated bound-magnetic polaron model.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Cr 2.37 Ga 3 Se 8 : A Quasi-Two-Dimensional Magnetic Semiconductor

We present a novel magnetic semiconductor, Cr 2.37 Ga 3 Se 8 , synthesized by partially replacing magnetic Cr 3+ in antiferromagnetic Cr 5+δ Se 8 with nonmagnetic Ga 3+ . The crystal structure of Cr 2.37 Ga 3 Se 8 was determined by both powder and single-crystal X-ray diffraction. The title compound crystallizes in a monoclinic structure with space group C2/m (No. 12). In Cr 2.37 Ga 3 Se 8 , the Cr atoms are surrounded by 6 Se atoms and form filled octahedral clusters, while Ga atoms are centered in the Se 4 tetrahedral clusters. The two kinds of clusters pack alternatingly along the c-axis, which results in a quasi-two-dimensional layered structure. The magnetization (M) measurement shows the development of short-range ferromagnetic coupling below the Curie-Weiss (CW) temperature θ CW ~ 92 K, evidenced by the nonlinear field dependence of M. However, the magnetic susceptibility exhibits a peak at low fields at ~18 K, indicating the existence of an antiferromagnetic interaction as well. Electronic structure calculations using the WIEN2k program in the local spin density approximation indicate that the magnetism arises exclusively from local moments of the Cr atoms. Here, the electrical resistivity measurement of the Cr 2.37 Ga 3 Se 8 sample confirms that this material is a semiconductor with the band gap ~0.26 eV. Meanwhile, the experimental band gap (~0.26 eV) is close to the theoretical prediction using the WIEN2k program (~0.35 eV).

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

The electronic structure, crystal fields, and magnetic anisotropy in RECo 5 magnets

The current progress in describing rare-earth-based magnets' electronic structure and magnetic properties is discussed. We use several currently popular electronic structure methods to show the typical values of critical parameters that define the physics of RECo 5 (RE = rare earth atom) materials. The magnetic moments and magnetic anisotropy of 4f atoms are obtained using several approaches, including anisotropic 4f-charge density-constrained DFT and DFT+HI methods. We also suggest the introduction of "penalty" functional for obtaining correct variational total energy in the traditional Hund's rule-constrained DFT-based techniques. The applicability and future extensions are discussed. The proposed combination of methods is potentially suitable for high-throughput computational searches of new rare-earth-containing magnetic materials.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2024

Inhomogeneous magnetic ordered state and evolution of magnetic fluctuations in Sr⁢(Co 1–x ⁢Ni x ) 2 ⁢P 2 revealed by 31 P NMR

SrCo 2 ⁢P 2 with a tetragonal structure is known to be a Stoner-enhanced Pauli paramagnetic metal being nearly ferromagnetic. Recently J. Schmidt et al. [Phys. Rev. B 108, 174415 (2023)] reported that a ferromagnetic ordered state is actually induced by a small Ni substitution for Co of x = 0.02 in Sr⁢(Co 1–x ⁢Ni x ) 2 ⁢P 2 where an antiferromagnetic ordered phase also appears by further Ni substitution with x = 0.06–0.35. Here, in this work, using nuclear magnetic resonance (NMR) measurements on 31 P nuclei, we have investigated how the magnetic properties change by the Ni substitution in Sr⁢(Co 1–x ⁢Ni x ) 2 ⁢P 2 from a microscopic point of view, especially focusing on the evolution of magnetic fluctuations with the Ni substitution and the characterization of the magnetically ordered states. The temperature dependencies of the 31 P spin-lattice relaxation rate divided by temperature (1/T 1 ⁢T) and Knight shift (K) for SrCo 2 ⁢P 2 are reasonably explained by a model where a double-peak structure for the density of states near the Fermi energy is assumed. Based on a Korringa ratio analysis using the T 1 and K data, ferromagnetic spin fluctuations are found to dominate in the ferromagnetic Sr⁢(Co 1–x ⁢Ni x ) 2 ⁢P 2 as well as the antiferromagnets where no clear antiferromagnetic fluctuations are observed. We also found the distribution of the ordered Co moments in the magnetically ordered states from the analysis of the 31 P-NMR spectra exhibiting a characteristic rectangular-like shape.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Local strain-dependent electronic structure and perpendicular magnetic anisotropy of a MnGaN 2D magnetic monolayer

Local strain-dependent spin-polarized electronic structure of a two-dimensional (2D) magnetic layer is an exciting property for practical applications. For example, it holds the promise for advanced ultrathin spintronic nanodevices with customized electronic and magnetic properties by local strain engineering. Here, we demonstrate that the spin-polarized electronic structure of a 2D manganese gallium nitride (MnGaN-2D) magnetic monolayer is sensitive to intrinsic local lattice strain, as proven by first-principles calculations and indicated by scanning tunneling spectroscopy measurements. Atomic resolution images reveal a highly non-Gaussian lattice spacing/strain distribution, while the spectroscopy reveals variations in the electronic density of states. Simulations of the MnGaN-2D monolayer based on first-principles calculations, including both isotropic and anisotropic strains, confirm a highly strain-dependent manganese partial density of states. Spin-orbit coupling is included which indicates either out-of-plane perpendicular magnetic anisotropy (PMA) or in-plane magnetic anisotropy, dependent on the type of strain whether compressive or tensile, suggesting that MnGaN-2D is magnetoelastic. The MnGaN-2D PMA is further supported by superconducting quantum interference device magnetometry measurements which reveal a high spin polarization of ~ 79 % at room temperature.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Concentration dependence of the wings of a dipole-broadened magnetic resonance line in magnetically diluted lattices

The singularities of the time autocorrelation functions (ACFs) of magnetically diluted spin systems with dipole–dipole interaction (DDI), which determine the high-frequency asymptotics of autocorrelation functions and the wings of a magnetic resonance line, are studied. Using the self-consistent fluctuating local field approximation, nonlinear equations are derived for autocorrelation functions averaged over the independent random arrangement of spins (magnetic atoms) in a diamagnetic lattice with different spin concentrations. The equations take into account the specificity of the dipole–dipole interaction. First, due to its axial symmetry in a strong static magnetic field, the autocorrelation functions of longitudinal and transverse spin components are described by different equations. Second, the long-range type of the dipole–dipole interaction is taken into account by separating contributions into the local field from distant and near spins. The recurrent equations are obtained for the expansion coefficients of autocorrelation functions in power series in time. From them, the numerical value of the coordinate of the nearest singularity of the autocorrelation function is found on the imaginary time axis, which is equal to the radius of convergence of these expansions. It is shown that in the strong dilution case, the logarithmic concentration dependence of the coordinate of the singularity is observed, which is caused by the presence of a cluster of near spins whose fraction is small but contribution to the modulation frequency is large. As an example a silicon crystal with different {sup 29}Si concentrations in magnetic fields directed along three crystallographic axes is considered.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Fractal Dimension Effect on the Magnetization Curves of Exchange-Coupled Clusters of Magnetic Nanoparticles

The effect of the fractal dimension of exchange-coupled clusters of magnetic nanoparticles on their magnetization curves is predicted by scaling estimates. These predictions form the basis for the experimental technique used for determining the fractal dimension of nanoparticle clusters from the magnetization curves. We estimate the reliability of determining the dimension by such methods with the help of micromagnetic simulation. It is shown that the effective dimension of magnetic correlation volumes, which is determined from analysis of the magnetization approaching saturation, is in conformity with the dimension of fractal clusters determined from analysis of their morphology. The dimension estimated from analysis of the coercive field on the particle size in a physically natural situation of the dipole–dipole interaction between nanoparticles provides estimates of the cluster dimension, which strongly differs from estimates obtained from analysis of their morphology.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Magnetization Reversal of Permalloy Microparticles with the Configuration Anisotropy by Magnetic-Force Microscopy

Abstract—Magnetic force microscopy has been used to study the distribution of the magnetization in permalloy microparticles with a configurational anisotropy. The triangular particles with different degrees of concavity of the lateral sides have been studied. An analysis of the results enables us to state that the particles can be in several quasi-homogeneous stable states. It is shown that the particle magnetization reversal can occur both stepwise and also via an intermediate state in the dependence on the particle orientation. It is demonstrated that the quasi-homogeneous magnetization orientation in a particle can be changed by a magnetic-force microscope probe.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Effect of Ion (Ar{sup +}) Irradiation on Cluster Magnetism and Magnetic Interactions in Fe{sub 67}Cr{sub 18}B{sub 15} Amorphous Alloy

The comparison of the resonance magnetic absorption spectra with the data on structure and magnetic properties of Fe{sub 67}Cr{sub 18}B{sub 15} amorphous samples has shown that a randomly inhomogeneous medium of amorphous alloy is multiphase. Two types of samples with the same chemical composition, but with a different clusterized structure, and the use of (Ar{sup +}) ion irradiation in the experiment made it possible to separate four basic phases with different magnetic properties. The basic phase α-(Fe,Cr) contains large clusters of D < 400 Å in size with a tendency to phase separation of iron (α-Fe) and chromium (α-Cr), which under irradiation, enhances the competing FM and AFM magnetic interactions and increases the intensity of the resonance magnetic absorption lines associated with α-Fe and α-Cr. The phase Fe{sub 3}B (D < 100 Å) is detected by independent line in the resonance absorption spectra only when its groupings are isolated from the α-(Fe,Cr) metal phase clusters. The fourth phase contains precluster groupings and disappears when the sample is irradiated.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Bright Gamma-Ray Flares Powered by Magnetic Reconnection in QED-strength Magnetic Fields

Strong magnetic fields in the magnetospheres of neutron stars (NSs) (especially magnetars) and other astrophysical objects may release their energy in violent, intense episodes of magnetic reconnection. While reconnection has been studied extensively, the extreme field strength near NSs introduces new effects: radiation cooling and electron–positron pair production. Using massively parallel particle-in-cell simulations that self-consistently incorporate these new radiation and quantum-electrodynamic effects, we investigate relativistic magnetic reconnection in the strong-field regime. We show that reconnection in this regime can efficiently convert magnetic energy to X-ray and gamma-ray radiation and thus power bright, high-energy astrophysical flares. Rapid radiative cooling causes strong plasma and magnetic field compression in compact plasmoids. In the most extreme cases, the field can approach the quantum limit, leading to copious pair production.

79 ASTRONOMY AND ASTROPHYSICS↗