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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 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Crystal and Magnetic Structures of Granular Powder Spinel Mn–Zn and Ni–Zn Ferrites

Some specific features of the crystal and magnetic structures of granular powder spinel-like ferrites Mn{sub 0.160}Mg{sub 0.404}Zn{sub 0.448}Fe{sub 2}O{sub 4}, Mn{sub 0.676}Zn{sub 0.227}Fe{sub 0.09}Fe{sub 2}O{sub 4}, Mn{sub 0.5792}Zn{sub 0.2597}Fe{sub 0.1612}Fe{sub 2}O{sub 4}, and Ni{sub 0.32}Zn{sub 0.68}Fe{sub 2}O{sub 4} have been studied by neutron diffraction. It has been established that the crystal structure of all the studied compounds has a cubic symmetry with space group Fd3̄m. Ferrimagnetic ordering is observed in all the studied structures. Based on the experimental data, the unit cell parameters and interatomic bond lengths of the studied compounds are determined alongside with the distribution of cations between octahedral and tetrahedral crystallographic positions in their cubic crystal structure. Corresponding average magnetic moments are calculated for different positions in their cubic structure. Some structural mechanisms of the formation of magnetic properties depending on the level of doping and the size of powder grains are discussed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Effects of Radiation Reaction Physics on High-Current Power Flow

In this study, we examine the effects of the radiation reaction force on electrons in a radial magnetically insulated transmission line (MITL) near a load with peak currents of 60+ MA. More specifically, we study the differences in electron motion and kinetic energy with or without radiation reaction physics using a novel guiding center drift approach that incorporates E $\times$ B and ∇B drifts. A key finding of this study is that an electron's magnetic moment, which would be conserved when radiation reaction physics is not incorporated, can be significantly reduced in magnetic fields on the order of 10,000's T when radiation reaction is included. The reduction of magnetic moment gives rise to a significant reduction in cycloidal kinetic energy as well as a reduction in the electron's ∇B drift.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
NASA NTRS1974

Theoretical and observational analysis of spacecraft fields

In order to investigate the dipolar and nondipolar contributions of spacecraft magnetic fields, a simple magnetic field model is proposed. This model consists of a number N of randomly oriented dipoles of strength M sub k in a given volume. Two sets of formulas are presented that give the rms multipole field components, first, for isotropic orientations of the dipoles at given positions and second, for isotropic orientations of the dipoles distributed uniformly throughout a cube or sphere. The statistical results for a cube (8 cu m in size) together with individual examples computed numerically show the following features. Beyond about 2- to 3-m distance from the center of the cube the field is dominated by an equivalent dipole. The magnitude of the magnetic moment of the dipolar part is approximated by N to the 1/2 power times M for equal magnetic moments or generally by the Pythagorean sum of the dipole moments. The radial component tend to be greater than either of the transverse components for the dipole portion as well as for the nondipolar field contributions.

Neubauer, F. M.↗
DOE OSTI2023

Activity-induced migration of viscous droplets on a solid substrate

Active matter exploits motion to induce changes in shape and conformation via external input. Here, in this paper, we establish theoretically that viscous liquid droplets containing magnetic nanoparticles with frozen-in magnetic moments, sitting on a solid substrate and surrounded by an ambient gas phase, can deform and migrate under the influence of a magnetic torque. The effect arises because the collective rotation of the magnetic nanoparticles at the liquid–gas interface tilts the droplet away from a symmetric configuration, breaks the reflection symmetry with respect to the centre axis, and leads to a left–right asymmetry of the contact angles. A sufficiently strong magnetic torque leads the contact angles to overcome hysteresis effects leading the droplet to migrate. We develop a general framework to explain how symmetry-breaking affects droplet migration. Thus previous results of droplet spreading and migration can be recovered as special cases. Such droplets can be employed as agents in active surfaces and can move against gravity, chemical and thermal gradients, providing a mechanism that could be utilized by both industry and medicine.

Aggarwal, A.↗
NASA NTRS1968

Intrinsic Magnetic Properties of the Lunar Body

Preliminary analysis of magnetic measurements by Explorer 35 in lunar orbit suggested an upper limit of 4 x 10(exp 20) gauss-cm3 for the magnetic moment of the moon. A more detailed analysis of a larger body of Explorer 35 data from measurements in the earth's magnetic tail has subsequently been performed. Reversal of the ambient tail field by 180deg when the moon and spacecraft traverse the neutral sheet permits a separation of permanent and induced field contributions to the total field observed near the moon. When compared to calculated permanent and induced field effects, the results of this analysis lead to new upper limits of 102' gauss-cm3 on the lunar magnetic moment and 4y on the lunar surface field. Limiting the moment induced in the moon by the magnetotail field permits an upper limit of 1.8 to be set on the bulk relative magnetic permeability of the moon.

Behannon, Kenneth W.↗
DOE OSTI2021

Structural, vibrational, thermal, and magnetic properties of mullite-type NdMnTiO 5 ceramic

Mullite-type $R$Mn 2 O 5 ($R$ = Y, rare-earth element) ceramics are of ongoing research attention because of their interesting crystal-chemical and magnetic properties. We report nuclear and magnetic structures of NdMnTiO 5 together with its spectroscopic, thermogravimetric, and magnetic properties. The polycrystalline sample is prepared by solid-state synthesis and characterized from neutron and X-ray powder diffraction data Rietveld refinements. NdMnTiO 5 crystallizes in the orthorhombic space group $Pbam$ with metric parameter $a$ = 755.20(1) pm, $b$ = 869.91(1) pm, $c$ = 582.42(1) pm, and $V$ = 382.62(1) 10 6 pm 3 . The Mn 3+ and Ti 4+ cations are observed to be located in the octahedral and pyramidal sites, respectively. The vibrational features in these polyhedral sites are characterized by Raman and Fourier transform infrared spectroscopes. The higher decomposition temperature of NdMnTiO 5 , compared to other $R$Mn 2 O 5 phases, is explained in terms of the higher bond strength of Ti-O bonds than those of Mn-O bonds. Temperature-dependent DC magnetic susceptibility suggests a paramagnetic to antiferromagnetic phase transition at 43(1) K. Inverse susceptibility in the paramagnetic region above 120 K follows the Curie-Weiss law, resulting in a magnetic moment of 6.33(1) μ B per formula unit. Neutron diffraction data collected at 7.5 K reveal that the magnetic moments of Nd 3+ and Mn 3+ in NdMnTiO 5 are incommensurately ordered with a propagation vector $k$ = (0, 0.238, 0.117).

36 MATERIALS SCIENCE↗
DOE OSTI2019

Study of Nucleation/Annihilation Process and Vortices Characteristics in Co/Py Rectangular Bilayers

Vortices are topological structures, which are characterized by circular organization of magnetic moments and by chirality. In this paper, we investigate the impact of film lateral dimensions and thicknesses on magnetization reversibility by applying an in-plane external magnetic field on Co(t{sub Co})/Py (3 nm) bilayers where the Py is the permalloy, a ferromagnetic alloy of nickel and iron (Ni{sub 80}Fe{sub 20}). The study is achieved by using appropriate micromagnetic simulations. We also show that the vortices number and their sizes can be controlled by playing on the lateral dimensions and the thickness of the bilayer.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Transition metal partially supported graphene: Magnetism and oscillatory electrostatic potentials

Using first-principles calculations here, we show that Mn and Cr layers under graphene exhibit almost zero magnetic moment due to anti-ferromagnetic order, while ferromagnetic coupling in Fe, Co, and Ni leads to large magnetic moment. The transition metal partially supported graphene, with a mixture of supported and pristine areas, exhibits an oscillatory electrostatic potential, thus alternating the electric field across the supported and pristine areas. Such an effect can be utilized to control mass transport and nanostructure self-organization on graphene at the atomic level.

36 MATERIALS SCIENCE↗
DOE OSTI2025

On transport of electrons in a magnetized plasma sheath

Electron trajectories are analyzed in the plasma sheath region in a magnetic field that intersects the surface at a shallow angle. Depending on the size of the Debye width relative to the electron gyroradius, λ D /ρ e , an electron either drifts in the sheath electric field or follows a sequence of reflections (“bouncing”) on the surface before reversing its parallel velocity. For thin sheath, λ D /ρ e ≪ 1, the conservation of the electron magnetic moment can be violated, depending on the ratio of the electron perpendicular and parallel velocities V ⊥ /V || and the magnetic field pitch angle with respect to the surface. Small-scale waviness of the surface can strongly amplify this effect, leading to violation of the magnetic moment conservation even for λ D /ρ e ≳ 1, which opens a channel of anomalous radial transport for electrons in plasma devices.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

X-ray spectroscopy of current-induced spin-orbit torques and spin accumulation in Pt / 3 d -transition-metal bilayers

An electric current flowing in Pt, a material with strong spin-orbit coupling, leads to spins accumulating at the interfaces by virtue of the spin Hall effect and interfacial charge-spin conversion. We measure the influence of these interfacial magnetic moments onto adjacent 3$d$ transition-metal layers by x-ray absorption spectroscopy and x-ray magnetic circular dichroism in a quantitative and element-selective way, with sensitivity below 10 -5 $_{μB}$ per atom. In Pt(6 nm)/Co(2.5 nm), the accumulated spins cause a deviation of the Co magnetization direction, which corresponds to an effective spin Hall angle of 0.08. The spin and orbital magnetic moments of Co are affected in equal proportion by the absorption of the spin current, showing that the transfer of orbital momentum from the recently predicted orbital Hall effect is either below our detection limit, or not directed to the 3$d$ states of Co. For Pt/NM (NM = Ti, Cr, Cu), we find upper limits for the amount of injected spins corresponding to about 3 × 10 -6 $_{μB}$ per atom.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

The Impurity Magnetic Susceptibility of Semiconductors in the Case of Direct Exchange Interaction in the Ising Model

The numerical simulation was applied to study the temperature dependence of the impurity magnetic susceptibility. The direct exchange interaction of the impurity magnetic moments randomly distributed in space was considered within the Ising model. When the temperature in a system decreases, the magnetic susceptibility behavior in this system ceases to comply with the Curie law, which is associated with the formation of a spin glass phase. It is shown that the expression of the preexponential factor in the formula for the direct exchange interaction considerably influences the temperature dependence of the magnetic susceptibility only in the case of ferromagnetic exchange.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Halo structure of 17 C

17 C has three states below the 16 C + n threshold with quantum numbers \(J^{P}=3/2^{+}, 1/2^{+}, 5/2^{+}\) . These states have relatively small neutron separation energies compared to the neutron separation and excitation energies of 16 C. This separation of scales motivates our investigation of 17 C in a halo effective field theory (Halo EFT) with a 16 C core and a valence neutron as degrees of freedom. In this paper, we discuss various properties of the three states such as electric radii, magnetic moments, electromagnetic transition rates and capture cross sections. In particular, we give predictions for the charge radius and the magnetic moment of the \( 1/2^{+}\) state and for neutron capture on 16 C into this state. Furthermore, we discuss the predictive power of the Halo EFT approach for the \( 3/2^{+}\) and \( 5/2^{+}\) states which are described by a neutron in a D -wave relative to the core.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

Noncollinear antiferromagnetic order in the buckled honeycomb lattice of magnetoelectric Co 4 Ta 2 O 9 determined by single-crystal neutron diffraction

Co 4 Ta 2 O 9 exhibits a three-dimensional magnetic lattice based on the buckled honeycomb motif. It shows unusual magnetoelectric effects, including the sign change and nonlinearity. These effects cannot be understood without the detailed knowledge of the magnetic structure. Herein, we report neutron diffraction and direction-dependent magnetic susceptibility measurements on Co 4 Ta 2 O 9 single crystals. In this work, below 20.3 K, we find a long-range antiferromagnetic order in the alternating buckled and flat honeycomb layers of Co 2+ ions stacked along the c axis. Within experimental accuracy, the magnetic moments lie in the ab plane. They form a canted antiferromagnetic structure with a tilt angle of ~14° at 15 K in the buckled layers, while the magnetic moments in each flat layer are collinear. This is directly evidenced by a finite (0, 0, 3) magnetic Bragg peak intensity, which would be absent in the collinear magnetic order. The magnetic space group is C2/c'. It is different from the previously reported C2/c' group, also found in the isostructural Co 4 Nb 2 O 9 . The revised magnetic structure successfully explains the major features of the magnetoelectric tensor of Co 4 Ta 2 O 9 within the framework of the spin-flop model.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2026

Deep generative learning of magnetic frustration in artificial spin ice from magnetic force microscopy images

Increasingly large datasets of microscopic images with nanoscale resolution facilitate the development of machine learning methods to identify and analyze subtle physical phenomena embedded within the images. In this work, microscopic images of honeycomb lattice spin-ice samples serve as datasets from which we automate the calculation of net magnetic moments and directional orientations of spin-ice configurations. In the first stage of our workflow, machine learning models are trained to accurately predict magnetic moments and directions within spin-ice structures. Variational Autoencoders (VAEs), an emergent unsupervised deep learning technique, are employed to generate high-quality synthetic magnetic force microscopy (MFM) images and extract latent feature representations, thereby reducing experimental and segmentation errors. The second stage of proposed methodology enables precise identification and prediction of frustrated vertices and nanomagnetic segments, effectively correlating structural and functional aspects of microscopic images. This facilitates the design of optimized spin-ice configurations with controlled frustration patterns, enabling potential on-demand synthesis.

36 MATERIALS SCIENCE↗
NASA NTRS1981

Magnetic fields and charged particles around major planets and their satellites

It is noted that whereas Jupiter and Saturn have magnetospheres whose large-scale structure can be understood by analogy with earth, the ways in which the magnetospheres differ are of great interest. At earth, large-scale processes are dominated by convective flows of plasma driven by the solar wind. At Jupiter, centrifugal effects that are driven by planetary rotation are critical. Magnetic particle sources include not only the ionosphere and solar wind (as at earth) but also satellites and rings. The internal planetary magnetic moments controlling the scale of the magnetosphere differ by orders of magnitude between Jupiter and earth. It is pointed out that where the magnetic moments have been modeled from spacecraft data, the restricted spatial sampling has biased the results and limited confidence in details of the models. Voyager data suggest that Io may itself be magnetized and surrounded by an entirely unfamiliar type of magnetosphere.

Kivelson, M. G.↗
DOE OSTI2017

Correlation between magnetostriction and magnetic structure in pseudobinary compounds Tb(Co 1-x Fe x ) 2

Giant low-field magnetostriction has been achieved in pseudobinary Laves phase compounds RR’T 2 (R and R’: rare earth elements; T: transition metal elements) around the ferromagnetic - ferromagnetic (ferro.-ferro.) transition temperature. Evolution of the magnetic structure across such transition requires comprehensive investigation. In this work, pseudobinary system Tb(Co 1-x Fe x ) 2 is selected to investigate the evolution of local magnetic moment, for which two end terminals TbCo 2 and TbFe 2 possess the rhombohedral (R) structure at the ferromagnetic state but with different magnetic ordering temperatures (T C ). Magnetometry measurements reveal that a composition independent ferromagnetic - ferromagnetic transition occurs at ~100 K despite the increased Curie temperature T C with raised Fe concentration in the Tb(Co 1-x Fe x ) 2 . Synchrotron XRD data reveal that both the lattice parameter and the lattice strain along the <111> direction are abnormally temperature dependent, accompanied with experimentally observed magnetostriction abnormality at 100 K. In-situ neutron powder diffraction (NPD) results show that the local magnetic moments of T2 (9e site) atoms are also abnormally temperature dependent, which is larger at 100 K than that at a lower temperature 50 K. Such findings indicate close correlations between the magnetic structure and the magnetostrictive effect in the pseudobinary RT 2 compounds.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Spin Seebeck effect near the antiferromagnetic spin-flop transition

In this work, we develop a low-temperature, long-wavelength theory for the interfacial spin Seebeck effect (SSE) in easy-axis antiferromagnets. The field-induced spin-flop (SF) transition of Néel order is associated with a qualitative change in SSE behavior: Below SF, there are two spin carriers with opposite magnetic moments, with the carriers polarized along the field forming a majority magnon band. Above SF, the low-energy, ferromagneticlike mode has magnetic moment opposite the field. This results in a sign change of the SSE across SF, which agrees with recent measurements on Cr 2 O 3 /Pt and Cr 2 O 3 /Ta devices. In our theory, SSE is due to a Néel spin current below SF and a magnetic spin current above SF. Using the ratio of the associated Néel to magnetic spin-mixing conductances as a single constant fitting parameter, we reproduce the field dependence of the experimental data and partially the temperature dependence of the relative SSE jump across SF.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Poor confinement in stellarators at high energy II

This work discusses particle resonances in stellarators. There are two important effects. First, resonances provide locations for Alfvén modes, which can cause significant particle loss. Second, if a resonance matches the period of the modulation of the equilibrium field magnitude it produces islands in particle orbits increasing in size with particle energy, also possibly causing loss. A previous publication suffered from a restriction to the consideration of deeply passing particle orbits, clearly showing the resonance islands. Large particle magnetic moment increases the effect of particle cross field drift, essential for this phenomenon, so passing particles with larger values of magnetic moment give larger islands. It is possible to avoid designs exhibiting such resonances.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗