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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 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Microscopic Phase Diagram of Eu(Fe 1-x Ni x )As 2 ( x = 0,0.04) Under Pressure

This study will go to establish the microscopic P-T phase diagram of recent 112-type iron-pnictides Eu(Fe 1-x Ni x )As- 2 (x = 0,0.04), high-pressure synchrotron Mossbauer spectroscopy experiments in 151 Eu and 57 Fe have been performed. In EuFeAs 2 application of pressure completely suppresses the itinerant electron magnetism from the Fe sublattice and the local-moment magnetism in Eu ions at similar to ~10 and similar to ~11.6 GPa, respectively. High-pressure x-ray diffraction experiments in EuFeAs 2 reveal an anomalous change in the lattice parameters and a discontinuity in volume around 10 GPa, suggesting an isostructural transition at this pressure. With Ni-doping (x = 0.04), a collapse of local magnetic order occurs at similar to ~8GPa, a lower critical pressure compared with the parent compound. In both systems, the suppression of local-moment magnetism is associated with a significant increase of mean valence in Eu ions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS2010

EPR Imaging at a Few Megahertz Using SQUID Detectors

An apparatus being developed for electron paramagnetic resonance (EPR) imaging operates in the resonance-frequency range of about 1 to 2 MHz well below the microwave frequencies used in conventional EPR. Until now, in order to obtain sufficient signal-to-noise radios (SNRs) in conventional EPR, it has been necessary to place both detectors and objects to be imaged inside resonant microwave cavities. EPR imaging has much in common with magnetic resonance imaging (MRI), which is described briefly in the immediately preceding article. In EPR imaging as in MRI, one applies a magnetic pulse to make magnetic moments (in this case, of electrons) precess in an applied magnetic field having a known gradient. The magnetic moments precess at a resonance frequency proportional to the strength of the local magnetic field. One detects the decaying resonance-frequency magnetic- field component associated with the precession. Position is encoded by use of the known relationship between the resonance frequency and the position dependence of the magnetic field. EPR imaging has recently been recognized as an important tool for non-invasive, in vivo imaging of free radicals and reduction/oxidization metabolism. However, for in vivo EPR imaging of humans and large animals, the conventional approach is not suitable because (1) it is difficult to design and construct resonant cavities large enough and having the required shapes; (2) motion, including respiration and heartbeat, can alter the resonance frequency; and (3) most microwave energy is absorbed in the first few centimeters of tissue depth, thereby potentially endangering the subject and making it impossible to obtain adequate signal strength for imaging at greater depth. To obtain greater penetration depth, prevent injury to the subject, and avoid the difficulties associated with resonant cavities, it is necessary to use lower resonance frequencies. An additional advantage of using lower resonance frequencies is that one can use weaker applied magnetic fields: For example, for a resonance frequency of 1.4 MHz, one needs a magnetic flux density of 0.5 Gauss approximately the flux density of the natural magnetic field of the Earth.

Hahn, Inseob↗
DOE OSTI2019

Electronic structures and magnetic performance related to spintronics of Sr{sub 0.875}Ti{sub 0.125}S

In this study, we have used the first-principle approaches of density functional theory to determine the electronic and magnetic performances related to spintronics applications of titanium (Ti)-substituted SrS such as Sr{sub 1−x}Ti{sub x}S at concentration x = 0.125. The results of electronic and magnetic properties by using TB–mBJ potential revealed that Sr{sub 0.875}Ti{sub 0.125}S compound is half-metallic ferromagnetic with a half-metallic gap and a spin polarization of 100%. The ferromagnetic nature of Sr{sub 0.875}Ti{sub 0.125}S material is confirmed by the ferromagnetic coupling between magnetic moments of Ti, Sr and S atoms. The total magnetic moment of integer Bohr magneton of 2 μ{sub B} and the large half-metallic gap of 1.245 suggest that this compound is a true half-metallic ferromagnet.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Absolute Magnetometry with He3

We report development of a highly accurate (parts per billion) absolute magnetometer based on 3He NMR. Optical pumping polarizes the spins, long coherence times provide high sensitivity, and the 3He electron shell effectively isolates the nuclear spin providing accuracy limited only by corrections including materials, sample shape, and magnetization. Our magnetometer was used to confirm calibration, to 32 ppb, of the magnetic-field sensors used in recent measurements of the muon magnetic moment anomaly g-2, which differs from the standard model by 2.4 ppm. With independent determination of the magnetic moment of 3He, this work will lead the way to a new absolute magnetometry standard.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

High-performance permanent-magnet materials based on CeFe 12

We perform first-principles calculations on the Mo/Zr-alloyed ThMn 12 -structure prototype CeFe 12 to explore its electronic and magnetic properties and potential for permanent magnet applications. A recent experiment has shown that the Mo/Zr-alloyed CeFe 12 phase with the symmetry 𝐼⁢4/𝑚⁢𝑚⁢𝑚 can be stabilized in bulk. It encourages an investigation into the intrinsic magnetic characteristics of the base structure CeFe 12 and the effect of transition metal alloying in it. Our calculations reveal that the base structure prototype CeFe 12 in its tetragonal phase exhibits uniaxial magnetic anisotropy with a magnetic anisotropy energy (𝐾 1 ) ∼ 1 MJ/m −3 and a substantial magnetic moment of ∼ 1.8T, showing its promise as a permanent magnet. The introduction of the stabilizing transition metals Zr, Mo, and W reduces these values but still keeps the materials very promising. Notably, when 50% of Ce is substituted by Sm in Mo-alloyed CeFe 12 , the 𝐾 1 is significantly enhanced, accompanied by a fairly decent magnetic moment of ∼ 1.2T. These findings establish this alloy as a strong candidate for high-performance permanent magnet applications. In conclusion, this study emphasizes the importance of strategic element substitution and site selection in transition metal-alloyed CeFe 12 to achieve both structural stability and remarkable magnetic properties.

Density of states↗
DOE OSTI2018

Tunable Magnetism and Half Metallicity in Ti-Doped Heusler Alloy Co{sub 2}CrAl: First-Principles Calculations

Using the first-principles calculations within density functional theory (DFT), we investigated magnetism, electronic structures, and half-metallicity stability of Heusler compound Co{sub 2}Cr{sub 1−x}Ti{sub x}Al. Besides, the origin of the half-metallic energy gap of Co{sub 2}CrAl is also revealed. With Ti concentration increases, the magnetic moment of the Cr atom linearly increases, while that of Co and Cr atoms linearly decreases The total magnetic moment of Co{sub 2}Cr{sub 1−x} Ti{sub x}Al agrees with the Slater–Pauling rule very well. The Fermi level shifts from a low energy zone of the minority spin gap to a highenergy zone with increasing Ti concentration x, and it lies in the middle of the gap when x = 0.5. The corresponding doped compound Co{sub 2}Cr{sub 0.5}Ti{sub 0.5}Al therefore possesses the most stable half metallicity.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Understanding the origin of magneto-crystalline anisotropy in pure and Fe/Si substituted SmCo 5

In this paper, we report magneto-crystalline anisotropy of pure and Fe/Si substituted SmCo5. The calculations were performed using the advanced density functional theory (DFT) including onsite electron-electron correlation and spin-orbit coupling. Si substitution substantially reduces both the uniaxial magnetic anisotropy and the magnetic moment. Fe substitution with the selective site, on the other hand, enhances the magnetic moment with a limited chemical stability. The magnetic hardness of the SmCo5 is governed by the Sm 4f localized orbital contribution. The 4f density of states (DOS) becomes flat and split with the substitution of Co (2c) with Si/Fe atoms, except with the Fe substitution at 3 g sites. It is also confirmed that Si substitution favors the thermodynamic stability on contrary to the diminished magnetic and anisotropic effects in SmCo5 at either sites.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Firefly Algorithm Applied to Noncollinear Magnetic Phase Materials Prediction

In most noncollinear crystal magnets, the number of metastable states is quite large and any calculation that tries to predict the ground state can fall into one of the possible metastable phases. In this work, we generalize the population based meta-heuristic firefly algorithm to the problem of the noncollinear magnetic phase ground state prediction within density functional theory (DFT). We extend the different steps in the firefly algorithm to this specific problem by using polarized constrained DFT calculations, whereby using Lagrange multipliers the directions of the atom magnetic moments remain fixed. By locking the directions of the magnetic moments at each search iteration, the method allows one to explore the entire Born–Oppenheimer energy surface of existing and physically plausible noncollinear configurations present in a crystal. Finally, we demonstrate that the number of minima can be large, which restrains the use of exhaustive searches.

Algorithms↗
DOE OSTI2026

Axionlike particles and sterile neutrinos solve the 𝐵 → 𝐾⁢$𝜈⁢\bar{𝜈}$ and 𝐵 → 𝜋⁢𝐾 puzzles

The recent measurement of the branching ratio of 𝐵 + → 𝐾 + +inv (where “inv” denotes invisible states) by the Belle II Collaboration is enhanced relative to the standard model expectation by 2.7⁢𝜎. An older puzzle persists in measurements of the branching ratios and 𝐶⁢𝑃 asymmetries of 𝐵 → 𝜋⁢𝐾 decays. We address these two anomalies in flavor-changing neutral current 𝐵 decays, with a short-lived axionlike particle (ALP) with mass close to that of the 𝜋 0 . In the model with the minimum number of new couplings, the ALP has couplings to the photon, top quark and a heavy sterile neutrino. The ALP contributes to the 𝐵 → 𝜋 0 ⁢𝐾 decays by mixing with the 𝜋 0 . It contributes to 𝐵 + → 𝐾 + + inv by its off-shell coupling to sterile neutrino pairs. The model can explain the excess in the total rate, but not the observed distribution of signal events. We make predictions for all 𝐵 → 𝐾 (*) + inv modes and for the rare kaon decays, 𝐾 + → 𝜋 + + inv and 𝐾 𝐿 → 𝜋 0 + inv. We find an appreciable contribution to the magnetic moment of the muon, and negligible contributions to the magnetic moment of the electron and 𝑏 → 𝑠⁢𝑒 + ⁢𝑒 − .

axion-like particles↗
DOE OSTI2019

First-Principles Investigation of Half-Metallic Ferromagnetism of a New 1:1:1:1 Type Quaternary Heusler Compound YRhTiSi

First-principles theory was applied to study the electronic, magnetic, and half-metallic behaviors of a new Y-based equiatomic quaternary Heusler compound YRhTiSi. We will come to study the physical properties of this compound and find it has the half-metallic nature in the ferromagnetic (FM) state. The total magnetic moment of this compound YRhTiSi is 2 μ{sub B}, which follows the famous Slater-Pauling rule, Mt = Zt − 18, Mt is the total magnetic moment and Zt is the total number of valence electrons. Based on its equilibrium and strained lattice constants, the magnetic and half-metallic behaviors of this compound have been discussed in detail. And we find that the H–M gap and the band gap can be regulated through the effect of uniform strain and the tetragonal deformation. A large H–M gap of 0.48 eV has been found in our work, which is nearly larger than any previous study. Furthermore, the formation and cohesive energies have also been discussed in our work to examine the phase stability of YRhTiSi. This theoretical investigation provides further insight into the application of Y-based compounds as spintronic materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Electronic, magnetic and structural properties of CoFeVAl and CoFeV 0.5 Mn 0.5 Al

Abstract In this study, we present results of a comprehensive computational and experimental study of CoFeVAl and CoFeV 0.5 Mn 0.5 Al Heusler alloys. It is shown that while CoFeVAl exhibits a fairly large degree of spin polarization, this material is not half-metallic due to the presence of the vanadium spin-down states at the Fermi level. However, replacing 50% of vanadium with manganese results in a nearly half-metallic transition, largely due to the shift of the Fermi level towards occupied states. Moreover, the half-metallicity of CoFeV 0.5 Mn 0.5 Al is rather robust in a wide range of considered mechanical strain and under experimentally observed B2-type atomic disorder, thus making this alloy potentially suitable for practical spintronic applications. Both considered alloys exhibit ferromagnetic alignment at larger lattice constants, aside from a relatively small magnetic moment of vanadium which is anti-aligned with the magnetic moments of Co, Fe and Mn. We have synthesized both CoFeVAl and CoFeV 0.5 Mn 0.5 Al alloys in cubic structure with some structural disorder using arc melting and annealing. The structural and magnetic properties of the synthesized CoFeV 0.5 Mn 0.5 Al alloy are in good agreement with the theoretical calculations but vary slightly from the parent compound.

Physics↗
DOE OSTI2024

Coherent spin wave excitation with radio-frequency spin–orbit torque

Spin waves, collective perturbations of magnetic moments, are both fundamental probes for magnetic physics and promising candidates for energy-efficient signal processing and computation. Traditionally, coherent propagating spin waves have been generated by radio frequency (RF) inductive Oersted fields from current-carrying electrodes. An alternative mechanism, spin–orbit torque (SOT), offers more localized excitation through interfacial spin accumulation but has been mostly limited to DC to kHz frequencies. SOT driven by RF currents, with potentially enhanced pumping efficiency and unique spin dynamics, remains largely unexplored, especially in magnetic insulators. Here, we conduct a comprehensive theoretical and computational investigation into the generation of coherent spin waves via RF-SOT in the prototypical yttrium iron garnet. We characterize the excitation of forward volume, backward volume, and surface modes in both linear and nonlinear regimes, employing single and interdigitated electrode configurations. We reveal and explain several unique and surprising features of RF-SOT compared to inductive excitation, including higher efficiency, distinct mode selectivity, and directional symmetry, a ~ $3π/4$ phase offset, reduced anharmonic distortion in the nonlinear regime, and the absence of second harmonic generation. These insights position RF-SOT as a promising new mechanism for future magnonic and spintronic applications.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Effect of Zn Concentration on the Structure, Morphology, and Magnetic Behavior of Ni{sub 1 − x}Zn{sub x}Fe{sub 2}O{sub 4} Ferrofluid

In this work, we investigated the effect of doping zinc ions onto nickel ferrite upon the structure, morphology, and magnetic properties of Ni{sub 1 − x}Zn{sub x}Fe{sub 2}O{sub 4} ferrite nanoparticles (x = 0, 0.25, and 0.75) prepared via co-precipitation method. X-ray diffraction analysis showed the presence of the most intense peak corresponding to the (311) crystallographic orientation of NiFe{sub 2}O{sub 4} cubic spinel phase, and the crystallite size obtained from Scherrer formula increased from 6.8 to 11.2 nm when the Zn concentration increases from x = 0 to x = 0.75. Fourier transform infrared spectroscopy analysis confirmed the presence of a prominent band associated to the vibrations of metal ions, as a feature of spinel ferrite phase formation, observing that their band positions were very sensitive to Zn doping concentration. Transmission electron microscopy studies allowed to determinate that for all Zn concentrations, the particle sizes are around 15 nm. The magnetic properties were studied by using the vibrating sample magnetometer at room temperature. The results reveal superparamagnetic behavior determined by the shape of the hysteresis loop, presenting decreased coercive magnetic field and increased saturation magnetization, with increased zinc concentration. Additionally, from field cooling and zero field cooling curves, we can observe the typical behavior of the blocking process assembly of superparamagnetic nanoparticles. Alternate current susceptibility measurements show that the blocking temperature is frequency dependent and shifts toward higher temperatures by increasing the frequency, a characteristic of superparamagnetic, and glassy systems. Furthermore, τ{sub 0}, related to the jump attempt frequency of the magnetic moment of the nanoparticle between the opposite directions of the magnetization easy axis, is in the range of 2 × 10{sup −10} and 7 × 10{sup −13} s for the three different Zn concentrations, which agrees with characteristic of non-interacting superparamagnetic systems.

36 MATERIALS SCIENCE↗
NASA NTRS1983

The adiabatic motion of charged dust grains in rotating magnetospheres

Adiabatic equations of motion are derived for the micrometer-sized dust grains detected in the Jovian and Saturn magnetospheres by the Pioneer 10 and 11 spacecraft. The adiabatic theory of charged particle motion is extended to the case of variable grain charge. Attention is focused on the innermost and outermost limits to the grain orbit evolution, with all orbits tending to become circular with time. The parameters such as the center equation of motion, the drift velocity, and the parallel equation of motion are obtained for grains in a rotating magnetosphere. Consideration is given to the effects of periodic grain charge-discharge, which are affected by the ambient plasma properties and the grain plasma velocity. The charge-discharge process at the gyrofrequency is determined to eliminate the invariance of the magnetic moment and cause the grain to exhibit radial movement. The magnetic moment increases or decreases as a function of the gyrophase of the charge variation.

Northrop, T. G.↗
DOE OSTI2020

Unraveling magneto-structural coupling of Ni 2 MnGa alloy under the application of stress and magnetic field using in situ polarized neutron diffraction

The magneto-structural evolution of a Ni 2 MnGa single crystal was investigated by in situ polarized neutron diffraction under both magnetic field and mechanical loading. The ability to separate the nuclear and magnetic scatterings by polarized neutrons enables simultaneous observations of the twin reorientation (through twin boundary motion) and magnetic moment configuration. It is found that under a 1.0 T saturating magnetic field, twin reorientation can be activated by compressive stress and is accompanied by a realignment of the magnetic moment, which follows the easy axis of the twin variant. On the other hand, compressive stress as small as 1.0 MPa can freeze the twin reorientation. The evolution of the magnetic scattering amplitudes suggests that the change in magnetization was mainly achieved through the magnetic domain wall motion, while the twin boundary motion was blocked.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Search for low-energy neutrinos from astrophysical sources with Borexino

We report on searches for neutrinos and antineutrinos from astrophysical sources performed with the Borexino detector at the Laboratori Nazionali del Gran Sasso in Italy. Electron antineutrinos ( $\bar{ν}_e$ ) are detected in an organic liquid scintillator through the inverse β -decay reaction. In the present work we set model-independent upper limits in the energy range 1.8-16.8 MeV on neutrino fluxes from unknown sources that improve our previous results, on average, by a factor 2.5. Using the same data set, we first obtain experimental constraints on the diffuse supernova $\bar{ν}_e$ fluxes in the previously unexplored region below 8 MeV. A search for $\bar{ν}_e$ in the solar neutrino flux is also presented: the presence of $\bar{ν}_e$ would be a manifestation of a non-zero anomalous magnetic moment of the neutrino, making possible its conversion to antineutrinos in the strong magnetic field of the Sun. We obtain a limit for a solar $\bar{ν}_e$ flux of 384 cm -2 s -1 (90% C.L.), assuming an undistorted solar 8 B neutrinos energy spectrum, that corresponds to a transition probability pνe→$\bar{ν}_e$< 7.2 ×10-5 (90% C.L.) for E $\bar{ν}_e$ > 1.8 MeV.At lower energies, by investigating the spectral shape of elastic scattering events, we obtain a new limit on solar 7 Be- ν e conversion into $\bar{ν}_e$ of pνe→$\bar{ν}_e$< 0.14 (90% C.L.) at 0.862 MeV. Last, we investigate solar flares as possible neutrino sources and obtain the strongest up-to-date limits on the fluence of neutrinos of all flavor neutrino below 3–7 MeV. Assuming the neutrino flux to be proportional to the flare’s intensity, we exclude an intense solar flare as the cause of the observed excess of events in run 117 of the Cl-Ar Homestake experiment.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2019

Promising Graphene-Like Half-Metallic Nanosheets TM-InSe (TM = Mn, Fe, and Co) Induced by TM Adsorption

Several half-metallic graphene-like nanosheets, namely transition metal (TM)-adsorbed monolayers (TM-InSe, TM = Mn, Fe, and Co), are predicted by the first-principles calculations. Their structural, electric, and magnetic properties are studied in detail. The adsorption energies of these nanosheets are negative so that they have stable adsorption structures, indicating that it is possible to prepare them in experiments. The pristine InSe nanosheet is a typical semiconductor, but TM-InSe nanosheets are conductive. They are possible half-metallic 2D materials. Calculated total magnetic moments of TM-InSe nanosheets are about 5.18, 3.93, and 1.28 μ{sub B} for TM = Mn, Fe, and Co, respectively. Their conductibility, half-metallicity, and magnetic moments come mainly from adsorbed TM ions, partially from In and Se ions. For Mn-InSe and Fe-InSe nanosheets, TM-3d4s and Se-4p{sub z} electrons enter into the molecular orbitals in high-spin sequence, but for the Co-InSe nanosheet, electrons enter into the molecular orbitals in lowspin sequence. Electronic structures of the Mn-InSe, Fe-InSe and Co-InSe nanosheets are σ{sup 1} ↑ σ{sup 1} ↓ d{sup 5} ↑ d{sup 1} ↓ σ*{sup 1} ↑, σ{sup 1} ↑ σ{sup 1} ↓ d{sup 5} ↑ d{sup 2} ↓ σ*{sup 1} ↑, and σ{sup 1} ↑ σ{sup 1} ↓ d{sup 5} ↑ d{sup 4} ↓, respectively. The total moments 5.00, 4.00, and 1.00 μ{sub B} of TM-InSe nanosheets based on these electronic structures are basically in accordance with calculated values, respectively.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2025

Electronic, magnetic, and structural properties of V2CoAl: Experimental and computational study

Here, we present results of combined experimental and computations study of V2CoAl, a Heusler alloy that exhibits nearly perfect spin-polarization. Our calculations indicate that this material maintains a high degree of spin-polarization (over 90%) in the wide range of lattice parameters, except at the largest considered unit cell volume. The magnetic alignment of V2CoAl is ferrimagnetic, due to the antialignment of the magnetic moments of vanadium atoms in their two sublattices. The calculated total magnetic moment per formula unit is nearly integer at the optimal lattice parameter and at the smaller volumes of the unit cell, but it deviated from the integer values as the unit cell expands. This is consistent with the calculated variation in the degree of spin polarization with lattice constant. The expected ferrimagnetic behavior has been observed in the arc-melted V2CoAl sample, with a Curie temperature of about 80 K. However, the saturation magnetization is significantly smaller than the theoretical prediction of ∼2 μB/f.u., most likely due to the observed B2-type atomic disorder. The samples exhibit metallic electron transport across the measurement range of 2 K to 300 K.

Kharel, Parashu (ORCID:0000000171330718)↗