Search NASA⌕ Search

SEARCH · Search NASA

Results for “MAGNETISM”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 631 records · Page 35
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

The application of macroscopic flakes for Fe-6.5%Si bulk magnetics with superior magnetic properties

Inductors are used in power electronics to convert current to different frequency and voltage. They are used extensively from where power is generated all the way to electric vehicles and portable electronic devices. The soft magnetic materials used in the inductors is critical for the performance of the inductors. Currently, a majority of the inductor uses powder core. The use of powder is not ideal as the 3D granule powders generate large demagnetization field working against the applied field, resulting in reduced permeability and efficiency. In this paper, 2D flakes were used to replace the 3D granules as the feedstock for fabricating inductor core. The crystalline Fe-Si based crystalline soft magnetic material in the form of flakes approximately 0.1mm thick, 1mm long and 2mm wide were prepared via melt spinning. The flakes were then coated with insulating materials before compacted into a toroid. The effect of coating thickness and concentration on magnetic properties of the toroidal sample are studied. It was also found that the magnetic cores made by flakes surpass the cores made by same size powder with larger permeability and lower iron losses.

Fe-6.5%Si Steel↗
DOE OSTI2023

Magnetic properties of Lu and Y doped Ce-Fe-B magnets

The growing demand for Nd2Fe14B magnets is exacerbating the current critical materials shortage. To reduce the amount of critical material in Nd2Fe14B magnets, chemical substitutions have been used and shown to improve the magnetic behavior, such as the Curie Temperature TC, anisotropy field Ha, and saturation magnetization MS.

Bretana, Alex↗
DOE OSTI2026

The Dependence of Electron-only Magnetic Reconnection on Plasma Beta and Magnetic Shear: Theory and Observations

We investigate the onset conditions for electron-only magnetic reconnection through an analysis of 86 reconnection events observed by the Magnetospheric Multiscale mission in magnetosheath and magnetospheric current sheets. Our study presents the first observational evidence that the occurrence of electron-only reconnection depends on both the magnetic-field shear angle (θ) across the current sheet and the cross-sheet electron beta jump, quantified either by the inflow electron beta difference (Δβ e ) or by a modified electron beta jump (Δβ$^*_e$) defined by the cross-sheet electron pressure difference normalized by the average of the inflow magnetic pressure in the two inflow regions. We extend the diamagnetic-drift suppression mechanism from standard reconnection to electron-only reconnection by deriving relations applicable to electron-scale current sheets. Using scaling estimates, the electron-only reconnection suppression relation is derived as Δβ$^*_e$ ≳ 2(L/d e ) tan (θ/2), while a natural extension of the ion-coupled reconnection suppression criterion is Δβ e ≳ 2(L/d e ) tan (θ/2). At low Δβ e and Δβ$^*_e$ values, reconnection is detected across a large range of magnetic shear (from low to high), whereas high Δβ e and Δβ$^*_e$ conditions restrict reconnection to large shear configurations: shear angles as small as θ ≈ 5° occur when Δβ e (or Δβ$^*_e$) ≲0.1. However, only events exceeding θ ≳ 70° are found when Δβ e ≳ 1.0; this apparent restriction weakens when employing Δβ$^*_e$, as the corresponding data points shift toward smaller values of the modified electron beta jump. These findings quantitatively support theoretical predictions of reconnection suppression in high-β e plasmas at low shears, attributed to X-line drift induced by pressure gradients across electron-scale current sheets.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Long-Time Variation of Magnetic Structure in (Pr x La 1-x )Co 2 Si 2 : Coexistence of Slow and Fast Processes in Magnetic Phase Transition

In this paper, long-time variations of the magnetic structure in PrCo 2 Si 2 and (Pr 0.98 La 0.02 )Co 2 Si 2 were studied by magnetization and time-resolved neutron scattering measurements. The amplitudes of magnetic Bragg peaks showed marked time variations after cooling or heating across the magnetic transition temperature T 1 between two different antiferromagnetic phases. However, the amplitude of the time variation decreased rapidly with increasing distance from T 1 . Finally, we analyzed the results on the basis of a phase transition model that includes the coexistence of fast and slow processes.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Magnetic diode in artificial magnetic honeycomb lattice

A magnetic artificial honeycomb lattice comprising a multiplicity of connecting elements separated by hexagonal cylindrical pores, wherein: (a) the hexagonal cylindrical pores: (i) have widths that are substantially uniform and an average width that is in a range of about 15 nm to about 20 nm; and (ii) are substantially equispaced and have an average center-to-center distance that is in a range of about 25 nm to about 35 nm; and (b) the connecting elements comprise a magnetic material layer, and the connecting elements have: (i) lengths that are substantially uniform and an average length that is in a range of about 10 nm to about 15 nm; (ii) widths that are substantially uniform and an average width that is in a range of about 4 nm to 8 nm; and (iii) a thickness of the magnetic material layer that is substantially uniform and an average thickness that is in a range of about 2 nm to about 8 nm; and (c) the magnetic artificial honeycomb lattice has a surface area, disregarding the presence of the hexagonal cylindrical pores, that is in a range of about 100 mm.sup.2 to about 900 mm.sup.2.

Singh, Deepak Kumar↗
DOE OSTI2023

Permanent magnet alloys for gap magnets

Provided are Ce/Co/Cu permanent magnet alloys containing certain refractory metals, such as Ta and/or Hf, and optionally Fe which represent economically more favorable alternative to Sm-based magnets with respect to both material and processing costs and which retain and/or improve magnetic characteristics useful for GAP MAGNET applications.

Palasyuk, Andriy↗
DOE OSTI2018

Spin-Dependent Thermoelectric Effects in Double-Barrier Magnetic Tunnel Junctions with a Non-magnetic Metal Spacer

Spin-dependent thermoelectric (TE) effects are studied in MgO-based double-barrier magnetic tunnel junctions with a non-magnetic metal spacer (DBMTJs-NM) in the linear response regime. Using non-equilibrium Green’s function (NEGF) formalism, the results show resonant peaks at specific thicknesses of the NM spacer because of the resonant tunneling effect through the DBMTJs-NM. Effects of average temperature and magnetization alignment are also described. Therefore, thermally charge and spin voltage lead to large spin-dependent TE effects by the DBMTJs-NM structures.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Annealing Effects on Microstructure and Magnetic Properties of (NdPr){sub 9.5}(FeNbCoCu){sub 79.5}(BC){sub 11} Nanocomposite Magnets

Annealing effects on microstructure and magnetic properties of (NdPr){sub 9.5}(FeNbCo){sub 79.5}(BC){sub 11} ribbons were investigated. It was observed that Nd{sub 2}Fe{sub 14}B and Fe{sub 3}B phases were directly formed at low spinning speed. Then, the alloys transformed to an amorphous state at a speed of 20 m/s. Annealed at 700 {sup ∘}C for 10 min, the amorphous alloys as-quenched at 20 m/s crystallized into a nanocomposite composed of Nd{sub 2}Fe{sub 14}B and α-Fe phases. The formation of Fe{sub 3}B phases was inhibited. The magnetic properties firstly increased and then decreased with the increasing of annealing time. The optimum magnetic properties were achieved in the alloys annealed at 700 {sup ∘}C for 10 min. The corresponding coercivity, remanence, and the maximum energy product was 427.5 kA/m, 0.94 T, and 101.2 kJ/m{sup 3}, respectively. In addition, fine and uniform grains were formed. The average grain size was 10 nm.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Characteristics of a Degenerate Neutron Gas in a Magnetic Field with Allowance for the Anomalous Magnetic Moment of the Neutron

General expressions for the dependence of the Fermi energy, pressure, and total energy of a degenerate neutron gas in a magnetic field on the magnitude of the field and the neutron concentration with allowance for the anomalous magnetic moment of the neutron have been obtained in implicit form, and the dependence of these quantities on the field is presented in graphical form for the neutron concentration C = 10{sup 38} cm{sup –3}, which is typical for neutron stars. Analytical estimates of the pressure have been made for the magnitude of the fields possible in neutron stars ~10{sup 17}–10{sup 19} G and this neutron concentration ~10{sup 38} cm{sup –3}, including when the neutron gas is close to its saturated state with preferred orientation of the anomalous magnetic moment of all the neutrons in alignment with the field. It is found that even such fields ~10{sup 17} G have practically no effect on the pressure in comparison with the case when the field is absent, an effect being possible only for В ~ 10{sup 18}–10{sup 19} G. The analytical dependence on the neutron concentration of the corresponding field B{sub S} at which the neutron gas transitions to the saturated state has been found in explicit form. It is established that for B > B{sub S} the indicated characteristics of the neutron gas, and likewise its state, no longer change.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
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↗
DOE OSTI2018

Regimes of magnetic reconnection in colliding laser-produced magnetized plasma bubbles

Here, we conduct a multiparametric study of driven magnetic reconnection relevant to recent experiments on colliding magnetized laser-produced plasmas using particle-in-cell simulations. Varying the background plasma density, plasma resistivity, and plasma bubble geometry, the 2D simulations demonstrate a rich variety of reconnection behaviors and show the coupling between magnetic reconnection and the global hydrodynamical evolution of the system. We consider both the collision between two radially expanding bubbles where reconnection is seeded by the pre-existing X-point and the collision between two flows in a quasi-1D geometry with initially anti-parallel fields where reconnection must be initiated by the tearing instability. At a baseline case of low-collisionality and low background density, the current sheet is strongly compressed to below scale of the ion-skin-depth scale, and rapid, multi-plasmoid reconnection results. Increasing the plasma resistivity, we observe a collisional slow-down of reconnection and stabilization of plasmoid instability for Lundquist numbers less than approximately S ~10 3 . Second, increasing the background plasma density modifies the compressibility of the plasma and can also slow down or even prevent reconnection, even in completely collisionless regimes, by preventing the current sheet from thinning down to the scale of the ion-skin depth. These results have implications for understanding recent and future experiments, and signatures for these processes for proton-radiography diagnostics of these experiments are discussed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

A Brillouin light scattering study of the spin-wave magnetic field dependence in a magnetic hybrid system made of an artificial spin-ice structure and a film underlayer

We present a combined Brillouin light scattering (BLS) and micromagnetic simulation investigation of the magnetic-field-dependent spin-wave spectra in a hybrid structure made of permalloy (NiFe) artificial spin-ice (ASI) systems, composed of stadium-shaped nanoislands, deposited on the top of an unpatterned permalloy film with a nonmagnetic spacer layer. The thermal spin-wave spectra were recorded by BLS as a function of the magnetic field applied along the symmetry direction of the ASI sample. Magneto-optic Kerr effect magnetometry was used to measure the hysteresis loops in the same orientation as the BLS measurements. Here, the frequency and the intensity of several spin-wave modes detected by BLS were measured as a function of the applied magnetic field. Micromagnetic simulations enabled us to identify the modes in terms of their frequency and spatial symmetry and to extract information about the existence and strength of the dynamic coupling, relevant only to a few modes of a given hybrid system. Using this approach, we suggest a way to understand if the dynamic coupling between ASI and film modes is present or not, with interesting implications for the development of future three-dimensional magnonic applications and devices.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Magnetic anisotropy in uranium monosulfide probed by magnetic torque measurements

We have studied the magnetic torque in uranium monosulfide (US) single crystals to explore the magnetic anisotropy in this material. Uranium monosulfide crystallizes in a cubic, NaCl-type of crystal structure and exhibits the largest magnetocrystalline anisotropy observed in cubic systems. By performing detailed torque measurements we observe a strongly anisotropic behavior in the paramagnetic phase due to crystal defects and quadrupolar pair interactions. Our studies also confirm the presence of a large anisotropy in the ferromagnetic state of the US system with the <100>, <111>, and <110> directions being the hard, easy, and intermediate axes, respectively. Furthermore, the anisotropy in the paramagnetic phase shows similar characteristics to the anisotropy observed in the ferromagnetic phase, as characterized by second and fourth rank susceptibility terms. The similarity of the anisotropic behaviors in paramagnetic and ferromagnetic phases is the consequence of strong magnetoelastic properties in this system, which possibly lead to the rhombohedral structural distortion, not only in the ferromagnetic phase but also in the paramagnetic phase (induced by applied magnetic field).

36 MATERIALS SCIENCE↗
DOE OSTI2021

Phonon Magnetic Moment from Electronic Topological Magnetization

The traditional theory of magnetic moments for chiral phonons is based on the picture of the circular motion of the Born effective charge, typically yielding a small fractional value of the nuclear magneton. Here we investigate the adiabatic evolution of electronic states induced by the lattice vibration of a chiral phonon and obtain an electronic orbital magnetization in the form of a topological second Chern form. We find that the traditional theory needs to be refined by introducing a k resolved Born effective charge, and identify another contribution from the phonon-modified electronic energy together with the momentum-space Berry curvature. The second Chern form can diverge when there is a Yang’s monopole near the parameter space of interest as illustrated by considering a phonon at the Brillouin zone corner in a gapped graphene model. We also find large magnetic moments for the optical phonon in bulk topological materials where nontopological contribution is also important. Our results agree with recent observations in experiments.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Optical properties of magnetic photonic crystals with an arbitrary magnetization orientation

We have studied the peculiarities of diffraction of light in magnetic photonic crystals at large values of magnetooptical activity parameter and modulation depth. We have considered the case of an arbitrary angle between the directions of the external static magnetic field and the normal to the layer. The problem has been solved by the modified Ambartsumyan layer summation method. It has been shown that the given system is nonreciprocal with respect to not only circular, but linear polarizations also. In this case, a new type of nonreciprocity is observed (namely, the relation R(α) ≠ R(–α) holds, where R is the reflection coefficient and α is the angle of incidence). It has been demonstrated that in the case of oblique incidence, there appears a new photonic forbidden band that is not selective relative to the polarization of incident light. We have detected strong dependences of reflectance, absorbance, transmittance nonreciprocity, and other characteristics on the angle between the direction of the external static magnetic field and the normal to the layer boundary. Such a system can be used as a controllable polarization filter and a mirror, as well as a source of circular (elliptic) polarization, a controllable optical diode, and so on.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

The mean energy loss by neutrino with magnetic moment in strong magnetic field with consideration of positronium contribution to photon dispersion

The process of radiative decay of the neutrino with a magnetic moment in a strong magnetic field with consideration of positronium influence on photon dispersion has been studied. Positronium contribution to the photon polarization operator induces significant modifications of the photon dispersion law and neutrino radiative decay amplitude. It has been shown that the mean energy loss of a neutrino with magnetic a moment significantly increases, when the positronium contribution to photon dispersion is taken into account.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Response of a magnetic nanoparticle lattice to a magnetic field pulse near the stability boundary

The dynamic response of a system being near the stable equilibrium boundary to an external magnetic field pulse is studied for 2D lattices of magnetic nanoparticles with cubic crystallographic anisotropy. The conditions under which magnetic moment oscillations from individual dipoles propagate to the entire system are revealed. This effect results in the lattice response are significantly larger in the external pulse duration and with an amplitude rather weakly depending on initial conditions and external field parameters, the processes during which the pulse results in reorientation of only individual lattice dipoles.

77 NANOSCIENCE AND NANOTECHNOLOGY↗