Search NASA⌕ Search

SEARCH · Search NASA

Results for “MAGNETS”

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 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
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↗
DOE OSTI2017

Three-dimensional Features of the Outer Heliosphere Due to Coupling between the Interstellar and Heliospheric Magnetic Field. V. The Bow Wave, Heliospheric Boundary Layer, Instabilities, and Magnetic Reconnection

The heliosphere is formed due to interaction between the solar wind (SW) and local interstellar medium (LISM). The shape and position of the heliospheric boundary, the heliopause, in space depend on the parameters of interacting plasma flows. The interplay between the asymmetrizing effect of the interstellar magnetic field and charge exchange between ions and neutral atoms plays an important role in the SW–LISM interaction. By performing three-dimensional, MHD plasma/kinetic neutral atom simulations, we determine the width of the outer heliosheath—the LISM plasma region affected by the presence of the heliosphere—and analyze quantitatively the distributions in front of the heliopause. It is shown that charge exchange modifies the LISM plasma to such extent that the contribution of a shock transition to the total variation of plasma parameters becomes small even if the LISM velocity exceeds the fast magnetosonic speed in the unperturbed medium. By performing adaptive mesh refinement simulations, we show that a distinct boundary layer of decreased plasma density and enhanced magnetic field should be observed on the interstellar side of the heliopause. We show that this behavior is in agreement with the plasma oscillations of increasing frequency observed by the plasma wave instrument onboard Voyager 1. We also demonstrate that Voyager observations in the inner heliosheath between the heliospheric termination shock and the heliopause are consistent with dissipation of the heliospheric magnetic field. The choice of LISM parameters in this analysis is based on the simulations that fit observations of energetic neutral atoms performed by Interstellar Boundary Explorer .

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Effect of Annealing on Perpendicular Magnetic Anisotropy and Low Saturation Magnetization of MgO/Co{sub 2}FeAl/Mo Trilayer Films

In this study, we report our approach to manipulate the strength of perpendicular magnetic anisotropy (PMA) at oxide/ferromagnetic metal of Heusler alloy (HA) interface by tuning the parameter of annealing temperature. Robust PMA energy density (K{sub eff}) of ∼ 0.43 × 10{sup 6} erg/cm{sup 3} and small saturation magnetization (M{sub s}) as low as ∼ 248 emu/cm{sup 3} have been achieved for MgO/Co{sub 2}FeAl (CFA)/Mo stacks at 400 {sup ∘}C. We identify that PMA energy is thermally stable up to the maximum temperature of 400 {sup ∘}C. Effect of annealing temperature on surface morphology, grain distribution, and surface roughness of the stacks are investigated by atomic force microscopy (AFM). Further, X-ray photoelectron spectroscopy (XPS) study demonstrates that the interfacial oxidation decides the strong PMA property at MgO/Co{sub 2}FeAl interface during the annealing process. This MgO/CFA/Mo trilayer system can be a suitable candidate for the development of low-power consumption, huge-density data storage, high-thermal stability against the annealing temperature, and nonvolatile magnetic memories.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Microstructure and Magnetic Properties of Exchange-Coupled Co{sub 72}Pt{sub 28}/Pt/Co{sub 81}Ir{sub 19} Composite Media for Perpendicular Magnetic Recording

In this work, we report the investigation of microstructure and magnetic properties of the Co{sub 72}Pt{sub 28}/Pt/Co{sub 81}Ir{sub 19} exchange-coupled composite (ECC) media using soft-layer (SL) of Co{sub 81}Ir{sub 19} with negative magnetocrystalline anisotropy (MA). Our TEM images show that the hard-layer (HL) exhibits a columnar type microstructure with well-isolated grains and the exchange-coupled SL with hcp-structure show the same texture. Strong coupling of the two layers have been evidenced by the magnetic characterization for all the studied films with Pt inter-layer thickness ranging from 0 to 2 nm. Importantly, these ECC media films have much lower coercivities and much higher thermal stabilities in the favor of high-density magnetic recording.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

An implicit, conservative and asymptotic-preserving electrostatic particle-in-cell algorithm for arbitrarily magnetized plasmas in uniform magnetic fields

Here, we introduce a new electrostatic particle-in-cell algorithm capable of using large timesteps compared to particle gyro-period under a uniform external magnetic field. The algorithm extends earlier electrostatic fully implicit PIC implementations with a new asymptotic-preserving particle-push scheme that allows timesteps much larger than particle gyroperiods. In the large-timestep limit, the integrator preserves all particle drifts, while recovering the full orbit for small timesteps. The scheme allows for a seamless, efficient treatment of particles with coexisting magnetized and unmagnetized species, and conserves energy and charge exactly without spoiling implicit solver performance. We demonstrate by numerical experiment with several problems of variable species magnetization (diocotron instability, modified two-stream instability, and drift instability) that orders of magnitude wall-clock-time speedups vs. the standard fully implicit electrostatic PIC algorithm are possible without sacrificing solution accuracy.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Chemical Control of Magnetism in the Kagome Metal CoSn 1 – x In x : Magnetic Order from Nonmagnetic Substitutions

As a two-dimensional structural motif, the kagome net produces many interesting magnetic and electronic properties. In particular, this lattice produces flat electronic bands with a large density of states. When the chemical potential is positioned within these flat bands, electronic instabilities can result. For the kagome metal CoSn, this alignment is not realized, the flat bands are completely filled, and the compound is a Pauli paramagnet. For this study, we have grown crystals and powders of CoSn 1 – x In x and shown that replacing Sn with In moves the chemical potential into the flat band region, as expected from simple electron counting. This is supported by band structure calculations, heat capacity measurements, and angle-resolved photoemission spectroscopy. The increased density of states results in the emergence of antiferromagnetic order evidenced by magnetic susceptibility, Mössbauer spectroscopy, and neutron diffraction data. The Néel temperature reaches a maximum of 32 K. The emergence of magnetic order when introducing a nonmagnetic element into a nonmagnetic kagome metal is striking. This work provides clear evidence that flat bands arising from electronically frustrated lattices in bulk crystals provide a new and powerful way to realize correlated ground states controlled by crystal chemistry.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Spin Solar Cell Phenomenon on a Single-Molecule Magnet (SMM) Impacted CoFeB-Based Magnetic Tunnel Junctions

The single-molecule magnet (SMM) is demonstrated here to transform conventional magnetic tunnel junctions (MTJs), a memory device used in present-day computers, into solar cells. For the first time, we demonstrated an electronic spin-dependent solar cell effect on an SMM-transformed MTJ under illumination from unpolarized white light. We patterned cross-junction-shaped devices to form a CoFeB/MgO/CoFeB-based MTJ. The MgO barrier thickness at the intersection between the two exposed junction edges was less than the SMM extent, which enabled the SMM molecules to serve as channels to conduct spin-dependent transport. The SMM channels yielded a region of long-range magnetic ordering around these engineered molecular junctions. Our SMM possessed a hexanuclear [Mn 6 (μ 3 -O) 2 (H 2 N-sao) 6 (6-atha) 2 (EtOH) 6 ] [H 2 N-saoH = salicylamidoxime, 6-atha = 6-acetylthiohexanoate] complex and thioesters end groups to form bonds with metal films. SMM-doped MTJs were shown to exhibit a solar cell effect and yielded ≈80 mV open-circuit voltage and ≈10 mA/cm 2 saturation current density under illumination from one sun equivalent radiation dose. A room-temperature Kelvin Probe AFM (KPAFM) study provided direct evidence that the SMM transformed the electronic properties of the MTJ’s electrodes over a lateral area in excess of several thousand times larger in extent than the area spanned by the molecular junctions themselves. As a result, the decisive factor in observing this spin-photovoltaic effect is the formation of SMM spin channels between the two different ferromagnetic electrodes, which in turn is able to catalyze the long-range transformation in each electrode around the junction area.

14 SOLAR ENERGY↗
DOE OSTI2023

Direct observation of electric field-induced magnetism in a molecular magnet

Abstract We report the direct observation of an electrically-induced magnetic susceptibility in the molecular nano- magnet [Fe 3 O(O 2 CPh) 6 (py) 3 ]ClO 4 · py, an Fe 3 trimer. This magnetoelectric effect results from the breaking of spatial inversion symmetry due to the spin configurations of the antiferromagnetic trimer. Both static and very low frequency electric fields were used. Fractional changes of the magnetic susceptibility of 11 ppb $$\pm 2$$ ± 2 per kVm -1 for the temperature range 8 . 5 < T < 13 . 5 K were observed for applied electric fields up to 62 kV m − 1 . The changes in susceptibility were measured using a tunnel diode oscillator operating at liquid helium temperatures while the sample is held at a higher regulated temperature.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2024

Constraints on 5 f -electron magnetism in Ga-stabilized $δ$-Pu from x-ray magnetic circular dichroism

Density-functional theory models of δ-Pu accurately predict crystal structure, phonon density of states, and unit cell volumes but require magnetic degrees of freedom which have never been experimentally verified. Some models invoke an on-site cancellation of spin and orbital moments, engendering a near-zero bulk magnetization, undetectable by most probes. Here, we employ x-ray magnetic circular dichroism at the Pu M 4,5 edges to directly probe spin and orbital moments using the magneto-optical sum rules. The data show no dichroism within experimental error, constraining polarized moments at 6 T and 3 K to μ L,S <0.1⁢μ B . Finally, these experiments point to the absence of even unconventional spin-orbit compensated order in δ-Pu.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effective anisotropy due to the surface of magnetic nanoparticles

Analytical solution has been discovered for the second-order effective anisotropy of magnetic nanoparticles of a cubic shape due to the surface anisotropy (SA) of the Néel type. Similarly to the spherical particles, for the simple cubic lattice the grand-diagonal directions (±1,±1,±1) are favored by the effective cubic anisotropy but the effect is twice as strong. Uniaxial core anisotropy and applied magnetic field cause screening of perturbations from the surface at the distance of the domain-wall width and reduce the effect of SA near the energy minima. Yet, screening disappears near the uniaxial energy barrier, and the uniform barrier state of larger particles may become unstable. For these effects the analytical solution is obtained as well, and the limits of the additive formula with the uniaxial and effective cubic anisotropies for the particle are established. Thermally-activated magnetization-switching rates have been computed by the pulse-noise technique for the stochastic Landau-Lifshitz equation for a system of spins.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗