Search NASA⌕ Search

SEARCH · Search NASA

Results for “Surface 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 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
NASA NTRS2020

The SUrvey for Pulsars and Extragalactic Radio Bursts - IV. Discovery and polarimetry of a 12.1-s radio pulsar

We report the discovery of PSR J2251−3711, a radio pulsar with a spin period of 12.1 s, the second longest currently known. Its timing parameters imply a characteristic age of 15 Myr, a surface magnetic field of 1.3 × 10^(13) G, and a spin-down luminosity of 2.9 × 10^(29) erg/s. Its dispersion measure of 12.12(1) pc/cu. cm leads to distance estimates of 0.5 and 1.3 kpc according to the NE2001 and YMW16 Galactic free electron density models, respectively. Some of its single pulses show an uninterrupted 180-deg sweep of the phase-resolved polarization position angle, with an S-shape reminiscent of the rotating vector model prediction. However, the fact that this sweep occurs at different phases from one pulse to another is remarkable and without straightforward explanation. Although PSR J2251−3711 lies in the region of the P − P˙ parameter space occupied by the X-ray isolated neutron stars (XINS), there is no evidence for an X-ray counterpart in our Swift XRT observation; this places a 99 per cent-confidence upper bound on its unabsorbed bolometric thermal luminosity of 1.1 × 10^(31) (d/1 kpc)^2 erg/s for an assumed temperature of 85 eV, where d is the distance to the pulsar. Further observations are needed to determine whether it is a rotation-powered pulsar with a true age of at least several Myr, or a much younger object such as an XINS or a recently cooled magnetar. Extreme specimens like PSR J2251−3711 help bridge populations in the so-called neutron star zoo in an attempt to understand their origins and evolution.

V Morello↗
NASA NTRS2022

High-energy Photon Opacity in the Twisted Magnetospheres of Magnetars

Magnetars are neutron stars characterized by strong surface magnetic fields generally exceeding the quantum critical value of 44.1 TG. High-energy photons propagating in their magnetospheres can be attenuated by QED processes like photon splitting and magnetic pair creation. In this paper, we compute the opacities due to photon splitting and pair creation by photons emitted anywhere in the magnetosphere of a magnetar. Axisymmetric, twisted dipole field configurations embedded in the Schwarzschild metric are treated. The paper computes the maximum energies for photon transparency that permit propagation to infinity in curved spacetime. Special emphasis is given to cases where photons are generated along magnetic field loops and/or in polar regions; these cases directly relate to resonant inverse Compton scattering models for the hard X-ray emission from magnetars and Comptonized soft gamma-ray emission from giant flares. We find that increases in magnetospheric twists raise or lower photon opacities, depending on both the emission locale and the competition between field-line straightening and field strength enhancement. Consequently, given the implicit spectral transparency of hard X-ray bursts and persistent "tail" emission of magnetars, photon splitting considerations constrain their emission region locales and the twist angle of the magnetosphere; these constraints can be probed by future soft gamma-ray telescopes such as COSI and AMEGO. The inclusion of twists generally increases the opaque volume of pair creation by photons above its threshold, except when photons are emitted in polar regions and approximately parallel to the field.

radiation mechanisms: non-thermal↗
NASA NTRSDate not supplied

Photometric Properties of Quiet Sun Observed With the DKIST and HINODE

The variability of irradiance is primarily influenced by surface magnetism, such as sunspots, faculae, and network structures. Each of these features contributes differently to the overall variability. However, the impact of small magnetic elements, which are commonly observed in high resolution images of the solar photosphere but remain unresolved in full-disk images used for irradiance modeling, is still a topic of debate. Understanding the influence of these small magnetic elements to the overall brightness, particularly in quiet regions, is fundamental to understanding irradiance fluctuations over decadal and longer temporal scales. We investigate the brightness of small-size magnetic elements using very high spatial resolution spectro-polarimetric observations acquired at different spectral ranges with the National Science Foundations Daniel K. Inouye Solar Telescope (DKIST) and with HINODE/SOT. Our results are compared to 3D MHD Small Solar Dynamo simulations obtained with the MURaM code.

SMD↗
NASA NTRS1975

Surface lubrication of magnetic tape

Friction minimization between magnetic media (tape, cards, drums, etc.) and magnetic transducer (heads, etc.) is a key requirement in recording systems. Results are presented for an investigation intended to eliminate previously encountered shortcomings of friction-reducing treatments by a deposition of an inert liquid film on a fully manufactured (cured) magnetic medium. The film contains no particles, represents a compound characterized by good lubricating and thermal properties, is inert with respect to the normal formulation constituents, and has low surface tension and vapor pressure characteristics. The deposited film need only be molecularly thin to impart adequate lubricating properties to the tape. The discussion covers the characteristics of the surface lubricant, method of application, and surface coated magnetic media test results. Greater than 5 million passes of the 3M 900 tape on a loop tester are achieved with no apparent effect on the tape and with head wear decreased by as much as a factor of ten

Wright, C. D.↗
DOE OSTI2021

FESS Design Simulations: methods, tools, & issues for the edge/scrape-off-layer region

This topic describes the plasma and neutral particles in the transition boundary region between the hot core plasma and the surrounding material walls. A key geometrical transition that occurs in this region is where the equilibrium magnetic field changes topology from a set of closed, nested magnetic flux surfaces inside the magnetic separatrix to flux surfaces, and therefore magnetic field lines that intersect material walls. Because the plasma exhaust heat flows very rapidly along the field lines, these intersection locations can have heat fluxes much higher than the walls can withstand. The most promising strategy pursued here to avoid this problem is injection of moderate-Z impurities that radiate the exhaust power over a much larger surface area on the walls, thus keeping the peak heat flux at or below the goal of 10 MW/m 2 . Further, the intrusion of injected and wall-sputtered impurities into the core region must be kept below certain limits to prevent degradation of the fusion power generated in the core.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Tuning Surface, Phase, and Magnetization of Superparamagnetic Magnetite by Ionic Liquids: Single-Step Microwave-Assisted Synthesis

Achieving colloidal and chemical stability in ferrofluids by surface modification requires multiple steps, including purification, ex situ modification steps, and operation at high temperatures. In this study, a single-step microwave-assisted methodology is developed for iron oxide nanoparticle (IONP) synthesis utilizing a series of imidazolium-based ionic liquids (ILs) with chloride, bis(trifluoromethylsulfonyl)imide, and pyrrolide anions as the reaction media, thus eliminating the use of volatile organics while enabling rapid synthesis at 80 °C as well as in situ surface functionalization. The characterized surface functionality, hydrodynamic particle size, magnetization, and colloidal stability of the IONPs demonstrate a strong dependence on the IL structure, ion coordination strength, reactivity, and hydrophilicity. The IONPs present primarily a magnetite (Fe 3 O 4 ) phase with superparamagnetism with the highest saturation magnetization at 81 and 73 emu/g at 10 and 300 K, respectively. Depending on the IL coating, magnetization and exchange anisotropy decrease by 20 and 2–3 emu/g (at 35 wt % IL), respectively, but still represent the highest magnetization achieved for coated IONPs by a coprecipitation method. Further, the surface-functionalized superparamagnetic magnetite nanoparticles show good dispersibility and colloidal stability in water and dimethyl sulfoxide at 0.1 mg/mL concentration over the examined 3 month period. This study reports on the intermolecular and chemical interactions between the particle surface and the ILs under synthetic conditions as they relate to the magnetic and thermal properties of the resulting IONPs that are well suited for a variety of applications, including separation and catalysis.

36 MATERIALS SCIENCE↗
NASA NTRS2007

The Stellar Imager (SI) Project: Resolving Stellar Surfaces, Interiors, and Magnetic Activity

The Stellar Imager (SI) is a UV/Optical. Space-Based Interferometer designed to enable 0.1 milli-arcsec (mas) spectral imaging of stellar surfaces and, via asteroseismology, stellar interiors and of the Universe in general. The ultra-sharp images of SI will revolutionize our view of many dynamic astrophysical processes by transforming point sources into extended sources, and snapshots into evolving views. The science of SI focuses on the role of magnetism in the Universe, particularly on magnetic activity on the surfaces of stars like the Sun. Its prime goal is to enable long-term forecasting of solar activity and the space weather that it drives. SI will also revolutionize our understanding of the formation of planetary systems, of the habitability and climatology of distant planets, and of many magneto-hydrodynamically controlled processes in the Universe. In this paper we discuss the science goals, technology needs, and baseline design of the SI mission.

Carpenter, Kenneth G.↗
NASA NTRS2007

The Stellar Imager (SI) - A Mission to Resolve Stellar Surfaces, Interiors, and Magnetic Activity

The Stellar Imager (SI) is a UV/Optical, Space-Based Interferometer designed to enable 0.1 milli-arcsecond (mas) spectral imaging of stellar surfaces and, via asteroseismology, stellar interiors and of the Universe in general. The ultra-sharp images of the Stellar Imager will revolutionize our view of many dynamic astrophysical processes by transforming point sources into extended sources, and snapshots into evolving views. SI's science focuses on the role of magnetism in the Universe, particularly on magnetic activity on the surfaces of stars like the Sun. SI's prime goal is to enable long-term forecasting of solar activity and the space weather that it drives. SI will also revolutionize our understanding of the formation of planetary systems, of the habitability and climatology of distant planets, and of many magneto-hydrodynamically controlled processes in the Universe. SI is included as a 'Flagship and Landmark Discovery Mission' in the 2005 NASA Sun Solar System Connection (SSSC) Roadmap and as a candidate for a 'Pathways to Life Observatory' in the NASA Exploration of the Universe Division (EUD) Roadmap (May, 2005). In this paper we discuss the science goals and technology needs of, and the baseline design for, the SI Mission (http://hires.gsfc.nasa.gov/si/) its ability to image the 'Biggest, Baddest, Coolest Stars'.

Carpenter, Kenneth↗
NASA NTRS1972

Magnetic hysteresis classification of the lunar surface and the interpretation of permanent remanence in lunar surface samples

A magnetic hysteresis classification of the lunar surface is presented. It was found that there is a distinct correlation between natural remanence (NRM), saturation magnetization, and the hysteresis ratios for the rock samples. The hysteresis classification is able to explain some aspects of time dependent magnetization in the lunar samples and relates the initial susceptibility to NRM, viscous remanence, and to other aspects of magnetization in lunar samples. It is also considered that since up to 60% of the iron in the lunar soil may be super paramagnetic at 400 K, and only 10% at 100 K, the 50% which becomes ferromagnetic over the cycle has the characteristics of thermoremanence and may provide for an enhancement in measurable field on the dark side during a subsatellite magnetometer circuit.

Wasilewski, P.↗
DOE OSTI2026

Collapsing of spin-split Fermi surfaces in the magnetic Weyl semimetal candidate EuAuSb

EuAuSb is a magnetic Weyl semimetal candidate that exhibits in-plane ferromagnetic ordering and a helical magnetic order across the plane at temperatures below 3.9 K. These magnetic characteristics can drive an interaction-induced reconstruction of the Fermi surface. Here, we report a rare instance of Fermi surface splitting and collapsing driven by exchange coupling, as revealed by strongly temperature-dependent quantum oscillation frequencies in EuAuSb. Shubnikov–de Haas measurements reveal two distinct quantum oscillation frequencies (𝐹 𝛼 = 80 T and 𝐹 𝛽 = 165 T) at 2 K. As the temperature increases toward 40 K, the oscillation peaks at these two frequencies gradually merge into a single peak centered around 128 T. This behavior signifies the collapse of the spin-split Fermi surfaces, driven by the weakening of short-range magnetic correlations and the exchange coupling between conduction electrons and local magnetic moments as temperature increases. Furthermore, our results are further supported by density functional theory calculations, angle-resolved photoemission spectroscopy, and magnetization measurements.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1978

Depositional and surface exposure history of the Shorty Crater core 74001/2 - FMR and magnetic studies

Surface exposure (maturity) indices and concentrations of FeO and metallic iron were determined at 0.5-cm intervals of the Apollo 17 core section, which sampled a pyroclastic deposit on the rim of Shorty Crater. The determinations showed that all of the soil in the core is extremely immature. An exposure history of the core is proposed: accumulation (about 3.6 billion years ago), shallow burial (during the first 20 million years), deep burial (till about 10-15 million years ago), followed by excavation (10-15 million years ago), and in situ reworking (till the present).

Morris, R. V.↗
NASA NTRS1984

Magnetic properties of Martian surface material

The hypothesis that the magnetic properties of the Martian surface material are due to the production of a magnetic phase in the clay mineral nontronite by transient shock heating is examined. In the course of the investigation a magnetic material is produced with rather unusual properties. Heating from 900 C to 1000 C, of natural samples of nontronite leads first to the production of what appears to be Si doped maghemite gamma (-Fe2O3). Although apparently metastable, the growth of gamma -Fe2O3 at these temprtures is unexpected, and its relative persistence of several hours at 1000 C is most surprising. Continued annealing of this material for longer periods promote the crystallization of alpha Fe2O3 and cristobalite (high temperature polymorph of SiO2). All available data correlate this new magnetic material with the cristobalite hence our naming it magnetic ferri cristobalite. Formation of this magnetic cristobalite, however, may require topotactic growth from a smectite precursor.

Hargraves, R. B.↗
DOE OSTI2022

Investigating a novel magnetic MAX phase nitride and its (001)-surfaces

We report magnetic MAX phases including their surfaces exhibit promising functional properties for magneto-electronic devices and self-monitoring smart coatings. By employing an integrated ab-initio approach, here we investigate a new member of the MAX phase, Mn 2 AuN. This compound satisfies the chemical, mechanical and dynamical stability criteria, leading to a possibility of its synthesis, and exhibits electronic and elastic anisotropy. The identified ferromagnetic configuration (with high Curie temperature) is the most energetically favorable among the five different spin configurations i.e., non-magnetic, ferromagnetic, and three anti-ferromagnetic. From the coatings perspective, the surface properties of Mn 2 AuN(001) terminations are investigated considering the four possible surface termination models. Remarkably, the magnetism does not get vanished even after cleaving the bulk unit cell into the (001)-surfaces. While evaluating the surface energetics in different chemical potentials, the N-001 terminated surface comes out to be the most stable termination contrasting with carbide MAX phases and is the only termination that exhibits the magnetic characteristics.

36 MATERIALS SCIENCE↗
NASA NTRS2018

Global High Resolution Crustal Magnetic Field at the Surface of the Moon from Low-Altitude Lunar Prospector Magnetic Gradient Data

We derived new vector gradients based models of crustal magnetic field at the lunar surface with data from the Lunar Prospector (LP) satellite using two model parameterization approaches: a global set of 35820 1° spaced (~30 km) equal area monopoles at 20 km below the surface (O’Brien and Parker, 1994; Olsen et al., 2017) and combined results of subsets of 100000 0.66° spaced monopoles at the same depth. We use the scheme of iteratively reweighted least-squares inversion to compute the initial model. Then the amplitudes of these monopoles are determined by minimizing the misfit to the components together with the global average of |Br| at the ellipsoid surface (i.e. applying a L1 model regularization of Br). In previous approaches using vector fields for modeling, we found that external field contamination leads to spurious anomalies in the downward continued field models even with stringent data selection criteria and ad-hoc noise removal techniques (e.g., satellite’s position in the Moon’s wake w.r.t. the solar wind and in the Earth’s magnetotail, internal/external dipoles fields removal, low-order polynomial removal, joint equivalent source cross-validation technique and visually removing remaining anomalous segments). On the other hand, with the use of gradients-only data (along-track first finite differences), we were able to completely bypass the ad-hoc techniques. Similar processing of Kaguya magnetic data, which have only higher altitude coverage over the most of the Moon except in the region of the South Pole–Aitken (SPA) basin, completely misses some of the anomalies seen in the Lunar Prospector data. The combined Lunar Prospector and Kaguya gradient-based models also severely degrade the derivation of the anomaly fields in many regions. Euler analysis of isolated anomaly features from the Reiner Gamma swirl suggests top depths of about 0.3 to 1.5 km and center depths of 10-14 km; in the region between Stein and Vallier craters north of the SPA basin our analysis suggests top depths of around 1.5 km and center depths of 13-15 km. With the spectral depth determination techniques, the SPA basin region yields depths to the base of magnetization ranging between 15 and 40 km. Three-dimensional modeling and the bulk magnetization determinations of the sources constrained by the Euler and spectral methods is underway.

Gradient↗
NASA NTRS1991

The source surface and photospheric magnetic field models

It is possible to reproduce the configuration of the neutral line on the solar source surface by the axial dipole at the center of the sun and a few fictitious dipoles on the photosphere. An attempt is made to identify the nature of such fictitious dipoles in the photospheric magnetic fields. It is shown that large-scale photospheric dipole fields can be identified clearly at the locations indicated by the fictitious dipoles when the photospheric field is very simple. They are found to be active regions.

Saito, T.↗
DOE OSTI2020

Unipolar arc plasmas on nanostructured tungsten surfaces under perpendicular magnetic field

Abstract Unipolar arcing is an important phenomenon in terms of wall erosion and the subsequent plasma contamination in nuclear fusion devices. In this study, unipolar arc plasmas are experimentally explored under the presence of the external magnetic field perpendicular to a tungsten (W) sample on which a ‘fuzz’ nanostructure surface is formed. It is found that the fuzz layer thickness, d fuzz , plays a dominant role in determining the motion of arc spots, the arc ignition probability, and arc plasma parameters. High-speed imaging reveals that the motion of arc spots becomes more collective, as d fuzz increases. Interestingly, arc spots make a circle while moving outward. With increasing d fuzz , the amount of eroded W atoms increases, as indicated from an observed increase in the total visible emission intensity, while the arc ignition probability is found to drop. The physical mechanisms are discussed, in detail, based on spectroscopic measurements of the electron temperature, obtained from Boltzmann plots of both W I and W II, and the electron density, determined from Stark broadening of W I lines.

Physics↗