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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS2005

An Expanding Radio Nebula Produced by a Giant Flare from the Magnetar SGR 1806-20

Soft gamma repeaters (SGRs) are "magnetars", a small class of slowly spinning neutron stars with extreme surface magnetic fields, B approx. 10(sup 15) gauss. On 2004 December 27, a giant flare was detected from the magnetar SGR 1806-20, the third such event ever recorded. This burst of energy, which resulted in the highest flux of gamma-rays ever measured from a celestial object, was detected by a variety of instruments and even caused an ionospheric disturbance in the Earth's upper atmosphere recorded around the globe. Here we report the detection of a very bright but rapidly-fading radio source at the position of SGR 1806-20 following this outburst. From day 6 to day 19 after the flare, we see a resolved, linearly polarized, radio nebula, expanding at a velocity of approximately 0.3c. To create this nebula, at least 4 x 10(exp 43) ergs of energy must have been emitted by the giant flare in the form of magnetic fields and relativistic particles. The steep decline of the radio flux may indicate episodic particle acceleration followed by adiabatic expansion, as could occur if the ejecta have energized a thin shell surrounding a preexisting cavity.

Gaensler, B. M.↗
NASA NTRS2014

Simulations of Emerging Magnetic Flux. II. The Formation of Unstable Coronal Flux Ropes and the Initiation of Coronal Mass Ejections

We present results from three-dimensional magnetohydrodynamic simulations of the emergence of a twisted convection zone flux tube into a pre-existing coronal dipole field. As in previous simulations, following the partial emergence of the sub-surface flux into the corona, a combination of vortical motions and internal magnetic reconnection forms a coronal flux rope. Then, in the simulations presented here, external reconnection between the emerging field and the pre-existing dipole coronal field allows further expansion of the coronal flux rope into the corona. After sufficient expansion, internal reconnection occurs beneath the coronal flux rope axis, and the flux rope erupts up to the top boundary of the simulation domain (approximately 36 Mm above the surface).We find that the presence of a pre-existing field, orientated in a direction to facilitate reconnection with the emerging field, is vital to the fast rise of the coronal flux rope. The simulations shown in this paper are able to self-consistently create many of the surface and coronal signatures used by coronal mass ejection (CME) models. These signatures include surface shearing and rotational motions, quadrupolar geometry above the surface, central sheared arcades reconnecting with oppositely orientated overlying dipole fields, the formation of coronal flux ropes underlying potential coronal field, and internal reconnection which resembles the classical flare reconnection scenario. This suggests that proposed mechanisms for the initiation of a CME, such as "magnetic breakout," are operating during the emergence of new active regions.

corona↗
DOE OSTI2025

Anomalies in the electromagnetic response and peculiarities of the domain structure in the magnetic Weyl semimetal Co 3⁢ Sn 2 ⁢S 2

In this paper, we present a comprehensive study of magnetic properties of Co 3 ⁢Sn 2 ⁢S 2 (CoSnS) crystals using macroscopic characterization and observations of the domain structure (DS) in a wide range of easy- and hard-axis fields (𝐻) and temperatures (𝑇). From macroscopic measurements, we derive temperature dependences of the basic magnetic parameters of the material [saturation magnetization 𝑀 𝑠 ⁡(𝑇), uniaxial anisotropy constant 𝐾⁡(𝑇), and exchange stiffness 𝐴⁡(𝑇)] and, based on them, calculate the thermodynamic magnetization 𝑀⁡(𝐻,𝑇) curves and DS parameters for pinning-free samples. We find important qualitative and quantitative differences between the theory and experiment defined by the efficient pinning of domain walls (DWs) in our samples. It turns out that, already at temperatures close to the ferromagnetic transition 𝑇 𝑐 , the DW dynamics falls into the heavy creep regime, resulting in a strong deferral of the DS adjustment into the equilibrium state. Here, we suggest that specific magnetic defects, responsible for pinning and causing field-tuned reproducible domain nucleation patterns observed in our high-quality samples, are pointlike. Recently found magnetic polarons formed around vacancies and impurities, which carry strong diamagnetic moments of spin-orbit nature and are intrinsic for CoSnS and expected in other Weyl semimetals, are a possible source of pinning yielding peculiar 𝑀⁡(𝐻,𝑇) response of CoSnS.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2026

Tunable symmetry breaking in a hexagonal-stacked moiré magnet

Symmetry plays a central role in defining magnetic phases, making tunable symmetry breaking across magnetic transitions highly desirable for discovering non-trivial magnetism. Magnetic moiré superlattices, formed by twisting two-dimensional magnetic crystals, have been theoretically proposed and experimentally explored as platforms for unconventional magnetic states. However, despite recent advances, the ability to tune symmetry breaking in moiré magnetism remains limited, as twisted two-dimensional magnets predominantly inherit the magnetic properties and symmetries of their constituent layers. Here, in this work, we demonstrate a clear evolution of symmetry in hexagonal-stacked twisted double-bilayer CrI 3 as the twist angle increases from 180° to 190°. Although the net magnetization remains zero across this twist-angle range, the magnetic phase breaks only the threefold rotational symmetry at 180°, but it breaks all the rotational, mirror and time-reversal symmetries at intermediate twist angles between 181° and 185°, and all broken symmetries are recovered at 190°. This pronounced symmetry breaking at intermediate twist angles is accompanied by metamagnetic behaviour, evidenced by symmetric double hysteresis loops around zero magnetic field. Together, these results reveal that hexagonal-stacked twisted double-bilayer CrI3 at intermediate twist angles hosts a distinct moiré magnetic phase, featuring periodic in-plane spin textures with broken rotational, mirror and time-reversal symmetries.

Sun, Zeliang (ORCID:0009000770748064)↗
DOE OSTI2026

Picolinate-based acyclic ligand for rare earth element extraction and separation

The rare earth elements (REEs) play an important role in many modern technologies, particularly those relevant to clean energy. Despite their increasing importance, obtaining them in elementally pure forms suitable for downstream applications is challenging due to their similar chemical properties. This problem has impeded efforts to efficiently and selectively extract them from end-of-life materials and electronic waste. Here, we report a cost-efficient acyclic picolinate-based chelator H 4 aapa. The REE stability constants (log K ML ) of this chelator were measured via pH potentiometric and UV-Visible spectrophotometric titrations, revealing it to preferably bind light over heavy REEs like many recently reported 18-membered macrocycles. Its REE complexes were characterized by X-ray crystallography and NMR spectroscopy, demonstrating that this chelator can attain different conformations. The unique properties of aapa were subsequently used to separate REEs via the dissolution of insoluble REE oxalate mixtures. This dissolution-based separation led to large separation factors, the most significant being that for the Ce 3+ /Lu 3+ pair (38.6) at pH 4. Leveraging the strong REE binding affinity of aapa, we further demonstrated this chelator can leach REEs from authentic end-of-life materials in the form of magnet waste and autocatalyst smelting (autocat) slag. With this approach, exposure of these materials to a 20 mM solution of aapa at neutral pH generates a metal-containing solution enriched in Nd 3+ and Dy 3+ by 56.9 wt% and 3.0 wt%, marking a 4-fold improvement over the use of 4 M HNO 3 .

Gao, Yangyang [University of California, Santa Bar↗
DOE OSTI2024

Multiferroicity and Topology in Twisted Transition Metal Dichalcogenides

Van der Waals heterostructures have recently emerged as an exciting platform for investigating the effects of strong electronic correlations, including various forms of magnetic or electrical orders. Here, we perform an unbiased exact diagonalization study of the effects of interactions on topological flat bands of twisted transition metal dichalcogenides (TMDs) at odd integer fillings. For hole-filling ν h = 1 , we find that the Chern insulator phase, expected from interaction-induced spin-valley polarization of the bare bands, is quite fragile, and gives way to spontaneous multiferroic order—coexisting ferroelectricity and ferromagnetism, in the presence of long-range Coulomb repulsion. We provide a simple real-space picture to understand the phase diagram as a function of interaction range and strength. Our findings establish twisted TMDs as a novel and highly tunable platform for multiferroicity, and we outline a potential route towards electrical control of magnetism in the multiferroic phase. Published by the American Physical Society 2024

Abouelkomsan, Ahmed (ORCID:0000000247873357)↗
DOE OSTI2024

Spin-Charge-Lattice Coupling across the Charge Density Wave Transition in a Kagome Lattice Antiferromagnet

Understanding spin and lattice excitations in a metallic magnetic ordered system forms the basis to unveil the magnetic and lattice exchange couplings and their interactions with itinerant electrons. Kagome lattice antiferromagnet FeGe is interesting because it displays a rare charge density wave (CDW) deep inside the antiferromagnetic ordered phase that interacts with the magnetic order. Here, we use neutron scattering to study the evolution of spin and lattice excitations across the CDW transition 𝑇 CDW in FeGe. While spin excitations below ∼100 meV can be well described by spin waves of a spin-1 Heisenberg Hamiltonian, spin excitations at higher energies are centered around the Brillouin zone boundary and extend up to ∼180 meV consistent with quasiparticle excitations across spin-polarized electron-hole Fermi surfaces. Furthermore, 𝑐-axis spin wave dispersion and Fe-Ge optical phonon modes show a clear hardening below 𝑇 CDW due to spin-charge-lattice coupling but with no evidence of a phonon Kohn anomaly. By comparing our experimental results with density functional theory calculations in absolute units, we conclude that FeGe is a Hund’s metal in the intermediate correlated regime where magnetism has contributions from both itinerant and localized electrons arising from spin polarized electronic bands near the Fermi level.

charge density waves↗
NASA NTRS1973

Celescope catalog of ultraviolet stellar observations

The catalog contains the observational results obtained by the Celescope Experiment during the first 16 months of operation of NASA's Orbiting Astronomical Observatory (OAO-2). It lists the results of the stellar observations, along with selected ground-based information obtained from the available literature. Lunar observations (Ahmad and Deutschman, 1972), as well as other analyses of the data, are being published as separate papers. These data are available in two forms: (1) magnetic tapes and the necessary utility programs for reading and printing the contents of the tapes; and (2) this catalog, transcribed from the magnetic-tape catalog. The magnetic tape version contains not only the compiled results but also the results of the individual observations from which these averaged data were compiled.

Davis, R. J.↗
NASA NTRS1974

Electronic magnification for astronomical camera tubes

Definitions, test schemes, and analyses used to provide variable magnification in the image section of the television sensor for large space telescopes are outlined. Experimental results show a definite form of magnetic field distribution is necessary to achieve magnification in the range 3X to 4X. Coil systems to establish the required field shapes were built, and both image intensifiers and camera tubes were operated at high magnification. The experiments confirm that such operation is practical and can provide satisfactory image quality. The main problem with such a system was identified as heating of the photocathode due to concentration of coil power dissipation in that vicinity. Suggestions for overcoming this disadvantage are included.

Vine, J.↗
NASA NTRS1975

University of Utah (Wallops) precision meteorological data digitizer

The data digitizing system takes pulsed signals from meteorological rocket sondes and radiosondes and converts the information (the time interval between pulses) into a digital form for magnetic recording and further processing by digital computer. The basic digitizer configuration contains a master sequencer that allows for data storage and release in an accumulator. Thus, the digitizer provides for convenient interfacing in real time monitoring.

Staffanson, F. L.↗
NASA NTRS1975

Four years experience in APMS star plate processing - Results and future plans

The present paper describes an automated system for measuring stellar proper motions on the basis of information contained in photographic plates. In this system, the images on a star plate are digitized by a scanning microdensitometer using light from a He-Ne gas laser, and a special-purpose computer arranges the measurements in computer-compatible form on magnetic tape. The scanning and image-reconstruction processes are briefly outlined, and the image-evaluation techniques are discussed. It is shown that the present system has been especially successful in measuring the proper motions of low-luminosity stars, including 119 stars with less than 1/10,000 of the solar bolometric luminosity. Plans for measurements of high-density Milky Way star plates are noted.

Newcomb, J. S.↗
NASA NTRS1976

Magnetic acceleration of winds from solar-type stars

The spin-down of solar type stars (F5 V to G3 V) is generally ascribed to the outflow of magnetized plasma in the form of a wind. Magnetically coupled stellar winds are thought to provide the dominant mechanism for angular momentum loss over the entire main-sequence lifetime of stars possessing hydrogen convective zones. The associated loss in rotational kinetic energy can strongly affect the energetics of winds emanating from such stars, for sufficiently high rotation rates and magnetic field strengths. In the present paper, an attempt is made to describe qualitatively how MHD plasma outflow from a rotating star adjusts itself to a broad range of stellar conditions, including fast, intermediate, and slow magnetic rotator configurations. Using the Weber and Davis (1967) model of MHD winds, it is shown that the magnetic deceleration of an MHD wind is of importance when the loss of rotational kinetic energy due to magnetic braking exceeds the energy flux due to thermal processes alone.

Belcher, J. W.↗
NASA NTRS1979

New models of solar faculae

A new semiempirical model of photospheric faculae is presented in tabular form. The magnetic field is estimated from horizontal pressure equilibrium without tension forces. The geometry of the flux tube is determined from this estimated magnetic field and an assumed flux of 4.4 x 10 to the 17th gauss sq cm. The model is discussed in relation to recent observations.

Chapman, G. A.↗
NASA NTRS1981

Computer simulation of a geomagnetic substorm

A global two-dimensional simulation of a substormlike process occurring in earth's magnetosphere is presented. The results are consistent with an empirical substorm model - the neutral-line model. Specifically, the introduction of a southward interplanetary magnetic field forms an open magnetosphere. Subsequently, a substorm neutral line forms at about 15 earth radii or closer in the magnetotail, and plasma sheet thinning and plasma acceleration occur. Eventually the substorm neutral line moves tailward toward its presubstorm position.

Lyon, J. G.↗
NASA NTRS1981

Magnetic loop behind an interplanetary shock - Voyager, Helios, and IMP 8 observations

The flow behind an interplanetary shock was analyzed through the use of magnetic field and plasma data from five spacecraft, with emphasis on the magnetic cloud identified by a characteristic variation of the latitude angle of the magnetic field. The size of the cloud was found to be about 0.5 AU in radial extent and greater than 30 deg in azimuthal extent, with its front boundary almost normal to the radial direction. Because the field direction of the magnetic cloud as it moved past the spacecraft was observed to rotate nearly parallel to a plane, it is thought that the field configuration of the cloud was essentially two-dimensional. These results further suggest that the lines of force in the magnetic cloud formed loops, but it could not be determined whether these loops were open or closed.

Burlaga, L.↗
NASA NTRS1980

Remote sensing of benthic microalgal biomass with a tower-mounted multispectral scanner

A remote sensing instrument was mounted on a 50-ft tower overlooking North Inlet Estuary, South Carolina in order to conduct a remote sensing study of benthic microalgae. The instrument was programmed to take multispectral imagery data along a 90 deg horizontal frame in six spectral bands ranging from 400-1050 nm and had a ground resolution of about 3 cm. Imagery measurements were encoded in digital form on magnetic tape and were stored, decoded, and manipulated by computer. Correlation coefficients were calculated on imagery data and chlorophyll a concentrations derived from ground truth data. The most significant correlation occurred in the blue spectral band with numerical values ranging from -0.81 to -0.88 for three separate sampling periods. Mean values of chlorophyll a for a larger section of mudflat were estimated using regression equations. The scanner has provided encouraging results and promises to be a useful tool in sampling the biomass of intertidal benthic microalgae.

Jobson, D. J.↗
NASA NTRS1986

Near-tail reconnection as the cause of cometary tail disconnections

In a cometary tail disconnection event the plasma tail appears to separate from the coma and to accelerate away from it. As this occurs a new tail begins to form. It is proposed that these disconnections arise in a manner analogous to geomagnetic substorms, i.e., by the formation of a strongly reconnecting region in the near tail that forms a magnetic island in the coma and ejects the plasma tail by strengthening the magnetic 'slingshot' within the tail. This reconnection process may be triggered by several different processes, such as interplanetary shocks or variations in the Alfven Mach number.

Russell, C. T.↗