scholarly journals Nanoscale analysis of superconducting Fe(Se,Te) epitaxial thin films and relationship with pinning properties

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Mario Scuderi ◽  
Ilaria Pallecchi ◽  
Antonio Leo ◽  
Angela Nigro ◽  
Gaia Grimaldi ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Thin Films ◽  
Large Scale ◽  
Mean Free Path ◽  
Coated Conductors ◽  
Epitaxial Thin Films ◽  
Field Orientation ◽  
Pinning Centers ◽  
The Magnetic Field ◽  
Pinning Properties

AbstractThe process of developing superconducting materials for large scale applications is mainly oriented to optimize flux pinning and the current carrying capability. A powerful approach to investigate pinning properties is to combine high resolution imaging with transport measurements as a function of the magnetic field orientation, supported by a pinning modelling. We carry out Transmission Electron Microscopy, Electron Energy Loss Spectroscopy and critical current measurements in fields up to 16 T varying the angle between the field and c-axis of Fe(Se,Te) epitaxial thin films deposited on CaF2 substrates. We find evidence of nanoscale domains with different Te:Se stoichiometry and/or rotated and tilted axes, as well as of lattice distortions and two-dimensional defects at the grain boundaries. These elongated domains are tens of nm in size along the in-plane axes. We establish a correlation between these observed microstructural features and the pinning properties, specifically strongly enhanced pinning for the magnetic field oriented in-plane and pinning emerging at higher fields for out-of-plane direction. These features can be accounted for within a model where pinning centers are local variations of the critical temperature and local variations of the mean free path, respectively. The identification of all these growth induced defects acting as effective pinning centers may provide useful information for the optimization of Fe(Se,Te) coated conductors.

scholarly journals Formation of the Musca filament: evidence for asymmetries in the accretion flow due to a cloud–cloud collision

2020 ◽  
Vol 644 ◽  
pp. A27
Author(s):  
L. Bonne ◽  
S. Bontemps ◽  
N. Schneider ◽  
S. D. Clarke ◽  
D. Arzoumanian ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Radiative Transfer ◽  
Velocity Gradient ◽  
Large Scale ◽  
Transverse Velocity ◽  
Local Magnetic Field ◽  
Filament Formation ◽  
Field Orientation ◽  
Physical Conditions ◽  
The Magnetic Field

Context. Dense molecular filaments are ubiquituous in the interstellar medium, yet their internal physical conditions and the role of gravity, turbulence, the magnetic field, radiation, and the ambient cloud during their evolution remain debated. Aims. We study the kinematics and physical conditions in the Musca filament, the ambient cloud, and the Chamaeleon-Musca complex to constrain the physics of filament formation. Methods. We produced CO(2–1) isotopologue maps with the APEX telescope that cut through the Musca filament. We further study a NANTEN2 12CO(1–0) map of the full Musca cloud, H I emission of the Chamaeleon-Musca complex, a Planck polarisation map, line radiative transfer models, Gaia data, and synthetic observations from filament formation simulations. Results. The Musca cloud, with a size of ~3–6 pc, contains multiple velocity components. Radiative transfer modelling of the CO emission indicates that the Musca filament consists of a cold (~10 K), dense (nH2 ∼ 104 cm−3) crest, which is best described with a cylindrical geometry. Connected to the crest, a separate gas component at T ~ 15 K and nH2 ∼ 103 cm−3 is found, the so-called strands. The velocity-coherent filament crest has an organised transverse velocity gradient that is linked to the kinematics of the nearby ambient cloud. This velocity gradient has an angle ≥30° with respect to the local magnetic field orientation derived from Planck, and the magnitude of the velocity gradient is similar to the transonic linewidth of the filament crest. Studying the large scale kinematics, we find coherence of the asymmetric kinematics from the 50 pc H I cloud down to the Musca filament. We also report a strong [C18O]/[13CO] abundance drop by an order of magnitude from the filament crest to the strands over a distance <0.2 pc in a weak ambient far-ultraviolet (FUV) field. Conclusions. The dense Musca filament crest is a long-lived (several crossing times), dynamic structure that can form stars in the near future because of continuous mass accretion replenishing the filament. This mass accretion on the filament appears to be triggered by a H I cloud–cloud collision, which bends the magnetic field around dense filaments. This bending of the magnetic field is then responsible for the observed asymmetric accretion scenario of the Musca filament, which is, for instance, seen as a V-shape in the position–velocity (PV) diagram.

scholarly journals Is the Magnetic Field Preserved During Core Formation?

2004 ◽  
Vol 221 ◽  
pp. 97-103
Author(s):  
Brenda C. Matthews ◽  
Shih-Ping Lai ◽  
Richard M. Crutcher ◽  
Christine D. Wilson
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Position Angle ◽  
Dark Cloud ◽  
Field Orientation ◽  
Nearby Star ◽  
Star Forming ◽  
Ordered Fields ◽  
Field Geometry ◽  
The Magnetic Field

We present recent JCMT and BIMA array polarimetry data of nearby star-forming regions in order to compare the core and cloud-scale magnetic field geometries in two regions of Orion. The similarity of the magnetic field geometry in these cores to that of their ambient clouds is contrasted with JCMT data toward the Barnard 1 dark cloud in Perseus, which reveal a different magnetic field orientation between the majority of the cores and the surrounding cloud; each of the cores exhibits a different mean polarization position angle. We conclude that the preservation of the magnetic field geometry is better in cores formed within clouds with ordered large scale structures. In Barnard 1, the cores may quickly exhibit a different polarization pattern if they have, for example, rotation which differs from the large scale cloud motions, or a weaker component of ordered fields. This could also explain why the cores exhibit such different geometries from each other in Barnard 1.

scholarly journals An observational correlation between magnetic field, angular momentum and fragmentation in the envelopes of Class 0 protostars?

2020 ◽  
Vol 644 ◽  
pp. A47
Author(s):  
Maud Galametz ◽  
Anaëlle Maury ◽  
Josep M. Girart ◽  
Ramprasad Rao ◽  
Qizhou Zhang ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Angular Momentum ◽  
Large Scale ◽  
Magnetic Energy ◽  
Line Emission ◽  
Strong Relationship ◽  
Field Orientation ◽  
Multiple Systems ◽  
Magnetic Field Orientation ◽  
The Magnetic Field

Aims. The main goal of the following analysis is to assess the potential role of magnetic fields in regulating the envelope rotation, the formation of disks and the fragmentation of Class 0 protostars in multiple systems. Methods. We use the Submillimeter Array to carry out observations of the dust polarized emission at 0.87 mm, in the envelopes of a large sample of 20 Class 0 protostars. We estimate the mean magnetic field orientation over the central 1000 au envelope scales to characterize the orientation of the main component of the organized magnetic field at the envelope scales in these embedded protostars. This direction is compared to that of the protostellar outflow in order to study the relation between their misalignment and the kinematics of the circumstellar gas. The latter is traced via velocity gradient observed in the molecular line emission (mainly N2H+) of the gas at intermediate envelope scales. Results. We discover a strong relationship between the misalignment of the magnetic field orientation with the outflow and the amount of angular momentum observed at similar scales in the protostellar envelope, revealing a potential link between the kinetic and the magnetic energy at envelope scales. The relation could be driven by favored B-misalignments in more dynamical envelopes or a dependence of the envelope dynamics with the large-scale B initial configuration. Comparing the trend with the presence of fragmentation, we observe that single sources are mostly associated with conditions of low angular momentum in the inner envelope and good alignment of the magnetic field with protostellar outflows, at intermediate scales. Our results suggest that the properties of the magnetic field in protostellar envelopes bear a tight relationship with the rotating-infalling gas directly involved in the star and disk formation: we find that it may not only influence the fragmentation of protostellar cores into multiple stellar systems, but also set the conditions establishing the pristine properties of planet-forming disks.

scholarly journals Thin-shell approach for modeling superconducting tapes in the H-Φ finite-element formulation

2021 ◽  
Author(s):  
Bruno de Sousa Alves ◽  
Valtteri Lahtinen ◽  
Marc Laforest ◽  
Frederic Sirois
Keyword(s):  
Magnetic Field ◽  
Finite Element ◽  
Thin Shell ◽  
Large Scale ◽  
Computational Cost ◽  
Coated Conductors ◽  
Element Formulation ◽  
Electromagnetic Modeling ◽  
Superconducting Tapes ◽  
The Magnetic Field

Abstract This paper presents a novel finite-element approach for the electromagnetic modeling of superconducting coated conductors with transport currents. We combine a thin-shell (TS) method to the H-Φ formulation to avoid the meshing difficulties related to the high aspect ratio of these conductors and reduce the computational burden in simulations. The interface boundary conditions in the TS method are defined using an auxiliary 1-D finite-element (FE) discretization of N elements along the thinnest dimension of the conductor. This procedure permits the approximation of the superconductor's nonlinearities inside the TS in a time-transient analysis. Four application examples of increasing complexity are discussed: (i) single coated conductor, (ii) two closely packed conductors carrying anti-parallel currents, (iii) a stack of twenty superconducting tapes and a (iv) full representation of a HTS tape comprising a stack of thin films. In all these examples, the profiles of both the tangential and normal components of the magnetic field show good agreement with a reference solution obtained with standard black2-D H-Φ formulation. Results are also compared with the widely used T-A formulation. This formulation is shown to be dual to the TS model with a single FE (N=1) in the auxiliary 1-D systems. The increase of N in the TS model is shown to be advantageous at small inter-tape separation and low transport current since it allows the tangential components of the magnetic field to penetrate the thin region. The reduction in computational cost without compromising accuracy makes the proposed model promising for the simulation of large-scale superconducting applications.

Evolution of Large-Scale Coronal Structures

1994 ◽  
Vol 144 ◽  
pp. 29-33
Author(s):  
P. Ambrož
Keyword(s):  
Magnetic Field ◽  
Field Line ◽  
Large Scale ◽  
Coronal Magnetic Field ◽  
Source Surface ◽  
Solar Cycles ◽  
Characteristic Relationship ◽  
The Magnetic Field ◽  
Coronal Structures

AbstractThe large-scale coronal structures observed during the sporadically visible solar eclipses were compared with the numerically extrapolated field-line structures of coronal magnetic field. A characteristic relationship between the observed structures of coronal plasma and the magnetic field line configurations was determined. The long-term evolution of large scale coronal structures inferred from photospheric magnetic observations in the course of 11- and 22-year solar cycles is described.Some known parameters, such as the source surface radius, or coronal rotation rate are discussed and actually interpreted. A relation between the large-scale photospheric magnetic field evolution and the coronal structure rearrangement is demonstrated.

scholarly journals An 84-μG Magnetic Field in a Galaxy at Z=0.692?

2008 ◽  
Vol 4 (S254) ◽  
pp. 95-96
Author(s):  
Arthur M. Wolfe ◽  
Regina A. Jorgenson ◽  
Timothy Robishaw ◽  
Carl Heiles ◽  
Jason X. Prochaska
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Faraday Rotation ◽  
Large Scale ◽  
Dynamo Model ◽  
Magnetic Field Generation ◽  
Interstellar Gas ◽  
Splitting Technique ◽  
Average Value ◽  
The Magnetic Field

AbstractThe magnetic field pervading our Galaxy is a crucial constituent of the interstellar medium: it mediates the dynamics of interstellar clouds, the energy density of cosmic rays, and the formation of stars (Beck 2005). The field associated with ionized interstellar gas has been determined through observations of pulsars in our Galaxy. Radio-frequency measurements of pulse dispersion and the rotation of the plane of linear polarization, i.e., Faraday rotation, yield an average value B ≈ 3 μG (Han et al. 2006). The possible detection of Faraday rotation of linearly polarized photons emitted by high-redshift quasars (Kronberg et al. 2008) suggests similar magnetic fields are present in foreground galaxies with redshifts z > 1. As Faraday rotation alone, however, determines neither the magnitude nor the redshift of the magnetic field, the strength of galactic magnetic fields at redshifts z > 0 remains uncertain.Here we report a measurement of a magnetic field of B ≈ 84 μG in a galaxy at z =0.692, using the same Zeeman-splitting technique that revealed an average value of B = 6 μG in the neutral interstellar gas of our Galaxy (Heiles et al. 2004). This is unexpected, as the leading theory of magnetic field generation, the mean-field dynamo model, predicts large-scale magnetic fields to be weaker in the past, rather than stronger (Parker 1970).The full text of this paper was published in Nature (Wolfe et al. 2008).

scholarly journals No-z Model for Magnetic Fields of Different Astrophysical Objects and Stability of the Solutions

Data ◽  
2021 ◽  
Vol 6 (1) ◽  
pp. 4
Author(s):  
Evgeny Mikhailov ◽  
Daniela Boneva ◽  
Maria Pashentseva
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Large Scale ◽  
Point Of View ◽  
Accretion Discs ◽  
Wide Range ◽  
Astrophysical Objects ◽  
Alpha Effect ◽  
The Stability ◽  
The Magnetic Field

A wide range of astrophysical objects, such as the Sun, galaxies, stars, planets, accretion discs etc., have large-scale magnetic fields. Their generation is often based on the dynamo mechanism, which is connected with joint action of the alpha-effect and differential rotation. They compete with the turbulent diffusion. If the dynamo is intensive enough, the magnetic field grows, else it decays. The magnetic field evolution is described by Steenbeck—Krause—Raedler equations, which are quite difficult to be solved. So, for different objects, specific two-dimensional models are used. As for thin discs (this shape corresponds to galaxies and accretion discs), usually, no-z approximation is used. Some of the partial derivatives are changed by the algebraic expressions, and the solenoidality condition is taken into account as well. The field generation is restricted by the equipartition value and saturates if the field becomes comparable with it. From the point of view of mathematical physics, they can be characterized as stable points of the equations. The field can come to these values monotonously or have oscillations. It depends on the type of the stability of these points, whether it is a node or focus. Here, we study the stability of such points and give examples for astrophysical applications.

scholarly journals Circumstellar environment of 55 Cancri

2020 ◽  
Vol 633 ◽  
pp. A48 ◽  
Author(s):  
C. P. Folsom ◽  
D. Ó Fionnagáin ◽  
L. Fossati ◽  
A. A. Vidotto ◽  
C. Moutou ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Stellar Wind ◽  
Large Scale ◽  
Rotation Axis ◽  
Doppler Imaging ◽  
Magnetic Pole ◽  
Average Strength ◽  
Detailed Understanding ◽  
The Magnetic Field ◽  
Circumstellar Environment

Context. 55 Cancri hosts five known exoplanets, most notably the hot super-Earth 55 Cnc e, which is one of the hottest known transiting super-Earths. Aims. Because of the short orbital separation and host star brightness, 55 Cnc e provides one of the best opportunities for studying star-planet interactions (SPIs). We aim to understand possible SPIs in this system, which requires a detailed understanding of the stellar magnetic field and wind impinging on the planet. Methods. Using spectropolarimetric observations and Zeeman Doppler Imaging, we derived a map of the large-scale stellar magnetic field. We then simulated the stellar wind starting from the magnetic field map, using a 3D magneto-hydrodynamic model. Results. The map of the large-scale stellar magnetic field we derive has an average strength of 3.4 G. The field has a mostly dipolar geometry; the dipole is tilted by 90° with respect to the rotation axis and the dipolar strength is 5.8 G at the magnetic pole. The wind simulations based on this magnetic geometry lead us to conclude that 55 Cnc e orbits inside the Alfvén surface of the stellar wind, implying that effects from the planet on the wind can propagate back to the stellar surface and result in SPI.

Large scale magnetic anomalies over western Canada and the Arctic: a discussion

1976 ◽  
Vol 13 (6) ◽  
pp. 790-802 ◽  
Author(s):  
R. L. Coles ◽  
G. V. Haines ◽  
W. Hannaford
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Elevated Temperatures ◽  
Magnetic Anomalies ◽  
The Arctic ◽  
Evolutionary Development ◽  
Magnetic Feature ◽  
Western Canada ◽  
Arctic Regions ◽  
The Magnetic Field

A contoured map of vertical magnetic field residuals (relative to the IGRF) over western Canada and adjacent Arctic regions has been produced by amalgamating new data with those from previous surveys. The measurements were made at altitudes between 3.5 and 5.5 km above sea level. The map shows the form of the magnetic field within the waveband 30 to 5000 km. A magnetic feature of several thousand kilometres wavelength dominates the map, and is probably due in major part to sources in the earth's core. Superimposed on this are several groups of anomalies which contain wavelengths of the order of a thousand kilometres. The patterns of the short wavelength anomalies provide a broad view of major structures and indicate several regimes of distinctive evolutionary development. Enhancement of viscous magnetization at elevated temperatures may account for the concentration of intense anomalies observed near the western edge of the craton.

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