Magnetic Fine Structure Research Articles

Stereoscopic diagnosing of a filament-cavity flux rope system by tracing the path of a two-sided-loop jet

ABSTRACT The fine magnetic structure is vitally important to understanding the formation, stabilization, and eruption of solar filaments, but so far, it is still an open question yet to be resolved. Using stereoscopic observations taken by the Solar Dynamics Observatory and Solar TErrestrial RElations Obsevatory, we studied the generation mechanism of a two-sided-loop jet (TJ) and the ejection process of the jet plasma into the overlying filament-cavity system. We find that the generation of the two-sided-loop jet was due to the magnetic reconnection between an emerging flux loop and the overlying filament. The jet’s two arms ejected along the filament axis during the initial stage. Then, the north arm bifurcated into two parts at about 50 Mm from the reconnection site. After the bifurcation, the two bifurcated parts were along the filament axis and the cavity which hosted the filament, respectively. By tracing the ejecting plasma flows of the TJ inside the filament, we not only measured that the magnetic twist stored in the filament was at least 5π but also found that the fine magnetic structure of the filament-cavity flux rope system is in well agreement with the theoretical results of Magnetic flux rope models.

Magnetized supersonic downflows in the chromosphere

The chromosphere above active regions (ARs) on the Sun hosts magnetized supersonic downflows. Studies of these supersonic downflows help to decipher the magnetic fine structure and dynamics of the chromosphere. We perform a statistical analysis of the magnetized supersonic downflows in a number of ARs at different evolutionary stages and survey their characteristics. We analyze spectro-polarimetric scans of parts of 13 ARs obtained in the infrared He I 10 830 Å triplet formed in the upper chromosphere recorded with the GREGOR Infrared Spectrograph mounted at the GREGOR solar telescope. We retrieve the line-of-sight velocities and the magnetic field vector using the HELIX+ inversion code that assumes Milne-Eddington atmospheres. We find magnetized supersonic downflows in all the ARs, with larger area coverage by such flows in ARs observed during their emerging phase. The fact that supersonic downflows were detected in all scans, albeit only covering a small fraction, 0.2–6.4%, of the observed field-of-view, suggests that they are a comparatively common phenomenon in the upper chromospheres of ARs. The supersonic downflows are found to be associated with many AR features, such as pores, sunspot umbrae, sunspot penumbrae, light bridges, plages, He I loops as part of arch filament systems characteristic of emerging fields, and filaments. Although several mechanisms are identified to be causing the supersonic downflows, by far the most common one appears to be the draining of plasma along the legs of rising magnetic loops. The loops mainly drain into forming pores. The line-of-sight velocities of the supersonic downflows reach values of up to 49 km s−1, and the velocity distribution shows multiple populations. Almost 92% of these supersonic downflows coexist with a subsonic flow component. The weaker, more horizontal fields associated with the supersonic component suggests that it is formed above the subsonic component.

The magnetic fine structure of the Sun’s polar region as revealed by Sunrise

Context. Polar magnetic fields play a key role in the solar magnetic cycle and they are the source of a significant portion of the interplanetary magnetic field. However, observations of the poles are challenging and hence our understanding of the polar magnetic environment is incomplete. Aims. We deduce properties of small-scale magnetic features in the polar region using high-resolution data and specifically aim to determine the flux per patch above which one magnetic polarity starts to dominate over the other. Methods. We study the high spatial resolution, seeing-free observations of the north solar polar region, obtained with the IMaX instrument on-board the balloon-borne SUNRISE observatory during June 2009, at the solar activity minimum. We performed inversions of the full Stokes vector recorded by IMaX to retrieve atmospheric parameters of the Sun’s polar region, mainly the temperature stratification and the magnetic field vector. Results. We infer kilo-Gauss (kG) magnetic fields in patches harbouring polar faculae, without resorting to a magnetic filling factor. Within these patches we find the maxima of the magnetic field to be near the dark narrow lanes, which are shifted towards the disc centre side in comparison to the maxima in continuum intensity. In contrast, we did not find any fields parallel to the solar surface with kG strengths. In addition to the kG patches, we found the polar region to be covered in patches of both polarities, which have a range of sizes. We find the field strength of these patches to increase with increasing size and flux, with the smaller patches showing a significant dispersion in field strength. The dominating polarity of the north pole during this phase of the solar cycle is found to be maintained by the larger patches with fluxes above 2.3 × 1017 Mx.

Hfszeeman95—A program for computing weak and intermediate magnetic-field- and hyperfine-induced transition rates

Hfszeeman95 is an updated and extended Fortran 95 version of the Hfszeeman program (Andersson and Jönsson, 2008). Given relativistic atomic state functions generated by the Grasp2018 package (Fischer et al., 2019), Hfszeeman95 together with the accompanying Matlab/GNU Octave program Mithit allows for: (1) the computation and plotting of Zeeman energy splittings of magnetic fine- and hyperfine structure substates as functions of the strength of an external magnetic field, (2) the computation of transition rates between different magnetic fine- and hyperfine structure substates in the presence of an external magnetic field and rates of hyperfine-induced transitions in the field free limit, (3) the synthesization of spectral profiles for transitions obtained from (2). With the new features, Hfszeeman95 and the accompanying Matlab/GNU Octave program Mithit are useful for the analysis of observational spectra and to resolve the complex features due to the splitting of the fine and hyperfine levels. Program summaryProgram Title:Hfszeeman95Program Files doi:http://dx.doi.org/10.17632/rv2vycs7pg.1Licensing provisions: GNU General Public License 3Programming language: Fortran 95, Matlab/GNU OctaveNature of problem: Calculation of transition energies and rates between different magnetic fine- and hyperfine structure substates in the presence of an external magnetic field and rates of hyperfine induced transitions in the field free limit. Synthesization of spectral profiles.Solution method: Wave functions for magnetic fine structure substates in the field free case are given by atomic state functions (ASFs). The ASFs are expansions over configuration state functions (CSFs) |ΓJMJ〉=∑γcγ|γJMJ〉.The ASFs are computed by the Grasp2018 relativistic atomic structure package (Fischer et al., 2018) and are supposed to be available. Wave functions for magnetic fine structure substates in an external magnetic field are expanded in a basis of ASFs |Γ˜MJ〉=∑ΓJdΓJ|ΓJMJ〉.Wave functions for magnetic hyperfine structure substates in an external magnetic field are expanded in a basis of the combined nuclear and atomic system |Γ˜IMF〉=∑ΓJFdΓJF|ΓIJFMF〉,where |ΓIJFMF〉 are coupled nuclear and atomic functions |ΓIJFMF〉=∑MI,MJ〈IJMIMJ|IJFMF〉|IMI〉|ΓJMJ〉.Reduced hyperfine and Zeeman matrix elements, used to construct the total interaction matrix in the given basis, are computed as sums over reduced one-particle matrix elements of orbitals building the CSFs. By diagonalizing the interaction matrix, Zeeman energy splittings of fine- and hyperfine structure substates are obtained together with the expansion coefficients of the basis functions. Transition rates between different magnetic fine- and hyperfine structure substates are computed as sums over reduced transition matrix elements between fine structure states weighted by the expansion coefficients of the basis functions and angular factors. Given energies of the magnetic substates along with transition rates, a synthetic spectrum is obtained by convolving the spectral lines with a Gaussian function with a user defined value of the full width half maximum (FWHM).Additional comments including restrictions and unusual features : 1. The complexity of the cases that can be handled is determined by the Grasp2018 package used for the generation of the atomic state functions. 2. The current programs can be used for the calculations of electric dipole (E1), electric quadrupole (E2), magnetic dipole (M1) and magnetic quadrupole (M2) magnetic-field- and hyperfine-induced transitions, which are caused by the mixing of states due to hyperfine and Zeeman interaction. 3. The present model does not include the necessary non-perturbative treatment of the uncommon case involving near-degeneracies where the radiative width of a fine structure state is of the same order as the hyperfine or magnetic-field perturbation; an effect often termed radiation damping (Indelicato et al., 1989 [1]; Robicheaux et al., 1995 [2]; Johnson et al., 1997 [3]).

Large Non-ergodic Magnetoelastic Damping in Ni–Mn–Ga Austenite

Resonant ultrasound spectroscopy was used to analyze magnetoelastic damping in Ni–Mn–Ga single crystals in austenite and premartensite phases. Crystals with different treatment were studied, exhibiting different density of antiphase boundaries (APBs), as confirmed by magnetic force microscopy, and different magnetic behavior. For a quenched single crystal with high density of APBs, extremely strong damping was observed in a broad temperature range in the austenite phase. It was shown that this damping is history-dependent, i.e., non-ergodic, appearing only during heating runs preceded by a premartensite → austenite transition. We suggest that this non-ergodicity results from the pinning of the fine magnetic domain structure on APBs and other defects.

Determination of fine magnetic structure of magnetic multilayer with quasi antiferromagnetic layer by using polarized neutron reflectivity analysis

We carried out polarized neutron reflectivity (PNR) analysis to determine the fine magnetic structure of magnetic multilayers with quasi-antiferromagnetic (quasi-AFM) layers realized by 90-deg coupling using two Co90Fe10 layers, and quantitatively evaluated the magnetization of quasi-AFM layers. Two types of samples with different buffer layers, Ru buffer and a NiFeCr buffer, were investigated and the average angles between the respective magnetization of the two Co90Fe10 layers were estimated to be +/− 39 degrees and +/− 53 degrees. In addition, less roughness was found in the NiFeCr buffer sample resulting stronger 90-deg coupling. A perfect quasi-AFM is expected to be realized by a flat interface of the magnetic multilayer.

Differential Emission Measure Plasma Diagnostics of a Long-Lived Coronal Hole

We use Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA) data to reconstruct the plasma properties from differential emission measure (DEM) analysis for a previously studied long-lived, low-latitude coronal hole (CH) over its lifetime of ten solar rotations. We initially obtain a non-isothermal DEM distribution with a dominant component centered around 0.9 MK and a secondary smaller component at 1.5 – 2.0 MK. We find that deconvolving the data with the instrument point spread function (PSF) to account for long-range scattered light reduces the secondary hot component. Using the 2012 Venus transit and a 2013 lunar eclipse to test the efficiency of this deconvolution, significant amounts of residual stray light are found for the occulted areas. Accounting for this stray light in the error budget of the different AIA filters further reduces the secondary hot emission, yielding CH DEM distributions that are close to isothermal with the main contribution centered around 0.9 MK. Based on these DEMs, we analyze the evolution of the emission measure (EM), density, and averaged temperature during the CH’s lifetime. We find that once the CH is clearly observed in EUV images, the bulk of the CH plasma reveals a quite constant state, i.e. temperature and density reveal no major changes, whereas the total CH area and the photospheric magnetic fine structure inside the CH show a distinct evolutionary pattern. These findings suggest that CH plasma properties are mostly “set” at the CH formation or/and that all CHs have similar plasma properties.

Pecularities of the magnetic structure and microwave properties in Ba(Fe1-xScx)12O19 (x

The peculiarities of the fine atomic and magnetic structure, magnetic properties and microwave characteristics under Sc-substitution were investigated in Ba(Fe1-xScx)12O19 (x ≤ 0.1) solid solutions. Structural data was obtained using neutron powder diffraction with high resolution on atomic level and was described in the frame of standard P63/mmc Space Group. Almost linear increase of the main lattice parameters and internal stress was explained by the difference in ionic radius of Fe3+ and Sc3+. Magnetic properties were determined by VSM and discussed in terms of Mossbauer studies. The non-linear behavior of the magnetic parameters was explained by the features of Sc3+ ions distribution in the hexaferrite structure and some deviation from strict collinearity in the direction of the magnetic vector. Concentration dependence of coercivity in the concentration range x ≥ 0.05 was explained by rapid frustration of the magnetic structure (destruction of the magnetic long range ordering due to weakening of the intrasublattice exchange interaction in Fe3+-O2--Fe3+ in the first and second coordination spheres). Microwave properties were investigated using a co-axial method in the high frequency range (20–60 GHz). It has been demonstrated that the nature of electromagnetic absorption in Ba(Fe1-xScx)12O19 (x ≤ 0.1) solid solutions is caused by natural ferromagnetic resonance. A good correlation was established between the theoretical calculation of the resonant frequency and the experimental results. It opens broad prospects for practical applications of substituted hexaferrites at higher frequencies.

Three-phase Evolution of a Coronal Hole. II. The Magnetic Field

Abstract We investigate the magnetic characteristics of a persistent coronal hole (CH) extracted from EUV imagery using Heliospheric and Magnetic Imager filtergrams over the period 2012 February–October. The magnetic field, its distribution, and the magnetic fine structure in the form of flux tubes (FTs) are analyzed in different evolutionary states of the CH. We find a strong linear correlation between the magnetic properties (e.g., signed/unsigned magnetic field strength) and the area of the CH. As such, the evolutionary pattern in the magnetic field clearly follows a three-phase evolution (growing, maximum, and decaying) as found from EUV data (Part I). This evolutionary process is most likely driven by strong FTs with a mean magnetic field strength exceeding 50 G. During the maximum phase they entail up to 72% of the total signed magnetic flux of the CH, but only cover up to 3.9% of the total CH area, whereas during the growing and decaying phases, strong FTs entail 54%–60% of the signed magnetic flux and cover around 1%–2% of the CH’s total area. We conclude that small-scale structures of strong unipolar magnetic field are the fundamental building blocks of a CH and govern its evolution.

Domain Walls in Bent Nanowires

Controlling the magnetic fine structure between two domains in a wire forms the basis of many promising applications, such as ``racetrack'' memory, sensors, and logic concepts for magnetic computing. This paper presents a study of V-shaped soft-magnetic nanowires, with regard to the influence of wire width, thickness, and bending angle on the prevalent type of domain wall. Domain patterns are imaged at high resolution via scanning electron microscopy with polarization analysis (SEMPA), and compared to micromagnetic simulations. Based on the results, a phenomenological model enables the predictable tuning of remanent wall type in such a nanowire.

Formation of micro- and nanosized particles of the Fe–Al–Co system in water solutions and its magnetic properties

Samples of the Fe–Al–Co system are obtained electrochemically in a water solution. The kinetic dependences that describe the processes that occur in microparticles of aluminum in water solutions are established. The phase composition of the synthesized samples is determined via X-ray diffraction and Mossbauer spectroscopy. It is shown that the main contribution to the fine magnetic structure of Fe–Al–Co is made by the magnetically ordered structure with a hyperfine field around 348 kOe formed by a mechanical mixture of FeCo and Al.

Fitting peculiar spectral profiles in He I 10830 Å absorption features

AbstractThe new generation of solar instruments provides better spectral, spatial, and temporal resolution for a better understanding of the physical processes that take place on the Sun. Multiple‐component profiles are more commonly observed with these instruments. Particularly, the Hei 10830 Å triplet presents such peculiar spectral profiles, which give information on the velocity and magnetic fine structure of the upper chromosphere. The purpose of this investigation is to describe a technique to efficiently fit the two blended components of the Hei 10830 Å triplet, which are commonly observed when two atmospheric components are located within the same resolution element. The observations used in this study were taken on 2015 April 17 with the very fast spectroscopic mode of the GREGOR Infrared Spectrograph (GRIS) attached to the 1.5‐m GREGOR solar telescope, located at the Observatorio del Teide, Tenerife, Spain. We apply a double‐Lorentzian fitting technique using Levenberg‐Marquardt least‐squares minimization. This technique is very simple and much faster than inversion codes. Line‐of‐sight Doppler velocities can be inferred for a whole map of pixels within just a few minutes. Our results show sub‐ and supersonic downflow velocities of up to 32km s–1 for the fast component in the vicinity of footpoints of filamentary structures. The slow component presents velocities close to rest. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Flows along arch filaments observed in the GRIS ‘very fast spectroscopic mode’

AbstractA new generation of solar instruments provides improved spectral, spatial, and temporal resolution, thus facilitating a better understanding of dynamic processes on the Sun. High-resolution observations often reveal multiple-component spectral line profiles, e.g., in the near-infrared He i 10830 Å triplet, which provides information about the chromospheric velocity and magnetic fine structure. We observed an emerging flux region, including two small pores and an arch filament system, on 2015 April 17 with the ‘very fast spectroscopic mode’ of the GREGOR Infrared Spectrograph (GRIS) situated at the 1.5-meter GREGOR solar telescope at Observatorio del Teide, Tenerife, Spain. We discuss this method of obtaining fast (one per minute) spectral scans of the solar surface and its potential to follow dynamic processes on the Sun. We demonstrate the performance of the ‘very fast spectroscopic mode’ by tracking chromospheric high-velocity features in the arch filament system.

Magnetic properties and fine structure of amorphous Fe–Ni–Si–B alloys

The magnetic properties and Mossbauer spectra of amorphous 2NSR alloy samples are investigated after quenching and after tempering for different times at 520°C. After quenching, the alloy is inhomogeneous. Tempering of alloy samples below the crystallization temperature (540°C) raises the Curie temperature and the mean superfine field at the iron nuclei. Tempering leads to complex changes in the saturation magnetization. The changes in magnetic properties are analyzed.

Benzene at 1 GHz. Magnetic field-induced fine structure

The deuterium NMR spectrum of benzene-d6 in a high field spectrometer (1GHz protons) exhibits a magnetic field-induced deuterium quadrupolar splitting Δν. The magnitude of Δν observed for the central resonance is smaller than that observed for the 13C satellite doublets Δν′. This difference, Δ(Δν)=Δν′−Δν, is due to unresolved fine structure contributions to the respective resonances. We determine the origins of and simulate this difference, and report pulse sequences that exploit the connectivity of the peaks in the 13C and 2H spectra to determine the relative signs of the indirect coupling, JCD, and Δν. The positive sign found for Δν is consonant with the magnetic field biasing of an isolated benzene molecule—the magnetic energy of the aromatic ring is lowest for configurations where the C6 axis is normal to the field. In the neat liquid the magnitude of Δν is decreased by the pair correlations in this prototypical molecular liquid.

Benzene at 1GHz. Magnetic field-induced fine structure

Benzene at 1GHz. Magnetic field-induced fine structure

Cancellation analysis of current density in solar active region NOAA10019

Solar flares are often associated with changes in the fine magnetic structure of the emitting active region. Such topological modification results in variations of both the scaling properties of the fields’ fluctuations, and the fractal dimension of the associated gradients. The use of cancellation analysis of the current density has been attempted for the identification and quantitative estimation of such changes. The characteristics of the magnetic vector as measured by THEMIS telescope for the active region NOAA10019 have been studied in this paper, suggesting the presence of disrupted current filaments. The variation of the fractal dimension of the current structures, and in particular their smoothing, is discussed in relationship with occurrence of one flare in the active region.

Magnetic fields in a limb flare on July 19, 2012

The magnetic field intensity in the limb solar flare of July 19, 2012, was measured by the Zeeman bisector splitting in the Hα line. An average magnetic field is established to attain 200 G at a measurement error of ±100 G in the top of a radiant flare loop at a height of about 40 Mm. The confinement of a strong magnetic field in the high coronal arcade at a relatively weak external field of the corona (about 1–2 G) is considered using a model of a force-free magnetic flux rope with a fine magnetic structure at a scale of about 300 km.

Multiple spectra of electron spin resonance in chiral molecule-based magnets networked by a single chiral ligand

A molecule-based magnet [Cr(CN)6][Mn(R/S)-pnH(H2O)](H2O) (termed R/S-GN) is a chiral crystal without an inversion center and mirror reflection, and its structural network is constructed using a chiral ligand diaminopropane (R/S)-pn. In S-GN, multiple spectra of ESR were observed below the magnetic ordering temperature by Morgunov et al. [Phys. Rev. B 77, 184419 (2008)]. They concluded that the phenomenon at the high field side occurred because the incommensurate magnetic structure resulted in a length-controllable superlattice of domain walls (the so-called chiral soliton lattice, CSL) under a dc magnetic field H applied perpendicular to the magnetic chiral axis. However, there multiple spectra were observed even for H nearly parallel to the chiral axis, a-axis, and their interpretation is unreasonable. Thus, we conducted an X-band electron spin resonance (ESR) measurement of R-GN under conditions similar to those of their experiment and performed Fourier spectrum analyses for the data of R-GN as an approach of physical characterization. By using two Lorentz spectra, the main ESR spectra for H // a were reproduced, and furthermore two prominent periodic modes were found by spectrum analyses based on Fourier transform. Two characteristic periods, p1 and p2 (<p1), are related by p1 = 2p2, and the temperature dependence of the multiplicity can be physically characterized with those of p1 and p2. The unique spectra observed below the magnetic ordering temperature are due not to hyperfine structure but magnetic fine structure, and it certainly originates from the existence of plural nonequivalent magnetic sites. Thus, it is unreasonable to consider CSL to explain the multiple ESR spectra observed independently of the field direction, whereas the observed complex spectra appeal wealthy scientific potentiality in chiral crystals.

Magnetic properties and structure of Fe83.3–85.8B7.0–4.5P9Cu0.7 nanocrystalline alloys

The effects of Fe content on the magnetic properties and fine structure of the nanocrystalline Fe-B-P-Cu alloys have been investigated, with the objective of enhancing their magnetic softness. The nanocrystalline Fe83.3+xB7−xP9Cu0.7 (x = 0.0–2.5) alloys annealed at 673 K consist of uniform α-Fe grains embedded in a residual amorphous phase, and the average α-Fe grain diameter decreases from 18.1 to 14.6 nm with increasing Fe content. At the same time, the saturation magnetic flux density (Bs) increases and the coercivity (Hc) decreases with increasing Fe content and the x = 1.0 alloy has a high Bs of 1.72 T and a low Hc of 2.9 A/m. At x = 2.0 or higher, however, Hc drastically deteriorates from the effect of the coarse α-Fe grains. The core loss (W) of the x = 1.0 alloy at 50 Hz-1.6 T is 0.26 W/kg, which is one-third of that for oriented magnetic steel. These results indicate that the magnetic properties and structure of nanocrystalline Fe-B-P-Cu alloys are strongly affected by Fe content.