scholarly journals Unveiling the three-dimensional magnetic texture of skyrmion tubes

2021 ◽  
Author(s):  
Daniel Wolf ◽  
Sebastian Schneider ◽  
Ulrich K. Rößler ◽  
András Kovács ◽  
Marcus Schmidt ◽  
...  
Keyword(s):  
Magnetic Energy ◽  
Electron Tomography ◽  
Three Dimensional ◽  
Magnetic Texture ◽  
Spin Structures ◽  
Topological Solitons ◽  
Magnetic Energy Density ◽  
Surfaces And Interfaces ◽  
Magnetic Skyrmions ◽  
Spin Texture

AbstractMagnetic skyrmions are stable topological solitons with complex non-coplanar spin structures. Their nanoscopic size and the low electric currents required to control their motion has opened a new field of research, skyrmionics, that aims for the usage of skyrmions as information carriers. Further advances in skyrmionics call for a thorough understanding of their three-dimensional (3D) spin texture, skyrmion–skyrmion interactions and the coupling to surfaces and interfaces, which crucially affect skyrmion stability and mobility. Here, we quantitatively reconstruct the 3D magnetic texture of Bloch skyrmions with sub-10-nanometre resolution using holographic vector-field electron tomography. The reconstructed textures reveal local deviations from a homogeneous Bloch character within the skyrmion tubes, details of the collapse of the skyrmion texture at surfaces and a correlated modulation of the skyrmion tubes in FeGe along their tube axes. Additionally, we confirm the fundamental principles of skyrmion formation through an evaluation of the 3D magnetic energy density across these magnetic solitons.

Possibility of an inverse cascade of magnetic helicity in magnetohydrodynamic turbulence

1975 ◽  
Vol 68 (4) ◽  
pp. 769-778 ◽  
Author(s):  
U. Frisch ◽  
A. Pouquet ◽  
J. LÉOrat ◽  
A. Mazure
Keyword(s):  
Energy Density ◽  
Large Scale ◽  
Magnetic Energy ◽  
Three Dimensional ◽  
Magnetic Helicity ◽  
Kinetic Energy Density ◽  
Magnetohydrodynamic Turbulence ◽  
Magnetic Energy Density ◽  
Upper Limit ◽  
Cross Correlations

Some of the consequences of the conservation of magnetic helicity$\int \rm{a.b}\it{d}^{\rm{3}}\rm{r\qquad (a\; =\; vector\; potential\; of\; magnetic\; field\; b)}$for incompressible three-dimensional turbulent MHD flows are investigated. Absolute equilibrium spectra for inviscid infinitely conducting flows truncated at lower and upper wavenumberskminandkmaxare obtained. When the total magnetic helicity approaches an upper limit given by the total energy (kinetic plus magnetic) divided bykmin, the spectra of magnetic energy and helicity are strongly peaked nearkmin; in addition, when the cross-correlations between the velocity and magnetic fields are small, the magnetic energy density nearkmingreatly exceeds the kinetic energy density. Several arguments are presented in favour of the existence of inverse cascades of magnetic helicity towards small wavenumbers leading to the generation of large-scale magnetic energy.

scholarly journals Stripe skyrmions and skyrmion crystals

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
X. R. Wang ◽  
X. C. Hu ◽  
H. T. Wu
Keyword(s):  
Field Theory ◽  
Quantum Field Theory ◽  
Information Technology ◽  
Ground States ◽  
Quantum Field ◽  
Number Density ◽  
Topological Solitons ◽  
Magnetic Skyrmions ◽  
Spin Texture

AbstractSkyrmions are important in quantum field theory and information technology for being topological solitons and for their attractive applications. Magnetic skyrmions are believed to be circular and stripy spin textures accompanied skyrmion crystals (SkXs) termed spiral/helical/cycloid orders have zero skyrmion number. Here we show that those stripy spin textures are skyrmions, siblings of circular skyrmions in SkXs and cousins of isolated circular skyrmions. Various irregular morphologies are the nature structures of skyrmions in the ground states. At the extreme of one skyrmion in the whole sample, the skyrmion is a ramified stripe. As the skyrmion number density increases, skyrmion shapes gradually change from ramified stripes to rectangular stripes, and eventually to circular objects. At a high skyrmion number density, SkXs are the preferred states. Our findings reveal the nature and properties of stripy spin texture, and open an avenue for manipulating skyrmions.

scholarly journals Topological defect-mediated skyrmion annihilation in three dimensions

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Max T. Birch ◽  
David Cortés-Ortuño ◽  
Nguyen D. Khanh ◽  
Shinichiro Seki ◽  
Aleš Štefančič ◽  
...  
Keyword(s):  
Topological Defect ◽  
Three Dimensional ◽  
Topological Defects ◽  
Two Dimensions ◽  
Three Dimensions ◽  
Elastic Band ◽  
Spin Structures ◽  
Transition Mechanism ◽  
Field Dependent ◽  
Magnetic Skyrmions

AbstractThe creation and annihilation of magnetic skyrmions are mediated by three-dimensional topological defects known as Bloch points. Investigation of such dynamical processes is important both for understanding the emergence of exotic topological spin textures, and for future engineering of skyrmions in technological applications. However, while the annihilation of skyrmions has been extensively investigated in two dimensions, in three dimensions the phase transitions are considerably more complex. We report field-dependent experimental measurements of metastable skyrmion lifetimes in an archetypal chiral magnet, revealing two distinct regimes. Comparison to supporting three-dimensional geodesic nudged elastic band simulations indicates that these correspond to skyrmion annihilation into either the helical and conical states, each exhibiting a different transition mechanism. The results highlight that the lowest energy magnetic configuration of the system plays a crucial role when considering the emergence and stability of topological spin structures via defect-mediated dynamics.

scholarly journals Spectropolarimetric diagnostics of unresolved magnetic fields in the quiet solar photosphere

2012 ◽  
Vol 8 (S294) ◽  
pp. 107-118 ◽  
Author(s):  
Nataliya G. Shchukina ◽  
Javier Trujillo Bueno
Keyword(s):  
Magnetic Field ◽  
Magnetic Energy ◽  
Zeeman Effect ◽  
Three Dimensional ◽  
Solar Photosphere ◽  
Magnetic Energy Density ◽  
Hanle Effect ◽  
Molecular Lines ◽  
Surface Convection ◽  
Ubiquitous Presence

AbstractA few years before the Hinode space telescope was launched, an investigation based on the Hanle effect in atomic and molecular lines indicated that the bulk of the quiet solar photosphere is significantly magnetized, due to the ubiquitous presence of an unresolved magnetic field with an average strength 〈B〉, ≈ 130 G. It was pointed out also that this “hidden” field must be much stronger in the intergranular regions of solar surface convection than in the granular regions, and it was suggested that this unresolved magnetic field could perhaps provide the clue for understanding how the outer solar atmosphere is energized. In fact, the ensuing magnetic energy density is so significant that the energy flux estimated using the typical value of 1 km/s for the convective velocity (thinking in rising magnetic loops) or the Alfvén speed (thinking in Alfvén waves generated by magnetic reconnection) turns out to be substantially larger than that required to balance the chromospheric energy losses. Here we present a brief review of the research that led to such conclusions, with emphasis on a new three-dimensional radiative transfer investigation aimed at determining the magnetization of the quiet Sun photosphere from the Hanle effect in the Sr I 4607 Å line and the Zeeman effect in Fe I lines.

Practical electron tomography

1995 ◽  
Vol 53 ◽  
pp. 742-743
Author(s):  
C.L. Woodcock
Keyword(s):  
Electron Tomography ◽  
Tomographic Reconstruction ◽  
Three Dimensional ◽  
3D Shape ◽  
Computational Resources ◽  
Shape Of Particles

Despite the potential of the technique, electron tomography has yet to be widely used by biologists. This is in part related to the rather daunting list of equipment and expertise that are required. Thanks to continuing advances in theory and instrumentation, tomography is now more feasible for the non-specialist. One barrier that has essentially disappeared is the expense of computational resources. In view of this progress, it is time to give more attention to practical issues that need to be considered when embarking on a tomographic project. The following recommendations and comments are derived from experience gained during two long-term collaborative projects.Tomographic reconstruction results in a three dimensional description of an individual EM specimen, most commonly a section, and is therefore applicable to problems in which ultrastructural details within the thickness of the specimen are obscured in single micrographs. Information that can be recovered using tomography includes the 3D shape of particles, and the arrangement and dispostion of overlapping fibrous and membranous structures.

Three-Dimensional reconstruction of isolated centrosomes by automated electron tomography

1994 ◽  
Vol 52 ◽  
pp. 310-311
Author(s):  
M.B. Braunfeld ◽  
M. Moritz ◽  
B.M. Alberts ◽  
J.W. Sedat ◽  
D.A. Agard
Keyword(s):  
Electron Tomography ◽  
Three Dimensional ◽  
Vital Role ◽  
Complex Nature ◽  
Animal Cells ◽  
Microtubule Organizing Center ◽  
Nucleation Sites ◽  
Dimensional Reconstruction ◽  
Organizing Center ◽  
Resolution Model

In animal cells, the centrosome functions as the primary microtubule organizing center (MTOC). As such the centrosome plays a vital role in determining a cell's shape, migration, and perhaps most importantly, its division. Despite the obvious importance of this organelle little is known about centrosomal regulation, duplication, or how it nucleates microtubules. Furthermore, no high resolution model for centrosomal structure exists.We have used automated electron tomography, and reconstruction techniques in an attempt to better understand the complex nature of the centrosome. Additionally we hope to identify nucleation sites for microtubule growth.Centrosomes were isolated from early Drosophila embryos. Briefly, after large organelles and debris from homogenized embryos were pelleted, the resulting supernatant was separated on a sucrose velocity gradient. Fractions were collected and assayed for centrosome-mediated microtubule -nucleating activity by incubating with fluorescently-labeled tubulin subunits. The resulting microtubule asters were then spun onto coverslips and viewed by fluorescence microscopy.

scholarly journals Can the Local Bubble explain the radio background?

2021 ◽  
Vol 502 (2) ◽  
pp. 2807-2814
Author(s):  
Martin G H Krause ◽  
Martin J Hardcastle
Keyword(s):  
Magnetic Field ◽  
Energy Density ◽  
Radio Emission ◽  
Magnetic Energy ◽  
Cosmic Ray ◽  
Observational Constraints ◽  
Local Bubble ◽  
Magnetic Energy Density ◽  
Magnetic Field Model ◽  
Radio Background

ABSTRACT The ARCADE 2 balloon bolometer along with a number of other instruments have detected what appears to be a radio synchrotron background at frequencies below about 3 GHz. Neither extragalactic radio sources nor diffuse Galactic emission can currently account for this finding. We use the locally measured cosmic ray electron population, demodulated for effects of the Solar wind, and other observational constraints combined with a turbulent magnetic field model to predict the radio synchrotron emission for the Local Bubble. We find that the spectral index of the modelled radio emission is roughly consistent with the radio background. Our model can approximately reproduce the observed antenna temperatures for a mean magnetic field strength B between 3 and 5 nT. We argue that this would not violate observational constraints from pulsar measurements. However, the curvature in the predicted spectrum would mean that other, so far unknown sources would have to contribute below 100 MHz. Also, the magnetic energy density would then dominate over thermal and cosmic ray electron energy density, likely causing an inverse magnetic cascade with large variations of the radio emission in different sky directions as well as high polarization. We argue that this disagrees with several observations and thus that the magnetic field is probably much lower, quite possibly limited by equipartition with the energy density in relativistic or thermal particles (B = 0.2−0.6 nT). In the latter case, we predict a contribution of the Local Bubble to the unexplained radio background at most at the per cent level.

scholarly journals Spin-texture-driven electrical transport in multi-Q antiferromagnets

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Soonbeom Seo ◽  
Satoru Hayami ◽  
Ying Su ◽  
Sean M. Thomas ◽  
Filip Ronning ◽  
...  
Keyword(s):  
Electrical Transport ◽  
Kondo Lattice ◽  
Magnetic Interactions ◽  
Temperature Phase ◽  
Fermi Surfaces ◽  
Magnetic Texture ◽  
Crystalline Anisotropy ◽  
Field Temperature ◽  
Kondo Lattice Model ◽  
Spin Texture

AbstractUnusual magnetic textures can be stabilized in f-electron materials due to the interplay between competing magnetic interactions, complex Fermi surfaces, and crystalline anisotropy. Here we investigate CeAuSb2, an f-electron incommensurate antiferromagnet hosting both single-Q and double-Q spin textures as a function of magnetic fields (H) applied along the c axis. Experimentally, we map out the field-temperature phase diagram via electrical resistivity and thermal expansion measurements. Supported by calculations of a Kondo lattice model, we attribute the puzzling magnetoresistance enhancement in the double-Q phase to the localization of the electronic wave functions caused by the incommensurate magnetic texture.

Three-Dimensional Nanoparticle Distribution and Local Curvature of Heterogeneous Catalysts Revealed by Electron Tomography

2007 ◽  
Vol 111 (31) ◽  
pp. 11501-11505 ◽  
Author(s):  
Edmund P. W. Ward ◽  
Timothy J. V. Yates ◽  
José-Jesús Fernández ◽  
David E. W. Vaughan ◽  
Paul A. Midgley
Keyword(s):  
Heterogeneous Catalysts ◽  
Electron Tomography ◽  
Three Dimensional ◽  
Local Curvature ◽  
Nanoparticle Distribution

scholarly journals Capturing Enveloped Viruses on Affinity Grids for Downstream Cryo-Electron Microscopy Applications

2013 ◽  
Vol 20 (1) ◽  
pp. 164-174 ◽  
Author(s):  
Gabriella Kiss ◽  
Xuemin Chen ◽  
Melinda A. Brindley ◽  
Patricia Campbell ◽  
Claudio L. Afonso ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Measles Virus ◽  
Influenza A ◽  
Electron Tomography ◽  
Three Dimensional ◽  
Nitrilotriacetic Acid ◽  
Dimensional Structure ◽  
Enveloped Viruses ◽  
Cryo Electron Microscopy ◽  
Human Immunodeficiency Virus Virus

AbstractElectron microscopy (EM), cryo-electron microscopy (cryo-EM), and cryo-electron tomography (cryo-ET) are essential techniques used for characterizing basic virus morphology and determining the three-dimensional structure of viruses. Enveloped viruses, which contain an outer lipoprotein coat, constitute the largest group of pathogenic viruses to humans. The purification of enveloped viruses from cell culture presents certain challenges. Specifically, the inclusion of host-membrane-derived vesicles, the complete destruction of the viruses, and the disruption of the internal architecture of individual virus particles. Here, we present a strategy for capturing enveloped viruses on affinity grids (AG) for use in both conventional EM and cryo-EM/ET applications. We examined the utility of AG for the selective capture of human immunodeficiency virus virus-like particles, influenza A, and measles virus. We applied nickel-nitrilotriacetic acid lipid layers in combination with molecular adaptors to selectively adhere the viruses to the AG surface. This further development of the AG method may prove essential for the gentle and selective purification of enveloped viruses directly onto EM grids for ultrastructural analyses.

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