scholarly journals Complex free-space magnetic field textures induced by three-dimensional magnetic nanostructures

2021 ◽  
Author(s):  
Claire Donnelly ◽  
Aurelio Hierro-Rodríguez ◽  
Claas Abert ◽  
Katharina Witte ◽  
Luka Skoric ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Domain Wall ◽  
Smart Materials ◽  
Free Space ◽  
Three Dimensional ◽  
Magnetic Nanostructures ◽  
New Physics ◽  
Three Dimensions ◽  
Stray Field ◽  
Double Helices

AbstractThe design of complex, competing effects in magnetic systems—be it via the introduction of nonlinear interactions1–4, or the patterning of three-dimensional geometries5,6—is an emerging route to achieve new functionalities. In particular, through the design of three-dimensional geometries and curvature, intrastructure properties such as anisotropy and chirality, both geometry-induced and intrinsic, can be directly controlled, leading to a host of new physics and functionalities, such as three-dimensional chiral spin states7, ultrafast chiral domain wall dynamics8–10 and spin textures with new spin topologies7,11. Here, we advance beyond the control of intrastructure properties in three dimensions and tailor the magnetostatic coupling of neighbouring magnetic structures, an interstructure property that allows us to generate complex textures in the magnetic stray field. For this, we harness direct write nanofabrication techniques, creating intertwined nanomagnetic cobalt double helices, where curvature, torsion, chirality and magnetic coupling are jointly exploited. By reconstructing the three-dimensional vectorial magnetic state of the double helices with soft-X-ray magnetic laminography12,13, we identify the presence of a regular array of highly coupled locked domain wall pairs in neighbouring helices. Micromagnetic simulations reveal that the magnetization configuration leads to the formation of an array of complex textures in the magnetic induction, consisting of vortices in the magnetization and antivortices in free space, which together form an effective B field cross-tie wall14. The design and creation of complex three-dimensional magnetic field nanotextures opens new possibilities for smart materials15, unconventional computing2,16, particle trapping17,18 and magnetic imaging19.

Compressible magnetoconvection in three dimensions: planforms and nonlinear behaviour

1995 ◽  
Vol 305 ◽  
pp. 281-305 ◽  
Author(s):  
P. C. Matthews ◽  
M. R. E. Proctor ◽  
N. O. Weiss
Keyword(s):  
Magnetic Field ◽  
Shear Flow ◽  
Three Dimensional ◽  
Two Dimensions ◽  
Three Dimensions ◽  
Nonlinear Behaviour ◽  
Two Dimensional ◽  
Horizontal Shear ◽  
Mean Flow ◽  
The Magnetic Field

Convection in a compressible fiuid with an imposed vertical magnetic field is studied numerically in a three-dimensional Cartesian geometry with periodic lateral boundary conditions. Attention is restricted to the mildly nonlinear regime, with parameters chosen first so that convection at onset is steady, and then so that it is oscillatory.Steady convection occurs in the form of two-dimensional rolls when the magnetic field is weak. These rolls can become unstable to a mean horizontal shear flow, which in two dimensions leads to a pulsating wave in which the direction of the mean flow reverses. In three dimensions a new pattern is found in which the alignment of the rolls and the shear flow alternates.If the magnetic field is sufficiently strong, squares or hexagons are stable at the onset of convection. Both the squares and the hexagons have an asymmetrical topology, with upflow in plumes and downflow in sheets. For the squares this involves a resonance between rolls aligned with the box and rolls aligned digonally to the box. The preference for three-dimensional flow when the field is strong is a consequence of the compressibility of the layer- for Boussinesq magnetoconvection rolls are always preferred over squares at onset.In the regime where convection is oscillatory, the preferred planform for moderate fields is found to be alternating rolls - standing waves in both horizontal directions which are out of phase. For stronger fields, both alternating rolls and two-dimensional travelling rolls are stable. As the amplitude of convection is increased, either by dcereasing the magnetic field strength or by increasing the temperature contrast, the regular planform structure seen at onset is soon destroyed by secondary instabilities.

scholarly journals Theory of magnetic reconnection in solar and astrophysical plasmas

2012 ◽  
Vol 370 (1970) ◽  
pp. 3169-3192 ◽  
Author(s):  
David I. Pontin
Keyword(s):  
Magnetic Field ◽  
Magnetic Reconnection ◽  
Three Dimensional ◽  
Three Dimensions ◽  
Astrophysical Plasmas ◽  
Current State ◽  
Fundamental Process ◽  
Recent Developments ◽  
The Magnetic Field ◽  
Theoretical Results

Magnetic reconnection is a fundamental process in a plasma that facilitates the release of energy stored in the magnetic field by permitting a change in the magnetic topology. In this paper, we present a review of the current state of understanding of magnetic reconnection. We discuss theoretical results regarding the formation of current sheets in complex three-dimensional magnetic fields and describe the fundamental differences between reconnection in two and three dimensions. We go on to outline recent developments in modelling of reconnection with kinetic theory, as well as in the magnetohydrodynamic framework where a number of new three-dimensional reconnection regimes have been identified. We discuss evidence from observations and simulations of Solar System plasmas that support this theory and summarize some prominent locations in which this new reconnection theory is relevant in astrophysical plasmas.

scholarly journals Magnetic micro-droplet in rotating field: numerical simulation and comparison with experiment

2017 ◽  
Vol 821 ◽  
pp. 266-295 ◽  
Author(s):  
J. Erdmanis ◽  
G. Kitenbergs ◽  
R. Perzynski ◽  
A. Cēbers
Keyword(s):  
Magnetic Field ◽  
Boundary Integral Equations ◽  
Three Dimensional ◽  
Dipolar Interaction ◽  
Boundary Integral ◽  
Rotating Magnetic Field ◽  
Three Dimensions ◽  
Triaxial Ellipsoid ◽  
Equilibrium Shapes ◽  
Magnetic Droplet

Magnetic droplets obtained by induced phase separation in a magnetic colloid show a large variety of shapes when exposed to an external field. However, the description of the shapes is often limited. Here, we formulate an algorithm based on three-dimensional boundary-integral equations for strongly magnetic droplets in a high-frequency rotating magnetic field, allowing us to find their figures of equilibrium in three dimensions. The algorithm is justified by a series of comparisons with known analytical results. We compare the calculated equilibrium shapes with experimental observations and find a good agreement. The main features of these observations are the oblate–prolate transition, the flattening of prolate shapes with the increase of magnetic field strength and the formation of starfish-like equilibrium shapes. We show both numerically and in experiments that the magnetic droplet behaviour may be described with a triaxial ellipsoid approximation. Directions for further research are mentioned, including the dipolar interaction contribution to the surface tension of the magnetic droplets, accounting for the large viscosity contrast between the magnetic droplet and the surrounding fluid.

Health Monitoring of Adhesive Joints Using Magnetostrictive Fillers

2008 ◽  
Author(s):  
Yarden B. Weber ◽  
Daniel Schweitzer ◽  
Hedva Bar ◽  
Doron Shilo
Keyword(s):  
Magnetic Field ◽  
Smart Materials ◽  
Three Dimensional ◽  
Local Stress ◽  
Magnetic Sensors ◽  
Clear Correlation ◽  
Stress Profile ◽  
Stress Monitoring ◽  
Load Bearing ◽  
The Magnetic Field

One major application for smart materials is measuring stresses or strains in load bearing structures. The ability to monitor structural health, and observe real time stress levels in load bearing platforms is a field of great interest. In this work, we develop and characterize a method for stress monitoring adhesively bonded joints by incorporating a magnetostrictive filler into the polymeric matrix. Magnetostrictive materials create a change in their surrounding magnetic field when subjected to strain, and thus serve as natural strain sensors, that require neither power supply nor any kind of wiring. A clear correlation between the stress and the magnetic field, which is measured at a distance of 20–60 mm from the specimen, is observed under both shear and compression loads. Moreover, there is a significant stress region in which the relationship between the stress and the magnetic field is approximately linear. This behavior demonstrates the possibility of monitoring the average stress in a specimen by a single magnetic sensor mounted at a distance from the specimen. Additionally, complete three dimensional mapping of the magnetic field around loaded specimens reveals that the specimen magnetization is not uniform and implies the existence of a correlation between the specimen magnetization and the stress field which was numerically computed. This behavior indicates the potential of mapping the local stress profile within a specimen by using an array of several magnetic sensors. The effects of magnetostrictive particle size and of applying a magnetic field during specimen polymerization are also discussed.

On the measurement of turbulent magnetic diffusivities: the three-dimensional case

2013 ◽  
Vol 735 ◽  
pp. 457-472
Author(s):  
F. Cattaneo ◽  
S. M. Tobias
Keyword(s):  
Magnetic Field ◽  
Three Dimensional ◽  
Passive Scalar ◽  
Three Dimensions ◽  
Two Dimensional ◽  
Large Aspect Ratio ◽  
Turbulent Diffusivity ◽  
Dynamo Action ◽  
Thermally Driven ◽  
Special Case

AbstractIt has been shown that it is possible to measure the turbulent diffusivity of a magnetic field by a method involving oscillatory sources. So far the method has only been tried in the special case of two-dimensional fields and flows. Here we extend the method to three dimensions and consider the case where the flow is thermally driven convection in a large-aspect-ratio domain. We demonstrate that if the diffusing field is horizontal the method is successful even if the underlying flow can sustain dynamo action. We show that the resulting turbulent diffusivity is comparable with, although not exactly the same as, that of a passive scalar. We were not able to measure unambiguously the diffusivity if the diffusing field is vertical, but argue that such a measurement is possible if enough resources are utilized on the problem.

scholarly journals Low-shear three-dimensional equilibria and vacuum magnetic fields with flux surfaces

2019 ◽  
Vol 85 (2) ◽  
Author(s):  
Wrick Sengupta ◽  
Harold Weitzner
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Three Dimensional ◽  
Three Dimensions ◽  
Toroidal Shell ◽  
Closed Field ◽  
Small Current ◽  
Starting Point ◽  
Vacuum Fields ◽  
Low Shear

Stellarators are generically small current and low plasma beta devices. Often the construction of vacuum magnetic fields with good magnetic surfaces is the starting point for an equilibrium calculation. Although in cases with some continuous spatial symmetry, flux functions can always be found for vacuum magnetic fields, an analogous function does not, in general, exist in three dimensions. This work examines several simple equilibria and vacuum magnetic field problems with the intent of demonstrating the possibilities and limitations in the construction of such states. Starting with a simple vacuum magnetic field with closed field lines in a topological torus (toroidal shell with a flat metric), we obtain a self-consistent formal perturbation series using the amplitude of the non-symmetric vacuum fields as a small parameter. We show that systems possessing stellarator symmetry allow the construction order by order. We further indicate the significance of stellarator symmetry in the amplitude expansion of the full ideal magnetohydrodynamics (MHD) problem as well. We then investigate the conditions that guarantee neighbouring flux surfaces given the data on one surface, by expanding in the distance from that surface. We show that it is much more difficult to find low shear vacuum fields with surfaces than force-free fields or ideal MHD equilibrium. Finally, we demonstrate the existence of a class of vacuum magnetic fields, analogous to ‘snakes’ observed in tokamaks, which can be expanded to all orders.

scholarly journals On heating of solar wind protons by the parametric decay of large-amplitude Alfvén waves

2018 ◽  
Vol 36 (6) ◽  
pp. 1647-1655 ◽  
Author(s):  
Horia Comişel ◽  
Yasuhiro Nariyuki ◽  
Yasuhito Narita ◽  
Uwe Motschmann
Keyword(s):  
Magnetic Field ◽  
Large Amplitude ◽  
Three Dimensional ◽  
Three Dimensions ◽  
Alfven Wave ◽  
Sound Waves ◽  
Parametric Decay ◽  
Left Handed ◽  
Propagating Waves ◽  
The Mean

Abstract. By three-dimensional hybrid simulations, proton heating is investigated starting from a monochromatic large-amplitude Alfvén wave with left-handed circular polarization launched along the mean magnetic field in a low-beta plasma. We find that the perpendicular scattering is efficient in three dimensions and the protons are heated by the obliquely propagating waves. The thermal core proton population is heated in three dimensions as well in the longitudinal and parallel directions by the field-aligned and obliquely propagating sound waves out of the parametric decay. The astrophysical context is discussed.

scholarly journals Momentum space toroidal moment in a photonic metamaterial

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Biao Yang ◽  
Yangang Bi ◽  
Rui-Xing Zhang ◽  
Ruo-Yang Zhang ◽  
Oubo You ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Domain Wall ◽  
Momentum Space ◽  
Condensed Matter ◽  
Three Dimensional ◽  
Vital Role ◽  
Condensed Matter Physics ◽  
Berry Curvature ◽  
Shaped Domain ◽  
The Magnetic Field

AbstractBerry curvature, the counterpart of the magnetic field in the momentum space, plays a vital role in the transport of electrons in condensed matter physics. It also lays the foundation for the emerging field of topological physics. In the three-dimensional systems, much attention has been paid to Weyl points, which serve as sources and drains of Berry curvature. Here, we demonstrate a toroidal moment of Berry curvature with flux approaching to π in judiciously engineered metamaterials. The Berry curvature exhibits a vortex-like configuration without any source and drain in the momentum space. Experimentally, the presence of Berry curvature toroid is confirmed by the observation of conical-frustum shaped domain-wall states at the interfaces formed by two metamaterials with opposite toroidal moments.

scholarly journals Three-dimensional simulations of non-resonant streaming instability and particle acceleration near non-relativistic astrophysical shocks

2019 ◽  
Vol 490 (1) ◽  
pp. 1156-1165 ◽  
Author(s):  
Allard Jan van Marle ◽  
Fabien Casse ◽  
Alexandre Marcowith
Keyword(s):  
Magnetic Field ◽  
Particle Acceleration ◽  
Three Dimensional ◽  
3D Models ◽  
Three Dimensions ◽  
Spectral Energy ◽  
Growth Speed ◽  
Field Amplification ◽  
Streaming Instability ◽  
2D And 3D

ABSTRACT We use particle-in-magnetohydrodynamics-cells to model particle acceleration and magnetic field amplification in a high-Mach, parallel shock in three dimensions and compare the result to 2D models. This allows us to determine whether 2D simulations can be relied upon to yield accurate results in terms of particle acceleration, magnetic field amplification, and the growth rate of instabilities. Our simulations show that the behaviour of the gas and the evolution of the instabilities are qualitatively similar for both the 2D and 3D models, with only minor quantitative differences that relate primarily to the growth speed of the instabilities. The main difference between 2D and 3D models can be found in the spectral energy distributions (SEDs) of the non-thermal particles. The 2D simulations prove to be more efficient, accelerating a larger fraction of the particles and achieving higher velocities. We conclude that, while 2D models are sufficient to investigate the instabilities in the gas, their results have to be treated with some caution when predicting the expected SED of a given shock.

Bifurcations of magnetic topology by the creation or annihilation of null points

1996 ◽  
Vol 56 (3) ◽  
pp. 507-530 ◽  
Author(s):  
E. R. Priest ◽  
D. P. Lonie ◽  
V. S. Titov
Keyword(s):  
Magnetic Field ◽  
Magnetic Energy ◽  
Three Dimensional ◽  
Two Dimensions ◽  
Three Dimensions ◽  
Comprehensive Treatment ◽  
Global Changes ◽  
Magnetic Topology ◽  
Cylindrically Symmetric ◽  
Saddle Node

Linear null points of a magnetic field may come together and coalesce at a secondorder null, or vice versa a second-order null may form and split, giving birth to a pair of linear nulls. Such local bifurcations lead to global changes of magnetic topology and in some cases release of magnetic energy. In two dimensions the null points are of X or O type and the flux function is a Hamiltonian; the magnetic field may undergo addle-centre, pitchfork or degenerate resonant bifurcations. In three dimensions the null points and their creation or annihilation by bifurcations are considerably more complex. The nulls possess a skeleton consisting of a spine curve and a fan surface and are of radial-type (proper or improper) or spiral-type; the type of null and the inclination of spine and fan depend on the magnitudes of the current components along and normal to the spine. In cylindrically symmetric fields a comprehensive treatment is given of the various types of saddle-node, Hopf and saddle-node—Hopfbifurcations. In fully three-dimensional situations examples are given of saddle-node and degenerate bifurcations, in which generically two nulls are created or destroyed and are joined by a separator field line, which is the intersection of the two fans. Furthermore, global bifurcations can create chaotic field lines that could perhaps trigger energy release in, for example, solar flares.

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