scholarly journals 50. Magneto-hydrostatic equilibrium in an external magnetic field

1958 ◽  
Vol 6 ◽  
pp. 499-503 ◽  
Author(s):  
P. A. Sweet
Keyword(s):  
Magnetic Field ◽  
External Magnetic Field ◽  
Electric Current ◽  
Virial Theorem ◽  
Magnetic Energy ◽  
Hydrostatic Equilibrium

The expression ∫∫∫all space ΔH2dv for a change in magnetic energy is shown to be incorrect when applied to a body carrying an electric current and situated in an external magnetic field. A modified expression is derived.Chandrasekhar's form of the virial theorem in a magnetic field is extended to the case where an external magnetic field is present.

scholarly journals Room temperature giant magnetostriction in single-crystal nickel nanowires

2019 ◽  
Vol 11 (1) ◽  
Author(s):  
Anastasios Pateras ◽  
Ross Harder ◽  
Sohini Manna ◽  
Boris Kiefer ◽  
Richard L. Sandberg ◽  
...  
Keyword(s):  
Magnetic Field ◽  
External Magnetic Field ◽  
Single Crystal ◽  
Room Temperature ◽  
Magnetic Energy ◽  
Mechanical Energy ◽  
Three Dimensional ◽  
Local Strain ◽  
Nickel Nanowires ◽  
Giant Magnetostriction

Abstract Magnetostriction is the emergence of a mechanical deformation induced by an external magnetic field. The conversion of magnetic energy into mechanical energy via magnetostriction at the nanoscale is the basis of many electromechanical systems such as sensors, transducers, actuators, and energy harvesters. However, cryogenic temperatures and large magnetic fields are often required to drive the magnetostriction in such systems, rendering this approach energetically inefficient and impractical for room-temperature device applications. Here, we report the experimental observation of giant magnetostriction in single-crystal nickel nanowires at room temperature. We determined the average values of the magnetostrictive constants of a Ni nanowire from the shifts of the measured diffraction patterns using the 002 and 111 Bragg reflections. At an applied magnetic field of 600 Oe, the magnetostrictive constants have values of λ100 = −0.161% and λ111 = −0.067%, two orders of magnitude larger than those in bulk nickel. Using Bragg coherent diffraction imaging (BCDI), we obtained the three-dimensional strain distribution inside the Ni nanowire, revealing nucleation of local strain fields at two different values of the external magnetic field. Our analysis indicates that the enhancement of the magnetostriction coefficients is mainly due to the increases in the shape, surface-induced, and stress-induced anisotropies, which facilitate magnetization along the nanowire axis and increase the total magnetoelastic energy of the system.

scholarly journals Tunnel Magnetoresistance of Fe3O4/MgO/Fe Nanostructures

2011 ◽  
Vol 2011 ◽  
pp. 1-3
Author(s):  
S. G. Chigarev ◽  
E. M. Epshtein ◽  
I. V. Malikov ◽  
G. M. Mikhailov ◽  
P. E. Zilberman
Keyword(s):  
Magnetic Field ◽  
External Magnetic Field ◽  
Magnetic Fields ◽  
Tunnel Junction ◽  
Magnetic Energy ◽  
Magnetic Tunnel Junction ◽  
Tunnel Magnetoresistance ◽  
Unidirectional Anisotropy ◽  
Layer Orientation ◽  
Layer Magnetization

A magnetic tunnel junction Fe3O4/MgO/Fe with (001) layer orientation is considered. The junction magnetic energy is analyzed as a function of the angle between the layer magnetization vectors under various magnetic fields. The tunnel magnetoresistance is calculated as a function of the external magnetic field. In contrast with junctions with unidirectional anisotropy, a substantially lower magnetic field is required for the junction switching.

scholarly journals Rotation induced by uniform and non-uniform magnetic fields in a conducting fluid carrying an electric current

RSC Advances ◽  
2016 ◽  
Vol 6 (113) ◽  
pp. 112641-112645 ◽  
Author(s):  
R. Shirsavar ◽  
M. Nasiri ◽  
A. Amjadi ◽  
A. Nejati ◽  
S. O. Sobhani ◽  
...  
Keyword(s):  
Magnetic Field ◽  
External Magnetic Field ◽  
Magnetic Fields ◽  
Electric Current ◽  
Conducting Fluid

External magnetic field induces controllable rotation in a conducting fluid carrying an electric current.

Relaxed states of an ideal MHD plasma with external magnetic field

1995 ◽  
Vol 53 (3) ◽  
pp. 373-385 ◽  
Author(s):  
G. Knorr ◽  
M. Mond ◽  
C. Grabbe
Keyword(s):  
Magnetic Field ◽  
External Magnetic Field ◽  
Vector Fields ◽  
Magnetic Energy ◽  
Adjoint Operator ◽  
Magnetic Helicity ◽  
Turbulent Transition ◽  
Ideal Mhd ◽  
Field Fluctuations ◽  
Base Vector

We study an ideal MHD plasma with the non-vanishing invariants energy, crosshelicity and magnetic helicity, confined in a cylinder with infinitely conducting walls and an externally applied magnetic field B0. The magnetic and velocity fields are expanded in base vector fields, satisfying Δ × Bλ = Bλ. Boundary conditions are imposed to make the curl a self-adjoint operator. The three invariants depend on the time-dependent coefficients of the base vector fields, and are used to construct the partition function to gather statistical information about the equlibrium thermodynamic state to which the plasma relaxes after a turbulent transition. For zero external magnetic field but large magnetic helicity, the energy resides preferentially in magnetic field fluctuations. A sizeable fraction of the kinetic energy initially present is transformed into magnetic energy. The energy condenses via an inverse cascade predominantly to the lowest energy eigenstate, in agreement with results obtained by Taylor. However, since we consider the whole spectrum of eigenstates, the energy does not exclusively occupy the lowest eigenstate. If the eigenvalues are densely spaced (as in a thin torus), the higher eigenmodes also contain appreciable amounts of energy, resulting in a finite pressure of the plasma. For constant and finite external magnetic field, the average induced magnetic field exactly cancels the external field. This indicates that, on a statistical average, the plasma is diamagnetic or superconducting. Superimposed on the average statistical state are fluctuations that may become large if the magnetic helicity is large.

scholarly journals The Microstructural Model of the Ferromagnetic Material Behavior in an External Magnetic Field

2021 ◽  
Vol 7 (1) ◽  
pp. 7
Author(s):  
Anatoli A. Rogovoy ◽  
Oleg V. Stolbov ◽  
Olga S. Stolbova
Keyword(s):  
Magnetic Field ◽  
External Magnetic Field ◽  
Domain Walls ◽  
Magnetic Energy ◽  
Spontaneous Magnetization ◽  
Magnetization Vector ◽  
Ferromagnetic Material ◽  
Extremum Problem ◽  
Material Behavior ◽  
Anisotropy Axis

In this paper, the behavior of a ferromagnetic material is considered in the framework of microstructural modeling. The equations describing the behavior of such material in the magnetic field, are constructed based on minimization of total magnetic energy with account of limitations imposed on the spontaneous magnetization vector and scalar magnetic potential. This conditional extremum problem is reduced to the unconditional extremum problem using the Lagrange multiplier. A variational (weak) formulation is written down and linearization of the obtained equations is carried out. Based on the derived relations a solution of a two-dimensional problem of magnetization of a unit cell (a grain of a polycrystal or a single crystal of a ferromagnetic material) is developed using the finite element method. The appearance of domain walls is demonstrated, their thickness is determined, and the history of their movement and collision is described. The graphs of distributions of the magnetization vector in domains and in domain walls in the external magnetic field directed at different angles to the anisotropy axis are constructed and the magnetization curves for a macrospecimen are plotted. The results obtained in the present paper (the thickness of the domain wall, the formation of a 360-degree wall) are in agreement with the ones available in the current literature.

The influence of a cylindrical cathode on the electro-vortex flow of liquid metal: Numerical simulations and laboratory experiments

2021 ◽  
Author(s):  
Vladislav Eltishchev ◽  
Sergei Mandrykin ◽  
Ilya Kolesnichenko
Keyword(s):  
Magnetic Field ◽  
External Magnetic Field ◽  
Liquid Metal ◽  
Electric Current ◽  
Laboratory Experiments ◽  
Vortex Flow ◽  
Qualitative Change ◽  
Critical Magnetic Field ◽  
Current Application ◽  
Cylindrical Cell

Abstract The electro-vortex flow of liquid metal in a cylindrical cell, placed into external vertical magnetic field, in case of axial electric current application is studied numerically and experimentally. The results are compared to those previously obtained in case of a localized electric current application. In the absence of the external magnetic field, the comparison shows no qualitative change in the flow structure. In presence of the external magnetic field, a poloidal motion is suppressed. A critical magnetic field of poloidal suppression is shown to be approximately 50% higher in case of axial electric current application.

Electric Current of Ferrofluid Depending on Temperature

2020 ◽  
Vol 833 ◽  
pp. 162-170
Author(s):  
Min Dai
Keyword(s):  
Magnetic Field ◽  
External Magnetic Field ◽  
Electric Current ◽  
Electric Energy ◽  
Carrier Liquid ◽  
The Relationship ◽  
Theory And Experiment

Without external magnetic field, the relationship between electric current of ferrofluid (MF) and temperature is discussed. The electric current is increasing linearly with temperature rising in ferrofluid with Fe3O4 particles distributed into water (MF-Fe3O4-W). Through theory and experiment proved, the carrier liquid only in MF-Fe3O4-W could not decide the ability of delivering electric energy of MF-Fe3O4-W. The electric current would be contributed to the movement of free electric charges (or ions) and colliding of electric polarized particles in MF-Fe3O4-W.

Transition to turbulent electric current sheet reconnection

1997 ◽  
Vol 57 (1) ◽  
pp. 35-45 ◽  
Author(s):  
RUSSELL B. DAHLBURG
Keyword(s):  
Magnetic Field ◽  
Energy Transfer ◽  
Kinetic Energy ◽  
Solar Corona ◽  
Electric Current ◽  
Magnetic Energy ◽  
Three Dimensional ◽  
Energy Losses ◽  
Neutral Sheet ◽  
Secondary Instabilities

Electric current sheets develop in the solar corona when different flux systems come into contact. At these sheets magnetic energy is transformed into heat and kinetic energy by means of reconnection. We have previously demonstrated how to accelerate neutral sheet energy conversion by means of a transition to turbulent reconnection via ideal, three-dimensional secondary instabilities, as conjectured by Montgomery. In this paper we describe how our previous results are modified by the presence of a finite mean sheetwise magnetic field. We find a stabilization from this field, due to a decrease in energy transfer from the basic magnetic field to the three-dimensional perturbed fields. An increase in perturbed dissipative energy losses is also observed.

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