Stability of a Rotating Compressible Stratified Plasma in the Presence of Hall Currents and Magnetic Resistivity

The dynamic instability in a horizontal layer of a rotaing compressible plasma of variable density has been investigated to examine the influence of the simultaneous presence of the effects of Hall currents and finite magnetic resistivity. The linearized stability analysis has been carried out through the normal mode technique. By making use of the existence of a variational principle which is shown to characterize the problem, proper solutions have been obtained for a semiinfinite plasma in which there is an exponential density gradient along the vertical. The dispersion relation obtained has been solved numerically and it is found that both the resistivity and the Hall currents have a destabilizing influence as the growth rate of the unstable disturbances increases with increasing values of the parameters characterizing these effects. On the other hand, the Coriolis forces are found to have a stabilizing influence for in this case the growth rate decreases with increasing rotation.     

Effects of Hall Currents and Gyroviscosity on the Instability of a Self-Gravitating Stratified Plasma

The instability in a horizontal layer of a partially ionized self gravitating plasma has been studied to include simultaneously the effects of Hall currents, viscosity and finiteness of Larmor radius (FLR). The ambient magnetic field is assumed to be uniform and vertical. Proper solutions have been obtained through the variational methods for a semi-infinite plasma in which the density has an exponential gradient along the vertical. The dispersion relation obtained has been solved numerically and it is found that the growth rate of unstable perturbations decreases with the effects of viscosity, neutral gas friction and FLR. The influence of effects of viscosity, neutral gas friction and FLR are consequently stabilizing. It is found that the Hall currents have a destabilizing influence as the growth rate is found to increase with this effect.     

Effects of Hall Currents on the Self-Gravitational Instability of a Finitely Conducting Plasma of Variable Density

The effects of Hall currents have been studied on the hydromagnetic stability of a self-gravitating, incompressible, viscous and finitely conducting plasma of variable density. For a uniform and horizontal magnetic field which is present, it is shown that the problem is characterized by a variational principle. Making use of this, proper solutions have been obtained for a semi-infinite plasma in which the density varies one-dimensionally (exponentially) along the vertical. The dispersion relation has been solved numerically for the different values of the parameters involved. It is found that the growth rate increases with both the Hall currents and resistivity, showing thereby the destabilizing character of these effects. However, the influence of viscosity is found to be stabilizing as the growth rate decreases with viscosity.     

Stability of a Stratified Layer of a Gravitating Partially Ionized Plasma

The instability in a stratified layer of a self-gravitating partially ionized plasma has been studied in the presence of effects of Hall currents. For a plasma permeated by a uniform vertical magnetic field, the dispersion relation has been obtained through variational method. It is found that the Hall currents have a destabilizing effect while the neutral gas frictional effects have a stabilizing influence.     

Gravitational Instability of a Thermally Conducting Plasma in an Oblique Magnetic Field

The combined influence of the effects of Hall currents, magnetic resistivity and viscosity have been studied on the gravitational instability of a thermally conducting homogeneous unbounded plasma in an oblique magnetic field. The solution has been obtained through the normal mode technique and the dispersion relation has been derived. It is shown that the Jeans' criterion for gravitational instability remains unchanged. Solving numerically the dispersion relation, the dependence of the growth rate of the gravitational unstable mode on the considered physical effects has been obtained for an astrophysical situation. For conditions prevailing in the magnetized collapsing clouds, the numerical calculations for the plot of growth rate against wave number has been obtained for several values of the parameters characterizing Hall currents magnetic resistivity viscosity thermal conductivity. It is found that magnetic resistivity and thermal conductivity have destabilizing influence while viscosity has stabilizing influence on the instability of the plasma of disturbance m(ϱ) = 9 × 10⁻³ kg.     

Frictional effects with neutrals and Rayleigh-Taylor instability of a compressible Hall plasma

The effect of neutral gas friction is considered on the Rayleigh-Taylor instability of a compressible plasma in the presence of Hall currents. The prevailing magnetic field is assumed to be uniform and horizontal. It is shown that the solution is characterized by a variational principle. Based on the variational principle the dispersion relation is derived for a composite plasma, confined between two horizontal planes at a finite distance, in which the density is stratified in the direction of gravity according to the exponential law. It is found that the effect of collisions with neutrals, Hall currents and compressibility of the medium have destabilizing influence as the wave number range which is stable in their absence, is rendered unstable by their presence.     

Gravitational Instability of a Rotating Viscous Thermally Conducting Plasma

This paper deals with the gravitational instability of an infinite homogeneous viscous rotating plasma of finite electrical conductivity in the combined presence of effects of Hall currents, finite Larmor radius (FLR) and thermal conductivity. The ambient magnetic field is assumed to be uniform and acting along the vertical direction. Both longitudinal and transverse modes of wave propagation have been studied. It is shown that Jean's criterion determines the gravitational instability even in the presence of the effects of thermal conductivity, viscosity, finite electrical conductivity, FLR, rotation and Hall currents. Further it is found that while FLR, viscosity and rotation have a stabilizing influence, both the thermal and the electrical conductivities have a destabilizing influence on the gravitational instability of a plasma.     

Gravitational Instability of a Rotating Viscous Finitely Conducting Plasma

The gravitational instability of infinite homogeneous plasma has been studied to include simultaneously the effects of rotations, Hall currents, viscosity, finite electrical conductivity and the finite Larmor radius (FLR). Both the longitudinal, and transverse modes of wave propagation have been studied. It is found that the gravitational instability is determined by Jeans' criterion even in the presence of effects of rotation, Hall currents, FLR, viscosity and finite conductivity whether included separately or jointly.     

Hall Currents and the Rayleigh-Taylor Instability of a Finitely Conducting Plasma in the Presence of Coriolis Forces

We have studied the effect of rotation on the development of Rayleigh-Taylor instability of an incompressible, viscous, Hall, finitely conducting plasma of variable density. The solution is developed, through variational methods, for a semi-infinite plasma in which the density varies exponentially along the vertical. It is found that the system is unstable for all wave numbers when the effects of magnetic resistivity are included. The effects of coriolis forces and viscosity on the growth rate of the unstable system are found to be stabilizing while that of Hall currents is destabilizing. Finite conductivity affects the growth rate of the unstable mode differently for the smaller and larger values of the wave numbers, destabilizing for the waves of large wave length and stabilizing for waves of small wave length.     

Finite Larmor radius and Hall effects on thermal instability of a compressible plasma

The effects of compressibility, finite Larmor radius (FLR) and Hall currents are considered on the thermal instability of a plasma in the presence of a uniform horizontal magnetic field. For stationary convection, the compressibility has a stabilizing effect whereas FLR and Hall currents have stabilizing as well as destabilizing effects. For (C _pβ/g)<1, the system is stable. The magnetic field, FLR and Hall currents introduce oscillatory modes in the system for (C _pβ/g)>1.     

Edge current switch of two-dimensional electron gas using carrier density control

We have investigated the effects of electron density discontinuity on the transports of edge currents of two-dimensional electron gas (2DEG). The electric field applied to a gate, which covers the 2DEG partially, gives rise to change in the carrier density and results in a density gradient, which deforms the edge currents. The transverse and longitudinal resistances were measured as functions of gate voltage V_G in the quantum Hall regime. The deviations of the longitudinal resistances from the normal quantum Hall resistances are attributed to the reflections of the edge currents under the influence of the abrupt density discontinuity. A switching behavior of the transverse resistance by controlling the gate voltage was observed when V_G=−2.2 and −2.0 V for magnetic field H=5 and 7.2 T, respectively.     

Vertical displacements of the current sheet and Hall currents

Vertical displacements of the peripheral regions of the current sheet with respect to its mean plane have been detected in the case of the sheet formation in the three-dimensional configuration with the X line and longitudinal component of the magnetic field. It has been shown that this effect is due to the generation of Hall currents and the appearance of vertically directed forces. Change in the sign of vertical displacements at the late stage of the sheet evolution has been detected, indicating the generation of opposite Hall currents when the direction of the main current near the side edges of the sheet changes. It has been shown that Hall currents significantly affect the structure of current sheets, and vertical oscillations of the peripheral regions of the current sheet, which appear owing to oppositely directed Hall currents, are involved in the dynamic processes in current sheets.     

铁磁/重金属双层薄膜结构中磁性状态的稳定性分析

本文在理论上研究了铁磁/重金属双层薄膜结构中自旋霍尔效应自旋矩驱动的磁动力学. 通过线性稳定性分析, 获得了以电流和磁场为控制参数的磁性状态相图. 发现通过调节电流密度和外磁场, 可以获得不同的磁性状态, 例如: 平面内的进动态、平面内的稳定态以及双稳态. 当外磁场的方向在一定的范围时, 通过调节电流密度可以实现磁矩的翻转和进动. 同时, 通过数值求解微分方程, 给出了这些磁性状态磁矩的演化轨迹.     

Interaction between Vacuum Arcs and Transverse Magnetic Fields with Application to Current Limitation

The interaction between diffuse vacuum arcs and magnetic fields applied transverse to the electrode axis has been investigated both theoretically and experimentally. For arc currents < 6 kA, Hall electric fields, generated by the interaction, bow the plasma out of contact with the anode and raise the arc voltage. In the presence of a parallel capacitor, the arc current falls to zero and the arc is extinguished. For arc currents of 6 to 15 kA, arc extinction can be achieved with an oscillatory magnetic field; during such extinctions the arc voltage remains in phase with the magnitude of the field. Arc extinction via magnetic field/vacuum arc interaction could have applications to ac-current limiters and dc breakers. The fault current limiter application is discussed in this paper.     

Hall effects on thermosolutal instability of a rotating plasma

Summary The thermosolutal instability of a rotating plasma in the presence of a uniform vertical magnetic field is studied to include the effects of Hall current. When the instability sets in as stationary convection for the case of no rotation, the Hall effects are found to be destabilizing. The stable solute gradient and rotation are found to have stabilizing effects. In the presence of rotation the Hall currents are found to be stabilizing forT ₁>M(1+x)². the case of overstability is also considered and it is shown that such solutions exist. The variation of the frequency with respect to the wave number at the neutral state is graphically shown. The authors of this paper have agreed to not receive the proofs for correction.     

Antisymmetric magnetoresistance in magnetic multilayers with perpendicular anisotropy

While magnetoresistance (MR) has generally been found to be symmetric in applied field in nonmagnetic or magnetic metals, we have observed antisymmetric MR in Co/Pt multilayers. Simultaneous domain imaging and transport measurements show that the antisymmetric MR is due to the appearance of domain walls that run perpendicular to both the magnetization and the current, a geometry existing only in materials with perpendicular magnetic anisotropy. As a result, the extraordinary Hall effect gives rise to circulating currents in the vicinity of the domain walls that contributes to the MR. The antisymmetric MR and extraordinary Hall effect have been quantitatively accounted for by a theoretical model.     

Hard-core Hall tube in superconducting circuits

The Hall tube as a minimum model to simulate the integer quantum Hall effect is essential for exploring topological physics, while it has not been constructed in the recent developing successfully experiments on superconducting circuits. In this work, we propose a feasible experiment scheme using three legs superconducting circuits with transmon qubits to realize a Hall tube. Then we first investigate its topological properties. Since the time-reversal, particle-hole, and chiral symmetries are all broken for the system, the Hall tube belongs to the A class of the Altland-Zirnbauer classification. We obtain the corresponding topological phase transition both numerically and analytically. Since the chirality is a key character of the quantum Hall effect, we secondly investigate the chiral physics in the Hall tube. We find the topological protected chiral edge currents and discuss its robustness. Finally, we give the possible experimental observations of the topological state and topological protected chiral edge currents.     

Spin Hall effect induced by resonant scattering on impurities in metals

The spin Hall effect is a promising way for transforming charge currents into spin currents in spintronic devices. Large values of the spin Hall angle, the characteristic parameter of the yield of this transformation, have been recently found in noble metals doped with nonmagnetic impurities. We show that this can be explained by resonant scattering off impurity states split by the spin-orbit interaction. By using as an example copper doped with 5d impurities we describe the general conditions and provide a guide for experimentalists for obtaining the largest effects.     

Measurement of the hall coefficient and the electric conductance of anisotropic semiconductor samples

The macroscopic theory of the Hall effect is considered in anisotropic semiconductor samples of rectangular form with low-resistivity electrodes. The shunting influence of the electrodes and the corresponding Hall currents on the magnitude of the Hall emf is considered. Simple relations are obtained and practical recommendations are given for computing the components of the tensor of the Hall coefficient and of the conductivity. The results are presented in a form convenient for practical use in analyzing anisotropic monocrystals and films.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 56–60, November, 1990.