Zener tunneling between the landau levels in quasi-two-dimensional electronic Corbino disks at large filling factors

The magnetotransport characteristics of quasi-two-dimensional electronic Corbino disks based on a wide GaAs quantum well with two filled subbands of size quantization are studied. At low temperatures and high magnetic fields, the Corbino disks exhibit the oscillations of differential conductivity, which are periodic with respect to dc electric field E _dc. It is shown that the observed oscillations are related to the Zener tunneling induced by E _dc. The tunneling occurs between the filled and empty Landau levels under conditions corresponding to the absence of the Hall field.     

Hall resistivity in ferromagnetic manganese-oxide compounds

The transport properties of manganese-oxides are studied using the spin correlation fluctuation scattering mechanism. It is shown that the Hall resistivity in a small magnetic field exhibits a maximum near the Curie point, and a strong field shifts the peak position to high temperature and suppresses the peak value; the dependence of the Hall resistivity on the magnetic field above T_c and below T_c is different. These results agree with the experimental curves qualitatively, but disagree quantitatively, which indicates that the spin correlation fluctuation scattering might not be the dominant mechanism of the colossal magnetoresistance. The double polaron mechanism due to strong electron-phonon and electron-spin coupling is proposed to be responsible for the colossal magnetoresistance in manganese-oxides.     

Combined breakdown in bismuth—Antimony semiconductor alloys

S-shaped current-voltage characteristics for Bi_1?xSb_x alloys are studied theoretically and experimentally. The phenomenon is shown to occur due to the combined interband breakdown, the impact ionization being caused both by the external electric field and the Hall field. The latter is governed by the proper magnetic field of the plasma current. The negative differential resistance (NDR) occurs for the range of currents where the impact ionization is growing intensively but the pinch effect is not yet developed to full extent. The phenomenon is enhanced if the impact ionization rate in the Hall field is greater than in the applied one.     

Magnetic Bloch states and Hall conductivity of a two-dimensional electron gas in a periodic potential without inversion center

Quantum states of 2D electrons are studied in a periodic potential without inversion center in the presence of a magnetic field. It is shown that the energy spectrum in magnetic subbands is not symmetric about the center of magnetic Brillouin zone E(k)≠E(?k). Singularities (phase branching points) of the electron wave function, which determine the quantization law of Hall conductivity σ_xy, are studied in the k space. It is found that a sharp change takes place in the number of points in the magnetic Brillouin zone and in the corresponding values of topological invariants determining the Hall conductivity of filled subbands. It is noted that the longitudinal conductivity of a lattice without inversion center placed in a magnetic field is not invariant with respect to a change in sign of the electric field, and a photovoltaic effect must arise in an ac electromagnetic field.     

双撕裂模非线性演化过程中有理面上的剪切流

在二维平板几何模型下,利用磁流体力学方程组数值模拟托卡马克装置中双撕裂模非线性演化过程中有理面上剪切流的时间和空间分布.结果表明,双撕裂模非线性演化的早期阶段,有理面上没有形成明显的剪切流.剪切流主要存在于快速磁重联阶段,随着磁重联的结束而逐渐消失,剪切流的强度和空间分布随磁岛的演化而改变.另外,较大的等离子体电阻加速磁重联,但是对剪切流的强度和变化趋势没有直接的影响.     

Antiferromagnet IrMn thickness dependence in exchange-biased perpendicular magnetic anisotropy based on CoFe/Pt/CoFe/[IrMn(tIrMn)] multilayers

The effect of the antiferromagnetic IrMn thickness upon the magnetic properties of CoFe/Pt/CoFe/[IrMn(t_IrMn)] multilayers is studied. An oscillatory interlayer coupling (IEC) has been shown in pinned CoFe/Pt(t_Pt)/CoFe/IrMn multilayers with perpendicular anisotropy. The period of oscillation corresponds to about 2 monolayers of Pt. The oscillatory behavior of IEC depends on the nonmagnetic metallic Pt thickness and is thought to be related to the antiferromagnetic ordering induced by the IrMn layer. From the extraordinary Hall voltage amplitude (EHA) curves as function of IrMn thickness, we report that the oscillation dependence of IEC for the [CoFe/Pt/CoFe] multilayer system induced by IrMn with spacer-layer thickness is a important features of perpendicular exchange biased system.     

High-field magnetoresistance and Hall effect in Bi2Sr2CuO x single crystals

We investigated the in-plane magnetoresistance and the Hall effect of high-quality Bi₂Sr₂CuO_x single crystals with T _c (midpoint) = 3.7–9.6 K in dc magnetic fields up to 23 T. For T < 10 K, the crystals show the classical positive magnetoresistance. Starting at T ≈ 14 K, an anomalous negative magnetoresistance appears at low magnetic fields; for T ≥ 40 K, the magnetoresistance is negative in the whole studied range of magnetic fields. Temperature and magnetic field dependences of the negative-magnetoresistance single crystals are qualitatively consistent with the electron interaction theory developed for simple semiconductors and disordered metals. As is observed in other cuprate superconductors, the Hall resistivity is negative in the mixed state and changes its sign with increasing field. The linear T-dependence of cotθ_H for the Hall angle in the normal state closely resembles that of the normal-state resistivity as expected for a Fermi liquid picture.     

Measurements of Hk and Ms in thin magnetic films by the angular dependence of the planar Hall effect

It is shown that the angular dependences of the planar Hall effect measured with infinite magnetic field and with magnetic field H⩾H_k have an intersection point and this fact is enough for measuring the anisotropy field H_k applying the method presented by Pastor, Ferreiro and Torres in J. Magn. Magn. Mat. 53 (1986) 349, 62 (1986) 101. The scaling of the Hall tension U proportional to M²_s in mV/Am^-1 gives a possibility for calculating the M_s-values of the films. These assumptions are verified for NiFe- and NiFeGe films with a uniaxial magnetic anisotropy.     

Induction kinetics in 2D electron systems at the Hall plateaus

Specific features of the induction excitation of 2D electron systems at the Hall plateaus are discussed. The corresponding kinetics is shown to have several frequency regimes. In the region ω ? ω_D, where ω_D is the frequency characteristic of the kinetics at the Hall plateaus, an induction-caused variation of electron density follows the magnetic-field variation with time. For the frequencies ω ≤ ω_D, a noticeable relaxation of the electron disturbance appears, and the induction polarization of 2D samples at the Hall plateaus noticeably decreases as compared to the maximum possible polarization. Finally, in the limit ω ≤ ω_slow, where ω_slow corresponds to another characteristic time of the quantum Hall effect, the so-called adiabatic approximation takes place with the 2D system responding to the derivative of magnetic field dH/dt rather than to the magnetic field itself H(t). The results of calculations are compared with the experimental data reported in the literature.     

Anomalous Hall effect in Cu and Fe codoped In2O3 and ITO thin films

We present a systematic study of the structure, magnetization, resistivity, and Hall effect properties of pulsed laser deposited Fe- and Cu-codoped In₂O₃ and indium-tin-oxide (ITO) thin films. Both the films show a clear ferromagnetism and anomalous Hall effect at 300 K. The saturated magnetic moments are almost the same for the two samples, but their remanent moments M_r and coercive fields H_C are quite different. M_r and H_C values of ITO film are much smaller than that of In₂O₃. The ITO sample shows a typical semiconducting behavior in whole studied temperature range, while the In₂O₃ thin film is metallic in the temperature range between 147 and 285 K. Analysis of different conduction mechanisms suggest that charge carriers are not localized in the present films. The profile of the anomalous Hall effect vs. magnetic field was found to be identical to the magnetic hysteresis loops, indicating the possible intrinsic nature of ferromagnetism in the present samples.     

Quantum corrections to the conductivity of a natural Nd<Subscript>2−<Emphasis Type="Italic">x</Emphasis></Subscript> Ce<Subscript>x</Subscript>CuO<Subscript>4</Subscript> superlattice

Temperature and magnetic field dependences of the resistivity and Hall coefficient in layered single-crystal Nd_2?xCe_xCuO₄ (x = 0.12) films are experimentally investigated and analyzed. It is shown that this material clearly exhibits quantum effects characteristic of 2D semiconductor structures: negative magnetoresistance caused by suppression of the interference quantum correction by a magnetic field, a near-logarithmic temperature dependence of the conductivity, and a temperature dependence of the Hall coefficient related to e-e interaction. It is shown that, when analyzing experimental data, it is necessary to take interlayer transitions into account. Such an approach provides quantitative agreement between experiment and the standard theory of quantum corrections.     

Effects of hall current on MHD Couette flow in a rotating system with arbitrary magnetic field

Author has studied the MHD Couette flow in a rotating environment with non- conducting walls in the presence of an arbitrary magnetic field. The solution in dimensionless form contains four pertinent flow parameters, viz. the Hartmann number, the rotation parameter which is the reciprocal of the Ekman number, the Hall current parameter, and the angle of inclination of the magnetic field to the positive direction of the axis of rotation. An interplay of hydromagnetic force and Coriolis force with an inclusion of Hall current plays a significant role in determining the MHD flow behaviour. The velocity and induced magnetic field distributions are depicted graphically. Also, the numerical results of shear stresses and the rate of mass flows are presented graphically.     

Kinetic effects in an La0.8Ba0.2MnO3 single crystal

Results are presented of a complex study of the magnetic and resistive properties, the Hall effect, the thermal emf, and the longitudinal Nernst-Ettingshausen effect of an La_0.8Ba_0.2MnO₃ single crystal at temperatures between 77 and 400 K. A maximum was observed near the Curie temperature T _c on the temperature dependences of the resistivity, the thermal emf, and the normal Hall coefficient. It was established that the Hall mobility remains constant near T _c. It is shown that these anomalies in the kinetic properties are attributable to a change in the position of the mobility edge relative to the Fermi level. A semiphenomenological theory is put forward to quantitatively describe the temperature and magnetic-field dependences of the resistivity and thermal emf of lanthanum manganites near the phase-transition temperature.     

Nature of magnetic impurity induced superparamagnetism and anomalous Hall effect in β-FeSi2 single crystals

The magnetic properties of β-FeSi₂ single crystals were investigated using magnetization and anomalous Hall effect measurements. These measurements clearly show the appearance of superparamagnetism, the origin of which is attributed to defect-induced magnetic aggregates. Unlike previous reports, based on our combined analysis using magnetization and the anomalous Hall effect, we found that two kinds of aggregates, which are magnetically distinct, exist in our samples. Among the two types found, one gives an anomalous Hall term, which follows a side-jump mechanism while the other is a completely new kind, suggesting that magnetic properties of β-FeSi₂ are very unconventional. The sizes of the aggregates were estimated from our experimental data.     

Concentration dependence of the anomalous Hall effect in Fe/SiO2 granular films below the percolation threshold

The anomalous Hall effect is studied on Fe_x(SiO₂)_1?x nanocomposite films with x<0.7 in the vicinity of the percolation transition (x _c ≈0.6). It is found that, as the transition is approached from the side of metallic conduction, the Hall angle nonmonotonically varies, passing through a minimum. A qualitative model for describing the concentration dependence of the anomalous Hall effect is proposed. The model is based on that of the conductivity of a two-phase system near the percolation threshold [9, 10]. The anomalous Hall effect is governed by two conduction channels: one of them (a conducting network) is formed by large metal clusters that are separated by narrow dielectric interlayers below the percolation threshold, and the other is represented by the dielectric part of the medium containing Fe grains; in this part of the medium, the anomalous Hall effect occurs through the interference of amplitudes from the tunneling junctions in a set of three grains. It is shown that, at x<x _c , the network may give rise to a “shunting” effect, which makes the effective Hall voltage even less than the Hall voltage of the dielectric component.     

Negative magnetoresistance and hall coefficient of a two-dimensional disordered system

Localization corrections to the longitudinal (δρ) and Hall (δρ_H) resistivities of a two-dimensional disordered system are calculated in all ranges of classical magnetic fields, up to the values at which the mean free path of charge carriers l is less than or of the order of the cyclotron radius R _c. It is shown that the physical reason for the departure of the l dependence of these resistivities from the logarithmic law ∝ ln(l _B /l)) (l _B is the magnetic length) at is the nonlocal process of diffusion in the Cooper channel, rather than the transition to a quasi-ballistic regime. Analytical expressions are obtained that allow one to analyze the interference effect in δρ and δρ_H in quantizing magnetic fields , including the quantum limit. Contrary to popular opinion, the localization corrections to ρ_H are shown to be nonzero. They have a sign opposite to that of the charge carriers and lead to a decrease in the magnitude of the Hall resistivity. Their field dependence has the same features and their relative magnitude is of the same order as in the case of the longitudinal resistivity. The quantum corrections to the Hall resistivity are due to the Larmor precession of the closed paths that electrons follow in the process of their multiple scattering by randomly distributed impurities.     

Spin Hall effect in nonmagnetic conductors under the classical Hall conditions

The spin Hall effect—the excitation of a spin flux by an electric current normal to it—is considered in a paramagnetic sample in disregard of the spin-orbit coupling in the classical Hall effect case, when the Pauli spin polarization is induced by the magnetic field H ₀ normal to the electric current.     

Integer and fractional quantum Hall effect in a strip of stripes

We study anisotropic stripe models of interacting electrons in the presence of magnetic fields in the quantum Hall regime with integer and fractional filling factors. The model consists of an infinite strip of finite width that contains periodically arranged stripes (forming supercells) to which the electrons are confined and between which they can hop with associated magnetic phases. The interacting electron system within the one-dimensional stripes are described by Luttinger liquids and shown to give rise to charge and spin density waves that lead to periodic structures within the stripe with a reciprocal wavevector 8k _F in a mean field approximation. This wavevector gives rise to Umklapp scattering and resonant scattering that results in gaps and chiral edge states at all known integer and fractional filling factors ν. The integer and odd denominator filling factors arise for a uniform distribution of stripes, whereas the even denominator filling factors arise for a non-uniform stripe distribution. We focus on the ground state of the system, and identify the quantum Hall regime via the quantized Hall conductance. For this we calculate the Hall conductance via the Streda formula and show that it is given by σ _H = νe ²/h for all filling factors. In addition, we show that the composite fermion picture follows directly from the condition of the resonant Umklapp scattering.     

Enhancement of the anomalous Hall effect and spin glass behavior in the bilayered manganite La2−2xSr1+2xMn2O7

The Hall resistivity and magnetization have been investigated in the ferromagnetic state of the bilayered manganite La_2−2xSr_1+2xMn₂O₇ (x=0.36). The Hall resistivity shows an increase in both the ordinary and anomalous Hall coefficients at low temperatures below 50 K, a region in which experimental evidence for the spin glass state has been found in a low magnetic field of 1 mT. The origin of the anomalous behavior of the Hall resistivity relevant to magnetic states may lie in the intrinsic microscopic inhomogeneity in a quasi-two-dimensional electron system.     

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.