Stationary structure of a high-frequency discharge maintained by a distributed electromagnetic source in the presence of an external magnetic field

The stationary structure of an axisymmetric high-frequency discharge maintained by a given source in an external dc magnetic field is investigated. The source is assumed to be a current wave that travels over the discharge tube surface in the direction of the external magnetic field. The source current has a single azimuthal component and its frequency belongs to the lower hybrid range. The main emphasis is placed on the special case where the electron heat conduction length across the external magnetic field exceeds considerably the tube radius. The dependences of discharge plasma parameters on the current amplitude and propagation constant along the tube have been found for this case. The results of numerical calculations of the distributions of the field and the power of the Joule loss in a discharge are presented.     

Mechanism of drift of stripe magnetic domains in ferrite-garnet single crystals

The drift of stripe magnetic domains in (111) single-crystal ferrite-garnet plates in an alternating magnetic field (25–1000 Hz) has been investigated. The dependences of the drift velocity of stripe domains on the field frequency and amplitude have been obtained for magnetic fields of different orientations. A dislocation drift mechanism is proposed. Enhanced motion of magnetic dislocations in a system of stripe domains is established.     

铁镓复合棒换能器设计及非线性驱动研究

提出了一种针对无偏场铁镓换能器非线性驱动方式,该方法通过设计输入电信号函数以匹配磁致伸缩非线性应变函数,从而实现换能器的简谐波输出。通过理论分析,寻找到中低磁场下简单信号实现非线性驱动——半频驱动。研制了复合棒铁镓换能器并在水池进行半频激励测试,结果表明,采用无偏场的半频驱动方式激励换能器在4.2 A电流时声源级达到192 dB,能够无失真工作,实验验证铁镓换能器非线性驱动具有可行性。对高磁场时的非线性驱动进行了理论仿真分析,并设计了非线性驱动信号。      

Ultracold molecule production via a resonant oscillating magnetic field

A novel atom-molecule conversion technique has been investigated. Ultracold 85Rb atoms sitting in a dc magnetic field near the 155 G Feshbach resonance are associated by applying a small sinusoidal oscillation to the magnetic field. There is resonant atom to molecule conversion when the modulation frequency closely matches the molecular binding energy. We observe that the atom to molecule conversion efficiency depends strongly on the frequency, amplitude, and duration of the applied modulation and on the phase space density of the sample. This technique offers high conversion efficiencies without the necessity of crossing or closely approaching the Feshbach resonance and allows precise spectroscopic measurements. Efficiencies of 55% have been observed for pure Bose-Einstein condensates.     

斜向磁化的YIG波导中静磁波传播特性

分析了斜向静磁场作用下磁光薄膜波导中传播的静磁正向体波特性,计算了YIG薄膜波导中静磁波传播常数以及与磁光耦合系数相联系的动态磁化强度对静磁波模数、频率和斜向场等的依赖关系.计算表明：静磁波频率f及模数m越大、磁场H_i及其偏角θ越小,静磁波传播常数K_s越大;零模静磁体波的（动态磁化强度）振幅远大于高模数的静磁体波振幅.在适当的静磁体波频率范围内,斜向偏置磁场可提高静磁体波的振幅,进而可以改善静磁波与导波光的相互作用特性和提高导波光的衍射效率. 关键词：     

Features of the magnetoplastic effect in a beryllium condensate

The effect of a weak dc magnetic field on inelastic characteristics of a magnesium-thermal beryllium condensate (99.95 wt % Be) has been studied. It has been shown that the magnetic field differently affects the defect subsystem of beryllium and, depending on sample treatment, leads to its hardening or softening. Based on an analysis of amplitude dependences of the internal friction and elastic moduli, the dislocation velocity after magnetic field exposure has been estimated. It has been shown that the magnetic aftereffect in Be is significantly stronger than the effect in situ.     

Noise-free frequency conversion of quantum states

In this paper,the frequency conversion of quantum states based on the intracavity nonlinear interaction is proposed.The fidelity of an input state after frequency conversion is calculated,and it is shown the noise-free frequency conversion of a quantum state can be achieved by injecting a strong signal field.The dependences of conversion efficiency on the pump parameter,extra losses and input state amplitude are also analysed.     

Direct and inverse magnetoelectric effect in layered composites in electromechanical resonance range: A review

A model is presented for the increase in magnetoelectric (ME) coupling in magnetostrictive-piezoelectric bilayers in the electromechanical resonance region. The ME voltage coefficients α_E have been estimated for transverse field orientations corresponding to minimum demagnetizing fields and maximum α_E. We solved the equation of medium motion taking into account the magnetostatic and elastostatic equations, constitutive equations, Hooke's law, and boundary conditions. The resonance enhancement of ME voltage coefficient for the bilayer is obtained at antiresonance frequency. To obtain the inverse ME effect, a pick up coil wound around the sample is used to measure the ME voltage due to the change in the magnetic induction in magnetostrictive phase. The measured static magnetic field dependence of ME voltage has been attributed to the variation in the piezomagnetic coefficient for magnetic layer. The frequency dependence of the ME voltage shows a resonance character due to the longitudinal acoustic modes in piezoelectric layer. The model is applied to specific cases of cobalt ferrite–lead zirconate titanate and nickel–lead zirconate titanate bilayers. Theoretical ME voltage coefficients versus frequency profiles are in agreement with data.     

Dynamic drift of the magnetic domains in ferrite-garnet crystals

The drift of stripe-domain walls in a (111) ferrite-garnet plate with orthorhombic anisotropy and quality factor Q < 1 in an alternating magnetic field of 30–1000 Hz was investigated. The obtained experimental dependences of the domain wall drift velocity on the magnetic field frequency and amplitude are compared to the corresponding theoretical dependences.     

垂直磁各向异性自旋阀结构中的铁磁共振

本文在理论上研究了垂直磁各向异性自旋阀结构中磁场激发和调节的铁磁共振. 通过线性展开包含自旋转移矩项的Landau-Lifshitz-Gilbert方程,获得了磁场激发和调节的铁磁共振谱. 给出了共振线宽、共振频率和共振磁场随直流电流密度大小和方向以及直流磁场的变化关系. 通过调节直流电流密度的大小和方向,系统的有效阻尼可以达到最小. 关键词： 自旋阀 自旋转移矩 垂直磁各向异性 铁磁共振     

A theory of the inverse magnetoelectric effect in layered magnetostrictive–piezoelectric structures

A theory of the inverse magnetoelectric effect in layered structures has been presented. The theory is based on solving the equations of elastodynamics and electrostatics separately for the magnetostrictive and piezoelectric phases, taking into account the conditions at the interface between the phases. Expressions for the coefficient of inverse magnetoelectric conversion through the parameters characterizing the magnetostrictive and piezoelectric phases have been obtained. Theoretical dependences of the inverse magnetoelectric conversion coefficient on the frequency of the alternating-current electric field for the three-layer PZT–Ni–PZT structure and the two-layer terfenol-D–PZT structure have been calculated. The results of the calculations are in good agreement with the experimental data.     

AC susceptibility of a cobalt aluminosilicate glass

The temperature, magnetic field, and frequency dependences of the ac susceptibility for an aluminosilicate glass containing 14.3 at% cobalt have been measured. These results show significant differences with the dc measurements in very low fields at all temperatures above and below the spin glass freezing temperature T_f.     

Frequency-dependent electromagnetic properties of the Pb-doped manganite measured in the transformer-type circuit

The dependence of the transformation coefficient of the four-pole network with the toroid core made of the La_0.6Pb_0.4MnO₃ manganite on dc biasing magnetic field and frequency was experimentally investigated. The factors which influence the value of the transmission coefficient are analyzed. In the megahertz frequency range the frequency dependence of the transformation coefficient has a resonant form with the position of the maximum and amplitude increasing with the dc biasing. The dc magnetic field dependence of the phase shift between the voltages in the primary and secondary windings was investigated. The results are interpreted taking into account the imaginary component of magnetic permeability of the core material.     

非晶态合金薄带与膜的巨磁电阻抗效应理论及计算

通过建立具有平面近横向各向异性场的非晶态合金薄带及膜的磁畴结构模型，利用线性化Maxwell方程组及Landau-Lifshitz方程，推出了在高频交变磁场及外加面内轴向直流磁场H_ex作用下的铁磁材料的与取向相关的磁导率表达式，得到了对方位角平均的相对磁导率及阻抗的计算式，导出了磁导率与张量磁化率分量间的关系，对材料磁导率的实部及虚部随H_ex的变化进行了计算，并给出了对应的磁谱图.建立的磁导率与外磁场的理论关系可将Panina及Kraus给出的理论结果统一起来. 关键词： 非晶态合金薄带及膜 取向相关磁导率 GMI效应理论与计算 近横向各向异性场     

Enhancement of the magnetoelectric coupling in an A-line shape magnetostrictive/piezoelectric structure

In this study, a new kind of magnetoelectric (ME) structure is designed with Terfenol-D, PZT-5A and nonmagnetic and nonelectric trestle. The configuration of this ME structure presents “A-line” type, PZT-5A and Terfenol-D are respectively bonded with the trestles, which adopt the knuckle joint assembly. Differently from the conventional ME layered structure, in the new structure, the deformation of the PZT-5A of larger size is driven by a Terfenol-D layer of smaller size at an external magnetic field. Since the driven force is applied at the ends of piezoelectric layer through the trestles, the whole piezoelectric layer can be completely stretched or compressed, and the larger voltage should be induced. For the new ME structure with mica trestle, the maximum value of ${\alpha }_E$ is twice higher than that for the conventional laminated ME structure. Furthermore, a wider range of response frequency is also observed in this structure. For the new ME structure with ABS trestle, the experimental results indicate that the maximum ME voltage coefficient is measured as high as 31.85 V/cm?Oe at 405 Oe.     

Microwave response to the magnetization switching of CoFeB/Ta/CoFeB spin valves and CoFeB films

Negative magnetoresistance modifying the quality factor of a microwave cavity under the magnetization switching of ferromagnetic layers has been discovered in a MgO/CoFeB/MgO/Ta film with a single ferromagnetic layer and a MgO/CoFeB/Ta/CoFeB/MgO/Ta spin valve consisting of two ferromagnetic CoFeB layers. The dependence of the first derivative dP/dH of the microwave absorption signal on the dc magnetic field of the spectrometer exactly reproduce the magnetic hysteresis loops of the sample. The slope of these dependences and the amplitude of dP/dH jumps under remagnetization of the layers are determined by the interplay of a negative magnetoresistance of individual layers and a positive giant magnetoresistance of the entire multilayer structure. The discovered phenomenon allows using microwave absorption for making a high-sensitivity contact-free indicator of the basic magnetization states of a spin valve.     

Magnetoelectric gradiometer

Gradiometer resembles in functionality a sensor measuring the magnetic field gradient whose sensitivity is determined the ability to quantify change with respect to base value. Magnetoelectric (ME) gradiometer designed in this study utilizes ME composites with ring-dot piezoelectric transformer structure working near electromechanical resonance, where ring acts as the input while dot acts as the output. Magnetostrictive disc was bonded on top of the output section resembling a bilayer composite structure. The resonance frequency of sample was found to be in the range of 91–94 kHz. The generated magnetic field due to converse ME effect interacts with the externally applied magnetic field producing flux gradient which is detected through the frequency shift and output voltage change of gradiometer. The measurements clearly illustrate that the proposed design has high sensitivity and it can be used for detecting magnetic field gradient.     

Emission Intensity Enhancement of DC Arc Plasma Induced by External Oscillating Magnetic Field

Direct current (dc) arc plasma with continuous aerosol supply was coupled with an external oscillatingmagnetic field of a few tens of mT and a frequency of up to 1 kHz. Such configuration was used to alter the plasma‐related radiative properties. The magnetic field was oriented perpendicularly to the electric field in the plasma and forced the arc column to oscillate as a whole with respect to the surrounding atmosphere. The magnitude of the appliedmagnetic.eld controls the amplitude of the oscillatory motion. Several parameters that can contribute to the radiative properties of the plasma were investigated (arc current, composition of aerosol introduced into the plasma, amplitude and frequency of the magnetic field applied). Spectral emission from different zones of the plasma column was measured by optical emission spectroscopy (OES). In comparison to steady‐state plasma, the applied magnetic field induces an intensity enhancement of emission of the most analytes considered. The intensity enhancement is strongly affected by the amplitude and frequency of plasma column oscillations, i.e. by plasma column velocity. Also, intensity enhancement depends on the plasma zone observed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

SH wave propagation in magnetic–electric periodically layered plates

In this paper, dispersive behavior and band structure of SH waves in magnetic–electric (ME) periodically layered plate are investigated by the transfer matrix method. Two kinds of unit cell form, one is piezoelectric (PE)/piezomagnetic (PM)/PE, and the other is PM/PE/PM, are considered in detailed. A peculiar case of the generalized single-celled plate is first presented and then the multi-celled periodical layered plates for discussion on the propagation behaviors and the band characteristics of SH waves, respectively. The effects on dispersive curves of four kinds of ME boundary conditions at the free surface of plates are discussed. Numerical examples for phase velocities or frequencies all show that the zero-order mode is non-dispersive both for single-celled and multi-celled periodically layered plates. The high modes of dispersive curves tend to the shear wave velocity of the slower sub-layer as frequencies increase both for these two structures. The frequency pass-band and frequency band gaps appear in multi-layered ME periodically layered plates. Electrical and magnetic boundary conditions, respectively, determine the dispersive curves for SH waves in the PE/PM/PE and PM/PE/PM periodically layered plates.