Radiofrequency magnetoresistance of Fe/Cr superlattices

The rf magnetoresistance of Fe/Cr superlattices is studied for two orientations of the current: parallel and across the superlattice layers. A mutually single-valued correspondence is established between the relative magnetoresistance measured at dc current and the change in the transmission coefficient of electromagnetic waves in the magnetic field. When rf currents flow across the layers, the relative change in the signal amplitude is proportional to twice the change in the electrical resistance of the superlattice and is of opposite sign. It is shown that the rf losses are determined by the surface resistance which is proportional to the superlattice thickness and inversely proportional to its conductivity. An equation is derived for the rf electric field distribution in the superlattice. It is established that when the thickness of the superlattice is small compared with the skin layer depth, field and current components which penetrate through the entire superlattice exist.     

Rectangular Waveguide With Metallic Nanostructure Driven by Magnetic Field

The changes in the propagation constant of the TE₁₀ mode of a rectangular waveguide with a metallic nanostructure, occurring under an external magnetic field have been investigated. Expressions for complex reflection and transmission coefficients have been derived. The dependence of the reflection coefficient upon the intensity of the external magnetic field is analyzed. It is shown that the experimental values of the propagation constant or the reflection and transmission coefficients can be used to estimate the value of the microwave magnetoresistance of nanostructures. Experiments on the measurement of the reflection and transmission coefficients in a waveguide with an (Fe/Cr)n nanostructure have been performed in millimeter and centimeter wave bands.     

对称抛物势阱磁性隧道结中的自旋输运及磁电阻效应

研究了两端具有铁磁接触的对称抛物势阱磁性隧道结(F/SPW/F)中自旋相关的隧穿概率和隧穿磁电阻,讨论了量子尺寸效应和Rashba 自旋轨道耦合作用对自旋极化输运特性的影响.研究结果表明:隧穿概率和隧穿磁电阻随抛物势阱宽度的增加发生周期性的振荡.抛物势阱深度的增加减小了隧穿概率和隧穿磁电阻的振荡频率.Rashba 自旋轨道耦合强度的增加加大了隧穿概率和隧穿磁电阻的振荡频率.隧穿概率和隧穿磁电阻的振幅和峰谷比强烈依赖于两铁磁电极中磁化方向的夹角. 关键词： 磁性隧道结 Rashba 自旋轨道耦合 隧穿概率 隧穿磁电阻     

Absorption of cnoidal electromagnetic waves by superlattice electrons in the process of impurity ionization

Absorption of cnoidal electromagnetic waves, which are the most general periodic solution to the sine-Gordon equation, by electrons of a one-dimensional quantum semiconductor superlattice in the process of impurity ionization is studied in terms of the semiclassical approximation. The dependence of the absorption coefficient on the electric field of an electromagnetic wave is found to be nonmonotone with a pronounced peak.     

Electromagnetic field penetration through lanthanum manganites

The process of electromagnetic field penetration through lead-doped lanthanum manganites exhibiting colossal magnetoresistance has been studied. The measurements have been performed in a range of radio frequencies from 20 kHz to 10 MHz in the temperature interval containing a magnetic phase transition. Application of a constant external magnetic field leads to an increase in the transmission coefficient. Relative variations of the electromagnetic field transmission coefficient are several times as large as the relative change in the dc magnetoresistance. The temperature dependence of the relative change in the transmission coefficient has been studied. Variations of the transmission coefficient sharply decrease in the vicinity of the phase transition temperature, but they still remain rather large at temperatures above the Curie point.     

Microwave-frequency spin-dependent tunneling in nanocomposites

The transmission coefficient of films of Co_51.5Al_19.5O₂₉, Co_50.2Ti_9.1O_40.7, Co_52.3Si_12.2O_35.5, and (Co_0.4Fe_0.6)₄₈(MgF)₅₂ ferromagnetic metal-insulator magnetic nanocomposites exhibiting tunneling magnetoresistance and the magnetorefractive effect for electromagnetic waves was studied in the frequency range 30–50 GHz. The transmission coefficient of the first two compositions varies strongly under an applied magnetic field, and its variation exhibits a linear correlation with the field dependence of magnetoresistance. For the other two compositions, the transmission coefficient does not depend on magnetic field. The data obtained are interpreted in terms of the concept of microwave spin-dependent tunneling.     

High-frequency magnetoimpedance in nanocomposites

The transmission of millimeter-range electromagnetic waves (30–50 GHz) through a magnetic nanocomposite thin film exhibiting tunnel magnetoresistance (TMR) is calculated. The relative change of transmission coefficient in an applied magnetic field due to the magnetorefractive effect is approximately linear with TMR and strongly depends on nanocomposite resistivity and film thickness. The obtained results are in a good agreement with experiment.     

亚波长金属波导的光传播和干涉特性研究

利用时域有限差分方法研究了亚波长金属波导TE波的传播特性和基于异常透射现象的干涉特性.对各种参量对驻波特性的影响及两列波导间的耦合特性进行了分析.研究发现,TE波在波导中传播时存在截止宽度,如果波导宽度小于截止宽度,TE波在波导中不能传播;如果波导宽度大于截止宽度,TE波的传播距离将随波导宽度变大而突然增加.当波导宽度达到或大于半波长时,TE波可以在波导中正常传播.金属波导的截止宽度与金属的吸收系数成正比.此外,由于光在亚波长金属波导透射时的异常透射现象,在亚波长金属波导中产生了TE波的干涉现象,能形成驻波.     

Linear magnetoresistance effect in lateral magnetic superlattices

Two-dimensional electron gas systems modulated by a lateral magnetic superlattice are proposed and the related magnetoresistance effect is described in this work. It is found that the magnetoresistance (MR) ratio of the given structures depends strongly on the uniform magnetic field, and the peaks of the MR ratio depressed linearly with the increase of the uniform magnetic field. This feature can be utilized in practical linear magnetoresistance (LMR) devices.     

Attenuation of electromagnetic waves in a semiconductor superlattice in a magnetic field

Magnetoplasma waves and inhomogeneous (complex) waves in an infinite semiconductor superlattice in a magnetic field are studied, and dispersion curves are obtained. It is shown analytically and numerically that, in periodic structures, among inhomogeneous waves, there are many complex waves for which the imaginary part of the wave vector is greater than the real part. The effect of dissipation in a medium on the dispersion curves of magnetoplasma waves is examined. The dependence of the minimum phase velocity on the collision frequency and the magnetic field strength is studied.     

Dispersion properties and field structures of eigenmodes of nonuniform plasma waveguides in a longitudinal magnetic field

We study the field structure and dispersion properties of a hybrid eigenmode guided by a nonuniform magnetized plasma waveguide. It is shown that the rotational and quasi-potential waves contribute to the formation of such a mode in the whistler frequency range. Depending on the plasma density, the rotational component of the hybrid mode is determined by either waves with complex transverse wave numbers or whistler waves, or by true surface waves. In the presence of an axial nonuniformity of the plasma in a channel, the transverse field structure of the propagating mode changes, which is stipulated by changes in both the values of transverse wave numbers and their dependence on the radial coordinate. It is found that the spectrum of axial wave numbers of eigenmodes of a plasma waveguide undergoes a pronounced condensation when smoothing the waveguide walls. The damping of the hybrid mode of a nonuniform waveguide due to electron collisions is found and it is shown that collisional losses determine the damping of waves trapped in the waveguide in the experiments on ionization self-channeling of whistler waves. We have found the effect of “displacing” the strong field from the inner core to the background outer region of the waveguide with increasing plasma density on its axis and broadening background region. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 49, No. 7, pp. 607–617, July 2006.     

单向声传播结构研究

受到电子二极管整流效应的启发,对单向声传播结构展开了一系列的理论与实验研究：将超晶格结构与非线性声学材料组合构成了可实现声整流效应的声二极管结构;通过将反对称弹性结构引入到复合结构板来产生Lamb波的不对称模式转化,设计了可实现Lamb波单向传播的线性声学结构;基于声子晶体的部分禁带特性,在有限尺度声学系统中设计并实现了单向声学波导结构;设计并实现了由纯板与声栅构成的声单向传播结构,具有小尺寸与高效率的特点,且声波出射角度可调;基于声学梯度材料设计了可在极宽频带内实现不对称声传播的声学结构。     

Controllable spin-dependent transport in silicene superlattice

Based on the transfer-matrix method, we theoretically investigate the spin-dependent transport properties in magnetic silicene superlattice in the presence of extrinsic Rashba spin–orbit interaction (RSOI). It is found that the spin transmission probability and spin conductivities can be efficiently controlled by the number of magnetic barriers. As the number of magnetic barriers increases, spin conductivities strongly decrease, and reduce to zero in the large on-site potential difference between A and B sublattices (Δ_z) region. The results indicate that a magnetic silicene superlattice exhibits a remarkable wavevector-dependent spin filtering effect. Also, the magnetoresistance (MR) ratio exhibits an oscillatory behavior with the Fermi energy. The MR ratio can be tuned by the Fermi energy, number of magnetic barriers and extrinsic RSOI. Specifically, in the presence of magnetic field the spin polarization can be observed, and increases by increasing the magnetic field.     

Light Penetration through a Tapered Waveguide

An approximate pattern of calculation of the field behavior in waveguides of variable radius is proposed. It is based on the assumption of a slow dependence of the radius on the longitudinal coordinate and is reduced to the solution of an ordinary differential equation. The dependences of the waveguide transmission on the frequency of radiation, entrance and exit radii, as well as the rate of radius variation along the axis are studied. The analysis is carried out within the range of parameters typical for optical fibers used in optical near‐field microscopy. It is shown that the increase in the rate of radius variation with the longitudinal coordinate will cause the transmission coefficient of the tapered waveguide to increase.     

Zener tunneling of light waves in an optical superlattice

We report on the observation of Zener tunneling of light waves in spectral and time-resolved transmission measurements, performed on an optical superlattice made of porous silicon. The structure was designed to have two photonic minibands, spaced by a narrow frequency gap. A gradient in the refractive index was introduced to create two optical Wannier-Stark ladders and, at a critical value of the optical gradient, tunneling between energy bands was observed in the form of an enhanced transmission peak and a characteristic time dependence of the transmission.     

Zn0.8Cd0.2Se-ZnSe应变层超晶格的激子发光和受激发射

本文用MOCVD技术在GaAs衬底上成功地制备了具有波导结构的Zn0.8Cd0.2Se-ZnSe应变层超晶格样品,在77K温度的光致发光光谱中观测到n=1的重空穴和轻空穴激子的辐射复合。在光泵浦下,在波导结构的F-P腔中观测到具有多模结构的受激发射,受激发射谱中的不同模具有不同的阈值功率密度;时间延迟衰减曲线的半宽度越窄,阈值光强越大.     

Localization and interaction effects in CdTeBi superlattices

The transport properties of CdTeBi superlattice have been measured as a function of the modulation wavelength. A logarithmic dependence with temperature was observed for the resistance at low temperature. The resistivity varied from 0.1 to 3.9 mΩcm at 1.7 K as the modulation wavelength varied from 177 to 81 A. A logarithmic behavior with H was observed for the transverse (longitudinal) magnetoresistance for low (high) fields. Samples were studied at temperatures down to 1.7 K and in magnetic fields up to 5 Tesla. No negative magnetoresistance as predicted by weak localization theory was observed. Hall coefficient measurements showed a logarithmic dependence with temperature which is indicative of Coulomb correlation effects (interaction theory). All measurements indicate that the transport behavior of CdTeBi superlattices is dominated by spin-orbit and/or interaction effects while weak localization plays a minimal role.     

Wave transmission through structural inserts

The transmission of waves through two discontinuities in a one-dimensional waveguide system is considered. Attention is focused on transmission through a structural insert, which is defined here to be a waveguide segment which is inserted into an otherwise continuous structural member with different properties. A general expression for the net transmission through the insert is found. It has bandpass/stop characteristics and its frequency average is somewhat greater than that normally assumed due to the coherent interaction of the waves in the insert. The particular case is then considered where the insert comprises a three-layer composite beam inserted in a thin beam which vibrates in bending. The composite beam comprises two elastic faceplates and a core filled with a tunable electro- or magneto-rheological fluid. The net transmission and the stop bands depend on the properties of the insert. Since these properties are tunable by adjusting the field to which the tunable fluid is exposed, then so too are the transmission characteristics of the insert.     

Oscillations of tunnel magnetoresistance in ferromagnet-insulator-ferromagnet structures

A model of spin-dependent electron transport in ferromagnet-insulator-ferromagnet structures that takes into account the potential relief, applied voltage, image forces, and scattering by the potential relief is developed. It is shown that tunnel magnetoresistance oscillations are caused by the nonmonotonic energy dependence of transmission coefficients and their split in the molecular field of the ferromagnet. Conditions are found under which the tunnel magnetoresistance is virtually independent of scattering by the interfaces.