Skin effect during propagation of high-power short-wavelength microwaves in a partially ionized semiconductor plasma

A study is made of the propagation of high-power electromagnetic waves in spatially inhomogeneous plasmas of thin semiconducting elements and films. The effect of surface recombination and an external magnetic field on the depth of penetration of an ionizing field into the semiconductor plasma is examined. Zh. Tekh. Fiz. 69, 135–136 (May 1999)     

Surface electromagnetic waves in thin-layer biaxial structure in a magnetic field

The conditions for the existence of surface electromagnetic waves at the planar interface between a homogeneous medium (vacuum) and a thin-layer periodic structure consisting of alternating semiconductor and dielectric layers in an external magnetic field have been investigated. This structure represents an optically biaxial crystal with the effective permittivity tensor components dependent both on the geometric parameters of the structure and on the physical characteristics (magnetic field strength, frequency, and thicknesses of the layers). It has been shown that the propagation of surface electromagnetic waves localized near the interface can occur in the thin-layer biaxial structure within specific ranges of frequencies and external magnetic field strengths.     

Intermediate regime for the diffraction of light on ultrasound in gyrotropic anisotropic crystals

An intermediate regime for the diffraction of light on ultrasound in gyrotropic anisotropic and cubic crystals in an external electric field is considered. A system of equations of the coupled waves, which describes acoustooptic diffraction in gyrotropic anisotropic crystals with consideration of the electrically induced optical anisotropy for a strong interaction between light and ultrasound, is presented. An intermediate regime for the diffraction of light on ultrasound in gyrotropic anisotropic crystals which is close to the Bragg regime for a weak acoustooptic interaction is studied. It is shown that the diffracted light is elliptically polarized and that the ellipticity and polarization azimuth of the diffracted wave depend on the anisotropy of the photoelasticity, the electrically induced anisotropy of the crystal in the external electric field, the gyrotropy, and the asymmetry of the diffraction structure. Zh. Tekh. Fiz. 67, 80–82 (September 1997)     

Dependence of the frequencies of magnetostatic waves on the magnetizing field in ferrite films

Analytical expressions are derived for the derivatives of the frequencies of magnetostatic waves with respect to the external magnetic field in anisotropic ferromagnetic films. Films having cubic anisotropy and 〈100〉, 〈110〉, and 〈111〉 surfaces are analyzed in detail. The frequency-field relations are used in an experimental determination of the temperature coefficients of the cubic anisotropy field and the saturation magnetization in an yttrium iron garnet film. Fiz. Tverd. Tela (St. Petersburg) 40, 2089–2092 (November 1998)     

Distribution of the local magnetic field of the vortex lattice near the surface of an anisotropic superconductor in oblique external magnetic fields

The distribution of the magnetic field in the unit cell of the Abrikosov vortex lattice near the surface of a uniaxial, anisotropic, type-II superconductor in an oblique external magnetic field is determined on the basis of the London model for the cases in which the symmetry axis is perpendicular and parallel to the boundary of the superconductor. The distribution of the local magnetic field is obtained as a function of the distance from the surface of the superconductor and the inclination angle of the external field. It is shown for an YBaCuO high-T _c superconductor that the investigation of the distribution function of the local magnetic field as a function of the angle of the external magnetic field relative to the symmetry axis and to the surface of the superconductor can yield important information about the anisotropic properties of the superconductor. Fiz. Tverd. Tela (St. Petersburg) 39, 1935–1939 (November 1997)     

The effect of a local field on Raman scattering in a uniaxial crystal

This paper discusses the Raman scattering of light in an anisotropic crystal in the crystal optics approximation, taking into account local fields acting on the molecules. It shows that the effect of the local field reduces to the introduction of the effective Raman polarizability tensor of the molecules, which depends both on the properties of the molecules themselves and on the characteristics of the crystal at the frequencies of the incident and scattered waves. Raman scattering cross sections are obtained in a uniaxial crystal for various types of incident waves. It is shown that, in the case of an extraordinary incident wave, the local field substantially affects how the cross section depends on the direction of incidence. Zh. éksp. Teor. Fiz. 112, 180–191 (July 1997)     

Magnetic field effects on the localization of electromagnetic waves in random 1D systems which are almost periodic

Abstract

The effects of an externally applied magnetic field on the Anderson localization of electromagnetic waves in an alternating layered system of vacuum and semiconducting slabs are studied. Specifically, a waveguide formed from perfectly conducting parallel plates which contain between them an array of vacuum and n-type semiconductor slabs is examined in the presence of an external static magnetic field applied parallel to both the plates and the slab surfaces. The widths of the slabs in the array are random but with a randomness such that the array of slabs is almost periodic, and we study only electromagnetic modes which propagate perpendicular to the slab surfaces. The localization length is obtained by studying the reflection and transmission properties of a finite array of slabs in the limit that it becomes semi-infinite. Two types of system are treated: (i) a reciprocal system which exhibits a localization length that does not depend on the sign of the applied magnetic field, and (ii) a non-reciprocal system which exhibits a localization length that depends on the sign of the applied magnetic field.     

Dispersion relation for surface-localized magnetic polaritons and magnetostatic waves in antiferromagnetic superlattice

In addition to the general dispersion equation for surface-localized magnetic polaritons and magnetostatic waves, which propagate in the system antiferromagnetic superlattice-antiferromagnet, we derive a simplified result for the long-wavelength limit λ?L (L is the period of superlattice) when the superlattice is found to behave like an anisotropic bulk medium (effective-medium approach). The dispersion curves and frequency region of the existence of the surface magnetic polaritons and magnetostatic waves are presented numerically for several values of the external magnetic field and for different antiferromagnetic materials.     

On the theory of electromagnetic surface waves in magnetized semiconductor plasma

The paper demonstrates existence of electromagnetic surface waves at the boundary separating a magnetized semiconductor plasma and a dielectric or metal. The external magnetic field is along the interface. As has been shown, slow surface waves of the helicon or Alfven type can exist only with their propagation vector directed obliquely with respect to the magnetic field. The ω-k relations have been found and ranges of existence established both in the frequency domain and that of angles between the propagation vector and the magnetic field.     

Dispersion properties of cyclotron waves in periodic semiconductor-insulator structures

The band spectrum of cyclotron waves propagating in a periodic layered semiconductor-insulator structure at an angle to an external magnetic field that is applied perpendicularly to the layers is calculated for two relationships between the characteristic frequencies of the semiconductor: ω_H>ω_P and ω_H<ω_P. The wave field distributions across the layers and over the period of the structure are analyzed. In both spectra, transmission bands arise when the conditions for dimensional resonance across the semiconductor layer are fulfilled. The graphic solution of the dispersion relation demonstrates that the cyclotron wave spectrum can be subdivided into two spectra of normal waves according to the Bloch wavenumbers of the periodic structure. The cases where the band spectra complement each other or overlap are considered.     

Electric dipole mechanism of the generation of electromagnetic radiation due to the spin transport in an InSb semiconductor

Conditions for the generation of electromagnetic radiation by spin-polarized electron transport through a junction made on the basis of an InSb semiconductor and an HgCr₂Se₄ or Co₂MnSb ferromagnetic material are investigated. It is shown that electromagnetic radiation from the junction appears only when the electron flow passing from the ferromagnet to the InSb semiconductor is polarized. The radiation intensity is found to depend on the direction of the external magnetic field with respect to the InSb crystal axes. Maximum intensity values are observed for the field directions corresponding to the highest probability of electric dipole spin transitions between Zeeman levels.     

Incommensurateness effects in a lattice Ginzburg-Landau model

This paper discusses the effect of magnetic translational symmetry on the vortex structure in superconducting crystals with a large basis in artificial Josephson media (regular lattices of superconducting clusters) prepared with opal as the base material. For external magnetic fields lower than the upper critical field, the lattice Ginzburg-Landau model reduces to the two-dimensional Frenkel’-Kontorova model which in some cases is exactly solvable, in which the crystal lattice plays the role of an “hard sublattice” while the deformable vortex lattice plays the role of a “soft sublattice.” It is shown that static shear waves in the vortex lattice are solutions to the two-dimensional sine-Gordon equation with an additional condition of incompressibility implied by flux quantization. The pinning energy is found as a function of the magnetic field, nearness to the transition line, and the crystal lattice constant. Fiz. Tverd. Tela (St. Petersburg) 39, 1158–1162 (July 1997)     

磁场中束缚极化子的有效质量

研究磁场中束缚极化子有效质量的性质,采用改进的线性组合算符和变分法讨论了磁场中强、弱耦合极化子的振动频率和有效质量与磁场B和库仑势的关系。以RbCl晶体为例进行了数值计算,结果表明:强耦合束缚磁极化子的振动频率λ和有效质量m^*随磁场B的增加而增大。弱耦合磁极化子的振动频率λ也随磁场的增加而增加,并且发现由于库仑势的存在,使得强耦合束缚磁极化子的振动频率λ和有效质量m^*有所增大。弱耦合磁极化子的有效质量仅和耦合强度α有关。     

Nonlinear spin excitations in a classical Heisenberg anisotropic helimagnet

The nonlinear spin excitations in an anisotropic helimagnet in the presence of a constant magnetic field are investigated in the classical continuum limit. The helical character is introduced into the model, in analogy with the twist in a cholesteric liquid crystal. After deriving a class of spin wave solutions for the stereographic representation of the Landau-Lifshitz equation, in-plane stationary spin configurations are obtained and their stability is analysed. When the external magnetic field is along the anisotropic axis, modulational instability is observed in the spin lattice, and when the external magnetic field is normal to the anisotropic axis, the spin configurations are unstable. The perturbed spin components show fluctuations in the tail region, while the velocity and amplitude of the soliton remain unaltered.     

Parametric excitation of spin waves in uniaxial ferrites

Parametric excitation of spin waves in uniaxial ferrites with large anisotropy is investigated theoretically. First-order processes in a sphere with arbitrary orientation of an external static magnetic field, in which case the pumping is oblique, are studied. The threshold field and the parameters of the excited spin waves are calculated numerically for two ferrites — easy-axis and easy-plane. Zh. Tekh. Fiz. 68, 65–71 (May 1998)     

Ion surface cyclotron waves at plasma-metal interfaces

The dispersion properties of slow electromagnetic surface waves propagating across a constant external magnetic field and along a plane plasma-metal interface at harmonics of the ion cyclotron frequency are studied. The motion of the plasma particles is described by a Vlasov-Boltzmann kinetic equation. The effects of the plasma size, the dielectric permittivity of the transition region between the plasma and metal, and the magnitude of the constant external magnetic field on the dispersion characteristics of ion surface cyclotron waves are studied. Zh. Tekh. Fiz. 69, 83–89 (October 1999)     

Phase transition in antiferromagnets with anisotropic exchange interactions and uniaxial anisotropy

Abstract

Following the Bogoliubov variational principle, the equilibrium and stability equations of the free energy for the two sublattice antiferromagnetic system with inter- and intrasublattice exchange interactions and with an external magnetic field are investigated. For the Ising spin system with uniaxial anisotropy, the phase diagrams have been calculated for various values of anisotropy constant d and the ratio of intra- to intersublattice interaction constants γ. It is shown that first-order, as well as second-order transitions, occur for γ > 0, whereas only a second-order transition occurs for γ ≦ 0, irrespective of the sign of d. Furthermore, similar calculations are extended for the anisotropic Heisenberg spin system and quite interesting phase diagrams have been obtained. Next, the effects of the anisotropic exchange interactions on the magnetic ordered states and the magnetizations of the singlet ground state system of spin one and with a uniaxial anisotropy term are investigated in the vicinity of the level crossing field H ? D/gμ _B . A field-induced ordered state without the transverse component of magnetization is shown to appear in a certain range of magnetic field as the spin dimensionality decreases. It has also turned out that the phase transition between this ordered state and the canted antiferromagnetic state ordinarily found for the isotropic singlet ground state system is of first order. Lastly, the stable spin configurations at a temperature of absolute zero for a two-sublattice uniaxial antiferromagnet under an external magnetic field of arbitrary direction are studied. In particular, the effects of a single ionic anisotropy D-term and anisotropy in the exchange interactions on the magnetic phases are investigated. The antiferromagnetic state has turned out to appear only for the external magnetic field along the easy axis of sublattice magnetization, and makes a first-order phase transition to the canted-spin state or the ferromagnetic state. For other field directions, no antiferromagnetic state appears and only a second-order phase transition between the canted-spin and the ferromagnetic states occurs. The critical field as a function of external field direction has been calculated for several D-values.     

Potential surface waves at the boundary of a metal with a magnetoactive plasma at finite pressure

The propagation of surface-type potential waves along the interfacial boundary of a plasma with an ideally conducting metal in an external magnetic field perpendicular to the boundary is examined. It is shown that a necessary condition for the existence of these waves in the system is a finite gas kinetic pressure. Dispersion relations for these waves and expressions for the penetration depth of the wave fields into the plasma are obtained, and they are studied numerically for various plasma parameters. The frequency region for propagation of these waves is found. It is also shown that in a nonzero external magnetic field a system of this kind has a range of frequencies in which the wave is a generalized surface wave. Zh. Tekh. Fiz. 69, 30–33 (November 1999)     

Electromagnetic waves reflection,transmission and absorption by graphene–magnetic semiconductor–graphene sandwich-structure in magnetic field: Faraday geometry

Electrodynamic properties of the graphene–magnetic semiconductor–graphene sandwich-structure have been investigated theoretically with taking into account the dissipation processes. Influence of graphene layers on electromagnetic waves propagation in graphene–semi-infinte magnetic semiconductor and graphene–magnetic semiconductor–graphene sandwich-structure has been analyzed. Frequency and field dependences of the reflectance, transmittance and absorbtance of electromagnetic waves by such structure have been calculated. The size effects associated with the thickness of the structure have been analyzed. The possibility of efficient control of electrodynamic properties of graphene–magnetic semiconductor–graphene sandwich-structure by an external magnetic field has been shown.     

Pressure anisotropy effects on nonlinear electrostatic excitations in magnetized electron-positron-ion plasmas

The propagation of linear and nonlinear electrostatic waves is investigated in a magnetized anisotropic electron-positron-ion (e-p-i) plasma with superthermal electrons and positrons. A two-dimensional plasma geometry is assumed. The ions are assumed to be warm and anisotropic due to an external magnetic field. The anisotropic ion pressure is defined using the double adiabatic Chew-Golberger-Low (CGL) theory. In the linear regime, two normal modes are predicted, whose characteristics are investigated parametrically, focusing on the effect of superthermality of electrons and positrons, ion pressure anisotropy, positron concentration and magnetic field strength. A Zakharov-Kuznetsov (ZK) type equation is derived for the electrostatic potential (disturbance) via a reductive perturbation method. The parametric role of superthermality, positron content, ion pressure anisotropy and magnetic field strength on the characteristics of solitary wave structures is investigated. Following Allen and Rowlands [J. Plasma Phys. 53, 63 (1995)], we have shown that the pulse soliton solution of the ZK equation is unstable to oblique perturbations, and have analytically traced the dependence of the instability growth rate on superthermality and ion pressure anisotropy.