Reflection and refraction of bulk acoustic waves in piezoelectrics under uniaxial stress

Basic equations that describe the conditions of reflection and refraction of bulk acoustic waves at the boundary between acentric crystalline media under uniaxial stress are presented. The effect of uniaxial stress on the anisotropy of reflection and refraction of bulk acoustic waves is numerically analyzed for boundaries of the crystal-vacuum, piezoelectric crystal-piezoelectric crystal, and piezoelectric crystal-elastic isotropic medium types.     

Reflection and refraction by interfaces of uniaxial crystals

We present a simple and complete approach to determining the directions and amplitudes of rays propagating through arbitrary systems of homogeneous and/or uniaxial materials. In the process we extend the work of Gu and Yen to full generality.     

Reflection and refraction of waves in oscillatory media

This paper uses the two-dimensional Brusselator model to study reflection and refraction of chemical waves. It presents some boundary conditions of chemical waves, with which occurence of observed phenomena at interface as refraction and reflection of chemical waves can be interpreted. Moreover, the angle of reflection may be calculated by using the boundary conditions. It finds that reflection and refraction of chemical waves can occur simultaneously even if plane wave goes from a medium with higher speed to a medium with lower speed, provided the incident angle is larger than the critical angle.     

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)     

Parametric excitation of spin waves in strongly anisotropic uniaxial ferrites

The thresholds of parametric spin-wave excitation are measured in a Ba₂Zn₂Fe₁₂O₂₂ easy-plane ferrite at a pumping frequency of 36 GHz in the temperature range from 5 to 350 K at different angles between the external dc magnetic field and the anisotropy axis, where the pumping is, in a general case, oblique. The dependences of the spin-wave damping parameter on wave number, temperature, and the angle between the spin-wave propagation direction and the anisotropy axis have been found. The results of measuring the ferromagnetic resonance parameters in this ferrite and an easy-axis Ba(Fe_0.95Sc_0.05)₁₂O₁₉ ferrite are presented. Conclusions on the relaxation processes in strongly anisotropic hexagonal ferrites are made. Fiz. Tverd. Tela (St. Petersburg) 41, 1652–1659 (September 1999)     

Reflection and refraction of acoustic waves from the insulator-magnetoacoustic material interface

The reflection and refraction of longitudinal and transverse acoustic waves by the plane interface between an insulator and an easy-plane antiferromagnet undergoing a magnetic-field-induced orientational phase transition are analyzed. The angles of refraction, as well as all four coefficients of wave conversion, can be effectively controlled by varying the field. Conditions for the appearance of the critical angles of internal reflection and the effect of the magnetic field on these angles are considered. A glancing wave radiated into the material is shown to be a possibility near the phase transition.     

Reflection and refraction of electromagnetic pulses at the boundary between vacuum and uniaxial crystal

Scientific-Research Institute of Radiophysics. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 31, No. 5, pp. 583–590, May, 1988.     

Magnetic properties and spin waves of bilayer magnets in a uniform field

The two-layer square lattice quantum antiferromagnet with spins 12 shows a zero-field magnetic order-disorder transition at a critical ratio of the inter-plane to intra-plane couplings. Adding a uniform magnetic field tunes the system to canted antiferromagnetism and eventually to a fully polarized state; similar behavior occurs for ferromagnetic intra-plane coupling. Based on a bond operator spin representation, we propose an approximate ground state wavefunction which consistently covers all phases by means of a unitary transformation. The excitations can be efficiently described as independent bosons; in the antiferromagnetic phase these reduce to the well-known spin waves, whereas they describe gapped spin-1 excitations in the singlet phase. We compute the spectra of these excitations as well as the magnetizations throughout the whole phase diagram. Received 23 April 2001     

Reflection and transmission of plane electromagnetic waves in uniaxial bianisotropic materials

Electromagnetic waves in the most general linear reciprocal uniaxial media are considered. The theory is appropriate for novel reciprocal microwave materials which have properties of chiral composites and omega structures (or both) and can be modeled by uniaxial bianisotropic constitutive relations. Field coupling terms in the media equations are assumed to be the most general uniaxial dyadics with symmetric and antisymmetric components. Plane eigenwaves in unbounded media are studied and the theory of reflection and transmission in plane layers is constructed.     

量子自旋波本征值及易轴型各向异性对其的影响

本文考虑体单轴各向异性利用界面重参数化方法从理论上严格推导了两层异质铁磁质中量子自旋波的本征值,并模拟计算了简立方晶格结构 (100) 第一布里渊区的能带结构,特别研究了易轴型体单轴各向异性对本征值的影响.结果发现在这样的体系中存在体模、禁闭模和界面模;各种本征模与体交换作用、界面交换作用、晶格自旋、原子层数有关,而且各向异性直接影响各种本征模的存在条件. 关键词： 铁磁薄膜 自旋波 各向异性     

Exchange interactions,spin waves,and transition temperatures in itinerant magnets

This contribution reviews an ab initio two-step procedure to determine exchange interactions, spin-wave spectra, and thermodynamic properties of itinerant magnets. In the first step, the self-consistent electronic structure of a system is calculated for a collinear spin structure at zero temperature. In the second step, parameters of an effective classical Heisenberg Hamiltonian are determined using the magnetic force theorem and the one-electron Green functions. The Heisenberg Hamiltonian and methods of statistical physics are employed in subsequent evaluation of magnon dispersion laws, spin-wave stiffness constants, and Curie/Néel temperatures. The applicability of the developed scheme is illustrated by selected properties of various systems such as transition and rare-earth metals, disordered alloys including diluted magnetic semiconductors, ultrathin films, and surfaces. A comparison to other ab initio approaches is presented as well.     

Angle step selection for geometrical-optics approximation in light scattering

On the basis of the Shannon sampling theorem, we present a relationship between the maximal scattering angle step and the radius of particles in the calculation of light scattering intensity distribution. For the first rainbow intensity application, the relationship between the maximal scattering angle step and radius of particles is derived from that between the ripple frequency and radius and refractive index of particles using this method. For the geometrical-optics approximation, the incident angle is used to calculate the scattering intensity distribution. To get the highest speed, the maximal incident angle step is necessary. The relationship between the maximal step of incident angle and radius of particles is deduced from the maximal scattering angle step equation. As indicated by our result, the maximal step of the incident angle is not a constant and it varies with incident angle.     

The energy bands of quantized spin waves and the uniaxial anisotropy in a biferromagnetic system

The eigenproblems of quantized spin waves in a (100) ferromagnetic bilayer system have been investigated theoretically using the interface rescaling approach. The energy-band structure of the system has been obtained and the effect of the uniaxial bulk anisotropy field of easy-axis type on the energy bands are explored thoroughly. It is found that all kinds of eigenmodes of the spin waves in the biferromagnetic system are determined by the bulk exchange coupling constant, the interface exchange coupling constant, the spin of lattice, the number of atomic layers and the uniaxial bulk anisotropy. Especially, we explore the effect of the uniaxial bulk anisotropy field of easy-axis type on the energy bands of first Brillouin zone and the existence condition of all kinds of the eigenmodes.     

Reflection and refraction of surface acoustic waves by a periodic domain structure

Reflection and refraction of surface acoustic waves by a periodic domain structure formed in lithium niobate is studied. A second harmonic generation is observed. A mechanism underlying the linear and nonlinear interactions of acoustic waves with a periodic domain structure is proposed.     

Reflection and transmission of electromagnetic plane waves from an uniaxial chiro-omega slab

Chiro-omega medium is a combination of the reciprocal chiral and omega media, and can be obtained by mixing helical and — shaped wire elements in the host medium. In this article the most general uniaxial chiro-omega medium is studied. The solutions for the dispersion equations and corresponding eigenwaves are derived. Transmission and reflection properties of a chiro-omega slab at a normal incidence are studied, and the polarization, direction of the polarization ellipse, and relative powers of transmitted and reflected waves are given. The results are applied to find suitable parameters for designing a polarization transformer. These results are compared with those obtained in earlier studies on wave propagation in a free uniaxial chiral space, where the effect of the boundaries of a proposed polarization transforming device have been neglected.     

单轴晶体中负折射现象的演示

用惠更斯作图法定性地说明了单轴晶体中负折射现象产生的基本原理,演示了YVO4晶体中发生的负折射现象.该实验有助于学生全面认识折射现象.     

Reflection of spin and spin-elastic waves at the interface of a ferromagnetic half-space

This paper considers the reflection of pure spin and spin-elastic (or magneto-elastic) waves at the interface of a ferromagnetic half-space and a vacuum. For pure spin waves two cases are considered, with exchange effects, and without. It is shown that when exchange effects are taken into account, volume spin waves in the ferromagnetic half space incident at the boundary with the vacuum generate a reflected volume spin wave, and an accompanying compound surface wave propagating along the boundary and consisting of two partial inhomogeneous spin waves in the ferromagnetic half-space and a partial magneto-static inhomogeneous surface wave in the vacuum. When exchange effects are neglected the incident wave generates only a reflected volume wave in the ferromagnetic half-space.

Reflection and transmission of spin-elastic (or magneto-elastic) waves has been considered only in the case of the absence of exchange effects. An incident volume wave generates a volume spin-elastic reflected wave and one inhomogeneous magneto-static accompanying surface wave.

Excitations of the magnetic field are not transmitted into the vacuum in both cases when the exchange effect is neglected. In all cases the reflection of a spin wave has the character of a full internal reflection.