Enhanced reactivity of domain walls in with sodium

A possible new high temperature superconducting phase was recently reported in WO ₃ :Na. We have examined the reaction between sodium vapour and WO ₃ , and compared the phases formed by the reaction to previously known WO ₃ phases. By using light microscopy and electron microprobe analysis, domain walls from the interior of the crystal are shown to have a much higher Na content than bulk material after reaction with Na vapour. This indicates preferential transport along the domain walls. The result is very similar to a reduction reaction of WO ₃ crystals in which twin walls lose oxygen preferentially. Oxygen deficient twin walls are superconducting with . Received 3 September 1999 and Received in final form 15 December 1999     

Effect of the inner structure of domain walls on the stability of an isolated stripe domain in a pulsed field

This paper studies the effect of the inner structure of domain walls on the stability of an isolated stripe domain localized in a thin ferromagnetic film against a pulse of magnetic field applied perpendicularly to the film surface. It is found that the value of the critical amplitude of the pulsed signal strongly depends on the value of the magnetizing field in which the system was initially placed. It is also established that the difference on stability of domains with unipolar and bipolar walls in pulsed fields diminishes as the amplitude of the magnetizing field decreases. Finally, the dependence of the region of stability in a pulse field on the parameters of the system is determined for various domain types. Zh. éksp. Teor. Fiz. 116, 1694–1705 (November 1999)     

A general finite difference time domain method for hybrid dispersive media model

The shift operator finite difference time domain (SO-FDTD) method is developed to deal with a hybrid dispersive media model. First, we prove that the complex permittivity of the hybrid dispersive media model can be described by a rational polynomial fraction with respect to jω. Then, the relation between electric displacement D and electric field strength E is derived in the time domain by introducing z_t as a shift operator. The constitutive relation in the discretized time domain and the recursive formulation of D and E available for FDTD computation are obtained. Finally, the reflection of the hybrid dispersive slab is computed. The computed results are in good agreement with that obtained by analytic method. This illustrates the generalization and the feasibility of the presented scheme.     

Drinfeld twist and the domain wall partition function of the eight-vertex model

With the help of the F-basis provided by the Drinfeld twist or factorising F-matrix for the spatial optical soliton model associated with the eight-vertex model, we calculate the partition function for the eight-vertex model on an N × N square lattice with domain wall boundary condition.     

Domain kinetics in the formation of a periodic domain structure in lithium niobate

The evolution of the domain structure in LiNbO₃ with polarization switching in an electric field is investigated experimentally. Special attention is given to the formation processes of a regular domain applicable to nonlinear optical devices. A new method based on the spontaneous backswitching effect is proposed for creating a regular structure with a period of 2.6 μm in LiNbO₃ with a thickness of 0.5 mm. Fiz. Tverd. Tela (St. Petersburg) 41, 1831–1837 (October 1999)     

Dynamics of domain walls in ultrathin magnetic films

The domain walls in ultrathin ferromagnetic films with uniaxial magnetic anisotropy are investigated theoretically. It is shown that taking account of the magnetodipole and magnetoelastic interactions leads to the appearance of an effective anisotropy with respect to the direction of the normal to the plane of the wall. The existence of a new type of domain walls—“corner” walls, at which the magnetization vector is rotated in the plane making a certain angle, which depends on the film parameters, with the plane of the domain wall and the static and dynamic properties of these walls are investigated. The dependence of the limiting velocity of the domain walls on the film thickness is found. Zh. éksp. Teor. Fiz. 112, 1476–1489 (October 1997)     

Ferroid properties and domain structure of barium titanate

Distinctive features of domain formation in ferroelectric crystals are discussed theoretically for the example of ferroelectric BaTiO₃, taking into account ferroid properties of higher order. Inclusion of ferroid properties makes it possible to refine the details of the domain formation, and in particular to explain the possible existence of charged domain walls in ferroelectric crystals. Fiz. Tverd. Tela (St. Petersburg) 39, 1634–1635 (September 1997)     

Dynamics of the intermediate state and domain walls in an external oscillating magnetic field

We study the dynamics of 90-degree domain walls in the intermediate state of antiferromagnets, the state being realized in a first-order spin-flop transition in an external magnetic field. We show that an additional oscillating external magnetic field leads to a drift in the domain walls and find the dependence of the drift velocity on the amplitude, frequency, and polarization of the oscillating field. Finally, we discuss the possibility of the domain structure drifting as a whole. Zh. éksp. Teor. Fiz. 112, 1374–1385 (October 1997)     

On the characteristic changes in the domain structure and conductivity of CsDSO4 crystals near the superionic phase transition

The appearance of a new domain structure against the background of the old domain structure is observed in CsDSO₄ crystals at 3 °C away from the superionic phase transition. It is established that the appearance of the new domain structure is accompanied by a gradual increase in the conductivity by 1.5–2 orders of magnitude, and then the conductivity increases abruptly by another two orders of magnitude at the temperature of the superionic phase transition. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 11, 871–875 (10 June 1996)     

Optical vortices in the scattering field of magnetic domain holograms

Experimental investigations and theoretical-model analyses have been made of the magnetooptic diffraction of light at ferrite garnet magnetic films with a banded domain structure which includes isolated magnetic grating defects in the form of “forks” and “breaks.” An analysis of the magnetic grating structure and the light diffraction field shows that in terms of its action on laser radiation, a banded domain grating is similar to a computer-synthesized phase hologram of an isolated pure screw-wavefront dislocation. It is shown that as a result of magnetooptic diffraction at a magnetic hologram, optical vortices may be reconstructed with a helicoidal wavefront carrying the topological charge l=±1,±2. Zh. Tekh. Fiz. 68, 54–58 (December 1998)     

一种处理色散介质问题的通用时域有限差分方法

色散介质的介电系数是频率的函数,使本构关系在时域成为卷积关系.这就给用时域有限差分方法计算色散介质中波的散射和传播带来了困难.现有算法往往要针对不同色散介质模型推导相应的递推公式,算法的通用性较差.本文完善和发展了移位算子-时域有限差分方法,使之成为一种处理色散介质电磁问题的通用方法.首先,证明了常见的三种色散介质模型(德拜模型、洛伦兹模型和德鲁模型)的介电系数均可以写成适于移位算子法计算的有理分式函数形式.然后,用/t代替jω,过渡到时域,再引入时域移位算子z_t代替时间微分算子来处理有理分式函数形式的介电系数,给出离散时域本构关系的表示式,进而导出时域有限差分方法当中电位移矢量和电场强度之间的关系.最后,计算了几种色散介质的电磁散射,数值结果表明了本文方法和程序的通用性和正确有效性. 关键词： 时域有限差分方法 色散介质 移位算子     

Polymorphism of biperiodic stripe domain structures

Magnetic-field-induced polymorphism of biperiodic stripe domain structures of films with a positive anisotropy constant and easy axis parallel to the normal to the surface is studied. A symmetry classification of the observed types of domain structures is performed, and the phase diagram of the films in the (H _⊥, H _∥) plane, where H _⊥ and H _∥ are, respectively, the components of the magnetic field vector perpendicular and parallel to the normal to the surface, is determined. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 9, 701–706 (10 May 1998)     

Dynamics of interphase domain walls during a Morin-type phase transition

The dynamics of 90-degree interphase domain walls during a first-order Morin-type spin-reorientation phase transition is studied theoretically. It is shown that an oscillatory motion of the walls with an amplitude that depends linearly on the field amplitude, as well as a drift motion of the wall at a velocity proportional to the square of the field amplitude, are driven by an external oscillating magnetic field. Drift of the entire domain structure as a whole is predicted to be possible. Fiz. Tverd. Tela (St. Petersburg) 41, 274–282 (February 1999)     

Phase transitions in a domain wall of the four-sublattice antiferromagnet La2CuO4 in a magnetic field

The effect of an external magnetic field on the characteristics of domain walls was studied in a four-sublattice antiferromagnet La₂CuO₄. It was shown that a transition of domain-wall structure from one type into other types is possible for certain values of the fields. The critical fields of the transition were determined. The phase diagram of the stability of different types of domain walls was constructed. Fiz. Tverd. Tela (St. Petersburg) 40, 1510–1513 (August 1998)     

Propagation of magnetostatic waves in unsaturated ferrite films with a strip domain structure

The propagation of surface and volume magnetostatic waves in unsaturated films of yttrium iron garnet is studied experimentally for the case when the wavelength greatly exceeds the domain width, while the domain width is comparable to the film thickness. The characteristics of these waves are examined for symmetric linear, asymmetric linear, and symmetric zigzag strip domain structures in the films. These characteristics cannot be explained by a theory based on averaging the magnetization over all the domains. Zh. éksp. Teor. Fiz. 111, 1016–1031 (March 1997)     

Macroscopic quantum resonance tunneling of domain walls

Results are presented of a theoretical investigation of the tunneling of magnetic domain walls, taking account of the interaction of the walls with the thermal system of the crystal. It is shown that thermal stimulation increases considerably the transmittance of the potential barriers during propagation of walls through a crystal. Fiz. Tverd. Tela (St. Petersburg) 40, 1855–1860 (October 1998)     

Suppression of the domain structure in uniaxial ferromagnetic films with a superconducting coating

Specific models of domain walls are used to investigate conditions for the single-domain state and quasi-single-domain states in structures with magnetic materials having a quality factor higher than one. It is shown that the critical thickness of the magnetic film in a tangentially magnetized system decreases monotonically as the magnetizing field increases from zero to the transition from the collinear to the homogeneous angular phase and then increases monotonically with increasing external field. In a thin isolated magnetic film, the size of the domains increases exponentially with decreasing thickness. This dependence is logarithmic near the transition to the single-domain state for a film coated on two sides and obeys a power law for a film coated on one side. The establishment of a single-domain state and characteristic features in the asymptotic behavior of the domain structure in magnetic films with and without coatings can be attributed to differences in the asymptotic behavior of the field of a single domain wall. Fiz. Tverd. Tela (St. Petersburg) 40, 1068–1074 (June 1998)     

Influence of the domain structure in a magnetizing field on the high-frequency susceptibility of a ferromagnet

The high-frequency properties of a biaxial domain-containing bulk ferromagnet in an external magnetic field with a modulated amplitude are investigated on the basis of the Landau-Lifshitz equations. The components of the frequency-dependent magnetic susceptibility tensor and the dependence of the resonant frequency of the uniform pulsation modes of a stripe domain on the amplitude of the external magnetic field are determined. Fiz. Tverd. Tela (St. Petersburg) 39, 671–675 (April 1997)     

Chaotic dynamics of interacting domain walls in uniaxial ferromagnetic films

The nonlinear dynamics of a periodic system of interacting domain walls in a thin ferromagnetic uniaxial film with transverse anisotropy is examined. The interaction between the domain walls takes place through the magnetostatic demagnifying fields of the domains. The equations of motion derived for such a system of walls are solved numerically by a 4–5th-order Runge-Kutta scheme, while the uniformity of the distributions of the phase trajectory, the form of the Poincaré cross section, and the spectral density of the vibrations serve as indicators of the type of oscillations. All the known types of oscillations are observed in a computer simulation of this nonlinear system: periodic, quasiperiodic, and chaotic. The computational results have a universal character for uniaxial, highly-anisotropic ferromagnetic films having a strip domain structure, since the results can be easily scaled for materials with different magnetic characteristics. Fiz. Tverd. Tela (St. Petersburg) 39, 2036–2039 (November 1997)     

Tunneling of magnetic domain walls in the quasirelativistic limit

An additional mechanism which increases the probability of tunneling of magnetic domain walls through defects of a crystal is discussed. In contrast to the thermally stimulated tunneling mechanisms described previously (c.f. Refs. 7 and 8), which arise when the wall acquires additional energy from the thermal system of the crystal, the latter mechanism is produced by the change in the structure of the walls themselves at high energies, which changes the character of their interaction with defects. The results of analytic and numerical analyses of this effect are reported. A discussion and an interpretation of existing experimental results. Fiz. Tverd. Tela (St. Petersburg) 41, 1264–1266 (July 1999)