Force,momentum and topology of a moving magnetic domain

The following general relations involving force, momentum and topological winding number of a translating magnetic domain are derived from the Landau—Lifshifz equation in a context appropriate to bubbles: The gyrotropic force tending to deflect a steadily moving domain is proportional to a mean winding number linear in Bloch-point coordinates. The time derivative of the canonical momentum for a domain of integer winding number is equal to the total force, which must include gyrotropic and dissipative terms. A new contour integral expresses the momentum in the limit of vanishing wall thickness. Approximate equations of quasi-steady domain motion are cast into a form resembling Hamiltion's equations for a particle. Discussion centers on applications to gradientless propagation, bubble saturation velocity, and the Blochline model of inertial effects, and on general limitations of the theory.     

Research on spectral domain immittance approach

In this paper, we have obtained the equations of electrodynamics for a gyrotropic medium using the Maxwell's equations. Through the Fourier Transforms (FT), the admittances of TM and TE modes in the electrically gyrotropic substrate and the magnetically gyrotropic substrate are given. Then we can use the spectral domain immittance approach to analyse the finline structures with a gyrotropic medium. The propating characteristics of the dominant mode in magnetized-ferrite-loaded double-layered finlines are studied, numerical results are presented which could be used in designing a finline displacement isolator.     

A note on debye potentials for spherically gyrotropic media

The Debye potentials are generalized to the case of electromagnetic fields in spherically gyrotropic media. A medium is called spherically gyrotropic if it is locally gyrotropic with the distinguished axis having a radial direction determined by a central point. Expressions for electromagnetic fields in terms of the generalized potentials are presented and the system of differential equations for the potentials is derived. The results are summarized in the form of a theorem. Basic facts about the Debye potentials in isotropic media are recalled.     

Electromagnetic waves in isotropic and gyrotropic media

Maxwell’s equations are considered for waves in transparent inhomogeneous anisotropic and gyrotropic media with time dispersion. A uniaxial inhomogeneous crystal is taken for an anisotropic medium and an isotropic heterogeneous medium in a constant electric field for a gyrotropic medium. The solutions for flat-layered and cylindrical media are presented in terms of Hertz potentials. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 82–86, March, 2008.     

Theoretical and experimental analysis of waveguide containing transversally magnetized strongly gyrotropic dissipative semiconductor layer

In this paper we present the Maxwell equations' solution method enabling to electrodynamically rigorously compute opened and screened waveguides containing transversally magnetized gyrotropic material. There have been theoretically and experimentally analysed a rectangular metal waveguide having along the narrow wall a gyrotropic dissipative layer ofn-InSb. There has been found the resonant waveguide losses' dependence on the magnitude of the biasing magnetic field. The correspondence of computed and experimental data is fairly good.     

A note on scalar Hertz potentials for gyrotropic media

The scalar Hertz potentials are generalized to the case of electromagnetic fields in gyrotropic media. Expressions for electromagnetic fields in terms of two potentials are presented and the system of differential equations for the potentials is derived. The result are summarized in the form of a theorem. The case of a stratified gyrotropic medium with parameters varying along the distinguished axis has been considered also. Scalar “superpotentials” satisfying a fourth-order partial differential equation are introduced. They allow expressions for electromagnetic fields to be found in terms of one scalar superpotential only. Basic results on scalar Hertz potentials in isotropic media are recalled. The research reported in this paper was carried out during S. Przeździecki's leave of absence from the Institute of Fundamental Technological Research, Polish Academy of Sciences, Świętokryzyska 21, PL-00-049 Warszawa, Poland.     

Interaction of the near field with a gyrotropic sectorial structure

A matrix method is proposed to obtain the characteristic equations for quantities governing the degree of the field singularity on the edge of sectorial gyrotropic structures. Exact analytic solutions are analyzed for giving mixed boundary conditions on the outer faces of a wedgelike domain.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 64–69, October, 1987.     

Fast domain wall dynamics in amorphous glass-coated microwires

Here we report on the domain wall dynamics in amorphous glass-coated FeCuNbSiB microwires measured in the temperature range from 77 up to 400 K. At low temperatures below 200 K, the domain wall velocity is proportional to the applied magnetic field. At temperatures above 200 K, two regions have been found: one with low domain wall mobility at low fields and another one with high domain wall mobility at high fields. The different regions of the domain wall dynamics are treated in terms of the change of the domain wall configuration from transversal to vortex one. Moreover, non-linear regime is shown at low fields at the temperature 373 K as a result of the domain wall interaction with the local defects.     

Efficiency of shear surface wave transformation by the motion of the confining domain wall

The transformation of a shear surface magnetoelastic wave by the motion of the 180° confining domain wall in a ferromagnet is considered. Changes in the wave spectrum due to the motion of the wall are correlated with the variations of the energies of the elastic and magnetic subsystems. The efficiency of surface wave transformation by the domain wall motion is estimated in terms of energy. The frequency dependences of the mean energy density of the wave are found. It is shown that the energy density grows with wall velocity.     

Photocurrent in gyrotropic Weyl semimetals

Photocurrents in the Weyl semimetals belonging to the gyrotropic symmetry classes have been theoretically studied. It has been shown that the circular photocurrent transverse to the direction of light incidence appears in weakly gyrotropic crystals with the C _nv (n = 3, 4, 6) symmetry only when spin-dependent terms both linear and quadratic or cubic in the quasimomentum, as well as a spin-independent term resulting in the tilt of the cone dispersion, are taken into account in the electron effective Hamiltonian. A polarization-independent magnetic-field-induced photocurrent, which is allowed only in gyrotropic systems, has been predicted. For crystals with the C_2v symmetry, a microscopic mechanism of the photocurrent in a quantized magnetic field, which is generated in direct optical transitions between the ground and first excited magnetic subbands, has been considered. It has been shown that this photocurrent becomes nonzero in the presence of the anisotropic tilt of dispersion cones.     

Photonic spectrum of magnetically gyrotropic planar layered structures

The photonic-crystal properties of a magnetically gyrotropic medium having a periodic planar layered domain structure are studied. The magnetic gyrotropy of the medium in the optical range is revealed in the permittivity tensor. The dispersion relation of the TM wave controlled by an external magnetic field is obtained and analyzed both in the fine-layered medium approximation and in the case where the ω(k) spectrum contains allowed bands and bandgaps in the wavenumber range under study. The effect of the symmetry of the structure on its spectrum is studied.     

Time-reversal symmetry-breaking in two-band superconductors

Competition between an interband Josephson interaction and a biquadratic interband interaction can break time-reversal symmetry when the interband interactions are very weak compared with the intraband interaction. We demonstrate this using the phenomenological Ginzburg–Landau free energy, taking into account terms essential for this phenomenon. This time-reversal symmetry-breaking state peels away a sheet of an interband phase difference soliton wall. This sheet is the domain wall between two different chiral states. The peeling reduces the formation energy of the domain wall. The domain wall can simultaneously erase the Meissner effect and the specific heat jump when the entropy invokes many domain walls, and its life time is prolonged by a pinning owing to an inhomogeneity such as surface roughness.     

Anomalies in second order elastic constants and gyrotropic constants of triglycine sulphate near phase transition

The anomalies in second order elastic constants and gyrotropic constants have been considered for the phase transition of triglycine sulphate. Expressions have been derived for the equilibrium values of order parameter and strain variables in both phases. Using Landau-Khalatnikov equation the fluctuation in order parameter is expressed in terms of fluctuations in strain variables. Substitution of these in free energy gives anomalies arising from Landau and coupling energies in second order elastic constants. The real part of the anomalies decreases steeply across the transition temperature and thereafter flatly tend to ferroelectric values. The anomalies in the components of the gyrotropic tensor have been derived and their temperature variation discussed.     

Optimal conditions of the acousto-optic interaction in crystals with gyrotropy

The conditions of the acousto-optic interaction in the crystals with gyrotropy are considered. The optimal length of the acousto-optic interaction and the diffraction efficiency in the gyrotropic direction are calculated. The diffraction efficiency is determined by the coupled wave method which allows calculation of the field interaction in the gyrotropic crystal [1]. It is theoretically shown and experimentally confirmed that the diffraction efficiency in the gyrotropic direction is independent of incident light polarization, when the polarization plane rotates by 45° along the interaction length.     

Coercivity of precipitation hardened cobalt rare earth 17:2 permanent magnets

The influence of the microstructure on the coercivity has been investigated by means of transmission electron microscopy. It is shown that a thin coherent (CoCu)₅Sm-cell boumdary phase, separating cells of 17:2-crystal structure, acts as a pinning centre for magnetic domain walls. The attractive interaction force is interpreted in terms of a micromagnetic theory for domain wall pinning. The coercive force is determined by the domain wall energy gradient and by the magnetoelastic coupling energy between domain wall stresses and lattice deformation strains. The calculated coercive force due to the lattice mismatch, originated by the cellular coherent precipitation structure, is comparable to the experimentally obtained values.     

The influence of magnetic impurities in the vortex core dynamics in magnetic nano-disks

In this work we have used spin dynamics simulations to study the gyrotropic frequency behavior in nano-disks of Permalloy with magnetic impurities. We consider the effect of attractive impurity and repulsive impurity placed near the vortex core gyrotropic trajectory. We observed that the gyrotropic frequency is affected by the presence of impurity. The gyrotropic frequency shift depends on the relative position between the impurity and the vortex core gyrotropic trajectory and if impurity is attractive or repulsive. Our results agree with the analytical model and with experimental behavior for the gyrotropic frequency shown in the literature.     

Generalization of a scattering theorem for plane-stratified gyrotropic media

A previously derived eigenmode scattering theorem for plane-stratified gyrotropic media established that the scattering matricesS andS′, defined, respectively, in terms of a given and a conjugate set of eigenmode amplitudes, are mutually transposed, i.e. , the theorem being valid specifically for the incoming and outgoing eigenmodes ofgyrotropic bounding media. In this paper the theorem is extended to include linearly and circularly polarized base-modes in theisotropic media which may bound the multilayered, gyrotropic structure. Transformation of the eigenmode scattering matrix leads to a generalization of the scattering theorem to include base modes which are not necessarily eigenmodes of the medium. In the important special case in which the ambient magnetic field is parallel to the plane of the stratification, the scattering matrix is shown to have a special symmetry whose form depends on the base modes chosen (eigenmodes, linear modes or circular modes).     

Readjustment of ferroelectric domain structure under the action of polarized light

Change in the 180 domain structure of a gyrotropic ferroelectric produced by circularly polarized light is considered. Due to circular dichroism the photoinduced polarization differs in adjacent domains with different spontaneous polarization directions, as a result of which the domain dimensions change, the period of the structure is decreased, and the crystal as a whole becomes photopolarized.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 17–20, June, 1984.     

On the conductivity of a magnetoactive turbulent plasma

The problem of determining the effective conductivity tensor of a magnetoactive turbulent plasma is considered in the approximation of isolated particles. Additional gyrotropic terms are shown to appear in the conductivity tensor in the presence of mean, nonzero magnetic helicity. The dispersion of propagating electromagnetic waves changes, additional modes and additional rotation of the polarization plane appear, and the waves can be amplified. The properties acquired by a plasma with helicity are similar to those observed in chiral and bianisotropic electrodynamic media.