Scattering of Wave Packets on the Surface of Topological Insulators in the Presence of Potential Barriers with Magnetization

The nonstationary Schrödinger equation is solved numerically by the Cayley method for wave packets that are formed from surface states on the surface of topological insulators and are scattered by a potential barrier, including a barrier with magnetization. The transmission coefficient and spin density distributions are calculated. Expressions are found for the static transmission coefficient through a barrier with the use of the plane-wave approximation and its generalization for wave packets. It is shown that the two-dimensional nature of wave packets leads to noticeable differences in the behavior of the transmission coefficient compared to that in the plane-wave scattering problem. For instance, two-dimensional packets exhibit a significant suppression of Klein tunneling in some energy regions. The results obtained show that the tunneling and spin density of localized wave-packet-type electronic states in structures based on topological insulators can be affected through potential barriers.     

Reflection and transmission of light by a ferromagnetic structure with a noncollinear orientation of the magnetization of layers

The transmission and reflection of light by a ferromagnetic structure with a noncollinear orientation of the magnetization vectors of layers lying in the plane of the film is considered. The characteristic matrix of the structure that relates the wave amplitudes at the entrance to the system and at the exit from it and that determines the magnetooptical properties of the structure is calculated. The magnetooptical characteristics of this structure are shown to significantly depend on the angle between the magnetization vectors of layers and on the number of layers. Both the magnitude and the character of these dependences are analyzed in relation to the angle of incidence and to the polarization of the incident wave. Such an analysis makes it possible to optimize the magnetooptical properties of this structure.     

Application of the thermal boson expansion to the Heisenberg antiferromagnet MnF2

We apply the thermal boson expansion which has been presented in refs. [1–3] to the Heisenberg isotropic antiferromagnet, submitted to an external field. Considering only spin waves with wave vectors up to a certain cut-off, the magnetization and the principal susceptibilities are calculated. The results are compared with the experimental data on MnF₂.     

Hysteresis of the characteristics of magnetostatic waves in ferrite films with stripe domains whose magnetization vectors are oriented close to the plane of the film

The propagation of zero-exchange spin waves (magnetostatic waves) is investigated in yttrium iron garnet films having a regular stripe domain structure with almost in-plane orientation of the domain magnetization vectors. The characteristics of the waves are studied for magnetizations of the film parallel and perpendicular to projections of the [111] crystallographic axes onto the plane of the film. It is established, in contrast with films having the domain magnetization vectors oriented close to the normal to the plane of the film, that both the propagation of magnetostatic waves and the variation of the parameters of the domain structure exhibit a distinctly pronounced hysteretic character as the magnetizing field is varied. The hysteresis of the amplitude-frequency response, equiphase, and dispersion curves of the magnetostatic waves is investigated. The authors examine how the hysteresis of these parameters is related to the hysteresis of the domain structure. The spectrum of magnetostatic waves is found to have an interval of wavelengths (wave numbers) that are not excited in the unsaturated film when the applied field is close to the saturation value, and this phenomenon as well exhibits hysteresis. Zh. éksp. Teor. Fiz. 114, 1430–1450 (October 1998)     

Magnetotransport in a graphene monolayer with two tunable magnetic barriers

The magnetotransport property for a monolayer graphene with two turnable magnetic barriers has been investigated by the transfer-matrix method. We show that the parameters of barrier height, width, and interval between two barriers affect the electron wave decaying length, which determine the conductance with parallel or antiparallel magnetization configuration, and consequently the tunneling magnetoresistance (TMR) for the system. Interestingly, a graphene attached by two barriers with different heights can produce a resonant TMR peak at low energy region one order of magnitude larger than that for the system with two same height barriers because that the asymmetry of magnetic barriers block the electron transmission in the case of antiparallel magnetization configuration. The results obtained here may be useful in understanding of electron tunneling in graphene and in designing of graphene-based nanodevices.     

Tunnel anisotropic magnetoresistance in graphene with Rashba spin-orbit interaction

Ballistic transport in a graphene-based normal/ferromagnetic barrier/normal junction in the presence of Rashba-type spin-orbit interaction (RSOI) is investigated by the non-equilibrium Green's function approach. It is found that due to the interplay between ferromagnetic exchange coupling and RSOI, the energy dispersion in the ferromagnetic barrier depends on the magnetization direction. The conductance changes by varying the magnetization direction, resulting in a tunnel anisotropic magnetoresistance (TAMR). The predicted TAMR effect oscillates with the RSOI strength or on-site energy, which is efficiently controllable by the gate voltage, making this junction very promising in spintronics applications.     

Vector model of electron spin echo envelope modulation due to nuclear hyperfine and zeeman interactions

The transverse electron spin magnetization of a paramagnetic center with effective spinS=1/2 interacting with nonquadrupolar nuclei may be presented as a function of pairs of nuclei magnetization vectors which precess around the effective magnetic field directions. Each vector of the pair starts its precession perpendicular to both effective fields. The free induction decay (FID) signal is proportional to the scalar product of the vectors for nuclear spinI=1/2. The electron spin echo (ESE) signal can be described with two pairs of magnetization vectors. The ESE shape is not equal to two back-to-back FID signals except in the absence of ESE envelope modulation. A recursion relation is obtained which allows calculation of ESE signals for larger nuclear spins in the absence of nuclear quadrupole interaction. This relation can be used to calculate the time course of the ESE signal for arbitrary nuclear spins as a function of the nuclear magnetization vectors. While this formalism allows quantitative calculation of modulation from nuclei, it also provides a qualitative means of visualizing the modulation based on simple magnetization vectors.     

Exact diagonalization of the S = 1/2 XY ferromagnet on finite bcc lattices to estimate T = 0 properties on the infinite lattice

In this paper finite bcc lattices are defined by a triple of vectors in two different ways - upper triangular lattice form and compact form. In Appendix A are lists of some 260 distinct and useful bcc lattices of 9 to 32 vertices. The energy and magnetization of the S = 1/2 XY ferromagnet have been computed on these bcc lattices in the lowest states for S _z = 0, 1/2, 1 and 3/2. These data are studied statistically to fit the first three terms of the appropriate finite lattice scaling equations. Our estimates of the T = 0 energy and magnetization agree very well with spin wave and series expansion estimates. Received 1st August 2000 and Received in final form 22 December 2000     

Inhomogeneous magnetostriction states in uniaxial ferromagnetic films

Surface magnetoelastic Love waves and nonuniform distributions of the magnetization and elastic strains are investigated in a uniaxial ferromagnetic film on a massive nonmagnetic substrate in a tangential external magnetic field. A new inhomogeneous phase is predicted having spatial modulation of the order parameter, arising from magnetostrictive coupling of the magnetization with lattice strains near the interface of the magnetoelastic and elastic media. It is shown that, at some critical magnetic field H _c, different from the orientational transition field in an isolated sample, a magnetoelastic Love wave propagating parallel to the magnetization vector in the film plane becomes unstable. The frequency and group velocity of the wave vanish at wave number k=k _c≠0 and the wave freezes, forming a domain structure localized in the film and adjoining substrate. Fiz. Tverd. Tela (St. Petersburg) 41, 665–671 (April 1999)     

Thermal activation of magnetization in Pr_2Fe_(14)B ribbons

The aftereffect field of thermal activation,which corresponds to the fluctuation field of a domain wall,is investigated via specific measurements of the magnetization behavior in Pr2Fe14B nanocrystalline magnets.The thermal activation is a magnetization reversal arising from thermal fluctuation over an energy barrier to an equilibrate state.According to the magnetic viscosity and the field sweep rate dependence of the coercivity,the calculated values of the fluctuation field are lower than the aftereffect field and in a range between those of domain walls and individual grains.Based on these results,we propose that the magnetization reversal occurs in multiple ways involving grain activation and domain wall activation in thermal activation,and the thermal activation decreases the coercivity by~0.2 kOe in the Pr2Fe14B ribbons.     

Quantum effects on magnetization due to ponderomotive force in cold quantum plasmas

The quantum effects on the magnetization due to the ponderomotive force are investigated in cold quantum plasmas. It is shown that the ponderomotive force of the electromagnetic wave induces the magnetization and cyclotron motion in quantum plasmas. We also show that the magnetic field would not be induced without the quantum effects in plasmas. It is also found that the quantum effect enhances the cyclotron frequency due to the ponderomotive force related to the time variation of the field intensity. In addition, it is shown that the magnetization diminishes with an increase of the frequency of the electromagnetic field.     

Orientational Relaxation in Ferromagnets with Isotropic Magnetoelectric Interaction among Subsystems

The frequency and orientational dependences of the internal friction of crystals caused by rotation of spontaneous magnetization vectors and polarization that develop in the process of longitudinal wave propagation are determined for ferromagnets having the BaTiO ₃-type symmetry with allowance for magnetoelectric interaction when the induced polarization is small compared with the spontaneous one. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 40–45, July, 2005.     

Orientational dependence of microeddy losses due to rotation processes in four-axis ferromagnets

On the basis of the common solution of the wave equation and the equations of rotational moments for four-axis multidomain ferromagnets with a given magneticphase distribution we find the orientational dependence of the microeddy losses caused by the reverse rotations of the spontaneous magnetization vectors of the domains.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 68–72, August, 1991.     

Time resolved magnetization dynamics of ultrathin Fe(001) films: spin-pumping and two-magnon scattering

The time-resolved magnetic response of ultrathin epitaxial Fe(001) films grown on GaAs(001) and covered by Au, Pd, and Cr capping layers was investigated by time and spatially resolved Kerr effect measurements. The magnetization was excited by an in-plane magnetic field pulse using the transient internal field generated at a Schottky barrier while the wavelength of the excitation (resonant mode) was roughly 4 microm. Each of the three cap layers affected the spin relaxation in a unique way. Au cap layers resulted in the bulk Gilbert damping of the Fe film. Pd cap layers caused an additional Gilbert damping due to spin-pump or spin-sink effects. Cr cap layers lead to a strong extrinsic damping which can be described by two-magnon scattering. In this case the strength of the extrinsic damping can be controlled by a field induced shift of the spin wave manifold with respect to the excited k vector.     

Effects of nonreciprocity in structure with noncollinear orientation of magnetization of layers

We study nonreciprocity effects that manifest themselves as a difference of transmissive and reflective optical properties for waves of the same polarization that are incident at the angles φ and -φ on a bilayer ferromagnetic structure with noncollinear orientation of the magnetization vectors of the layers in the plane of the film. We consider specific features of these effects and show that the nonreciprocity of the optical properties can be controlled by varying the angle between the magnetization vectors of the layers.     

Coupling of frustrated ising spins to the magnetic cycloid in multiferroic TbMnO(3)

We report on diffraction measurements on multiferroic TbMnO(3) which demonstrate that the Tb- and Mn-magnetic orders are coupled below the ferroelectric transition T(FE) = 28 K. For T相似文献   

Reflexions sur sol dur,interferences et effet d'ecran

The interference effects of the sound energy from a source and that from a reflected wave on the ground are investigated in the particular case of measurements of noise reduction due to the use of a barrier.The influence of these effects on model experiments are also investigated.     

Manipulating the magnetic structure of Co core/CoO shell nanoparticles: implications for controlling the exchange bias

We present an experimental study of the effects of oxidation on the magnetic and crystal structures of exchange biased epsilon-Co/CoO core-shell nanoparticles. Transmission electron microscopy measurements reveal that oxidation creates a Co-CoO interface which is highly directional and epitaxial in quality. Neutron diffraction measurements find that below a Néel temperature TN of approximately 235 K the magnetization of the CoO shell is modulated by two wave vectors, q1=(1/2 1/2 1/2)2pi/a and q2=(100)2pi/a. Oxidation affects the q1 component of the magnetization very little, but hugely enhances the q2 component, resulting in the magnetic decompensation of the core-shell interface. We propose that the large exchange bias effect results from the highly ordered interface between the Co core and CoO shell, and from enhanced core-shell coupling by the uncompensated interface moment.     

Particle image velocimetry measurements of wave-current interaction in a laboratory flume

The hydrodynamics of wave-current interaction is of interest to those concerned with marine and offshore structures. In particular the fluid loading characteristic may be radically altered in a sea state consisting of a mean current flow mixed with freely propagating gravity waves.

The present paper describes water flume experiments, using Particle Image Velocimetry (PIV), executed to examine hydrodynamics of wave-current interaction. A variety of wave and current conditions were investigated to determine the major influences on the combined flow.

This paper describes the experimental procedures used to obtain simultaneous measurements of the resulting wave velocity vectors over an extended region of the wave. It also describes how the directional ambiguity inherent in the basic PIV method was resolved by ‘pulse tagging’ technique.

Velocity vectors under waves at various phase points for different current and wave conditions are presented and compared in some cases with measurements derived using Laser Doppler Anemometry (LDA). The resulting velocity vectors are used to estimate how the mutual interaction, between wave and current, effect the calculation of structural loads using Morrison's equation.     

Second magnon in antiferromagnets

Hydrodynamic equations are derived microscopically for Heisenberg antiferromagnets with inclusion of quasimomentum as an almost conserved quantity. For finite external and anisotropy fields, the hydrodynamic quantities are magnetization, energy and momentum density. At small fields, the propagating mode is essentially an oscillation of the local temperature. For high fields it is a wave in the longitudinal magnetization. In the absence of both fields, the staggered magnetization and not the magnetization itself is coupled to momentum and energy. The propagating mode is mainly an energy wave. The propagating part in the staggered magnetization is inversely proportional to the wavelength.