Phase and amplitude collective modes of an incommensurate spin density wave

We examine the collective modes of an incommensurate quasi-one-dimensional spin density wave associated with oscillations in the phase and amplitude of its complex order parameter. Using a linear response formalism that ensures gauge- and translational-invariance the effects of the Coulomb repulsion in the particle-particle channel are shown to simply renormalise the velocity of the massless phase mode to a value higher than the Fermi velocity. Analytic results for the frequency and damping of the massive amplitude mode are presented. These two longitudinal collective modes remain decoupled for arbitrary wavevector q.     

Ultrashort videopulses of a transverse wave field in a spin system with an anisotropic spin-spin interaction

The propagation is analyzed of a circularly polarized ultrashort videopulse of a transverse wave field in a spin system with an anisotropic spin-spin interaction. Several physical realizations of the given model are proposed. Soliton-like solutions are obtained without approximating the rotating wave and slowly varying envelopes. It is shown that the formation of a connected state of a two-component videopulse is possible for propagation velocities falling in a specific interval of values.Pacific Ocean Oceanological Institute, Far Eastern Branch, Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 114–119, July, 1993.     

Intersubband collective excitations in a quasi-two-dimensional electron system in external magnetic field

The spectrum of collective excitations in a quasi-two-dimensional electron system was studied by the method of Raman scattering spectroscopy. In an applied magnetic field, such systems exhibit collective excitations related to the electron transitions between dimensionally quantized subbands with a change in the Landau level index (intersubband Bernstein modes). It is shown that these modes interact with the fundamental intersubband excitations of the charge and spin densities, the interaction energy being determined by the excitation quasimomentum. Interaction of the intersubband Bernstein modes and the fundamental intersubband excitations with quasi-two-dimensional LO phonons was studied. Behavior of the new branches of collective excitations in a quasi-two-dimensional electron system possessing more than one occupied Landau level was studied and the nature of these branches was determined.     

Exact soliton solution of spin chain with an external magnetic field in linear wave background

Employing a simple, straightforward Darboux transformation we construct exact N-soliton solution for anisotropic spin chain driven by an external magnetic field in linear wave background. As a special case the explicit one- and two-soliton solution dressed by the linear wave corresponding to magnon in quantum theory is obtained analytically and its property is discussed in detail. The dispersion law, effective soliton mass, and the energy of each soliton are investigated as well. Our result show that the stability criterion of soliton is related with anisotropic parameter and the amplitude of the linear wave.     

Dipole-exchange spin wave spectrum in an anisotropic ferromagnetic waveguide with a rectangular cross section

A theory has been constructed that strictly describes the spectrum of dipole-exchange spin waves in an arbitrarily magnetized anisotropic ferrite waveguide with a rectangular cross section. The theory takes into account the spatial inhomogeneity of the internal magnetic field in the waveguide cross section. The influence of parameters of the ferrite waveguide on the distribution of the internal magnetic field in the waveguide cross section is analyzed. The dispersion characteristics of two waveguide types most widely used in practice are investigated. The dipole-exchange spin wave spectra calculated for a transversely magnetized waveguide are presented and the distributions of the dynamic magnetization in the waveguide cross section for several types of volume and localized spin-wave modes are constructed.     

Collective rearrangement of spin excitation spectrum of antiferromagnet with magnetic impurities in external magnetic field

Antiferromagnetic resonance (AFMR) in Co_1?cMn_cF₂ (c ～ 10^-4) in the external magnetic field is investigated. It was established that coherent and incoherent rearrangements (CR and ICR) of spectrum in the region of AFMR and impurity lines crossing are possible in the same sample depending on field orientation. Topology of the phase diagram of spin excitation (SE) spectrum in variables c-H is obtained.     

任意磁化方向铁氧体电磁散射时域有限差分分析的Z变换方法

利用坐标系转换矩阵给出实验室系中饱和磁化铁氧体的频域磁化率张量, 采用部分分式展开方法通过Z变换得到磁化率张量的Z域形式, 给出了任意磁化方向铁氧体电磁散射的Z变换-时域有限差分算法. 计算了饱和磁化铁氧体球的同极化和交叉极化后向雷达散射截面, 结果表明了算法的正确有效性. 关键词： Z变换 饱和磁化铁氧体 电磁散射 时域有限差分方法     

Axial-homogeneous oscillations in semiconductor rod with an arbitrary direction of the magnetic field

Theoretical and numerical studies of the electromagnetio properties of the semiconductor rod with an arbitrary direction of the external magnetic field was carried out. It was investigated new types of surface oscillations in semiconductor rod and the regions of their existence with help of exact dispersion equation. It was considered unreciprocal effect at the deviation of external magnetic field direction into opposite.     

Planar spin chain with competing interactions in an external magnetic field

The 1D classical planar model with nearest neighbor (NN) and next nearest neighbor (NNN) competing interactions is studied at finite temperature in presence of an external magnetic field by the transfer matrix method. In particular we are interested into helix configurations supported by an exchange competition strong enough. The short range order (SRO) is strictly related to the zero temperature long range order (LRO). Our exact calculation makes possible the comparison with the current expectation that a discontinuous helix-fan transition occurs before the continuous fan-collinear transition takes place. This feeling is based on the extrapolation of low field-high field zero temperature expansions. We find strong evidence that this expectation is fulfilled when the turn angle of the helix is lesser than /2, whereas for turn angles greater than /2 the discontinuous transition does not take place and the helix changes continuously to a collinear configuration as the magnetic field is increased. Our conclusion is based on the analysis of the SRO at finite temperature exactly calculated by the transfer matrix method and on the zero temperature exact calculation of the minimum energy of commensurate configurations.     

Long time evolution of a spin interacting with a spin bath in arbitrary magnetic field

We introduce a completely different method to calculate the evolution of a spin interacting with a sufficient large spin bath,especially suitable for treating the central spin model in a quantum dot(QD).With only an approximation on the envelope of central spin,the symmetry can be exploited to reduce a huge Hilbert space which cannot be calculated with computers to many small ones which can be solved exactly.This method can be used to calculate spin-bath evolution for a spin bath containing many(say,1000)spins,without a perturbative limit such as strong magnetic field condition,and works for long-time regime with sufficient accuracy.As the spin-bath evolution can be calculated for a wide range of time and magnetic field,an optimal dynamic of spin flip-flop can be found,and more sophisticated approaches to achieve extremely high polarization of nuclear spins in a QD could be developed.     

Phase transition in a plasma with anisotropic electron distribution in an external magnetic field

A phase transition is discussed that can occur in a plasma with substantially different transverse and longitudinal temperatures of electrons moving in a magnetic field, ?. The Debye cloud surrounding an ion sharply contracts as T_∥ decreases or the magnetic field increases. The effect of larger radiative electron-ion recombination cross sections compared with their theoretical values is explained; this effect is observed in storage rings with electron cooling systems (coolers). The role played by the phase transition in the crystallization of ion beams is discussed.     

Soliton dynamics and elastic collisions in a spin chain with an external time-dependent magnetic field

In this paper, we investigate the nonlinear dynamics of a Heisenberg spin chain with an external time-oscillating magnetic field. Such dynamics can be described by a Landau–Lifshitz-type equation. We apply the Darboux transformation method to the linear eigenvalue problem associated with this equation, and obtain the multi-soliton solution with a purely algebraic iterative procedure. Through the analytical analysis and graphical illustrations for the solutions obtained, we discuss in detail the effects of an external magnetic field on the nonlinear wave. Under the action of an external field, although the amplitude, width and depth of soliton vary periodically with time and its symmetry property is changeable, the soliton can also propagate stably and it possesses particle-like behavior.     

Nonlinear dynamics of a continuum Heisenberg spin chain with an anisotropy and an external magnetic field

By stereographically projecting the spin vector onto a complex plane in the equations of motion for a continuum Heisenberg spin chain with an anisotropy (an easy plane and an easy axis) and an external magnetic field, the effect of the magnetic field for integrability of the system is discussed. Then, introducing an auxiliary parameter, the Lax equations for Darboux matrices are generated recursively. By choosing the constants, the Jost solutions are satisfied the corresponding Lax equations. The exact soliton solutions are investigated, then the total magnetic momentum and its z-component are obtained. These results show that the solitary waves depend essentially on two velocities which describe a spin configuration deviating from a homogeneous magnetization. The depths and widths of solitary waves vary periodically with time. The center of an inhomogeneity moves with a constant velocity, while the shape of soliton also changes with another velocity and this shape is not symmetrical with respect to the center. The total magnetic momentum and its z-component vary with time.     

Inelastic tunnel transport of electrons through an anisotropic magnetic structure in an external magnetic field

Quantum transport of electrons through a magnetic impurity located in an external magnetic field and affected by a substrate is considered using the Keldysh diagram technique for the Fermi and Hubbard operators. It is shown that in a strongly nonequilibrium state induced by multiple reflections of electrons from the impurity, the current-voltage (I–V) characteristic of the system contains segments with a negative conductivity. This effect can be controlled by varying the anisotropy parameter of the impurity center as well as the parameters of coupling between the magnetic impurity and metal contacts. The application of the magnetic field is accompanied by an increase in the number of Coulomb steps in the I–V curve of the impurity. The effect of appreciable magnetoresistance appears in this case. We demonstrate the possibility of switching between magnetic impurity states with different total spin projection values in the regime of asymmetric coupling of this impurity with the contacts.     

用外磁场控制电流感应磁化翻转效应中的临界电流方法

应用基于磁动力学方程的宏观唯象模型,研究了弱外磁场下纳米尺度赝自旋阀结构的电流感应磁化翻转效应.在统一考虑铁磁/非磁界面的自旋相关散射以及铁磁层中的自旋积累和弛豫过程后,给出了赝自旋阀结构在弱外磁场下的磁化翻转条件和临界电流.对该效应的数值计算解释了弱外磁场下赝自旋阀结构的电阻-电流回线的偏移,并给出了用外磁场控制电流感应磁化翻转效应中的临界电流方法. 关键词： 电流感应磁化翻转 外磁场 临界电流 赝自旋阀