Toward the theory of spin waves on the surface of a nanotube with a superlattice in a magnetic field

Electron spin waves on the surface of a semiconductor nanotube with a superlattice in a magnetic field have been considered. The spin-wave spectra and regions of collisionless wave damping have been found. It has been shown that the spin waves do not exhibit damping on small-radius tubes with a degenerate electron gas.     

Dipolar surface spin waves in antiferromagnets

We present calculations for dipolar surface spin waves in antiferromagnets at low temperatures. We calculate bulk and surface spin wave spectra for long wavelengths in the magnetostatic mode region. The different phases in an applied field along the easy axis are discussed with special emphasis on the spin flop- and paramagnetic phase. Nonreciprocal features of the surface spin waves are discussed. Numerical applications for GdAlO₃ are given.     

Cross-phase modulation of surface magnetostatic spin waves

This paper explains the modulation instability of two surface magnetostatic spin waves simultaneously propagating in a ferromagnetic film. Self-modulation of the spin waves appears when their power reaches a threshold, and this is a sign of cross-phase modulation. The parameters of the unstable process are calculated, and the gains of the perturbation amplitudes are determined. The results published earlier on the experimental detection of the cross-phase modulation of spin waves are explained. Zh. éksp. Teor. Fiz. 116, 2058–2068 (December 1999)     

Stern-Gerlach spin filter using surface acoustic waves

We propose the ambipolar carrier transport by surface acoustic waves (SAWs) in a semiconductor quantum well (QW) for the realization of the Stern-Gerlach (SG) experiment in the solid phase. The well-defined and very low carrier velocity in the moving SAW field leads to a large deflection angle and thus to efficient spin separation, even for the weak field gradients and short (μm-long) interaction lengths that can be produced by micromagnets. The feasibility of a SG spin filter is discussed for different QW materials.     

Reflection and scattering of spin waves by surface roughness of a ferromagnet

Abstract

A detailed theory of volume spin wave reflection from the randomly rough surface of a ferromagnet is presented. The contribution to damping of the reflected wave is calculated. This contribution is due to the scattering of the initial volume wave into secondary surface and volume spin waves. The value of damping is proportional to the correlation length and the square of the roughness amplitude. Numerical calculations of the attenuation rate as a function of the angle of incidence and the ratio between the surface anisotropy and the wavenumber are provided. They yield the angle of incidence where the attenuation has a maximum. In analogy to optics, this angle is similar to the Brewster angle. Numerical estimations of damping and a comparison of its value with the ferromagnetic resonance linewidth are also made. Finally, the results of the calculation of the scattering of surface exchange spin waves by surface roughness are presented and discussed.     

Spin waves on the surface of the nonferromagnetic nanotube in magnetic field

Propagating in the nonferromagnetic electron gas on the cylindrical nanotube's surface spin waves in longitudinal magnetic field are considered. The spectrum of electrons in the Hartree-Fock approximation was applied. The dynamic spin susceptibility of a degenerate electron gas was derived using the random phase approximation. The spectra of intra-subband and inter-subband magnons were calculated in quasiclassical and quantum limits. The quantity of spin waves spectrum branches depends on the amount of filled subbands. In case the filled subband numbers are large, the wave's frequencies undergo oscillations of de Haas-van Alphen and Aharonov-Bohm types with the electron density and the magnetic induction changes.     

Magnetically tunable Airy-like beam of magnetostatic surface spin waves

In this Letter,we report an Airy-like beam of magnetostatic surface spin wave(Ai BMSSW)supported on the ferromagnetic film,which is transferred from the optical field.The propagation properties of Ai BMSSW were verified with micromagnetic simulation.From simulation results,the typical parabolic trajectory of the Airy-type beam was observed with an exciting source encoding 3/2 phase pattern.The simulation results coincide well with design parameters.Furthermore,simulated results showed that the trajectories of the Ai BMSSW could be tuned readily with varied external magnetic fields.This work can extend the application scenario of spin waves.     

Existence and propagation character of spatial spin surface waves

The problem of existence and the propagation character of spatial spin surface waves in ferromagnic media are considered. The condition of existence of a surface wave is obtained depending on the physical constants of the medium and on the angle made by the wave vector direction with the direction of the axis of easy magnetization of a ferromagnet. The regions of change of wave numbers, where the transmission of a surface wave becomes impossible (zone of silence), are determined. Formulas for determining the phase velocity and penetration depth of the surface wave are found. It is shown that with a certain choice of the wave vector direction one can achieve the necessary localization of the spin wave at the surface of the body.     

Effect of surface spin waves on the magnetization of thin films

The theoretical calculation of the magnetization across the thickness of the film shows that it may be either lower or higher near the surface than at the centre of the film depending on the surface anisotropy. For intermediate surface anisotropy values the plots of magnetization vs distance from the surface show several extrema. The temperature dependences of magnetization show only small departures from the usual theoretical behaviour of thin films for the cases when surface spin waves are present. The given examples are calculated for uniaxial h.c.p. Heisenberg ferromagnet.     

Electrically tunable spin polarization in a carbon nanotube spin diode

We have studied the current through a carbon-nanotube quantum dot with one ferromagnetic and one normal-metal lead. For the values of gate voltage at which the normal lead is resonant with the single available nondegenerate energy level on the dot, we observe a pronounced decrease in the current for one bias direction. We show that this rectification is spin dependent, and that it stems from the interplay between the spin accumulation and the Coulomb blockade on the quantum dot. The degree of resulting spin polarization is fully and precisely tunable using the gate and bias voltages.     

Accounting for the local surface geometry in the classical theory of spin waves

The effect of the surface energy on the formation of the spin spectrum is considered. Different aspects are examined of the effect of the surface on the energy spectrum of the system associated with structural features of the surface structure. The calculations are carried out for the spectrum of elementary excitations of a ferromagnetic system that is bounded by a surface. Calculations are conducted following the standard method of the Hamiltonian diagonalization. Relationships are obtained that completely determine the surface spectrum in the zero approximation in the spin-spin interaction.     

Energy gap of spin nanotube

Recently some quantum spin systems on tube lattices, so-called spin nanotubes, have been synthesized. They are expected to be interesting low-dimensional systems like the carbon nanotubes. As a first step of theoretical study on the spin nanotube, we investigate the three-leg spin tube, which is the simplest one, using numerical analyses of finite clusters and a finite-size scaling technique. The spin gap, which is one of the most interesting quantities reflecting the macroscopic quantum effect, was revealed to be open for any finite rung exchange couplings, in contrast to the three-leg spin ladder system which is gapless. We also found a quantum phase transition caused by an asymmetric rung interaction. When one of the three rung coupling constants is changed, the spin gap vanishes very rapidly.     

Longitudinal spin waves as secondary excitations of the spin system of a ferromagnet

The method of two-time Green's functions is used to calculate the natural oscillations of the longitudinal component of the spontaneous magnetization of a ferromagnet. The spectrum of these oscillations or spin waves has no gap, even when magnetic interactions are taken into account. For smallk the spectrum of longitudinal spin waves has the same properties as secondary excitations of the spin system of a ferromagnet In which the primary excitations are transverse (ordinary) spin waves.Translated from Izvestiya VUZ. Fizika, No. 4, pp. 82–85, April, 1970.     

Spherical spin waves

The spin waves in a two-sublattice ferrimagnetic sphere are derived from the equation of motion for the sublattice magnetization. The pinning conditions are discussed and the results are compared with those obtained by numerical diagonalization of corresponding Heisenberg hamiltonian. For a sphere with the diameter of about 40 lattice constants the continuum approximation is fully applicable for estimation of some (long wavelength) spin wave energies and angle of the core spins. The transition probabilities seem to be considerably overestimated by this method.Dedicated to Dr. Svatopluk Krupika on the occasion of his 65th birthday.The author wishes to thank Dr. V. Kamberský for many valuable discussions which enabled him to improve the text.     

非均匀交换各向异性铁磁介质的非线性表面自旋波

利用Landau-Lifshitz 方程，研究了具有非均匀交换各向异性的半无限大铁磁体的非线性表 面自旋波理论。导出了部分钉扎纯交换铁磁介质的磁化强度所满足的边界条件和非线性表面 自旋波的色散关系，并获得了自旋波振幅沿z方向驻波的一维非线性Schrdinger方程和包 络振幅沿平面传播的二维非线性Schrdinger方程，结果表明铁磁体磁化强度的包络振幅随时空变化的性质是由二维非线性Schrdinger方程决定的。因此预言铁磁介质的表面非线性激发应是二维孤波的形式。对于弱非线性表面自旋波，对非线性Schrdinger方程存在孤子形式解的可能性作了讨论. 关键词： 表面自旋波 Landau-Lifshitz方程 非线性Schrdinger方程 孤子     

Some special features of the transition to chaos in the self-modulation of surface spin waves

The results of experimental investigations of the transition from regular to stochastic self-modulation of intense surface spin waves are presented. It is found that the transition to chaos follows the scenario of a sequence of period-doubling bifurcations. The fractal dimensions and the Kolmogorov entropy are determined for different regimes. The experiments are performed on an apparatus consisting of a microwave oscillator with a spin-wave delay line in the feedback circuit. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 4, 243–246 (25 August 1997)     

The effect of parametrically excited spin waves on the dispersion and damping of magnetostatic surface waves in ferrite films

This paper describes an experimental study of variations of the dispersion and damping of magnetostatic surface waves in ferrite films, caused by three-and four-magnon interactions with parametric spin waves excited by an auxiliary surface magnetostatic pump wave with frequency f _p. The variations in the dispersion and damping were identified, respectively, with variations Δk″ in the real part and Δk′ in the imaginary part of the wave number of the surface magnetostatic wave. The Δk″ and Δk′ values were determined from the ratio of the changes of the phase increment Δφ and the amplitude increment ΔA of the surface magnetostatic wave to the length L of the nonequilibrium section of the film, where the parametric spin waves exist. It is found that, when three-magnon decay processes are allowed for the pump wave and the surface magnetostatic probe wave, the probe wave can substantially alter the distribution of the parametric spin waves in the film. Zh. éksp. Teor. Fiz. 115, 318–332 (January 1999)     

Electron spin polarization in a rotating triplet

The triplet model of electron spin polarization in fluid media is evaluated. The model consists of an initial singlet molecule rotating in a static, externally applied magnetic field. Intersystem crossing into different zero-field states is represented by a rate matrix diagonal in the molecular frame, and this matrix is expressed as an effective spin operator. The triplet rotates, and the motion affects the polarization in the laboratory frame, and also causes spin relaxation in the triplet manifold. The triplet is chemically quenched, and the polarization appears in the doublet fragments. The model is treated in a density matrix formalism and on the basis of anisotropic rotational diffusion of the triplet molecule. Explicit expressions are obtained in terms of the molecular parameters, the various rate constants, and the rotational correlation time.