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     

圆柱状铁磁体中的偶极-交换自旋波

对于轴向磁化的圆柱状铁磁体,同时考虑偶极作用和交换作用,得到了偶极-交换自旋波的本征方程,给出了频谱的数值结果。当自旋波波矢β较小,即偶极能起主要作用时,相当于静磁模的结果,β较大,即交换能起主要作用时,过渡到宏观自旋波交换模理论的结果。     

四阶色散非线性薛定谔方程的明暗孤立波和怪波的形成机制

本文研究了四阶色散非线性薛定谔方程的明暗孤立波和怪波的形成机制,该模型既可以模拟高速光纤传输系统中超短脉冲的非线性传输和相互作用,又可以描述具有八极与偶极相互作用的一维海森堡铁磁链的非线性自旋激发现象.本文首先通过对四阶色散非线性薛定谔方程的相平面分析,发现由其约化得到的二维平面自治系统具有同宿轨道和异宿轨道,并在相应条件下求得了方程的明孤立波解和暗孤立波解,从而揭示了同异宿轨道和孤立波解的对应关系;其次,基于非零背景平面上的精确一阶呼吸子解,给出了呼吸子的群速度和相速度的显式表达式,进而分析得出呼吸子的速度存在跳跃现象.最后,为了验证在跳跃点处呼吸子可以转化为怪波,将呼吸子解在速度跳跃条件下取极限获得了一阶怪波解,从而证实怪波的产生与呼吸子速度的不连续性有关.     

铁磁/反铁磁双层薄膜中自旋波特性研究

本文在一维海森堡模型的基础上,采用界面参数化方法,研究了非周期性边界条件下,铁磁/反铁磁双层薄膜中自旋波低温激发问题.重点讨论了表面各项异性对薄膜中自旋波谱、色散关系的影响.结果表明:表面各向异性对铁磁层中自旋波谱影响较大,对色散关系影响甚微。     

磁性纳米颗粒系统偶极相互作用的Monte Carlo研究

采用局域Monte Carlo方法模拟不同易轴分布的简单立方排列单分散单畴Fe纳米颗粒系统的ZFC-FC曲线及磁滞回线.结果表明：随着偶极相互作用的增强，系统的阻塞温度T_B逐渐增大，且ZFC曲线的峰变宽.说明偶极相互作用使得系统的有效能垒提高，分布宽度增加.研究FC曲线磁化强度的倒数与温度关系，发现偶极相互作用系统中存在反铁磁有序.系统的阻塞态及超顺磁态的磁滞回线表明，极低低温下，随着偶极相互作用的增强，系统的矫顽力和剩磁减小，偶极相互作用阻碍系统的磁化；系统处于超顺磁态，各向异性作用及偶极相互作用使得系统的磁化曲线偏离Langevin曲线且偶极相互作用展现出退磁相互作用效应.偶极相互作用增强，系统磁化曲线与Langevin曲线偏差量的最大值向低场移动.在偶极相互作用下，易轴与外场夹角为45°的磁性纳米颗粒系统的平均有效能垒和有效能垒分布宽度较易轴随机分布系统的大.     

爆轰波在炸药-金属界面上的折射分析

针对爆轰波在炸药-金属界面上折射时由实验获得的金属折射冲击波压力与经典爆轰波极曲线理论预测的压力存在显著差异这一问题, 本文展开了进一步的理论和数值模拟分析研究. 首先通过分析指出经典爆轰波极曲线理论的缺陷, 并对爆轰波极曲线理论进行了改进, 改进爆轰波极曲线理论给出了炸药爆轰波折射类型以及折射冲击作用点处的压力值. 然后发展了一个基于次特征理论来数值求解爆轰反应流动控制方程的二阶中心型Lagrange方法, 并数值模拟了一个典型的炸药爆轰波折射实验. 改进爆轰波极曲线理论和数值模拟分析结果表明, 爆轰波折射类型有三种:反射冲击波的正规折射、带Mach反射的非正规折射、无反射波的正规折射, 并且金属折射冲击波压力值随入射角增大而单调减小.     

超晶格Heisenberg磁性的研究(Ⅱ)——低温自旋波

在低温条件下,严格求解了超晶格自旋波格林函数的运动方程,计算了低温自旋波的色散关系及态密度,并解析地求得了超晶格中自旋波的刚度系数。     

一维光子晶体全反射隧穿的色散特性

利用介质材料的色散关系和特征矩阵法研究了一维光子晶体中TE波和TM波的全反射隧穿效应随色散的变化特征.TE波和TM波全反射隧穿导带的频率中心随色散强度的增加而降低,频率宽度随色散强度的增加而增大.TE波和TM波的全反射隧穿导带的频率中心随入射角的增加而升高,频率宽度随入射角的增加而减小.这些研究结果拓宽了对一维光子晶体中TE波和TM波波全反射隧穿效应的认识.     

玻色凝聚的原子自旋链中的非线性自旋波

研究了囚禁在光晶格中的旋量玻色-爱因斯坦凝聚体(BEC)形成的原子自旋链中的相干非线性自旋波的激发与调制不稳定性.通过解析分析，得到了调制不稳定性的一般判据以及其对原子自旋的长程耦合的依赖关系.在蓝失谐和红失谐光晶格的情况下，分别具体分析了长程非线性自旋耦合，包括光诱导的和静磁诱导的偶极-偶极相互作用对相干自旋波调制不稳定性的影响.     

扭结孤子牛顿动力学行为的奇异摄动理论

利用奇异摄动展开,发展了一种研究sine-Gordon扭结孤子动力学行为的理论,得到了在恒定外力作用下sine-Gordon扭结孤子类似于经典粒子,其运动遵守牛顿运动定律.同时,还得到了它在传播过程中所辐射的色散波的一个形式简单的解析表达式. 关键词： 扭结孤子 奇异摄动展开 动力学行为     

非对称条形纳磁体的铁磁共振频率和自旋波模式

通过建立微波激励下的非对称条形多铁纳磁体的微磁模型,研究了倾斜角和缺陷角对该形纳磁体的铁磁共振谱和自旋波模式的影响.通过对微磁仿真得到的动态磁化数据进行分析发现,非对称条形纳磁体倾斜角度增加,铁磁共振频率随之增加,而这一现象与纳磁体的缺陷角度无关.倾斜角不变,非对称条形纳磁体的铁磁共振频率与缺陷角度呈单调递增关系,并且不同缺陷角度纳磁体的自旋波模式显示出极大的差异.非对称条形纳磁体与矩形纳磁体相比,它的自旋波模式局部化,具体为非对称条形纳磁体的自旋波模式不对称且高进动区域存在于边缘,表现为非对称边缘模式.倾斜角改变导致纳磁体内部退磁场变化,引起纳磁体边缘模式的移动,而中心模式对倾斜角的变化并不敏感.最后,对建立的模型在高频微波磁场激励下的磁损耗进行了分析,验证了模型的可靠性.这些结论说明缺陷角和倾斜角可用于纳磁体自旋波模式和铁磁共振频率的调谐,所得结果为可调纳磁微波器件的设计提供了重要的理论依据和思路.     

Electron spin resonance of magnetic materials in high fields and high frequencies

Observation and analysis of electron spin resonance of many kinds of magnetic materials have been performed with high frequencies provided by Gunn oscillators, backward traveling wave tubes and far-infrared lasers and also with a vector network analyzer in both pulsed high magnetic fields up to 40 T and steady field up to 20 T. The magnetic behavior of quantum spin systems and metallic materials has been investigated.     

Random generation of coherent solitary waves from incoherent waves

The random generation of coherent solitary waves from incoherent waves in a medium with an instantaneous nonlinearity has been observed. One excites a propagating incoherent spin wave packet in a magnetic film strip and observes the random appearance of solitary wave pulses. These pulses are as coherent as traditional solitary waves, but with random timing and a random peak amplitude.     

Current controlled spin reversal of nanomagnets with giant uniaxial anisotropy

Since a giant magnetic anisotropy of 9 meV per atom has been realized on a Pt surface, we use the kinetic Monte Carlo method to study the spin dynamics of a nanomagnet that is made by putting a line of such adatoms on a thin metallic strip so that the fixed spins are coupled very weakly and a spin-polarized current can be injected into the strip. There is a magnetization hysteresis versus the current because of the giant anisotropy. The hysteresis loop is diminished exponentially with the temperature increasing. The magnetization can be controlled by injecting a spin-polarized current.     

Electromagnetic soliton propagation in an anisotropic Heisenberg helimagnet

We study the nonlinear spin dynamics of Heisenberg helimagnet under the effect of electromagnetic wave (EM) propagation. The basic dynamical equation of the spin evolution governed by Landau–Lifshitz equation resembles the director dynamics of the twist in a cholestric liquid crystal. With the use of reductive perturbation technique the perturbation is invoked for the spin magnetization and magnetic field components of the propagating electromagnetic wave. A steady-state solution is derived for the weakly nonlinear regime and for the next order, the components turn around s plane perpendicular to the propagation direction. It is found that as the electromagnetic wave propagates in the medium, both the magnetization and magnetic field modulate in the form of kink soliton modes by introducing amplitude fluctuation in the tail part of the same.     

Spin injection-driven switching in a magnetic junction

We investigate a perpendicular electric current passing through a “ferromagnetic nanojunction”, that is through some layered nanosized structure of spin-valve type, containing two ferromagnetic metallic layers. Spacer may be used between the metallic layers to prevent the rotation of the moving spin phases. Such an arrangement is typical for spin valves: one of the metallic layers has strongly pinned magnetic lattice and the other one has free magnetic lattice and free mobile spins. Further the conditions are derived to provide a very high nonequilibrium spin injection level. It appears that the so-called spin resistances of the constitutive layers should be in definite relations to each other. These relations lead to the situation where the spin injection becomes dominant and significantly suppresses the “ordinary” spin-transfer torque. As a result, the threshold current becomes lowered down to 2-3 and even more orders of magnitude.     

On the Cutoff Wavelength of Rectangular-Shaped Microshield Line by Edge Element Method

In this paper, the cutoff characteristic of rectangular-shaped microshield transmission line has been analysed by edge element method. Dependence of cutoff wavelengths on the thickness of metallic signal strip, dielectric constant of dielectric substrate and the width of the rectangular-shaped ground conductor are presented in tabular form. Numerical results in this paper have important values in design of rectangular-shaped microshield lines in microwave and millimeter wave integrated circuits.     

Spin Hall effect on edge magnetization and electric conductance of a 2D semiconductor strip

The intrinsic spin Hall effect on spin accumulation and electric conductance in a diffusive regime of a 2D electron gas has been studied for a 2D strip of a finite width. It is shown that the spin polarization near the flanks of the strip, as well as the electric current in the longitudinal direction, exhibit damped oscillations as a function of the width and strength of the Dresselhaus spin-orbit interaction. Cubic terms of this interaction are crucial for spin accumulation near the edges. As expected, no effect on the spin accumulation and electric conductance have been found in case of Rashba spin-orbit interaction.     

Spin filtering magnetic modulation and spin-polarization switching in hybrid ferromagnet/semiconductor structures

Electron spin-polarization modulation with a ferromagnetic strip of in-plane magnetization is analyzed in a hybrid ferromagnet/semiconductor filter device.The dependencies of electron spin-polarization on the strip’s magnetization strength,width and position have been systematically investigated.A novel magnetic control spin-polarization switch is proposed by inserting a ferromagnetic metal(FM)strip eccentric in relation to off the center of the spin filter,which produces the first energy level spin-polarization reversal.It is believed to be of significant importance for the realization of semiconductor spintronics multiple-value logic devices.     

Electronic spin precession and interferometry from spin-orbital entanglement in a double quantum dot

A double quantum dot inserted in parallel between two metallic leads can entangle the electron spin with the orbital (dot index) degree of freedom. An Aharonov-Bohm orbital phase can be transferred to the spinor wave function, providing a geometrical control of the spin precession around a fixed magnetic field. A fully coherent behavior occurs in a mixed orbital-spin Kondo regime. Evidence for the spin precession can be obtained, either using spin-polarized metallic leads or by placing the double dot in one branch of a metallic loop.