量子自旋波本征值及易轴型各向异性对其的影响

本文考虑体单轴各向异性利用界面重参数化方法从理论上严格推导了两层异质铁磁质中量子自旋波的本征值,并模拟计算了简立方晶格结构 (100) 第一布里渊区的能带结构,特别研究了易轴型体单轴各向异性对本征值的影响.结果发现在这样的体系中存在体模、禁闭模和界面模;各种本征模与体交换作用、界面交换作用、晶格自旋、原子层数有关,而且各向异性直接影响各种本征模的存在条件. 关键词： 铁磁薄膜 自旋波 各向异性     

各向异性磁介质中的静磁交换模

继作者对Damon和Easbach(简称DE)理论在长波部分的修正,本文探讨了DE理论在短波部分的适应性,研究了具有单轴各向异性和弱交换作用的偶极自旋模式,给出了临界角的表达式,并分析了频率-波矢空间的实际图象。所得结果与铁磁共振的频谱实验结果较好地符合。 关键词：     

偶极旋量玻色-爱因斯坦凝聚体在外场中的自旋混合动力学

探讨了外场中偶极旋量玻色-爱因斯坦凝聚体的静态和动力学行为.研究结果表明,可以调节外场、自旋交换相互作用和偶极-偶极相互作用来调控三组分之间的隧穿,控制布居数动力学演化范围和相对相位动力学行为. 关键词： 玻色-爱因斯坦凝聚 偶极-偶极相互作用 自旋混合动力学     

交换作用涨落所引起的铁磁共振线宽

本文同时考虑自旋矩和交换积分的室间涨落,计算了在一个次点阵上有二类阳离子无规分布的铁氧体的铁磁共振线宽。这种不均匀性使由微波场所激发的一致进动散射为与之简併的自旋波。Clogston等用来解释此线宽的赝偶极作用涨落是估计过高了,它与我们现在所考虑的交换作用涨落相比实际上可以略去。我们计算的结果不仅给出了足够大的线宽,它在数量级上与许多反型尖晶石型铁氧体的实验结果相同,并且自然地解释了镁锰铁氧体和无序锂铁氧体的线宽非常小的原因。     

非线性偶极-交换表面自旋波的包络孤立子解

介绍了非线性表面自旋波理论研究的新进展 ,并对前人的理论做了推广 ,针对具有非均匀交换各向异性的偶极 交换铁磁介质的非线性表面自旋波的性质和行为进行了较为系统的理论研究. The new progress in the theoretical investigation on nonlinear surface spin waves is reviewed, and the theory mentioned above is generalized. A relatively systematical investigation on the behaviors and properties of the nonlinear surface spin waves in dipole-exchange ferromagnetic media with inhomogeneous exchange anisotropy is developed.     

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.     

耦合磁性杂质理论

一、Kondo及 AG(Abrikosov Gorkov) 的孤立磁性杂质理论 在非磁性金属或合金中掺有少量(10-6—10-3)的带有局域磁矩的原子所构成的体系称为稀磁合金.其中的传导电子(S)和局域电子(d)之间有库仑作用.它的一部分交换作用称为sd交换作用,相应的哈密顿量是其中表示传导电子波矢为k、自旋为a的产生、消灭算符,表示局域电子在格点i上自旋为β的产生、消灭算符,Sβ’β及分别代表局域电子和传导电子的自旋算符的矩阵元,J为交换积分常数,N为格点数.这个哈密顿量的主要特点是当s电子和d电子散射时,可以发生自旋倒向,如图1所示.图中小圆表示s电子,…     

铁磁体中缺陷对自旋波的影响

本文提出了一个处理磁性杂质或其他缺陷在磁性晶体中对自旋波频谱的影响的一般理论方法,并特别着重讨论了局域模自旋波。以一维线性格子为例进行计算的结果显示出:一个代位磁性杂质,可能产生不只一个高于连续带顶的局域模。其产生的条件和其能级位置均通过J′S′/JS和J′/J表达出来,这里S′和S各为杂质原子和基质原子的自旋量子数,J′和J各为杂质与近邻之间和一般近邻之间的交换作用系数。高度集中的应变和间隙原子如致使邻近处的交换作用增大,也导致局域模的出现。我们也考虑了磁偶极矩相互作用的影响,证明其并不破坏这些局域模的     

磁场及体各向异性对面心立方双层铁磁薄膜能带的影响

利用二次量子化方法研究了由相同面心立方结构(100)材料构成的铁磁性双层薄膜,重点讨论了磁场及体各向异性对面心立方双层铁磁薄膜能带的影响.结果表明,无论界面为铁磁性界面交换作用或反铁磁性界面交换作用,磁场及各向异性场对对称薄膜中的自旋波存在方式及整个能带形状没有影响,只是影响整个激发模的能量.磁场和各向异性常数越大,自旋波能量越高.     

BCVIG单晶的布里渊散射

用布里渊散射技术测量了BCVIG(Bi_3-2xCa_2xFe_5-xV_xO₁₂)单晶的磁振子散射谱,同Sande-rcock,Wettling对YIG以及刘玉龙等人对Bi-YIG单晶的测量相比,我们得到了除主峰之外的连续谱带。按照偶极-交换自旋波理论讨论了测到的自旋波谱。测量还表明BCVIG单晶的自旋波劲度系数D比YIG和Bi-YIG单晶大得多,讨论了D增大的原因,研究了D与入射激光功率的关系。 关键词：     

Spin wave dispersion of FeBO3 at small wavevectors

Brillouin scattering from thermally excited magnons and ferromagnetic resonance are used to determine the spin wave dispersion of the low-frequency spin wave branch in FeBO₃, a transparent weak ferromagnet. In addition to the dominant exchange and Zeeman contributions, the investigation takes into account magnetic dipole and magnetoelastic interactions. Due to the antisymmetric exchange enhancement the material exhibits a broad spin wave band and a large gap energy at small magnetic fields. Competing directional dependences of the dipole and the exchange energy produce a degeneracy of spin waves with a certain magnitude of the wavevector propagating in different directions. The gap energy is shown to be due to magnetoelastic coupling, whereas the contribution of the anisotropy in the easy plane is negligible atT=300 K.     

Magnetostatic volume waves in exchange-coupled ferrite films

The influence of exchange coupling of layers on the propagation of magnetostatic dipole volume waves in normally and tangentially magnetized two-layer epitaxial ferrite structures is investigated. It is shown that the indicated influence is manifested in the form of dynamic spin pinning effects on the interlayer boundary and formation of a common dipole-exchange wave spectrum for the entire structure. In this case, at the synchronism frequencies of the dipole and exchange waves the losses of the dipole waves grow and anomalous segments appear in the dispersion. In films magnetized in the “hard” direction relative to the axis of normal uniaxial surface anisotropy the magnetostatic dipole volume waves can interact resonantly with the surface spin waves supported by the boundaries with pinned spins. Zh. Tekh. Fiz. 68, 97–110 (July 1998)     

Collective spin excitations in 2D paramagnet with dipole interaction

The collective spin excitations in the unbounded 2D paramagnetic system with dipole interactions are studied. The model Hamiltonian includes Zeeman energy and dipole interaction energy, while the exchange vanishes. The system is placed into a constant uniform magnetic field which is orthogonal to the lattice plane. It provides the equilibrium state with spin ordering along the field direction, and the saturation is reached at zero temperature. We consider the deviations of spin magnetic moments from its equilibrium position along the external field. The Holstein-Primakoff representation is applied to spin operators in low-temperature approximation. When the interaction between the spin waves is negligible and only two-magnon terms are taken into account, the Hamiltonian diagonalisation is possible. We obtain the dispersion relation for spin waves in the square and hexagonal honeycomb lattice. Bose-Einstein statistics determine the average number of spin deviations, and total system magnetization. The lattice structure does not influence on magnetization at the long-wavelength limit. The dependencies of the relative magnetization and longitudinal susceptibility on temperature and external field intensity are found. The internal energy and specific heat of the Bose gas of spin waves are calculated. The collective spin excitations play a significant role in the properties of the paramagnetic system at low temperature and strong external magnetic field.     

The influence of magnetoelastic coupling of exchange spin waves on the spectrum of magnetoacoustic vibrations in planar structures

The influence of coupling between exchange spin waves and acoustic waves on the spectrum of magnetoelastic vibrations in planar structures (such as a ferrite film-dielectric substrate structure) is investigated theoretically. A strong magnetoelastic coupling is observed in a narrow spectrum of magnetoacoustic modes that corresponds to the phase matching of the exchange magnetostatic and acoustic modes. An explanation is offered for the experimental results obtained earlier by the authors, according to which the linear excitation of exchange acoustic and dipole exchange acoustic modes occurs in a spectral range corresponding to the resonance magnetoelastic coupling of exchange modes irrespective of the degree of pinning of surface spins in the ferrite film. It is demonstrated that the exchange acoustic and dipole exchange acoustic modes can be excited in films with free surface spins due to a substantial transformation of the structure of normal modes of the magnetization vector and elastic displacements in the range of the phase matching of the exchange spin and acoustic modes.     

Detection of the electron spin resonance of two-dimensional electrons at large wave vectors

We have investigated the electron spin resonance at nonzero wave vector in GaAs single quantum wells by combining the virtues of high frequency surface acoustic wave generation to produce excitations with large wave numbers with a sensitive optical scheme to detect resonant absorption. The observed large deviations from the single particle Zeeman energy are attributed to the exchange interaction. The enhancement of the electronic g* factor is, however, substantially smaller compared with theoretical predictions for spin waves when adopting a bare Coulomb interaction potential.     

Reflection of spin and spin-elastic waves at the interface of a ferromagnetic half-space

This paper considers the reflection of pure spin and spin-elastic (or magneto-elastic) waves at the interface of a ferromagnetic half-space and a vacuum. For pure spin waves two cases are considered, with exchange effects, and without. It is shown that when exchange effects are taken into account, volume spin waves in the ferromagnetic half space incident at the boundary with the vacuum generate a reflected volume spin wave, and an accompanying compound surface wave propagating along the boundary and consisting of two partial inhomogeneous spin waves in the ferromagnetic half-space and a partial magneto-static inhomogeneous surface wave in the vacuum. When exchange effects are neglected the incident wave generates only a reflected volume wave in the ferromagnetic half-space.

Reflection and transmission of spin-elastic (or magneto-elastic) waves has been considered only in the case of the absence of exchange effects. An incident volume wave generates a volume spin-elastic reflected wave and one inhomogeneous magneto-static accompanying surface wave.

Excitations of the magnetic field are not transmitted into the vacuum in both cases when the exchange effect is neglected. In all cases the reflection of a spin wave has the character of a full internal reflection.     

Excitation of spin waves localized on a moving domain wall in a two-layer ferromagnetic film

The problem of excitation of spin waves in a two-layer magnetic film with a sharp interface between the layers is solved on the basis of Slonchevskii equations. The equations describing spin wave excitation along the film thickness are derived. The results are limited to zeroth approximation in the smallness parameter ɛ, viz. the ratio of the energy of magnetic dipole forces to the anisotropy energy. The power dissipated by such oscillations is calculated.     

杂质散射引起的亚铁磁体的共振线宽

本文得到了具有二个等价次点阵的椭球亚铁磁体的二支自旋波频谱,它们的频率对波矢的依赖关系与椭球铁磁体的相类似。基于此频谱和交换作用涨落引起的自旋波散射机制,计算了一致共振和交换共振的线宽。对一致共振,用等效铁磁模型得到的结论仍然成立:非磁性杂质离子和自旋等于同一次点阵上基质离子自旋的杂质离子,对一致共振线宽没有贡献。但这二类杂质离子对交换共振线宽有贡献。用我们的简化亚铁磁模型对各种铁氧体算得的一致共振线宽差别很大。对许多尖晶石型铁氧体,交换作用涨落可能是引起一致共振线宽的主要机制。对于铁氧体,由此机制引起的交换共振线宽其数量级为几十奥。     

Oscillatory energy exchange between waves coupled by a dynamic artificial crystal

We describe a general mechanism of controllable energy exchange between waves propagating in a dynamic artificial crystal. We show that if a spatial periodicity is temporarily imposed on the transmission properties of a wave-carrying medium while a wave is inside, this wave is coupled to a secondary counterpropagating wave and energy oscillates between the two. The oscillation frequency is determined by the width of the spectral band gap created by the periodicity and the frequency difference between the coupled waves. The effect is demonstrated with spin waves in a dynamic magnonic crystal.