Dynamic magnetic susceptibility of a two-layer film in a strong magnetic field

A theoretical study is reported of the effect of interlayer exchange coupling on the resonance properties of a two-layer magnetic film with “easy-axis” and “easy-plane” anisotropic layers in a strong tilted magnetic field. The dependence of the resonance fields on the tilting angle of the external magnetic field to the film has been obtained, the tensor of integrated high-frequency film susceptibility has been found, and its dependence on the strength and orientation of the external field, as well as on layer thickness, has been analyzed. The results obtained agree with the available experimental data.     

磁场和耦合强度对极化子有效质量和平均声子数的影响

应用线性组合算符和幺正变换方法,研究磁场和耦合强度对极化子有效质量和平均声子数的影响.数值计算表明:极化子的有效质量随耦合强度的增加而增加,这是由于耦合强度增加时,电子与晶格振动之间的相互作用增加所致;而磁场强度增加时,有效质量是先增加,达到一个极大值后,再逐渐减少,出现共振现象.平均声子数随耦合强度的增加而增加,当磁场强度大于共振时的磁场强度时,随磁场强度的增加而减少,反之,结论相反.     

On the domain ferromagnetic resonance in bubble lattice exposed to the in-plane field

The domain ferromagnetic resonance (DFMR) of a bubble lattice was measured on garnet films magnetized in the film plane. More than three theoretically predicted DFMR modes were observed as before on magnetoplumbite platelets in the same measurement configuration. The forms of the dispersion curves (frequency/field graphs) of these modes were found to be similar for both materials. The strongly different magnetic parameters of both sample types enabled us to obtain new information about the character of the excited modes. Due to a good optical transparency and high magnetooptical contrast of the garnet films the dispersion of the DFMR modes could be correlated with the actual domain structure.I wish to express my thanks to A. Kolodrubec for the help with microwave measurements and to V. Kamberský and R. Gemperle for a useful discussion.     

铁磁共振法测磁各向异性

采用铁磁共振方法,研究了铁磁/反铁磁双层膜系统中,因交换耦合以及磁晶各向异性而产生的有效各向异性场.结果表明:被测系统有无交换偏置场以及其正负号性质等均能在共振谱中得到辨析.结果还显示:沿着不同结晶方向施加外磁场,共振场的行为与磁晶各向异性以及铁磁/反铁磁交换耦合作用而诱发的单向各向异性等密切相关.将共振频率的变化看成外磁场(包括其方向和大小)的函数,研究得到了单向各向异性,立方各向异性等对共振频率的影响,并同实验结果做了很好的比较. 关键词： 铁磁/反铁磁双层膜 交换耦合 铁磁共振 单向各向异性     

磁性多层薄膜中交换各向异性研究

采用铁磁共振理论研究了自旋阀体系中交换各向异性场和两铁磁薄膜厚度对体系性质的影响,得到系统色散关系的解析表达式.研究表明:体系中存在的交换各向异性场H_E对声学模和光学模的共振场均有影响(其对声学模的影响较大).而且还发现声学模共振场随A,B层铁磁薄膜厚度的变化关系依赖于系统中交换各项异性场的强弱;相反,光学模共振场随两铁磁层厚度的增加始终增强.     

Stability criteria of Rayleigh ‐ Taylor modes in magnetized plasmas

The Rayleigh ‐ Taylor (RT) instability is investigated analytically in an inhomogeneous plasma in an external magnetic field. For the case of two distinct fluid layers separated by a sharp boundary and for a fluid of a continuously varying density, RT dispersion relations have been obtained and analyzed. Stability criteria of the excited modes are disscussed with respect to the mode propagation relative to the applied magnetic field. The magnetic field is found to act as a stabilizer up to a threshold value that can be determined from the dispersion relation.     

外应力场下双层铁磁薄膜中的铁磁共振性质

用铁磁共振方法得到了双层铁磁薄膜的色散关系解析表达式.发现共振场依赖于层间耦合强度和应力场.假定层间为反铁磁性耦合，且铁磁层Ａ有较强的平面内各向异性.随着外磁场的增强，铁磁层Ｂ中的磁化强度突然由最初的反平行转为平行，从而导致色散曲线的阶跃，并且发现光学模阶跃幅度比声学模大.随着应力场的增强，Ｂ层中磁化强度反转所需的外磁场减弱.此外，在不同的交换耦合强度和应力场下，光学模共振场对外磁场方向的依赖性较强. 关键词： 双层铁磁薄膜 界面相互作用 应力各向异性场 铁磁共振     

Theory of electromagnetic wave propagation in superlattices with optically anisotropic layers

A formalism is developed to find the photon dispersion relations in superlattice systems having layers with low optical symmetry or having magnetic layers. This formalism is an exact solution of the first order Maxwell's equations including all the information for the anisotropic optical response tensors and including the coupling of the TE and TM modes. Based on a 4×4 matrix approach for solving complicated reflection and transmission problems in stratified anisotropic media and employing a plane wave expansion of the field components to take into account the periodicity of the superlattices, the photon dispersion relation can be obtained numerically with a simple algorithm. This result is useful in predicting the absence of certain electromagnetic modes along the superlattice axis, and in identifying observed resonances with a particular excitations of the system.     

Magnetic field effects on the optical response of a film with a rough surface: Voigt geometry

Using the Rayleigh–Fano modal approach we investigate the optical response of a metallic film with a deterministic rough surface taking into account an external magnetic field in the Voigt geometry. For P-polarized light incident onto a deterministic rough surface we calculate the specular and first-order scattered field amplitudes. We also explore the nonreciprocity property and the coupling of the incident light with the surface magnetoplasmons. It is obtained that the magnetic field strength may increase the gap between two minima produced by the splitting of the minima of the zero-field specular reflection. The dispersion relations of the surface magnetoplasmons predict the possible experimental excitation and detection of these modes.     

Spin Wave Spectra in a Ferromagnetic/Non-magnetic Superlatt ice with Antiparallel Magnetization

The transfer-matrix method is employed to investigate the spin waves in a ferromagnetic/non-magnetic superlat tice with an antiferromagnetic coupling between interfacial ferromagnetic layers across a non-magnetic spacer layers and the an tiparaUel magnetizations between neighboring ferromagnetic films. The dispersion relation of the spin waves is obtained. The effects of the thickness of the magnetic layers, the antiferromagnetic coupling strength and concentration of magnetic atoms at the interface on the spin wave spectra are discussed in detail.     

外应力场下铁磁/反铁磁双层膜系统中的自旋波

采用自由能极小的方法研究了铁磁/反铁磁双层膜系统在外应力场下的一致进动自旋波性质，即铁磁共振现象. 本模型中铁磁层很薄可看成单畴结构，但具有单轴磁晶各向异性和立方磁晶各向异性；而反铁磁层仅具有单轴磁晶各向异性，但其厚度趋于半无穷. 推导出了该系统的铁磁共振频率和频谱宽度的解析式. 结果表明，外应力场和界面交换耦合或反铁磁磁强度仅在弱磁场下对系统的铁磁共振有影响，且系统的铁磁共振行为按磁场强度可分为两支，其区分弱磁场和强磁场的临界场依赖于外应力场的方向. 另一方面，应力场方向的改变可借助于反铁磁层磁畴变化对铁磁层磁晶各向异性轴有影响. 关键词： 铁磁/反铁磁双层膜 界面耦合强度 铁磁共振 应力场     

Dispersion of doppleron-phonon modes in strong coupling regime

The dispersion equation for doppleron-phonon modes was constructed and solved analytically in the strong coupling regime. The Fermi surface model proposed previously for calculating the doppleron spectrum in an indium crystal was used. It was shown that in the vicinity of doppleron-phonon resonance, the dispersion curves of coupled modes form a gap qualitatively different from the one observed under helicon-phonon resonance: there is a frequency interval forbidden for existence of waves of definite circular polarization depending upon direction of the external DC magnetic field. The physical reason for it is interaction of the waves which have oppositely directed group velocities.     

三层介质超声谐振模式随材料和界面粘接性能变化的演变规律

在用超声波谐振对粘接材料的粘接强度进行无损评估时, 不同模式对粘接强度的敏感程度受到众多因素和参数的影响, 对检测结果的可靠性至关重要. 基于多层介质中声传播和界面弱粘接边界条件的理论模型, 将一个上下非对称的金属-粘接剂-金属三层结构的平面波反射系数函数中的谐振模式看作是上下铝金属层各自的Lamb波频散模式通过夹心粘接剂层相互耦合后叠加组成. 改变影响结构粘接强度的因素, 即粘接剂的性能参数(声阻抗、密度、厚度)和界面切向劲度系数k_t来分析三层结构谐振模式耦合方式的变化,得出结论: 粘接结构粘接性能的变化基本上不改变与被粘铝层相关的固有部分的Lamb波模式, 而它们的耦合模式则在谐振频率上产生平移并会与固有模式进行交换和替代; 不同参数的变化引起的模式演变有各自的规律, 大多可彼此区分.     

The study of exchange coupling in NiFe/Cu/IrMn trilayer structures by MOKE and FMR measurements

The exchange coupling strength of NiFe/Cu/IrMn trilayer films was examined with both a new magneto optical Kerr effect (MOKE) method developed for the exchange coupling field determination and ferromagnetic resonance (FMR) measurements. We found that the value for exchange coupling field obtained by the MOKE technique coincided with FMR result with high accuracy. Other peculiarities of FMR measurements due to interlayer exchange coupling such as angular dependence of resonance field on Cu spacer thickness are also shown in the article.     

Gilbert damping in the layered antiferromagnet CrCl3

We theoretically and experimentally studied the Gilbert damping evolution of both acoustic and optical magnetic resonance modes in the layered flake Cr Cl;with an external magnetic field H applied in plane.Based on a Lagrangian equation and a Rayleigh dissipation function,we predicted that the resonance linewidth△H as a function of microwave frequencyωis nonlinear for both acoustic and optical modes in the Cr Cl;flake,which is significantly different from the linear relationship of△H-ωin ferromagnets.Measuring the microwave transmission through the Cr Cl;flake,we obtained theω–H dispersion and damping evolution△H–ωfor both acoustic and optical modes.Combining both our theoretical prediction and experimental observations,we concluded that the nonlinear damping evolution△H–ωis a consequence of the interlayer interaction during the antiferromagnetic resonance,and the interlayer Gilbert dissipation plays an important role in the nonlinear damping evolution because of the asymmetry of the non-collinear magnetizaiton between layers.     

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.     

The modes of an ultra-cold strongly magnetized charged Bose gas

The modes of a strongly magnetized charged Bose gas are presented for ultra-low temperatures. For longitudinal oscillations propagating parallel to the magnetic field the dispersion relation is found to be dominated by the one-dimensional field-free plasmon dispersion relation as found by Alexandrov, Beere and Kabanov recently in reference [1], while for propagation perpendicular to the magnetic field they are found to be influenced by the cyclotron motion of the particles. Dispersion relations for these modes known as Bernstein modes are given near the cyclotron frequency and its first two harmonics. The dispersion relations for transverse modes in the system are then presented for the cases of photon propagation perpendicular and parallel to the direction of the magnetic field. Received: 3 July 1997 / Revised: 12 August 1997 / Accepted: 4 November 1997     

Theory of magnetostatic waves in a ferrite film with transition layers

A dispersion relation is derived for magnetostatic waves in a ferrite film with inhomogeneous layers near the interfaces. It is shown that the transition layers can be taken into account using a single integrated parameter, namely, the effective film thickness. It is established that the layered structure of the film causes an extra wave damping. The relations obtained can be used to analyze the dispersion and damping of the main modes of magnetostatic waves.     

Anisotropy of the spin-wave resonance spectrum in the case of a dissipative mechanism of spin pinning

Mechanisms leading to anisotropy of dispersion curves of the spin-wave resonance spectrum in magnetic multilayer films are investigated experimentally and theoretically. One of the reasons for the considerable increase in the dispersion-curve slope for the static magnetic field directions intermediate between the parallel and normal ones in relation to the film plane is shown to be connected to the alteration of the equilibrium orientation of magnetization. This factor (in addition to the dominant dissipative mechanism of the spin pinning and to the reactive or dispersive properties of a layer with strong damping) is established to affect the wavenumbers of standing spin waves and cause a difference between the dispersion curves for normal and parallel orientations of the dc magnetic field.     

Bulk and surface magnetostatic modes in superlattices

General dispersion equations for the magnetostatic modes in infinite and semi-infinite superlattices are derived by the transfer matrix method for the case of superlattices with an elementary unit consisting of N (N arbitrary) ferromagnetic layers. The films are assumed to be magnetized parallel to the film surfaces and parallel to an external magnetic field. Explicit forms of the dispersion equations, together with exemplary dispersion curves of surface modes and bands of bulk waves, are given in the case of N = 2.