Tunable Optical Mode Ferromagnetic Resonance in FeCoB/Ru/FeCoB Synthetic Antiferromagnetic Trilayers under Uniaxial Magnetic Anisotropy

Ferromagnetic resonance (FMR) is one of the most important characteristics of soft magnetic materials, which practically sets the maximum operation speed of these materials. There are two FMR modes in exchange coupled ferromagnet/nonmagnet/ferromagnet sandwich films. The acoustic mode has relatively lower frequency and is widely used in radio‐frequency/microwave devices, while the optical mode is largely neglected due to its tiny permeability even though it supports much higher frequency. Here, a realistic method is reported to enhance the permeability in the optical mode to an applicable level. FeCoB/Ru/FeCoB trilayers are carefully engineered with both uniaxial magnetic anisotropy and antiferromagnetic interlayer exchange coupling. This special magnetic structure exhibits a high optical mode frequency up to 11.28 GHz and a maximum permeability of 200 at resonance. An abnormally low inverse switch field (<200 Oe, less than 1/5 of the single layer) is observed which can effectively switch the system from optical mode with higher frequency into acoustic mode with lower frequency. The optical mode frequency and inverse switch field can be controlled by tailoring the interlayer coupling strengths and the uniaxial anisotropy fields, respectively. The tunable optical mode resonance thus can increase operation frequency while reduce operation field overhead in FMR based devices.     

Influence of substrate on the high-frequency permeability of thin iron films

The ferromagnetic resonance (FMR) spectra of thin metallic films obtained by magnetron deposition on polymeric and ceramic substrates are investigated in the strip line at frequencies of 0.13–12 GHz via frequency and external magnetic field sweeping. The influence of mechanical stresses on the FMR spectra of films deposited on an elastic (polyethylene rephthalate) substrate is discussed. The magnetostriction contribution to the anisotropy field of a film, as well as the influence of tensile stresses on the quasi-static permeability and FMR frequency, is estimated. It is demonstrated that the microwave properties of a thin metallic film are also specified by the properties of the substrate with such a film. A distinction in the magnetic properties of films with the same composition, which are deposited on different substrates, is explained in terms of the magnetostriction effect.     

Mechanical Strain‐Tunable Microwave Magnetism in Flexible CuFe2O4 Epitaxial Thin Film for Wearable Sensors

Purely mechanical strain‐tunable microwave magnetism device with lightweight, flexible, and wearable is crucial for passive sensing systems and spintronic devices (noncontact), such as flexible microwave detectors, flexible microwave signal processing devices, and wearable mechanics‐magnetic sensors. Here, a flexible microwave magnetic CuFe₂O₄ (CuFO) epitaxial thin film with tunable ferromagnetic resonance (FMR) spectra is demonstrated by purely mechanical strains, including tensile and compressive strains, on flexible fluorophlogopite (Mica) substrates. Tensile and compressive strains show remarkable tuning effects of up‐regulation and down‐regulation on in‐plane FMR resonance field (H_r), which can be used for flexible tunable resonators and filters. The out‐of‐plane FMR spectra can also be tuned by mechanical bending, including H_r and absorption peak. The change of out‐of‐plane FMR spectra has great potential for flexible mechanics‐magnetic deformation sensors. Furthermore, a superior microwave magnetic stability and mechanical antifatigue character are obtained in the CuFO/Mica thin films. These flexible epitaxial CuFO thin films with tunable microwave magnetism and excellent mechanical durability are promising for the applications in flexible spintronics, microwave detectors, and oscillators.     

Microwave acoustics

During the last few years, generation and propagation of acoustic waves have been extended to frequencies high into the gigacycle region. This paper deals with microwave acoustics, with emphasis on effects and techniques utilized at cryogenic temperatures. The extremely short wavelengths require the use of single crystal propagation media, free from defect scattering, supercooled to reduce wave attenuation from phonon interactions. Interactions of acoustic phonons with other phonons, electrons or holes, and spin waves are possible, with interchanges of energy that can produce attenuation or amplification of acoustic waves. The fundamental characteristics of acoustic wave propagation in crystanine media are discussed, with a review of experimental techniques and results. Microwave acoustic waves in solids and transducers suited to generation and detection are discussed, and a basic analysis of plane wave piezoelectric coupling is presented.     

Spin transport and microwave self-oscillations in magnetic heterostructures with giant magnetoresistance

The phenomena of spin transport and spin-transfer torque between layers of a magnetic hetero-structure with conducting and tunneling interlayers, which can lead to switching of micromagnetic states in the structure??s layers and microwave generation, are considered. The features of spin transport in the field-emission mode for magnetic tunnel structures and problems of the current generation of spin waves in the magnetic film during local spin pumping are discussed. The possibility of the phase locking of the system of nanogenerators on a common magnetic platform and prospects for using nanogenerators based on the effect of spin transport in microwave communication engineering are analyzed.     

微波静磁波模式特性分析

全面分析了磁光薄膜波导中磁化方向对微波静磁波传播模式的影响。给出了不同模式的静磁波色散方程和带宽的一般表达式,首次完整地展现了静磁波的模式分布图。所得结论可用于分析倾斜磁场在改善基于静磁波的新型磁光B ragg器件衍射性能方面所起的作用。     

Application of the smith chart in the analysis of the relaxation properties of magnetostatic oscillations and spin waves in ferrite films

The relaxation properties of three main types of magnetostatic oscillations in a magnetostatic film resonator and nonlinear processes (parametric excitation of spin waves in the first and second bands in the presence of the tangential magnetization of the gallium-substituted yttrium-iron garnet film and foldover in the regime of normal magnetization) are studied in the frequency range 0.8–4.5 GHz. An original method is proposed for the determination of thresholds of the parametric excitation of spin waves using the deformations of Smith chart caused by variations in the measurement power level. The method is used in the highaccuracy analysis of the frequency dependences of threshold power in the presence of tangential magnetization in the regimes of resonances of both surface and backward volume magnetostatic waves. The frequencyfield dependences of the absorption spectra of three main types of magnetostatic oscillations in the linear regime are used to determine the saturation magnetization, anisotropy fields, and unloaded Q factors of resonator at each mode and to calculate the relaxation parameters of the corresponding magnetostatic oscillations. The experimentally measured threshold pump powers are used to calculate the relaxation line widths of the parametrically excited spin waves with the aid of the improved theory of parametric processes that takes into account both cubic and uniaxial anisotropy of the film.     

Magnetic anisotropy in (Ga,Mn)As on GaAs(1 1 3)As studied by magnetotransport and ferromagnetic resonance

The magnetic anisotropy of a 40-nm-thick (Ga,Mn)As film with 5% Mn grown on GaAs(1 1 3)A is studied by means of magnetotransport and ferromagnetic resonance (FMR) spectroscopy. In addition to the cubic and a weak uniaxial in-plane anisotropy, two uniaxial out-of-plane contributions along [1 1 3] and [0 0 1] are found. Using the anisotropy parameters determined from FMR, the longitudinal and transverse resistivities measured as a function of magnetic field orientation and strength are well modelled within the framework of a single ferromagnetic domain. In particular, the low-field data which are strongly affected by sudden jumps of the magnetization are well reproduced.     

Resonant enhancement of magnetic damping driven by coherent acoustic phonons in thin Co2FeAl film epitaxied on GaAs

The magnetic dynamics of a thin Co₂FeAl film epitaxially grown on GaAs substrate was investigated using the timeresolved magneto-optical Kerr measurement under an out-of-plane external field.The intrinsic magnetic damping constant,which should do not vary with the external magnetic field,exhibits an abnormal huge increase when the precession frequency is tuned to be resonant with that of the coherent longitudinal acoustic phonon in the Co₂FeAl/GaAs heterostructure.The experimental finding is suggested to result from the strong coherent energy transfer from spins to acoustic phonons via magnetoelastic effect under a resonant coupling condition,which leads to a huge energy dissipation of spins and a greatly enhanced magnetic damping in Co₂FeAl.Our experimental findings provide an experimental evidence of spin pumping-like effect driven by propagating acoustic phonons via magnetoelastic effect,suggesting an alternative approach to the possible long-range spin manipulation via coherent acoustic waves.     

超导电路与体声波谐振器组成的量子iSWAP门方案

高保真度量子门的物理实现是量子计算和量子通信的关键技术之一。根据电路量子声动力学和量子电动力学,提出了由两个具有较长相干时间的超导transmon qubit和一个具有高机械品质因数的薄膜体声波谐振器组成的量子门方案,体声波谐振器起到类似微波光子通道的作用,使两个transmon qubit之间实现量子态交互。该文先用Butterworth van Dyke模型分析体声波谐振器在方案中的等效电路,构建系统的量子化哈密顿量,再用二能级原子 声子混合量子态形式编码系统的量子态,通过调节外磁场来调控系统的输入态,系统的输出态可通过测量模块得到。在Jaynes Cummings模型下,该系统能完成具有高保真度的量子相位交换（iSWAP）门操作。     

A Short History of Microwave Acoustics

Microwave acoustics may be defined as the subject embodying the propagation of acoustic waves in solid-state materials at-micron-order wavelengths where analysis, design, and componentry realizations are similar to those used by the microwave engineer exploiting electromagnetic waves. Microwave acoustics has a short history, being about 25 years old, but is underpinned by the theory of sound propagation due to Lord Rayleigh of 100 years ago. Microwave acoustic components inherently have several distinct physical origins including volume acoustic waves in solids excited by piezoelectric thin-film transducers and magnetic propagating modes in yttrium iron garnet, both at conventional microwave frequencies; the later surface acoustic-wave (SAW) technology for operation at VHF/UHF and the realm of acoustooptics, which can embody any of the earlier three. Over its 25-year history, microwave acoustics has matured to become a necessary building-block in many radar and communication systems for efficiently carrying out real-time analog signal processing. Contributions to microwave acoustics have been truly international and have spanned many diverse disciplines. The growth of this subject has led to the formation of several companies dedicated to its application.     

Acoustic convolution using nonlinear surface-wave interactions in a piezoelectric semiconductor

Experimental observations of nonlinear interactions in photo-conducting CdS are reported for oppositely travelling 17 MHz surface acoustic waves. The results for acoustic convolution and 2nd-harmonic generation indicate that the piezoelectric electron?phonon interaction may have important application to nonlinear signal-processing techniques employing surface waves.     

提高液体中脉冲激光致声转换效率的理论研究

从液体中脉冲激光致声的理论出发,讨论了热膨胀机制下提高光声转换效率的措施,并着重讨论了不同液体媒质的特性对转换效率的影响;基于Helmholtz共振器的共振频率和放大特性理论,讨论了通过共振光声池的设计提高光声转换效率的可行性;指出在对光致声波可重复性和可控制性没有特殊要求的情况下,可采用高功率光纤激光器,通过汽化机制或介电击穿机制激发声波,提高转换效率.     

Fabrication Method,Ferromagnetic Resonance Spectroscopy and Spintronics Devices Based on the Organic-Based Ferrimagnet Vanadium Tetracyanoethylene

Organic-based magnetic materials have been used for spintronic device applications as electrodes of spin aligned carriers and spin-pumping substrates. Their advantages over more traditional inorganic magnets include reduced magnetic damping and lower fabrication costs. Vanadium tetracyanoethylene, V[TCNE]_x (x ≈ 2), is an organic-based ferrimagnet with an above room-temperature magnetic order temperature (T_c ≈ 400 K). V[TCNE]_x has deposition flexibility and can be grown on a variety of substrates via low-temperature chemical vapor deposition (CVD). A systematic study of V[TCNE]_x thin-film CVD parameters to achieve optimal film quality, reproducibility, and excellent magnetic properties is reported. This is assessed by broadband ferromagnetic resonance (FMR) that shows most narrow linewidth of ≈1.5 Gauss and an extremely low Gilbert damping coefficient. The neat V[TCNE]_x films are shown to be efficient spin injectors via spin pumping into an adjacent platinum layer. Also, under an optimized FMR linewidth, the V[TCNE]_x films exhibit Fano-type resonance with a continuum broadband absorption in the microwave range, which can be readily tuned by the microwave frequency.     

Giant Electric Field Tuning of Magnetic Properties in Multiferroic Ferrite/Ferroelectric Heterostructures

Multiferroic heterostructures of Fe₃O₄/PZT (lead zirconium titanate), Fe₃O₄/PMN‐PT (lead magnesium niobate‐lead titanate) and Fe₃O₄/PZN‐PT (lead zinc niobate‐lead titanate) are prepared by spin‐spray depositing Fe₃O₄ ferrite film on ferroelectric PZT, PMN‐PT and PZN‐PT substrates at a low temperature of 90 °C. Strong magnetoelectric coupling (ME) and giant microwave tunability are demonstrated by a electrostatic field induced magnetic anisotropic field change in these heterostructures. A high electrostatically tunable ferromagnetic resonance (FMR) field shift up to 600 Oe, corresponding to a large microwave ME coefficient of 67 Oe cm kV^?1, is observed in Fe₃O₄/PMN‐PT heterostructures. A record‐high electrostatically tunable FMR field range of 860 Oe with a linewidth of 330–380 Oe is demonstrated in Fe₃O₄/PZN‐PT heterostructure, corresponding to a ME coefficient of 108 Oe cm kV^?1. Static ME interaction is also investigated and a maximum electric field induced squareness ratio change of 40% is observed in Fe₃O₄/PZN‐PT. In addition, a new concept that the external magnetic orientation and the electric field cooperate to determine microwave magnetic tunability is brought forth to significantly enhance the microwave tunable range up to 1000 Oe. These low temperature synthesized multiferroic heterostructures exhibiting giant electrostatically induced tunable magnetic resonance field at microwave frequencies provide great opportunities for electrostatically tunable microwave multiferroic devices.     

垂直不均匀磁场中静磁波的传播特性

本文理论分析了垂直不均匀磁场作用下磁性薄膜中静磁波的传播特性,具体计算了抛物线分布的不均匀磁场对静磁对表镣波振幅的影响,计算表明,在适当分布的不均匀场作用下,与均匀磁场情形相比,波导中传播的 振幅有所增加,从而也增强了静民导波光相互作用时的射效应。     

Interaction of acoustic waves with nuclear spins in solids

A review of the interactions of high-frequency acoustic waves with nuclear spins in solids is presented here. These interactions result from the modulation of internal magnetic fields and electric field gradients by the impressed acoustic wave. The acoustic technique is especially useful in investigating the coupling of nuclear spins to the lattice vibrations (phonons) of the solid, and in many ways serves to complement the technique of nuclear magnetic resonance. After a qualitative introduction, the theory of nuclear spin-phonon absorption is given, both for the general case and for the special case of dynamic electric quadrupole coupling. The techniques of direct acoustic absorption and of acoustic saturation are described, and a brief summary is given of the results obtained to date.     

Design of a Full Waveguide Bandwidth High-Power Isolator

An analysis of the microwave fields in rectangular waveguide indicates that circular polarization of the H-vector components exists at two planes only and the location of these planes is frequency dependent. Also, an examination of Kittel's theory reveals that resonance in ferrites can be made to occur at different frequencies for a constant value of dc magnetic biasing field provided the ferrites are characterized by different values of saturation magnetization. These two effects have been used concurrently in the design of an X-band waveguide isolator for operation over a 45 per cent bandwidth, and at high power levels. The theory underlying the design of this isolator is presented. Included is a treatment of the parameters which affect the isolator design. Finally, an operative isolator is described and its experimental characteristics are reported.     

The loss mechanism in a composite acoustic microwave resonator based on a sapphire single crystal

Acoustic loss in a composite longitudinal-wave resonator structure operating in the microwave band are studied. The resonator structure contains a rather thick sapphire plate coated with a piezoelectric film with electrodes. It is shown that, in a wide frequency band, attenuation is determined by interaction with acoustic phonons. The role of diffraction loss is discussed. Scattering of acoustic waves by asperities of reflecting surfaces is considered, and the contribution of scattered acoustic waves to the total loss is estimated.     

磁光薄膜波导中光导波的模式转换和衍射效率计算

根据耦合模理论,应用微扰方法分析了Ｂｉ：ＹＩＧ薄膜波导中斜向静磁场对静磁波与导波光相互作用的影响,计算了斯托克斯和反斯托克斯相互作用中导波光的模式转换效率和衍效率。