A nanometric electron multiplexer

A simple nanostructure resonantly coupling two semiconductor quantum wires is proposed as an electron multiplexer, which selectively transfers electrons of a given energy E₀ from one wire to the other, while letting all the neighbouring states within a certain energy range around E₀ propagate virtually unaffected along the input wire. Closed-form expressions are derived for characteristic wire lengths within the coupling structure facilitating such a directional transfer, which enables one to determine optimal parameters for the device fabrication.     

Second magnon in antiferromagnets

Hydrodynamic equations are derived microscopically for Heisenberg antiferromagnets with inclusion of quasimomentum as an almost conserved quantity. For finite external and anisotropy fields, the hydrodynamic quantities are magnetization, energy and momentum density. At small fields, the propagating mode is essentially an oscillation of the local temperature. For high fields it is a wave in the longitudinal magnetization. In the absence of both fields, the staggered magnetization and not the magnetization itself is coupled to momentum and energy. The propagating mode is mainly an energy wave. The propagating part in the staggered magnetization is inversely proportional to the wavelength.     

磁子转矩翻转磁矩研究

磁子是自旋波量子化的准粒子。磁子具有在绝缘磁性材料中无热耗散、低阻尼、长距离传输自旋的优势,避免了因电荷流动而产生焦耳热,可以克服日益显著的器件发热问题,因此磁子器件在低功耗信息存储与计算领域具有潜在应用前景。文章首先介绍了自旋波和磁子的概念,磁子具有的优势和研究价值;然后总结了磁子在铁磁和反铁磁绝缘体中输运以及新型磁子器件方面的最新研究结果;最后详细介绍了室温下实现磁子转矩驱动磁矩翻转的最新研究工作。这些工作对发展磁子学,实现低功耗、高速磁子型器件及应用具有较为重要的现实意义。     

High frequency magnon generation by nonequilibrium electrons and the instability of the magnon system

The high frequency magnon generation by nonequilibrium electrons polarized opposite the magnetization vector is investigated. At some conditions the avalanche-type generation of magnons with wavevectors along the magnetization takes place and the magnon system becomes unstable.     

Effect of optical phonon‐magnon interaction on the magnon softening at finite temperature

A magnon‐phonon interaction model is set up in a two‐dimensional ferromagnetic compound square‐lattice system. Using the Matsubara Green function theory we calculated the magnon dispersion curves on the main symmetric line in Brillouin zone, compared the influences of the magnetic ion optical phonon with non‐magnetic ion optical phonon on the magnetic excitation of the system and discussed the influences of various parameters on the magnon softening. The lower Debye temperature of ferromagnetic materials is, the more likely the magnon softening occurs. It turned out that the optical phonon‐magnon coupling plays an important role on the magnon softening, the longitudinal optical phonon contributes the most to the magnon softening and magnon damping. It is also found that the contribution of the non‐magnetic ion to the magnon softening and magnon damping is more significant than that of magnetic ion when the mass of the magnetic ion is less than that of the non‐magnetic ion, or the mass of magnetic ion and the non‐magnetic ion are equal.     

Phonon and magnon widths in metamagnets

Microscopic expressions for the couplings of the phonons corresponding to the rigid motions of the waters of hydration with both transverse and longitudinal spin fluctuations are given for the linear chain metamagnetic systems FeCl₂·2H₂O, CoCl₂·2H₂O, and CoBr₂·2H₂O. The processes which can give large, temperatures dependent widths of spin waves and of some phonons for temperatures approaching the Neél temperature are discussed.     

Independent magnon states on magnetic polytopes

For many spin systems with constant isotropic antiferromagnetic next-neighbour Heisenberg coupling the minimal energies E _min(S) form a rotational band, i.e. depend approximately quadratically on the total spin quantum number S, a property which is also known as Landé interval rule. However, we find that for certain coupling topologies, including recently synthesised icosidodecahedral structures this rule is violated for high total spins. Instead the minimal energies are a linear function of total spin. This anomaly results in a corresponding jump of the magnetisation curve which otherwise would be a regular staircase. Received 27 August 2001 and Received in final form 18 October 2001     

非线性激发的磁激子对的振荡特性

通过分析放置于微波谐振腔中的磁有序晶体中的磁激子对激励过程，推导出了磁激子对的运动方程，发现磁激子对不能被认为是两个单个的磁激子的一般组成，而是可以整体的看作为一个具有非线性行为的单模谐振子.依据微波谐振腔与磁激子对集体形成的谐振器之间的耦合作用的机理，可以定性解释在有关磁激子对激励实验中所出现的双峰现象.     

Cherenkov magnon excitations by a sub-relativistic magnetic monopole

A magnetic monopole moving faster than the magnon phase velocity in a given magnetic medium will create a magnon Cherenkov radiation in this medium. Typical velocities of interest are in the ～10^?4c range. In this range most non-induction detection mechanisms are inefficient.     

Effect of photons on the magnon splitting

The self energy of a uniform magnon due to splitting into two magnons of oppositely directed momenta is calculated in the presence of a magnon-photon interaction, and it is found that the magnons and the photons form excitations of mixed character. Thus there is a net correction to the magnon splitting due to an interference.     

Dispersion properties of a nonreciprocal magnon crystal

A magnon crystal is created on the basis of a metal–dielectric–ferrite structure inserted into a spatially periodic magnetic field. The dispersion characteristics of the crystal are measured using a movable probe. The nonreciprocity of the magnon crystal is determined. This property is reflected in the difference betwen the dispersion characteristics of waves propagating in opposite directions. It is shown that the Brillouin zone is located asymmetrically with respect to zero in the space of wave numbers.     

Phonons in a magnon superfluid and symmetry-breaking field

Recent experiments [1,2] on the measurement of the spectrum of the Goldstone collective mode of a coherently precessing state in ³He-B are discussed using the presentation of the coherent-spin precession in terms of the Bose-Einstein condensation of magnons. The mass in the spectrum of the Goldstone boson—a phonon in the superfluid magnon liquid—is induced by the symmetry-breaking field, which is played by the RF magnetic field. The text was submitted by the author in English.     

八信道高温超导多路器的实验研究

文中首先分析八信道高温超导多路器设计的方案,以及实现八信道高温超导多路器的技术;给出了用MgO基片为衬底,YBCO超导膜制备的高温超导滤波器设计仿真曲线及实际测试曲线;并对多路器所用制冷器的制冷量进行了计算;最后给出八信道高温超导多路器的实际测试曲线。     

ATR mode of surface magnon polaritons on YIG

The first discussion on ATR mode of surface magnon polaritons on semi- infinite YIG is presented for the Otto configuration (polyethylene-air-YIG geometry). Damping and the effect of retardation are included in the analysis. The thickness of the air layer appropriate for ATR measurements is determined.     

Quantum magnonics: The magnon meets the superconducting qubit

The techniques of microwave quantum optics are applied to collective spin excitations in a macroscopic sphere of a ferromagnetic insulator. We demonstrate, in the single-magnon limit, strong coupling between a magnetostatic mode in the sphere and a microwave cavity mode. Moreover, we introduce a superconducting qubit in the cavity and couple the qubit with the magnon excitation via the virtual photon excitation. We observe the magnon–vacuum-induced Rabi splitting. The hybrid quantum system enables generation and characterization of non-classical quantum states of magnons.     

Monte Carlo simulation of nanometric cutting

Nanometric cutting of single-crystal materials at conventional cutting speeds (5?m?s^?1) is simulated for the first time using a new Monte Carlo method that is applicable to systems that are neither canonical nor microcanonical. This is accomplished by defining a local temperature in the cutting zone using the thermal analysis developed by Komanduri and Hou for conventional machining. Extension of this method to the nanometric regime permits an accurate estimate of the local temperature in cutting. This temperature is then employed in the Boltzmann probability distribution function that is used to determine the acceptance–rejection of Monte Carlo moves in the simulation. Since cutting speed is closely related to cutting temperature, the cutting speed enters the calculation via the thermal analysis equations. The method is applied to nanometric cutting of single-crystal aluminium with the crystal oriented in the (001) plane and cut in the [100] direction. Three positive rake cutting tools, namely 10°, 30° and 45°, are employed to investigate the effect of the rake angle on the forces, the specific energy and the nature of the chip formation. The method is evaluated by direct comparison with corresponding molecular dynamics simulations conducted under the same conditions.