Voltage shift of hysteresis loops of SrBi2Ta2O9 thin films under unipolar stress

Voltage shifts of hysteresis loops of metalorganic decomposition (MOD)-derived SrBi₂Ta₂O₉ (SBT) thin films, known as imprint, have been observed after exposing the thin-film capacitors to unipolar pulses. The voltage shift changes with cumulative total time at maximum voltage, following a relationship with no pulse-width dependence. The origin of the voltage shift is briefly discussed in terms of an internal bias field induced by injected electrons trapped at positive polarity. The pulse-measurement responses are greatly affected by the internal bias field, even though no imprint failure was observed up to 10¹⁰ unipolar pulses. The voltage shift and asymmetric properties can be removed easily by applying bipolar pulses of saturation amplitude. Received: 27 June 2000 / Accepted: 16 August 2000 / Published online: 5 October 2000     

Relic Density of Asymmetric Dark Matter in Modified Cosmological Scenarios

We discuss the relic abundance of asymmetric Dark Matter particles in modified cosmological scenarios where the Hubble rate is changed with respect to the standard cosmological scenario. The modified Hubble rate leaves its imprint on the relic abundance of asymmetric Dark Matter particles if the asymmetric Dark Matter particles freeze-out in this era. For generality we parameterize the modification of the Hubble rate and then calculate the relic abundance of asymmetric Dark Matter particles and anti-particles. We find the abundances for the Dark Matter particles and anti-particles are enhanced in the modified cosmological models. The indirect detection signal is possible for the asymmetric Dark Matter particles due to the increased annihilation rate in the modified cosmological models. Applying Planck data, we find the constraints on the parameters of the modified cosmological models.     

GdFeCo/TbFeCo磁超分辨磁光记录薄膜研究

用磁控溅射法制备了GdFeCo/TbFeCo交换耦合两层薄膜,利用不同温度的克尔磁滞回线和VSM磁滞回线研究了读出层(GdFeCo)变温磁化方向变化过程.结果表明,随温度升高读出层从平面磁化转变为垂直磁化,交换耦合两层薄膜具有中心孔探测磁超分辨的基本性能.转变过程主要受饱和磁化强度（M_s）的影响,在GdFeCo的补偿温度附近,读出层的磁化强度较小,退磁场能也较小,在交换耦合的作用下,使读出层(GdFeCo)的磁化方向发生转变.磁化方向的转变在75℃~125℃的温度范围内变化较快.     

Bending properties of two- and three-dimensional-shaped nanoparticles fabricated via substrate conformal imprint lithography

Nanoimprinting enables the implementation of nanoparticle shapes with complex 2D shapes involving different materials. In addition to these objects, this article presents 3D-shaped nanoparticles fabricated by substrate conformal imprint technique. The imprint polymer AMONIL is used either in pure form or in combination with fluorescent dyes for the preparation of particles. The substrate conformal imprint lithography process, including etching and particle release, is conducted for both materials in a similar fashion. In this work, cuboidal particles with a high aspect ratio (1:120) are compared to particles with a T-shaped cross section with respect to their abilities to enhance or reduce their stiffness. Additionally, particles with a high aspect ratio are compared to particles with a lower aspect ratio (1:20). The local stiffness is found to depend strongly on the particle thickness and the geometry of their cross section. Thicker and 3D T-shaped particles present higher local stiffness than thinner and 2D cuboidal-shaped particles. The local bending angle was determined to be 77° for 2D-shaped particles and 83° for 3D-shaped particles, of the same total height of 176 nm. Very thin particles (<50 nm) of high aspect ratio prefer to curl finally forming loops.     

Imprinted bidirectional waveguide platform for large-core optical transceiver

We introduce a new configuration for large-core optical transceiver platforms based on asymmetric three-dimensional multimode Y junctions. We developed a simply structured bidirectional waveguide platform without using a wavelength division multiplexing filter or angled mirror. This structure was designed with two different size waveguides by using the three-dimensional ray-tracing method. This structure transmitted nearly 100% power in each direction, upstream and downstream. This simple and cost-effective structure was fabricated by the imprint process using a metallic master fabricated by an ultraprecision machining method. The experimental results show that this structure is suitable for bidirectional communications in large-core optical transceivers at 155 Mbits/s.     

Spatial dependence of the frequency spectrum of a rotating optical beam

A rotating optical beam displaced relative to the rotational axis becomes polychromatic due to the rotational Doppler effect. The case where the initial beam has the form of a superposition of two Laguerre-Gauss modes and carries an elementary image in the form of an asymmetric intensity distribution is considered. The spatial distribution of the monochromatic components in the beam cross section is determined.     

Microstructure of high-pressure-synthesized diamonds under rapid quenching and electron irradiation

A type of synthetic diamond single crystal about 0.4–0.5 mm in dimension prepared under high pressure–high temperature (HPHT) in the presence of a FeNi molten catalyst was quenched from HPHT and irradiated with 300 keV electrons at room temperature. Transmission electron microscopy was employed to examine the microstructure of the diamond single crystal before and after electron irradiation. It was found that there exists a large amount of cellular interfaces in the quenched diamond sample, which indicates the growth condition of the diamond under HPHT. Hexagonal dislocation loops about several tens of nanometers in dimension were observed in the high-pressure-synthesized diamond single crystal before electron irradiation, which strongly suggests that a number of vacancies were quenched-in due to rapid quenching from high temperature at the end of diamond synthesis, and were aggregated in the synthetic diamond to form vacancy disks on the (111) plane, the collapse of such vacancy disks forming vacancy-type dislocation loops. After electron irradiation, it was found that defect clusters present as interstitial-character dislocation loops were formed in the electron-irradiated region of the diamond. The interstitial dislocation loops grow with increase of the irradiation time. The present study, in comparison to previous work on ion implantation on diamond, indicates that electron irradiation does not induce a phase transformation but produces interstitial dislocation loops due to the migration of interstitial atoms and vacancies. The result of the study directly indicates that interstitials and vacancies in diamond are mobile at room temperature under electron irradiation. Nitrogen, as the most important kind of impurity contained in the HPHT as-grown diamond, probably acts as nucleation of the interstitial loops. Received: 16 November 2001 / Accepted: 12 June 2002 / Published online: 17 December 2002 RID="*" ID="*"Corresponding author. E-mail: yinlw@sdu.edu.cn     

Exchange bias in patterned FeMn/NiFe bilayers

Electron beam lithography and ion beam etching have been used to pattern a wire-like array in FeMn/NiFe bilayers. The variation of hysteresis loops with the etching depth in FeMn layer has been presented, and it has been found that with increasing etching depth the coercivity increases and M–H loops show an asymmetric kink. Detailed studies of the magnetic behaviors of the asymmetric kink in the patterned sample with 3.5 nm thick FeMn layer have been performed, and a magnetization component perpendicular to the wire direction has been observed.     

氢离子辐照纯钒中形成的位错环

钒合金作为聚变堆候选材料, 其辐照损伤行为一直是关注的重点. 研究辐照时形成的位错环的性质, 其意义在于揭示纯钒中辐照空洞的长大机理. 这种机理表现为不同类型位错环对点缺陷吸收的偏压不同, 从而影响金属的辐照肿胀. 本文利用加速器对纯钒薄膜样品进行氢离子辐照, 然后, 利用透射电镜的inside-outside方法分析氢离子辐照所形成的位错环的类型. 结果表明, 在氢离子辐照纯钒中没有发现柏氏矢量b=<110>的位错环, 只有柏氏矢量b=1/2<111>和b=<110>的位错环, 这两种位错环的惯性面处于{110}-{112}之间. 能确定性质的位错环全部为间隙型位错环, 未发现空位型位错环.     

On the effects of a general form of the initial runout on the oscillation frequencies and critical speeds of a spinning disk

This paper is concerned with the effect of the lack of flatness on the dynamics of spinning disks. Of particular interest is the study of the effect of an unsymmetrical initial runout on the oscillation frequencies and the critical speeds of the spinning disks. It is assumed that a spinning disk is initially warped in an initial asymmetric shape. Using Von Karman's plate theory, the equations of motion are derived in a rotating frame. Taking advantage of the orthogonal properties of the eigenfunctions of a stationary disk, the lateral displacement and the stress function are expressed as their summation. Since these eigenfunctions produce an orthonormal space, any shape and level of initial runout can be written as their summation also. Using Galerkin's method, the equations of motion are discretized and a set of coupled linear equations are found taking into account the effect of an initial arbitrary runout. The numerical results are found to have a good agreement with those obtained using ANSYS. It is found that the natural frequencies of the spinning disk calculated in the space fixed frame increases due to an initial runout. When the initial runout is assumed to be asymmetric, it is found that, due to asymmetric stress distributed in the disk, a frequency split between the backward and forward traveling waves of a given preferential mode of a stationary disk occurs. It is also seen that in some cases the initial runout in the form of the (n,m) mode has the least effect on the natural frequencies of the backward traveling waves of the same mode. As such it is observed that in the case the critical speed the (n,m) mode is less sensitive to an initial runout in the form of the (n,m) mode. To verify the accuracy of the numerical predictions, experiments were conducted on two disks, one which was flat and the other that had an initial nonflatness in the form of the (0,2) mode. The numerical and experimental results indicate a close correspondence.     

Observation of the external-ac-current-induced dc voltage proportional to the steady current in superconducting loops

A dc voltage induced by an external ac current was observed in a system of asymmetric aluminum loops at temperatures corresponding to 0.95–0.98 of the superconducting transition temperature. The voltage magnitude and sign change periodically in a magnetic field with a period corresponding to the magnetic flux quantum through the loop. The amplitude of these oscillations depends nonmonotonically on the amplitude of ac current and is almost independent of its frequency in the range from 100 Hz to 1 MHz. The observed phenomenon is interpreted as the result of displacing the loop into a dynamic resistive state by the external current, where the loop is “switched” back and forth between the closed superconducting state with a nonzero steady current and the nonclosed state with a nonzero resistance along the loop circle. It is shown that voltages are summed up in a system of loops connected in series. For systems with one, three, and twenty loops, the voltage reaches 10, 40, and 300 μ V, respectively.     

Spontaneous supercurrent induced by ferromagnetic pi junctions

We present magnetization measurements of mesoscopic superconducting niobium loops containing a ferromagnetic (PdNi) pi junction. The loops are prepared on top of the active area of a micro-Hall sensor based on high mobility GaAs/AlGaAs heterostructures. We observe asymmetric switching of the loop between different magnetization states when reversing the sweep direction of the magnetic field. This provides evidence for a spontaneous current induced by the intrinsic phase shift of the pi junction. In addition, the presence of the spontaneous current near zero applied field is directly revealed by an increase of the magnetic moment with decreasing temperature, which results in half integer flux quantization in the loop at low temperatures.     

Micromagnetic simulation of magnetic vortex cores in circular permalloy disks: Switching behavior in external magnetic field

Switching behaviors of magnetic vortex cores under external magnetic field in submicron circular permalloy disks have been systematically studied by using micromagnetic simulations. Simulation results show that the vortex core is stable in out-of-plane field even when it is located at the edge of the disk. The out-of-plane switching field H_sw is strongly dependent on the thickness of the disk. The core polarity and the vortex chirality can be modulated simultaneously on purpose by using a tilted field far smaller than the out-of-plane switching field H_sw. Moreover, it is found that the core polarities in asymmetric disks do not follow the direction of the z projection of the external saturation field.     

基于中心-射线模型的印鉴识别方法及其应用

支票中的有效印鉴是支票流通有效性的重要体现。通过对支票印鉴有效性的识别来达到对支票流通有效性识别的目的。根据我国支票图像的特点提出了基于中心_射线模型的有效印鉴识别方法。该方法是通过对印鉴各成份区域之间拓扑关系的识别来达到对有效印鉴识别的目的。在将该方法用于我国支票印鉴识别的同时,还利用了印鉴的色彩特征。实验结果表明,该方法可有效地识别我国支票中的有效印鉴,有效印鉴识别的错误排除率为0%,错误接收率为23.8%。     

Topology-like dynamical behavior of magnetization reversal in exchange-bias systems

In an exchange-bias system, the barriers with intrinsic potential energy may be asymmetric due to unidirectional anisotropy. Based on the Stoner-Wohlfarth model, we show that the asymmetric barriers may lead to four kinds of dynamical process underlying the hysteresis-loop measurement. These kinds of dynamical processes are different in a topology-like property, which can be controlled by the orientation of the external field. In our study, a new analysis approach has been proposed to reveal the dynamical behaviors of magnetization reversal. With this approach, coercivity, exchange-bias field, and asymmetry of hysteresis loops can be quantitatively obtained.     

The distribution of dislocations in slip bands of Fe-3% Si alloy single crystals deformed by bending

The distribution of dislocations at the ends of slip bands was studied by etching on surfaces parallel to the slip plane. In these places the slip band is formed by groups of asymmetric dislocation loops several hundred microns wide. The long mixed-type parts of these loops running nearly equidistantly and lying in near planes, are the equilibrium arrangement of dislocations of the same sign in the shear stress gradient. From the results we can judge that the dislocation sources are at larger distances from the ends of the slip bands and that the dislocation groups at the ends of the slip bands are sources of large stress fields.     

Double Loops and Pitchfork Symmetry Breaking Bifurcations of Optical Solitons in Nonlinear Fractional Schrödinger Equation with Competing Cubic-Quintic Nonlinearities

Symmetry breaking bifurcations of solitons are investigated in framework of a nonlinear fractional Schrödinger equation (NLFSE) with competing cubic-quintic nonlinearity. Some prototypical characteristics of the symmetry breaking, featured by transformations of symmetric and antisymmetric soliton families into asymmetric ones, are found. Stable asymmetric solitons emerge from unstable symmetric and antisymmetric ones by way of two different symmetry breaking scenarios. A twisting branch, featured with double loops bifurcation, bifurcates off from the base branch of symmetric soliton solutions and crosses it, then merges into the base branch driven by the competitive nonlinear effect. A supercritical pitchfork bifurcation is bifurcated from the branch of antisymmetric soliton solutions and gives rise to a supercritical pitchfork bifurcation. Stability of the soliton families is explored by linear stability analysis. With the increase of the Lévy index, stability region induced by the twisting loops bifurcation is expanded. However, stability region of the pitchfork bifurcation is shrunk on the parameter plane of the Lévy index and the soliton power.     

Reconstruction of emission coefficients for a non-axisymmetric coupling arc by algebraic reconstruction technique

A preliminary investigation of tomographic reconstruction of an asymmetric arc plasma has been carried out. The objective of this work aims at reconstructing emission coefficients of a non-axisymmetric coupling arc from measured intensities by means of an algebraic reconstruction technique (ART). In order to define the optimal experimental scheme for good quality with limited views, the dependence of the reconstruction quality on three configurations (four, eight, ten projection angles) are presented and discussed via a displaced Gaussian model. Then, the emission coefficients of a free burning arc are reconstructed by the ART with the ten-view configuration and an Abel inversion, respectively, and good agreement is obtained. Finally, the emission coefficient profiles of the coupling arc are successfully achieved with the ten-view configuration. The results show that the distribution of emission coefficient for the coupling arc is different from centrosymmetric shape. The ART is perfectly suitable for reconstructing emission coefficients of the coupling arc with the ten-view configuration, proving the feasibility and utility of the ART to characterize an asymmetric arc.     

Observation of a half step magnetization in the {Cu3}-type triangular spin ring

We report pulsed field magnetization and ESR experiments on a {Cu3} nanomagnet, where antiferromagnetically coupled Cu(2+) (S = 1/2) ions form a slightly distorted triangle. The remarkable feature is the observation of a half step magnetization, hysteresis loops, and an asymmetric magnetization between a positive and a negative field in a fast sweeping external field. This is attributed to an adiabatic change of magnetization. The energy levels determined by ESR unveil that the different mixing nature of a spin chirality of a total S = 1/2 Kramers doublet by virtue of Dzyaloshinskii-Moriya interactions is decisive for inducing half step magnetization.     

The effects of annealing on the structure and magnetic properties of CoNi patterned nanowire arrays

NiCo alloy nanowire arrays were fabricated by using an electrochemical method in a porous anodic aluminum oxide (PAO) template. X-ray-diffraction results showed that there was a preferred orientation in the CoNi nanowire arrays with Ni content ranging from 0.2 to 0.8 in the as-electro-deposited state, while a random orientation was observed after the sample was heat treated in an argon atmosphere. When the shape anisotropy is very high in the sample, it is found that the squareness (Mr/Ms) of the hysteresis loops for the samples is only about 0.6 before annealing, but increases to about 0.9 after annealing. All the results are discussed qualitatively and an explanation for the magnetic reversal mechanism in terms of a localized magnetization model is given. As the CoNi alloy nanowire arrays have high bit densities, they can be used as perpendicular magnetic recording media of high-density quantum magnetic disks. Received: 8 January 2001 / Accepted: 6 June 2001 / Published online: 30 August 2001