Resonance magnetoplasticity in the EPR scheme under ultralow magnetic fields

Resonance relaxation displacements of dislocations in NaCl crystals exposed to crossed ultralow magnetic fields (static field B = 26–261 μT and radiofrequency field B ～ 3 μT) in the electron paramagnetic resonance scheme are studied. The effect is also observed in the magnetic field of the Earth when crossed with a pulsed pump field with a resonance duration of ～0.5 μs. Changes in the microhardness of crystals of ZnO, triglycine sulfate, and potassium hydrogen phthalate after their exposure to the magnetic field of the Earth and the orthogonally directed pump field are found out.     

The response of the dielectric susceptibility to an external electric field around the phase transition temperature in Li:KTaO3

Experimental results of measurements of dielectric susceptibility vs applied electric field at various temperatures on 3.5 and 8% Li: KTaO₃ are presented. It is found that there is an enhancement of the dielectric susceptibility as a function of increasing applied electric field at temperatures below ～ 90 K for the 8% Li crystal and at temperatures below ～ 60 K for the 3.5% Li crystal. The results are consistent with a slightly first-order phase transition.     

铜基碳纳米管薄膜的制备及其强流脉冲发射特性研究

为了研究碳纳米管薄膜的强流脉冲发射特性, 采用酞菁铁高温热解方法在机械抛光铜基底上直接生长了碳纳米管薄膜 (Cu-CNTs), Cu-CNTs生长方向各异. 在20 GW脉冲功率源系统中采用二极结构对Cu-CNTs的强流脉冲发射特性进行研究, 研究结果表明: 在单脉冲发射条件下, 随脉冲电场峰值的增大, Cu-CNTs薄膜的发射电流峰值呈线性增加, 当宏观场强为15.5 V/μ时, 发射脉冲电流的峰值可达到5.56 kA, 对应的发射电流密度0.283 kA/cm², 当宏观场强达到32.0 V/μ时, 发射脉冲电流的峰值可达到18.19 kA, 对应的发射电流密度0.927 kA/cm², 发射电流能力明显优于已有报道. 在相同峰值, 连续多脉冲情况下, 碳纳米管薄膜具有良好的发射可重复性, 且发射性能稳定. 关键词： 强流脉冲发射 碳纳米管 铜基底 稳定性     

箭载双臂式电场仪的原理与设计

在介绍双臂式电场仪探测原理的基础上,给出了子午工程探空火箭搭载的双臂式电场仪的具体设计.为了降低探针的不对称和不一致性,采用了铝制球形探针设计,使用石墨涂层以减少表面不均匀性,并采用独特的外形设计来消除支撑臂阴影影响|在信号处理部分,为了能提高系统动态范围,采用了分频段处理的方法.最后,结合整体系统设计的需要提出了几点误差考虑,并给出了系统性能测试结果.所设计的电场仪带宽0～5 MHz,直流探测范围为0.1 mV/m～±1 V/m,交流探测范围为10 μV/m～50 mV/m,可以实现对电场强度为0～±1 V/m的空间电场进行二维测量.     

Electron localization and superconductivity in very thin epitaxially grown Ag films on Ge (001)

Transport properties of very thin (2.5 monolayer) films of Ag epitaxially grown on clean Ge (001) substrates are reported. The films consist of a monolayer coverage plus isolated three dimensional islands. Below ～70°K the conductivity is dominated by the metal film and displays the temperature and electric and magnetic field dependences characteristic of metallic weak localization in two dimensions. Below ～2°K the resistance drops rapidly in a manner resembling an incomplete superconducting transition. The resistance is restored by application of a magnetic field of ～20 KGauss at 0.6°K.     

依据光谱研究闪电回击通道核心的特征参数

闪电回击通道核心中的大电流及其强电磁辐射是引发多种雷电灾害的主要根源。随着现代科技的飞速发展,闪电防护工作显得越为重要。为了完善闪电防护系统,需要从描述闪电回击通道核心的特征参数入手深入研究闪电通道形成和发展过程的微观物理机制。截至目前,光谱观测是获取闪电通道核心特征参数的最佳手段。2015年夏天在青海高原地区的野外试验中,利用由高速摄像机作为记录系统组装的无狭缝光栅摄谱仪,结合快天线地面电场测量仪,记录到一次包括四个回击的云地闪电放电过程的光谱以及与之同步的快电场变化信息。依据光谱,结合等离子体理论计算得到闪电回击通道核心的电导率。在此基础上,应用闪电电动力学模型计算了闪电回击速度、峰值电流、贯穿通道核心的电磁场以及通道核心单位长度的峰值功率等特征参数。结果表明,回击速度在(1.2～2.3)×108 m·s-1的范围内;贯穿回击通道核心的轴向电场、径向电场和磁感应强度的最大值分别在(1.42～1.74)×105 V·m-1,(8.22～9.99)×108 V·m-1和(1.51～2.83) T的范围内。当闪电回击的峰值电流在(7.52～24.05) kA的范围内时,回击通道核心的峰值功率在(0.63～1.92)×109 W·m-1的范围内。另外,分析了电导率、起始电场峰值、回击速度和峰值电流与峰值功率之间的相关性,结果发现峰值电流和峰值功率具有良好的线性关系。研究结果可为探索闪电回击通道形成和发展过程的微观物理机制提供参考依据。     

Exchange bias tuned by cooling field in La0.2Ca0.8MnO3 nanoparticles

We report the magnetic properties in the nanosized charge ordering manganite La_0.2Ca_0.8MnO₃ with an average particle size ～50 nm. The sample exhibits ferromagnetism at low temperatures. The exchange bias phenomenon is observed when the sample is cooled down in an external magnetic field. Moreover, the exchange bias field is dependent on the cooling field and shows a maximum of ～520 Oe under a cooling field ～5 kOe. The exchange bias effect can be attributed to the exchange coupling between the ferromagnetic shell and antiferromagnetic core. The decrease of exchange bias field in high cooling field can be attributed to the growth of ferromagnetic component under high cooling field.     

Effect of magnetic field on the IR optical properties of dielectrics

Magnetic-field induced changes revealed in reflectance spectra R(λ) of nonmagnetic dielectrics Al₂O₃, LiF, and MgO in the IR range (λ = 2.5–25 μm) are reported. The reflectance spectra are shown to have specific features in the vicinity of the wavelengths corresponding to optical phonon mode excitation in these crystals, with the magnetic field giving rise to a noticeable change of reflectance ΔR/R(λ) at these wavelengths. The value of ΔR/R(λ) for p-(s-) polarized IR radiation in a magnetic field of ～13 kOe is ～0.6% (～0.4%) for Al₂O₃ at λ ≈ 9.6 μm, ～1.63% (～1.15) for LiF at λ ≈ 11.1 μm, and ～ 0.07 (～0.2%) for MgO at λ ≈ 11.7 μm, respectively. These changes can be increased substantially by irradiating the dielectric crystals by x-ray radiation. It is shown that the optical and magnetooptical properties of the above dielectrics in the IR spectral region can be described in terms of the polaron excitation theory.     

Electro-optical effects at the discrete and continuum exciton states in GaAs

We report electroreflectance spectra from a GaAs-Au Schottky barrier interface, in the region of the fundamental energy gap, at a temperature of ～ 1.8 K. Both the ground exciton level and the continuum of states are investigated separately, by operating in the small modulation and in the on-off field limit, respectively. The field profile is monitored by I–V, C-V, and photovoltage measurements. It is found that, even at ～ 1.8K, a high surface field is generally present. This moves the actual reflecting boundary of the exciton-polariton away from the surface and affects the ER lineshape through field-induced inhomogeneity effects and interference across the high field layer below the surface. The spectra corresponding to the states of the continuum are discussed in terms of the recent calculations of photon-assisted tunneling with coulomb interaction.     

高功率微波窗内外表面闪络击穿流体模拟研究

建立理论模型,将电磁场时域有限差分方法与等离子体流体模型结合,编制一维电磁场与等离子流体耦合程序,数值研究了3 GHz高功率微波窗内外表面闪络击穿的不同物理过程.研究结果表明:外表面闪络击穿中,输出微波脉宽缩短(未完全截止),窗体前均方根场强呈驻波分布,波节与波腹位置不变,窗体外表面形成有一层高密(约10~(21)·m~(-3)量级)极薄(约mm量级)等离子体(扩散缓慢),入射波可部分透过该薄层等离子体,脉宽缩短主要源于等离子体吸收效应;降低初始等离子体密度、厚度、入射波场强及缩短入射波脉宽等方式,可不同程度地改善输出脉宽缩短效应.内表面闪络击穿中,窗体前均方根场强亦出现驻波分布f但波节与波腹位置随时间变化),等离子体向波源方向运动;强释气下,输出脉宽缩短(未完全截止),形成多丝状高密(约10~(21)·m~(-3)量级)极薄(约mm量级)等离子体区域(扩散缓慢),间距1/4微波波长,脉宽缩短主要源于等离子体吸收效应;弱释气、低场强下,脉宽缩短有所改善(但最终截止),形成多带状致密(约10~(18)·m~(-3)量级)略厚(mm-cm量级)等离子体区域(扩散较快),间距1/4波长,脉宽缩短主要源于等离子体吸收效应;弱释气、高场强下,脉宽缩短严重(很快截止),形成块状高密(约10~(21)·m~(-3)量级)较厚(约cm量级)等离子体区域(扩散迅速),脉宽缩短主要源于等离子体反射效应.     

A ∼20 ps resolution crystal streak camera

This paper describes the design and performance of a streak camera based on a LiNbO₃ electro-optic deflector. The camera has a total sweep time of ～4 ns and a temporal resolution of ～20 ps for ～0.5 μm radiation. Operation between ～0.35 μm and ～5.2 μm with either coherent or incoherent light is possible. Consequently the camera has many potential applications in the field of picosecond optical chronoscopy.     

带分划板的变倍双目望远镜

本文叙述了原苏联的ＢＫ７～１２×３５，ＢＫ７～１４×３６和ＢＰ１０～１６×４０变倍双目望远镜。给出了这些变倍双目望远镜与固定放大率双目望远镜相比的实验室试验结果。试验结果表明原苏联研制的变倍双目望远镜在光学和技术性能方面基本上与固定放大率双目望远镜不相上下。而且表明研制带分划板的变倍双目望远镜将会导致放大率变化范围的增加，可观察角视场的增大，结构的改进和重量的减轻。     

High pressures, low temperatures, and magnetic field effects on AgFeAsSe3 and AgFeSbSe3 properties

A procedure for synthesizing AgFeAsSe₃ and AgFeSbSe₃ is presented, and their electric and magnetic properties are investigated over a wide range of temperatures, pressures, and magnetic field variation. At 100–400K, the samples are characterized by semiconductor properties. Under pressures of ～25 and ～24 GPa, the electric properties of AgFeAsSe₃ and AgFeSbSe₃ change greatly.     

Response of colloidal liquids containing magnetic holes of different volume densities to magnetic field characterized by transmission measurement

This paper systematically investigates the response of colloidal liquids containing magnetic holes of different volume densities to magnetic field by conventional transmission measurements. It finds that the enhancement in the transmission of such a colloidal liquid under a magnetic field exhibits a strong dependence on the volume density of magnetic holes. A linear increase in the maximum enhancement factor is observed when the volume density of magnetic holes is below a critical level at which a maximum enhancement factor of ～150 is achieved in the near infrared region. Once the volume density of magnetic holes exceeds the critical level, a sharp drop of the maximum enhancement factor to ～2 is observed. After that, the maximum enhancement factor increases gradually till a large volume density of ～9%. By monitoring the arrangement of magnetic holes under a magnetic field, it reveals that the colloidal liquids can be classified into three different phases, i.e., the gas-like, liquid-like and solid-like phases, depending on the volume density of magnetic holes. The response behaviour of colloidal liquids to magnetic field is determined by the interaction between magnetic holes which is governed mainly by their volume density. A phase transition, which is manifested in the dramatic reduction in the maximum enhancement factor, is clearly observed between the liquid-like and solid-like phases. The optical switching operations for colloidal liquids in different phases are compared and the underlying physical mechanisms are discussed.     

A high-gradient accelerator based on a faster-than-light radiation source

A wide-band microwave generator using a faster-than-light source is proposed to be used as a charged particle accelerator. According to theoretical estimates, an electric field amplitude as high as ～10¹¹ V/m or more can be attained at the focus of a paraboloidal emitting surface with a focal parameter of ～1 m. These estimates are supported by numerical calculations. The schematic diagram of such an accelerator is suggested.     

Pressure dependence of the ordering temperature of the quasi two-dimensional ferromagnet (CH3NH3)2CuCℓ4

From magnetic susceptibility measurements we have determined the ordering temperature T_C of ferromagnetic (CH₃NH₃)₂CuC?₄ as a function of hydrostatic pressure up to P ～ 11 kbar. The increase of T_C, ～ 30% for ～ 11 kbar, is roughly quadratic with P. The data are discussed in terms of the P-dependence of the effective interlayer exchange field H_É.     

Production of cold CN molecules by photodissociating ICN precursors in brute-force field

We theoretically investigate the production of cold CN molecules by photodissociating ICN precursors in a brute-force field. The energy shifts and adiabatic orientation of the rotational ICN precursors are first investigated as a function of the external field strength. The dynamical photofragmentation of ICN precursors is numerically simulated for cases with and without orienting field. The CN products are compared in terms of their velocity distributions. A small portion of the CN fragments are recoiled to near zero speed in the lab frame by appropriately selecting the photo energy for dissociation. With a precursor ICN molecular beam of ～ 1.5 K in rotational temperature, the production of low speed CN fragments can be improved by more than 5 times when an orienting electrical field of 100 k V/cm is present. The corresponding production rate for decelerated fragments with speeds ≤ 50 m/s is simulated to be about ～2.1×10~(-4) and CN number densities of 10~(8) –10~(10) cm~(-3) can be reached with precursor ICN densities of ～10~(12) –10~(14) cm~(-3) from supersonic expansion.     

Spatial-temporal measurements of magnetic fields in laser-produced plasmas

The results of an investigation of the electromagnetic wave polarization, probing high-temperature laser plasma, as well as spatial-temporal structure of the magnetic fields, electron density, current density, and electron drift velocity are presented. To create the plasma, plane massive Al targets were irradiated with the second harmonic of a phoenix Nd laser at intensities up to 5·10¹⁴ W/cm². It was shown that the magnetooptical Faraday effect is the main mechanism responsible for the changing polarization of the probing wave. Magnetic fields up to 0.4 MG with electron densities ∼10²⁰ cm⁻³ were measured. Analysis of the magnetic field spatial distribution showed that the current density achieved the value ∼90 MA/cm² on the laser axis. The radial structure of the magnetic field testified to the availability of the reversed current in the laser plasma. The spatial and temporal resolutions in these experiments were equaled to ∼5 μsec and ∼50 psec, respectively. Translated from Preprint No. 35 of the Lebedev Physics Institute, Moscow, 1993.     

Fe84Zr3.5Nb3.5B8Cu1薄带的动态磁化过程

由于铁磁性样品的交流磁化率虚部χ″随磁场强度H的变化是非线性的，在低场(0～12 mT)有一个与铁磁共振信号强度相当的低场非共振信号. 利用ESR谱仪测量交流磁化率虚部χ″对磁场强度H的一次微分随磁场强度的变化dχ″/dH～H，研究Fe₈₄Zr_3.5Nb_3.5B₈Cu₁合金薄带的动态磁化特性. 合金薄带样品是各向异性的，易磁化轴（易轴）在薄带的横向方向，外加磁场H在易轴方向. 样品在可逆磁化区域(0～2.0 mT)和趋近饱和的磁化区域(9.0 mT以上)，dχ″/dH=0；在不可逆畴壁移动过程中，当H为4.2 mT 时, χ″(H)达到最大值χ_max；在磁畴转动过程中，χ″(H)正比于H²（瑞利区）；而实验中却发现，在某些区域交流磁化率虚部χ″(H) 与磁场强度H的n次方即Hⁿ(n≥3)有关；而且发现，在一定区域，有三段不可逆畴壁移动和磁畴转动交替出现的现象. 在这一过程中，dχ″/dH为常数的磁场范围分别为4.8～5.2mT, 5.8～6.4 mT, 8.0～8.5 mT, 其常数相对值分别为1：0.85：0.60. 样品的交流磁化率虚部χ″对磁场H的微分dχ″/dH随磁场H的这一变化规律反映了不可逆畴壁移动和磁畴转动交替发生的微观过程.     

Layer-by-layer analysis of charge state distribution of field evaporated ions from the W(011) plane

A charge state distribution of the field evaporated ions is layer-by-layer analyzed in a W(011) plane by using an atom-probe field ion microscope. A specimen temperature is varied from ～ 20 to ～ 250 K. The results indicate that at any temperature, the surface tungsten atoms field evaporate as triply and quadruply ions from the (011) plane, and the quadruply charged ions are always detected during the final collapse of the plane. They are also discussed on the basis of the post-ionization model.