Development and prospects of Very Small Angle Neutron Scattering(VSANS) techniques

Very Small Angle Neutron Scattering(VSANS) is an upgrade of the traditional Small Angle Neutron Scattering(SANS) technique which can cover three orders of magnitude of length scale from one nanometer to one micrometer. It is a powerful tool for structure calibration in polymer science, biology, material science and condensed matter physics. Since the first VSANS instrument, D11 in Grenoble, was built in 1972, new collimation techniques,focusing optics(multi-beam converging apertures, material or magnetic lenses, and focusing mirrors) and higher resolution detectors combined with the long flight paths and long incident neutron wavelengths have been developed.In this paper, a detailed review is given of the development, principles and application conditions of various VSANS techniques. Then, beam current gain factors are calculated to evaluate those techniques. A VSANS design for the China Spallation Neutron Source(CSNS) is thereby presented.     

Magnetization Reversal Mechanism for CoFeB Ferromagnetic Nanotube Arrays

CoFeB nanotube arrays are fabricated in anodic aluminum oxide （AAO） membranes and track etched polycarbonate （PCTE） membranes by using an electrochemical method, and their magnetic properties are investigated by vibrating sample magnetometry. The coercivity Hc and remanent squareness SQ of these CoFeB nanotube arrays are derived from hysteresis loops as a function of angle between the field and tube axis, The He（8） curves for CoFeB nanotube arrays in AAO and PCTE membranes show M-type variation, while they change shape from M to mountain-type as the tube length increases. However, the overall easy axis perpendicular to tube axis does not change with tube length. The different angular dependences are attributed to different magnetization reversal mechanisms.     

Scattering of neutrons on a Bose condensate

The spectrum of noncondensate excitations in neutron scattering on bosons is obtained in the framework of the Bogoliubov models both for liquid ⁴He and a dilute gas. The problem is solved using a path-integral representation of the partition function of the system. We describe the influence of scattering of neutrons on a Bose condensate in a stationary (time-independent) picture in the Gibbs equilibrium ensemble. This influence is a stationary boson response, and it depends on the initial neutron momentum k, transfer momentum p, and the neutron-boson interaction λ, which is related to the scattering length. The contribution of the neutrons to the initial Bogoliubov spectrum is found to be important for “quasi-elastic” scattering on the noncondensate, while the contribution of deep inelastic scattering is small; no contribution from elastic scattering on the Bose condensate is found. In the case of liquid Helium, the response is unlikely to be observable for all values p. On the other hand, for a gas one may expect a visible effect, in particular for a small momentum transfer p and a small density of the Bose condensate ϱ.     

Neutron Spectroscopy of Norbornane

Results of inelastic incoherent neutron scattering (IINS) on norbornane are reported. The IINS spectra in the low-temperature phases display low-frequency internal vibration modes very well. The assignment of these modes is proposed in reference to the results of the calculations of the structure and dynamics of isolated molecules by semi-empirical quantum chemistry methods.     

Electronic Transport in Magnetic Domain-wall Structure

The resistivity due to the domain wall in the presence of impurities in a ferromagnetic metallic wire is calculated based on the linear response theory. Assuming the local spin distribution to be spin-spiral the modification of the band structure has been obtained exactly. With this modified band structure we calculate the conductivity of the system as a function of electronic filling and show that the domain-wall contribution to the resistance can be positive or negative depending on the dimensionality, the position of the Fermi energy on the band structure and the strength of the electron local spin interaction of the system.     

偏振光在多层散射介质中传输的蒙特卡罗模拟研究

基于米氏散射理论,运用斯托克斯-穆勒形式,结合子午面法和拒绝法,提出了偏振光在多层散射介质中传输的蒙特卡罗模型,并首次分析了当菲涅耳公式失效时,多层介质界面处的全反射行为.同时用该模型研究了微粒直径和介质折射率对漫反射和漫透射的影响.结果表明:无论是折射率匹配介质还是非匹配介质,当粒子浓度一致时,漫反射率都随微粒直径的增加而增加,随介质折射率的增加而减小,而漫透射率则相反.研究结果为生物组织的偏振光散射研究提供了理论验证模型.     

偏振光在多层散射介质中传输的蒙特卡罗模拟研究*

基于米氏散射理论,运用斯托克斯-穆勒形式,结合子午面法和拒绝法,提出了偏振光在多层散射介质中传输的蒙特卡罗模型,并首次分析了当菲涅耳公式失效时,多层介质界面处的全反射行为.同时用该模型研究了微粒直径和介质折射率对漫反射和漫透射的影响.结果表明：无论是折射率匹配介质还是非匹配介质,当粒子浓度一致时,漫反射率都随微粒直径的增加而增加,随介质折射率的增加而减小,而漫透射率则相反.研究结果为生物组织的偏振光散射研究提供了理论验证模型.     

Letter: Behavior of Magnetic Tubes in Neutron Star's Interior

It is found from Maxwell's equations that the magnetic field lines are good analogues of relativistic strings. It is shown that the superconducting current in the neutron star's interior causes local rotation of magnetic flux tubes carrying quantized flux.     

Neutron Scattering on Magnetic Materials Under Extreme Conditions

Many materials exhibit various magnetic phenomena as a function of magnetic field, temperature and/or pressure. Usually, bulk magnetic measurements provide first information on the magnetic state of the material by measuring their response on the applied magnetic field. However, it is necessary to investigate materials also on a microscopic scale. This is often done by means of neutron scattering. In this contribution we discuss basic ideas of this method and we report on few experimental results obtained with a split-pair coil 14.5 T superconducting magnet which can be combined with dilution stick offering temperatures as low as 30 mK and/or with a small clamped-type pressure cell which offers pressure up to 1.0 GPa.     

双甘氨肽与高定向热解石墨的散射动力学研究

本文通过反应力场来研究中性双甘氨肽与高取向热解石墨的碰撞动力学过程,分别模拟初始入射角度为0o、20o、45o和70o以及入射能量为481.5 kJ/mol和表面温度为677 K的情况,并且确定和分析了散射产物的角度分布、平动能分布、内能分布和表面滞留时间分布. 双甘氨肽是一种多原子分子,具有较多的低频振动模式和较强的表面吸附相互作用,这些使得碰撞过程的表面滞留时间较长和容易造成能量损失,尤其是表面法线方向. 由于碰撞分子的动量沿表面法线方向上明显地发生损失,而沿表面平行方向上的动量则会大部分保留,因此,其散射角通常会呈现出超镜面反射分布,并且末态的平动能要远小于所谓硬立方模型的预测值. 本文加深了多肽分子与高取向热解石墨碰撞及其能量转移过程的认识和理解,有助于设计在稀薄大气中收集这类大分子的中性气体浓缩器.     

银纳米粒子对组装阵列中耦联分子拉曼散射的影响

分别用硼氢化钠和氢气还原法制备了两种不同的银溶胶(I和II),并采用自组装技术将银纳米粒子组装到对巯基苯胺(PATP)修饰的光滑银基底表面,形成银纳米粒子亚单层二维阵列。比较两种阵列中PATP的表面增强拉曼光谱发现,溶胶II所得阵列中的PATP的b2振动得到了较大的增强,即存在较大程度的电荷转移,说明银纳米粒子的性质直接影响了耦联分子的光谱特征。对溶胶Ⅰ进行离心处理,组装,得到的拉曼特征与阵列II类似。就溶胶II的银纳米粒子而言,组装结构中可能形成Ag-N化学键,从而导致更强的氨基与银粒子的相互作用。     

纳米结构和薄膜材料的拉曼 布里渊研究(英文)

在过去三十年中,对多种纳米结构和薄膜材料进行了拉曼 布里渊散射的研究.得到一些特征量的变化,如半高宽,峰位的改变;由此可得系列微结构参量.由于纳米(含薄膜)结构的基本特征:小,大,多,断和(相)移;即小的尺度,大的体表比,多的界面,断裂的波矢和相位的偏移的特证,在非弹性光散射谱中得到明显的展示:多种无序结构特征;三叉晶界特征;波矢断裂引发的折迭,由此形成的频隙;光学声子的带隙;相位偏移或失配在谱中的表现为过阻尼特征等.此外,本文还给出了该领域中非弹性光散射的某些概念.     

基于Stoner-Wohlfarth 模型磁性纳米颗粒的磁化反转

纳米磁性材料由于其特殊的磁学性能,近年来,在许多领域受到了广泛的应用。在基础理 论研究中,人们提出了各种描述纳米磁性材料的理论;另一方面,计算机计算能力以及实验手段 的提高,使得应用计算机进行材料设计以及探测单个纳米颗粒的磁学特性成为可能。这使得人们 对纳米磁性材料的理解更加深入。本篇论文介绍了磁性纳米颗粒的磁化反转机制的基本理论与实 验研究的最新进展。本文首先从磁性材料中基本的相互作用入手说明这些相互作用在纳米尺度下 的表现形式,随后详细介绍了基于Stoner-Wohlfarth 模型计算机模拟方法,最后简单介绍两种 可以用来研究单个纳米颗粒磁化反转实验手段以及相关的实验结果。     

Magnetic Properties of Monocrystal 57Fe/V Multilayers Investigated by CEMS,Nuclear Resonance Reflectivity in the Time Domain and Polarized Neutron Scattering

Hyperfine Interactions - We have performed a depth selective investigation of monocrystalline samples with composition [57Fe(10 ML)/V(5 ML)]20 and [57Fe(7 ML)/V(10 ML)]29 by means of synchrotron...     

Field-and Current-Driven Magnetization Reversal and Dynamic Properties of CoFeB-MgO-Based Perpendicular Magnetic Tunnel Junctions

We report a perpendicular magnetic tunnel junction(p MTJ) cell with a tunnel magnetoresistance(TMR) ratio of nearly 200% at room temperature based on Co Fe B/Ta/Co Fe B as the free layer(FL) and a synthetic antiferromagnetic(SAF) multilayer [Pt/Co]/Ru/[Pt/Co]/Ta/Co Fe B as the reference layer(RL). The field-driven magnetization switching measurements show that the p MTJs exhibit an anomalous TMR hysteresis loop. The spin-polarized layer Co Fe B of SAF-RL has a lower critical switching field than...     

Magnetization Reversal of Single-Molecular Magnets by a Spin-Polarized Current

We study the magnetization reversal of single-molecular magnets by a spin-polarized current in the framework of the spinor Boltzmann equation. Because of the spin–orbit coupling, the spin-polarized current will impose a non-zero spin transfer torque on the single-molecular magnets, which will induce the magnetization switching of the latter. Via the s–d exchange interaction between the conducting electrons and single-molecular magnets,we can investigate the magnetization dynamics of single-molec...     

共振光散射法测定三聚氰胺

应用共振散射光谱技术建立三聚氰胺检测新方法。三聚氰胺可使甲醇体系在567nm处的共振散射光明显增强。在优化实验条件下,体系的ΔI值与三聚氰胺的浓度在0.7—16.0mg/L之间具有良好的线性关系,线性方程为ΔIRLS=40.53C(mg/L)-2.64,r=0.9993;检出限为0.21mg/L;样品加标回收率为92.6%—102.3%。方法灵敏,操作简便,分析成本低,用于奶粉中三聚氰胺的测定,结果满意。     

Diffusion Studies with Synchrotron Radiation and with Neutron Scattering

With scattering methods we are able to detect the elementary diffusion jump. This is a report on investigations with methods working in the time domain, i.e., nuclear resonant scattering of synchrotron radiation and neutron spin echo. The accent of this paper is on diffusion in ordered alloys. We finish with an outlook on what will be possible with the upcoming potential of future synchrotron sources. This revised version was published online in August 2006 with corrections to the Cover Date.     

Magnetic Transitions in Fe 3 Pt Invar Alloy Under High Pressure and Temperature Studied by Inelastic X-ray Scattering

The magnetic properties of the Invar alloy Fe 72 Pt 28 have been investigated by X-ray emission spectroscopy as a function of temperature up to 900 K and pressure up to 25 GPa. With increasing temperature and pressure, the amplitude of the Fe local moment, deduced from the Fe K g line satellite intensity, is reduced. Both the temperature and pressure dependence are interpreted in terms of transitions from a high-spin state to a low-spin state. This behavior provides a microscopic picture of the Fe magnetism in Invar alloys in agreement with the 2 n state model.