Parity-violating electron scattering at the MAMI facility in Mainz

We report here on a new measurement of the parity-violating (PV) asymmetry in the scattering of polarized electrons on unpolarized protons performed at the MAMI accelerator facility in Mainz. This experiment is the first to use counting techniques in a parity violation experiment. The kinematics of the experiment is complementary to the earlier measurements of the SAMPLE Collaboration at the MIT-Bates accelerator and the HAPPEX Collaboration at Jefferson Lab. After discussing the experimental context of the experiments, the setup at MAMI and preliminary results are presented.Received: 1 November 2002, Published online: 15 July 2003PACS: 12.15.-y Electroweak interactions - 25.30.Bf Elastic electron scatteringF.E. Maas: For the A4 Collaboration     

dHvA observation of spin-dependent scattering by magnetic pairs of Co impurities in Au

We report the first dHvA observations of interaction effects between impurities, via measurements of the spin-dependent scattering of conduction electrons by magnetic pairs of Co impurities in Au. The local moment associated with Co pairs produces the only spin-dependent scattering in these dilute alloys because isolated Co impurities (which are also present) carry no local moment at low temperatures. The results are used to estimate the concentration (or average separation) of magnetic pairs.     

核子中夸克的极化

根据强子张量和向前的虚光子康普顿散射振幅之间的关系,用虚光子总吸收截面表达了核子的自旋结构函数和它的第一矩. 在夸克模型中计算了小动量转移区的虚光子的总吸收截面,进而得到了第一矩的理论结果,导出了质子中夸克的极化. 合理地解释了EMC和SLAC的实验结果.     

Magnetic depth profiling of Fe/Au multilayer using neutron reflectometry

We present unpolarized and polarized neutron reflectometry data on Fe/Au multilayer sample for characterizing the layer structure and magnetic moment density profile. Fe/Au multilayer shows strong spin-dependent scattering at interfaces, making it a prospective GMR material. Fe/Au multilayer with bilayer thickness of 130 Å was grown on Si substrate by RF magnetron sputtering technique. Unpolarized neutron reflectivity measurement yields nuclear scattering length density profile. The magnetic scattering length density profile has been obtained from polarized neutron reflectivity measurements.     

中、高能电子被SO2分子散射的微分截面、动量转移截面及弹性积分截面

在考虑分子内成键原子间的电子云重叠效应的基础上, 提出了一种能够准确计算“中、高能电子-分子”散射的微分截面、动量转移截面及弹性积分截面的修正势方法. 利用可加性规则、使用Hartree-Fock波函数并采用被这一方法修正过的复光学势, 在100—1000eV内对电子被SO₂分子散射的微分截面、动量转移截面及弹性积分截面进行了计算, 并将计算结果与实验及其他理论结果进行比较. 结果表明, 利用这一修正过的复光学势及可加性规则获得的微分截面比利用未修正的复光学势及可加性规则得到的结果准 关键词： 可加性规则 微分截面 动量转移截面 电子散射     

Spin-resolved impurity phase shifts in CuMn

Information deduced from spin-resolved scattering and exchange energy measured via the de Haas - van Alphen effect allows an examination of two recent calculations of the Mn magnetic impurity resonance in Cu. The resulting d-number N_d and spin S are in good agreement, lending further evidence for nearly integer number of d-electrons and a small $\text{long-range}$ magnetic moment. A substantial difference in majority spin density at E_F leads to an explanation for the non-observation of the Mn resonance in optical and photoemission measurements on CuMn.     

Determination of the LO phonon energy by using electronic and optical methods in AlGaN/GaN

The longitudinal optical (LO) phonon energy in AlGaN/GaN heterostructures is determined from temperature-dependent Hall effect measurements and also from Infrared (IR) spectroscopy and Raman spectroscopy. The Hall effect measurements on AlGaN/GaN heterostructures grown by MOCVD have been carried out as a function of temperature in the range 1.8-275 K at a fixed magnetic field. The IR and Raman spectroscopy measurements have been carried out at room temperature. The experimental data for the temperature dependence of the Hall mobility were compared with the calculated electron mobility. In the calculations of electron mobility, polar optical phonon scattering, ionized impurity scattering, background impurity scattering, interface roughness, piezoelectric scattering, acoustic phonon scattering and dislocation scattering were taken into account at all temperatures. The result is that at low temperatures interface roughness scattering is the dominant scattering mechanism and at high temperatures polar optical phonon scattering is dominant.     

Magnetic properties of the hexagonal NdNi5 and NdCu5 compounds

Magnetization and resistivity measurements performed on the hexagonal NdNi₅ and NdCu₅ compounds are presented. For NdNi₅, magnetization was measured on a single crystal along the three main axes of the orthohexagonal cell. This compound orders ferromagnetically at T_c = 7 K, a being the easy magnetization axis. Quantitative analysis of the experimental data led to the determination of the 4f-Nd and 3d-Ni contributions to the magnetization. In particular crystal field parameters were determined which account for inelastic neutron scattering data. Two original features of the compounds magnetic behaviour due to crystal field effects are noted: i) in the basal plane a large anisotropy of the magnetic moment which strongly increases with the magnetic field between 11 and 130 kOe; ii) a large decrease of the Nd moment during the rotation toward the c axis driven by the field. NdCu₅ orders also ferromagnetically at 15 K. The Nd moment lies perpendicular to c, and its reduction by the crystal field seems smaller than in NdNi₅.     

Implication of local moment at Ti and Fe sites for the electrical and magneto-transport properties of degenerate semiconducting Ti?-xFexO?-d epitaxial films

We have investigated the effect of local magnetic moment on the electrical and magneto-transport properties of thin films of the degenerate semiconductor Ti(1-x)Fe(x)O(2-d) (x = 0,0.04). The electrical measurements of these films reveal high temperature metallic behavior and resistivity minima. The behavior below the resistivity minimum temperature is ascribed to Kondo like scattering. The coupling between the local moment and the charge carriers is reflected in the magnetoresistance measurements in these films. This work indicates competition between the magnetic ordering mechanism by J(RKKY) and the moment screening mechanism by J(Kondo). Accordingly the role of carrier density in achieving the magnetic ordering in such materials either by defect engineering or by transition metal doping is discussed.     

How well do we know the electromagnetic form factors of the proton?

Recent measurements of recoil polarization in elastic scattering have been used to extract the ratio of the electric to the magnetic proton form factors. These results disagree with Rosenbluth extractions from cross-section measurements, indicating either an inconsistency between the two techniques, or a problem with either the polarization transfer or cross-section measurements. To obtain precise knowledge of the proton form factors, we must first understand the source of this discrepancy.Received: 1 November 2002, Published online: 15 July 2003PACS: 25.30.Bf Elastic electron scattering - 13.40.Gp Electromagnetic form factors - 14.20.Dh Protons and neutrons     

Binary nuclear molecules of an α-particle and a heavier cluster

A simple nuclear molecule is used as a model to interpret the band structure observed in elastic α-scattering and α-transfer reactions in the sd-shell. As in spectra of halogen acid molecules the bands have even and odd spins and parities. Due to the broadening and fine structure of the rotational levels they are characterized as giant resonances. The big moment of inertia and the line broadening is discussed in terms of performed measurements of scattering and the (α,p) reaction. A fine structure of prominent peaks in the inelastic scattering crosssections hints at the existence of rotational states with an α-particle orbiting an excited core.     

Elastic and vibrational properties of cobalt to 120 GPa

Impulsive stimulated light scattering and Raman spectroscopy measurements have been made on hcp cobalt to a static pressure of 120 GPa. We find that at pressures above 60 GPa the shear elastic modulus and the Raman frequency of the E(2g) transverse optical phonon exhibit a departure from a linear dependence on density. We relate this behavior to a collapse of the magnetic moment under pressure that has been predicted theoretically, but until now not observed experimentally.     

Sizing Polydisperse Dispersions by Focused Beam Reflectance and Small Angle Static Light Scattering

In this work, two different methods for particle characterization, namely focused beam reflectance and small angle static light scattering, are quantitatively compared. The results are presented in the form of moment ratios of the particle size distribution, i.e., the number weighted diameter, D_1/0, and the volume weighted diameter, D_4/3, for a broad range of particle size distributions ranging from 20 to 400 μm. Various aqueous dispersions including narrow, broad, and bimodal particle size distributions of spherical shaped ceramic beads were used in the comparison. It was found that the moment ratios obtained by focused beam reflectance measurements and small angle static light scattering correlate well, in the case of spherical particles. Furthermore, it was found that the D_1/0 values obtained by focused beam reflectance measurements are more sensitive to the presence of a small fraction of fine particles in a bimodal distribution than those obtained by small angle static light scattering.     

Soft X-ray resonant magnetic scattering studies on Fe/CoO exchange bias system

We have used soft X-ray resonant magnetic scattering (XRMS) to search for the presence of an effective ferromagnetic moment belonging to the antiferromagnetic (AF) layer which is in close contact with a ferromagnetic (F) layer. Taking advantage of the element specificity of the XRMS technique, we have measured hysteresis loops of both Fe and CoO layers of a CoO(40 Å)/Fe (150 Å) exchange bias bilayer. From these measurements we have concluded that the proximity of the F layer induces a magnetic moment in the AF layer. The F moment of the AF layer has two components: one is frozen and does not follow the applied magnetic field and the other one follows in phase the ferromagnetic magnetization of the F layer. The temperature dependence of the F components belonging to the AF layer is shown and discussed.     

Measurement of the spatial backscattering impulse-response at short length scales with polarized enhanced backscattering

In this Letter, we describe an easy to implement technique to measure the spatial backscattering impulse-response at length scales shorter than a transport mean free path with resolution of better than 10 μm using the enhanced backscattering phenomenon. This technique enables spectroscopic measurements throughout the visible range and sensitivity to all polarization channels. Through a combination of Monte Carlo simulations and experimental measurements of latex microspheres, we explore the various sensitivities of our technique to both intrinsic sample properties and extrinsic instrumental properties. We conclude by demonstrating the extraordinary sensitivity of our technique to the shape of the scattering phase function, including higher order shape parameters than the anisotropy factor (or first moment).     

Evolution of magnetism in iron from the atom to the bulk

The evolution of the magnetic moment in iron clusters containing 20-400 atoms is investigated using first-principles numerical calculations based on density-functional theory and real-space pseudopotentials. Three families of clusters are studied, characterized by the arrangement of atoms: icosahedral, body-centered cubic centered on an atom site, and body-centered cubic centered on the bridge between two neighboring atoms. We find an overall decrease of magnetic moment as the clusters grow in size towards the bulk limit. Clusters with faceted surfaces are predicted to have magnetic moment lower than other clusters with similar size. As a result, the magnetic moment is observed to decrease as function of size in a nonmonotonic manner, which explains measurements performed at low temperatures.     

Local moment ferromagnetism in CeRu2Ga2B

Magnetization, specific heat, and electrical resistivity measurements for polycrystalline specimens of CeRu(2)Ga(2)B reveal local moment ferromagnetic order at a Curie temperature T(C) = 16.3 K. Specific heat measurements show that the phase transition is second order and the low temperature behavior indicates that the Ce f-electron states do not hybridize strongly with the conduction electron states. Electrical resistivity measurements demonstrate large spin disorder scattering of conduction electrons for T ≥ T(C). Results for a single crystal are also reported, where T(C) = 15.4 K. While results for the polycrystal and single crystal specimens are qualitatively similar, the differences between them suggest that crystalline disorder plays a role in how the magnetism develops.     

Neutron scattering length of lithium and boron and their isotopes

Coherent neutron scattering lengths and free cross sections were measured in order to determine the spin dependent scattering lengths of the isotopes of Li and B. The transmission measurements on Li at neutron energies of 0.51 meV, 1.26 eV and 5.19 eV delivered data for the⁶Li-abundances in the samples and for the free scattering cross section of⁷Li. By means of experiments on 15 different samples of lithium compounds we obtained the complex spin state scattering lengths for the bound atoms to be: (ie81-01) Measurements on 3 boron samples with different enrichments led to (ie81-02) A review on slow neutron scattering and resonance data shows an over all consistency of all values.     

Small angle diffuse neutron scattering: Measurements on V2O3 in the temperature range 400–600 K

Cold neutron small-angle scattering measurements on pure V₂O₃ in the high-temperature transition domain shows an anomalous feature namely a peak and a bump in the range 500–570 K. It is suggested that a plausible origin of this anomaly is the formation of giant “correlation” clusters of size ～ 600 Å and a magnetic moment density ～ 10^-7 μ/ų as the system suffers a broad M-I transition.