Quantum Beam Sci., Volume 2, Issue 3 (September 2018) – 5 articles

Muon spin rotation ( $\mu$ SR) spectra recorded for manganese silicide MnSi and interpreted in terms of a quantitative analysis constrained by symmetry arguments were recently published. The magnetic structures of MnSi in zero-field at low temperature and in the conical phase near the magnetic phase transition were shown to substantially deviate from the expected helical and conical structures. Here, we present material backing the previous results obtained in zero-field. First, from simulations of the field distributions experienced by the muons as a function of relevant parameters, we confirm the uniqueness of the initial interpretation and illustrate the remarkable complementarity of neutron scattering and $\mu$ SR for the MnSi magnetic structure determination. Second, we present the result of a $\mu$ SR experiment performed on MnSi crystallites grown in a Zn-flux and compare it with the previous data recorded with a crystal obtained from Czochralski pulling. We find the magnetic structure for the two types of crystals to be identical within experimental uncertainties. We finally address the question of a possible muon-induced effect by presenting transverse field $\mu$ SR spectra recorded in a wide range of temperature and field intensity. The field distribution parameters perfectly scale with the macroscopic magnetization, ruling out a muon-induced effect. Full article

Unalloyed nickel aluminide has important applications but lacks ductility at room temperature. In this study, iron-added nickel aluminide alloys exhibit plasticity enhancement. The nickel aluminide alloys are prepared with different iron contents (0, 0.25, and 1 at%) to study their plasticity. The indentation-induced deformed areas are mapped by the synchrotron X-ray diffraction to compare their plastic zones. A complimentary tight binding calculation and generalized embedded atom method demonstrate how the Fe-addition enhances the plasticity of the iron-added nickel aluminide alloys. Full article

The time-of-flight neutron diffraction data collected in-situ on Oak Ridge National Laboratory’s (ORNL, Oak Ridge, TN, USA) VULCAN and Los Alamos National Laboratory’s (LANL, Los Alamos, NM, USA) High-Pressure-Preferred-Orientation (HIPPO) diffractometers have been analyzed complementarily to show the texture evolution during annealing of a cold-rolled Al-2%Mg alloy. The texture analysis aimed to identify the components present in the initial rolling (or deformation) texture and in the thermally-activated recrystallization texture, respectively. Using a quasi-Monte-Carlo (QMC) approach, a new method has been developed to simulate the weighted texture components, and to obtain inverse pole figures for both rolling and normal directions. As such, distinct recrystallization pathways during annealing in isochronal conditions, can be revealed in terms of the evolution of the texture components and their respective volume fractions. Moreover, the recrystallization kinetics associated with the cube and random texture components are analyzed quantitatively using a similar approach developed for differential scanning calorimetry (DSC). Full article

We investigated the antiferromagnetic phase transition in the frustrated and multiferroic hexagonal manganites h-YMnO ${}_3$ (YMO) and h-(Y ${}_{0.98}$ Eu ${}_{0.02}$ )MnO ${}_3$ (YEMO). Elastic neutron scattering was used to study, in detail, the phase transition in YMO and YEMO under zero pressure and in YMO under a hydrostatic pressure of 1.5 GPa. Under conditions of zero pressure, we found critical temperatures of $T_{\mathrm{N}}=71.3\left(1\right)$ K and $72.11\left(5\right)$ K and the critical exponent $0.22\left(2\right)$ and $\beta =0.206\left(3\right)$ , for YMO and YEMO, respectively. This is in agreement with earlier work by Roessli et al. Under an applied hydrostatic pressure of 1.5 GPa, the ordering temperature increased to $T_{\mathrm{N}}=75.2\left(5\right)$ K, in agreement with earlier reports, while $\beta$ was unchanged. Inelastic neutron scattering was used to determine the size of the anisotropy spin wave gap close to the phase transition. From spin wave theory, the gap is expected to close with a critical exponent, ${\beta }^{\prime }$ , identical to the order parameter $\beta$ . Our results indicate that the gap in YEMO indeed closes at $T_{\mathrm{N}}=72.4\left(3\right)$ K with ${\beta }^{\prime }=0.24\left(2\right)$ , while the in-pressure gap in YMO closes at 75.2(5) K with an exponent of ${\beta }^{\prime }=0.19\left(3\right)$ . In addition, the low temperature anisotropy gap was found to have a slightly higher absolute value under pressure. The consistent values obtained for $\beta$ in the two systems support the likelihood of a new universality class for triangular, frustrated antiferromagnets. Full article

Neutron diffraction is an effective and nondestructive method to investigate inner structure and stress distribution inside bulk materials and components. Compared with X-ray diffraction, neutron diffraction allows a relatively high penetration depth and covers a larger gauge volume, enabling it to measure the lattice structure and three-dimensional (3D) distribution of residual stress deep inside thick sample materials. This paper presents the recent development of a Residual Stress Neutron Diffractometer (RSND) at the Key Laboratory for Neutron Physics of the Chinese Academy of Engineering Physics, Institute of Nuclear Physics and Chemistry, Mianyang, China. By integrating multiple instruments such as a loading frame, Kappa goniometer, and coupling system, the RSND was constructed as a suitable platform for various neutron diffraction experiments, including residual stress measurement, in situ observation, and texture analysis. Neutron diffraction measurement can be used to study various materials such as steels, aluminum alloys, and titanium alloys, as well as various components such as turbine discs and welding parts. An evaluation method for both polycrystalline and monocrystalline materials was developed, and this method was found to have the capability of solving an agelong technical challenge in characterizing monocrystalline materials. Furthermore, by introducing a texture and thermomechanical coupling system, it is now possible to make effective in situ observations of the structural evolution in single crystal materials under high-temperature tensile conditions. Full article