Neutron Diffraction Measurements Research Articles

Synthesizing pseudo-Kossel lines from neutron transmission data. II. Validation with neutron diffraction data

A new method to recover the orientation matrix of a single crystal with a known unit cell by analyzing synthesized pseudo-Kossel lines from time-of-flight neutron transmission data has been outlined in a companion article [Dessieux et al. (2023). J. Appl. Cryst. 56, https://dx.doi.org/10.1107/S1600576723001346; referred to here as Article I]. In this work, validation of this new technique is presented by employing experimental neutron transmission and diffraction measurements performed on two copper single-crystal specimens. Time-of-flight spectra were recorded during rotation (ω) of the single crystals about a vertical axis perpendicular to the incident neutron beam. The λ–ω maps recorded in transmission are utilized to determine the crystal orientation with respect to the neutron beam, following the procedure presented in Article I. To validate the indexing procedure, the crystal orientations are compared with those obtained via conventional methods using the diffraction data. The resulting pseudo-Kossel lines across the 2D detectors are also observed for the first time.

Single-crystal growth and physical properties of LaMn0.86Sb2

Single crystals of ${\mathrm{LaMn}}_{0.86}{\mathrm{Sb}}_{2}$ were synthesized via the flux method. Band structure calculation indicates the existence of Dirac dispersion below the Fermi level as expected for the square-net-based materials. Magnetization in combination with neutron diffraction measurements suggests that the magnetic structure below ${T}_{\mathrm{N}}=146 \mathrm{K}$ can be described by a G-type antiferromagnetic structure with a weak spin canting. A spin-flop transition was observed when external magnetic fields were applied parallel to the $c$ axis. Negative magnetoresistance is observed at low temperatures, likely originating from the spin alignment effect. Our results indicate that ${\mathrm{LaMn}}_{1\ensuremath{-}x}{\mathrm{Sb}}_{2}$ has Dirac dispersion and a vacancy tunable magnetism, which could be a potential platform for studying the interplay of magnetism, charge transport, and possible topological band.

Magnetic ordering and chirality in multiferroic Dy1-xHoxMnO3 (x = 0.2)

Effect of substitution Dy by Ho on the magneto-electric behavior of the compound Dy0.8Ho0.2MnO3 was investigated by the different methods of polarized and classical neutron diffraction and macroscopic methods. It is shown that substitution by Ho of 20% on the position of Dy do not change overall crystal symmetry of compound. It remains of Pbnm type down to the very low temperatures. Magnetic ordering, its temperature and field evolution was determined by the use of single crystal neutron diffraction and magnetization measurements. Chiral type of magnetic structure on Mn subsystem is confirmed below Tc ≈ 16 K. Using polarized neutron diffraction the 3-component character of rare earth magnetic ordering in Dy0.8Ho0.2MnO3 in contrast to DyMnO3 could be revealed. It was shown that doping by 20% Ho suppresses the spontaneous rare-earth ordering with its own propagation vector and provides the situation when two magnetic subsystems, manganese and rare earth ones have a coherent incommensurate spatial propagation. The influence of the external electric field on the magnetic chirality could be directly evidenced, proving strong magneto-electric coupling in multiferroic phase. The study of the electric polarization under similar temperatures and fields on the same samples provides the direct correlation between the results of the microscopic and macroscopic investigations.

Structure and Physical Properties of Mg93-xZnxCa7 Metallic Glasses.

The Mg-Zn-Ca system has previously been proposed as the most suitable biodegradable candidate for biomedical applications. In this work, a series of ribbon specimens was fabricated using a melt-spinning technique to explore the glass-forming ability of the Mg-Zn-Ca system along the concentration line of 7 at.% of calcium. A glassy state is confirmed for Mg50Zn43Ca7, Mg60Zn33Ca7, and Mg70Zn23Ca7. Those samples were characterised by standard methods to determine their mass density, hardness, elastic modulus, and crystallisation temperatures during devitrification. Their amorphous structure is described by means of pair distribution functions obtained by high-energy X-ray and neutron diffraction (HEXRD and ND) measurements performed at large-scale facilities. The contributions of pairs Mg-Mg, Mg-Zn, and Zn-Zn were identified. In addition, a transformation process from an amorphous to crystalline structure is followed in situ by HEXRD for Mg60Zn33Ca7 and Mg50Zn43Ca7. Intermetallic compounds IM1 and IM3 and hcp-Mg phase are proposed to be formed in multiple crystallisation eventss.

Effect of Si/Al addition on magnetic properties of Fe-Co alloy

Fe-Co alloys are promising materials for high power density motors, since they have higher Bs than Fe-Si steels which are most commonly used as the motor cores. It is known, however, that the Fe-Co alloys generally have poor workability due to an existence of the brittle phase, ordered B2. In this study, effects of Co content and Si/Al addition with the Fe-Co alloys on the workability and magnetic properties were investigated. The neutron diffraction measurements of the Fe-Co alloys with different Co contents of 5, 18, 27, and 49 mass% were first conducted to know the existence of the ordered B2 phase. The result showed that the B2 phase was observed in the Fe-Co alloys with Co contents of 27 and 49 mass%, while the alloys with 5 and 18 mass% did not contain it, which suggests the latter two alloys have the better workability. Then, we checked the effect of Si/Al addition on the magnetic properties of the 82Fe-18Co alloy, and found that the co-addition of Si/Al reduce the coercivity, Hc to about 60 A/m and iron loss to less than 170 W/kg while maintaining a high B value at 30 000 A/m above 2.2 T.

Magnetic structure of the two-dimensional XY antiferromagnet Sr2CoSi2O7 studied using single-crystal neutron diffraction

We report a combined polarized and unpolarized neutron diffraction study on a multiferroic ${\mathrm{Sr}}_{2}{\mathrm{CoSi}}_{2}{\mathrm{O}}_{7}$ (SCSO) single crystal below and above the antiferromagnetic ordering temperature ${\mathrm{T}}_{N}$ = 6.5 K. Unpolarized neutron diffraction measurements at 15 K confirm the melilite-type tetragonal $P\overline{4}{2}_{1}m$ space group as the parent structure of SCSO. The low temperature study at 2.3 K, in contrast, reveals symmetry lowering with the orthorhombic $Cm{m}^{\ensuremath{'}}{2}^{\ensuremath{'}}$ and $P{2}_{1}{2}_{1}^{\ensuremath{'}}{2}^{\ensuremath{'}}$ magnetic space groups being equally possible. In these $Cm{m}^{\ensuremath{'}}{2}^{\ensuremath{'}}$ and $P{2}_{1}{2}_{1}^{\ensuremath{'}}{2}^{\ensuremath{'}}$ magnetic space groups we obtain a very similar ordered magnetic moment about 2.86 and $2.94\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{B}/{\mathrm{Co}}^{2+}$, respectively, which lies in the $\mathit{ab}$ plane. Our spin polarized flipping ratio measurements under an applied magnetic field of 6 T in the paramagnetic state support the results of our bulk magnetization data, indicating strong easy-plane spin anisotropy, responsible for the in-plane order below ${\mathrm{T}}_{N}$.

Zigzag magnetic order and possible Kitaev interactions in the spin-1 honeycomb lattice KNiAsO4

Despite the exciting implications of the Kitaev spin Hamiltonian, finding and confirming the quantum spin-liquid state have proven incredibly difficult. Recently, the applicability of the model has been expanded through the development of a microscopic description of a spin-1 Kitaev interaction. Here we explore a candidate spin-1 honeycomb system, ${\mathrm{KNiAsO}}_{4}$, which meets many of the proposed criteria to generate such an interaction. Bulk measurements reveal an antiferromagnetic transition at $\ensuremath{\sim}19$ K which is generally robust to applied magnetic fields. Neutron diffraction measurements show magnetic order with a $\mathbf{k}=(\frac{3}{2},0,0)$ ordering vector which results in the well-known ``zigzag'' magnetic structure thought to be adjacent to the spin-liquid ground state. Field-dependent diffraction shows that while the structure is robust, the field can tune the direction of the ordered moment. Inelastic neutron scattering experiments show a well-defined gapped spin-wave spectrum with no evidence of the continuum expected for fractionalized excitations. Modeling of the spin waves shows that the extended Kitaev spin Hamiltonian is are generally necessary to model the spectra and reproduce the observed magnetic order. First-principles calculations suggest that the substitution of Pd on the Ni sublattice may strengthen the Kitaev interactions while simultaneously weakening the exchange interactions thus pushing ${\mathrm{KNiAsO}}_{4}$ closer to the spin-liquid ground state.

Incommensurate helimagnetic structure of Ba(Fe1−xScx)12O19 determined by single-crystal neutron diffraction

Sc-substituted hexagonal ferrite $\mathrm{Ba}{({\mathrm{Fe}}_{1\text{\ensuremath{-}}x}{\mathrm{Sc}}_{x})}_{12}{\mathrm{O}}_{19}$ has an incommensurate helimagnetic structure. However, the incommensurate helimagnetic structure has not been sufficiently determined, and the mechanism via which the helimagnetism develops has not been studied. Time-of-flight-Laue single-crystal neutron diffraction measurements were performed at 4--6 K on single-crystal samples of $\mathrm{Ba}{({\mathrm{Fe}}_{1\text{\ensuremath{-}}x}{\mathrm{Sc}}_{x})}_{12}{\mathrm{O}}_{19}$ having Sc concentrations of $x=0$, 0.128, 0.153, and 0.193. The incommensurate helimagnetic structure was determined by analyzing the magnitude and direction of the ${\mathrm{Fe}}^{3+}$ magnetic moments at the five Fe1--Fe5 sites ($2a, 4e, 4{f}_{1}, 4{f}_{2}$, and $12k$). The development mechanism of the helimagnetic structure was discussed from the standpoint of superexchange interaction. The crystal structure analyses revealed that the Sc substitution enabled two significant events, namely, the coordination changes of ${\mathrm{Fe}}^{3+}$ and ${\mathrm{Sc}}^{3+}$ at the $\mathrm{Fe}2(4e)$ site, resulting in the shortened bond distances of Fe2-O1 and the preferred substitution of ${\mathrm{Fe}}^{3+}$ at the $\mathrm{Fe}4(4{f}_{2})$ site with ${\mathrm{Sc}}^{3+}$. The magnetic structure analyses revealed that the helimagnetic structure of $\mathrm{Ba}{({\mathrm{Fe}}_{1\text{\ensuremath{-}}x}{\mathrm{Sc}}_{x})}_{12}{\mathrm{O}}_{19}$ is a cone type whose base is in the $ab$ plane and height is in the $c\text{\ensuremath{-}}\mathrm{axis}$ direction. The magnetic moments of $\mathrm{Fe}2(4e), \mathrm{Fe}4(4{f}_{2})$, and $\mathrm{Fe}5(12k)$ are aligned with distinct angles, leading to the helimagnetic structure of $\mathrm{Ba}{({\mathrm{Fe}}_{1\text{\ensuremath{-}}x}{\mathrm{Sc}}_{x})}_{12}{\mathrm{O}}_{19}$, and can be explained by assuming that there is an antiferromagnetic superexchange interaction ${J}_{5}$ between $\mathrm{Fe}2(4e)$ and $\mathrm{Fe}5(12k)$ that is negligible in the $x=0$ crystal. The shorter bond distance of Fe2-O1 in Sc-rich crystals revealed by the crystal structure analyses enhances the superexchange interaction ${J}_{5}$. However, the ${\mathrm{Sc}}^{3+}$ preference for $\mathrm{Fe}4(4{f}_{2})$ weakens ${J}_{3}$ and ${J}_{4}$. The relatively strong ${J}_{5}$ leads to competition among the three superexchange interactions, ${J}_{3}, {J}_{4}$, and ${J}_{5}$, resulting in the development of the helimagnetic structure. These findings facilitate the understanding of the essentials of the basic magnetic material $\mathrm{Ba}{\mathrm{Fe}}_{12}{\mathrm{O}}_{19}$.

Exchange bias effect and inhomogeneous magnetism in 6H Ba3CoFeRuO9: Role of structural site disorder

Structural, magnetic, electrical and thermal investigations on ternary barium ruthenate Ba3CoFeRuO9 (BCFRO) reveal the role of the two different octahedral B-site in creating locally varying competing antiferromagnetic and ferromagnetic interactions. BCFRO forms in 6H hexagonal structure in the P63/mmc space group. Neutron diffraction and specific heat capacity measurements affirmed the absence of any long-range ordering and structural transition in the compound. DC thermomagnetic studies evidences spin glass magnetism with Tg ∼ 50 K. A large exchange bias (EB) field of 3.48 kOe is obtained at 3 K under a cooling field of 50 kOe. Careful analysis indicates, EB in our system stems from inhomogeneous magnetism owing to spatially varying chemical composition. Competing ferromagnetic and antiferromagnetic phases giving rise to spin glass behaviour is the manifestation of site disorder induced by mixed valences of magnetic ions. The exchange bias training effect in our system follows spin relaxation model of rotatable and frozen spins which are exchange coupled at the interface. Strong electron localisation occurs by virtue of the specific 6H structure with corner shared octahedral 2a site and face shared octahedral 4f site. The electrical and thermal transport in BCFRO follows Efros-Shklovskii variable range hopping (ES VRH) model below 150 K. The high resistivity of BCFRO at low temperatures is also reflected in the low thermal conductivity and huge Seebeck coefficient.

Evolution of the magnetic structure in overdoped antiferromagnetic La1−xCaxMnO3(0.51≤x≤0.69) manganites: A neutron diffraction study

The ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}{\mathrm{MnO}}_{3}$ series of compounds with antiferromagnetic ground states ($x\ensuremath{\ge}1/2$) have been extensively studied due to the novel spin, orbital, and charge-ordering states observed when the calcium concentration is a simple fraction ($x=1/2,\phantom{\rule{0.28em}{0ex}}2/3$, and 3/4). The ground states of these compositions have been explained by the Goodenough charge, orbital, and spin ordering model. An important issue remaining is the elucidation of how the ground state changes when $x$ is not a simple number. Here we study the magnetic structure of ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}{\mathrm{MnO}}_{3}$ for $0.51\ensuremath{\le}x\ensuremath{\le}0.69$ using powder neutron diffraction measurements supported by magnetization data. For compositions with $0.51\ensuremath{\le}x\ensuremath{\le}0.56$, the magnetic structure, which we term as an incommensurate charge exchange (CE) structure can be described by two propagation vectors ${\mathbf{k}}_{\mathrm{C}}=[1/2,0,1/2]$ and ${\mathbf{k}}_{\mathrm{E}}=[{\ensuremath{\varepsilon}}_{\mathrm{E}},0,1/2]$. In the second one, the component parallel to the ${\mathbf{a}}^{*}$ axis of the reciprocal lattice changes with the ${\mathrm{Mn}}^{4+}$ concentration $x$ as ${\ensuremath{\varepsilon}}_{\mathrm{E}}\ensuremath{\approx}x\ensuremath{-}1/2$ providing, thus, an unambiguous signature of the adoption of an incommensurate magnetic structure. As $x$ gradually increases, the diffraction data reveal that two magnetic phases---one adopting the incommensurate CE, and one adopting the commensurate ``2/3'' magnetic structure--co-exist in the concentration regime of $0.57\ensuremath{\le}x\ensuremath{\le}0.61$. Around the simple fraction $x=2/3$, the magnetic structure can be also described by three propagation vectors, the commensurate ${\mathbf{k}}_{\mathrm{E}}=[0,0,1/2]$, ${\mathbf{k}}_{\mathrm{C}}=[1/2,0,1/2]$, and an incommensurate ${\mathbf{k}}_{2/3}=[1/3+{\ensuremath{\varepsilon}}_{2/3},0,1/2]$ propagation vector with ${\ensuremath{\varepsilon}}_{2/3}$ taking negative/zero/positive values for $x$ smaller than/equal to/larger than 2/3, respectively. Our experimental results for $0.51\ensuremath{\le}x\ensuremath{\le}0.56$ are neither in favor of a stripe structure consisting of a fine mixture of $x=1/2$ and $x=2/3$ phases (phase separation) nor of a defect structure in which an appropriate amount of ${\mathrm{Mn}}^{3+}$-O sheets have been replaced by ${\mathrm{Mn}}^{4+}$-O sheets (defect structure). A sinusoidal modulated structure has been used as a possible candidate in explaining the experimental neutron diffraction magnetic Bragg peaks. This result may be linked to the presence of a mixed orbital state of the manganese ions.

Crystal orientations of 1,3,5-triamino-2,4,6-trinitrobenzene-based polymer bonded explosives during the pressing process by neutron diffraction

Hot-pressed 1,3,5-triamino-2,4,6-trinitrobenzene (TATB)-based polymer bonded explosives (PBX) will show significant anisotropic and irreversible expansion properties, resulting in both the deterioration of their performance and weapon reliability issues. The anisotropic mechanical and irreversible expansion characteristics of TATB-based PBX have shown to be closely related to the crystal orientation. In this work, the orientations of TATB crystals in PBX under different thermal–mechanical coupling loading conditions were studied by neutron diffraction measurement technology. The microstructures were observed by computed tomography (CT) and scanning electron microscopy (SEM), and the effects of hot pressing parameters (temperature and pressure) on the TATB crystal orientation were systematically analyzed. Combining the density and compression strength of the formed samples, the optimal hot pressing parameters were determined. The results showed that during the in-situ compression process, the TATB crystals would be reoriented. The rotation angle of the (002) plane was mainly concentrated within a 35° angle from the perpendicular pressing direction. After hot compaction, the rotation angle moved from 35° to 52°, and the orientation of the TATB crystals had obvious rebound phenomenon. The (002) plane orientation degree was related to the deformation, fragmentation, and reorientation of the TATB crystals, as well as the phase transition, thermal softening, and gap filling of the binder, and the interfacial interactions. In order to obtain higher detonation energy, better mechanical properties and better shape stability of the formed samples, (120 °C, 140 MPa) was selected as the optimal hot pressing parameters for TATB-based PBX. • Neutron diffraction was developed for the TATB crystal orientation measurement. • The TATB crystal reorientation during pressing process was obtained. • The effect of the temperature and pressure on the reorientation was quantified. • The mechanism of the crystal reorientation during pressing process was analyzed.

Observation of proton-transfer-coupled spin transition by single-crystal neutron-diffraction measurement.

The application of single-crystal neutron diffraction (SCND) to observe proton-transfer phenomena in crystalline compounds exhibiting unusual protonation states or proton dynamics has garnered significant research interest in recent years. However, proton tautomerism, which results in different protonation states before and after proton transfer, has never been observed using the SCND technique. Thus, to observe the proton tautomerism phenomenon by SCND measurements, we developed an iron(II) complex that forms a large crystal and exhibits a proton-transfer-coupled spin transition (PCST). The presence of the two types of proton tautomers was determined by conventional analysis of the proton position by X-ray crystallography, infrared spectroscopy, and density functional theory calculations. Finally, our results confirmed that proton tautomerism was successfully observed for the first time using variable-temperature SCND measurements.

Dislocation Density of Electron Beam Powder Bed Fusion Ti–6Al–4V Alloys Determined via Time-Of-Flight Neutron Diffraction Line-Profile Analysis

Ti–6Al–4V alloys undergo a multiple phase transformation sequence during electron beam powder bed fusion (EB-PBF) additive manufacturing, forming unique dislocation substructures. Thus, determining the dislocation density is crucial for comprehensively understanding the strengthening mechanisms and deformation behavior. This study performed time-of-flight neutron diffraction (TOF-ND) measurements of Ti–6Al–4V alloys prepared via EB-PBF and examined the dislocation density in the as-built and post-processed states using convolutional multiple whole profile (CMWP) fitting. The present TOF-ND/CMWP approach successfully determined the bulk-averaged dislocation density (6.8 × 1013 m−2) in the as-built state for the α-matrix, suggesting a non-negligible contribution of dislocation hardening. The obtained dislocation density values were comparable to those obtained by conventional and synchrotron X-ray diffraction (XRD) measurements, confirming the reliability of the analysis, and indicating that the dislocations in the α-matrix were homogeneously distributed throughout the as-built specimen. However, the negative and positive neutron scattering lengths of Ti and Al, respectively, lowered the diffraction intensity for the Ti–6Al–4V alloys, thereby decreasing the lower limit of the measurable dislocation density and making the analysis difficult.

Finite element modelling for mitigation of residual stress and distortion in macro-scale powder bed fusion components

Powder bed fusion (PBF) has attracted significant attention in many applications due to its capability of fabricating complex and customized metal parts. However, the potential for high inherent residual stresses that produce distortion in additive manufacturing (AM) components prevents more widespread application of the AM technique. Efficient and accurate prediction of residual stress and distortion at component-level (macro-scale) is a complex task. Although process-level (meso-scale) thermo-mechanical simulations have resulted in accurate predictions for small-scale parts, the computational times (typically weeks) and memory requirements for application of such methods to component-level are prohibitive. The main goal of the current study therefore is to present an efficient and accurate finite element (FE) simulation method with detailed validation for PBF manufacture of a complex 3D Inconel 625 benchmark bridge component (macro-scale). The simulation results are successfully validated against the published benchmark experimental measurements from neutron diffraction, X-ray diffraction (XRD), contour method and coordinate measurement machine (CMM) by the National Institute of Standards and Technology (NIST) laboratory. A key additional novelty of the present work is the investigation of the effects of substrate removal and preheating on mitigation of residual stresses and distortions using the validated model. Ultimately, these results will guide the selection of optimal manufacturing protocols and integration of the FE-based AM modelling for industrial application with complex geometries. The ultimate aim of the present work is to facilitate fatigue life prediction of complex geometry AM components including residual stress effects, for example, conformally-cooled injection moulding dies (for different material than Inconel 625).

Spin-singlet ground state of the coupled Jeff = 12 alternating chain system Sr2Co(SeO3)3

We report a detailed study of the structural, magnetic, thermodynamic, and electronic properties of a coupled ${J}_{\mathrm{eff}}$ = $\frac{1}{2}$ alternating chain ${\mathrm{Sr}}_{2}\mathrm{Co}{({\mathrm{SeO}}_{3})}_{3}$ compound using magnetic susceptibility $\ensuremath{\chi}(T)$, magnetic specific heat ${C}_{\mathrm{m}}(T)$, magnetization, and neutron diffraction measurements along with first-principles calculations. The first-principles calculations based on the density functional theory suggest that ${\mathrm{Sr}}_{2}\mathrm{Co}{({\mathrm{SeO}}_{3})}_{3}$ forms a quasi-one-dimensional chain with bond alternation and interchain interactions. $\ensuremath{\chi}(T), {C}_{\mathrm{m}}(T),$ and neutron powder diffraction measurements confirm that no long-range magnetic ordering occurs down to 100 mK. Instead, a maximum in $\ensuremath{\chi}(T)$ and ${C}_{\mathrm{m}}(T)$ and an exponential drop of $\ensuremath{\chi}(T)$ and ${C}_{p}(T)$ as $T\ensuremath{\rightarrow}0$ K point to a spin-singlet ground state. The analysis of $\ensuremath{\chi}(T)$ and ${C}_{\mathrm{m}}(T)$ based on a ${J}_{1}\text{\ensuremath{-}}{J}_{2}$ alternating Heisenberg model shows the bond alternation $\ensuremath{\alpha}={J}_{2}/{J}_{1}\ensuremath{\approx}0.7$ and a spin gap of $\mathrm{\ensuremath{\Delta}}\ensuremath{\approx}3$ K. Our work demonstrates that ${\mathrm{Sr}}_{2}\mathrm{Co}{({\mathrm{SeO}}_{3})}_{3}$ is a coupled alternating chain system based on spin-orbit entangled ${J}_{\mathrm{eff}}$ = $\frac{1}{2}$.

New Insights into the Volume Isotope Effect of Ice Ih from Polarizable Many-Body Potentials.

The anomalous volume isotope effect (VIE) of ice Ih is calculated and analyzed based on the quasi-harmonic approximation to account for nuclear quantum effects in the Helmholtz free energy. While a lot of recently developed polarizable many-body potential functions give a normal VIE contrary to experimental results, we find that one of them, MB-pol, yields the anomalous VIE in good agreement with the most recent high-resolution neutron diffraction measurements─better than DFT calculations. The short-range three-body terms in the MB-pol function, which are fitted to CCSD(T) calculations, are found to have a surprisingly large influence. A vibrational mode group decomposition of the zero-point pressure together with a hitherto unconsidered benchmark value for the intramolecular stretching modes of H2O ice Ih obtained from Raman spectroscopy data unveils the reason for the VIE: a delicate competition between the latter and the librations.

Advanced in-situ experimental techniques for characterization of deformation mechanisms in magnesium alloys

A combination of advanced in-situ experimental techniques, comprised of neutron diffraction, acoustic emission (AE), and in-situ electron backscattered diffraction (EBSD) was selected to provide extensive insight into the deformation behavior of magnesium alloys based on their mutual complementarity. The potential and limitations of these techniques were shown and discussed in the scope of the study of the influence of the crystallographic texture influence on the activity of individual deformation mechanisms in a hot-rolled sheet of the AZ31 magnesium alloy. The neutron diffraction experiments coupled with a recording of the AE signal allowed monitoring of the twinning activity and the evolution of its dynamics from nucleation toward twin growth. The AE suggested microplastic behavior, which was confirmed by the lattice strain evolution analysis for the sample compressed in the sheet normal direction. The in-situ EBSD experiments provided direct observation of the deformed microstructure, including the formation of twinning bands and the transition from twin nucleation to growth with progressing strain, being in very good agreement with the indirect neutron diffraction and AE measurements. Furthermore, the subsequent analysis of the EBSD maps enabled the quantification of the twinned volume fraction and its qualitative comparison with the evolution measured by neutron diffraction. The EBSD-based slip trace analysis revealed a notable non-Schmid basal activity and offered insight into the mechanisms accommodating strain once the twinning was exhausted.

Analysis of hierarchical microstructural evolution in electron beam powder bed fusion Ti–6Al–4V alloys via time-of-flight neutron diffraction

Ti–6Al–4V alloys prepared via electron beam powder bed fusion (EB-PBF) generally exhibit a hierarchical microstructure consisting of columnar β-grains, an acicular α-matrix, and nanoscale β-precipitates at α-lath interfaces. In this study, we performed time-of-flight neutron diffraction measurements to investigate the texture and volume fraction of EB-PBF Ti–6Al–4V alloys via Rietveld texture analysis (RTA). The high-intensity neutron source enabled the analysis of the nanosized β-phase precipitates at the α-lath interfaces. The results indicate that the α- and β-textures of the as-built specimen can be ascribed to multiple Burgers orientation relationships among the prior β-phase, α-laths, and nanosized β-phase precipitates, which are not clearly understood. The as-built texture was maintained during post-processing, suggesting that texture manipulation in EB-PBF fabrication is important for controlling the crystallographic orientations of the built components, even after post-processing. RTA allowed a precise quantification of the β-phase fraction, which was found to have increased in post-processed specimens. The results would contribute to a comprehensive understanding of the microstructural evolution of such alloys, which is vital for the modeling and optimization of alloy performance.

Direct measurement of the evolution of magnetism and superconductivity toward the quantum critical point

Nontrivial quantum states can be realized in the vicinity of the quantum critical point (QCP) in many strongly correlated electron systems. In particular, an emergence of unconventional superconductivity around the QCP strongly suggests that the quantum critical fluctuations play a central role in the superconducting pairing mechanism. However, a clear signature of the direct coupling between the superconducting pairing states and the quantum criticality has not yet been elucidated by the microscopic probes. Herein, we present muon spin rotation/relaxation and neutron diffraction measurements in the superconducting dome of CeCo(In1 - xZnx)5. It was found that a magnetically ordered state develops at x≥ 0.03, coexisting with the superconductivity. The magnitude of the ordered magnetic moment is continuously reduced with decreasing x, and it disappears below x∼ 0.03, indicating a second-order phase transition and the presence of the QCP at this critical Zn concentration. Furthermore, the magnetic penetration depth diverges toward the QCP. These facts provide evidence for the intimate coupling between quantum criticality and Cooper pairing.

Creating and controlling Dirac fermions, Weyl fermions, and nodal lines in the magnetic antiperovskite Eu3PbO

The band topology of magnetic semimetals is of interest both from the fundamental science point of view and with respect to potential spintronics and memory applications. Unfortunately, only a handful of suitable topological semimetals with magnetic order have been discovered so far. One such family that hosts these characteristics is the antiperovskites, ${A}_{3}B\mathrm{O}$, a family of 3D Dirac semimetals. The $A={\mathrm{Eu}}^{2+}$ compounds magnetically order with multiple phases as a function of the applied magnetic field. Here, by combining band structure calculations with neutron diffraction and magnetic measurements, we establish the antiperovskite ${\mathrm{Eu}}_{3}\mathrm{Pb}\mathrm{O}$ as a new topological magnetic semimetal. This topological material exhibits a multitude of different topological phases with ordered Eu moments which can be easily controlled by an external magnetic field. The topological phase diagram of ${\mathrm{Eu}}_{3}\mathrm{Pb}\mathrm{O}$ includes an antiferromagnetic Dirac phase, as well as ferro- and ferrimagnetic phases with both Weyl points and nodal lines. For each of these phases, we determine the bulk band dispersions, the surface states, and the topological invariants by means of ab initio and tight-binding calculations. Our discovery of these topological phases introduces ${\mathrm{Eu}}_{3}\mathrm{Pb}\mathrm{O}$ as a new platform to study and manipulate the interplay of band topology, magnetism, and transport.