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The execution and analysis of complex experiments are challenged by the vast dimensionality of the underlying parameter spaces. Although an increase in data-acquisition rates should allow broader querying of the parameter space, the complexity of experiments and the subtle dependence of the model function on input parameters remains daunting owing to the sheer number of variables. New strategies for autonomous data acquisition are being developed, with one promising direction being the use of Gaussian process regression (GPR). GPR is a quick, non-parametric and robust approximation and uncertainty quantification method that can be applied directly to autonomous data acquisition. We review GPR-driven autonomous experimentation and illustrate its functionality using real-world examples from large experimental facilities in the USA and France. We introduce the basics of a GPR-driven autonomous loop with a focus on Gaussian processes, and then shift the focus to the infrastructure that needs to be built around GPR to create a closed loop. Finally, the case studies we discuss show that Gaussian-process-based autonomous data acquisition is a widely applicable method that can facilitate the optimal use of instruments and facilities by enabling the efficient acquisition of high-value datasets. Gaussian process regression (GPR) is a powerful, non-parametric and robust technique for uncertainty quantification and function approximation that can be applied to optimal and autonomous data acquisition. This Review introduces the basics of GPR and discusses several use cases from different fields.

With the advancement of artificial intelligence and machine learning methods, autonomous approaches are recognized to have great potential for performing more efficient scattering experiments. In our view, it is crucial for such approaches to provide thorough evidence about respective performance improvements in order to increase acceptance within a scientific community. Therefore, we propose a benchmarking procedure designed as a cost-benefit analysis that is applicable to any scattering method sequentially collecting data during an experiment. For a given approach, the performance assessment is based on how much benefit, given a certain cost budget, it is able to acquire in predefined test cases. Different approaches thus get a chance for comparison and can make their advantages explicit and visible. Key components of the procedure, i.e., cost measures, benefit measures, and test cases, are made precise for the setting of three-axes spectrometry (TAS) as an illustration. Finally, we discuss neglected aspects and possible extensions for the TAS setting and comment on the procedure’s applicability to other scattering methods. A Python implementation of the procedure to simplify its utilization by interested researchers from the field is also provided.

The coupling of spin, charge and lattice degrees of freedom results in the emergence of novel states of matter across many classes of strongly correlated electron materials. A model example is unconventional superconductivity, which is widely believed to arise from the coupling of electrons via spin excitations. In cuprate high-temperature superconductors, the interplay of charge and spin degrees of freedom is also reflected in a zoo of charge and spin-density wave orders that are intertwined with superconductivity. A key question is whether the different types of density waves merely coexist or are indeed directly coupled. Here we profit from a neutron scattering technique with superior beam-focusing that allows us to probe the subtle spin-density wave order in the prototypical high-temperature superconductor La$${}_{1.88}$$ 1.88 Sr$${}_{0.12}$$ 0.12 CuO$${}_{4}$$ 4 under applied uniaxial pressure to demonstrate that the two density waves respond to the external tuning parameter in the same manner. Our result shows that suitable models for high-temperature superconductivity must equally account for charge and spin degrees of freedom via uniaxial charge-spin stripe fluctuations.

Despite decades of intense researches, the enigmatic pseudo-gap (PG) phase of superconducting cuprates remains an unsolved mystery. In the last 15 years, various symmetry breakings in the PG state have been discovered, spanning an intra-unit cell (IUC) magnetism, preserving the lattice translational (LT) symmetry but breaking time-reversal symmetry and parity, and an additional incipient charge density wave breaking the LT symmetry upon cooling. However, none of these states can (alone) account for the partial gapping of the Fermi surface. Here we report a hidden LT-breaking magnetism uisng polarized neutron diffraction. Our measurements reveal magnetic correlations, in two different underdoped $\rm YBa_{2}Cu_{3}O_{6.6}$ single crystals, that settle at the PG onset temperature with i) a planar propagation wave vector $(\pi,0) \equiv (0,\pi)$, yielding a doubling or quadrupling of the magnetic unit cell and ii) magnetic moments mainly pointing perpendicular to the $CuO_{2}$ layers. The LT-breaking magnetism is at short range suggesting the formation of clusters of 5-6 unit cells. Together with the previously reported IUC magnetism, it yields a hidden magnetic texture of the $CuO_{2}$ unit cells hosting loop currents, forming large supercells which may be crucial for elucidating the PG puzzle., Comment: 5 figures, supplementary file upon request

International audience; Chromium disilicide CrSi2 is an interesting compound for thermoelectric applications. In order to decrease its lattice thermal conductivity that mainly limits its performance, two main routes have been investigated thus far, either increasing the unit cell disorder or creating multiple interfaces through nanostructuring. Here, we explore the effect of the latter route by investigating in detail the effect of the grain size reduction and residual microstrains on the lattice dynamics and lattice thermal conductivity. The phonon dispersion curves were measured on single-crystalline CrSi2 using inelastic neutron scattering, while the generalized vibrational density of states (GVDOS) was determined on bulk and nanostructured CrSi2. All experimental results are consistent with our density functional theory calculations. The results show that the optical phonons contribute from 50 to 70% of the lattice thermal conductivity. The temperature variations in the GVDOS of CrSi2 follow a quasi-harmonic behavior, which explains its rather large lattice thermal conductivity measured on the single-crystalline specimen. In addition, the GVDOS of nanocrystalline CrSi2 evidences a spectral weight transfer at low energy, which is related to a decrease in both the Debye temperature and the sound velocities that may be ascribed to an increase in both the interface density and internal strain. These observations explain the strong decrease in the lattice thermal conductivity observed in our prior study on densified nanostructured CrSi2 pellets.

Inelastic neutron scattering spectra in the antiferromagnetic ferroborates ${\mathrm{Nd}}_{1\ensuremath{-}x}{\mathrm{Tb}}_{x}{\mathrm{Fe}}_{3}{({\mathrm{BO}}_{3})}_{4}$ ($x$ = 0, 0.1, 0.2, and 1) reveal various magnetic excitations of the interacting iron and rare-earth subsystems. We observe an evolution of the magnetic system from ``easy-plane'', in the Tb-free ($x$ = 0) case, to ``easy-axis'' anisotropy for samples substituted with Tb. The spectra show hybridized Fe and Nd branches, which are determined by the Fe-Nd exchange splitting of the ground-state ${\mathrm{Nd}}^{3+}$ doublet. In the easy-plane configuration, near the Brillouin zone center, there are two different pairs of anticrossing quasiacoustic Fe and Nd modes in contrast to the easy-axis state, where the two corresponding pairs of the branches are degenerated. The high-energy (exchange) branches are similar in both spin configurations. The Ising-type anisotropy of the Tb ion prevents the magnetic moment from precession. The increasing of the Tb content changes the effective magnetic anisotropy and stabilizes the easy-axis state. The spin-wave dispersion in the substituted and pure $\mathrm{Tb}{\mathrm{Fe}}_{3}{({\mathrm{BO}}_{3})}_{4}$ compounds, which have the same, easy-axis magnetic structure, but different crystal symmetry, strongly differ. The observed spectra were analysed in the frame of linear spin-wave theory and the exchange parameters were determined.

We present triple-axis neutron scattering studies of static and dynamic magnetic stripes in an optimally oxygen-doped cuprate superconductor, ${\mathrm{La}}_{2}{\mathrm{CuO}}_{4+y}$, which exhibits a clean superconducting transition at ${T}_{c}=42\phantom{\rule{0.28em}{0ex}}\mathrm{K}$. Polarization analysis reveals that the magnetic stripe structure is equally represented along both of the tetragonal crystal axes and that the fluctuating stripes display significant weight for in-plane as well as out-of-plane spin components. Both static magnetic order as well as low-energy fluctuations are fully developed in zero applied magnetic field and the low-energy spin fluctuations at $\ensuremath{\hbar}\ensuremath{\omega}=0.3\text{--}10\phantom{\rule{0.28em}{0ex}}\mathrm{meV}$ intensify on cooling. We interpret this as an indication that superconductivity and low-energy spin fluctuations coexist microscopically in spatial regions which are separated from domains with static magnetic order.

Quantum spin systems exhibit an enormous range of collective excitations, but their spin waves, gapped triplons, fractional spinons, or yet other modes are generally held to be mutually exclusive. Here we show by neutron spectroscopy on SeCuO$_3$ that magnons, triplons, and spinons are present simultaneously. We demonstrate that this is a consequence of a structure consisting of two coupled subsystems and identify all the interactions of a minimal magnetic model. Our results serve qualitatively to open the field of multi-excitation spin systems and quantitatively to constrain the complete theoretical description of one member of this class of materials., 8 pages, 5 figures

BACKGROUND The renin-angiotensin-aldosterone system plays a key role in blood pressure (BP) regulation and is the target of several antihypertensive medications. Renal denervation (RDN) is thought to interrupt the sympathetic mediated neurohormonal pathway as part of its mechanism of action to reduce BP. OBJECTIVES The purpose of this study was to evaluate plasma renin activity (PRA) and aldosterone before and after RDN and to assess whether these baseline neuroendocrine markers predict response to RDN. METHODS Analyses were conducted in patients with confirmed absence of antihypertensive medication. Aldosterone and PRA levels were compared at baseline and 3 months post-procedure for RDN and sham control groups. Patients in the SPYRAL HTN-OFF MED Pivotal trial were separated into 2 groups, those with baseline PRA >= 0.65 ng/ml/h (n = 110) versus < 0.65 ng/ml/h (n = 116). Follow-up treatment differences between RDN and sham control groups were adjusted for baseline values using multivariable linear regression models. RESULTS Baseline PRA was similar between RDN and control groups (1.0 +/- 1.1 ng/ml/h vs. 1.1 +/- 1.1 ng/ml/h; p = 0.37). Change in PRA at 3 months from baseline was significantly greater for RDN compared with control subjects (-0.2 +/- 1.0 ng/ ml/h; p = 0.019 vs. 0.1 +/- 0.9 ng/ml/h; p = 0.14), p = 0.001 for RDN versus control subjects, and similar differences were seen for aldosterone: RDN compared with control subjects (-1.2 +/- 6.4 ng/dl; p = 0.04 vs. 0.4 +/- 5.4 ng/dl; p = 0.40), p = 0.011. Treatment differences at 3 months in 24-h and office systolic blood pressure (SBP) for RDN versus control patients were significantly greater for patients with baseline PRA >= 0.65 ng/ml/h versus < 0.65 ng/ml/h, despite similar baseline BP. Differences in office SBP changes according to baseline PRA were also observed earlier at 2 weeks post-RDN. CONCLUSIONS Plasma renin activity and aldosterone levels for RDN patients were significantly reduced at 3 months when compared with baseline as well as when compared with sham control. Higher baseline PRA levels were associated with a significantly greater reduction in office and 24-h SBP. (SPYRAL PIVOTAL SPYRAL HTN-OFF MED Study; NCT02439749) (J Am Coll Cardiol 2021;77:2909-19) (c) 2021 The Authors. Published by Elsevier on behalf of the American College of Cardiology Foundation. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Anisotropic low-temperature properties of the cubic spinel helimagnet $\mathrm{Zn}{\mathrm{Cr}}_{2}{\mathrm{Se}}_{4}$ in the single-domain spin-spiral state are investigated by a combination of neutron scattering, thermal conductivity, ultrasound velocity, and dilatometry measurements. In an applied magnetic field, neutron spectroscopy shows a complex and nonmonotonic evolution of the spin-wave spectrum across the quantum-critical point that separates the spin-spiral phase from the field-polarized ferromagnetic phase at high fields. A tiny spin gap of the pseudo-Goldstone magnon mode, observed at wave vectors that are structurally equivalent but orthogonal to the propagation vector of the spin helix, vanishes at this quantum critical point, restoring the cubic symmetry in the magnetic subsystem. The anisotropy imposed by the spin helix has only a minor influence on the lattice structure and sound velocity but has a much stronger effect on the heat conductivities measured parallel and perpendicular to the magnetic propagation vector. The thermal transport is anisotropic at $T\ensuremath{\lesssim}2\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, highly sensitive to an external magnetic field, and likely results directly from magnonic heat conduction. We also report long-time thermal relaxation phenomena, revealed by capacitive dilatometry, which are due to magnetic domain motion related to the destruction of the single-domain magnetic state, initially stabilized in the sample by the application and removal of magnetic field. Our results can be generalized to a broad class of helimagnetic materials in which a discrete lattice symmetry is spontaneously broken by the magnetic order.

Potassium chromium jarosite, KCr3(OH)(6)(SO4)(2) (Cr-jarosite), is considered a promising candidate to display spin liquid behavior due to the strong magnetic frustration imposed by the crystal structure. However, the ground state magnetic properties have been debated, since Cr-jarosite is notoriously non-stoichiometric. Our study reports the magnetic properties for deuterated KCr3(OD)(6)(SO4)(2) on chemically well-defined samples, which have been characteried by a combination of powder X-ray diffraction, neutron diffraction, solid state NMR spectroscopy, and scanning electron microscopy with energy dispersive spectroscopy. Eight polycrystalline samples, which all contained only 1-3% Cr vacancies were obtained. However, significant substitution (2-27%) of potassium with H2O and/or H3O+ was observed and resulted in pronounced stacking disorder along the c-axis. A clear second-order transition to an antiferromagnetically ordered phase at T-N = 3.8(1) K with a small net moment of 0.03 mu(B) per Cr3+-ion was obtained from vibrating sample magnetometry and temperature dependent neutron diffraction. The moment is attributed to spin canting caused by the Dzyaloshinskii-Moriya interaction. Thus, our experimental results imply that even ideal potassium chromium jarosite will exhibit magnetic order below 4 K and therefore it does not qualify as a true spin liquid material.

Potassium chromium jarosite, KCr

The dimerized quantum magnet ${\mathrm{BaCuSi}}_{2}{\mathrm{O}}_{6}$ was proposed as an example of ``dimensional reduction'' arising near the magnetic-field-induced quantum critical point (QCP) due to perfect geometrical frustration of its interbilayer interactions. We demonstrate by high-resolution neutron spectroscopy experiments that the effective intrabilayer interactions are ferromagnetic, thereby excluding frustration. We explain the apparent dimensional reduction by establishing the presence of three magnetically inequivalent bilayers, with ratios $3\ensuremath{\mathbin:}2\ensuremath{\mathbin:}1$, whose differing interaction parameters create an extra field-temperature scaling regime near the QCP with a nontrivial but nonuniversal exponent. We demonstrate by detailed quantum Monte Carlo simulations that the magnetic interaction parameters we deduce can account for all the measured properties of ${\mathrm{BaCuSi}}_{2}{\mathrm{O}}_{6}$, opening the way to a quantitative understanding of nonuniversal scaling in any modulated layered system.

Inelastic neutron scattering has been used to study the in-plane Cu-O bond-stretching mode in oxygen-doped ${\mathrm{La}}_{1.94}{\mathrm{Sr}}_{0.06}{\mathrm{CuO}}_{4.035}$ $({T}_{c}=38\phantom{\rule{0.28em}{0ex}}\text{K})$ and ${\mathrm{La}}_{2}{\mathrm{CuO}}_{4+\ensuremath{\delta}}$ $({T}_{c}=43\phantom{\rule{0.28em}{0ex}}\text{K})$. Similar to results from optimally doped ${\mathrm{La}}_{1.85}{\mathrm{Sr}}_{0.15}{\mathrm{CuO}}_{4}$ $({T}_{c}=35\phantom{\rule{0.28em}{0ex}}\text{K})$, we observe anomalous features in the dispersion of this half-breathing mode in the form of a softening halfway through the Brillouin zone. Considering the differences in electronic structure and local environment between the oxygen- and strontium-doped compounds with similar ${T}_{\text{c}}$, we rule out a connection between the phonon anomaly and structural instabilities related to the specific dopant type. We interpret the phonon anomaly as a signature of correlated charge fluctuations ubiquitous in optimally doped superconductors.

Quantum spin liquids (QSLs) are exotic states of matter characterized by emergent gauge structures and fractionalized elementary excitations. The recently discovered triangular lattice antiferromagnet YbMgGaO$_4$ is a promising QSL candidate, and the nature of its ground state is still under debate. Here, we use neutron scattering to study the spin excitations in YbMgGaO$_4$ under various magnetic fields. Our data reveal a dispersive spin excitation continuum with clear upper and lower excitation edges under a weak magnetic field ($H=2.5$ T). Moreover, a spectral crossing emerges at the $\Gamma$ point at the Zeeman-split energy. The corresponding redistribution of the spectral weight and its field-dependent evolution are consistent with the theoretical prediction based on the inter-band and intra-band spinon particle-hole excitations associated with the Zeeman-split spinon bands, implying the presence of fractionalized excitations and spinon Fermi surfaces in the partially magnetized YbMgGaO$_4$., Comment: published version

CeCuAl3 crystallizing in the tetragonal BaNiSn3-type structure and CeCuxAl4–x solid solutions were investigated by means of elastic and inelastic neutron scattering. Powder neutron diffraction brought information on both temperature evolution of crystallographic parameters and magnetic order at low temperatures. No structural change was observed in the investigated temperature range from 1.5 to 300 K. Weak magnetic peaks outside nuclear Bragg positions observed in solid solutions with 0.90 ≤ x ≤ 1.10 were described by the propagation vector k = (0.40 + δx, 0.60 + δy, 0), where δx ≈ 0.02 and δy ≈ 0.01. The magnetic structure of CeCu0.75Al3.25 consists of two components: an anti-ferromagnetic one described by the same k and a ferromagnetic one with k0 = (0, 0, 0) and magnetic moments lying within the tetragonal basal plane. The evolution of magnetic excitations as a function of Cu–Al concentration in CeCuxAl4–x was studied by inelastic neutron scattering. The measured spectra of CeCuAl3 and the solution wit...

A detailed neutron scattering study of the Shastry–Sutherland material SrCu2(BO3)2 verifies the existence of a 4-spin plaquette singlet phase in this system.

Complex bound states of magnetic excitations, known as Bethe string, were predicted almost a century ago to exist in one-dimensional quantum magnets 1. The dispersions of the string states have so far remained the subject of intensive theoretical studies 2-7. By performing neutron scattering experiments on the one-dimensional Heisenberg-Ising antiferromagnet SrCo2V2O8 in high longitudinal magnetic fields, we reveal in detail the dispersion relations of the string states over the full Brillouin zone, as well as their magnetic field dependences. Furthermore the characteristic energy, the scattering intensity and linewidth of the observed string states exhibit excellent agreement with our precise Bethe Ansatz calculations. Our results establish the important role of string states in the quantum spin dynamics of one-dimensional systems, and will invoke studies of their dynamical properties in more general many-body systems., Main manuscript: 6 pages, 4 figures, Supplementary information: 8 pages, 6 figures, 1 table

Terbium gallium garnet (TGG), ${\mathrm{Tb}}_{3}{\mathrm{Ga}}_{5}{\mathrm{O}}_{12}$, is well known for its applications in laser optics but also exhibits complex low-temperature magnetism that is not yet fully understood. Its low-temperature magnetic order is determined by means of time-of-flight neutron powder diffraction. It is found to be a multiaxial antiferromagnet with magnetic ${\mathrm{Tb}}^{3+}$ ions forming six sublattices of magnetic moments aligned parallel and antiparallel to the $\ensuremath{\langle}100\ensuremath{\rangle}$ crystallographic directions of the cubic unit cell. The structure displays strong easy-axis anisotropy with respect to a twofold axis of symmetry in the local orthorhombic environment of the ${\mathrm{Tb}}^{3+}$ sites. The crystal-field splitting within the single-ion ground-state manifold is investigated by inelastic neutron scattering on powder samples. A strong temperature dependence of the quasidoublet ground state is observed and revised parameters of the crystal-field Hamiltonian are given. The results of bulk magnetic susceptibility and magnetization measurements are in good agreement with values based on the crystal-field model down to 20 K, where the onset of magnetic correlations is observed.

Tb2Ti2O7 presents an ongoing conundrum in the study of rare-earth pyrochlores. Despite the expectation that it should be the prototypical unfrustrated noncollinear Ising antiferromagnet on the pyrochlore lattice, it presents a puzzling correlated state that persists to the lowest temperatures. Effects which can reintroduce frustration or fluctuations are therefore sought, and quadrupolar operators have been implicated. One consequence of strong quadrupolar effects is the possible coupling of magnetic and lattice degrees of freedom, and it has previously been shown that a hybrid magnetoelastic mode with both magnetic and phononic character is formed in Tb2Ti2O7 by the interaction of a crystal field excitation with a transverse-acoustic phonon. Here, using polarized and unpolarized inelastic neutron scattering, we present a detailed characterization of the magnetic and phononic branches of this magnetoelastic mode, particularly with respect to their composition, the anisotropy of any magnetic fluctuations, and also the temperature dependence of the different types of fluctuation that are involved. We also examine the dispersion relations of the exciton branches that develop from the crystal field excitation in the same temperature regime that the coupled mode appears, and find three quasidispersionless branches where four are expected, each with a distinctive structure factor indicating that they are nonetheless cooperative excitations. We interpret the overall structure of the spectrum as containing four branches, one hybridized with the phonons and gaining a strong dispersion, and three remaining dispersionless.

When charged particles in periodic lattices are subjected to a constant electric field, they respond by oscillating. Here we demonstrate that the magnetic analogue of these Bloch oscillations are realised in a ferromagnetic easy axis chain. In this case, the “particles” undergoing oscillatory motion in the presence of a magnetic field are domain walls. Inelastic neutron scattering reveals three distinct components of the low energy spin-dynamics including a signature Bloch oscillation mode. Using parameter-free theoretical calculations, we are able to account for all features in the excitation spectrum, thus providing detailed insights into the complex dynamics in spin-anisotropic chains.

We report neutron scattering measurements of single-crystalline YFe_{2}Ge_{2} in the normal state, which has the same crystal structure as the 122 family of iron pnictide superconductors. YFe_{2}Ge_{2} does not exhibit long-range magnetic order but exhibits strong spin fluctuations. Like the iron pnictides, YFe_{2}Ge_{2} displays anisotropic stripe-type antiferromagnetic spin fluctuations at (π, 0, π). More interesting, however, is the observation of strong spin fluctuations at the in-plane ferromagnetic wave vector (0, 0, π). These ferromagnetic spin fluctuations are isotropic in the (H, K) plane, whose intensity exceeds that of stripe spin fluctuations. Both the ferromagnetic and stripe spin fluctuations remain gapless down to the lowest measured energies. Our results naturally explain the absence of magnetic order in YFe_{2}Ge_{2} and also imply that the ferromagnetic correlations may be a key ingredient for iron-based materials.

The challenge of one-dimensional systems is to understand their physics beyond the level of known elementary excitations. By high-resolution neutron spectroscopy in a quantum spin ladder material, we probe the leading multiparticle excitation by characterizing the two-magnon bound state at zero field. By applying high magnetic fields, we create and select the singlet (longitudinal) and triplet (transverse) excitations of the fully spin-polarized ladder, which have not been observed previously and are close analogs of the modes anticipated in a polarized Haldane chain. Theoretical modelling of the dynamical response demonstrates our complete quantitative understanding of these states., Comment: 6 pages, 3 figures plus supplementary material 7 pages 5 figures

YFeO

The H5 program with the complete rebuild of the guide system and the upgrade or renovation of all instruments leads to a tremendous increase of the instrument performances. The improvement was obtained both in terms of more useful flux and upgrade of the different instruments (e.g. higher field density for IN15). In addition, the industrial application instrument D50 offers an addition to the ILL instrument suite (see p. 27 in this issue). With the commissioning of the new spin echo spectrometer WASP in 2016, the H5 program will be completed and a considerable improvement for the ILL instrument park will be finalized.

The α-MnS-based Fe X Mn 1− X S (0 x x = 0) to 200 K ( x = 0.29) observed in these materials is accompanied by a decrease in the NaCl-type cubic lattice parameters. It is established that at the symmetry transformation in the compositions with x = 0.25 and 0.29 the structural transition occurs, which is followed by the magnetic transition. These features make the Fe X Mn 1− X S solid solutions interesting for both fundamental study of the interrelation between the magnetic, electrical, and structural properties in MnO-type strongly correlated electron systems and application.

Since the seminal ideas of Berezinskii, Kosterlitz and Thouless, topological excitations are at the heart of our understanding of a whole novel class of phase transitions. In most of the cases, those transitions are controlled by a single type of topological objects. There are however some situations, still poorly understood, where two dual topological excitations fight to control the phase diagram and the transition. Finding experimental realization of such cases is thus of considerable interest. We show here that this situation occurs in BaCo$_2$V$_2$O$_8$, a spin-1/2 Ising-like quasi-one dimensional antiferromagnet when subjected to a uniform magnetic field transverse to the Ising axis. Using neutron scattering experiments, we measure a drastic modification of the quantum excitations beyond a critical value of the magnetic field. This quantum phase transition is identified, through a comparison with theoretical calculations, to be a transition between two different types of solitonic topological objects, which are captured by different components of the dynamical structure factor., 9 pages, 4 figures; 10 additional pages of supplemental information containing 6 figures

We report on the first single crystal study of SrTm2O4. Magnetization measurements along the crystallographic axes of a nearly stoichiometric Sr1.07(3)Tm2.07(6)O4.00(2) sample show either a positive or a negative Curie–Weiss temperature indicative of a competition between antiferromagnetic and ferromagnetic couplings. The field-dependent magnetization suggests an effective Zeeman splitting of the high-level J-multiplets above ∼8.3 T and that the paramagnetism may originate from only one of the two inequivalent Tm3+ crystallographic sites. Our single-crystal polarized neutron scattering and powder unpolarized neutron diffraction data show no evidence for either long- or short-range magnetic order even down to ∼65 mK. We reveal two TmO6 octahedral distortion modes, i.e., one distortion is stronger than the other especially at low temperatures, which is attributed to different crystal fields of the two inequivalent octahedra. Therefore, the compound SrTm2O4 is unique and different from its brethren in the family of frustrated SrRE2O4 (RE = rare earth) magnets. We propose that crystal field anisotropy may dominate over weak dipolar spin interactions in SrTm2O4, thereby leading to a virtually non-ordered magnetic state.

CeCuAl

Recently, by using deep learning methods, a computer is able to surpass or come close to matching human performance on image analysis and recognition. This advanced methods could also help extracting features from neutron scattering experimental data. Those data contain rich scientific information about structure and dynamics of materials under investigation. Deep learning could help researchers better understand the link between experimental data and materials properties. Moreover,it could also help to optimize neutron scattering experiment by predicting the best possible instrument configuration. Among all possible experimental methods, we begin our study on the small-angle neutron scattering (SANS) data and by predicting the structure geometry of the sample material at an early stage. This step is a keystone to predict the experimental parameters to properly setup the instrument as well as the best measurement strategy. In this paper, we propose to use transfer learning to retrain a convolutional neural networks (CNNs) based pre rained model to adapt the scattering images classification, which could predict the structure of the materials at an early stage in the SANS experiment. This deep neural network is trained and validated on simulated database, and tested on real scattering images.

Mineral selective magnetizing flash roasting in oxidizing atmosphere was tested successfully for the improved low intensity magnetic separation of siderite from ankerite and other gangue minerals within ore. The magnetization process was simulated with particle bed tests permeated with artificial combustion gas. The phase transition and the gas composition were measured simultaneously during temperature and time-dependent neutron diffraction experiments. The physical background of the rapid phase transition and the nature of the SO2 absorption are discussed. Apart from the scientific background, the effects on the process technique are outlined.

A quantum critical point (QCP) is a singularity in the phase diagram arising due to quantum mechanical fluctuations. The exotic properties of some of the most enigmatic physical systems, including unconventional metals and superconductors, quantum magnets, and ultracold atomic condensates, have been related to the importance of the critical quantum and thermal fluctuations near such a point. However, direct and continuous control of these fluctuations has been difficult to realize, and complete thermodynamic and spectroscopic information is required to disentangle the effects of quantum and classical physics around a QCP. Here we achieve this control in a high-pressure, high-resolution neutron scattering experiment on the quantum dimer material TlCuCl3. By measuring the magnetic excitation spectrum across the entire quantum critical phase diagram, we illustrate the similarities between quantum and thermal melting of magnetic order. We prove the critical nature of the unconventional longitudinal ("Higgs") mode of the ordered phase by damping it thermally. We demonstrate the development of two types of criticality, quantum and classical, and use their static and dynamic scaling properties to conclude that quantum and thermal fluctuations can behave largely independently near a QCP., 6 pages, 4 figures. Original version, published version available from Nature Physics website

Structure and magnetic properties of Pb 3 (Mn 1− x Fe x ) 7 O 15 single crystals with х =0–0.2 grown by spontaneous crystallization from solution in melt have been investigated. All the crystals belong to the hexagonal space group P6 3 /mcm . The magnetic properties appeared to be strongly dependent on the iron doping level. At small ( х =0.05) dopant concentrations, the value of magnetization and Neel temperature T N decrease insignificantly ( T N =70 K). With increasing х , the three-dimensional magnetic ordering does not occur and temperature dependences of magnetization at х ≥0.1 exhibit spin-glass-like features in the low-temperature region.

${\mathrm{CePd}}_{2}{\mathrm{Al}}_{2\ensuremath{-}x}{\mathrm{Ga}}_{x}$ compounds crystallizing in the tetragonal ${\mathrm{CaBe}}_{2}{\mathrm{Ge}}_{2}$-type structure (space group $P4/nmm$) and undergoing a structural phase transition to an orthorhombic structure ($Cmme$) at low temperatures were studied by means of neutron scattering. The amplitude-modulated magnetic structure of ${\mathrm{CePd}}_{2}{\mathrm{Al}}_{2}$ is described by an incommensurate propagation vector $\stackrel{P\vec}{k}=({\ensuremath{\delta}}_{x},\frac{1}{2}+{\ensuremath{\delta}}_{y},0)$ with ${\ensuremath{\delta}}_{x}=0.06$ and ${\ensuremath{\delta}}_{y}=0.04$. The magnetic moments order antiferromagnetically within the $ab$ planes stacked along the $c$ axis and are arranged along the direction close to the orthorhombic $a$ axis with a maximum value of 1.5(1) ${\ensuremath{\mu}}_{\mathrm{B}}/{\mathrm{Ce}}^{3+}$. ${\mathrm{CePd}}_{2}{\mathrm{Ga}}_{2}$ reveals a magnetic structure composed of two components: the first is described by the propagation vector $\stackrel{P\vec}{{k}_{1}}=(\frac{1}{2},\phantom{\rule{0.16em}{0ex}}\frac{1}{2},\phantom{\rule{0.16em}{0ex}}0)$, and the second one propagates with $\stackrel{P\vec}{{k}_{2}}=(0,\frac{1}{2},0)$. The magnetic moments of both components are aligned along the same direction---the orthorhombic [100] direction---and their total amplitude varies depending on the mutual phase of magnetic moment components on each Ce site. The propagation vectors $\stackrel{P\vec}{{k}_{1}}$ and $\stackrel{P\vec}{{k}_{2}}$ describe also the magnetic structure of substituted ${\mathrm{CePd}}_{2}{\mathrm{Al}}_{2\ensuremath{-}x}{\mathrm{Ga}}_{x}$ compounds, except the one with $x=0.1.\phantom{\rule{0.28em}{0ex}}{\mathrm{CePd}}_{2}{\mathrm{Al}}_{1.9}{\mathrm{Ga}}_{0.1}$ with magnetic structure described by $\stackrel{P\vec}{k}$ and $\stackrel{P\vec}{{k}_{1}}$ stays on the border between pure ${\mathrm{CePd}}_{2}{\mathrm{Al}}_{2}$ and the rest of the series. Determined magnetic structures are compared with other Ce 112 compounds. Inelastic neutron scattering experiments disclosed three nondispersive magnetic excitations in the paramagnetic state of ${\mathrm{CePd}}_{2}{\mathrm{Al}}_{2}$, while only two crystal field (CF) excitations are expected from the splitting of ground state $J=\frac{5}{2}$ of the ${\mathrm{Ce}}^{3+}$ ion in a tetragonal/orthorhombic point symmetry. Three magnetic excitations at 1.4, 7.8, and 15.9 meV are observed in the tetragonal phase of ${\mathrm{CePd}}_{2}{\mathrm{Al}}_{2}$. A structural phase transition to an orthorhombic structure shifts the first excitation up to 3.7 meV, while the other two excitations remain at almost the same energy. The presence of an additional magnetic peak is discussed and described within the Thalmeier-Fulde CF-phonon coupling (i.e., magnetoelastic coupling) model generalized to the tetragonal point symmetry. The second parent compound ${\mathrm{CePd}}_{2}{\mathrm{Ga}}_{2}$ does not display any sign of additional magnetic excitation. The expected two CF excitations were observed. The development of magnetic excitations in the ${\mathrm{CePd}}_{2}{\mathrm{Al}}_{2\ensuremath{-}x}{\mathrm{Ga}}_{x}$ series is discussed and crystal field parameters determined.

This article provides a more integrative approach toward channel choice than previous research by considering all stages of the buying process (search, purchase, and after-sales), and by taking channel attributes, experience, and spillover effects into account when examining consumers' channel choice intentions. The authors show that such an integrative perspective is important as channel attributes, experience, and spillover matter for consumers' channel choices in all stages of the buying process. Notably, the study stresses the importance of channel experience and spillover effects for explaining consumers' channel choice intentions in the different stages of the buying process. Channel experience effects occur when using the channel increases the likelihood that the consumer will use the very same channel on the next occasion. Spillover effects result when the likelihood of using a channel in one stage of the buying process affects the likelihood of choosing that channel in another stage. The results show that both effects influence consumers' channel choice intentions over and above channel attributes. Importantly, the model results strongly pledge for studying attribute, experience, and spillover effects simultaneously.

In the version of this Letter originally published, the year for ref. 30 was incorrectly listed as 2009; it should have been 2004. This has now been corrected.

YFeO$_3$ and LaFeO$_3$ are members of the rare-earth orthoferrites family with \textit{Pbnm} space group. Using inelastic neutron scattering, the low-energy spin excitations have been measured around magnetic Brillouin zone center. Splitting of magnon branches and non-zero magnon gap is observed for both compounds, which is similar to the behavior observed in multiferroic BiFeO$_3$. Spin wave calculations which include both Dzyaloshinsky-Moriya interactions and single-ion anisotropy in the spin-Hamiltonian comprehensively accounts for all the experimentally observed features. Our results offer insight into the unifying physics underlying the Fe$^{3+}$-based perovskites as well as their distinguishing characteristics., 7 pages, 4 figures

We report on the crystallographic structure of the layered compound Pb 3 Mn 7 O 15 . Previous analysis based on laboratory X-ray data at room temperature gave contradictory results in terms of the description of the unit cell. Motivated by recent magnetic bulk measurements of this system [N.V. Volkov, K.A. Sablina, O.A. Bayukov, E.V. Eremin, G.A. Petrakovskii, D.A. Velikanov, A.D. Balaev, A.F. Bovina, P. Boni, E. Clementyev, J. Phys. Condens. Matter 20 (2008) 055217], we re-investigated the chemical structure with high-resolution synchrotron powder diffraction at temperatures between 15 and 295 K. Our results show that the crystal structure of stoichiometric Pb 3 Mn 7 O 15 has a pronounced 2-dimensional character and can be described in the orthorhombic space group Pnma.

In light of mature markets and increasing competitive pressure, retaining the existing customer base becomes crucial for the future success of a firm. As a consequence, firms are increasingly interested in understanding the factors influencing and driving customer retention. One factor that is hypothesized to have an impact on customer retention is the growing use of the Internet channel. Firms are interested in understanding whether and how the Internet use induces a change in customer retention. The aim of this paper is to empirically quantify the impact of Internet use on customer retention when accounting for potentially present self-selection. Furthermore, the paper will derive managerial implications on how to use customer channel migration to improve overall customer retention. The results of the empirical study indicate a strong positive impact of Internet use on customer retention. Hence, migrating customers to the Internet channel has the potential to increase overall retention rates.

Single crystals of the α-MnS-based FexMn1-xS (x = 0-0.3) solid solutions are prepared and shown to be new Mott materials with the rock salt structure.

The high-energy branch of the spin-wave spectrum of CuB 2 O 4 in the incommensurate magnetic phase was investigated by means of a linear spin-wave theory. The influence of the intersubsystem interactions on the spectrum of the “strong” subsystem was taken into account as the effective field in the framework of the mean-field approach. The comparison with the inelastic neutron scattering experiment leads to the conclusion about the additional “spiral anisotropy” appearance due to the dynamical interaction through the “weak” subsystem fluctuations (the “order due to disorder” mechanism) in the incommensurate phase.

International audience; Iron based high temperature superconductors have several common features with superconducting cuprates, including the square lattice and the proximity to an antiferromagnetic phase. The magnetic excitation spectrum below Tc of shows an hourglass-shaped dispersion with a resonance around the commensurate point . In a previous inelastic neutron scattering study, we showed that the hourglass-shaped dispersion is most likely a prerequisite for superconductivity, while the consequences are the opening of a gap and a shift of spectral weight. In this paper we follow the evolution of the hourglass shaped dispersion under applied pressure up to 12 kbar. Our results show that that the pressure-induced 37% increase of Tc is concomitant with a change in the magnetic excitation spectrum, with an increase of the hourglass energy by 38%.