This article presents the results of inelastic scattering studies of neutrons and copper and silver chalcogenides at a temperature of 300 K in the non-superionic phase. We were the first to obtain dynamic structural factors and generalized the phonon densities of the states of these compounds. Inelastic peaks observed at energies of 3–5 meV presumably correspond to the acoustic vibrations of phonons. The phonon spectra of copper and silver chalcogenides have features characteristic of compounds that are structurally disordered.

The strongly correlated system Ho11B12 with boron sublattice Jahn-Teller instability and nanoscale electronic phase separation (dynamic charge stripes) was studied in detail by inelastic neutron scattering (INS), magnetometry and heat capacity measurements at temperatures in the range 3-300 K. From the analysis of registered INS spectra, we determined parameters of the cubic crystal field at holmium sites, B4=- 0.333 meV and B6= -2.003 meV (in Stevens notations), with an unconventional large ratio B6/B4 pointing on the dominant role of conduction electrons in the formation of a crystal field potential. The molecular field in the antiferromagnetic state, Bloc = (1.75+- 0.1) T has been directly determined from the INS spectra together with short-range order effects detected in the paramagnetic state. A comparison of measured magnetization in diluted Lu0.99Ho0.01B12 and concentrated HoB12 single crystals showed a strong suppression of Ho magnetic moments by antiferromagnetic exchange interactions in holmium dodecaboride. To account explicitly for the short-range antiferromagnetic correlations, a self-consistent holmium dimer model was developed that allowed us to reproduce successfully field and temperature variations of the magnetization and heat capacity in the cage-glass phase of HoB12 in external magnetic fields.

2 dimerized antiferromagnetic-ferromagnetic quantum spin-chain BaCu2V2O8 E. S. Klyushina, 2, ∗ A.T.M.N. Islam, J. T. Park, E. A. Goremychkin, † E. Wheeler, B. Klemke, and B. Lake 2 Helmholtz-Zentrum Berlin für Materialien und Energie, 14109 Berlin, Germany Institut für Festkörperphysik, Technische Universität Berlin, 10623 Berlin, Germany Heinz Maier-Leibnitz Zentrum, TU München, 85747 Garching, Germany Rutherford Appleton Laboratory, Chilton, Didcot, Oxon OX11 0QX, United Kingdom Institut Laue-Langevin, Boite Postale 156X, F-38042 Grenoble Cedex 9, France

The novel quantum magnet BaCu2V2O8 was recently discovered to be a rare physical realization of a one-dimensional antiferromagnetic-ferromagnetic dimerized chain which displays strongly correlated phenomena at elevated temperatures [E. S. Klyushina et al., Phys.Rev.B 93, 241109(R) (2016)]. This paper presents an extended study of the Hamiltonian of BaCu2V2O8 at base temperature. Static susceptibility and inelastic neutron scattering data are compared to several theoretical models. An analytical relation for the dynamic structure factor of the complex unit cell of BaCu(2)V(2)O(8 )is derived and used to identify the intrachain exchange paths. Further analysis using the first moment of the dynamic structure factor was employed to determine the exchange path responsible for the intradimer interaction. This analysis reveals that the dimer chain is formed by a dominant antiferromagnetic exchange interaction J(intra) = 40.92 meV which is realized via the Cu-O-V(II)-O-Cu superexchange path and a weak ferromagnetic coupling J(intra) = -11.97 meV which arises within the copper-oxygen double plaquettes.

The formation of the structural and dynamic properties of La 2 Zr 2 O 7 in the process of crystallization at the isothermal annealing of initially amorphous precursors obtained by the coprecipitation of corresponding salts has been studied by neutron spectroscopy. The existence of vibrational states characteristic of hydrogen, which is in one or another of the possible chemical states and is incorporated into a solid matrix, has been detected in the spectra of amorphous and fluorite phases. The DFT calculation of the phonon density of states has been performed to analyze the energy structure of experimental phonon spectra for various phases of the La 2 Zr 2 O 7 compound. The amount of hydrogen in the fluorite phase has been estimated.

P. Babkevich, ∗ A. Finco, 2 M. Jeong, B. Dalla Piazza, I. Kovacevic, G. Klughertz, 3 K. W. Krämer, C. Kraemer, D. T. Adroja, E. Goremychkin, T. Unruh, 7 T. Strässle, A. Di Lieto, 10 J. Jensen, and H. M. Rønnow Laboratory for Quantum Magnetism, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland ICFP, Département de physique, École normale supérieure, 45 rue d’Ulm, 75005 Paris, France Institut de Physique et Chimie des Matériaux de Strasbourg, CNRS and Université de Strasbourg, Bôıte Postale 43, F-67034 Strasbourg, France Department of Chemistry and Biochemistry, University of Bern, CH-3012 Bern, Switzerland ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX11 0QX, United Kingdom Forschungsneutronenquelle Heinz Maier-Leibnitz (FRM II), Technische Universität München 85748 Garching, Germany Lehrstuhl für Kristallographie und Strukturphysik, Friedrich-Alexander-Universität Erlangen-Nürnberg, Physik Department 91058 Erlangen, Germany Laboratory for Neutron Scattering, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland Dipartimento di Fisica, Universita di Pisa, Largo B. Pontecorvo 3, I-56127 Pisa, Italy NEST Istituto di Nanoscienze-CNR, Piazza S. Silvestro 12, I-56127 Pisa, Italy Niels Bohr Institute, Universitetsparken 5, 2100 Copenhagen, Denmark (Dated: October 13, 2018)

The possibility of increasing the sensitivity of a neutron detector based on a TlInSe 2 crystal by introducing the 6 Li isotope into this crystal is investigated. Introduction of the isotope is conducted by the method of electrochemical intercalation from aqueous and nonaqueous solutions of LiCl and also from the melt of the LiCl–KCl eutectic. It is shown that intercalation by the electrochemical method from a LiCl solution in propylene carbonate, performed along the “c” axis of the crystal (along strong bond chains) is efficient. The attained concentration of introduced lithium amounts to (1–1.2) × 10 21 cm –3 , which increased the sensitivity of the detector by approximately four times. Good agreement between the calculated and experimental values of the detector sensitivity is demonstrated.

Исследовалась возможность увеличения чувствительности детектора нейтронов на основе полупроводника TlInSe2 путем введения в кристалл изотопа лития 6Li. Введение проводилось методом электрохимической интеркаляции из водных и неводных растворов LiCl, а также из расплава эвтектики LiCl-KCl. Показана эффективность интеркалирования электрохимическим методом из раствора LiCl в пропиленкарбонате, проводимого вдоль оси "с" кристалла (вдоль цепочек сильной связи). Достигнутая концентрация введенного лития составила (1-1.2)· 1021 см-3, что примерно вчетверо увеличило чувствительность детектора. Показано хорошее согласие между рассчитанным и фактическим значением чувствительности детектора. DOI: 10.21883/FTP.2017.06.44555.8170

Present status of the measurements of the neutron lifetime is shortly reviewed. We report the inelastic neutron scattering measurement of the density of vibrational states G(ω) of two fluoropolymers, which are promising coating materials for the storage of ultracold neutrons (UCNs) in closed volumes covered with polymer film. From determined G(ω), we calculate the expected UCN loss coefficients.

The magnetic properties of the two-dimensional, S = 1 honeycomb antiferromagnet BaNi2V2O8 have been comprehensively studied using dc susceptibility measurements and inelastic neutron scattering techniques. The magnetic excitation spectrum is found to be dispersionless within experimental resolution between the honeycomb layers, while it disperses strongly within the honeycomb plane where it consists of two gapped spin-wave modes. The magnetic excitations are compared to linear spin-wave theory allowing the Hamiltonian to be determined. The first-and second-neighbor magnetic exchange interactions are antiferromagnetic and lie within the ranges 10.90 meV <= J(n) <= 13.35 meV and 0.85 meV <= J(nn) <= 1.65 meV, respectively. The interplane coupling J(out) is four orders of magnitude weaker than the intraplane interactions, confirming the highly two-dimensional magnetic behavior of this compound. The sizes of the energy gaps are used to extract the magnetic anisotropies and reveal substantial easy-plane anisotropy and a very weak in-plane easy-axis anisotropy. Together these results reveal that BaNi2V2O8 is a candidate compound for the investigation of vortex excitations and Berezinsky-Kosterliz-Thouless phenomenon.

Inelastic neutron scattering (INS) and specific heat measurements have been performed on the intermediate valence compound CeRuSi3, which is isostructural to the noncentrosymmetric pressure-induced superconductors CeRhSi3, CeIrSi3, and CeCoGe3. INS measurements at 7 K reveal a broad peak at (58.5 +/- 1.4) meV, while at 300 K, broad quasielastic scattering is observed. This indicates a large Kondo temperature of T-K similar to 680 K. The magnetic contribution to the specific heat (C-mag) has a value of gamma = 62.5(1) mJ/mol K-2 at low temperatures and above about 100 K can be well accounted for by the Coqblin-Schrieffer model with a characteristic temperature of T-0 = 680 K, which is further evidence that CeRuSi3 is in the intermediate valence regime.

We present a systematic study of the crystal-field interactions in the LiRF4 (R = Gd, Ho, Er, Tm, and Yb) family of rare-earth magnets. Using detailed inelastic neutron scattering measurements, we have been able to quantify the transition energies and wave functions for each system. This allows us to quantitatively describe the high-temperature susceptibility measurements for the series of materials and make predictions based on a mean-field approach for the low-temperature thermal and quantum phase transitions. We show that coupling between crystal field and phonon states leads to line-shape broadening in LiTmF4 and level splitting in LiYbF4. Furthermore, using high-resolution neutron scattering from LiHoF4, we find anomalous broadening of crystal-field excitations which we attribute to magnetoelastic coupling.

We report inelastic neutron scattering experiments on a single crystal of the intermediate valence compound CePd3. At 300 K the magnetic scattering is quasielastic, with halfwidth of 23 meV, and is independent of momentum transfer Q. At low temperature, the Q-averaged magnetic spectrum is inelastic, exhibiting a broad peak centered near Emax = 55 meV. These results, together with the temperature dependence of the susceptibility, 4f occupation number, and specific heat, can be fit by the Kondo/Anderson impurity model. The low temperature scattering near Emax, however, shows significant variations with Q, reflecting the coherence of the 4f lattice. The intensity is maximal at (1/2, 1/2,0), intermediate at (1/2,0,0) and (0,0,0), and weak at (1/2,1/2,1/2). We discuss this Q-dependence in terms of current ideas about coherence in heavy fermion systems.

The Fe1+yTe1-xSex series of materials is one of the prototype families of Fe-based superconductors. To provide further insight into these materials, we present systematic inelastic neutron scattering measurements of the low-energy spin excitations for x = 0.27, 0.36, 0.40, and 0.49. These measurements show an evolution of incommensurate spin excitations towards the (1/2,1/2,0) wave vector with doping. Concentrations (x = 0.40 and 0.49) which exhibit the most robust superconducting properties have spin excitations closest to (1/2,1/2,0) and also exhibit a strong spin resonance in the spin excitation spectrum below T-c. The resonance signal appears to be closer to (1/2,1/2,0) than the underlying spin excitations. We discuss the possible relationship between superconductivity and spin excitations at the (1/2,1/2,0) wave vector and the role that interstitial Fe may play.

M. Smidman,1,* D. T. Adroja,2,† A. D. Hillier,2 L. C. Chapon,3 J. W. Taylor,2 V. K. Anand,2 R. P. Singh,1 M. R. Lees,1 E. A. Goremychkin,2,4 M. M. Koza,3 V. V. Krishnamurthy,5 D. M. Paul,1 and G. Balakrishnan1,‡ 1Department of Physics, University of Warwick, Coventry CV4 7AL, United Kingdom 2ISIS Facility, STFC, Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX11 0QX, United Kingdom 3Institut Laue-Langevin, Boı̂te Postale 156, 38042 Grenoble Cedex 9, France 4School of Physics and Astronomy, University of Southampton, Southampton SO17 1BJ, United Kingdom 5School of Physics, Astronomy and Computational Sciences, George Mason University, Fairfax, Virginia 22030, USA (Received 1 August 2013; published 18 October 2013)

We use inelastic neutron scattering (INS) spectroscopy to study the magnetic excitations spectra throughout the Brillouin zone in electron-doped iron pnictide superconductors BaFe2-xNixAs2 with x = 0.096,0.15,0.18. While the x = 0.096 sample is near optimal superconductivity with T-c = 20 K and has coexisting static incommensurate magnetic order, the x = 0.15,0.18 samples are electron overdoped with reduced T-c of 14 and 8 K, respectively, and have no static antiferromagnetic (AF) order. In previous INS work on undoped (x = 0) and electron optimally doped (x = 0.1) samples, the effect of electron doping was found to modify spin waves in the parent compound BaFe2As2 below similar to 100 meV and induce a neutron spin resonance at the commensurate AF ordering wave vector that couples with superconductivity. While the new data collected on the x = 0.096 sample confirm the overall features of the earlier work, our careful temperature dependent study of the resonance reveals that the resonance suddenly changes its Q width below T-c similar to that of the optimally hole-doped iron pnictides Ba0.67K0.33Fe2As2. In addition, we establish the dispersion of the resonance and find it to change from commensurate to transversely incommensurate with increasing energy. Upon further electron doping to overdoped iron pnictides with x = 0.15 and 0.18, the resonance becomes weaker and transversely incommensurate at all energies, while spin excitations above similar to 100 meV are still not much affected. Our absolute spin excitation intensity measurements throughout the Brillouin zone for x = 0.096,0.15,0.18 confirm the notion that the low-energy spin excitation coupling with itinerant electron is important for superconductivity in these materials, even though the high-energy spin excitations are weakly doping dependent.

The magnetic states of the noncentrosymmetric pressure-induced superconductor CeCoGe3 have been studied with magnetic susceptibility, muon spin relaxation (mu SR), single-crystal neutron diffraction, and inelastic neutron scattering (INS). CeCoGe3 exhibits three magnetic phase transitions at T-N1 = 21, T-N2 = 12, and T-N3 = 8 K. The presence of long-range magnetic order below T-N1 is revealed by the observation of oscillations of the asymmetry in the mu SR spectra between 13 and 20 K and a sharp increase in the muon depolarization rate. Single-crystal neutron-diffraction measurements reveal magnetic Bragg peaks consistent with propagation vectors of k = (0,0, 2/3) between T-N1 and T-N2, k = (0,0, 5/8) between T-N2 and T-N3 and k = (0,0, 1/2) below T-N3. An increase in intensity of the (110) reflection between T-N1 and T-N3 also indicates a ferromagnetic component in these phases. These measurements are consistent with an equal moment two-up two-down magnetic structure below T-N3 with a magnetic moment of 0.405(5)mu(B)/Ce. Above T-N2, the results are consistent with an equal moment two-up one-down structure with a moment of 0.360(6)mu(B)/Ce. INS studies reveal two crystal-electric-field (CEF) excitations at similar to 19 and similar to 27 meV. From an analysis with a CEF model, the wave functions of the J = 5/2 multiplet are evaluated along with a prediction for the magnitude and direction of the ground-state magnetic moment. Our model correctly predicts that the moments order along the c axis, but the observed magnetic moment of 0.405(5)mu(B) is reduced compared to the predicted moment of 1.0 mu(B). This is ascribed to hybridization between the localized Ce3+ f electrons and the conduction band. This suggests that CeCoGe3 has a degree of hybridization between that of CeRhGe3 and the noncentrosymmetric superconductor CeRhSi3.

Magnetic fluctuations in the molecular-intercalated FeSe superconductor Li{x}(ND2){y}(ND3){1-y}Fe2Se2 (Tc = 43K) have been measured by inelastic neutron scattering from a powder sample. The strongest magnetic scattering is observed at a wave vector Q ~ 1.4 A^{-1}, which is not consistent with the (pi,0) nesting wave vector that characterizes magnetic fluctuations in several other iron-based superconductors, but is close to the (pi, pi/2) position found for A{x}Fe{2-y}Se2 systems. At the energies probed (~ 5kB Tc), the magnetic scattering increases in intensity with decreasing temperature below Tc, consistent with the superconductivity-induced magnetic resonance found in other iron-based superconductors.

High-temperature superconductivity in iron pnictides occurs when electrons and holes are doped into their antiferromagnetic parent compounds. Since spin excitations may be responsible for electron pairing and superconductivity, it is important to determine their electron/hole-doping evolution and connection with superconductivity. Here we use inelastic neutron scattering to show that while electron doping to the antiferromagnetic BaFe 2 As 2 parent compound modifies the low-energy spin excitations and their correlation with superconductivity (<50 meV) without affecting the high-energy spin excitations (>100 meV), hole-doping suppresses the high-energy spin excitations and shifts the magnetic spectral weight to low-energies. In addition, our absolute spin susceptibility measurements for the optimally hole-doped iron pnictide reveal that the change in magnetic exchange energy below and above T c can account for the superconducting condensation energy. These results suggest that high- T c superconductivity in iron pnictides is associated with both the presence of high-energy spin excitations and a coupling between low-energy spin excitations and itinerant electrons.