A5063280405- Nuclear Physics and Applications
- Advanced Condensed Matter Physics
- Magnetic and transport properties of perovskites and related materials
- High-pressure geophysics and materials
- X-ray Diffraction in Crystallography
- Physics of Superconductivity and Magnetism
- Rare-earth and actinide compounds
- Atomic and Subatomic Physics Research
- Multiferroics and related materials
- Thermodynamic and Structural Properties of Metals and Alloys
- Radiation Detection and Scintillator Technologies
- Theoretical and Computational Physics
- Solid-state spectroscopy and crystallography
- Advanced Chemical Physics Studies
- nanoparticles nucleation surface interactions
- Material Dynamics and Properties
- Advanced NMR Techniques and Applications
- Inorganic Fluorides and Related Compounds
- Magnetic properties of thin films
- Quantum, superfluid, helium dynamics
- Inorganic Chemistry and Materials
- Surface and Thin Film Phenomena
- Iron-based superconductors research
- Advancements in Solid Oxide Fuel Cells
- Crystal Structures and Properties
Forschungszentrum Jülich
2015-2024
European Spallation Source
2015-2024
RWTH Aachen University
2009
Donostia International Physics Center
2005-2006
Ian's Friends Foundation
1989-2005
University of Georgia
1998
The magnetic properties of dilute semiconductors (DMSs) are calculated from first-principles by mapping the ab initio results on a classical Heisenberg model. By using Korringa--Kohn--Rostoker coherent-potential approximation (KKR-CPA) method within local-density approximation, electronic structure (Ga, Mn)N and Mn)As is calculated. Effective exchange coupling constants ${J}_{ij}$'s determined embedding two Mn impurities at sites $i$ $j$ in CPA medium ${J}_{ij}$ formula Liechtenstein et al....
Inelastic neutron scattering measurements on several Tl filled skutterudites (${\mathrm{T}\mathrm{l}}_{0.5}{\mathrm{C}\mathrm{o}}_{3.5}{\mathrm{F}\mathrm{e}}_{0.5}{\mathrm{S}\mathrm{b}}_{12}$, ${\mathrm{T}\mathrm{l}}_{0.8}{\mathrm{C}\mathrm{o}}_{3}\mathrm{F}\mathrm{e}{\mathrm{S}\mathrm{b}}_{12}$, and ${\mathrm{T}\mathrm{l}}_{0.8}{\mathrm{C}\mathrm{o}}_{4}{\mathrm{S}\mathrm{b}}_{11}\mathrm{S}\mathrm{n}$) all show a sharp peak in the vibrational density of states at...
An overview is provided of the 15 neutron beam instruments making up initial instrument suite European Spallation Source (ESS), and being made available to user community. The ESS source consists a high-power accelerator target station, providing unique long-pulse time structure slow neutrons. design considerations behind structure, moderator geometry layout are presented. 15-instrument two small-angle instruments, reflectometers, an imaging beamline, single-crystal diffractometers; one for...
Inelastic neutron scattering measurements on thermoelectric Zn4Sb3 reveal a dominant soft local phonon mode at 5.3(1) meV. The form factor of this is characteristic for dumbbells vibrating preferably along the dumbbell axis and can be related to vibration Sb dimers c axis. Lorentzian width corresponds short lifetimes 0.39(2) ps yields an estimate thermal conductivity that agrees quantitatively with recent steady state measurements. Heat capacity are consistent Einstein model describing...
Y0.5Ca0.5BaCo4O7 contains kagomé layers of Co ions, whose spins are strongly coupled, with a Curie-Weiss temperature -2200 K. At low temperature, T=1.2 K, our diffuse neutron scattering study polarization analysis reveals characteristic spin correlations close to predicted two-dimensional coplanar ground state staggered chirality. The absence three-dimensional long-range antiferromagnetic order indicates negligible coupling between the layers. intensities consistent high S=3/2 states Co2+ in...
The homogeneous short-range-order (SRO) equilibrium state of a quenched ${\mathrm{Ni}}_{0.89}$${\mathrm{Cr}}_{0.11}$ alloy was studied by diffuse neutron scattering. Intensity maxima due to short-range order were found at 1(1/20 reciprocal lattice points. Values for the atomic interaction energies are calculated 30 neighboring shells from SRO parameters use inverse Monte Carlo method and compared results based on mean-field approximation (Krivoglaz-Clapp-Moss). By direct calculation Ising...
We present a detailed study of magnetism in ${\mathrm{LuFe}}_{2}{\mathrm{O}}_{4}$, combining magnetization measurements with neutron and soft x-ray diffraction. The magnetic phase diagram the vicinity ${T}_{N}$ involves metamagnetic transition separating an antiferro- ferrimagnetic phase. For both phases spin structure is refined by Observed diffuse scattering far above explained terms near degeneracy phases.
Inelastic neutron scattering measurements on ${\mathrm{Ba}}_{8}{\mathrm{Ga}}_{16}{\mathrm{Ge}}_{30}$ and ${\mathrm{Sr}}_{8}{\mathrm{Ga}}_{16}{\mathrm{Ge}}_{30}$ indicate the presence of soft local modes with Einstein oscillator energies $4.9\ifmmode\pm\else\textpm\fi{}0.1$ $4.4\ifmmode\pm\else\textpm\fi{}0.1\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$, which are associated lowest ``rattling'' mode Ba(B) Sr(B) guests, respectively. Nuclear inelastic...
Abstract Because of the neutron’s special properties, neutron diffraction may be considered one most powerful techniques for structure determination crystalline and related matter. Neutrons can released from nuclear fission, spallation processes, also low-energy reactions, they then used in powder, time-of-flight, texture, single crystal, other techniques, all which are perfectly suited to clarify crystal magnetic structures. With high flux sufficient brilliance, excels diffuse scattering,...
We present systematic ab initio calcultions for the interaction energies of impurity pairs in Cu, Ni, Ag, and Pd. The calculations are based on local-density theory apply Korring-Kohn-Rostoker Green's-function method spherical potentials. full nonspherical charge density is used to calculate double-counting contributions total energy. In particular, we nearest- next-nearest-neighbor 3d 4sp elements Cu Ni as well similar 4d 5sp Ag Pd: these interactions determine ordering or segregation...
The density of phonon states in the thermoelectric material Yb${}_{14}$MnSb${}_{11}$ has been studied first by inelastic neutron scattering and second an element-specific way nuclear x-ray scattering. low sound velocity 1880(50) m/s as obtained from can be identified important reason for heat transport this system. high melting temperature contrasts with energy all phonons ($<$25 meV) relates to unusual lack softening modes temperature, when comparing observed at ambient temperatures 1200 K....
The ambitious instrument suite for the future European Spallation Source whose civil construction started recently in Lund, Sweden, demands a set of diverse and challenging requirements neutron detectors. For instance, unprecedented high flux expected on samples to be investigated diffraction or reflectometry experiments requires detectors that can handle counting rates, while investigation sub-millimeter protein crystals will only possible with large-area achieve position resolution as low...
The local structure of syndiotactic poly(methyl methacrylate) (PMMA) has been investigated by combining neutron scattering and fully atomistic molecular dynamics simulations. Selectively deuterating parts the PMMA monomer, we have accessed five different partial factors in glassy state neutrons, polarization analysis allowed isolating coherent contribution to total scattering. In addition, temperature dependence static factor determined on deuterated sample. measured show qualitatively...
The temperature dependence of charge order in ${\mathrm{Fe}}_{2}{\mathrm{OBO}}_{3}$ was investigated by resistivity and differential scanning calorimetry measurements, M\"ossbauer spectroscopy, synchrotron x-ray scattering, revealing an intermediate phase between room 340 K, characterized coexisting mobile immobile carriers, incommensurate superstructure modulations with temperature-dependent propagation vector $(\frac{1}{2},0,\ensuremath{\tau})$. arise from specific antiphase boundaries low...
Crystals of the type ${\mathrm{Rb}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$(${\mathrm{NH}}_{4}$${)}_{\mathrm{x}}$${\mathrm{H}}_{2}$PO $_{4}$ are frustrated due to competing interactions rubidium and ammonium which favor ferroelectric antiferroelectric configurations, respectively, within hydrogen-bond system. The temperature, wave-vector, frequency dependences diffuse scattering reported for a fully deuterated crystal this with an concentration 62 mol %. Diffuse streaks observed along 〈100〉...
The A-site spinel material, CoAl2O4, is a physical realization of the frustrated diamond-lattice antiferromagnet, model in which predicted to contain unique incommensurate or `spin-spiral liquid' ground states. Our previous single-crystal neutron scattering study instead classified it as `kinetically-inhibited' where long ranged correlations collinear Neel state are blocked by freezing domain wall motion below first-order phase transition at T* = 6.5 K. current paper expands on our original...
The critical exponents for the average chirality, ${\ensuremath{\beta}}_{c}=0.90(3),$ and chiral susceptibility, ${\ensuremath{\gamma}}_{c}=0.68(6),$ are determined spin-ordering transition in helimagnet Ho. ${\ensuremath{\beta}}_{c}$ is extraordinarily large twice higher than predicted value universality class, while ${\ensuremath{\gamma}}_{c}$ agreement with this scenario. staggered magnetization exponent to be \ensuremath{\beta}=0.38(1). difference...
An Ising-model description of the L${1}_{0}$ structure in fcc AB binary alloys with antiferromagnetic nearest-neighbor coupling (${\mathit{J}}_{\mathrm{nn}}$0) and ferromagnetic next-nearest-neighbor interaction (${\mathit{J}}_{\mathrm{nnn}}$>0) leads to frustration bulk but a stable c(2\ifmmode\times\else\texttimes\fi{}2) superstructure for free (010) surface. Using Monte Carlo simulations ${\mathit{J}}_{\mathrm{nnn}}$/${\mathit{J}}_{\mathrm{nn}}$=-0.05, we show that surface orders at...
Studies of diffuse magnetic scattering largely benefit from the use a multi-detector covering wide angles. Therefore, different contributions to that originate magnetic, nuclear coherent, and spin-incoherent can be separated by so-called XYZ-polarization analysis. In past this method has been successfully applied analysis polycrystalline samples disordered materials. Single crystal studies exploit vector properties spin correlations are particular interest for furthering our understanding...
The magnetic structure of MnNCN, the nitrogen equivalent MnO, and first carbodiimide a non-${d}^{10}$ transition metal ever made, has been determined on basis spin-polarized neutron-diffraction data close to absolute zero temperature. $S=5/2$ moments high-spin ${\text{Mn}}^{2+}$ ions lie within $ab$ hexagonal sheets exhibit an antiferromagnetic ordering between along $c$ axis. Below N\'eel point (28 K), temperature-dependent pattern exists due frustration inside sheets, characterized by...