A5079236690- Nuclear Physics and Applications
- Physics of Superconductivity and Magnetism
- Advanced Condensed Matter Physics
- Magnetic and transport properties of perovskites and related materials
- Atomic and Subatomic Physics Research
- High-pressure geophysics and materials
- Theoretical and Computational Physics
- Radiation Detection and Scintillator Technologies
- Nuclear reactor physics and engineering
- Characterization and Applications of Magnetic Nanoparticles
- Multiferroics and related materials
- Magnetic properties of thin films
- Iron oxide chemistry and applications
- Quantum, superfluid, helium dynamics
- Rare-earth and actinide compounds
- Magnetic Properties and Synthesis of Ferrites
- Iron-based superconductors research
- Magnetism in coordination complexes
- Geomagnetism and Paleomagnetism Studies
- Superconductivity in MgB2 and Alloys
- X-ray Diffraction in Crystallography
- Superconducting Materials and Applications
- Quantum and electron transport phenomena
- Advanced NMR Techniques and Applications
- Advanced X-ray Imaging Techniques
University of Copenhagen
2016-2025
European Spallation Source
2010-2020
Helmholtz-Zentrum Berlin für Materialien und Energie
2018
University of Maryland, College Park
2017
Northwestern University
2017
National Institute of Standards and Technology
2017
Institute for Complex Systems
2016
Technical University of Denmark
1999-2011
Lund University
2000-2010
Forschungszentrum Jülich
2007
The magnetic properties of hematite $(\ensuremath{\alpha}\ensuremath{-}{\mathrm{Fe}}_{2}{\mathrm{O}}_{3})$ particles with sizes about 16 nm have been studied by use M\"ossbauer spectroscopy, magnetization measurements, and neutron diffraction. nanoparticles are weakly ferromagnetic at temperatures least down to 5 K a spontaneous that is only slightly higher than bulk hematite. At $T\ensuremath{\gtrsim}100\mathrm{K}$ the spectra contain doublet, which asymmetric due relaxation in presence an...
Abstract We present version 1.0 of the McStas freeware program package for neutron simulations. The is based upon a special meta-language designed Monte Carlo ray-tracing calculations and includes library spectrometer components visualization tools. A detailed simulation Rise triple-axis TASl shows good agreement with experiments. invite researchers to use this contribute development component library.
Neutron scattering is used to characterize the magnetism of vortices for optimally doped high-temperature superconductor La(2-x)Sr(x)CuO4 (x = 0.163) in an applied magnetic field. As temperature reduced, low-frequency spin fluctuations first disappear with loss vortex mobility, but then reappear. We find that state can be regarded as inhomogeneous mixture a superconducting fluid and material containing nearly ordered antiferromagnet. These experiments show many other properties cuprate...
Abstract Total control over the electronic spin relaxation in molecular nanomagnets is ultimate goal design of new molecules with evermore realizable applications spin-based devices. For single-ion lanthanide systems, strong spin–orbit coupling, potential are linked to energetic structure crystal field levels and quantum tunneling within ground state. Structural engineering timescale these events via appropriate fields represents a fundamental challenge for synthetic chemist, since tunnel...
We present an overview of, and introduction to, the general-purpose neutron simulation package McStas.We basic principles behind Monte Carlo ray-tracing simulations of neutrons performed in a few simple examples.We implementation McStas, status its use community.Finally, we briefly discuss planned development package.
The McStas neutron ray-tracing simulation package is a collaboration between Risø DTU, ILL, University of Copenhagen and the PSI. During its lifetime, has evolved to become world leading software in area scattering simulatio
A key element of the success McStas is component layer where users and developers alike are contributing to description new physical models features. In McStas, components realise all elements simulated instrument from source via optics samples detector. this second review paper package, we present an overview classes in McStas: sources, monitors, optics, samples, misc, contrib. Within each class give thorough examples high-quality components, including their algorithms example use. We two...
Quantum matter phases may co-exist microscopically even when they display competing tendencies. A fundamental question is whether such a competition can be avoided through the elimination of one phase while other condenses into ground state. Here, we present high-resolution neutron spectroscopy study low-energy spin excitations in high-temperature superconductor La1.855Sr0.145CuO4. In normal state, find magnetic fluctuations at incommensurate reciprocal lattice positions where...
Measurements are reported of the magnetic field dependence excitations in quantum critical state spin S=1/2 linear chain Heisenberg antiferromagnet copper pyrazine dinitrate (CuPzN). The complete spectrum was measured at k(B)T/J< or =0.025 for H=0 and H=8.7 T, where system is approximately 30% magnetized. At H=0, results agreement with exact calculations dynamic correlation function a two-spinon continuum. there multiple overlapping continua incommensurate soft modes. boundaries these...
We study the magnetic-field-induced quantum phase transition from a gapped that has no magnetic long-range order into gapless in spin-1/2 ladder compound bis(2,3-dimethylpyridinium) tetrabromocuprate (DIMPY). At temperatures below about 1 K, specific heat attains an asymptotic linear temperature dependence, characteristic of Tomonaga-Luttinger liquid. Inelastic neutron scattering and measurements both phases are good agreement with theoretical calculations, demonstrating DIMPY is first model...
This article presents the Monte Carlo simulation package McXtrace , intended for optimizing X-ray beam instrumentation and performing virtual experiments data analysis. The system shares a structure code base with popular neutron McStas is good complement to standard software SHADOW . open source, licensed under General Public License, does not require user have access any proprietary its operation. of described in detail, various examples are given showcase versatility procedure outline...
The magnetic excitation spectrum in the two-dimensional (2D) S = 1/2 Heisenberg antiferromagnet copper deuteroformate tetradeuterate has been measured for temperatures up to T approximately J/2, where J 6.31+/-0.02 meV is 2D exchange coupling. For T<<J, a dispersion of zone boundary energy observed, which attributed wave vector dependent quantum renormalization. At higher temperatures, spin-wavelike excitations persist, but are found broaden and soften. By combining our data with numerical...
This paper presents material properties particularly suited to be measured with helium scattering techniques. Below a specific science case example illustrating the measurement of electron–phonon coupling constant <italic>λ</italic> on topological insulator surface.
We use magnetic susceptibility and inelastic neutron scattering measurements to show that copper benzoate, Cu(${\mathrm{C}}_{6}$${\mathrm{D}}_{5}$COO${)}_{2}$\ensuremath{\cdot}${3\mathrm{D}}_{2}$O, is a quasi-one-dimensional S=1/2 antiferromagnet with an exchange constant J = 1.57 meV. Below T=0.8 K ferromagnetic contribution the marks onset of canted three-dimensional (3D) antiferromagnetic order. An external field suppresses this effect, measured in high shows only response chain. The...
We present the first triple-axis neutron scattering measurements of magnetic fluctuations in nanoparticles using an antiferromagnetic reflection. Both superparamagnetic relaxation and precession modes $\ensuremath{\sim}15\mathrm{nm}$ hematite particles are observed. The results have been consistently analyzed on basis a simple model with uniaxial anisotropy N\'eel-Brown theory for relaxation.
We show that antiferromagnetic nanoparticles of $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{Fe}}_{2}{\mathrm{O}}_{3}$ (hematite) under wet conditions can attach into chains along a common [001] axis. Electron microscopy shows such typically consist two to five particles. X-ray and neutron diffraction studies both structural magnetic correlations exist across the interfaces direction. This gives direct evidence for exchange coupling between Exchange suppress superparamagnetic relaxation...
We report significant details of the magnetic structure and spin dynamics ${\mathrm{LiFePO}}_{4}$ obtained by single-crystal neutron scattering. Our results confirm a previously reported collinear rotation spins away from principal $b$ axis, they determine that is toward $a$ axis. In addition, we find spin-canting component along $c$. The possible causes these components are discussed, their significance for magnetoelectric effect analyzed. Inelastic scattering three directions reveals...
Abstract The rational design of the magnetic anisotropy molecular materials constitutes a goal primary importance in magnetism. Indeed, applications nanomagnets, such as single‐molecule magnets and refrigerants, depend on full control over this property. Axially anisotropic systems are frequently classified easy axis or plane, depending whether lowest energy is obtained by application field parallelly perpendicularly to unique axis. Here, three lanthanide complexes studied function...
The garnet compound Yb$_3$Ga$_5$O$_{12}$ is a fascinating material that considered highly suitable for low-temperature refrigeration, via the magnetocaloric effect, in addition to enabling exploration of quantum states with long-range dipolar interactions. It has previously been theorized effect can be enhanced, , magnetic soft mode excitations which hyperkagome structure would derived from an emergent formed nanosized 10-spin loops. We study field dependence bands effective spin $S = 1/2$...
Previous studies of elliptical neutron guides have shown that they transport neutrons with fewer reflections than traditional a constant cross section, thus reducing losses. True guides, however, are tedious to produce. Therefore, we use the simulation package McStas investigate effect approximating shape by linearly tapering guide pieces. The study concerns both simple model and more complex system corresponding BIFROST instrument, currently under construction at European Spallation Source...