A5036618335- Rare-earth and actinide compounds
- Advanced Condensed Matter Physics
- Iron-based superconductors research
- Physics of Superconductivity and Magnetism
- Magnetic and transport properties of perovskites and related materials
- Magnetic Properties of Alloys
- Multiferroics and related materials
- Inorganic Chemistry and Materials
- Magnetic properties of thin films
- High-pressure geophysics and materials
- Topological Materials and Phenomena
- Microstructure and Mechanical Properties of Steels
- Theoretical and Computational Physics
- Metallurgy and Material Forming
- Ferroelectric and Piezoelectric Materials
- Corporate Taxation and Avoidance
- Crystal Structures and Properties
- Solid-state spectroscopy and crystallography
- Inorganic Fluorides and Related Compounds
- Nuclear materials and radiation effects
- Superconductivity in MgB2 and Alloys
- Atomic and Subatomic Physics Research
- Acoustic Wave Resonator Technologies
- X-ray Diffraction in Crystallography
- Electronic and Structural Properties of Oxides
Oak Ridge National Laboratory
2016-2025
University of Johannesburg
2024
Government of the United States of America
2022
University of Tennessee at Knoxville
2014-2021
Quantum Science Center
2012-2020
Physical Sciences (United States)
2016
Purdue University West Lafayette
2008-2012
Mahidol University
2011
National Institute of Advanced Industrial Science and Technology
2011
Suzuki (Japan)
2011
We present results from a detailed experimental investigation of LaFeAsO, the parent material in series ``FeAs'' based oxypnictide superconductors. Upon cooling, this undergoes tetragonal-orthorhombic crystallographic phase transition at $\ensuremath{\sim}160\text{ }\text{K}$ followed closely by an antiferromagnetic ordering near 145 K. Analysis these transitions using temperature dependent powder x-ray and neutron-diffraction measurements is presented. A magnetic moment...
Abstract Elucidating the nature of magnetism a high-temperature superconductor is crucial for establishing its pairing mechanism. The parent compounds cuprate and iron-pnictide superconductors exhibit Néel stripe magnetic order, respectively. However, FeSe, structurally simplest iron-based superconductor, shows nematic order ( T s =90 K), but not in phase, ground state intensely debated. Here we report inelastic neutron-scattering experiments that reveal both spin fluctuations over wide...
Inelastic neutron scattering measurements on single crystals of superconducting BaFe1.84Co0.16As2 reveal a magnetic excitation located at wave vectors (1/2 1/2 L) in tetragonal notation. On cooling below T_{C}, clear resonance peak is observed this vector with an energy 8.6(0.5) meV, corresponding to 4.5(0.3) k_{B}T_{C}. This good agreement the canonical value 5 k_{B}T_{C} cuprates. The spectrum shows strong dispersion plane but very weak along c axis, indicating that fluctuations are two...
In this review, we present a summary of experimental studies magnetism in Fe-based superconductors. The doping dependent phase diagram shows strong similarities to the generic cuprates. Parent compounds exhibit magnetic order together with structural transition both which are progressively suppressed allowing superconductivity emerge. stripe-like spin arrangement Fe moments magnetically ordered state identical in-plane structure for RFeAsO (R=rare earth) and AFe2As2 (A=Sr, Ca, Ba, Eu K)...
We report neutron scattering measurements on single crystals of BaFe$_{1.92}$Co$_{0.08}$As$_2$. The magnetic Bragg peak intensity is reduced by 6 % upon cooling through T$_C$. spin dynamics exhibit a gap 8 meV with anisotropic three-dimensional (3d) interactions. Below T$_C$ additional appears at an energy $\sim$4.5(0.5) similar to previous observations resonance in other Fe-based superconductors. No further gapping the excitations observed below for energies down 2 meV. These suggest...
We investigated the series of temperature and field-driven transitions in LuFe2O4 by optical Mössbauer spectroscopies, magnetization, x-ray scattering order to understand interplay between charge, structure, magnetism this multiferroic material. demonstrate that charge fluctuation has an onset well below ordering transition, supporting "order fluctuation" mechanism for development superstructure. Bragg splitting large magneto-optical contrast suggest a low-temperature monoclinic distortion...
The anharmonic lattice dynamics of rock-salt thermoelectric compounds SnTe and PbTe are investigated with inelastic neutron scattering (INS) first-principles calculations. experiments show that, surprisingly, although is closer to the ferroelectric instability, phonon spectra in exhibit a more character. This behavior reproduced calculations temperature-dependent self-energy. Our simulations reveal how nesting dispersions induces prominent features self-energy, which account for measured INS...
The metal-insulator transition (MIT) is one of the most dramatic manifestations electron correlations in materials. Various mechanisms producing MITs have been extensively considered, including Mott (electron localization via Coulomb repulsion), Anderson (localization disorder), and Peierls distortion a periodic one-dimensional lattice) mechanisms. One additional route to MIT proposed by Slater, which long-range magnetic order three dimensional system drives MIT, has received relatively...
Polar nanoregion vibrations control the ultrahigh piezoelectric response of relaxor-based ferroelectrics used in applications.
Abstract Low dimensional quantum magnets are interesting because of the emerging collective behavior arising from strong fluctuations. The one-dimensional (1D) S = 1/2 Heisenberg antiferromagnet is a paradigmatic example, whose low-energy excitations, known as spinons, carry fractional spin 1/2. These modes can be reconfined by application staggered magnetic field. Even though considerable progress has been made in theoretical understanding such magnets, experimental realizations this...
The experimental realization of magnetic skyrmion crystals in centrosymmetric materials has been driven by theoretical understanding how a delicate balance anisotropy and frustration can stabilize topological spin structures applied fields. Recently, the material Gd_{2}PdSi_{3} was shown to host field-induced crystal, but stabilization mechanism remains unclear. Here, we employ neutron-scattering measurements on an isotopically enriched polycrystalline sample quantify interactions that drive...
We present single crystal neutron diffraction measurements on multiferroic ${\mathrm{LuFe}}_{2}{\mathrm{O}}_{4}$. Magnetic reflections are observed below transitions at 240 and 175 K indicating that the magnetic interactions in ${\mathrm{LuFe}}_{2}{\mathrm{O}}_{4}$ three-dimensional character. The structure is refined as a ferrimagnetic spin configuration transition. Below significant broadening of peaks along with buildup diffuse component to scattering.
X-ray scattering by multiferroic ${\mathrm{LuFe}}_{2}{\mathrm{O}}_{4}$ is reported. Below 320 K, superstructure reflections indicate an incommensurate charge order with propagation close to $(\frac{1}{3}\frac{1}{3}\frac{3}{2})$. The corresponding configuration, also found electronic structure calculations as most stable, contains polar $\mathrm{Fe}/\mathrm{O}$ double layers antiferroelectric stacking. Diffuse at 360 $(\frac{1}{3}\frac{1}{3}0)$ propagation, indicates ferroelectric short-range...
We use neutron scattering to show that spin waves in the iron chalcogenide ${\mathrm{Fe}}_{1.05}\mathrm{Te}$ display novel dispersion clearly different from both first principles density functional calculations and recent observations related pnictide ${\mathrm{CaFe}}_{2}{\mathrm{As}}_{2}$. By fitting a Heisenberg Hamiltonian, we find although nearest-neighbor exchange couplings two systems are quite different, their next-nearest-neighbor (NNN) similar. This suggests superconductivity...
We study experimentally and theoretically the electronic magnetic properties of two insulating double perovskites that show similar atomic structure but different properties. In magnetization measurements, La${}_{2}$ZnIrO${}_{6}$ displays weak ferromagnetic behavior below 7.5 K, whereas La${}_{2}$MgIrO${}_{6}$ shows antiferromagnetic ${T}_{N}$ $=$ 12 K. Electronic calculations find observed in is fact due to canted antiferromagnetism. The also predict La${}_{2}$MgIrO${}_{6}$, intriguingly,...
Abstract Antiferromagnetic correlations have been argued to be the cause of d -wave superconductivity and pseudogap phenomena exhibited by cuprates. Although antiferromagnetic response in state has reported for a number compounds, there exists no information structurally simple HgBa 2 CuO 4+δ . Here we report neutron-scattering results (superconducting transition temperature T c ≈71 K, *≈305 K) that demonstrate absence two most prominent features magnetic excitation spectrum cuprates:...
The low energy spin excitation spectrum of the breathing pyrochlore ${\mathrm{Ba}}_{3}{\mathrm{Yb}}_{2}{\mathrm{Zn}}_{5}{\mathrm{O}}_{11}$ has been investigated with inelastic neutron scattering. Several nearly resolution limited modes no observable dispersion are observed at 250 mK while, elevated temperatures, transitions between excited levels become visible. To gain deeper insight, a theoretical model isolated ${\mathrm{Yb}}^{3+}$ tetrahedra parametrized by four anisotropic exchange...
The rich physics manifested by 5d oxides falls outside the Mott-Hubbard paradigm used to successfully explain electronic and magnetic properties of 3d oxides. Much consideration has been given extent which strong spin-orbit coupling (SOC), in limit increased bandwidth reduced electron correlation, drives formation novel states, as through existence metal-insulator transitions (MITs). SOC is believed play a dominant role 5d5 systems such iridates (Ir4+), undergoing MITs may or not be...
In quantum magnets, magnetic moments fluctuate heavily and are strongly entangled with each other, a fundamental distinction from classical magnetism. Here, inelastic neutron scattering measurements, we probe the spin correlations of honeycomb lattice magnet YbCl3. A linear wave theory single Heisenberg interaction on lattice, including both transverse longitudinal channels response, reproduces all key features in spectrum. particular, identify Van Hove singularity, clearly observable sharp...
The kagome lattice is a fertile platform to explore topological excitations with both Fermi-Dirac and Bose-Einstein statistics. While relativistic Dirac fermions flat bands have been discovered in the electronic structure of metals, spin received less attention. Here, we report inelastic neutron scattering studies prototypical magnetic metal FeSn. spectra display well-defined waves extending 120 meV. Above this energy, become progressively broadened, reflecting interactions Stoner continuum....
Spiral spin liquids are correlated paramagnetic states with degenerate propagation vectors forming a continuous ring or surface in reciprocal space. On the honeycomb lattice, spiral present novel route to realize emergent fracton excitations, quantum liquids, and topological textures, yet experimental realizations remain elusive. Here, using neutron scattering, we show that liquid is realized van der Waals magnet FeCl_{3}. A of scattering directly observed, which indicates emergence an...
The asymmetric distribution of chiral objects with opposite chirality is great fundamental interest ranging from molecular biology to particle physics. In quantum materials, states can build on inversion-symmetry-breaking lattice structures or emerge spontaneous magnetic ordering induced by competing interactions. Although the handedness a state be changed through external fields, flipping has yet discovered. We present experimental evidence via changing temperature in topological magnet...