A5001540105- Magnetic and transport properties of perovskites and related materials
- Advanced Condensed Matter Physics
- Multiferroics and related materials
- Physics of Superconductivity and Magnetism
- Rare-earth and actinide compounds
- High-pressure geophysics and materials
- Magnetic Properties of Alloys
- Theoretical and Computational Physics
- Magnetic properties of thin films
- Ferroelectric and Piezoelectric Materials
- Nuclear Physics and Applications
- Solid-state spectroscopy and crystallography
- Atomic and Subatomic Physics Research
- Topological Materials and Phenomena
- Quantum, superfluid, helium dynamics
- Iron-based superconductors research
- Metallic Glasses and Amorphous Alloys
- Crystal Structures and Properties
- Electronic and Structural Properties of Oxides
- Magnetic Properties and Applications
- X-ray Diffraction in Crystallography
- Quantum many-body systems
- Transition Metal Oxide Nanomaterials
- Inorganic Fluorides and Related Compounds
- Advanced ceramic materials synthesis
Oak Ridge National Laboratory
2015-2024
University of Tennessee at Knoxville
2010-2019
Quantum Science Center
2012-2018
Ibaraki University
2018
Japan Atomic Energy Agency
2018
Karlsruhe Institute of Technology
2014
University of Messina
2011
Florida International University
2007-2008
University of California, Santa Cruz
1999
Southern Illinois University Carbondale
1995
The discovery of high-temperature superconductivity in doped copper oxides, which their insulating forms are nearly ideal two-dimensional spin-1/2 Heisenberg antiferromagnets, has stimulated great interest finding additional examples such magnetic systems. We find that ${\mathrm{Sr}}_{2}$${\mathrm{IrO}}_{4}$, the ${\mathrm{K}}_{2}$${\mathrm{NiF}}_{4}$ structure and should have a 5${\mathit{d}}^{5}$ low-spin (S=1/2) electronic configuration, develops ferromagnetic moment near 250 K. small...
We have combined single-crystal neutron and x-ray diffractions to investigate the magnetic crystal structures of honeycomb lattice Na${}_{2}$IrO${}_{3}$. The system orders magnetically below $18.1(2)$ K with Ir${}^{4+}$ ions forming zigzag spin chains within layered network an ordered moment $0.22(1){\ensuremath{\mu}}_{\text{B}}/\text{Ir}$ site. Such a configuration sharply contrasts N\'eel or stripe states proposed in Kitaev-Heisenberg model. structure refinement reveals that Ir atoms form...
We use neutron scattering to demonstrate the presence of lattice polarons and their short-range correlations for several samples La1-xCaxMnO3 in Ca doping range 0.15</=x</=0.3. establish dependence orientation, commensuration, coherence length polaron show that populations correlated uncorrelated are intimately related transport properties materials.
We use high-resolution synchrotron x-ray and neutron diffraction to study the geometrically frustrated triangular lattice antiferromagnet $\mathrm{Cu}\mathrm{Fe}{\mathrm{O}}_{2}$. On cooling from room temperature, $\mathrm{Cu}\mathrm{Fe}{\mathrm{O}}_{2}$ undergoes two antiferromagnetic phase transitions with incommensurate commensurate magnetic order at ${T}_{N1}=14\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ ${T}_{N2}=11\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, respectively. The occurrence of these...
We report a single-crystal neutron diffraction study of the layered $\rm Sr_2IrO_4$. This work unambiguously determines magnetic structure system and reveals that spin orientation rigidly tracks staggered rotation IrO_6$ octahedra in The long-range antiferromagnetic order has canted configuration with an ordered moment 0.208(3) $μ_B$/Ir site within basal plane; detailed examination canting yields 0.202(3) 0.049(2) $μ_B$/site for axis b axis, respectively. It is intriguing forbidden nuclear...
Elastic and inelastic neutron scattering was used to study two ferromagnetic manganites A$_{1-x}$B$_{x}$MnO$_3$ (x $\approx$ 0.3) with $T_c$=197.9 K 300.9 K. The spin dynamical behavior of these is similar at low temperatures, but drastically different temperatures around $T_c$. While the formation clusters size ($\sim20$ \AA) dominates dynamics 197.9 sample close $T_c$, paramagnetic transition for more conventional. These results, combined seemingly inconsistent earlier reports, reveal...
Magnetic susceptibility, resistivity, Seebeck, Hall, and powder x-ray neutron-diffraction measurements were used to characterize single crystals of FeSi polycrystalline samples ${\mathrm{Fe}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ir}}_{\mathit{x}}$Si for x0.2. The Rietveld refinement low-temperature data on showed no change in the space group structural anomalies from 4 300 K. transport 700 K are consistent with characterization as a narrow-gap semiconductor...
Thermoelectrics are promising by directly generating electricity from waste heat. However, (sub-)room-temperature thermoelectrics have been a long-standing challenge due to vanishing electronic entropy at low temperatures. Topological materials offer new avenue for energy harvesting applications. Recent theories predicted that topological semimetals the quantum limit can lead large, non-saturating thermopower and quantized thermoelectric Hall conductivity approaching universal value. Here,...
Inelastic neutron scattering was used to systematically investigate the spin-wave excitations (magnons) in ferromagnetic manganese perovskites. In spite of large differences Curie temperatures ($T_C$s) different manganites, their low-temperature spin waves were found have very similar dispersions with zone boundary magnon softening. From wavevector dependence lifetime effects and its correlation optical phonon modes, we argue that a strong magneto-elastic coupling is responsible for observed...
The spin-wave excitations of the geometrically frustrated triangular lattice antiferromagnet ${\mathrm{CuFeO}}_{2}$ have been measured using high resolution inelastic neutron scattering. Antiferromagnetic interactions up to third nearest neighbors in $ab$ plane (${J}_{1}$, ${J}_{2}$, ${J}_{3}$, with ${J}_{2}/{J}_{1}\ensuremath{\approx}0.44$ and ${J}_{3}/{J}_{1}\ensuremath{\approx}0.57$), as well out-of-plane coupling (${J}_{z}$, ${J}_{z}/{J}_{1}\ensuremath{\approx}0.29$) are required...
The spin-wave excitations of the multiferroic ${\mathrm{MnWO}}_{4}$ have been measured in its low-temperature collinear commensurate phase using high-resolution inelastic neutron scattering. These can be well described by a Heisenberg model with competing long-range exchange interactions and single-ion anisotropy term. magnetic are strongly frustrated within zigzag spin chain along $c$ axis between chains $a$ axis, while coupling $b$ is much weaker. balance these results noncollinear...
Multiferroic hexaferrites have been extensively investigated because they exhibit ferroelectricity associated with noncollinear magnetic orders in relatively low field and high temperature regions. To understand the static dynamical spin-polarization coupling such systems, it is necessary to determine structures spin-wave modes. This impossible for polycrystalline samples. Here, authors successfully grown single crystals of BaSrCo${}_{2}$Fe${}_{12}$AlO${}_{22}$ by means a laser floating zone...
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTPreparation and Structural Characterization of Two New Phases Aluminum TrifluorideNorman Herron, David L. Thorn, Richard Harlow, Glover A. Jones, John B. Parise, Jaime Fernandez-Baca, Thomas VogtCite this: Chem. Mater. 1995, 7, 1, 75–83Publication Date (Print):January 1995Publication History Published online1 May 2002Published inissue 1 January 1995https://pubs.acs.org/doi/10.1021/cm00049a013https://doi.org/10.1021/cm00049a013research-articleACS...
We report on the remarkably robust ferroelectric state in multiferroic compound ${\mathrm{Mn}}_{1\ensuremath{-}x}{\mathrm{Zn}}_{x}{\mathrm{WO}}_{4}$. Substitution of magnetic ${\mathrm{Mn}}^{2+}$ with nonmagnetic Zn${}^{2+}$ reduces exchange and provides control various states ${\mathrm{MnWO}}_{4}$. Only $5%$ Zn substitution results complete suppression frustrated collinear (paraelectric) low-temperature phase. The helical phase develops as ground state. is stable up to a high level more...
We use single-crystal neutron diffraction to determine the crystal structure symmetry and magnetic evolution in rhodium doped iridates $\rm Sr_2Ir_{1-x}Rh_{x}O_4$ ($0\leq x \leq 0.16$). Throughout this doping range, retains a tetragonal (space group $I4_1/a$) with two distinct Ir sites unit cell forming staggered IrO_6$ rotation. Upon Rh doping, order is suppressed moment of Ir$^{4+}$ reduced from 0.21 \mu_B$/Ir for $x=0$ 0.18 $x=0.12$. The at $x=0.12$ different that parent compound while...
The electron-phonon interaction (EPI) is instrumental in a wide variety of phenomena solid-state physics, such as electrical resistivity metals, carrier mobility, optical transition, and polaron effects semiconductors, lifetime hot carriers, transition temperature BCS superconductors, even spin relaxation diamond nitrogen-vacancy centers for quantum information processing. However, due to the weak EPI strength, most have focused on electronic properties rather than phonon properties. One...
The question as to whether or not ferroelectric ice, named ice XI, exists in a stable low-temperature phase attracts much interest. This arose condensed-matter issue and became of interest astronomy (e.g., does XI exist on Pluto?) because astronomical observations identified the existence crystalline our solar system. From neutron diffraction experiments, we found temperature conditions for transformation largest fraction into using lowest level impurity dopant. finding bulk crystal ordered...
We present inelastic neutron scattering experiments on a single-domain crystal of lightly doped La1.96Sr0.04CuO4. find that the magnetic excitation spectrum in this insulating phase with diagonal incommensurate spin modulation is remarkably similar to superconducting regime, where bond parallel. In particular, we dispersion slope at low energy essentially independent doping and temperature over significant range. The which excitations cross commensurate antiferromagnetic wave vector...
We report inelastic neutron scattering measurements that provide a distinct dynamical ``fingerprint'' for the multiferroic ground state of 3.5% Ga-doped ${\text{CuFeO}}_{2}$. The complex is stabilized by displacement oxygen atoms, which contribute to coupling predicted in ``spin-driven'' model. By comparing observed and calculated spectrum spin excitations, we conclude magnetic distorted screw-type configuration with distribution turn angles.
We use inelastic neutron scattering to show that superconductivity in electron-underdoped NaFe0.985Co0.015As induces a dispersive sharp resonance near E(r1)=3.25 meV and broad dispersionless mode at E(r2)=6 meV. However, similar measurements on overdoped superconducting NaFe0.935Co0.045As find only single E(r)=7 connect these results with the observations of angle-resolved photoemission spectroscopy gaps electron Fermi pockets are anisotropic underdoped material but become isotropic case....
We present a comprehensive single-crystal neutron diffraction investigation of the Mn${}_{1\ensuremath{-}x}$Co${}_{x}$WO${}_{4}$ with $0.02\ensuremath{\le}x\ensuremath{\le}0.30$. At lower concentration $x\ensuremath{\le}0.05$, system is quickly driven into multiferroic phase spin structure forming an elliptical spiral order similar to parent compound. The reduction electric polarization ascribed tilting plane. For $x\ensuremath{\sim}0.075$, magnetic undergoes spin-flop transition that...
Neutron scattering and magnetometry measurements have been used to study phase transitions in LaCoO3 (LCO). For H ≤ 100 Oe, evidence for a ferromagnetic (FM) transition is observed at Tc ≈ 87 K. 1 kOe 60 kOe, no apparent. all H, Curie–Weiss analysis shows predominantly antiferromagnetic (AFM) interactions T > Tc, but the lack of long-range AFM order indicates magnetic frustration. We argue that weak ferromagnetism bulk LCO induced by lattice strain, as case with thin films nanoparticles. The...