A5082411042- Magnetic and transport properties of perovskites and related materials
- Magnetic properties of thin films
- Advanced Condensed Matter Physics
- Electronic and Structural Properties of Oxides
- Multiferroics and related materials
- Nuclear Physics and Applications
- Magnetic Properties and Applications
- Magnetic Properties of Alloys
- Atomic and Subatomic Physics Research
- Theoretical and Computational Physics
- Physics of Superconductivity and Magnetism
- Microstructure and mechanical properties
- High-pressure geophysics and materials
- Characterization and Applications of Magnetic Nanoparticles
- Quantum, superfluid, helium dynamics
- ZnO doping and properties
- Rare-earth and actinide compounds
- Ferroelectric and Piezoelectric Materials
- Geomagnetism and Paleomagnetism Studies
- Metallic Glasses and Amorphous Alloys
- Metal and Thin Film Mechanics
- Molecular Junctions and Nanostructures
- Surface Roughness and Optical Measurements
- X-ray Diffraction in Crystallography
- Radiation Detection and Scintillator Technologies
Oak Ridge National Laboratory
2015-2024
University of Tennessee at Knoxville
2017-2024
Johns Hopkins University
2023
NIST Center for Neutron Research
2023
National Institute of Standards and Technology
2023
Pennsylvania State University
2008-2023
Joint Institute for Computational Sciences
2020-2023
Los Alamos National Laboratory
2008-2022
Government of the United States of America
2022
Lancashire Care NHS Foundation Trust
2022
The new alpha-Fe(Te,Se) superconductors share the common iron building block and ferminology with LaFeAsO BaFe(2)As(2) families of superconductors. In contrast predicted commensurate spin-density-wave order at nesting wave vector (pi, 0), a completely different magnetic composition tunable propagation (deltapi, deltapi) was determined for parent compound Fe_{1+y}Te in this powder single-crystal neutron diffraction study. antiferromagnetic survives as short-range one even highest T_{C}...
Polarized neutron reflectometry is used to probe the in-plane projection of net-magnetization vector $\stackrel{\ensuremath{\rightarrow}}{\mathrm{M}}$ polycrystalline Fe films exchange coupled twinned (110) $\mathrm{MnF}{}_{2}$ or $\mathrm{FeF}{}_{2}$ antiferromagnetic (AF) layers. The magnetization reversal mechanism depends upon orientation cooling field with respect microstructure AF, and whether applied increased (or decreased from) a positive saturating field; i.e., asymmetric. sample...
Superlattices of $({\mathrm{LaMnO}}_{3}{)}_{2n}/({\mathrm{SrMnO}}_{3}{)}_{n}$ ($1\ensuremath{\le}n\ensuremath{\le}5$), composed the gapped insulators ${\mathrm{LaMnO}}_{3}$ and ${\mathrm{SrMnO}}_{3}$, undergo a metal-insulator transition as function $n$, being metallic for $n\ensuremath{\le}2$ insulating $n\ensuremath{\ge}3$. Measurements transport, magnetization, polarized neutron reflectivity reveal that ferromagnetism is relatively uniform in state, strongly modulated high suppressed...
We have used the unique spatial sensitivity of polarized neutron and soft x-ray beams in reflection geometry to measure depth dependence magnetization across interface between a ferromagnet an antiferromagnet. The net uncompensated near responds applied field, while spins antiferromagnet bulk are pinned, thus providing means establish exchange bias.
Abstract Strong Coulomb repulsion and spin–orbit coupling are known to give rise exotic physical phenomena in transition metal oxides. Initial attempts investigate systems, where both of these fundamental interactions comparably strong, such as 3 d 5 complex oxide superlattices, have revealed properties that only slightly differ from the bulk ones constituent materials. Here we observe interfacial between antiferromagnetic insulator SrMnO paramagnetic SrIrO is enormously yielding an...
Abstract Oxygen vacancies in complex oxides are indispensable for information and energy technologies. There several means to create oxygen bulk materials. However, the use of ionic interfaces has not been fully explored. Herein, we report an oxide nanobrush architecture designed high-density interfacial vacancies. An atomically well-defined (111) heterointerface between fluorite CeO 2 bixbyite Y O 3 is found induce a charge modulation 3+ Ce 4+ ions enabled by chemical valence mismatch two...
The violation of Baryon Number, $\mathcal{B}$, is an essential ingredient for the preferential creation matter over antimatter needed to account observed baryon asymmetry in universe. However, such a process has yet be experimentally observed. HIBEAM/NNBAR %experiment program proposed two-stage experiment at European Spallation Source (ESS) search number violation. will include high-sensitivity searches processes that violate by one or two units: free neutron-antineutron oscillation...
Data reduction is a critical step in small-angle neutron scattering experiment. It corrects the data for instrument-specific artefacts, making it ready analysis, interpretation, as well comparison against collected with different instruments. Here, drtsans software package developed at Oak Ridge National Laboratory EQ-SANS, GP-SANS, and Bio-SANS instruments, which are located Spallation Neutron Source High Flux Isotope Reactor, described. The rigorous development methods employed have...
Quantitative x-ray-diffraction measurements of ultrafine-grained (nanocrystalline) Pd samples and a coarse-grained polycrystalline reference foil were obtained using synchrotron radiation. The intensity profiles the Bragg reflections from nanocrystalline considerably better represented by Lorentzian functions than Gaussian functions, indicating that large fraction peaks was found in tails reflections. remaining differed only slightly for different grain-sized materials, therefore, atomic...
Abstract Quantitative X-ray diffraction measurements made over a temperature range 16–300K on Pd sample of 8·3nm median grain size were compared with data acquired from coarse-grained reference sample. The larger Debye-Waller parameter nanocrystalline was found to be due increased static displacements atoms their equilibrium sites the in material. Consistent this behaviour, strain distribution determined width intensity peaks significantly broader than No grain-size-correlated differences...
Using polarized neutron reflectometry, we obtained separate depth profiles for pinned and unpinned magnetization across the interface of a ferromagnet/antiferromagnet bilayer as function sign exchange bias. The are nonuniform extend well beyond chemical interface, suggesting an interfacial region magnetically distinct from its surroundings. A model that includes moments in ferromagnet antiferromagnet is developed complete description data.
We have found ferromagnetism in epitaxially grown superlattices of CaRuO(3)/CaMnO(3) that arises one unit cell at the interface. Scanning transmission electron microscopy and energy loss spectroscopy indicate difference magnitude Mn valence states between center CaMnO(3) layer interface region is consistent with double exchange interaction among ions Polarized neutron reflectivity thickness dependence bias field together interfacial only limited to each The moment alternates 1 μ(B)/interface...
We observe interfacial ferromagnetism in superlattices of the paramagnetic metal LaNiO3 and antiferromagnetic insulator CaMnO3. exhibits a thickness dependent metal-insulator transition we find emergence to be coincident with conducting state LaNiO3. That is, only which layers are metallic exhibit ferromagnetism. Using several magnetic probes, have determined that arises single unit cell CaMnO3 at interface. Together these results suggest can attributed double exchange interaction among Mn...
The coexistence and coupling of ferroelasticity magnetic ordering in a single material offers great opportunity to realize novel devices with multiple tuning knobs. Complex oxides are particularly promising class materials find multiferroic interactions due their rich phase diagrams, sensitive external perturbations. Still, there very few examples these systems. Here, we report the observation twin domains ferroelastic LaCoO3 epitaxial films geometric control structural symmetry intimately...
A scintillator-based Timepix3 (TPX3) detector was developed to resolve the high-frequency modulation of a neutron beam in both spatial and temporal domains, as required for spin-echo experiments. In this system, light from scintillator is manipulated with an optical lens intensified using image intensifier, making it detectable TPX3 chip. Two different scintillators, namely, 6LiF:ZnS(Ag) 6LiI:Eu, were investigated achieve high resolution needed modulated small-angle scattering (SEMSANS)...
MnF(2)/Fe bilayers exhibit asymmetric magnetization reversal that occurs by coherent rotation on one side of the loop and nucleation propagation domain walls other loop. Here, we show polarized neutron reflectometry, magnetization, magnetotransport measurements for samples with good crystalline "quality" is a two-stage process, due to stable state perpendicular cooling field direction. The result remarkably asymmetrically shaped hysteresis loops.
We present an investigation of the effect ferromagnetic layer thickness on exchange bias and coercivity enhancement in antiferromagnet/ferromagnet bilayers. At low temperatures both closely follow inverse relationship, contrary to several recent theoretical predictions. Furthermore, temperature dependence as a function ferromagnet provides clear evidence for existence two distinct regimes. These regimes were probed with conventional magnetometry, anisotropic magnetoresistance, polarized...
We studied the magnetic properties of La$_{0.7}$Ca$_{0.3}$MnO$_3$ / YBa$_2$Cu$_3$O$_{7-\delta}$ superlattices. Magnetometry showed that with increasing layer thickness saturation magnetization per decreases. From polarized neutron reflectometry we determined this reduction is due to an inhomogenous depth profile arising from suppression near interface. Electron energy loss spectroscopy indicates increased 3d band occupation Mn atoms in layers at Thus, ferromagnetic order interface most...
The structural and magnetic transitions in the shape-memory alloy ${\text{Ni}}_{2}\text{MnGa}$ can be tuned as a function of temperature by adding dopants. By altering free energy such that coincide, giant magnetocaloric effect is created near room temperature. We show, using x-ray absorption spectroscopy circular dichroism, how Cu, substituted for Mn, pulls transition downward also, counterintuitively, increases delocalization Mn magnetism. At same time, this reinforces Ni-Ga chemical bond,...
Polarized neutron reflectivity measurements of a ferromagnetic ${[{({\text{LaMnO}}_{3})}_{11.8}/{({\text{SrMnO}}_{3})}_{4.4}]}_{6}$ superlattice reveal modulated magnetic structure with an enhanced magnetization at the interfaces where ${\text{LaMnO}}_{3}$ was deposited on ${\text{SrMnO}}_{3}$ (LMO/SMO). However, opposite (SMO/LMO) are found to have reduced moment. The asymmetry is accompanied by corresponding in lateral structural roughness two observed via electron microscopy,...
Using polarized neutron reflectometry we measured the spin-dependent reflectivity from four LaAlO(3)/SrTiO(3) superlattices. Our results imply that upper limit for magnetization averaged over lateral dimensions of sample induced by an 11 T magnetic field at 1.7 K is less than 2 G. SQUID magnetometry superlattice samples sporadically finds enhanced moment, possibly due to experimental artifacts. These observations set important restrictions on theories which a strongly magnetism interface...
The effects of hydrogen (H2) and deuterium (D2) absorption were studied in two Co/Pd multilayers with perpendicular magnetic anisotropy (PMA) using polarized neutron reflectivity (PNR). PNR was measured an external field H applied the plane sample magnetization M confined for μ_o H= 6.0 T partially out at 0.65 T. Nominal thicknesses Co Pd layers 2.5 Å 21 Å, respectively. Because these small values, actual layer chemical composition, thickness, interface roughness parameters determined from...
Using polarized neutron reflectometry, we observe an induced magnetization of $75\ifmmode\pm\else\textpm\fi{}25\text{ }\mathrm{kA}/\mathrm{m}$ at 10 K in a ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}{\mathrm{MnO}}_{3}$ $(\mathrm{LSMO})/{\mathrm{BiFeO}}_{3}$ superlattice extending from the interface through several atomic layers ${\mathrm{BiFeO}}_{3}$ (BFO). The BFO is explained by density functional theory, where size band gap plays important role. Considering classical exchange field between...