A5081782230- Magnetic and transport properties of perovskites and related materials
- Multiferroics and related materials
- Advanced Condensed Matter Physics
- Ferroelectric and Piezoelectric Materials
- Acoustic Wave Resonator Technologies
- Electronic and Structural Properties of Oxides
- Particle Accelerators and Free-Electron Lasers
- Rare-earth and actinide compounds
- Advanced X-ray Imaging Techniques
- High-pressure geophysics and materials
- Superconducting Materials and Applications
- Physics of Superconductivity and Magnetism
- Microwave Dielectric Ceramics Synthesis
- Solid-state spectroscopy and crystallography
- Magnetic Properties of Alloys
- X-ray Spectroscopy and Fluorescence Analysis
- Magnetic Properties and Synthesis of Ferrites
- Iron-based superconductors research
- Photorefractive and Nonlinear Optics
- Magnetic properties of thin films
- Particle accelerators and beam dynamics
- Catalytic Processes in Materials Science
- Crystallography and Radiation Phenomena
- Iron oxide chemistry and applications
- Inorganic Chemistry and Materials
University of Michigan
2025
Pohang University of Science and Technology
2014-2023
Pohang Accelerator Laboratory
2008-2023
Institute for Basic Science
2018
Government of the Republic of Korea
2017
Rutgers, The State University of New Jersey
1999-2012
Tsinghua University
2008
Indian Institute of Science Bangalore
2004
Rutgers Sexual and Reproductive Health and Rights
2001
Alcatel Lucent (Germany)
2000-2001
The construction of Pohang Accelerator Laboratory X-ray Free-Electron Laser (PAL-XFEL), a 0.1-nm hard free-electron laser (FEL) facility based on 10-GeV S-band linear accelerator (LINAC), is achieved in Pohang, Korea by the end 2016. 1.11 km-long building was completed 2014, and installation LINAC undulators started January 2015. LINAC, together with beamlines, commissioning began April 2016, first lasing FEL line 14 June progress PAL-XFEL its commission are reported here.
Following recent advancements in cryo-electron microscopy (cryo-EM) instrumentation and software algorithms, the next bottleneck achieving high-resolution cryo-EM structures arises from sample preparation. To overcome this, we developed a graphene-based affinity grid, Graffendor (GFD) to target low-abundance endogenous protein complexes. maintain grid quality consistency within single batch of 36 grids, established one-step crosslinking batch-production method using genetically modified ALFA...
We investigated the orbital anisotropy of ${\mathrm{GaFeO}}_{3}$ using Fe ${L}_{2,3}$-edge x-ray magnetic circular dichroism and polarization dependent O $K$-edge absorption spectroscopy. found that system shows a considerably large momentum anisotropic Fe-O bonding, which are unexpected in half-filled ${d}^{5}$ such as ${\mathrm{GaFeO}}_{3}$. The bonding anisotropies, turn out to be induced by lattice distortions with exotic off-centering site movements, contribute magnetocrystalline energy...
A reentrant charge ordering transition occurs within the $\ensuremath{\mu}\mathrm{m}$-scale phase-separated manganite ${(\mathrm{La},\mathrm{Pr})}_{5∕8}{\mathrm{Ca}}_{3∕8}\mathrm{Mn}{\mathrm{O}}_{3}$. This low-temperature state, in which charge-ordered and ferromagnetic-metallic phases coexist, accompanies spin-glass-like magnetism. Furthermore, thermal conductivity measurements reveal an irreversibility characteristic of a freezing lattice degrees freedom, strongly suggesting presence...
We discovered an unprecedented magnitude of the $1/f$ noise near Curie temperature ${(T}_{c})$ in low-${T}_{c}$ manganites. The scaling behavior and resistance provides strong evidence percolation nature ferromagnetic transition polycrystalline samples. steplike changes with temperature, observed for single crystals, suggest that size domains depends on crystallites.
Thin films of perovskite manganite La0.7Ca0.3MnO3 were grown epitaxially on SrTiO3(100), MgO(100) and LaAlO3(100) substrates by the pulsed laser deposition method. Microscopic structures these thin film samples as well a bulk sample fully determined x-ray diffraction measurements. The unit cells three have different shapes, i.e., contracted tetragonal, cubic, elongated tetragonal for SrTiO3, MgO, LaAlO3, respectively, while cell is cubic. It found that with cubic show smaller peak...
The isovalent substitution of Te for Se in the superconducting $\ensuremath{\alpha}\text{-FeSe}$ raises ${T}_{C}$ where average chalcogen--Fe bond angle decreases and chalcogen-Fe distance increases. Locally, however, ions do not share same site have two distinct $z$ coordinates, contrast to what is presumed $P4/nmm$ symmetry. local between chalcogens Fe increases with substitution, consistent rise ${T}_{C}$, Fe--Te bonds become shorter than binary FeTe, while Fe--Se stay as binary. Ab...
A strong relaxation mode was observed in the paraelectric phase of barium titanate (BaTiO3) single crystals by Brillouin scattering study and found to correlate with softening longitudinal acoustic increase hypersonic damping. These observations support existence polar percursors their electrostrictive coupling strain caused waves, consistent former studies evidencing off-centered Ti ions high-symmetry cubic phase. critical slowing down has been clearly vicinity cubic-tetragonal transition,...
Using synchrotron x-ray and neutron diffraction, we disentangle spin-lattice order in highly frustrated ${\mathrm{ZnCr}}_{2}{\mathrm{O}}_{4}$ where magnetic chromium ions occupy the vertices of regular tetrahedra. Upon cooling below 12.5 K quandary antialigning spins surrounding triangular faces tetrahedra is resolved by establishing weak interactions on each triangle through an intricate lattice distortion. However, resulting spin not simply a N\'eel state strong bonds, but rather complex...
Spin–orbit coupling results in technologically-crucial phenomena underlying magnetic devices like memories and energy-efficient motors. In heavy element materials, the strength of spin–orbit becomes large to affect overall electronic nature induces novel states such as topological insulators spin–orbit-integrated Mott states. Here we report an unprecedented charge-ordering cascade IrTe2 without loss metallicity, which involves localized with diamagnetic Ir4+–Ir4+ dimers. The cooling,...
Iron is one of the most studied chemical elements due to its sociotechnological and planetary importance; hence, understanding structural transition dynamics vital interest. By combining a short pulse optical laser an ultrashort free electron pulse, we have observed subnanosecond iron from high-quality x-ray diffraction data measured at 50-ps intervals up 2500 ps. We unequivocally identify three-wave structure during initial compression two-wave decaying shock, involving all known types (α-,...
We use a spatially resolved, direct spectroscopic probe for electronic structure with an additional sensitivity to chemical compositions investigate high-quality single crystal samples of La(1/4)Pr(3/8)Ca(3/8)MnO3, establishing the formation distinct insulating domains embedded in metallic host at low temperatures. These are found be least order magnitude larger size compared previous estimates and exhibit memory effects on temperature cycling absence any perceptible inhomogeneity,...
We report a strain-induced magnetoelectric coupling in BaTiO3/Fe3O4 ferroelectric core/ferrimagnetic shell nanoparticles. The temperature-dependent magnetoresistance and magnetization clearly show several jumps near the structural phase transition temperatures of BaTiO3. Below Verwey temperature Fe3O4, i.e., at 20 K, dielectric constant decreases continuously upon application an external magnetic field, observed magnetodielectric curve does not follow square magnetization. discuss effect...
The insulator-metal transition in single crystal La(5/8-y)Pr(y)Ca(3/8)MnO3 with y=0.35 was studied using synchrotron x-ray diffraction, electric resistivity, magnetic susceptibility, and specific heat measurements. Despite the dramatic drop resistivity at temperature Tmi, charge-ordering (CO) peaks exhibit no anomaly this continue to grow below Tmi. Our data suggest then, that addition CO phase, another insulating phase is present Tco. In picture, due changes within latter phase. does not...
We report an intriguing magnetodielectric coupling in BaTiO3∕γ-Fe2O3 dielectric core/ferrimagnetic shell nanoparticles. The constant steeply increases with magnetic field, and the frequency dependent curve shows a resonancelike peak at high temperatures, while it decreases smoothly field no appears low temperatures. attribute observed to Maxwell-Wagner effect combined magnetoresistance temperatures possible spin-lattice its modification near interfaces
We present comprehensive studies of strain effects on the spin reorientation transition (SRT), so-called Morin transition, in α-Fe2O3(0001) films. The epitaxial films were grown with a Cr2O3 buffer layer Al2O3(0001) substrates through an oxide molecular beam epitaxy. antiferromagnetic axis was monitored by using Fe L2-edge X-ray magnetic linear dichroism. found to introduce compressive into film due its 1.6% smaller in-plane lattice constant. degree is monotonically reduced increase α-Fe2O3...
We investigated temperature $(T)$- and magnetic field-dependent optical conductivity spectra $\ensuremath{\sigma}(\ensuremath{\omega})$ of a ${\mathrm{La}}_{5/8\ensuremath{-}y}{\mathrm{Pr}}_{y}{\mathrm{Ca}}_{3/8}{\mathrm{MnO}}_{3}(y\ensuremath{\approx}0.35)$ single crystal, showing intriguing phase coexistence at low T. At ${T}_{\mathrm{C}}<T<{T}_{\mathrm{CO}},$ dominant charge-ordered produces large gap energy $\ensuremath{\sim}0.4 \mathrm{eV}.$ $T<{T}_{\mathrm{C}},$ least two absorption...
The anomalous enhancement in dielectric (ε&gt;6000) and piezoelectric constant (d33&gt;600 pC/N) the tetragonal side (x=35%) of morphotropic phase boundary (MPB) has been observed polycrystalline (1−x)Pg(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-PT). On other hand, x-ray peak position shifts under electric field (E) demonstrate that intrinsic response becomes maximum at MPB (x=33%–34%), which may be associated with recently discovered monoclinic phase. Intensity change Bragg peaks E indicates 90°...
The intrinsic linewidth ${\ensuremath{\Gamma}}_{\mathrm{TA}}$ of the transverse acoustic phonon observed in relaxor ferroelectric compound $\mathrm{Pb}({\mathrm{Mg}}_{1/3}{\mathrm{Nb}}_{2/3}{)}_{0.8}{\mathrm{Ti}}_{0.2}{\mathrm{O}}_{3}$ (PMN-20%PT) begins to broaden with decreasing temperature around 650 K, nearly 300 K above transition ${T}_{c} (\ensuremath{\sim}360 \mathrm{K}).$ We speculate that this anomalous behavior is directly related condensation polarized, nanometer-sized, regions...
Comprehensive x-ray scattering studies, including resonant at Mn L, Tb and M edges, were performed on single crystals of TbMn2O5 for crystallographic data to elucidate the nature its commensurate incommensurate phases. The results provide direct evidence symmetry lowering ferroelectric phase driven by magnetically induced lattice modulations show presence multiple magnetic orders. competing orders under spin-frustrated geometry are believed cause discommensuration result in...
Epitaxial thin films of multiferroic perovskite BiMnO3 were synthesized on SrTiO3 substrates, and orbital ordering magnetic properties the investigated. The Mn3+ eg orbitals at a wave vector (¼¼¼) was detected by Mn K-edge resonant X-ray scattering. This peculiar order inherently contains frustration. While bulk is known to exhibit simple ferromagnetism, frustration enhanced in-plane compressive strains in brings about cluster-glass-like properties.
Based on the detailed Mn L(2,3)-edge x-ray resonant scattering results, we report a new complexity in magnetic order of multiferroic orthomangnites, which has been considered as simple A-type cycloid inducing ferroelectricity. The Dzyaloshinskii-Moriya interaction involved orthorhombic distortion brings F-type canting from A type, and ordering type becomes off-phase synchronized bc TbMnO(3) or tilted antiphase ab Eu(3/4)Y(1/4)MnO(3). is responsible for field-driven multiferroicity to weak...
We report an overview of soft X-ray scientific instruments and optics at the free electron laser (FEL) Pohang Accelerator Laboratory, with selected first-commissioning results. The FEL exhibited a pulse energy 200 μJ/pulse, width &lt;50 fs full half maximum, bandwidth 0.44% photon 850 eV. Monochromator resolving power 10 500 was achieved. estimated total time resolution between optical pulses &lt;270 fs. A resonant inelastic scattering spectrometer set up; its commissioning results...