A5076926939- Magnetic and transport properties of perovskites and related materials
- Advanced Condensed Matter Physics
- Multiferroics and related materials
- Organic and Molecular Conductors Research
- Solid-state spectroscopy and crystallography
- Electronic and Structural Properties of Oxides
- Magnetism in coordination complexes
- Physics of Superconductivity and Magnetism
- Spectroscopy and Quantum Chemical Studies
- Crystallization and Solubility Studies
- Advanced Chemical Physics Studies
- X-ray Diffraction in Crystallography
- Ferroelectric and Piezoelectric Materials
- Perovskite Materials and Applications
- Transition Metal Oxide Nanomaterials
- Rare-earth and actinide compounds
- Magneto-Optical Properties and Applications
- Crystal Structures and Properties
- Nonlinear Dynamics and Pattern Formation
- Nonlinear Optical Materials Research
- Thermal Expansion and Ionic Conductivity
- Magnetic Properties and Synthesis of Ferrites
- Photochemistry and Electron Transfer Studies
- Catalysis and Oxidation Reactions
- High-pressure geophysics and materials
Tokyo Institute of Technology
2015-2024
Tokyo University of Science
2008-2024
Institute of Science Tokyo
2024
Japan Science and Technology Agency
2012
The University of Tokyo
1995-2008
National Institute of Advanced Industrial Science and Technology
1999-2008
Joint Research Center
2000-2002
Optical spectra and their temperature dependence have been investigated for a prototypical double-exchange ferromagnet ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{MnO}}_{3}$ ( $x\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.175$). The optical conductivity spectrum above ${T}_{c}$ is characterized by interband transitions between the exchange-split bands gradually changes into intraband excitations with decrease of temperature, accompanied conspicuous transfer spectral...
A single crystal of ordered double perovskite oxide ${\mathrm{Sr}}_{2}{\mathrm{FeMoO}}_{6},$ a conducting ferromagnet with ${T}_{C}\ensuremath{\sim}420\mathrm{K},$ has been prepared by the floating zone method, and magnetic electronic properties have investigated. It found that ordinary anomalous Hall coefficients are negative positive, respectively, density conduction electrons is estimated at $1.1\ifmmode\times\else\texttimes\fi{}{10}^{22}{\mathrm{cm}}^{\mathrm{\ensuremath{-}}3},$...
Electric, thermal, optical, and magnetic properties have been investigated for ferromagnetic (ferrimagnetic) ordered double perovskites, A2CrReO6 (A=Sr Ca). Sr2CrReO6 is found to be a metallic ferromagnet with high Curie temperature (TC=635 K), possibly the highest-TC half metal among perovskite family. By contrast, Ca2CrReO6 Mott insulator TC of 360 K.
Optical conductivity spectra and their variation with temperature doping level x have been investigated for single crystals of ${\mathrm{La}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Sr}}_{\mathrm{x}}$${\mathrm{MnO}}_{3}$n(0\ensuremath{\leqslant}x\ensuremath{\leqslant}0.3). For the low-doped insulating crystal (x=0.1) which shows a ferromagnetic state at low temperature, spectral weight optical increases only in inner-gap region around 0.5 eV, but no Drude part emerges due to carrier...
The spin gap energy (\ensuremath{\approx} 30 meV) associated with the low-spin ($S=0$) to high-spin ($S=2$) transition in LaCo${\mathrm{O}}_{3}$ was proved be considerably smaller than charge 0.1 eV) which estimated by optical spectroscopy. Hole doping ground state of leads formation localized magnetic polarons unusually high number ($S=10\ensuremath{-}16$), can viewed as a precursor doping-induced ferromagnetic metallic state.
Infrared spectroscopy of a ${\mathrm{LaCoO}}_{3}$ crystal has revealed anomalous splitting the phonon modes as well their intensity variation with temperature during spin-state transition. The observed results can be interpreted in terms local lattice distortion arising from Jahn-Teller effect thermally excited intermediate-spin (S=1) state ${\mathrm{Co}}^{3+}$ ions. A possible role ${\mathrm{e}}_{\mathrm{g}}$ orbital ordering is discussed analysis split Co-O stretching modes.
We have investigated the diffuse phase transition accompanying formation of submicrometric ferromagnetic-metallic (FM) domains embedded in antiferromagnetic charge-ordered state ${\mathrm{Nd}}_{1/2}{\mathrm{Ca}}_{1/2}{\mathrm{MnO}}_{3}$ crystals, which is caused by quenched random field originating from Cr impurities substituted on Mn sites. The fraction FM volume or size cluster can be controlled to a large extent magnetic-field annealing as well content. observed phenomena are reminiscent...
Structural and electronic properties have been investigated for a series of Re-based ordered double perovskites, ${A}_{2}M{\mathrm{ReO}}_{6}$ $(A$=Sr,Ca; $M$=Mg,Sc,Cr,Mn,Fe,Co,Ni,Zn), which contain some prospective candidates the high-temperature half-metals future spin-electronic use. Neutron diffraction measurements revealed variation Re-O bond length with change its effective valence states depending on counter M ion, namely, ${\mathrm{Re}}^{6+}$- or ${\mathrm{Re}}^{5+}$-based insulating...
Optical spectra have been investigated for the prototypical Mott-Hubbard (MH) insulators ${\mathrm{LaTiO}}_{3}$ and ${\mathrm{YTiO}}_{3}$, their solid solutions ${\mathrm{La}}_{\mathit{x}}$${\mathrm{Y}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{TiO}}_{3}$. The MH gap shows a critical variation with x or equivalently change of one-electron bandwidth W. By an extrapolation rapidly varying electron correlation strength (U\ifmmode \tilde{}\else \~{}\fi{}=U/W), we could determine relative...
The global phase diagram for the spin and orbital ordering has been investigated perovskite-type $R{\mathrm{VO}}_{3}$ $(R$ being a rare-earth ion or Y) by measurements of specific heat, magnetization, Raman-scattering spectra. $(R=\mathrm{Lu}\ensuremath{-}\mathrm{Pr}),$ in which large tilting ${\mathrm{VO}}_{6}$ tends to stabilize collective Jahn-Teller distortion, shows structural transition concomitantly with G-type (OO) at temperature far above C-type magnetic temperature. By contrast...
The thermally induced insulator-metal transition (IMT) has been investigated for single crystals of undoped and lightly doped ${\mathrm{LaCoO}}_{3}$ by measurements the optical-conductivity spectra, resistivity, Hall coefficient up to 800 K. IMT around 500 K, where spin-state from nonmagnetic $(S=0)$ ground state intermediate-spin $(S=1)$ is nearly completed, characterized a large energy-scale change electronic structure as well steep increase carrier number typical metallic value due...
A phase transition in an organic charge-transfer complex, which originates from the neutral-ionic valence instability, can be tuned toward zero kelvin with use of external pressure or chemical modification as a control parameter. The diagram and observed dielectric behaviors are typical quantum paraelectricity, yet this zero-kelvin point namely, critical point, accompanies large fluctuation molecular charge, demonstrated by vibrational mode spectra. result indicates that π-electron transfer...
Correlated electron systems can undergo ultrafast photoinduced phase transitions involving concerted transformations of electronic and lattice structure. Understanding these phenomena requires identifying the key structural modes that couple to states. We report photoresponse molecular crystal Me4P[Pt(dmit)2]2, which exhibits a charge transfer similar between thermally accessible states, demonstrate how femtosecond diffraction be applied directly observe associated motions. Even for such...
We propose a method of rapid construction structural–magnetic–electronic phase diagram doped Mott insulators. The composition-spread is utilized for fabricating film whose doping concentration varies from 0 to 1 continuously. concurrent x-ray diffractometer that measures diffraction spectra all the composition simultaneously, scanning superconducting quantum interference device microscope, and infrared optical spectroscopy are employed characterizing film. A demonstration given colossal...
Insulator-metal transitions and related electronic structures have been investigated for single crystals of perovskite-type cobalt oxides $R\mathrm{Co}{\mathrm{O}}_{3}(R=\mathrm{L}\mathrm{a},\phantom{\rule{0ex}{0ex}}\mathrm{P}\mathrm{r},\phantom{\rule{0ex}{0ex}}\mathrm{N}\mathrm{d},\phantom{\rule{0ex}{0ex}}\mathrm{S}\mathrm{m},\phantom{\rule{0ex}{0ex}}\mathrm{E}\mathrm{u},\phantom{\rule{0ex}{0ex}}\mathrm{a}\mathrm{n}\mathrm{d}\phantom{\rule{0ex}{0ex}}\mathrm{G}\mathrm{d})$ with $R$-dependent...
A comprehensive study of magnetic, optical, and magnetooptical properties was carried out for single crystals the spinel-type Cr 2 X 4 ( =Mn, Fe, Co, Cu, Zn, Cd; =O, S, Se). The optical reflectivity measurements 0.1–30 eV revealed a wide variation in electronic structures on large energy scale between oxides =O) chalcogenides =S For =Fe we observed intra-atomic d – transitions 2+ ions with tetrahedral coordination, successfully deduced crystal field splitting Δ E , Racah parameter B...
We have investigated the ultrafast spin and charge dynamics in course of a photoinduced phase transition from an insulator with short-range order orbital (OO) to ferromagnetic metal perovskite-type Gd0.55Sr0.45MnO3. Transient reflectivity changes suggest that metallic state is formed just after photoirradiation decays within approximately 1 ps. The magnetization, however, increases time constant 0.5 ps 10 relatively slow increase magnetization attributable magnetic-field-induced alignment...
This work reviews the experimental studies on photo-induced cooperative phenomena (photo-induced phase transitions, PIPT), which are related to ultrafast structural and electronic-state dynamics. The review includes a brief history of this research field. current growth PIPT is facilitated by deep collaboration between quantum beam science materials science. Meanwhile, owing developments in technology, concept itself has largely expanded. In initial stage research, dynamical process was...
Organic molecular Mott insulators, in which carriers are localized as a result of the electron correlation, showed nonlinear electric conduction upon application high field along stacking axis. The current-driven low-resistive state potassium 7,7,8,8-tetracyanoquinodimethanane was stabilized down to 2 kelvin, where metallic path visible with microscope. current flow caused stripe-like periodic phase-segregation into carrier-rich and carrier-poor regions path.
The magnetic-field dependence of optical spectra and their anisotropy have been investigated for a single crystal ${\mathrm{Pr}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}{\mathrm{MnO}}_{3} \phantom{\rule{0ex}{0ex}}(x=0.4)$ at 30 K. charge-ordered (CO) state is transformed into ferromagnetic metallic by magnetic field 6.5 T, which manifested in huge change over wide photon-energy region (0.05 eV--3 eV). observed magnitude the with external has elucidated terms spin- orbital-ordering structures CO state.
A single-crystalline film of Sr2CoO4 with square-lattice CoO2 sheets (K2NiF4-type structure) was synthesized, and its electronic properties were characterized. The compound exhibited both ferromagnetic metallic behaviors, a fairly high Curie temperature T(C) approximately 250 K, in contrast to the superconductivity recently found triangular-lattice CoO2-sheet compound. film's large magnetoresistance current perpendicular plane showed field-hysteretic behavior analogous tunneling...
The electronic and magnetic properties of perovskite superlattices composed five unit-cell layers ferromagnetic metal ${\mathrm{La}}_{0.6}{\mathrm{Sr}}_{0.4}{\mathrm{MnO}}_{3}$ nonmagnetic band insulator ${\mathrm{SrTiO}}_{3}$ with varying layer thickness have been systematically investigated. well-defined periodic stacking no sign interlayer diffusion. spin canting at the interfaces in manifests itself as a suppressed magnetization huge magnetoresistance subsisting to low temperature....
The quasistable state in the photoinduced phase transition for quasi-one-dimensional quarter-filled organic conductor $(\mathrm{EDO}\mathrm{\text{\ensuremath{-}}}\mathrm{TTF}{)}_{2}{\mathrm{PF}}_{6}$ has been examined by ultrafast reflective measurements and time-dependent model calculations incorporating both electron-electron electron-phonon interactions. transient optical conductivity spectrum over a wide probe photon-energy range revealed that photoexcitation induced new type of...
We have systematically synthesized single-crystalline thin films of layered perovskites Sr2MO4 (M = Ti, V, Cr, Mn, and Co) which cannot be obtained in a form bulk crystal apart from M Mn. The two-dimensional electronic structure these M4+ oxides, ranging correlated insulator to ferromagnetic metal, has been investigated by using their optical conductivity spectra with polarizations E is perpendicular c parallel c, reveal systematic variation the charge gap, Mott-Hubbard or charge-transfer...