Results for "Zenji Hiroi"

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Frustrated Magnetism of Pharmacosiderite Comprising Tetrahedral Clusters Arranged in the Primitive Cubic LatticeAug 07 2018We show that pharmacosiderite is a novel cluster antiferromagnet comprising frustrated regular tetrahedra made of spin-5/2 Fe3+ ions that are arranged in the primitive cubic lattice. The connectivity of the tetrahedra and the inter-cluster interaction ... More
Structural instability of the rutile compounds and its relevance to the metal-insulator transition of VO2Mar 08 2015The metal-insulator transition (MIT) of VO2 is discussed with particular emphasis on the structural instability of the rutile compounds toward dimerization. Ti substitution experiments reveal that the MIT is robust up to 20% Ti substitutions and occurs ... More
One-dimensionalization by Geometrical Frustration in the Anisotropic Triangular Lattice of the 5d Quantum Antiferromagnet Ca3ReO5Cl2Apr 12 2019We report on the emergence of antiferromagnetic spin chains from two-dimensionally aligned spins on the anisotropic triangular lattice (ATL) in the insulating calcium rhenium oxychloride Ca3ReO5Cl2. The compound contains Re6+ ions each with one unpaired ... More
Magnetic Phase Diagram of the Breathing Pyrochlore Antiferromagnet LiGa1-xInxCr4O8Mar 31 2015The spinel oxides LiGaCr4O8 and LiInCr4O8 contain size-alternating pyrochlore lattices of spin-3/2 Cr3+ tetrahedra with different magnitudes of alternation. We show here that the solid solutions LiGa1-xInxCr4O8 between these two 'breathing' pyrochlore ... More
Crystal Chemistry and Magnetic Properties of Manganese Zinc Alloy "YMn2Zn20" Comprising a Mn Pyrochlore LatticeMar 22 2012The chemical composition, crystal structure, and magnetic properties of a manganese zinc alloy with an ideal composition of YMn2Zn20, which comprises a pyrochlore lattice made of Mn atoms, are reported. The compound is stable only when In or Al is partially ... More
Breathing Pyrochlore Lattice Realized in A-Site Ordered Spinel Oxides LiGaCr4O8 and LiInCr4O8Jan 29 2013A unique type of frustrated lattice is found in two A-site ordered spinel oxides, LiGaCr4O8 and LiInCr4O8. Because of the large size mismatch between Li+ and Ga3+/In3+ ions at the A site, the pyrochlore lattice, made up of Cr3+ ions carrying spin 3/2, ... More
Distorted Kagome Lattice Generated by a Unique Orbital Arrangement in the Copper Mineral KCu3As2O7(OH)3Feb 14 2012Jan 29 2013We study polycrystalline samples of KCu3As2O7(OH)3, a new candidate spin-1/2 kagome antiferromagnet, by magnetic susceptibility and heat capacity measurements above 2 K. The unique arrangement of the 3z2 - r2 and x2 - y2 orbitals on the Cu2+ kagome net ... More
Anomalous Flux Pinning in ?-Pyrochlore Oxide Superconductor KOs2O6Feb 18 2006The superconducting transition of the ?-pyrochlore oxide KOs2O6 with Tc = 9.60 K is studied by resistivity measurements under various magnetic fields using a high-quality single crystal. The reentrant behavior of superconductivity is observed near Tc ... More
Observation of Magnetic Monopoles in Spin IceAug 25 2009Sep 11 2009Excitations from a strongly frustrated system, the kagome ice state of the spin ice Dy2Ti2O7 under magnetic fields along a [111] direction, have been studied. They are theoretically proposed to be regarded as magnetic monopoles. Neutron scattering measurements ... More
Low Temperature Symmetry of Pyrochlore Oxide Cd2Re2O7Jul 20 2002Aug 09 2002We report the X-ray study for the pyrochlore oxide Cd2Re2O7. Two symmetry-lowering structural transitions were observed at Ts1=200K and Ts2=120K. The former is of the second order from the ideal cubic pyrochlore structure with space group Fd-3m to a tetragonally ... More
Magnetic State Selected by Magnetic Dipole Interaction in Kagome Antiferromagnet NaBa$_{2}$Mn$_{3}$F$_{11}$Dec 19 2017Feb 18 2018We have studied the ground state of the classical Kagome antiferromagnet NaBa$_{2}$Mn$_{3}$F$_{11}$. Strong magnetic Bragg peaks observed in the $d$-spacing shorter than 6.0 \AA\ were indexed by the propagation vectors of $\boldsymbol{k}_{0} = (0,0,0)$. ... More
Vesignieite BaCu3V2O8(OH)2 as a Candidate Spin-1/2 Kagome AntiferromagnetJan 15 2009A polycrystalline sample of vesignieite BaCu3V2O8(OH)2 comprising a nearly ideal kagome lattice composed of Cu2+ ions carrying spin 1/2 has been synthesized and studied by magnetization and heat capacity measurements. Magnetic susceptibility shows a neither ... More
Photocarrier injection and the I-V characteristics of La0.8Sr0.2MnO3/SrTiO3:Nb heterojunctionsApr 16 2004Oxide heterojunctions made of p-type L0.8Sr0.2MnO3 (LSMO) and niobium-doped n-type SrTiO3 (STO:Nb) have been fabricated by the pulsed laser deposition (PLD) technique and are characterized under UV light irradiation by measuring the current-voltage, photovoltaic ... More
Discontinuous Lifshitz Transition Achieved by Band-Filling Control in NaxCoO2Feb 23 2010Precise band-filling control is performed on a strongly correlated electron system NaxCoO2, by changing the Na content, and the influence of this on the magnetic and thermodynamic properties is studied. It has been discovered that a phase boundary between ... More
Ferromagnetic Ising Spin Chains Emerging from the Spin Ice under Magnetic FieldJun 10 2003Sep 19 2003A spin-ice compound dysprosium titanate, Dy2Ti2O7, is studied by specific heat measurements in magnetic fields applied along the [110] direction of the cubic unit cell. Above a magnetic field of 0.4 T a relatively sharp peak at T = 1.1 K in the specific ... More
New beta-Pyrochlore Oxide Superconductor CsOs2O6Apr 09 2004The discovery of a new beta-pyrochlore oxide superconductor CsOs2O6 with Tc = 3.3 K is reported. It is the third superconductor in the family of beta-pyrochlore oxides, following KOs2O6 with Tc = 9.6 K and RbOs2O6 with Tc = 6.3 K. The Tc of this series ... More
Helical order and multiferroicity in the $S=1/2$ quasi-kagome system KCu$_3$As$_2$O$_7$(OD)$_3$Apr 11 2014Several Cu$^{2+}$ hydroxide minerals have recently been identified as candidate realizations of the $S=1/2$ kagome Heisenberg model. In this context, we have studied the distorted system KCu$_3$As$_2$O$_7$(OD)$_3$ using neutron scattering and bulk measurements. ... More
Magnetic Properties of the Spin-1/2 Deformed Kagome Antiferromagnet EdwardsiteMay 11 2013We prepared a powder sample of edwardsite Cd2Cu3(SO4)2(OH)6 4H2O, which is a new candidate compound for the spin-1/2 kagome antiferromagnet, and studied its magnetic properties by magnetic susceptibility and heat capacity measurements. Edwardsite has ... More
Photocarrier Injection and Current-Voltage Characteristics of a La0.8Sr0.2MnO3/SrTiO3:Nb Heterojunction at Low TemperatureApr 11 2005An epitaxial heterojunction made of a p-type perovskite manganite La0.8Sr0.2MnO3 film and an n-type strontium titanate SrTiO3:Nb substrate has been fabricated by the pulsed laser deposition technique. The I - V characteristics and photovoltaic properties ... More
Kagome-Triangular Lattice Antiferromagnet NaBa2Mn3F11Mar 10 2014A new type of magnetically frustrated lattice is found in the layered fluoride NaBa2Mn3F11. A kagome-type array of regular triangles composed of Mn2+ ions (spin 5/2) deforms so as to generate the next-nearest-neighbor interaction J2 between three out ... More
Novel Phase Transitions in the Breathing Pyrochlore Lattice: 7Li-NMR on LiInCr4O8 and LiGaCr4O8Nov 06 2014We report 7Li-NMR studies on LiInCr4O8 and LiGaCr4O8, in which Cr3+ ions with spin 3/2 form a breathing pyrochlore lattice, a network of tetrahedra with alternating sizes. In LiInCr4O8 with large alternation, the nuclear relaxation rate 1/T1 shows an ... More
Chemical trends of superconducting properties in pyrochlore oxidesDec 29 2006Chemical trends of fundamental superconducting parameters and normal-state properties are described for a family of pyrochlore oxide superconductors. Particularly, the change of Tc from 1.0 K for alpha-pyrochlore Cd2Re2O7 to 3.3 K (A = Cs), 6.3 K (Rb), ... More
High Pressure Effects on Superconductivity in the beta-pyrochlore Oxides AOs2O6 (A=K, Rb, Cs)Jul 23 2004Recently new pyrochlore oxides superconductors AOs2O6 (A=K,Rb,Cs) were found and we measured the pressure dependence of magnetization up to 1.2 GPa in order to deduce the pressure effect of Tc in the three beta-pyrochlore oxides. It is found that the ... More
Magnetic Order in the Spin-1/2 Kagome Antiferromagnet VesignieiteSep 21 2012Dec 06 2012We report results of magnetic susceptibility and 51V- and 63,65Cu-NMR measurements on a high-quality powder sample of vesignieite BaCu3V2O8(OH)2, a candidate for the spin-1/2 kagome antiferromagnet. We observed a twostep magnetic transition: the appearance ... More
Orbital Arrangements and Magnetic Interactions in the Quasi-One-Dimensional Cuprates ACuMoO_4(OH) (A = Na, K)May 20 2015A new spin-1/2 quasi-one-dimensional antiferromagnet KCuMoO_4(OH) is prepared by the hydrothermal method. The crystal structures of KCuMoO_4(OH) and the already-known Na-analogue, NaCuMoO_4(OH), are isotypic, comprising chains of Cu^{2+} ions in edge-sharing ... More
Superconductivity in an Einstein Solid AxV2Al20 (A = Al and Ga)Dec 22 2011A cage compound AxV2Al20 (Al10V), that was called an Einstein solid by Caplin and coworkers 40 years ago, is revisited to investigate the low-energy, local vibrations of the A atoms and their influence on the electronic and superconducting properties ... More
Crystal structure of the pyrochlore oxide superconductor KOs$_2$O$_6$Dec 28 2005We report the single-crystal X-ray analysis of the structure of the pyrochlore oxide superconductor KOs$_2$O$_6$. The structure was identified as the $\beta$-pyrochlore structure with space group $Fd\bar{3}m$ and lattice constant $a$ = 10.089(2)~\AA at ... More
Frustrated Magnetism of the Maple-Leaf-Lattice Antiferromagnet MgMn$_3$O$_7$$\cdot$3H$_2$OAug 08 2018We present a novel hydrated layered manganate MgMn$_3$O$_7$$\cdot$3H$_2$O as a maple-leaf-lattice (MLL) antiferromagnet candidate. The MLL is obtained by regularly depleting 1/7 of the lattice points from a triangular lattice so that the magnetic connectivity ... More
A new macroscopically degenerate ground state in the spin ice compound Dy2Ti2O7 under a magnetic fieldJul 23 2002The low temperature magnetic properties of pyrochlore compound Dy2Ti2O7 in magnetic fields applied along the [111] direction are reported. Below 1 K, a clear plateau has been observed in the magnetization process in the field range 2~9 kOe, followed by ... More
The second phase transition in the pyrochlore oxide Cd2Re2O7Mar 08 2002Evidence for another phase transition at 120 K in the metallic pyrochlore oxide Cd2Re2O7, following the structural transition at 200 K and followed by the superconducting transition at 1.0 K, is given through resistivity, magnetoresistance, specific heat, ... More
Neutron Scattering Study of the Localized Mode in the beta-Pyrochlore Superconductors AOs2O6Jul 10 2007Oct 10 2007Inelastic neutron scattering and neutron powder diffraction experiments were carried out to investigate a localized mode, proposed from various bulk measurements, in the beta-pyrochlore AOs2O6 (A=K, Rb, Cs). The localized mode was identified in all the ... More
Synthesis of anti-perovskite-type carbides and nitrides from metal oxides and melamineApr 12 2019Four anti-perovskite-type compounds, ZnNNi3, ZnCNi3, SnNCo3, and SnCCo3, are synthesised through reactions between ingredient metal oxides and organic compound melamine (C3H6N6). ZnNNi3 and ZnCNi3 are selectively synthesised by choosing different reaction ... More
A brief comment on the chemical formulae of the rare earth iron arsenide oxide superconductorsMay 30 2008Just a brief comment on the chemical formulae of the rare earth iron arsenide oxide superconductors
Rattling-Induced Superconductiviy in the Beta-Pyrochlore Oxides AOs2O6Jun 25 2009The superconducting properties of two beta-pyrochlore oxides, CsOs2O6 and RbOs2O6, are studied by thermodynamic and transport measurements using high-quality single crystals. It is shown that the character of superconductivity changes systematically from ... More
Pyrochlore Oxide Superconductor Cd2Re2O7 RevisitedDec 11 2017The superconducting pyrochlore oxide Cd2Re2O7 is revisited with a particular emphasis on the sample-quality issue. The compound has drawn attention as the only superconductor (Tc = 1.0 K) that has been found in the family of {\alpha}-pyrochlore oxides ... More
Magnetic Transitions under Ultrahigh Magnetic Fields of up to 130 T in the Breathing Pyrochlore Antiferromagnet LiInCr4O8Apr 10 2017The magnetization processes of the spin-3/2 antiferromagnet LiInCr4O8 comprising a "breathing" pyrochlore lattice, which is an alternating array of small and large tetrahedra, are studied under ultrahigh magnetic fields of up to 130 T using state-of-the-art ... More
Erratum to Three Papers on the beta-Pyrochlore Oxide SuperconductorsOct 13 2005Oct 17 2005The magnitude of magnetic fields given in the three papers that report on the superconductivity of the beta-pyrochlore oxides is corrected.
Second Anomaly in the Specific Heat of beta-Pyrochlore Oxide Superconductor KOs2O6Feb 02 2005Jul 29 2005Resistivity and specific heat have been measured on a single crystalline sample of the beta-pyrochlore oxide superconductor, KOs2O6. It is found that a second peak in specific heat, which may evidence an unknown phase transition, appears around Tp ~ 7.5 ... More
Itinerant-Electron Magnet of the Pyrochlore Lattice: Indium-Doped YMn2Zn20Aug 04 2010Aug 05 2010We report on a ternary intermetallic compound, "YMn2Zn20", comprising a pyrochlore lattice made of Mn atoms. A series of In-doped single crystals undergo no magnetic long-range order down to 0.4 K, in spite of the fact that the Mn atom carries a local ... More
Large Diamagnetism of AV2Al20 (A = Y and La)Nov 01 2012We find anomalously large diamagnetic responses in the cage compounds AV2Al20 where A = Y and La, not A = Al0.3, Sc0.4, and Lu, despite the apparent similarities in crystal and electronic structures among these compounds. The magnetic susceptibilities ... More
Specific Heat of the beta-Pyrochlore Oxide Superconductors CsOs2O6 and RbOs2O6Jan 31 2005Jul 29 2005Two beta-pyrochlore oxide superconductors, CsOs2O6 and RbOs2O6, are studied thermodynamically by measuring specific heat on polycrystalline samples. It is found that a Sommerfeld coefficient ? is nearly equal, 20 mJ/K2 mol Os, in the two oxides with different ... More
Thermodynamic Properties of the Kagome Lattice in VolborthiteAug 11 2010Thermodynamic investigations on volborthite (Cu3V2O7(OH)2 2H2O), which possesses a two-dimensional kagome structure of S-1/2 spins, are presented. The low-temperature heat capacities of volborthite and its Zn analogue compound were measured by the relaxation ... More
Magnetization Plateaus in the Spin-1/2 Kagome Antiferromagnets: Volborthite and VesignieiteMar 16 2011The magnetization of two spin-1/2 kagome antiferromagnets, volborthite and vesignieite, has been measured in pulsed magnetic fields up to 68 T. A magnetization plateau is observed for each compound near the highest magnetic field. Magnetizations at saturation ... More
Rattling and Superconducting Properties of the Cage Compound GaxV2Al20Oct 24 2012Low-energy rattling modes and their effects on superconductivity are studied in the cage compound GaxV2Al20. A series of polycrystalline samples of 0 < x =< 0.6 are examined through resistivity, magnetic susceptibility, and heat capacity measurements. ... More
A Magnetic Transition Probed by the Ce Ion in Square-Lattice Antiferromagnet CeMnAsOJul 31 2011We examined the magnetic properties of the square-lattice antiferromagnets CeMnAsO and LaMnAsO and their solid solutions La1-xCexMnAsO by resistivity, magnetic susceptibility, and heat capacity measurements below room temperature. A first-order phase ... More
Spinodal Decomposition in the TiO2-VO2 SystemJun 11 2013Spinodal decomposition is a ubiquitous phenomenon leading to phase separation from a uniform solution. We show that a spinodal decomposition occurs in a unique combination of two rutile compounds of TiO2 and VO2, which are chemically and physically distinguished ... More
A novel crystal polymorph of volborthite, Cu3V2O7(OH)2 2H2OSep 14 2012A new polymorph of volborthite [tricopper(II) divanadium(V) heptaoxide dihydroxide dihydrate], Cu3V2O7(OH)2 2H2O, has been discovered in a single crystal prepared by hydrothermal synthesis. X-ray analysis reveals that the monoclinic structure has the ... More
YCr6Ge6 as a Candidate Compound for a Kagome MetalDec 10 2012We show that YCr6Ge6, comprising a kagome lattice made up of Cr atoms, is a plausible candidate compound for a kagome metal that is expected to exhibit anomalous phenomena such as flat-band ferromagnetism. Resistivity, magnetization, and heat capacity ... More
Superconductivity and Rattling under High Pressure in the beta-Pyrochlore Oxide RbOs2O6Sep 26 2011Rattling-induced superconductivity in the beta-pyrochlore oxide RbOs2O6 is investigated under high pressures up to 6 GPa. Resistivity measurements in a high-quality single crystal show that the superconducting transition temperature Tc increases gradually ... More
Unique Phase Transition on Spin-2 Triangular Lattice of Ag2MnO2May 24 2008Ag2MnO2 is studied as a possible candidate compound for an antiferromagnetic XY spin model on a triangular lattice. In spite of the large Curie-Weiss temperature of -430 K found in magnetic susceptibi-lity, Mn3+ spins with S = 2 do not undergo a conventional ... More
Weak ferromagnetic order breaking the threefold rotational symmetry of the underlying kagomé lattice in CdCu$_3$(OH)$_6$(NO$_3$)$_2\cdot$H$_2$OMar 28 2017Novel magnetic phases are expected to occur in highly frustrated spin systems. Here we study the structurally perfect kagom\'e antiferromagnet CdCu$_3$(OH)$_6$(NO$_3$)$_2\cdot$H$_2$O by magnetization, magnetic torque, and heat capacity measurements using ... More
Superconducting properties of the pyrochlore oxide Cd2Re2O7Nov 08 2001Dec 04 2001We report the superconducting properties of the pyrochlore oxide Cd2Re2O7. The bulk superconducting transition temperature Tc is about 1.0 K, and the upper critical field Hc2 determined by the measurement of specific heat under magnetic fields is 0.29 ... More
Superconducting weak link generated on a linear array of substrate steps in ultrathin films of YBa2Cu3O7-xDec 17 2009We have studied a three-unit-cell-thick YBa2Cu3O7-x (YBCO) superconducting film grown on a slightly vicinal SrTiO3 substrate that was polished from the (001) plane by a small miscut angle (less than 0.5 degrees). This produced, on its surface, a linear ... More
Photocarrier Injection to Transition Metal OxidesJan 04 2003Jan 07 2003This paper has been withdrawn by the author(s), due a crucial error in the data.
Upper critical field and de Haas-van Alphen oscillations in KOs$_2$O$_6$ measured in a hybrid magnetMay 18 2010Jul 27 2010Magnetic torque measurements have been performed on a KOs$_2$O$_6$ single crystal in magnetic fields up to 35.3 T and at temperatures down to 0.6 K. The upper critical field is determined to be $\sim$30 T. De Haas-van Alphen oscillations are observed. ... More
Split Fermi Surfaces of the Spin-Orbit-Coupled Metal Cd2Re2O7 Probed by de Haas-van Alphen EffectMar 28 2018The superconducting pyrochlore oxide Cd2Re2O7 shows a structural transition with inversion symmetry breaking (ISB) at Ts1 = 200 K. A recent theory [L. Fu, Phys. Rev. Lett. 115, 026401 (2015)] suggests that the origin is an electronic instability that ... More
High-pressure study on the superconducting pyrochlore oxide Cd2Re2O7Nov 20 2001Dec 04 2001Superconducting and structural phase transitions in a pyrochlore oxide Cd2Re2O7 are studied under high pressure by x-ray diffraction and electrical resistivity measurements. A rich P-T phase diagram is obtained, which contains at least two phases with ... More
$J_1-J_2$ Square-Lattice Heisenberg Antiferromagnets with 4$d^1$ spins: AMoOPO$_4$Cl (A = K, Rb)Feb 09 2017Magnetic properties of AMoOPO$_4$Cl (A = K, Rb) with Mo$^{5+}$ ions in the 4$d^1$ electronic configuration are investigated by magnetization, heat capacity and NMR measurements on single crystals, combined with powder neutron diffraction experiments. ... More
Magnetoelastic couplings in the deformed Kagomé quantum spin lattice of volborthiteMar 12 2019Microscopic spin interactions on a deformed Kagom\'{e} lattice of volborthite are investigated through magnetoelastic couplings. A negative longitudinal magnetostriction $\Delta L<0$ in the $b$ axis is observed, which depends on the magnetization $M$ ... More
Precise Control of Band Filling in NaxCoO2Apr 09 2007Electronic properties of the sodium cobaltate NaxCoO2 are systematically studied through a precise control of band filling. Resistivity, magnetic susceptibility and specific heat measurements are carried out on a series of high-quality polycrystalline ... More
High-Field ESR Measurements of S=1/2 Kagome Lattice Antiferromagnet BaCu$_3$V$_2$O$_8$(OH)$_2$Dec 22 2009High-field electron spin resonance (ESR) measurements have been performed on vesignieite BaCu$_3$V$_2$O$_8$(OH)$_2$, which is considered as a nearly ideal model substance of $S$=1/2 kagome antiferromagnet, in the temperature region from 1.9 to 265 K. ... More
High-field Phase Diagram and Spin Structure of Volborthite Cu3V2O7(OH)2/2H2OOct 03 2011Jan 10 2012We report results of 51V NMR experiments on a high-quality powder sample of volborthite Cu3V2O7(OH)2/2H2O, a spin-1/2 Heisenberg antiferromagnet on a distorted kagome lattice. Following the previous experiments in magnetic fields $B$ below 12 T, the NMR ... More
Magnetic State Selected by Magnetic Dipole Interaction in Kagome Antiferromagnet NaBa$_{2}$Mn$_{3}$F$_{11}$Dec 19 2017We have studied the ground state of the classical Kagome antiferromagnet NaBa$_{2}$Mn$_{3}$F$_{11}$. Strong magnetic Bragg peaks observed in the $d$-spacing shorter than 6.0 \AA\ were indexed by the propagation vectors of $\boldsymbol{k}_{0} = (0,0,0)$. ... More
Spin reorientation in the square-lattice antiferromagnets RMnAsO (R = Ce, Nd): Density functional analysis of the spin exchange interactions between the rare-earth and transition-metal ionsMay 29 2012The spin reorientation (SR) phenomenon of the square-lattice antiferromagnets RMnAsO (R = Ce, Nd) was investigated by analyzing the spin exchange interactions between the rare-earth and transition-metal ions (R3+ and Mn2+, respectively) on the basis of ... More
Superconducting and Structural Transitions in the β-Pyrochlore Oxide KOs2O6 under High PressureSep 02 2010Rattling-induced superconductivity in the {\beta}-pyrochlore oxide KOs2O6 is investigated under high pressure up to 5 GPa. Resistivity measurements in a high-quality single crystal reveal a gradual decrease in the superconducting transition temperature ... More
Emergence of nontrivial magnetic excitations in a spin liquid state of kagome volborthiteAug 01 2016When quantum fluctuations destroy underlying long-range ordered states, novel quantum states emerge. Spin-liquid (SL) states of frustrated quantum antiferromagnets, in which highly-correlated spins keep to fluctuate down to very low temperatures, are ... More
All-in/all-out magnetic domains: X-ray diffraction imaging and magnetic field controlJul 21 2014Long-range non-collinear all-in/all-out magnetic order has been directly observed for the first time in real space in the pyrochlore Cd$_2$Os$_2$O$_7$ using resonant magnetic microdiffraction at the Os L$_3$ edge. Two different antiferromagnetic domains ... More
Magnetization "Steps" on a Kagome Lattice in VolborthiteFeb 18 2009Feb 21 2009Magnetic properties of the spin-1/2 kagome-like compound volborthite are studied using a high-quality polycrystalline sample. It is evidenced from magnetization and specific heat measurements that the spins on the kagome lattice still fluctuate at low ... More
NaCuMoO_4(OH) as a Candidate Frustrated J_1-J_2 Chain Quantum MagnetSep 04 2014In a frustrated J_1-J_2 chain with the nearest-neighbor ferromagnetic interaction J_1 and the next-nearest-neighbor antiferromagnetic interaction J_2, novel magnetic states such as a spin-nematic state are theoretically expected. However, they have been ... More
Novel Rattling of K Atoms in Aluminium-Doped Defect Pyrochlore TungstateOct 30 2013Nov 04 2013Rattling dynamics have been identified as fundamental to superconductivity in defect pyrochlore osmates and aluminium vanadium intermetallics, as well as low thermal conductivity in clathrates and filled skutterudites. Combining inelastic neutron scattering ... More
Large and homogeneous mass enhancement in the rattling-induced superconductor KOs$_2$O$_6$Jan 26 2012May 18 2012We have determined the Fermi surface in KOs$_2$O$_6$ ($T_c$ = 9.6 K and $B_{c2} \sim$ 32 T) via de Haas-van Alphen (dHvA) oscillation measurements and a band structure calculation. We find effective masses up to 26(1) $m_e$ ($m_e$ is the free electron ... More
"Visible" 5d orbital states in a pleochroic oxychlorideApr 12 2019Transition metal compounds sometimes exhibit beautiful colors. We report here on a new oxychloride Ca3ReO5Cl2 which shows unusually distinct pleochroism; that is, the material exhibits different colors depending on viewing directions. This ple-ochroism ... More
Phase diagram of multiferroic KCu$_3$As$_2$O$_7$(OD)$_3$Feb 10 2017The layered compound KCu$_3$As$_2$O$_7$(OD)$_3$, comprising distorted kagome planes of $S=1/2$ Cu$^{2+}$ ions, is a recent addition to the family of type-II multiferroics. Previous zero field neutron diffraction work has found two helically ordered regimes ... More
Superconductivity phase diagram of Se-substituted CeO0.5F0.5Bi(S1-xSex)2Nov 12 2015We investigated the effects of Se substitution on the lattice constants and superconducting properties of CeO0.5F0.5Bi(S1-xSex)2. With increasing Se concentration, the a lattice constant increased, while the c lattice constant did not show any significant ... More
Grain boundaries in ultrafine grained materials processed by severe plastic deformation and related phenomenaMar 29 2012Grain boundaries in ultrafine grained (UFG) materials processed by severe plastic deformation (SPD) are often called "non-equilibrium" grain boundaries. Such boundaries are characterized by excess grain boundary energy, presence of long range elastic ... More
Magnetostriction studies up to megagauss fields using fiber Bragg grating techniqueOct 24 2018Jan 10 2019We here report magnetostriction measurements under pulsed megagauss fields using a high-speed 100 MHz strain monitoring system devised using fiber Bragg grating (FBG) technique with optical filter method. The optical filter method is a detection scheme ... More
Giant Phonon Softening and Enhancement of Superconductivity by Phosphorus Doping of BaNi2As2Apr 23 2012The effects of phosphorus doping on the structural and superconducting phase transitions of BaNi$_2$(As$_{1-x}$P$_x$)$_2$ were studied. The specific heat, resistivity, and magnetic susceptibility were measured. The results revealed an abrupt increase ... More
Phase Diagram and Spin Dynamics in Volborthite with a Distorted Kagome LatticeJun 16 2009Aug 19 2009We report 51V-NMR study on a high-quality powder sample of volborthite Cu3V2O7(OH)2/2H2O, a spin-1/2 Heisenberg antiferromagnet on a distorted kagome lattice formed by isosceles triangles. In the magnetic fields below 4.5 T, a sharp peak in the nuclear ... More
Evolution of superconductivity in BiS2-based superocnductor LaO0.5F0.5Bi(S1-xSex)2Oct 24 2014Jan 06 2015We have systematically investigated the crystal structure, magnetic susceptibility, and electrical resistivity of the BiS2-based superconductor LaO0.5F0.5Bi(S1-xSex)2 (x = 0 - 0.7). With expanding lattice volume by Se substitution, bulk superconductivity ... More
Increase in Tc and change of crystal structure by high-pressure annealing in BiS2-based superconductor CeO0.3F0.7BiS2Apr 25 2014Aug 05 2014Recently, several types of BiS2-based superconductor such as Bi4O4S3, REO1-xFxBiS2 (RE: rare earth) and Sr1-xLaxFBiS2 have been discovered. In this study, we have investigated the crystal structure and the superconducting properties for two kinds of polycrystalline ... More
High-temperature thermoelectric properties of novel layered bismuth-sulfide LaO1-xFxBiS2Dec 17 2013We have investigated the high-temperature thermoelectric properties of the layered compound LaO1-xFxBiS2. The electrical resistivity of LaOBiS2 showed an anomalous behavior; a metal-semiconductor transition was observed around 270 K. It was found that ... More
Heat-capacity anomalies in the presence of high magnetic fields in the spin-chain compound, Ca3Co2O6Jul 08 2004Heat-capacity behavior in the presence of externally applied magnetic field (H) up to 140 kOe is investigated (2-35 K) for the quasi-1-dimensional compound, Ca3Co2O6, believed to order magnetically with the so-called partially disordered anti-ferromagnetic ... More
Tuning the spin dynamics of kagome systemsNov 09 2011Despite the conceptional importance of realizing spin liquids in solid states only few compounds are known. On the other side the effect of lattice distortions and anisotropies on the magnetic exchange topology and the fluctuation spectrum are an interesting ... More
Role of electron-electron and electron-phonon interaction effect in the optical conductivity of VO2Mar 13 2006We have investigated the charge dynamics of VO2 by optical reflectivity measurements. Optical conductivity clearly shows a metal-insulator transition. In the metallic phase, a broad Drude-like structure is observed. On the other hand, in the insulating ... More
Spin-1/2 Triangular Lattice with Orbital Degeneracy in a Metallic Oxide Ag2NiO2Dec 21 2005A novel metallic and magnetic transition metal oxide Ag2NiO2 is studied by means of resistivity, magnetic susceptibility, specific heat and X-ray diffraction. The crystal structure is characterized by alternating stacking of a Ni3+O2 layer and a (Ag2)+ ... More
Chemical pressure effect on superconductivity of BiS2-based Ce1-xNdxO1-yFyBiS2 and Nd1-zSmzO1-yFyBiS2Aug 12 2014Jun 23 2015We have systematically investigated the crystal structure and the magnetic properties of BiS2-based superconductor Ce1-xNdxO1-yFyBiS2 (x = 0 - 1.0, y = 0.3, 0.5 and 0.7) and Nd1-zSmzO1-yFyBiS2 (x = 0 - 0.8, y = 0.3, 0.5 and 0.7). In the REOBiS2 system, ... More
Element Substitution Effect on Superconductivity in BiS2-Based NdO_{1-x}F_xBiS_2Apr 25 2014Aug 05 2014Recently, new layered superconductors having a BiS2-type conduction layer have been discovered. NdO1-xFxBiS2 is a typical BiS2-based superconductor with a maximum Tc of 5.4 K. In this study, the effect of element substitution within the superconducting ... More
Comoving Space Density and Obscured Fraction of High-Redshift Active Galactic Nuclei in the Subaru/{\it XMM-Newton} Deep SurveyAug 24 2012We study the comoving space density of X-ray-selected luminous active galactic nuclei (AGNs) and the obscured AGN fraction at high redshifts ($3 < z < 5$) in the Subaru/{\it XMM-Newton} Deep Survey (SXDS) field. From an X-ray source catalog with high ... More
Structure and mechanical behavior of ultrafine-grained aluminum-iron alloy stabilized by nanoscaled intermetallic particlesMar 22 2019Ultrafine-grained aluminum alloys offer interesting multifunctional properties with a combination of high strength, low electrical resistivity, and low density. However, due to thermally induced grain coarsening, they typically suffer from an intrinsic ... More
Spin correlation in kagomé ice state: neutron scattering study of the dipolar spin ice Dy_{2}Ti_{2}O_{7} under magnetic field along [111]Nov 20 2006Nov 21 2006We have investigated the kagom\'{e} ice state in the frustrated pyrochlore oxide Dy_{2}Ti_{2}O_{7} under magnetic field along a [111] axis. Spin correlations have been measured by neutron scattering and analyzed by Monte-Carlo simulation. The kagom\'{e} ... More
Quasiparticle Excitation in the Superconducting Pyrochlore Cd2Re2O7 Probed by Muon Spin RotationDec 25 2001The quasiparticle excitations in the mixed state of Cd2Re2O7 have been studied by means of muon spin rotation/relaxation. The temperature dependence of the magnetic penetration depth (lambda) is consistent with a nearly isotropic superconducting order ... More
Magnetic and superconducting properties of Cd2Re2O7: Cd NMR and Re NQRJan 14 2002We report Cd NMR and Re NQR studies on Cd2Re2O7, the first superconductor among pyrochlore oxides Tc=1 K. Re NQR spectrum at zero magnetic field below 100 K rules out any magnetic or charge order. The spin-lattice relaxation rate below Tc exhibits a pronounced ... More
Enhancement of Tc by uniaxial lattice contraction in BiS2-based superconductor PrO0.5F0.5BiS2Jan 29 2014Apr 23 2014We investigated the crystal structure and superconducting properties of As-grown and high-pressure-annealed PrO0.5F0.5BiS2. We found that the high-pressure annealing generates uniaxial lattice contraction along the c axis. Both As-grown and high-pressure-annealed ... More
Kagomé ice state in the dipolar spin ice Dy_{2}Ti_{2}O_{7}Jul 31 2006Sep 18 2006We have investigated the kagom\'{e} ice behavior of the dipolar spin-ice compound Dy_{2}Ti_{2}O_{7} in magnetic field along a [111] direction using neutron scattering and Monte Carlo simulations. The spin correlations show that the kagom\'{e} ice behavior ... More
Photoemission study of the metal-insulator transition in VO_2/TiO_2(001) : Evidence for strong electron-electron and electron-phonon interactionDec 04 2003We have made a detailed temperature-dependent photoemission study of VO_2/TiO_2(001) thin films, which show a metal-insulator transition at \sim 300 K. Clean surfaces were obtained by annealing the films in an oxygen atmosphere. Spectral weight transfer ... More
Superconductivity in Rh$_2$Ga$_9$ and Ir$_2$Ga$_9$ without Inversion SymmetryJun 05 2007Superconductivity with $T_{\rm c}$ $\simeq$ 2 K was discovered in the intermetallic binary compounds Rh$_2$Ga$_9$ and Ir$_2$Ga$_9$. This is the first observation of superconductivity in the Rh-Ga and Ir-Ga binary systems. Both compounds crystallize in ... More
Spin-1/2 Kagome Like Lattice in Volborthite Cu3V2O7(OH)2-H2ONov 08 2001Nov 10 2001A novel cuprate Volborthite, Cu3V2O7(OH)2-2H2O, containing an S-1/2 (Cu 2+ spin) kagome-like lattice is studied by magnetic susceptibility, specific heat, and 51 V NMR measurements. Signs for neither long-range order nor spin-gapped singlet ground states ... More
Correlation between crystal structure and superconductivity in LaO0.5F0.5BiS2Jun 14 2013Nov 18 2013Correlation between crystal structure and superconducting properties of the BiS2-based superconductor LaO0.5F0.5BiS2 was investigated. We have prepared LaO0.5F0.5BiS2 polycrystalline samples with various lattice constants. It was found that the annealing ... More
In-plane chemical pressure essential for superconductivity in BiCh2-based (Ch: S, Se) layered structureApr 06 2015Apr 08 2015BiCh2-based superconductors (Ch: S, Se) are a new series of layered superconductor. However, mechanisms for the emergence of superconductivity in BiCh2-based superconductors have not been clarified. In this study, we have investigated crystal structure ... More
Classical Spin Nematic Transition in LiGa$_{0.95}$In$_{0.05}$Cr$_4$O$_8$Jun 26 2017We present the results of a combined $^7$Li NMR and diffraction study on LiGa$_{0.95}$In$_{0.05}$Cr$_4$O$_8$, a member of LiGa$_{1-x}$In$_{x}$Cr$_4$O$_8$ "breathing" pyrochlore family. Via specific heat and NMR measurements, we find that the complex sequence ... More