I. Watanabe

RIKEN, Вако, Saitama, Japan

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Publications (316)495.54 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: A diffusive behavior of Li+ ion in a garnet-type oxide, Li5+xLa3ZrxNb2−x012 with x=0–2, has been investigated by both a positive muon-spin relaxation (μ+SR) and quasi-elastic neutron scattering (QENS) technique using powder samples. The μ+SR results revealed that Li+ ions start to diffuse above ~150 K for the whole samples measured. The activation energy of Li diffusion (Ea) estimated from the μ+SR data was in good agreement with Ea obtained by the QENS measurements. However, both Eas were about a half of Ea of ionic conductivity of Li+ (σLi), whichwas evaluated by AC-impedance measurements on sintered pellets. This indicated the serious effect of grain boundary and/or surface on Ea. Furthermore, since the diffusion coefficient of Li+ estimated by μ+SR is roughly independent of x, the number of mobile Li+ in the garnet lattice was found to be the predominant parameter to determine σLi.
    Solid State Ionics 06/2014; 262:585-588. · 2.05 Impact Factor
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    ABSTRACT: We have used the pulsed muon source at ISIS to study high-temperature Na-ion dynamics in the quasi-one-dimensional (Q1D) metallic antiferromagnet NaV2O4. By performing systematic zero-field and longitudinal-field measurements as a function of temperature we clearly distinguish that the hopping rate increases exponentially above Tdiff=250 K. The data is well fitted to an Arrhenius type equation typical for a diffusion process, showing that the Na-ions starts to be mobile above Tdiff . Such results makes this compound very interesting for the tuning of Q1D magnetism using atomic-scale ion-texturing through the periodic potential from ordered Na-vacancies. Further, it also opens the door to possible use of NaV2O4 and related compounds in energy related applications.
    06/2014;
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    ABSTRACT: We have studied low-temperature magnetic properties as well as high-temperature lithium ion diffusion in the battery cathode materials LixNi1/3Co1/3Mn1/3O2 by the use of muon spin rotation/relaxation. Our data reveal that the samples enter into a 2D spin-glass state below TSG=12 K. We further show that lithium diffusion channels become active for T>Tdiff=125 K where the Li-ion hopping-rate [nu(T)] starts to increase exponentially. Further, nu(T) is found to fit very well to an Arrhenius type equation and the activation energy for the diffusion process is extracted as Ea=100 meV.
    06/2014;
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    ABSTRACT: Longitudinal-field muon-spin-relaxation (LF-μSR) measurements in TlCu1-xMgxCl3 were carried out to investigate the spin dynamics in the non-magnetic impurity doped spin gap system. As reported before, in the case of x ≥ 0.006, LF-μSR time spectra are well fitted by the two components function, which means the phase separation to a spin frozen region and to a spin flucuating region. In this report, we focus on the spin fluctuating region, and discuss the gradual change in its magnetic properties with increasing the Mg-doping.
    Journal of Physics Conference Series 04/2014; 502(1):012041.
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    ABSTRACT: Longitudinal-field muon-spin-relaxation measurements have revealed inhomogeneous distribution of the internal magnetic field at temperatures above the bulk superconducting (SC) transition temperature, $T_{\rm c}$, in slightly overdoped Bi$_2$Sr$_2$Ca$_{1-x}$Y$_x$Cu$_2$O$_{8+\delta}$. The distribution width of the internal magnetic field, $\Delta$, evolves continuously with decreasing temperature toward $T_{\rm c}$. The origin of the increase in $\Delta$ is discussed in terms of the creation of SC domains in a sample.
    04/2014;
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    ABSTRACT: A diffusive behavior of Li+ ion in a garnet-type oxide, Li5+xLa3ZrxNb2-xO12 with x = 0-2, has been investigated by both a positive muon-spin relaxation (μ+SR) and quasi-elastic neutron scattering (QENS) technique using powder samples. The μ+SR results revealed that Li+ ions start to diffuse above ~150 K for the whole samples measured. The activation energy of Li diffusion (Ea) estimated from the μ+SR data was in good agreement with Ea obtained by the QENS measurements. However, both Eas were about a half of Ea of ionic conductivity of Li+ (sLi), which was evaluated by AC-impedance measurements on sintered pellets. This indicated the serious effect of grain boundary and/or surface on Ea. Furthermore, since the self-diffusion coefficient of Li+ estimated by μ+SR is roughly independent of x, the number of mobile Li+ in the garnet lattice was found to be the predominant parameter to determine sLi.
    JPS Conference Proceedings. 03/2014; 2:010303.
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    ABSTRACT: Lithium cobalt dioxide (LiCoO2) belongs to a family of layered CoO2-based materials and has considerable interests in both fundamental physics and technological applications in lithium-ion batteries. We report the results of structural, electrochemical, magnetic susceptibility (χ), electron paramagnetic resonance (EPR), and muon-spin rotation and relaxation (μSR) measurements on powder Lix 0CoO2 samples, where the nominal Li/Co ratios (x0) were 0.95, 1.00, 1.02, 1.05, and 1.10, respectively. Structural, electrochemical, and χ measurements suggested that the sample with x0 = 1.02 is very close to single stoichiometric LiCoO2 (ST LCO) phase and that the Co ions in the x0 = 1.02 sample are in a nonmagnetic low-spin state with S = 0 (t62g). However, both EPR and μSR revealed that the x0 = 1.02 (ST-LCO) sample includes a large amount of nonordered magnetic phase in the temperature (T ) range between 100 and 500 K. The volume fraction of such magnetic phase was found to be �45 vol% at 300 K by μSR, indicating an intrinsic bulk feature for ST-LCO. In fact, structural and photoelectron spectroscopic analyses clearly excluded the possibility that the nonordered magnetism is caused by impurities, defects, or surfaces. Because EPR and μSR sense static and dynamic nature of local magnetic environments, we concluded that Co spins in ST-LCO are fluctuating in the EPR and μSR time-windows. We also proposed possible origins of such nonordered magnetism, that is, a spin-state transition and charge disproportionation.
    Physical Review B 03/2014; 89(9):094406. · 3.66 Impact Factor
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    ABSTRACT: The most fundamental limitations of a muon-spin relaxation experiment can be the lack of knowledge of the implantation site of the muon and the uncertainty about the muon's perturbation of its host. Here we review some of the work done on the 'muon site problem' in the solid state and highlight some recent applications of electronic structure calculations that have successfully characterized the quantum states of muons in a number of insulating compounds containing fluorine, in a number of pnictide superconductors, and in ZnO.
    Physica Scripta 12/2013; 88:068510. · 1.03 Impact Factor
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    ABSTRACT: We present the muon spin relaxation/rotation spectra in the multiferroic compound (Cu,Zn)$_{3}$Mo$_{2}$O$_{9}$. The parent material Cu$_{3}$Mo$_{2}$O$_{9}$ has a multiferroic phase below $T_{\rm N}$ = 8.0 K, where the canted antiferromagnetism and the ferroelectricity coexist. The asymmetry time spectra taken at RIKEN-RAL pulsed muon facility show a drastic change at $T_{\rm N}$. At low temperatures the weakly beating oscillation caused by the static internal magnetic fields in the antiferromagnetic phase was observed in Cu$_{3}$Mo$_{2}$O$_{9}$ and the lightly ($0.5\%$) Zn-doped sample. From the fitting of the oscillating term, we obtain the order parameter in these samples: ferromagnetic moment in two sublattices of antiferromagnet. In the heavily ($5.0\%$) Zn-doped sample, the muon-spin oscillation is rapidly damped. The frequency-domain spectrum of this sample suggests a formation of magnetic superstructure.
    12/2013;
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    ABSTRACT: The magnetic ground state of the Rh-doped Kondo semiconductor CeRu2Al10 [Ce(Ru1−xRhx)2Al10] is investigated with the muon spin relaxation method. Muon spin precession with two frequencies is observed in the x=0 sample, while only one frequency is present in the x=0.05 and 0.10 samples, which is attributed to the broad static field distribution at the muon site. The internal field at the muon site is enhanced from about 180 G in the x=0 sample to about 800 G in the Rh-doped samples, supporting the spin-flop transition as suggested by the magnetization measurement, and the boundary of different magnetic ground states is identified around x=0.03. The drastic change of magnetic ground state by a small amount of Rh doping (3%) indicates that the magnetic structure in CeRu2Al10 is not robust and can be easily tuned by external perturbations such as electron doping. The anomalous temperature dependence of the internal field in CeRu2Al10 is suggested to be attributed to the hyperfine interaction between muons and conduction electrons.
    Physical Review B 09/2013; 88(11). · 3.66 Impact Factor
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    ABSTRACT: It has been nearly 27 years since the discovery of the first high temperature (high-Tc) superconductor on LaBaCuO by Benorz & Muller in 1986 [1], in which the mechanism of how high-Tc superconductor happening remain unsolved up until now. La2CuO4 are a parent compound for La2-xSrxCuO4 superconductor, where show antiferromagnetic behavior on based temperature. By adding Sr doping about 0.05 its properties become superconductor. According to previous experimental and theoretical study [2,3], magnetism plays quite an important role for LaBaCuO. μSR was one of the good tools to investigate magnetic properties of magnetic materials, but its utiliy is limited by the lack of knowledge of the muon implantation site and because of that we need to know where muon was staying on crystals. For many years many methods already proposed to determine the muon site in La2CuO4, but always lead to different sites from one to another. This lead to many confusion for researcher who want to continue and go to deeper understanding about magnetic behavior using μSR. On the present study, we reinvestigated the previous study sites by using dipole field and density functional theory calculation to see the relaxation and energy behavior for each sites. For the dipole calculation we used two kind of magnetic moment from experiment and theoretical, and expand the structure to be 50 A˚ radius. The potential minima position also included to be tested as the possible muon sites, GGA PBE correction was used to see the different behavior between them. The purpose of this investigation is the first step to find out the general method for muon sites determination, that can applied for many cases.
    09/2013;
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    ABSTRACT: Muon spin relaxation results on the pyrochlore iridate Nd2Ir2O7 are reported. Spontaneous coherent muon spin precession below the metal-insulator transition (MIT) temperature of about 33 K is observed, indicating the appearance of a long-range magnetic ordering of Ir4+ moments. With further decrease in temperature, the internal field at the muon site increases again below about 9 K. The second increase of internal field suggests the ordering of Nd3+ moments, which is consistent with a previous neutron experiment. Our results suggest that the MIT and magnetic ordering of Ir4+ moments have a close relationship and that the large spin-orbit coupling of Ir 5d electrons plays a key role for both MIT and the mechanism of the magnetic ordering in pyrochlore iridates in the insulting ground state.
    Physical Review B. 08/2013; 88(6).
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    ABSTRACT: The superconducting properties of the noncentrosymmetric superconductor LaPt3Si were investigated by μSR spectroscopy. Within experimental accuracy, spontaneous internal fields were not observed in the superconducting phase by zero-field μSR experiments. Transverse-field μSR experiments revealed the coexistence of the intermediate and mixed states in the superconducting phase, which are characteristic features of type-I and type-II superconductors, respectively. We found that the observed anomalous field distribution is consistent with the results of a recent numerical calculation for type-1.5 superconductors.
    Journal of the Physical Society of Japan 08/2013; 82(8):4713-. · 2.09 Impact Factor
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    ABSTRACT: In the temperature dependence of magnetization, the Heusler compound Ru1.9Fe0.1CrSi exhibits a peak at a temperature which is defined as TN*. Below that temperature strong irreversibility occurs, the onset temperature of which is defined as Tg. However, no evidence of long-range order has been found. In this study the magnetic properties of these anomalies were investigated using zero-field (ZF) and longitudinal-magnetic-field (LF) muon-spin-relaxation (μSR) measurements. In the temperature dependence of the relaxation rate of ZF-μSR, a peak at ∼16 K was observed, which agrees with Tg. LF-μSR measurements as a function of magnetic field reveal the existence of a static internal magnetic field at 0.3 K. Around TN*∼30 K, we detected no anomalies that can be associated with a magnetic phase transition in the temperature dependence of the relaxation rate of μSR, but a large decrease in the initial asymmetry was observed. LF-μSR measurements suggest that the internal magnetic field appears even around TN*. These results suggest that around TN* independent spin-frozen regions form inhomogeneously. With decreasing temperature these regions gradually develop, and eventually, at Tg spin-glass freezing occurs with correlations over the whole sample.
    Physical Review B 07/2013; 88(2). · 3.66 Impact Factor
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    ABSTRACT: We report on muon-spin-relaxation (μSR) experiment of organic semiconductor spiro-linked compound 2′,7′-bis(N,N–diphenylamino)-2-(5-(4–tert-butylphenyl)-1,3,4-oxadiazol-2-yl)-9,9-spirobifluorene (Spiro-DPO) measured at temperatures between 8 and 300 K and at longitudinal fields up to 395 mT in order to study charge transport properties in organic semiconductor. The μSR time spectra were analyzed by using Risch and Kehr (RK) function and it indicates a transition from one-dimensional hopping transport of charge carriers at low temperatures to two- or three-dimensional hopping transport at high temperatures (>75 K).
    Organic Electronics 01/2013; 14(1):62–66. · 3.84 Impact Factor
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    ABSTRACT: Li diffusive behavior in garnet-type oxides has been investigated by quasi-elastic neutron scattering (QENS) and muon-spin relaxation (µSR) measurements. The QENS signal increased with temperature (T) above 300 K due to Li+ motion. The activation energy obtained from the relationship between the QENS intensities and T-1 was lower about a half of that estimated by electrochemical measurements. By combining QENS and µSR results, we found that a diffusion coefficient of Li+ strongly depends on the number of mobile Li+.
    Journal of the Physical Society of Japan 01/2013; 82SA:SA004. · 2.09 Impact Factor
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    ABSTRACT: Aiming to find magnetic states in the Mn+1AXn phases, we measured the magnetic susceptibility, the resistivity, and nuclear magnetic resonance of Cr2GaX (X=N and C). Zero-field and longitudinal-field muon spin relaxation experiments were also applied to Cr2GaN. A magnetic phase transition, most probably to the spin-density-wave (SDW) state, has been found in Cr2GaN at TN=170 K in contrast to the Pauli paramagnetism in the carbide counterpart Cr2GaC. The origin of the SDW transition is interpreted in terms of possible Fermi-surface nesting in the two-dimensional-like electronic structure.
    Physical Review B 01/2013; 88:134401. · 3.66 Impact Factor
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    ABSTRACT: We report on transverse field muon spin rotation measurements of the magnetic penetration depth λ in the iron-based superconductor KFe2As2 in order to investigate the superconducting gap mechanism. We have found that temperature dependence of λ shows multiple gap like behavior and λ depends on the field. These results suggests the existence of quasiparticle excitations outside the vortices.
    Journal of Physics Conference Series 12/2012; 400(2):2087-.
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    ABSTRACT: Zero-field and longitudinal-field muon-spin-relaxation measurements have been performed in partially Fe-substituted La2-xSrxCu1-yFeyO4 in a wide range of hole concentration, to investigate the magnetic state induced by the Fe substitution recently suggested from the neutron-scattering measurements [Phys. Rev. Lett. 107, 127002 (2011)]. It has been found that the magnetic transition temperature is notably enhanced through the 1% Fe substitution in a wide range of hole concentration where superconductivity appears in Fe-free La2-xSrxCuO4. In the underdoped regime, the Fe-induced magnetic order can be understood in terms of the concept of stripe pinning by Fe as in the case of the Zn-induced one in La2-xSrxCu1-yZnyO4. In the overdoped regime, on the other hand, the Fe-induced magnetic order is short-ranged, which is distinct from the stripes. It is plausible that a spin-glass state of Fe spins derived from the Ruderman-Kittel-Kasuya-Yosida interaction is realized in the overdoped regime, suggesting a change of the ground state from the strongly correlated state to the Fermi-liquid state with hole doping in La-214 high-Tc cuprates.
    Physical review. B, Condensed matter 07/2012; 86(1). · 3.77 Impact Factor
  • Risdiana, T. Adachi, I. Watanabe, Y. Koike
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    ABSTRACT: Muon-spin-relaxation measurements have been performed in the overdoped regime of hole-doped high-Tc superconductor La2-xSrxCuO4 and electron-doped Pr1-xLaCexCuO4 with Cu partially replaced by Zn, in order to understand the role of stripe pinning to the superconductivity. It has been found that dynamically fluctuating stripes of spins and charges probably exist in a wide range of hole concentration in the hole-doped cuprates and that it is possible that they play an important role in the appearance of superconductivity. On the other hand, no clear symptom of stripe pinning has been observed in the electron-doped cuprates.
    06/2012;

Publication Stats

1k Citations
495.54 Total Impact Points

Institutions

  • 2001–2014
    • RIKEN
      Вако, Saitama, Japan
    • The University of Electro-Communications
      • Department of Applied Physics and Chemistry
      Tokyo, Tokyo-to, Japan
  • 1999–2010
    • The University of Tokyo
      • Department of Basic Medical Sciences
      Edo, Tōkyō, Japan
    • Tohoku University
      • Department of Applied Physics
      Sendai, Kagoshima, Japan
    • Tokyo University of Science
      • Department of Fire Science and Technology
      Edo, Tōkyō, Japan
    • Nihon University
      • Department of Cardiology
      Tokyo, Tokyo-to, Japan
  • 2009
    • Toyota Central R & D Labs., Inc.
      Nagoya, Aichi, Japan
  • 2008
    • University of Hyogo
      • Graduate School of Material Science
      Akō, Hyogo-ken, Japan
  • 1999–2001
    • High Energy Accelerator Research Organization
      • Institute of Materials Structure Science
      Tsukuba, Ibaraki, Japan
  • 2000
    • University of California, San Francisco
      • Division of General Internal Medicine
      San Francisco, CA, United States
  • 1998
    • Tokyo Institute of Technology
      • Department of Physics
      Tokyo, Tokyo-to, Japan
  • 1997
    • Tokyo Medical University
      • Department of Emergency and Critical Care Medicine
      Edo, Tōkyō, Japan
  • 1988–1994
    • Hokkaido University
      • • Department of Physics
      • • Division of Physics
      Sapporo-shi, Hokkaido, Japan