S. Murayama

Muroran Institute of Technology, Муроран, Hokkaido, Japan

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Publications (96)210.97 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: We performed low-temperature specific heat measurements on slightly underdoped samples of monolayer cuprate superconductors Bi(2)Sr(2-x)Ln(x)CuO(6+delta) (Ln = La, Eu, Ln-Bi2201) under magnetic fields H. In La-Bi2201, the coefficient gamma of T-linear term in the electronic specific heat C-el at T << T-c shows root H dependence, as expected in d(x)(2)-y(2) -wave superconductors. In Eu-Bi2201, gamma shows almost the same root H dependence as that of La-Bi2201 below H similar to 2 T, while gamma is suppressed above H similar to 2 T and deviates downward from the root H curve of La-Bi2201. This result suggests the the gap and the electronic excitation spectrum near nodes are modified in Eu-Bi2201 except the region of the Fermi surface in the immediate vicinity of nodes.
    No preview · Article · Sep 2015 · International Journal of Modern Physics B
  • Y. Amakai · D. Yoshii · S. Murayama · H. Takano · N. Momono · Y. Obi · K. Takanashi
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    ABSTRACT: We have measured the magnetic susceptibility χ, specific heat Cp and resisitivity ρ on sputtered structure-disordered Ce80-yLayRu20 alloys. The χ for y <= 70 follows the Curie-Weiss law in the measurement temperature region. The paramagnetic effective magnetic moment peff is about 1.8 μB/Ce-atom for y = 0 and decreases with increasing the La-concentration (0.6 μB/Ce-atom for y = 70). The Cp follows linear relation of temperature above 7 K for all the samples. The specific heat coefficient γ shows about 200 mJ/molK2 for y = 0 and decreases rapidly with increasing La-concentration. We found the -log T dependence of the ρ in the La-substituted samples. Magnitude and temperature range of the -log T contribution to the whole resistivity increase with increasing the La concentration. On the other hand, we have observed superconducting behaviors of the resistivity ρ = 0 and a large diamagnetization at low temperature (T < 3 K) for y = 80.
    No preview · Article · Dec 2012 · Journal of Physics Conference Series
  • N. Momono · S. Kuribayashi · Y. Amakai · S. Murayama · S. Torii · H. Takano
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    ABSTRACT: We examine the effect of mechanical milling on the superconducting transition temperature Tc in stripe-ordered La1.6-xNd0.4SrxCuO4 with x~1/8. The X-ray diffraction patterns of samples milled for 24h show that the orthorhombicity is slightly reduced, in addition to the reduction of crystallite size and the increase of lattice strain, by mechanical milling. The Tc is enhanced by the mechanical milling, although the magnitude of the diamagnetic signal is largely suppressed. The enhancement of Tc suggests that the static stripe is suppressed in the mechanically milled sample.
    No preview · Article · Dec 2012 · Journal of Physics Conference Series
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    ABSTRACT: We have measured the susceptibility χ and resistivity ρ on single-crystalline Ce1-xLaxRu2Si2 for 0 <= x <= 0.8 in directions parallel (//) and perpendicular (⊥) to the c-axis. The χ// for 0.1 <= x <= 0.7 indicates a Curie-Weiss form at T > 20 K and a typical AF maximum at TN. A significant crossover between TN and the magnitude of the Weiss temperature |Θ| occurs at about x = 0.2. The ρ⊥ shows a gap-type upturn at TN for 0.1 <= x <= 0.185 with rather a downward bend ρ// at around TN. The upturn in ρ⊥ at TN disappears for x = 0.2 with a sharp maximum ρ// at TN. A sharp peak in ρ⊥ takes place at TN for 0.3 <= x <= 0.7 with the sharp maximum ρ// at TN for 0.4 <= x <= 0.6. These results can be interpreted as the evolution from the itinerant SDW in the heavy-fermion band for 0.1 <= x < 0.2 to the AF ordering with the local moment for x > 0.2 up to x = 0.7.
    No preview · Article · Dec 2012 · Journal of Physics Conference Series
  • D Abe · Y Amakai · S Murayama · N Momono · H Takano · T Nakano · K Matsubayashi · Y Uwatoko
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    ABSTRACT: We have measured the susceptibility χ and resistivity ρ on single-crystalline Ce1−x Lax Ru2Si2 for 0 ≤ x ≤ 0.8 in directions parallel (//) and perpendicular (⊥) to the c-axis. The χ// for 0.1 ≤ x ≤ 0.7 indicates a Curie-Weiss form at T > 20 K and a typical AF maximum at T N. A significant crossover between T N and the magnitude of the Weiss temperature |Θ| occurs at about x = 0.2. The ρ⊥ shows a gap-type upturn at T N for 0.1 ≤ x ≤ 0.185 with rather a downward bend ρ// at around T N. The upturn in ρ⊥ at T N disappears for x = 0.2 with a sharp maximum ρ// at T N. A sharp peak in ρ⊥ takes place at T N for 0.3 ≤ x ≤ 0.7 with the sharp maximum ρ// at T N for 0.4 ≤ x ≤ 0.6. These results can be interpreted as the evolution from the itinerant SDW in the heavy-fermion band for 0.1 ≤ x x > 0.2 up to x = 0.7.
    No preview · Article · Jan 2012 · Journal of Physics Conference Series
  • Y. Amakai · S. Murayama · Y. Obi · H. Takano · N. Momono · K. Takanashi
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    ABSTRACT: We have measured the thermal expansion on structure-disordered (a-)Ce xY80-xMn20 alloys. The linear thermal expansion ΔL/L for all the samples shows a monotonic increase with increasing temperature. In the thermal expansion coefficient α for x ≥ 51, anomalous deviation from a conventional Debye curve was observed at low temperature and increased with increasing Ce concentration. The magnetic contribution α4f estimated from the equation α(a-Ce xY80-xMn20) - α(a-Y80Mn 20) increases with increasing the Ce concentration and exhibits a maximum in the low temperature for x ≥ 51. These behaviors in α4f are interpreted as the formation of the heavy fermion state in the structure-disordered alloys.
    No preview · Article · Jul 2011 · Journal of the Physical Society of Japan
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    ABSTRACT: We have measured the susceptibility χ and resistivity ρ on single-crystalline Ce0.87La0.13(Ru1-xRhx) 2Si2 for 0 ≤ x ≤ 0.4 in directions parallel (||) and perpendicular () to the c-axis. The χ|| for 0 ≤ x ≤ 0.3 indicates a typical AF maximum at TN. The ρ for x = 0 and 0.05 shows a gap-type anomaly at TN. The ρ|| indicates a weak inflection at around TN for x = 0 and a clear shoulder at T N for x = 0.05. For 0.1 ≤ x ≤ 0.3 the gap-type anomaly in ρ disappears and a gap-type jump has been detected in p|| at TN. These behaviors suggest that the Fermi-surface nesting along the a-axis for x = 0 followed by a transverse SDW ordering changes into the nesting along the c-axis followed by a longitudinal SDW ordering for 0.1 ≤ x ≤ 0.3.
    No preview · Article · Jan 2011 · Journal of the Physical Society of Japan
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    ABSTRACT: The Raman scattering experiments were carried out in Zn-doped and Zn-free Bi2Sr2CaCu2O8+y with optimal hole concentration below and above T c . The energy of pair-breaking peak in the B 1g Raman spectrum, corresponding to the magnitude of superconducting gap 2Δ 0, is suppressed by 1% Zn-doping. In the normal state, the B 1g Raman spectrum for Zn-doped sample shows no pseudogap behaviour, suggesting that the pseudogap is strongly smeared by Zn-doping.
    No preview · Article · Jul 2010 · Journal of Superconductivity and Novel Magnetism
  • Source
    H. Takano · T. Sugiue · Y. Amakai · N. Momono · S. Murayama
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    ABSTRACT: We performed mechanical milling of the A15-type superconductor Nb3Sn with transition temperature Tc = 18K. Tc decreased with increasing milling time, a result similar to that of Di, Loeff and Bakker, except that Tc seemed to decrease discontinuously with milling time. X-ray diffraction (XRD) patterns were taken using a conventional X-ray diffractometer with CuKa radiation at room temperature. The height of the Bragg peaks lowered and their width broadened after milling, but the patterns of the A15 structure persisted for up to 48 h of milling. We compared the XRD patterns of Nb3Sn with simulations using REATAN-2000, and obtained evidence that the site random disorder of Nb and Sn atoms in the A15 structure caused the decrease in Tc.
    Full-text · Article · Jan 2010 · Journal of Physics Conference Series
  • N Momono · T Kurosawa · M Naito · M Oda · M Ido · Y Aamakai · H Takano · S Murayama · A Sakai
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    ABSTRACT: The Raman scattering spectra of optimally doped Bi2Sr2Ca(Cu1-xZnx)2O8+δ (x=0 and x=0.01) have been measured below and above the superconducting transition temperature Tc. In B1g Raman spectrum, a broad pair-breaking peak is observed at T<<Tc for x=0.01 as well as for Zn free Bi2212. The peak energy of the B1g spectrum for x=0.01 (~350 cm-1) is much smaller than that of the Zn-free sample (~510 cm-1), suggesting that the (effective) superconducting gap is largely suppressed by 1% Zn-doping.
    No preview · Article · Mar 2009 · Journal of Physics Conference Series
  • Y. Amakai · S. Murayama · Y. Obi · H. Takano · N. Momono · K. Takanashi
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    ABSTRACT: We have analyzed the magnetic susceptibility on sputtered structure-disordered (a-) Ce(x)Ru(100-x) alloys for 15 <= x <= 80 from 1.8 to 280 K published previously. The magnetic susceptibility chi for x >= 39 shows a typical Curie-Weiss paramagnetic behavior in the measurement temperature region. The effective magnetic moment p(eff) is about 1.8 mu(B) for x = 80 and decreases rapidly with decreasing the Ce-concentration (p(eff) approximate to 0.16 mu(B)/Ce-atom, for x = 39). The Weiss temperature theta for the Ce-rich side shows a negative value and the absolute value decreases with decreasing the Ce-concentration. The chi for x <= 23 has a very small Curie-Weiss term above 4 K and a large diamagnetic susceptibility has been observed below 4 K, suggesting the superconductivity (T(c) = 3.4 K for x = 15). The superconducting transition temperature T(c) increases linearly with decreasing the Ce-concentration as shown in the previous resistivity measurement.
    No preview · Article · Mar 2009 · Journal of Physics Conference Series
  • S. Ishiuchi · H. Naruse · S. Murayama · Y. Amakai · T. Nakano · Y. Uwatoko
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    ABSTRACT: We have measured the susceptibility chi and resistivity rho on single-crystalline Ce0.8La0.2(Ru1-xRhx)2Si2 in directions parallel parallel and perpendicular (bot) to the c-axis. The chiparallel for each Rh concentration increases with decreasing temperature, and then rapidly decreases for x = 0.8, indicating the AF transition at the Néel temperature TN. The rhoparallel for x = 0 shows a cusp at around TN = 5.5 K, however, rhobot indicates a broad maximum at higher temperature than TN and a rapid decrease at much lower temperature than TN, without evidence of a gap-type AF ordering. The rhobot for x = 0.2 indicates a clear cusp at about TN. Such sharp anomaly in rhobot once disappears for x = 0.6 and is again observed at TN for x >=0.8 probably due to another type of the AF ordering.
    No preview · Article · Mar 2009 · Journal of Physics Conference Series
  • T. Nakano · S. Murayama · G. Oomi

    No preview · Article · Jan 2009 · Journal of the Magnetics Society of Japan
  • H. Niki · K. Okamura · R. Mahoe · M. Yogi · Y. Amakai · H. Takano · S. Murayama · Y. Obi
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    ABSTRACT: In order to investigate a heavy-fermion like behavior on Ce-rich side of amorphous CexMn100-x alloys system, the 55Mn NMR measurements on the powdered sample of amorphous Ce62Y19Mn19, being diluted with non-magnetic Y, have been carried out in the temperature range from 1.8 to 270 K. A broadened resonance spectrum containing five NQR lines is observed in the measuring temperature region. Temperature dependences of Quadrupole coupling constant (e2Qq) and the line width of 55Mn NMR are obtained by means of analysis of each spectrum. Temperature dependence of the line width is expressed by the Curie-Weiss law with Tc = -12.0 K. The 1/(T1T) is rapidly increased in proportion to inverse square root of temperature with decreasing temperature, but it keeps almost constant below about 6 K, which shows the heavy-fermion state in Ce62Y19Mn19.
    No preview · Article · Jan 2009 · Journal of Physics Conference Series
  • H. Niki · K. Okamura · M. Yogi · Y. Amakai · H. Takano · S. Murayama · Y. Obi
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    ABSTRACT: In order to investigate the heavy-fermion like behavior of amorphous alloy CexMn100-xCexMn100-x, the NMR measurements of 55Mn (I=52) in Ce65Mn35 have been carried out from 4.2 to 270 K using powdered sample. A broadened NMR spectrum containing five NQR lines split due to NQR interaction is observed. Quadrupole coupling constant 3e2Qq/2I(2I-1)h3e2Qq/2I(2I-1)h is gradually changed from about 1.8 MHz at 4.2 K to about 1.6 MHz at 270 K. Temperature dependence of the line width is expressed in the Curie–Weiss law with θp=-10.5K. The value of Knight shift would be almost constant from 4.2 to 270 K.
    No preview · Article · Apr 2008 · Physica B Condensed Matter
  • Y. Amakai · S. Murayama · H. Takano · M. Mizutani · K. Asano · Y. Obi · K. Takanashi
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    ABSTRACT: We have measured the specific heat on sputtered amorphous (a-) CexRu100-x alloys for 15⩽x⩽80 from 5 to 300 K. The Cp/T nicely follows a function of γ+BT2 above 8 K in each Ce concentration. In the Ce-rich side (x⩾67), the electronic specific coefficient γ shows a very large value (γ=180 mJ/mol K2 at x=80), suggesting formation of the heavy fermion (dense Kondo) state at low temperature. However, the γ decreases rapidly with decreasing the Ce concentration. In the Ru-rich side (x<39), the γ becomes less than 10 mJ/mol K2 and the superconductivity occurs. This γ-value is almost the same as for a-Ce20-yLayRu80 in each La concentration, where the superconductivity occurs at the same superconducting temperature Tc. We made the Kadowaki Woods plot from the coefficient A of the T2 term in resistivity and γ in the Ce-rich side. The value of A/γ2 for present alloys shows about 3.5×10-6 μ Ω cm(mol K2/mJ)2.
    No preview · Article · Mar 2007 · Journal of Magnetism and Magnetic Materials
  • Source
    H. Takano · H. Kokubo · T. Kinami · Y. Amakai · S. Murayama
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    ABSTRACT: Annealing effect on superconductivity of mechanically milled MgB2 has been studied using X-ray diffraction (XRD) and magnetization measurements. The crystalline MgB2 showed superconductivity at Tc=39K and MgB2 milled for a long period indicates another superconductivity at about 8K. The absolute value of the diamagnetization of the mechanically milled MgB2 after annealing at 550∘C increased at about 21K and 39K with decreasing temperature, though its XRD patterns were little different from that of the as-milled sample. These results suggest that the superconductivity of the disordered MgB2 induced by mechanical milling is affected strongly by a little difference of structural disorder.
    Full-text · Article · Mar 2007 · Journal of Magnetism and Magnetic Materials
  • Y. Obi · S. Murayama · Y. Amakai · Y. Okada · K. Asano
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    ABSTRACT: The structure of disordered (amorphous) CexRu100-x alloys have some characteristic features which are inherent in the heavy fermion (dense Kondo) nature. In the Ru rich region (15⩽x⩽40), the superconducting behavior appears. With increasing Ru-concentration Tc increases monotonically and simultaneously the paramagnetic moment decreases due to increase in the valence fluctuation. The superconductivity in these alloys is thought to be correlated to the 4f-electron state. In the Ce rich region (x⩾47) the electric resistivity at low temperature exhibits the ρ=AT2 relation with a large coefficient A. This implies that the coherent Kondo state is realized in the low temperature region. Thus, the amorphous Ce–Ru alloy is recognized to be one of the dense Kondo alloys.
    No preview · Article · May 2006 · Physica B Condensed Matter
  • Y. Amakai · S. Murayama · H. Takano · Y. Okada · K. Asano · Y. Obi
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    ABSTRACT: We have measured the specific heat and the resistivity on sputtered amorphous (a-) Ce80−xYxMn20 alloys (x=10, 20, 30, 50 and 70), substituted by Y for dense Kondo a-Ce–Mn alloy. The electronic specific heat coefficient γ shows the large value (γ=133mJ/molK2) at x=10 and decreases with increase of the Y concentration linearly. The resistivity at low temperature shows the T2 dependence and the large coefficient A at x=10, 20. However, the T2 dependence was not observed for x⩾30. Thus, a-Ce80−xYxMn20 for x⩽20 is also the dense Kondo system. We made Kadowaki–Woods plot from A and γ of a-Ce–Mn and a-Ce-Y-Mn alloys. The ratio of A/γ2 for a-Ce-Y-Mn is much larger than the value of a-Ce–Mn alloy.
    No preview · Article · May 2006 · Physica B Condensed Matter
  • Y OBI · S MURAYAMA · Y AMAKAI · K ASANO
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    ABSTRACT: Binary amorphous alloy system CexMn100-x shows the dense Kondo behavior in the Ce-rich side. This fact is confirmed by the large T2 coefficient A of electrical resistivity at low temperature and also the large linear specific heat coefficient γ. The result of logA versus logγ2 plot for Ce-rich samples shows the systematic change, but deviates from the Kadowaki–Woods (KW) relation. If we take the orbital degeneracy of Ce 4f-electron into account, according to Kontani's recent analysis, the result satisfies the generalized KW-relation. Therefore, present amorphous Ce–Mn alloy seems to form the dense Kondo state or the heavy-fermion state at low temperature.
    No preview · Article · Apr 2005 · Physica B Condensed Matter

Publication Stats

835 Citations
210.97 Total Impact Points

Institutions

  • 1992-2015
    • Muroran Institute of Technology
      • • Department of Applied Sciences
      • • Materials Science Unit
      Муроран, Hokkaido, Japan
  • 2001
    • Tokyo Medical University
      • Division of Neurology
      Edo, Tōkyō, Japan
  • 2000
    • Tokyo Women's Medical University
      • Department of Neurology
      Edo, Tokyo, Japan
  • 1993-2000
    • The University of Tokyo
      • Department of Neurology
      Tōkyō, Japan
  • 1998
    • Toranomon Hospital
      Edo, Tōkyō, Japan
  • 1997
    • Japan Research Institute
      Edo, Tōkyō, Japan
  • 1995-1996
    • Yokohama Rosai Hospital
      Yokohama, Kanagawa, Japan
  • 1986-1993
    • Hokkaido University
      • Division of Physics
      Sapporo, Hokkaidō, Japan