S. Murayama

Muroran Institute of Technology, Муроран, Hokkaidō, Japan

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Publications (133)263.75 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: The structure and magnetic properties of Tm1- y Y y Mn1- x Co x O3 with 0 ≦ x ≦ 0.5 and 0 ≦ y ≦ 0.3 were investigated by X-ray diffraction, specific heat and magnetization measurements. Thulium manganite TmMnO3 prepared by solid-state synthesis at ambient pressure is hexagonal and antiferromagnetic with a Nèel temperature T N of 86 K. The substitution of Y for Tm in TmMnO3 does not greatly affect the fundamental hexagonal structure. The magnetization and specific heat measurement results for Tm1- y Y y MnO3 can be qualitatively explained in terms of the dilution effect of Tm by Y. On the other hand, the structure of TmMn1- x Co x O3 changes gradually from hexagonal to orthorhombic with the substitution of Co for Mn; hexagonal and orthorhombic phases coexist in samples for x ≦ 0.3 whereas TmMn0.6Co0.4O3 is almost a single orthorhombic phase. The magnetization of TmMn0.6Co0.4O3 in a field of 250 Oe increases rapidly at about 60K with decreasing temperature. The difference between zero-field-cooled (ZFC) and field-cooled (FC) magnetizations increases remarkably at about 60 K. Moreover, the temperature dependences of the ZFC and the FC magnetizations exhibit peaks at about 40 and 30K, respectively. Thus, TmMn1- x Co x O3 exhibits complex magnetic properties.
    Journal- Korean Physical Society 08/2013; 63(3):546-548. · 0.51 Impact Factor
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    ABSTRACT: We report the magnetic properties of the polycrystalline C15 Laves-phase rare-earth compound SmRu2. The sample of SmRu2 was made by using an arc-melt method and was annealed under 500 °C in vacuumed quartz tube for 50 hours. The magnetic susceptibility χ of SmRu2 follows a Curie-Weiss law at temperature above 80 K. The effective paramagnetic moment p eff is 1.39 µ B /Sm-atom, and the Weiss temperature θ has a positive value of 42 K. The low-temperature χ for T < 60 K increases rapidly with decreasing temperature. In the resistivity ρ and the specific heat C p , we found an inflection and a jump, respectively, at about 55 K. Furthermore, we observed a hysteresis in the magnetic field dependence of the magnetization at 2 K. These experimental results suggest that the C15 Laves-phase compound SmRu2 is a ferromagnetic material with T C ˜ 55 K.
    Journal- Korean Physical Society 08/2013; 63(3):377-379. · 0.51 Impact Factor
  • Yingjie Li, Ikuo Nakai, Yusuke Amakai, Shigeyuki Murayama
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    ABSTRACT: We report the local structure of amorphous alloys CexRu100-x (x=9, 43 and 80) and a C15 Laves phase compound CeRu2 determined from an extended x-ray absorption fine structure measurements near Ru K edge and Ce K edge. The structure analyses indicate that the Ce-Ru and Ru-Ru interatomic distances of amorphous CexRu100-x are constant for all of the Ce concentration, while the Ce-Ce distance increases with increasing the Ce content. The interatomic distance of Ru-Ru in the amorphous alloy system is as same as that of the CeRu2 compound. The Ce-Ce interatomic distance of amorphous CexRu100-x is closely connected with the Ce valence.
    Journal of Physics Conference Series 04/2013; 430(1):2110-.
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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.
    Journal of Physics Conference Series 12/2012; 391(1):2001-.
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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.
    Journal of Physics Conference Series 12/2012; 391(1):2002-.
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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.
    Journal of Physics Conference Series 12/2012; 400(2):2077-.
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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.
    Journal of Physics Conference Series 01/2012; 391(1).
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    ABSTRACT: The superconducting critical temperature (=Tc) in the Ru1-xSnxSr2GdCu2O8 has a maximum at ˜48 K for x = 0.2. So we synthesized the compound in which Gd3+ was partially replaced with Ca2+ expecting Tc higher than one of RuSr2GdCu2O8. The procedure (annealing temperature, times and mixing process) used to synthesize Ru0.8Sn0.2Sr2Gd1-yCayCu2O8 for Cay (y = 0, 0.01, 0.03) was slightly different from one applied in the other report on Ru1-xSnxSr2GdCu2O8. Here the measurement of the normal state resistivity (=rho), XRD and magnetization were carried out. In the result, the curves of rho vs. T for y(=0, 0.01) and (=0.03) showed semiconducting with cusp, and superconducting behavior, respectively. TcON showed ˜43 K in the sample for y = 0.03.
    Physica C Superconductivity 01/2010; 470. · 0.72 Impact Factor
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    ABSTRACT: We have measured the magnetic susceptibility chi on structure-disordered CexY80-xMn20 alloys from 2 to 280 K. The chi shows a typical Curie-Weiss (CW) paramagnetic behavior above 20 K in each concentration x. In the Ce-poor region of x = 62, the spin-glass transition disappears and the CW paramagnetic behavior remains down to the low temperature limit. The Weiss temperature theta is negative for all the samples and almost constant in the Ce-poor side. However, the absolute value of theta increases with increasing Ce-concentration in the Ce-rich region. We have interpreted this fact as an increase of the antiferromagnetic c-f coupling, namely the Kondo effect, with the Ce-concentration.
    Journal of Physics Conference Series 01/2010; 200(1).
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    ABSTRACT: The superconducting critical temperature (=Tc) in the Ru1−xSnxSr2GdCu2O8 has a maximum at ∼48K for x=0.2. So we synthesized the compound in which Gd3+ was partially replaced with Ca2+ expecting Tc higher than one of RuSr2GdCu2O8. The procedure (annealing temperature, times and mixing process) used to synthesize Ru0.8Sn0.2Sr2Gd1−yCayCu2O8 for Cay (y=0, 0.01, 0.03) was slightly different from one applied in the other report on Ru1−xSnxSr2GdCu2O8. Here the measurement of the normal state resistivity (=ρ), XRD and magnetization were carried out. In the result, the curves of ρ vs. T for y(=0, 0.01) and (=0.03) showed semiconducting with cusp, and superconducting behavior, respectively. TcON showed ∼43K in the sample for y=0.03.
    Cancer Genetics and Cytogenetics - CANCER GENET CYTOGENET. 01/2010; 470.
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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.
    Journal of Physics Conference Series 01/2010; 200(3).
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    ABSTRACT: We report the x-ray absorption near edge structure at the Ce L3 edge for amorphous alloys CexRu100-x (x=9, 43, and 80) and a C15 Laves phase compound CeRu2, which consists of a couple of peaks characteristic of 4f1 and 4f0 configurations. This indicates that Ce atoms of these materials are in a mixed valence state. The spectra are fitted to one arctangent and two Lorentzian functions. The Ce valence estimated from relative areas of the Lorentzian peaks varies linearly with Ce content. The transition into the continuum along with both peaks shifts to lower energy with increasing Ce concentration. We find a linear relation between the transition energy and the valence.
    Journal of the Physical Society of Japan 09/2009; 78(9):4717-. · 2.09 Impact Factor
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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.
    Journal of Physics Conference Series 03/2009; 150(5):052167.
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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.
    Journal of Physics Conference Series 01/2009; 150(4).
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    ABSTRACT: We have analyzed the magnetic susceptibility on sputtered structure-disordered (a-) CexRu100-x alloys for 15
    Journal of Physics Conference Series 01/2009; 150(4).
  • T. Nakano, S. Murayama, G. Oomi
    Journal of the Magnetics Society of Japan 01/2009; 33(2):35-37.
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    ABSTRACT: We have measured the specific heat Cp and the resistivity ρ on sputtered amorphous CexY80−xMn20 alloys. The low-temperature specific heat has been found to follow Cp=γT+βT3 for all the samples. The T-linear coefficient γ increases linearly with increasing Ce concentration and becomes very large (γ>100 mJ mol−1 K−2) in the Ce-rich region. The γCe per Ce atom is about 200 mJ Ce-mol−1 K−2 and almost independent of the Ce concentration. The large γCe has been interpreted in terms of the electronic specific heat owing to the 4f-electron mixed with conduction electrons. In the resistivity ρ, the −log T dependence has been observed at low temperature for x≥51, which suggests the formation of the dense Kondo state. The ρ vs T for x≥62 exhibits a maximum and decreases as ρ∝AT2 with a large coefficient A down to the low-temperature limit. These results suggest the formation of a heavy fermion state as the ground state for x≥62. We made the Kadowaki-Woods (KW) plot for x≥62 and found the A/γ2 value to be much smaller than that of the conventional KW relation probably due to the f-orbital degeneracy.
    Physical review. B, Condensed matter 01/2009; 79(24). · 3.77 Impact Factor
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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.
    Journal of Physics Conference Series 01/2009; 150(4).
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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.
    Physica B Condensed Matter 04/2008; 403(s 5–9):930–931. · 1.28 Impact Factor
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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.
    Journal of Magnetism and Magnetic Materials 03/2007; 310(2):416-418. · 2.00 Impact Factor

Publication Stats

542 Citations
263.75 Total Impact Points

Institutions

  • 1993–2010
    • Muroran Institute of Technology
      • Materials Science Unit
      Муроран, Hokkaidō, Japan
  • 2002
    • Tokyo Metropolitan Institute of Gerontology
      Edo, Tōkyō, Japan
  • 2000–2001
    • Tokyo Medical University
      • Division of Neurology
      Edo, Tōkyō, Japan
  • 1993–1998
    • The University of Tokyo
      • • Department of Neuroscience
      • • Faculty & Graduate School of Medicine
      Tokyo, Tokyo-to, Japan
  • 1997
    • Japan Research Institute
      Edo, Tōkyō, Japan
  • 1986–1989
    • Hokkaido University
      • Division of Physics
      Sapporo-shi, Hokkaido, Japan
    • University of Duisburg-Essen
      Essen, North Rhine-Westphalia, Germany