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Magnetic Excitation Spectra of Superconducting Ca-Fe-Pt-As System 査読有り

M. Sato, T. Kawamata, Y. Kobayashi, Y. Yasui, Takefumi Iida, Kazunori Suzuki, Masayuki Itoh, Taketo Moyoshi, Kiyoichiro Motoya, Ryoichi Kajimoto, Mitsutaka Nakamura, Yasuhiro Inamura, and Masatoshi Arai

Journal of the Physical Society of Japan 80 巻頁： 093709-(1-4) 2011年

Study of Ni-Doping Effect of Specific Heat and Transport Properties for LaFe1-yNiyAsO0.89F0.11 査読有り

T. Kawamata, E. Satomi, Y. Kobayashi, M. Itoh, and M. Sato

Journal of the Physical Society of Japan 80 巻頁： 084720-(1-5) 2011年

Crystal Structure of New Pt-Doped Fe Pnictide Superconductors 査読有り

80 巻頁： 073710-(1-3) 2011年

Magnetic Ordering in V-Layers of the Superconducting System of Sr2VFeAsO3 査読有り

S. Tatematsu, E. Satomi, Y. Kobayashi, and M. Sato

J. Phys. Soc. Jpn. 79 巻 ( 12 ) 頁： 123712-(1-4) 2010年12月

Distinct physical behaviors of LaFe1-yCoyAsO0.89F0.11 between the superconducting and nonsuperconducting metallic regions of y divided by y similar to 0.05

Sato M., Kobayashi Y., Lee S. C., Takahashi H., Moyoshi T.

PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 470 巻頁： S475 - S477 2010年12月

On the non-superconducting state in the phase diagram of NaxCoO2 center dot yH(2)O

Sato Masatoshi, Kobayashi Yoshiaki, Moyoshi Taketo

PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 470 巻頁： S752 - S754 2010年12月

NMR studies on the superconducting symmetry of iron pnictide systems

Kobayashi Yoshiaki, Lee Sang Chul, Takahashi Hidefumi, Moyoshi Taketo, Sato Masatoshi

PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 470 巻頁： S472 - S474 2010年12月

Magnetic excitations of superconducting LaFeAsO0.89F0.11

Moyoshi T., Lee S. C., Tatematsu S., Yasui Y., Kobayashi Y., Sato M., Kakurai K.

PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 470 巻頁： S470 - S471 2010年12月

Studies on the superconducting state of NaxCoO2 center dot yH(2)O - Overview

Sato Masatoshi, Kobayashi Yoshiaki, Moyoshi Taketo

PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 470 巻頁： S673 - S677 2010年12月

⁷⁵As-NMR Studies of LaFeAsO_1-xF_x for Various x Values 査読有り

Yoshiaki Kobayashi, Erika Satomi, Sang Chul Lee, and Masatoshi Sato

Journal of the Physical Society of Japan 79 巻 ( 9 ) 頁： 093709-(1-4) 2010年9月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

Results of ⁷⁵As NMR and NQR measurements are reported for superconducting samples of LaFeAsO_1-xF_Rx with various x values. The x dependent widths of the superconducting transition and those of the NQR spectra indicate that the optimally doped LaFeAsO_1-xF_x sample with the superconducting transition temperature T_c=28 K has the smallest width or smallest inhomogeneity of the superconducting order parameter Δ. In the analyses of the temperature (T) dependence of the NMR longitudinal relaxation rate 1/T₁, we have tried to use a simple relation 1/T₁~Tⁿ to see how fast 1/T₁ decreases when the superconducting order parameter grows. The relation holds rather well in the T region of ~0.3T_c<T=<T_c, and n varies from 2.5-6 with varying x, having the maximum value 5-6 at the optimal x. These results indicate that the x dependence of n originates from the spatial distribution of Δ, and that the T^5-6 behavior is considered to be intrinsic to this system.

DOI： 10.1143/JPSJ.79.093709

Superconducting Transition Temperatures and Transport Properties of LaFe1-yRuyAsO0.89F0.11 and LaFeAsO0.89-xF0.11+x 査読有り

Satomi Erika, Lee Sang Chul, Kobayashi Yoshiaki, Sato Masatoshi

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 79 巻 ( 9 ) 頁： 094702 (6 pages) 2010年9月

High-Temperature Multiferroic State of RBaCuFeO5 (R = Y, Lu, and Tm)

Kawamura Yuji, Kai Takahiro, Satomi Erika, Yasui Yukio, Kobayashi Yoshiaki, Sato Masatoshi, Kakurai Kazuhisa

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 79 巻 ( 7 ) 2010年7月

Superconducting transition temperature and the thickness of CoO2 planes of NaxCoO2 center dot yH(2)O

Moyoshi Taketo, Kobayashi Yoshiaki, Yasui Yukio, Sato Masatoshi, Kakurai Kazuhisa

SOLID STATE SCIENCES 12 巻 ( 5 ) 頁： 656 - 659 2010年5月

Effects of Ru Doping on the Transport Behavior and Superconducting Transition Temperature of NdFeAsO0.89F0.11 査読有り

Lee Sang Chul, Satomi Erika, Kobayashi Yoshiaki, Sato Masatoshi

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 79 巻 ( 2 ) 頁： 023702-(1-4) 2010年2月

Studies on Effects of Impurity Doping and NMR Measurements of La 1111 and/or Nd 1111 Fe-Pnictide Superconductors 査読有り

Sato Masatoshi, Kobayashi Yoshiaki, Lee Sang Chul, Takahashi Hidefumi, Satomi Erika, Miura Yoko

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 79 巻 ( 1 ) 頁： 014710-(1-10) 2010年1月

NMR studies on the superconducting symmetry of iron pnictide systems 査読有り

Y. Kobayashi, S.C. Lee, H. Takahashi, T. Moyoshi, M. Sato

Physica C: Superconductivity 470 巻頁： S472-S474 2010年

Studies on Effects of Impurity Doping and NMR Measurements of La 1111 and/or Nd 1111 Fe-Pnictide Superconductors 査読有り

Masatoshi Sato, Yoshiaki Kobayashi, Sang Chul Lee, Hidefumi Takahashi, Erika Satomi, and Yoko Miura

Journal of the Physical Society of Japan 79 巻 ( 1 ) 頁： 014710 2009年12月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

Measurements of the electrical resistivity rho, Hall coefficient RH, thermoelectric power S, and the electronic specific heat coefficient gamma have been carried out for samples of LnFe1-yMyAsO1-xFx (Ln=La, Nd; M=Co, Mn; x=0.11) obtained by doping M atoms into the superconducting LnFeAsO1-xFx (Ln 1111) system. The NMR longitudinal relaxation rate 1/T1 has also been measured for samples of LaFe1-yCoyAsO1-xFx with various x values. Co atoms doped into the superconducting LnFeAsO1-xFx are nonmagnetic, and the rate of Tc-suppression absolute value of dTc/dx by Co atoms has been found to be too small to be explained by the pair-breaking effect expected for the S+- superconducting symmetry proposed as the most probable symmetry for the system. This result throws a serious doubt on whether the symmetry is realized in the system. Instead of the pair breaking, two mechanisms of Tc suppression by the doped impurities have been found: One is the electron localization, which appears when the sheet resistance r/sheet exceeds h/4e2=6.45 k-ohme, and the other is the disappearance (or reduction in the area) of the hole Fermi surfaces around the Gamma point in the reciprocal space. The latter mechanism has been observed when the number of electrons increases with increasing Co doping level and the system changes from an anomalous metal to an ordinary one. Regarding the two distinct T dependences of the NMR longitudinal relaxation rate 1/T₁ of LaFeAsO_1-xF_x, we discuss the origin of such a difference, and show that, at least, the T^2.5-3.0-like dependence of 1/T₁ cannot be considered as the experimental evidence for the S+- symmetry of Delta.

DOI： 10.1143/JPSJ.79.014719/

Studies of Multiferroic System LiCu2O2: I. Sample Characterization and Relationship between Magnetic Properties and Multiferroic Nature 査読有り

Yukio Yasui, Kenji Sato, Yoshiaki Kobayashi, and Masatoshi Sato

J. Phys. Soc. Jpn. 78 巻 ( 8 ) 頁： 084720-(1-5) 2009年8月

*Studies of Multiferroic System of LiCu2O2: II. Magnetic Structures of Two Ordered Phases with Incommensurate Modulations 査読有り

Yoshiaki Kobayashi, Kenji Sato, Yukio Yasui, Taketo Moyoshi, Masatoshi Sato, and Kazuhisa Kakurai

Journal of the Physical Society of Japan 78 巻 ( 8 ) 頁： 084721-(1-5) 2009年8月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

Neutron diffraction and 7Li-NMR have been applied to determine the three dimensional magnetic structures of the multiferroic system LiCu2O2, which has four chains (ribbon chains) of edge-sharing CuO4 square planes in a unit cell. First, we have confirmed that there are successive magnetic transitions at TN1 = 24.5 K and TN2 = 22.8 K. In the T region between TN1 and TN2, the quasi one-dimensional spins (S = 1/2) of Cu2+ ions within a chain have a collinear and sinusoidally modulated structure with Cu-moments parallel to the c-axis and with the modulation vector along the b-axis. At T < TN2, an ellipsoidal helical spin structure with the incommensurate modulation has been found. We present detailed parameters, describing the modulation amplitudes, helical axis vectors as well as the relative phases of the modulations of four ribbon chains, which can well reproduce both the NMR and neutron results, in the two magnetically ordered phases. This finding of the rather precise magnetic structures enables us to discuss the relationship between the magnetic structure and the multiferroic nature of the present system in zero magnetic field, as presented in our companion paper (paper I), and open a way how to understand the reported electric polarization under the finite magnetic field.

Studies of Multiferroic System LiCu2O2: I. Sample Characterization and Relationship between Magnetic Properties and Multiferroic Nature

Yasui Yukio, Sato Kenji, Kobayashi Yoshiaki, Sato Masatoshi

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 78 巻 ( 8 ) 2009年8月

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