Shinya Sato

The University of Tokyo, Edo, Tōkyō, Japan

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Publications (6)8.64 Total impact

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    ABSTRACT: We report an 75As-NMR study on iron (Fe)-based superconductors with thick perovskitetype blocking layers Sr4(Mg0.5-xTi0.5+x)2O6Fe2As2 with x=0 and 0.2. We have found that antiferromagnetic (AFM) order takes place when x=0, and superconductivity (SC) emerges below Tc=36 K when x=0.2. These results reveal that the Fe-pnictides with thick perovskitetype blocks also undergo an evolution from the AFM order to the SC by doping electron carriers into FeAs planes through the chemical substitution of Ti+4 ions for Mg+2 ions, analogous to the F-substitution in LaFeAsO compound. The reason why the Tc=36 K when x=0.2 being higher than the optimally electron-doped LaFeAsO with Tc=27 K relates to the fact that the local tetrahedron structure of FeAs4 is optimized for the onset of SC.
    Journal of the Physical Society of Japan 03/2012; 81(5). · 2.09 Impact Factor
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    ABSTRACT: Recently we have discovered several new layered iron pnictides having extremely thick blocking layers [1]. These compounds have up to 5 sheets of perovskite-type layers between iron pnictide layers. Similar to LiFeAs, these compounds showed bulk superconductivity without intensive carrier doping, and the Tc of the compounds are 40 K-class. On the other hand, the relationship between Tc and the iron-plane interlayer distance suggested that Tc of the iron based superconductor is basically determined by the local structure of Fe2As2 layer. It is thought that there is still considerable room for the development of new layered iron pnictide compounds, due to the structural and chemical flexibility of the blocking layer. However, the results suggest that optimization of the local structure of Fe2As2 layers and the dimensionality of the crystal structure may not lead to further enhancement of Tc. Their structural features as well as physical properties will be presented.[4pt] [1] H. Ogino et al., APL 97 (2010) 072506
    03/2011;
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    ABSTRACT: We have discovered homologous series of iron pnictide superconductors ( Fe <sub>2</sub> As <sub>2</sub>)[ Ca <sub>n+1</sub>( Sc , Ti )<sub>n</sub> O <sub>y</sub>] (n=3,4,5) . These compounds have extremely thick blocking layers up to quintuple perovskite layers sandwiched by the Fe <sub>2</sub> As <sub>2</sub> layers. These samples exhibited bulk superconductivity with relatively high T<sub> c </sub> up to 42 K. The relationship between T<sub> c </sub> and the iron-plane interlayer distance suggested that T<sub> c </sub> of the iron based superconductor is basically determined by the local structure of Fe <sub>2</sub> As <sub>2</sub> layer.
    Applied Physics Letters 09/2010; · 3.79 Impact Factor
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    ABSTRACT: Since the discovery of high-Tc superconductivity in LaFeAs(O,F), development of the materials having iron or nickel pnictide layers are subject of study. As presented in last APS March meeting, we have discovered iron and nickel pnictide oxide superconductors with perovskite-type oxide layers[1]. Until now, several compounds of this system have been found such as (M'2Pn2)(Sr4M2O6) [M' = Fe, Ni; Pn = P, As; M = Sc, Cr, (Mg,Ti)]. These compounds have higher pnictogen heights and lower Pn-Fe-Pn angles compared to REFeAsO system. These features of the system may lead to realization of high-Tc superconductivity. Recently we discovered new material belongs to this kind of system. Structural features and physical properties of the compounds in this system as well as new compound will be presented. [1] H. Ogino et al., Supercond. Sci. Technol. 22 (2009) 075008.
    03/2010;
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    ABSTRACT: We have discovered a new iron pnictide oxide superconductor (Fe2As2)(Sr4(Mg,Ti)2O6). This material is isostructual with (Fe2As2)(Sr4M2O6) (M = Sc, Cr, V), which were found in previous studies. The structure of this compound is tetragonal with a space group of P4/nmm and consists of the anti-fluorite type FeAs layer and perovskite-type block layer. The lattice constants are a = 3.935 A and c = 15.952 A for (Fe2As2)(Sr4MgTiO6). Bulk superconductivity with Tc(onset) of ~26 K was observed for a partially Co substituted sample. Moreover, Co-free and Ti-rich samples exhibited higher Tc(onset)'s above 35 K, which were further enhanced by applying high pressures up to ~43 K. Comment: Resubmission of arXiv:0909.2945 with new data
    Superconductor Science and Technology 12/2009; · 2.76 Impact Factor
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    ABSTRACT: We have discovered a new iron pnictide oxide superconductor (Fe2As2)(Sr4(Mg,Ti)2O6). This material is isostructual with (Fe2As2)(Sr4M2O6) (M = Sc, Cr), which was found in our previous study. The structure of this compound is tetragonal with a space group of P4/nmm and consists of the anti-fluorite type FeAs and perovskite-type blocking layers. The lattice constants are a = 3.935 A and c = 15.952 A for (Fe2As2)(Sr4MgTiO6). In both magnetization and resistivity measurements, this compound exhibits superconductivity below 10 K. Moreover, ratio of Mg and Ti in this compound can be changed toward Ti-rich composition. (Fe2As2)(Sr4Mg1-xTi1+xO6) phase is obtained at 0 < x as a main phase, and Tc and superconducting volume fraction increase with increasing x. The highest Tc(onset) was confirmed at 39 K for x = 0.6 in resistivity measurement. Comment: This paper has been withdrawn because new version of the paper has been submitted as arXiv:0912.1840
    09/2009;