Neutron diffraction study of 154SmFeAsO1-xDx

Hot issue in unconventional superconductors (SC) is why the 2nd highest-Tc of 56 K after cuprates is accomplished in the 1111-type iron-oxyarsenides LnFeAsO1-xFx (Ln $=$ lanthanide). Recently, utilizing a hydride-substitution-method (O2- $=$ H- $+$ e-) in the LnFeAsO1$-$xHx [1], we found a second SC phase in 0.18 $\le $ x $\le $ 0.45 at Ln $=$ La in addition to the first one adjacent to the antiferromagnetic (AFM) order [2], and another AFM order accompanying a unique structural transition in over-doped region x \textgreater 0.4 [3]. However, since the Tc of La-system is lower than the other systems, i.e., Ln $=$ Ce, Sm and so on, it is still unclear whether the second AFM phase is essential for their high-Tc or not. Thus, we synthesized the isotope-substituted 154SmFeAsO1-xDx and performed neutron powder diffraction (NPD) to examine the structural and magnetic properties of the high-Tc 1111 system. In this talk, we show the results of NPD data and discuss the relation between the superconducting, magnetic, and structural properties of the 154SmFeAsO1-xDx and electron-doping-effect on it. [1] T. Hanna, et al. PRB 85, 024521 (2011). [2] S. Iimura, et al. Nat.Commun. 3, 943 (2012). \newline [3] M. Hiraishi et al. Nat. Phys. 10, 300 (2014).