Browsing by Author "Green, MA"

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    Direct synthesis of chromium perovskite oxyhydride with a high magnetic-transition temperature
    (Wiley Online Library, 2014-09-22) Tassel, C; Goto, Y; Kuno, Y; Hester, JR; Green, MA; Kobayashi, Y; Kageyama, H
    We report a novel oxyhydride SrCrO2H directly synthesized by a high-pressure high-temperature method. Powder neutron and synchrotron X-ray diffraction revealed that this compound adopts the ideal cubic perovskite structure equation image with O2−/H− disorder. Surprisingly, despite the non-bonding nature between Cr 3d t2g orbitals and the H 1s orbital, it exhibits G-type spin ordering at TN≈380 K, which is higher than that of RCrO3 (R=rare earth) and any chromium oxides. The enhanced TN in SrCrO2H with four Cr-O-Cr bonds in comparison with RCr3+O3 with six Cr-O-Cr bonds is reasonably explained by the tolerance factor. The present result offers an effective strategy to tune octahedral tilting in perovskites and to improve physical and chemical properties through mixed anion chemistry. © 2014, Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
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    Magnetic-field-induced instability of the cooperative paramagnetic state in ZnxCo(4-x)(OD)6Cl2
    (American Physcical Society, 2012-05-29) Dissanayake, SE; Chan, C; Ji, S; Lee, J; Qiu, Y; Rule, KC; Lake, B; Green, MA; Hagihala, M; Zheng, XG; Ng, TK; Lee, SH
    Using elastic and inelastic neutron scattering techniques with and without application of an external magnetic field H, the magnetic ground states of ZnxCo(4-x)(OD)6Cl2 (x = 0,1) were studied. Our results show that for x = 0, the ground state is a magnetic long-range ordered (LRO) state where each tetrahedron forms an "umbrella"-type structure. On the other hand, for x = 1, no static ordering was observed down to 1.5 K, which resembles the behavior found in the isostructural quantum system ZnxCo(4-x)(OD)6Cl2. When H field is applied, however, the x = 1 system develops the same LRO state as x = 0. This indicates that the x = 1 disordered state is in the vicinity of the x = 0 ordered state. © 2012, American Physical Society.
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    T-c enhancement by aliovalent anionic substitution in superconducting BaTi2(Sb1-xSnx)2O
    (Physical Society Japan, 2013-07-01) Nakano, K; Yajima, T; Takeiri, F; Green, MA; Hester, JR; Kobayashi, Y; Kageyama, H
    BaTi2Sb2O is a T-c = 1.2 K superconductor with a d(1) square lattice, and isovalent Bi substitution for Sb can increase its T-c to 4.6 K (BaTi2Bi2O), accompanied by the complete suppression of charge density wave (CDW) or spin density wave (SDW) transition. In the present study, we demonstrate that aliovalent Sn substitution (hole doping) also increases T-c up to 2.5 K for BaTi2(Sb0.7Sn0.3)(2)O, while suppressing CDW/SDW transition only slightly. The overall electronic phase diagram of BaTi2(Sb, Sn)(2)O is qualitatively similar to that of cation-substituted (hole-doped) (Ba,Na)Ti2Sb2O, but quantitative differences such as in T-c are observed, which is discussed in terms of Ti-Pn hybridization and chemical disorder. © 2013, Physical Society of Japan