Browsing by Author "Hayashi, N"
Now showing 1 - 4 of 4
Results Per Page
Sort Options
- ItemCharge-order melting in charge-disproportionated perovskite CeCu3Fe4O12(Americal Chemical Society, 2014-10-21) Yamada, I; Etani, H; Hayashi, N; Mizumaki, M; Ueda, S; Abe, H; Liss, KD; Studer, AJ; Ozaki, T; Mori, S; Takahashi, R; Irifune, TA novel quadruple perovskite oxide CeCu3Fe4O12 has been synthesized under high-pressure and high-temperature conditions of 15 GPa and 1473 K. (57)Fe Mössbauer spectroscopy displays a charge disproportionation transition of 4Fe(3.5+) → 3Fe(3+) + Fe(5+) below ∼270 K, whereas hard X-ray photoemission and soft X-ray absorption spectroscopy measurements confirm that the Ce and Cu valences are retained at approximately +4 and +2, respectively, over the entire temperature range measured. Electron and X-ray diffraction studies reveal that the body-centered cubic symmetry (space group Im3̅, No. 204) is retained at temperatures as low as 100 K, indicating the absence of any types of charge-ordering in the charge-disproportionated CeCu3Fe4O12 phase. The magnetic susceptibility and neutron powder diffraction data illustrate that the antiferromagnetic ordering of Fe ions is predominant in the charge-disproportionated CeCu3Fe4O12 phase. These findings suggest that CeCu3Fe4O12 undergoes a new type of electronic phase in the ACu3Fe4O12 series and that the melting of the charge-ordering in CeCu3Fe4O12 is caused by the substantial decrease in the Fe valence and the resulting large deviation from the ideal abundance ratio of Fe(3+):Fe(5+) = 1:1 for rock-salt-type charge-ordering. © 2014, American Chemical Society.
- ItemColor centers in NaCl single crystals induced by pulsed intense relativistic electron beams to simulate radiation bursts in Europa(IOP Publishing, 2019-03-26) Toba, R; Kikuchi, K; Imada, G; Thorogood, GJ; Hayashi, N; Maynard-Casely, HE; Suematsu, H; Nakayama, T; Suzuki, T; Niihara, KTo simulate the burst irradiation environment of Europa, single crystals of NaCl were irradiated by pulsed intense relativistic electron beams (PIREBs) with a peak energy of 6 MeV, a current of −800 A, and a pulse width of 70 ns. After irradiation, the optical absorption of the samples was measured, and results indicated that the irradiation induced F- and F2-centers. The density of F-centers was estimated to be 8.9 × 1016 cm−3 from 1 shot of PIREB irradiation with 6 MeV. The absorbed energy to form F-centers by PIREB was comparable but slightly higher than those induced by conventional direct current accelerators. The effect of pulsed heating, which should be taken into account for the detection of NaCl on Europa, is discussed. © 2019 The Japan Society of Applied Physics
- ItemField-induced ferromagnetism of Fe4+-perovskite system, Sr(1-x)BaxFeO3 (0 ≤x≤1)(The Physical Society of Japan, 2013-09-05) Hayashi, N; Yamamoto, T; Kitada, A; Matsuo, A; Kindo, K; Hester, JR; Kageyama, H; Takano, MA series of cubic perovskite-type oxides, Sr1-xBaxFe4+O3 (0≤x≤1 ), have been studied through measurements of neutron diffraction and magnetization. It has been found that their helical spin structure changes from the G-type to the A-type with increasing Ba content at x∼0.85 . The application of an external magnetic field induces ferromagnetism with ∼3.5 µB/Fe, and the strength of the critical field decreases markedly from 39 T for SrFeO3 to 0.3 T for BaFeO3. The transition process can be categorized into three: SrFeO3, Sr0.4Ba0.6FeO3, and BaFeO3 types. © 2013 The Physical Society of Japan
- ItemImpact of lanthanoid substitution on the structural and physical properties of an infinite-layer iron oxide(American Chemical Society, 2016-11-01) Yamamoto, T; Ohkubo, H; Tassel, C; Hayashi, N; Kawasaki, S; Okada, T; Yagi, T; Hester, JR; Avdeev, M; Kobayashi, Y; Kageyama, HThe effect of lanthanoid (Ln = Nd, Sm, Ho) substitution on the structural and physical properties of the infinite-layer iron oxide SrFeO2 was investigated by X-ray diffraction (XRD) at ambient and high pressure, neutron diffraction, and 57Fe Mössbauer spectroscopy. Ln for Sr substituted samples up to ∼30% were synthesized by topochemical reduction using CaH2. While the introduction of the smaller Ln3+ ion reduces the a axis as expected, we found an unusual expansion of the c axis as well as the volume. Rietveld refinements along with pair distribution function analysis revealed the incorporation of oxygen atoms between FeO2 layers with a charge-compensated composition of (Sr1–xLnx)FeO2+x/2, which accounts for the failed electron doping to the FeO2 layer. The incorporated partial apical oxygen or the pyramidal coordination induces incoherent buckling of the FeO2 sheet, leading to a significant reduction of the Néel temperature. High-pressure XRD experiments for (Sr0.75Ho0.25)FeO2.125 suggest a possible stabilization of an intermediate spin state in comparison with SrFeO2, revealing a certain contribution of the in-plane Fe–O distance to the pressure-induced transition. © 2016 American Chemical Society