E. Ogura
Tokyo Metropolitan University
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Featured researches published by E. Ogura.
Synthetic Metals | 1999
Toshiaki Enoki; Takashi Umeyama; Masaya Enomoto; Jun-Ichi Yamaura; K. Yamaguchi; Akira Miyazaki; E. Ogura; Yoshiyuki Kuwatani; Masahiko Iyoda; K. Kikuchi
Abstract Magnetic properties are discussed for several TTF-based molecular magnets from the viewpoints of π-electron-based low-dimensional magnets and π-d interaction systems. These are summarized with a Mott-Hubbard system with an interplay of magnetism and electron transport (BEDT-TTT) 2 Br·CH 2 (OH)CH 2 OH, a triangular-lattice spin frustration system (C 1 TET-TTF) 2 Br, a π-electron-mediated superexchange magnet BMT-TTFI 2 ·FeX 4 (X=Cl,Br), a 2D π-d interaction system (BEDT-TTF) 3 CuBr 4 , and a metallic magnet (DMET) 2 FeBr 4
Molecular Crystals and Liquid Crystals | 2002
Akira Miyazaki; Masaya Enomoto; Junichi Nishijo; Kengo Enomoto; Toshiaki Enoki; E. Ogura; Takahiro Takano; Yoshiyuki Kuwatani; Masahiko Iyoda
Structure, transport properties and magnetism of the following π- d systems based on TTF-type salts with magnetic ions are investigated. i) C 1 TET-TTF·FeBr 4 : The magnetic anions form zigzag chains, whose property is described in terms of triangular-based ladder systems accompanied with weak ferromagnetism. Its magnetic properties are affected by the sulfur-to-selenium or bromine-to-chlorine substitution. ii) (EDO-TTFI 2 ) 2 M(mnt) 2 (M=Ni, Pt): Both donor and anion molecules form segregated one-dimensional columns, which are connected via short -CN···I- contacts. These salts show the coexistence of metallic conductivity on the donors and ferromagnetic interaction between localized moments on the anions. iii) (DMET) 2 FeBr 4 : The donor molecules form one-dimensional column with metallic conductivity, whereas the magnetic anions form square-lattice layers and show antiferromagnetic transition. The coincidence of the anomalies on magnetization curves and magnetoresistance supports the presence of π- d interaction between these two layers.
Journal of Materials Chemistry | 1999
Masahiko Iyoda; E. Ogura; Kenji Hara; Yoshiyuki Kuwatani; Hiroyuki Nishikawa; Tatsuo Sato; Koichi Kikuchi; Isao Ikemoto; Takehiko Mori
Charge-transfer and radical ion salts of 4,5,4′″,5′″-tetramethylthio-, 4,5,4′″,5′″-bis(ethylenedithio)-, and 4,5,4″′,5″′-bis(ethylenedioxy)-4′,4″-bitetrathiafulvalenes showed fairly high electric conductivities, reflecting the effect of stoichiometry control.
Molecular Crystals and Liquid Crystals | 1999
Akira Miyazaki; Takashi Umeyama; Toshiaki Enoki; E. Ogura; Yoshiyuki Kuwatani; Masahiko Iyoda; Hiroyuki Nishikawa; Isao Ikemoto; Koichi Kikuchi
Abstract The crystal structure and the physical properties of the radical ion salts BMT-TTFI2·FeX4 (X ˭ Br, Cl) and (DMET)2FeBr4 are investigated. The structures of BMT-TTFI2·FeX4 are characterized as the sheets made of dimerized donor molecules and one-dimensional anion chains. These salts show three-dimensional Curie-Weiss behavior accompanied with antiferromagnetic transitions, with the highest Neel temperature (T N= 15 K) among the π-d interaction based magnets for the FeBr4 salt. Within a crystal of (DMET)2FeBr4, the donor molecules form one-dimensional columns, between which magnetic anion sheets are inserted. This salt is metallic down to T MI = 200 K, above which the Curie-Weiss type magnetism is described in terms of donor and anion spins, in spite of the metallic condaction of the salt. Below T MI the magnetism is governed by anion spins, and an antiferromagnetic phase transition takes place at T N=3.5 K.
Synthetic Metals | 2003
Toshiaki Enoki; H. Yamazaki; Junichi Nishijo; Akira Miyazaki; K. Ugawa; E. Ogura; Yoshiyuki Kuwatani; Masahiko Iyoda; Yuri V. Sushko
Charge transfer complexes of EDO-TTFX, (X=Br, I) form low-D structures featured with coordination-like-bond formation of X with counter anions, giving unconventional magnetic conductive systems with magnetic anions. (EDO-TTFI 2 ) 2 M(nmt) 2 (M=Pt. Ni) are 1D conductors interacting with ferromagnetic ID M(mnt) 2 chains. Applying pressure gives a unique ferromagnetic domain formation. 2D (EDO-TTFBr 2 ) 2 FeBr 4 is metallic, where ID FeBr 4 chains take an antiferromagnetic transition at a very high T N (=13.5K) with a short-range-order effect around the resistivity minimum (30K), suggesting the presence of strong π-d interaction.
Archive | 2004
Toshiaki Enoki; M. Aimatsu; H. Yamazaki; Kazuki Okabe; Junichi Nishijo; Kengo Enomoto; Akira Miyazaki; Kouhei Ugawa; E. Ogura; Yoshiyuki Kuwatani; Masahiko Iyoda; Oleg Naumenko; Yuri V. Sushko
Unconventional magnetic properties of various TTF-based π-d interaction systems are presented. (D)2FeBr4 (D=DMET, EDTDM) are quasi-2D metals consisting of alternating stacking of donor π-electron conducting sheets and square lattice d-spins of FeBr4 - anion sheets. The magnetoresistance is strongly affected by changes of Fe3+ spin arrangement in the ordered state. Especially, for (EDTDM)2FeBr4, a large negative magnetoresistance appears in the vicinity of an MI transition. In (EDO-TTFBr2)2FeX4 (X=C1, Br) having similar sandwich structure to (D)2FeBr4, the presence of the Br atom of the donor bonded semicovalently to X atom of FeX4 - gives strong π-d interaction, which produces a strong correlation between the electron transport and magnetism in addition to a high Neel temperature with a complicated spin structure. (EDO- TTFI2)M(mnt)2 (M=Ni, Pt) are featured by a combination of 1D metal of EDO-TTFI2 columns and 1D ferromagnetic chain of M(mnt)2. For M=Pt, weak AF inter-chain interaction brings about a metamagnetic feature. The application of pressure enhances ferromagnetic features with an anomalous hysteretic hump.
Solid State Communications | 2000
Junichi Nishijo; E. Ogura; Jun-Ichi Yamaura; Akira Miyazaki; Toshiaki Enoki; Takahiro Takano; Yoshiyuki Kuwatani; Masahiko Iyoda
Synthetic Metals | 2003
Junichi Nishijo; E. Ogura; Jun-Ichi Yamaura; Akira Miyazaki; Toshiaki Enoki; Takahiro Takano; Yoshiyuki Kuwatani; Masahiko Iyoda
Journal of Solid State Chemistry | 2002
Akira Miyazaki; Kengo Enomoto; Kazuki Okabe; H. Yamazaki; Junichi Nishijo; Toshiaki Enoki; E. Ogura; K. Ugawa; Yoshiyuki Kuwatani; Masahiko Iyoda
Heterocycles | 2001
Masahiko Iyoda; Yoshiyuki Kuwatani; E. Ogura; Kenji Hara; Hironori Suzuki; Takahiro Takano; Koji Takeda; Junichi Takano; K. Ugawa; Masato Yoshida; Haruo Matsuyama; Hiroyuki Nishikawa; Isao Ikemoto; Takehiro Kato; Naoki Yoneyama; Junichi Nishijo; Akira Miyazaki; Toshiaki Enoki