11 research outputs found

    機能性金属酸化物の第一原理電子状態計算及び吸光スペクトル

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    学位の種別: 課程博士審査委員会委員 : (主査)東京大学教授 大越 慎一, 東京大学教授 山内 薫, 東京大学教授 佃 達哉, 東京大学教授 合田 圭介, 東京大学准教授 山野井 慶徳University of Tokyo(東京大学

    Nanometer-size hard magnetic ferrite exhibiting high optical-transparency and nonlinear optical-magnetoelectric effect

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    Development of nanometer-sized magnetic particles exhibiting a large coercive field (Hc) is in high demand for densification of magnetic recording. Herein, we report a single-nanosize (i.e., less than ten nanometers across) hard magnetic ferrite. This magnetic ferrite is composed of ε-Fe2O3, with a sufficiently high Hc value for magnetic recording systems and a remarkably high magnetic anisotropy constant of 7.7 × 106 erg cm−3. For example, 8.2-nm nanoparticles have an Hc value of 5.2 kOe at room temperature. A colloidal solution of these nanoparticles possesses a light orange color due to a wide band gap of 2.9 eV (430 nm), indicating a possibility of transparent magnetic pigments. Additionally, we have observed magnetization-induced second harmonic generation (MSHG). The nonlinear optical-magnetoelectric effect of the present polar magnetic nanocrystal was quite strong. These findings have been demonstrated in a simple iron oxide, which is highly significant from the viewpoints of economic cost and mass production.UTokyo Research掲載「世界最小ハードフェライト磁石の開発に成功」 URI: http://www.u-tokyo.ac.jp/ja/utokyo-research/research-news/the-worlds-smallest-hard-ferrite-magnet.htmlUTokyo Research "The world\u27s smallest hard ferrite magnet" URI: http://www.u-tokyo.ac.jp/en/utokyo-research/research-news/the-worlds-smallest-hard-ferrite-magnet.htm

    Mesoscopic bar magnet based on ε-Fe2O3 hard ferrite

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    Ferrite magnets have a long history. They are used in motors, magnetic fluids, drug delivery systems, etc. Herein we report a mesoscopic ferrite bar magnet based on rod-shaped ε-Fe2O3 with a large coercive field (>25 kOe). The ε-Fe2O3–based bar magnet is a single crystal with a single magnetic domain along the longitudinal direction. A wide frequency range spectroscopic study shows that the crystallographic a-axis of ε-Fe2O3, which corresponds to the longitudinal direction of the bar magnet, plays an important role in linear and non-linear magneto-optical transitions, phonon modes, and the magnon (Kittel mode). Due to its multiferroic property, a magnetic-responsive non-linear optical sheet is manufactured as an application using an ε-Fe2O3–based bar magnet, resin, and polyethylene terephthalate. Furthermore, from the viewpoint of the large coercive field property, we demonstrate that a mesoscopic ε-Fe2O3 bar magnet can be used as a magnetic force microscopy probe

    Diagnostic accuracy of 64-slice computed tomography for detecting angiographically significant coronary artery stenosis in an unselected consecutive patient population: comparison with conventional invasive angiography

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    BACKGROUND: Multislice computed tomography (MSCT) is a promising noninvasive method of detecting coronary artery disease (CAD). However, most data have been obtained in selected series of patients. The purpose of the present study was to investigate the accuracy of 64-slice MSCT (64 MSCT) in daily practice, without any patient selection. METHODS AND RESULTS: Using 64-slice MSCT coronary angiography (CTA), 69 consecutive patients, 39 (57%) of whom had previously undergone stent implantation, were evaluated. The mean heart rate during scan was 72 beats/min, scan time 13.6 s and the amount of contrast media 72 mL. The mean time span between invasive coronary angiography (ICAG) and CTA was 6 days. Significant stenosis was defined as a diameter reduction of > 50%. Of 966 segments, 884 (92%) were assessable. Compared with ICAG, the sensitivity of CTA to diagnose significant stenosis was 90%, specificity 94%, positive predictive value (PPV) 89% and negative predictive value (NPV) 95%. With regard to 58 stented lesions, the sensitivity, specificity, PPV and NPV were 93%, 96%, 87% and 98%, respectively. On the patient-based analysis, the sensitivity, specificity, PPV and NPV of CTA to detect CAD were 98%, 86%, 98% and 86%, respectively. Eighty-two (8%) segments were not assessable because of irregular rhythm, calcification or tachycardia. CONCLUSION: Sixty-four-MSCT has a high accuracy for the detection of significant CAD in an unselected patient population and therefore can be considered as a valuable noninvasive technique

    Phonon-Mode Calculation, Far- and Mid-Infrared, and Raman Spectra of an ε‑Ga<sub>0.5</sub>Fe<sub>1.5</sub>O<sub>3</sub> Magnet

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    Gallium-substituted epsilon iron oxide (ε-Ga<sub>0.5</sub>Fe<sub>1.5</sub>O<sub>3</sub>) has drawn attention because its millimeter wave absorption frequency meets the millimeter wave radar frequency for automobiles. We report the phonon modes of ε-Ga<sub>0.5</sub>Fe<sub>1.5</sub>O<sub>3</sub>, which has an orthorhombic structure in the <i>Pna</i>2<sub>1</sub> space group. First-principles phonon-mode calculations show that ε-Ga<sub>0.5</sub>Fe<sub>1.5</sub>O<sub>3</sub> has 117 optical phonon modes (fundamental vibrations) with symmetries of A<sub>1</sub>, A<sub>2</sub>, B<sub>1</sub>, and B<sub>2</sub> as well as three acoustic phonon modes. The phonon density of states demonstrates that the movements of Fe and Ga contribute to the phonon modes in the lower energy region of 20–370 cm<sup>–1</sup>, while the movements of O contribute to the phonon modes in the higher energy region of 370–720 cm<sup>–1</sup>. We directly measure the optical phonon modes of ε-Ga<sub>0.48</sub>Fe<sub>1.52</sub>O<sub>3</sub> nanoparticles using far- and mid-infrared (IR) and Raman spectroscopies, which agree well with those obtained by first-principles phonon-mode calculations. Additionally, the thermodynamic parameters of the internal energy (<i>U</i>), the vibrational entropy (<i>S</i><sub>vib</sub>), and the Helmholtz energy (<i>A</i>) are calculated and understood through the investigation of the phonon modes. Heat capacity measurements confirm that the observed thermodynamic parameters are consistent with the predicted values

    Structural Phase Transition between γ‑Ti<sub>3</sub>O<sub>5</sub> and δ‑Ti<sub>3</sub>O<sub>5</sub> by Breaking of a One-Dimensionally Conducting Pathway

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    The phase transition between gamma-trititanium-pentoxide (γ-Ti<sub>3</sub>O<sub>5</sub>) and delta-trititanium-pentoxide (δ-Ti<sub>3</sub>O<sub>5</sub>) was clarified from both experimental and theoretical viewpoints. With decreasing temperature, the monoclinic <i>I</i>2/<i>c</i> crystal structure of γ-Ti<sub>3</sub>O<sub>5</sub> was found to switch to a monoclinic <i>P</i>2/<i>a</i> crystal structure of δ-Ti<sub>3</sub>O<sub>5</sub> due to lowering of symmetry. Electrical conductivity (σ) measurement shows that γ-Ti<sub>3</sub>O<sub>5</sub> behaves like a metallic conductor with a σ value of 4.7 S cm<sup>–1</sup> at 320 K, while δ-Ti<sub>3</sub>O<sub>5</sub> shows a semiconductive property with a σ value of 2.5 × 10<sup>–5</sup> S cm<sup>–1</sup> at 70 K. Optical measurement also supports that γ-Ti<sub>3</sub>O<sub>5</sub> is a metallic conductor, while δ-Ti<sub>3</sub>O<sub>5</sub> is a semiconductor with a band gap of 0.07 eV. First-principles calculations show that γ-Ti<sub>3</sub>O<sub>5</sub> is a metallic conductor, and the energy state on the Fermi energy is composed of the 3d orbital of Ti and 2p orbital of O with one-dimensional linkage along the crystallographic <i>c</i>-axis. On the contrary, δ-Ti<sub>3</sub>O<sub>5</sub> has a band gap, and the energy state around the Fermi energy is split into the valence band and the conduction band, which are assigned to the lower and upper Hubbard bands, respectively. Thus, the phase transition between γ-Ti<sub>3</sub>O<sub>5</sub> and δ-Ti<sub>3</sub>O<sub>5</sub> is caused by breaking of a one-dimensionally conducting pathway due to a Mott–Hubbard metal–insulator phase transition

    Structural Phase Transition between γ‑Ti<sub>3</sub>O<sub>5</sub> and δ‑Ti<sub>3</sub>O<sub>5</sub> by Breaking of a One-Dimensionally Conducting Pathway

    No full text
    The phase transition between gamma-trititanium-pentoxide (γ-Ti<sub>3</sub>O<sub>5</sub>) and delta-trititanium-pentoxide (δ-Ti<sub>3</sub>O<sub>5</sub>) was clarified from both experimental and theoretical viewpoints. With decreasing temperature, the monoclinic <i>I</i>2/<i>c</i> crystal structure of γ-Ti<sub>3</sub>O<sub>5</sub> was found to switch to a monoclinic <i>P</i>2/<i>a</i> crystal structure of δ-Ti<sub>3</sub>O<sub>5</sub> due to lowering of symmetry. Electrical conductivity (σ) measurement shows that γ-Ti<sub>3</sub>O<sub>5</sub> behaves like a metallic conductor with a σ value of 4.7 S cm<sup>–1</sup> at 320 K, while δ-Ti<sub>3</sub>O<sub>5</sub> shows a semiconductive property with a σ value of 2.5 × 10<sup>–5</sup> S cm<sup>–1</sup> at 70 K. Optical measurement also supports that γ-Ti<sub>3</sub>O<sub>5</sub> is a metallic conductor, while δ-Ti<sub>3</sub>O<sub>5</sub> is a semiconductor with a band gap of 0.07 eV. First-principles calculations show that γ-Ti<sub>3</sub>O<sub>5</sub> is a metallic conductor, and the energy state on the Fermi energy is composed of the 3d orbital of Ti and 2p orbital of O with one-dimensional linkage along the crystallographic <i>c</i>-axis. On the contrary, δ-Ti<sub>3</sub>O<sub>5</sub> has a band gap, and the energy state around the Fermi energy is split into the valence band and the conduction band, which are assigned to the lower and upper Hubbard bands, respectively. Thus, the phase transition between γ-Ti<sub>3</sub>O<sub>5</sub> and δ-Ti<sub>3</sub>O<sub>5</sub> is caused by breaking of a one-dimensionally conducting pathway due to a Mott–Hubbard metal–insulator phase transition
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