研究者総覧

小西 健介 (コニシ ケンスケ)

  • 大学院理工学研究科 数理物質科学専攻 准教授
Last Updated :2020/11/10

研究者情報

学位

  • 博士(工学)(九州大学)

J-Global ID

研究キーワード

  • 酸化物ナノ微粒子の磁性   固体物理学   

研究分野

  • ナノテク・材料 / ナノ構造物理 / ナノ磁性体
  • 自然科学一般 / 磁性、超伝導、強相関系 / 磁性

経歴

  • 2007年04月 - 現在  愛媛大学大学院理工学研究科 数理物質科学専攻准教授
  • 2006年04月 - 2007年03月  愛媛大学大学院理工学研究科 数理物質科学専攻助教授
  • 2003年01月 - 2006年03月  愛媛大学理学部 物理学科助教授
  • 1994年04月 - 2002年12月  愛媛大学理学部 物理学科助手

学歴

  • 1989年04月 - 1993年04月   九州大学   工学研究科   応用物理学専攻 博士後期課程
  • 1987年04月 - 1989年03月   九州大学   工学研究科   応用物理学専攻 修士課程
  • 1982年04月 - 1987年03月   東京理科大学   理工学部   物理学科

所属学協会

  • 日本磁気学会   日本物理学会   

研究活動情報

論文

  • M. Mito, K. Tsuruta, T. Tajiri, N. Ikeda, M. Ohkuma, A. Kohno, K. Konishi, H. Deguchi
    AIP Advances 10 2 025220 - 025220-7 2020年02月 [査読有り]
     研究論文(学術雑誌) 
    The ferromagnetic state of the spin-polarized ferromagnet La1−xSrxMnO3 is stabilized in the metallic region by strong coupling between localized spins in the t2g orbital and conduction electrons in the eg orbital. We prepared polycrystalline La1−xSrxMnO3 films (x = 0.15, 0.25, or 0.30) by deposition on an oxidized Si substrate. The three types of La1−xSrxMnO3 films were in the ferromagnetic rhombohedral phase, and their Curie temperatures, TC, evaluated from the midpoint of ac magnetization, were 305 K, 335 K, and 338 K, respectively. By applying expansion-mode acoustic vibration to the crystal structure of La1−xSrxMnO3, we observed a remarkable decrease (as large as 70 K) in TC. The applied structural perturbation causes a decrease in the possibility of conduction electron hopping and an increase in the Jahn–Teller distortion. The former is more effective for decreasing TC than the latter.
  • T. Tajiri, H. Deguchi, M. Mito, K. Konishi, S. Miyahara, A. Kohno
    Physical Review B 98 6 064409 - 064409-9 2018年08月 [査読有り]
     研究論文(学術雑誌) 
    We synthesized magnetically frustrated DyMn2O5 nanoparticles in pores of mesoporous silica, with particle sizes ranging from 7 to 20 nm, and investigated their magnetostructural correlation. We found that the lattice constants of the DyMn2O5 nanoparticles deviated from those of the bulk crystal below ∼12 nm and their crystallographic structures at the unit cell level were distorted. The size dependences of the blocking temperature and coercive field drastically change at ∼12 nm. In addition, the Weiss temperature depends strongly on particle size, and its sign changes at ∼12 nm. It is considered that such features can be realized owing to the distortion caused by the ligand atoms at the surface. The orbital structures of the magnetic sites are easily modified due to the distortion of the ligand ions at the surface, so that the correlation between the crystal structure and magnetic properties can be enhanced. Moreover, magnetization of the nanoparticle results in quasi-superparamagnetic behavior. Monte Carlo calculation of the nanoparticles indicates that such a feature is realized due to the quasi-free spins induced at the surface by magnetic frustration.
  • Nguyen Hoa Hong, Mohammed Benali Kanoun, Jang-Gun Kim, Timur Sh. Atabaev, Kensuke Konishi, Satoshi Noguchi, Makio Kurisu, Souraya Goumri-Said
    Journal of Physical Chemistry C 122 5 2983 - 2989 2018年02月 [査読有り]
     研究論文(学術雑誌) 
    The alkaline-earth iron perovskites AFeO3 are interesting materials since their ferromagnetic domains could be controlled by an applied magnetic field. However, to be exploited for applications, there are still some flaws related to their antiferromagnetic or ferromagnetic behavior at low temperatures. In our work, we have attempted to synthesize pristine BaFeO3 with Ba to partially or fully substitute Sr or Ca in order to tailor the magnetic properties of the host compound as expected for applications. We found that powders of (Ca/Sr/Ba) FeO3 showed an increased enhancement of magnetic properties in comparison to BaFeO3 films. In particular, the (Ca/Sr)0.5Ba0.5FeO3 nanopowders have demonstrated a Curie temperature well above room temperature along with an increased magnetic moment. A considerable coercivity is also surprisingly obtained as a typical signature for a hard magnetic material. First-principles calculations were performed to get an insight into the Ca/Sr influence on the lattice structure, and oxygen vacancies behavior of BaxCa(Sr)1-xFeO3. It was found that doping can lead to an increase of the magnetic moment per Fe atom. However, Ca/Sr-site substitution at the Ba-site of the perovskite exhibits an increasing of magnetic moment per Fe when O vacancies are introduced. This current study shows a new way to exploit this revisited-type of orthoferrites for spintronic applications.
  • Nguyen Thi My Duc, Nguyen Thi, Khanh Van, Makio Kurisu, Kensuke Konishi, Phan Manh Huong, Ngo Thu Huong
    VNU Journal of Science: Mathematics - Physics 32 4 6 - 11 2016年12月 [査読有り]
     研究論文(学術雑誌) 
    In this study, the perovskite manganites REMnO3 (with RE = La, Nd, Pr) were prepared by a solid-state reaction. The structure and magnetic properties of these samples are reported. The crystal structure of the samples is cubic with LaMnO3 and is orthorhombic with NdMnO3 and PrMnO3 samples. The surface of LaMnO3 sample is dense and quite tight, while the surface of two samples PrMnO3 and NdMnO3 are more porous than LaMnO3 sample surface. The temperature and magnetic field dependent of the magnetizations for all the samples were measured. All the samples are paramagnetic. The maximum value of magnetizations at magnetic field H = 12 kOe for the samples LaMnO3, PrMnO3 and NdMnO3 are 2.32 (emu/g), 1.11 (emu/g) and 0.97 (emu/g), respectively. It shows that the Mmax of LaMnO3 is greater than the Mmax for PrMnO3 and NdMnO3 samples. The results showed the existence of both ferromagnetic and antiferromagnetic phase in all the samples. The Curie temperature, Weiss temperature and Curie constant are ditermined. A comparision of the magnetic property in our samples with the other one is discussed in this paper.
    Keywords: Magnetic material, REMnO3, perovskite
  • T. Naito, H. Yamamoto, K. Konishi, K. Kubo, T. Nakamura, H. Mayama
    Advanced Material Science 1 1 15 - 21 2016年04月 [査読有り]
     研究論文(学術雑誌) 
    It has been known that sample dimension and lattice defects affect critical behavior of superconductivity. Particular type of porous samples called fractal bodies have well-defined non-integer dimensions dependent exclusively on the geometrical feature of structures. Differences in sample dimension and lattice defects are quantitatively described by such fractal dimensions (Ds). Powder samples of high-T<sub>C</sub> cuprates with 2.5 < D < 3 were prepared, and their superconducting properties were compared as regards critical temperature T<sub>C</sub>, critical current J<sub>C</sub>, and critical magnetic field H<sub>C</sub>. While the variation in H<sub>C</sub> for different Ds was within experimental error (for the lower H<sub>C</sub>) or too high to be measured (for the upper H<sub>C</sub>), T<sub>C</sub> and J<sub>C</sub> correlated with D: they both exhibited complex patterns of D-dependence immediately below D = 3 and maximum enhancement of ∽0.7% in T<sub>C</sub> and ∽7% in J<sub>C</sub> were observed. The observed behavior is semi-quantitatively explained by considering fractal structures of the samples. In addition, the D-dependences of T<sub>C</sub> and J<sub>C</sub> are explained with the same quantitative discussion as those of Néel temperatures of fractal CoO powder samples. This suggests underlying universal physics for cooperative phenomena in fractal dimensions.
  • Structure, Electrical Properties, and Application Possibility as Solid Oxide Fuel Cells Cathode Materials of (La2Ni04±δ)1-x(BaTiO3)x (x=0.0-0.5) Composites
    Le Thi Anh Thu, Ha Thi Huong, Nguyen Ngoc Dinh, Huynh Dang Chinh, Dang Thi Minh Hue, Makio Kurisu, Kensuke Konishi, Bach Thanh Cong
    Journal of Science and Technology 54 1A 66 - 71 2016年 [査読有り]
     研究論文(研究会,シンポジウム資料等)
  • Study on Properties of Core-shell composites (La2NiO4)1-x(BaTiO3)x
    Le Thi Anh Thu, Nguyen Ngoc Dinh, Huynh Dang Chinh, Nguyen Thi Hue, Nguyen Duc Dung, Makio Kurisu, Kensuke Konishi, Bach Thanh Cong
    VNU Journal of Science: Mathematics – Physics 31 1S 24 - 30 2015年10月 [査読有り]
     研究論文(学術雑誌)
  • M. Mito, H. Goto, K. Nagai, K. Tsuruta, H. Deguchi, T. Tajiri, K. Konishi
    JOURNAL OF APPLIED PHYSICS 118 14 145901 - 145901-6 2015年10月 [査読有り]
     研究論文(学術雑誌) 
    We investigated the effects of hydrostatic pressure on an isotropic Nd2Fe14B magnet (the exact chemical formula is Nd2.0Fe14.1B) consisting of nanocrystals, with the size of approximately 30 nm, by magnetization measurements at pressures (P's) up to 9.3GPa and structural analyses up to 4.3GPa. Magnetization curves were measured by using a miniature diamond anvil cell made of Ti alloy with spatially uniform magnetization. The initial value of coercive field H-c at 300K is 840 kA/m (= 10.6 kOe), and H-c initially increases to approximately 1180 kA/m (= 15.0 kOe) almost linearly against the pressure. The increase in H-c, however, saturates at around P = 3GPa. The change in H-c is understood by the decrease in the saturation magnetization M-s within the framework of the constant anisotropy of the single domain phase. The crystalline strain increases for P<1GPa. Afterward, the crystalline size (D) starts to decrease with increasing pressure, and the reduction tends to saturate at above approximately 3GPa. Furthermore, the change in Ms is actually related with both the change in strain and that in D. The data on the temperature dependence of H-c at P = 0, 6.6, and 9.3GPa exhibit pressure-induced suppression of the Curie temperature. The maximum energy product decreases with increasing pressure over the whole temperature range. (C) 2015 AIP Publishing LLC.
  • Takayuki Tajiri, Seiya Saisho, Masaki Mito, Hiroyuki Deguchi, Kensuke Konishi, Atsushi Kohno
    JOURNAL OF PHYSICAL CHEMISTRY C 119 2 1194 - 1200 2015年01月 [査読有り]
     研究論文(学術雑誌) 
    We synthesized NiO nanoparticles in the pores of mesoporous silica, with particle sizes ranging from 2.6 to 22 nm, and investigated their crystal structure and magnetic properties. The size dependence of the crystal structure exhibited a change in behavior across the critical size of 3 nm. The lattice constants attained maximal values at approximately 3 nm and asymptotically decreased with increasing particle size, reaching the values for the bulk crystal. The rhombohedral distortion of crystallographic structure increased with decreasing particle size for particle sizes below approximate to 10 nm and was maximum at approximate to 3 nm. The size dependence of lattice strain also exhibited a maximum at 3 nm. The magnetic properties such as the coercive field, anisotropy energy, blocking temperature, and shell moment exhibited maxima for particle sizes between 3 and 10 nm. These results suggest that the magnetic behavior is generated by the change in the magnetic anisotropy constant originating from the changes in the crystal structure.
  • Toshio Naito, Tomoaki Karasudani, Naoki Nagayama, Keishi Ohara, Kensuke Konishi, Shigeki Mori, Takahiro Takano, Yukihiro Takahashi, Tamotsu Inabe, Shota Kinose, Sadafumi Nishihara, Katsuya Inoue
    EUROPEAN JOURNAL OF INORGANIC CHEMISTRY 24 4000 - 4009 2014年08月 [査読有り]
     研究論文(学術雑誌) 
    The simple molecular salt NMQ[Ni(dmit)(2)] (NMQ = N-methylquinolinium, dmit = 1,3-dithiol-2-thione-4,5-dithiolate) functions as a diamagnetic insulator with an activation energy E-a(dark) of 0.20 eV. However, at 300 K, it exhibits ca. 40 times higher conductivity (sigma(UV)) under UV irradiation [(375 +/- 5) nm, 15.7 mW cm(-2)] than it does under dark conditions (sigma(dark)). The ratio sigma(UV)/sigma(dark) rapidly increases with decreasing temperature and reaches ca. 880 at 200 K. From the temperature dependence of sigma(UV), the activation energy under irradiation E-a(UV) is 0.12 eV. These observations cannot be explained as the result of sample heating during UV irradiation. Rather, the X-ray photoelectron spectra of the sulfur and nickel atoms, the calculated band structure, and the UV/Vis spectra of the salt can all be explained consistently as follows: charge transfer between the Ni(dmit)(2) moieties upon exposure to 375 nm UV light induces melting of the charge-ordered state and produces the unusually large photoconductivity of NMQ[Ni(dmit)(2)].
  • T. Zhuang, K. Hiraoka, M. Kurisu, K. Konishi, T. Kamimori, I. Nakai
    JPS Conference Proceedings, Proceedings of the International Conference on Strongly Correlated Electron Systems (SCES2013) 3 011069 - 011069-4 2014年06月 [査読有り]
     研究論文(国際会議プロシーディングス) 
    Single crystals of YbIn1−xCdxCu4 compounds with 0 ≤ x ≤ 1 were synthesized by flux method. X-ray powder diffraction results show that all samples have the C15b type crystal structure. Electrical resistivity, magnetic susceptibility, and Yb-LIII edge XANES spectra were measured. XANES results show that the Yb valence in YbIn1−xCdxCu4 decreases from 2.96 ± 0.02 to 2.80 ± 0.02 at 300 K and from 2.85 ± 0.02 to 2.78 ± 0.02 at 10 K, with increasing Cd content x. The Yb valence in Cd-rich samples shows only weak temperature dependence, suggesting that Yb ions are in a valence fluctuation state similar to the low temperature phase of YbInCu4.
  • Timur Sh. Atabaev, Makio Kurisu, Kensuke Konishi, Nguyen Hoa Hong
    American Journal of Nano Research and Applications 2 1 13 - 16 2014年02月 [査読有り]
     研究論文(学術雑誌) 
    This study has investigated the effect of dopant concentration on the luminescent emission of Er3+ in ZrO2 nanocrystals. The structure and morphology of the resulting nanocrystals were characterized by X-ray diffraction and field emission scanning electron microscope. The room-temperature optical properties of synthesized nanocrystals were studied by photoluminescence spectroscopy. The dependence of the luminescence emission on the doping concentration was examined to determine the optimum Er3+ concentration in the samples. Strong luminescence quenching was also observed in samples with high Er3+ concentrations in the ZrO2 host lattice. The luminescent erbium doped zirconia nanocrystals are promising for applications such as fluorescent biomarkers, optical display systems, lamps, etc.
  • T. Tajiri, N. Terashita, K. Hamamoto, H. Deguchi, M. Mito, Y. Morimoto, K. Konishi, A. Kohno
    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 345 288 - 293 2013年11月 [査読有り]
     研究論文(学術雑誌) 
    We synthesized DyMnO3 nanoparticles with particle sizes of about 7.5-15.3 nm in the pores of mesoporous silica and investigated their crystal structure and magnetic properties. As the particle size decreased, the lattice constants of the DyMnO3 nanoparticles deviated from those of the bulk crystal, and the Jahn-Teller distortion in the nanoparticle systems decreased. In addition, the estimated lattice strain increased with decreasing particle size. The DyMnO3 nanoparticles showed superparamagnetic behavior. The blocking temperature and the coercive field increased with decreasing particle size, and this behavior was contrary to the usual magnetic size effects. It is deduced that these unique size dependences of the magnetic properties for the DyMnO3 nanoparticles were derived from the changes in lattice constants and lattice strain. The anisotropic lattice deformation in the crystal structure of the nanoparticles induces an enhancement of the magnetic anisotropy, which results in the increase in blocking temperature and coercive field with decreasing particle size. (c) 2013 Elsevier B.V. All rights reserved.
  • T. Naito, H. Yamamoto, K. Okuda, K. Konishi, H. Mayama, D. Yamaguchi, S. Koizumi, K. Kubo, T. Nakamura
    EUROPEAN PHYSICAL JOURNAL B 86 10 1 - 9 2013年10月 [査読有り]
     研究論文(学術雑誌) 
    It is well-known that cooperative properties such as magnetic ordering can depend on the samples' dimensions (Ds) in a qualitative way. However, there have been no samples with well-defined non-integer Ds. The dimension of a given sample has been always discussed on the anisotropy of the electronic/crystal/magnetic structures, which has no definition suitable for quantitative discussion on dimensions vs. properties. On the other hand a particular type of porous samples, i.e. fractal bodies, can have well-defined non-integer Ds dependent exclusively on the geometrical feature of structures, and physical properties of such materials remains unexplored. This paper reports on magnetic ordering in samples covering 2.5 <= D <= 3, in addition to a way of precise control of the fractal dimensions of given samples simply by wax (alkylketene dimer). The results show that the magnetic ordering temperatures, i.e. Neel temperatures (T(N)s), of CoO depend on D, and rapidly enhance immediately below D = 3. This means that one can control or enhance the critical temperature simply by tuning D with keeping the remaining magnetic properties unchanged.
  • Kensuke Konishi, Taiga Sakurai, Yutaro Nagano, Naoto Manabe, Yugo Morimoto
    JOURNAL OF THE KOREAN PHYSICAL SOCIETY 63 3 672 - 675 2013年08月 [査読有り]
     研究論文(学術雑誌) 
    Sub-micrometer-sized hollow spheres assembled from MFe2O4 (M= Ni, Mg) nanoparticles have been prepared by using the template method with a wet chemical process. A superparamagnetic-type blocking process is observed in the zero-field-cooled (ZFC) and the field-cooled (FC) magnetizations and magnentic susceptibilities. Furthermore, a spin-glass-like behavior due to surface spin freezing is found in Ni-ferrite nanoparticles. The surface spin freezing temperatures T (f) are quite a bit lower than the blocking temperature, and the magnetic field dependence is different between the nanoparticles and the fabricated hollow spheres. The spin-glass nature of the Ni-ferrite nanoparticle is demonstrated by the magnetice field dependence of T (f) following the well known Almeida-Thouless (AT) line. In contrast, the T (f)(H) of the hollow Ni-ferrite sphere hints at failure of the Gabay-Toulouse theory as well as the AT theory.
  • Toshio Naito, Tomoaki Karasudani, Shigeki Mori, Keishi Ohara, Kensuke Konishi, Takahiro Takano, Yukihiro Takahashi, Tamotsu Inabe, Sadafumi Nishihara, Katsuya Inoue
    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 134 45 18656 - 18666 2012年11月 [査読有り]
     研究論文(学術雑誌) 
    UV irradiation reversibly switches a new insulating and nonmagnetic molecular crystal, BPY[Ni(dmit)(2)](2) (BPY = N,N'-ethylene-2,2'-bipyridinium; Ni(dmit)(2) = bis(1,3-dithiole-2-thione-4,5-dithiolato)nickelate(III)), into a magnetic conductor. This is possible because the bipyridyl derivative cations (BPY2+) trigger a photochemical redox reaction in the crystal to produce a change of similar to 10% in the filling of the Ni(dmit)(2) valence band, leaving localized spins on the BPY themselves. In the dark, almost all of the BPY molecules are closed shell cations, and most of the Ni(dmit)(2). radical anions form spin singlet pairs; thus, this material is a diamagnetic semiconductor. Under UV irradiation, a photocurrent is observed, which enhances the conductivity by 1 order of magnitude Electron-spin resonance. measurements indicate that the 'UV:. irradiation reversibly generates. carriers and localized spins on the Ni(dmit)(2). and the BPY, respectively: This high photoconductivity can be explained by charge transfer (CT) transitions between Ni(dmit)(2) and BPY in the UV region. In other words, the photoconduction and "photomagnetism" can be described as reversible optical control of the electronic states between an ionic salt (BPY2+/[Ni(dmit)(2)](-), nonmagnetic insulator) and a CT complex (BPY2(1-delta)+/[Ni(dmit)(2)]((1-delta)-) (delta approximate to 0.1), magnetic conductor) in the solid state.
  • Aya Ouchi, Masaharu Ishikura, Kensuke Konishi, Shin Ichi Nagaoka, Kazuo Mukai
    Lipids 44 10 935 - 943 2009年10月 [査読有り]
     研究論文(学術雑誌) 
    A kinetic study of the prooxidant effect of α-tocopherol was performed. The rates of allylic hydrogen abstraction from various unsaturated fatty acid esters (ethyl stearate 1, ethyl oleate 2, ethyl linoleate 3, ethyl linolenate 4, and ethyl arachidonate 5) by α-tocopheroxyl radical in toluene were determined, using a double-mixing stopped-flow spectrophotometer. The second-order rate constants (k p) obtained are <1 × 10-2 M-1s-1 for 1, 1.90 × 10-2 M-1s-1 for 2, 8.33 × 10-2M -1s-1 for 3, 1.92 × 10-1 M -1s-1 for 4, and 2.43 × 10-1M -1s-1 for 5 at 25.0 °C. Fatty acid esters 3, 4, and 5 contain two, four, and six -CH2 - hydrogen atoms ctivated by two π-electron systems (-C=C-CH2-C=C-). On the other hand, fatty acid ester 2 has four -CH2- hydrogen atoms activated by a single π-electron system (-CH2-C=C-CH2-). Thus, the rate constants, k abstr/H, given on an available hydrogen basis are k p/4 = 4.75 × 10-3M-1s-1 for 2, k p/2 = 4.16 × 10-2 M-1s-1 for 3, k p/4 = 4.79 × 10-2M-1s -1 for 4, and k p/6 = 4.05 × 10-2M -1s-1 for 5. The k abstr/H values obtained for 3, 4, and 5 are similar to each other, and are by about one order of magnitude higher than that for 2. From these results, it is suggested that the prooxidant effect of α-tocopherol in edible oils, fats, and low-density lipoproteins may be induced by the above hydrogen abstraction reaction. © 2009 AOCS.
  • T Maehara, K Konishi, T Kamimori, H Aono, H Hirazawa, T Naohara, S Nomura, H Kikkawa, Y Watanabe, K Kawachi
    JOURNAL OF MATERIALS SCIENCE 40 1 135 - 138 2005年01月 [査読有り]
     研究論文(学術雑誌) 
    Selection of ferrite powder was carried out to realize a thermal coagulation technique in which tumors are locally heated by an application of alternating magnetic field from external coils. Magnesium ferrite (MgFe2O4) showed the largest increase in temperature (AT) under an alternating magnetic field in all the ferrites examined. For all the samples, AT value under alternating magnetic field was increased with an increase in frequency (200-500 kHz). The heating ability for the Mg-ferrite was ca. 1.4 W/g under alternating magnetic field of 4.0 kA/m (200 W, 370 kHz). The heating ability in alternating magnetic field was clearly depended on the magnitude of the hysteresis loss for the ferrite powder. (C) 2005 Springer Science + Business Media, Inc.
  • C Matsuoka, T Ishida, T Maehara, K Konishi
    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 272 Pt.3 2426 - 2427 2004年05月 [査読有り]
     研究論文(学術雑誌) 
    Thermal coagulation technique in which tumors are locally heated up to 60-80 degreesC can be realized by application of AC magnetic field from external coils to tumors covered with magnetic particles. We study numerically the temperature distribution in living tissue containing ferrite powder. With this temperature distribution, we calculate the magnitude of damaged region in tissue including a tumor and show a relation between tumor radii and the power of AC magnetic field. (C) 2004 Elsevier B.V. All rights reserved.
  • K Konishi, T Maehara, T Kamimori, H Aono, T Naohara, H Kikkawa, Y Watanabe, K Kawachi
    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 272 Pt.3 2428 - 2429 2004年05月 [査読有り]
     研究論文(学術雑誌) 
    In order to realize a thermal coagulation technique in which tumors are locally heated up to 60-80 degreesC by inductive heating and necrotized, selection of ferrite powder and frequency are performed. We investigate the heating properties by applying AC magnetic field for various ferrite powders (micrometer size of the particles). The temperature rise for Mg-ferrite (MgFe2O4) powder is the largest around 360 kHz in our samples. It has sufficient heating ability for thermal coagulation therapy against cancer. (C) 2003 Elsevier B.V. All rights reserved.
  • Nakai, I, H Tange, K Konishi, T Kamimori, A Chikazawa, Y Motegi
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 72 5 1184 - 1190 2003年05月 [査読有り]
     研究論文(学術雑誌) 
    We have observed a large magnetovolurne effect in a melt spun Gd-rich amorphous magnet Gd67Ni33 .The magnet shows the forced volume magnetostriction of a positive value of 3.76 x 10(-5) T-1 at 4.4 K, which is almost as same as that of a typical Invar alloy Fe65Ni35, and the spontaneous volume magnetostriction of 1.97 x 10(-3) at 6.9 K. Both volume magnetostrictions are proportional to the square of temperature. They are explained in the framework of spin fluctuation theory for weak itinerant electron magnets. The effect supports that the Ni constituent has a magnetic moment in the amorphous phase with such a low Ni concentration unlike crystalline Gd-Ni compounds. We propose a simple relation of estimating the magnetic moment which causes the magnetovolume effect. It gives the Ni moment of 0.61 mu(B) per atom at 0 K and the magnetovolume coupling constant of 1.20 x 10(-14) A(-2) m(-2). We also discuss the arrangement of the magnetic moment in the ground state.
  • T Maehara, K Konishi, T Kamimori, H Aono, T Naohara, H Kikkawa, Y Watanabe, K Kawachi
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 41 3A 1620 - 1621 2002年03月 [査読有り]
     研究論文(学術雑誌) 
    To develop materials for achieving local hyperthermia, we investigate the heating of various ferrite and metal powders by applying an external AC magnetic field. In comparison with magnetite powder, which has often been used in previous experiments, Mg-ferrite powder is more applicable for achieving local hyperthermia.
  • T. Kamimori, K. Kinoshita, J. Mochimaru, K. Konishi, H. Tange
    Journal of Magnetism and Magnetic Materials 226-230 I 993 - 995 2001年 [査読有り]
     研究論文(学術雑誌) 
    The measured magnetovolume effect of Fe sublattice in R2Fe 17, dTc/dV and dMs/dV are 3.8×10 3K/nm3 and 1.8 × 101 μB/ nm3/Fe. However, these magnetovolume effects cannot explain the elevation of Tc caused by the nitrogenation and the substitution of Si for Fe in Y2Fe17 compounds. On the contrary, the Fe sublattice in R2Fe17Si3 compounds has very small dTc/dV. The elevation of Tc is caused by the reduction of Invar properties of iron sublattice in the R2Fe17 compounds. © 2001 Elsevier Science B.V. All rights reserved.
  • Zenmyo K, Kubo H, Deguchi H, Konishi K, Takeda K
    Journal of the Physical Society of Japan 69 12 3980 - 3982 2000年12月 [査読有り]
     研究論文(学術雑誌) 
    In the specific heat measurements of Fe1-xMnxCl2·2H2O with competing exchange interactions and anisotropies, two peaks are observed in Fe-rich region and one sharp peak is observed in Mn-rich region. In the ac susceptibility measurements at a lower temperature than Néel point TN, no anomalies are observed in Fe-rich region and a broad maximum is observed in Mn-rich region. These results imply the existence of "intermediate" phase at the low temperature region.
  • Kensuke Konishi, Tatsuo Kamimori, Hatsuo Tange, Hiroyuki Deguchi, Tatsuya Kawae, Kazuyoshi Takeda
    Physica B: Condensed Matter 284-288 II 1275 - 1276 2000年 [査読有り]
     研究論文(学術雑誌) 
    The magnetic properties of Ce2Fe17-xAlx (8 ≤ x ≤ 13) have been studied by susceptibility, magnetization and heat capacity. Susceptibility and heat capacity studies indicate that two magnetic ordered phases are newly found besides spin-glass phase. The Weiss temperature turns from positive to negative for x ≥ 12. The origin of new phases may be accounted for by preferential site occupation of Al atoms and the competition among exchange interactions. © 2000 Elsevier Science B.V. All rights reserved.
  • T Kamimori, K Koyama, Y Mori, M Asano, K Kinoshita, J Mochimaru, K Konishi, H Tange
    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 177 Pt.2 1119 - 1120 1998年01月 [査読有り]
     研究論文(学術雑誌) 
    The Curie temperature, lattice parameters and the Fe-57 Mossbauer spectra were studied on Y2Fe17-xMx, where M = Al(0 less than or equal to x less than or equal to ), Si(0 less than or equal to x less than or equal to 3.5) and Ga(0 less than or equal to x less than or equal to 11). The analysis of Mossbauer spectrum shows the preferential site occupation of M atoms. The preference has little dependence on M. The behavior of the Curie temperature is closely related not to the lattice dimension but to the preferential site occupation of M. (C) 1998 Elsevier Science B.V. All rights reserved.
  • H Tange, T Matsuyama, A Chikazawa, K Konishi, T Kamimori
    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 177 Pt.1 125 - 126 1998年01月 [査読有り]
     研究論文(学術雑誌) 
    Spin glass (SG) and Invar effect for amorphous Fe-91(Zr1-xBx)(9) [x = 0-0.4] alloys have been investigated. Curie temperature. T-c, and spin freezing point, T-f, have been obtained from measurements of AC susceptibility chi(AC). The value of T-c increases with increasing B content, but T-f decreases and vanishes at around x = 0.7. These behaviors are explained by the Sherington-Kirkpatrick model. The pressure effect of T-c, dT(c)/dp, has been obtained indirectly from measurements of forced volume magnetostriction d omega/dH. The curve of dT(c)/dp versus T-c indicates that the measured samples are in the magnetically inhomogeneous state (MIS) according to the Wagner-Wohlfarth discussion. The relation between SG and MIS of samples are discussed. (C) 1998 Elsevier Science B.V. All rights reserved.
  • Mukai K, Konishi K, Nedachi K, Takeda K
    Journal of Physical Chemistry 100 23 9658 - 9663 1996年12月 [査読有り]
     研究論文(学術雑誌) 
    Magnetic properties of organic radical crystals, 3-(4-chlorophenyl)-1,5-dimethyl-6-thioxoverdazyl (p-CDTV) and 3-(4-bromophenyl)-1,5-dimethyl-6-thioxoverdazyl (p-BDTV), have been studied by measuring the heat capacity and ac susceptibility above 0.13 K in external magnetic fields of 0-30 kOe. p-CDTV has been found to be a new ferromagnet with a Curie temperature of T c = 0.68 ±0.02 K. p-CDTV behaves as a quasi-one-dimensional Heisenberg ferromagnet with the intrachain exchange interaction of 2J/k B = +12.0 ± 0.6 K above the transition temperature T c. The interchain exchange interaction zJ'/k B was estimated to be +0.21 ± 0.02 K, where z is the number of interchain bonds per spin. p-BDTV, on the other hand, behaves as a one-dimensional Heisenberg antiferromagnet with negative exchange interaction of 2J/k B = -41.2 K. © 1996 American Chemical Society.
  • Mukai K, Konishi K, Nedachi K, Takeda K
    Molecular Crystals and Liquid Crystals Science and Technology Section A: Molecular Crystals and Liquid Crystals 278-279 195 - 208 1996年12月 [査読有り]
     研究論文(国際会議プロシーディングス) 
    Magnetic properties of organic radical crystal, 3-(4-chlorophenyl)-1,5-dimethyl-6-thioxoverdazyl (p-CDTV), have been studied by measuring heat capacity and ac susceptibility above 0.13 K in external magnetic fields of 0-30 kOe. The p-CDTV has been found to be a new and bulk ferromagnet with the second highest Curie temperature T C=0.68 ± 0.02 K of genuine organic ferromagnet. The p-CDTV behaves as a quasi-one-dimensional Heisenberg ferromagnet with the intrachain exchange interaction of 2J/k B=+12.0 ± 0.6 K above the transition temperature T c. The interchain exchange interaction zJ′/k B was estimated to be +0.21 ± 0.02 K, where z is the number of interchain bonds per spin.
  • Konishi K, Takeda K, Tamura M, Kinoshita M
    Molecular Crystals and Liquid Crystals Science and Technology Section A: Molecular Crystals and Liquid Crystals 278-279 115 - 122 1996年12月 [査読有り]
     研究論文(国際会議プロシーディングス) 
    The magnetic properties of the β-phase p-NPNN have been investigated by the simultaneous observation of heat capacity and ac-susceptibility under hydrostatic pressures in magnetic fields. A drastic reduction of the Curie temperature from 0.61 K at an ambient pressure to 0.35 K at 7.2 kbar has been observed. The magnetic heat capacity under 7.2 kbar shows a characteristic shoulder of a two-dimensional Heisenberg ferromagnet with spin S=1/2, just above the heat capacity peak. By the application of weak external fields up to 1 kOe, the peak disappears and the shoulder grows its height and shifts to higher temperatures, as in the case of one-dimensional Heisenberg ferromagnets in external fields.
  • M Mito, H Nakano, M Ito, M Hitaka, T Kawae, K Konishi, K Mukai, K Takeda
    CZECHOSLOVAK JOURNAL OF PHYSICS 46 2107 - 2108 1996年 [査読有り]
     研究論文(学術雑誌) 
    The magnetic susceptibility of 3-(4-chlorophenyl)-1,5-dimethyl-6-thioxoverdazyl (p-CDTV) has been measured down to 0.2 Ii under hydrostatic pressures. The ordering temperature of T-c = 0.65 K at the ambient pressure is found to increase under pressure up to T-c = 0.80 K at 6.0 kbar, giving the demonstrative temperature independent susceptibility of a ferromagnetic state at low temperatures. This pressure dependence is the opposite direction to that observered in the other organic ferromagnet beta-phase p-NPNN, and is interpreted in terms of tne virtual charge transfer mechanism rather than pressure effects on the dipolar interactions.
  • Takeda K, Konishi K, Tamura M, Kinoshita M
    Physical Review B - Condensed Matter and Materials Physics 53 6 3374 - 3380 1996年 [査読有り]
     研究論文(学術雑誌) 
    The pressure effects on intermolecular magnetic interactions in a prototype and genuine organic ferromagnet, β-phase crystal of p-nitrophenyl nitronyl nitroxide, have been studied by the simultaneous measurements of magnetic susceptibility and heat capacity under the hydrostatic pressure of the range 0-7.7 kbar. A reduction of the Curie temperature from 0.61 K at an ambient pressure to 0.35 K at 7.2 kbar has been observed. This makes a significant contrast to the pressure-induced enhancement of the Néel temperature of organic antiferromagnets. The reduction of exchange interactions in the present compound is verified by the estimation of the ground-state energy under the pressures. Another remarkable feature of the results is a lowering of magnetic lattice dimensionality under pressure; the heat capacity curve under the pressure P = 7.2 kbar shows the short-range-ordering behavior expected of a low-dimensional Heisenberg ferromagnetic above the Curie temperature. This suggests that the interactions between the adjacent ac planes are relatively weakened to other interactions in the compressed crystal. These observed results are interpreted in terms of the virtual charge transfer mechanism rather than pressure effects on the dipolar interactions.
  • K. Takeda, K. Konishi, M. Tamura, M. Kinoshita
    Thermochimica Acta 266 175 - 184 1995年11月 [査読有り]
     研究論文(学術雑誌) 
    The magnetic interactions in β-phase p-NPNN (p-nitrophenyl nitronyl nitroxide), a prototype genuine organic ferromagnet, have been studied by simultaneous measurements of magnetic heat capacity and susceptibility under hydrostatic pressures. A drastic reduction of the Curie temperature from 0.6 K at ambient pressure to 0.35 K at 7.2 kbar has been observed. This makes a significant contrast to the pressure-induced enhancement of the Néel temperature of organic antiferromagnets. A lowering of the magnetic lattice dimensionality is also observed at temperatures slightly above the Curie temperature under pressure. These observations are interpreted in terms of the virtual charge transfer mechanism. © 1995.
  • K. Takeda, K. Konishi, M. Hitaka, K. Nedachi, K. Mukai
    Journal of Magnetism and Magnetic Materials 140-144 3 1635 - 1636 1995年 [査読有り]
     研究論文(学術雑誌) 
    An experimental check of quantum statistics for the most isotropic Heisenberg ferromagnet in one dimension has been carried out with a genuine organic 1,5 dimethylverdazyl radical crystal. A prototype Heisenberg ferromagnetic behavior, including magnetic susceptibility with the critical index γ = 2.0 and field dependence of heat capacity, is observed. © 1995.
  • K. Takeda, K. Konishi, M. Hitaka, T. Kawae, T. Tamura, M. Kinoshita
    Journal of Magnetism and Magnetic Materials 140-144 2 1451 - 1452 1995年 [査読有り]
     研究論文(学術雑誌) 
    Under hydrostatic pressure, a drastic reduction of the Curie temperature TC(p) of β-phase p-NPNN, a genuine organic ferromagnet, has been found from TC(p0) = 0.61 K (p = p0 = 0.001 kbar) to TC(p) = 0.35 K (p = 7.2 kbar), for example. The results are discussed in comparison with the positive effect of pressure on the Néel temperatures of organic antiferromagnets. © 1995.
  • K. Takeda, K. Konishi, K. Nedachi, K. Mukai
    Physical Review Letters 74 9 1673 - 1676 1995年 [査読有り]
     研究論文(学術雑誌) 
    Using a genuine organic ferromagnetic radical crystal (C10H10N4SCl) which was synthesized recently, we experimentally examined the results of quantum statistics for a one-dimensional Heisenberg ferromagnet with spin S=12. The characteristic thermodynamical properties expected of the most isotropic Heisenberg system, such as magnetic susceptibilities with the critical index of γ=2.0 and field dependence of magnetic heat capacity, are herein revealed. © 1995 The American Physical Society.
  • K. Mukai, K. Konishi, K. Nedachi, K. Takeda
    Journal of Magnetism and Magnetic Materials 140/144 Pt 2 1449 - 1450 1995年01月 [査読有り]
     研究論文(国際会議プロシーディングス) 
    The organic radical crystal, 3-(4-chlorophenyl)-1,5-dimethyl-6-thioxoverdazyl (p-CDTV), has been revealed to be a new and bulk ferromagnet with the second highest Curie temperature TC = (0.67 ± 0.02) K of genuine organic ferromagnets by the simultaneous measurements of heat capacity and magnetic susceptibility. On the other hand, 3-(4-bromophenyl)-1,5-dimethyl-6-thioxoverdazyl (p-BDTV) behaves as a one-dimensional antiferromagnet with an intermolecular interaction of 2J kB = -41.2 K. © 1995.
  • Takeda Kazuyoshi, Konishi Kensuke, Tamura Masafumi, Kinoshita Minoru
    Molecular Crystals and Liquid Crystals Science and Technology Section A: Molecular Crystals and Liquid Crystals 273 pt 3 57 - 66 1995年 [査読有り]
     研究論文(学術雑誌) 
    The ferromagnetism of β-phase p-nitrophenyl nitronyl nitroxide has been established by various measurements at an ambient pressure. To get further insight into the magnetic interactions, the pressure effect on the magnetic and thermal properties has been examined in the pressure range of 0-7.7 kbar. Important feature of the results is twofold. One is a reduction of the Curie temperature with applied pressure. This suggests that the exchange interactions are mainly responsible for determination of the Curie temperature. Dipolar couplings are estimated to be too small to explain the observed Curie temperature. The other is the lowering of the lattice dimensionality. The heat capacity curve under the pressure of 7.2 kbar coincides with the theory for a two-dimensional Heisenberg ferromagnet above the Curie temperature. This suggests that the interactions between the neighboring ac-plane are more affected by compression of the crystal.
  • K. Konishi, T. Hattori, H. Deguchi, K. Takeda
    Journal of Physics: Condensed Matter 6 12 2341 - 2346 1994年 [査読有り]
     研究論文(学術雑誌) 
    Heat capacities of Ne adsorbed in the one- and three-dimensional channels in the high-silica zeolites ZSM-23 and ZSM-5 have been observed in the temperature range from 2 K to 23 K for various concentrations of Ne. For lower concentrations of Ne, the low-temperature heat capacities for both the one-dimensional and the three-dimensional channels, both about 5.5 AA in diameter, are described by the Einstein model, which implies that Ne atoms are localized independently or construct clusters of minute size in the channels. However, for the higher concentration where channels are nearly filled with Ne atoms, the heat capacities of Ne reflect the difference between the topological channel structures of the two zeolites. In the case of three-dimensional channels, the heat capacity is revealed to be well reproduced by the Debye model for a continuous solid with the characteristic temperature Theta D=29 K, which is unexpectedly smaller than the values Theta 3D approximately=67 K for the bulk solid Ne and Theta 2D approximately=50 K for the two-dimensional solid Ne. This suggests the possibility of an unusual softening effect of phonons in solid of Ne in the three-dimensional network of channels. While the heat capacity of Ne in the one-dimensional channels cannot be understood in terms of the one-dimensional Debye model, it can be explained using the Einstein model. These results for the classical Ne particle are significant when compared with the thermal behaviour of He in the same zeolites, which reflects the characteristic quantum effect at low temperatures.
  • Jun Yamauchi, Kazuyoshi Takeda, Kensuke Konishi
    Molecular Crystals and Liquid Crystals Science and Technology. Section A. Molecular Crystals and Liquid Crystals 233 1 97  Informa {UK} Limited 1993年09月 [査読有り]
     研究論文(学術雑誌)
  • K. Konishi, H. Deguchi, K. Takeda
    Journal of Physics: Condensed Matter 5 11 1619 - 1632 1993年 [査読有り]
     研究論文(学術雑誌) 
    The heat capacities of 4He and 3He atoms adsorbed in porous high-silica zeolites having channels about 5.5 AA in diameter have been measured below 6 K. In neither atom is the expected quantum degeneracy detected. In one-dimensional channels, in which the direct positional exchange of atoms is prohibited, the heat capacity depends linearly on temperature, T, as C=AT. This result can be understood by the tunnelling two-level system model for glasses or amorphous solids at very low temperatures. The large zero-point motion of the helium atom is reflected in the enormous value of the coefficient A, and in the wider temperature range of the linear term than in glasses. In three-dimensional channels, the heat capacity of helium atoms shows a shoulder around 2 K for lower atomic concentrations. The result below 2 K is reproduced by a consideration of discrete energy levels enhanced in the crossing space of channels. For higher concentrations the heat capacity shows a linear temperature dependence, which can be understood using the same picture as in the case of the one-dimensional system.
  • Bi Jin, Nobuo Iwata, Toru Shigeoka, Kazuyoshi Takeda, Kensuke Konishi, Hiroyuki Deguchi
    Japanese Journal of Applied Physics 32 S3 334  Japan Society of Applied Physics 1993年01月 [査読有り]
     研究論文(国際会議プロシーディングス)
  • K TAKEDA, K KONISHI, H DEGUCHI, N IWATA, T SHIGEOKA
    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 104 901 - 902 1992年02月 [査読有り]
     研究論文(学術雑誌) 
    In the magnetically commensurate phases in the axially anisotropic compounds PrCo2Si2, the paramagnetic ions with individual entropy k(B)In 2 has been detected to be immersed regularly by the heat capacity measurement and the adiabatic magnetization experiment. The possibility of the phase-slipping of the sinusoidal exchange field has been suggested to be driven by the variation of temperature in zero field.
  • K OKUDA, S NOGUCHI, K KONISHI, H DEGUCHI, K TAKEDA
    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 104 817 - 818 1992年02月 研究論文(学術雑誌) 
    Magnetic and electronic properties of two kinds of copper oxides with the linear chains linked by planar CuO4, Ca2CuO3 and Li2CuO2, were investigated by magnetic susceptibility (chi), specific heat (C(p)) and XPS measurements. Ca2CuO3 has scarcely any magnetic contribution to chi and C(p) in striking contrast with Li2CuO2 which shows 3D-AF magnetic ordering at 9.3 K. They are discussed on the linear chain model.
  • K TAKEDA, K KONISHI, H DEGUCHI, N IWATA, T SHIGEOKA
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 60 8 2538 - 2541 1991年08月 [査読有り]
     研究論文(学術雑誌) 
    In the commensurate phases with the wave vector k(0, 0, k) for k = 13/14 and k = 7/9 in the intermetallic rare earth compound PrCo2Si2, paramagnetic ions with individual entropy k(B) ln 2 have been found to be immersed regularly by the direct analysis of the observed heat capacity in zero external magnetic field. The possibility of phase slipping of the sinusoidal exchange field has also been discussed as driven by the variation of temperature in zero field.
  • Hiroyuki Deguchi, Kensuke Konishi, Kazuyoshi Takeda, Norikiyo Uryu
    Physica B: Physics of Condensed Matter 165-166 1 571 - 572 1990年 [査読有り]
     研究論文(学術雑誌) 
    Thermal properties of 3He and 4He adsorbed in high-silica zeolites have been studied in the temperature range 0.8-10 K for various helium concentration. In the case of ZSM-23 having one-dimensional(1-d) channels, helium behaves as a semi-quantum liquid. In ZSM-5 with three-dimensional (3-d) channel structure, the heat capacity of helium shows a characteristic shoulder around 2 K. This seems to be due to the motion of helium atoms trapped within the crossing space of the channels in ZSM-5. © 1990.
  • K TAKEDA, H DEGUCHI, T HOSHIKO, K KONISHI, K TAKAHASHI, J YAMAUCHI
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 58 9 3361 - 3370 1989年09月 [査読有り]
     研究論文(学術雑誌) 
    Magnetic and thermal properties have been studied on two kinds of organic free radicals, TANOL(2,2,6,6-tetramethyl-4-piperidinol-l-oxyl) and TPV(1,3,5-triphenylverdazyl), where the unpaired electrons are localized on the NO bond in the former compound but delocalized on the larger molecular orbitals in the latter. TANOL has been confirmed magnetically as a typical one-dimensional Heisenberg system with localized quantum spins coupled with the exchange constant J/kB=-5.2K. On the other hand, the experimental results on TPV can not reasonably be understood on the basis of a localized model with the possible paths of magnetic interactions such as a railroad trestle lattice. It is suggested that organic free radicals offer promising real systems for getting essential physical phenomena which can check model Hamiltonians for a delocalized and frustrated quantum system.

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