Faculty Profiles - TAKEDA Naoya

Papers - TAKEDA Naoya

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Ferromagnetic interaction and superconductivity of CeCu2Si2 Reviewed

M. Ishikawa, N. Takeda, P. Ahmet, Y. Karaki, H. Ishimoto, D. Huo, J. Sakurai

Journal of Physics and Chemistry of Solids 63 ( 6-8 ) 1165 - 1169 2002

Language：English Publishing type：Research paper (scientific journal)

We have recently reported our finding of a weakly ferromagnetic phase and two superconducting phases in the Cu-deficient and Cu-rich region of the homogeneity range, respectively, for the heavy-electron compound CeCu2Si2. We herein report more detailed results of the specific heat, magnetic susceptibility, resistivity (R), magnetoresistance (ΔR) and thermopower for many different compositions. We confirmed the slightly re-entrant behavior in the Hc2(T) curve and a change of regime in the ΔR at about 0.35 K above Hc2(T) for the low-Tc phase. Above about 0.75 K, the normal state of this phase exhibited no magnetoresistance up to 70 kOe, while that of high-Tc phase and the weakly ferromagnetic phase did a slightly positive ΔR. These differences in the three phases may provide an important clue to better understanding of the heavy-electron superconductivity of CeCu2Si2. © 2002 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0022-3697(02)00120-8

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Electronic structure of the filled skutterudite compound (formula presented)

K. Kanai, N. Takeda, S. Nozawa, T. Yokoya, M. Ishikawa, S. Shin

Physical Review B - Condensed Matter and Materials Physics 65 ( 4 ) 1 - 4 2002

Publishing type：Research paper (scientific journal)

Ultrahigh-resolution photoemission spectra of (formula presented) reveal crossover behavior into a low carrier state. The density of states (DOS) around the Fermi level (formula presented) decreases on lowering temperature and the semimetalliclike DOS is observed at 5.9 K. The temperature dependence of DOS at (formula presented) is explained in terms of the development of the coherence. The smaller hybridization strength between the Ru- (formula presented) state and the (formula presented) state prevents the hybridization gap from opening in (formula presented) which is realized in (formula presented). © 2002 The American Physical Society.

DOI： 10.1103/PhysRevB.65.041105

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Ferromagnetic exchange coupling of vanadium(IV) d pi spins across pyrimidine rings: Dinuclear complexes of oxovanadium(IV) bis(1,1,1,5,5,5-hexafluoropentane-2,4-dionate) bridged by pyrimidine derivatives Reviewed

T Ishida, S Mitsubori, T Nogami, N Takeda, M Ishikawa, H Iwamura

INORGANIC CHEMISTRY 40 ( 27 ) 7059 - 7064 2001.12

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER CHEMICAL SOC

Dinuclear oxovanadium(IV) complexes bridged by pyrimidine derivatives, L[VO(hfac)(2)](2) [L = pyrimidine (PM), 4-methylpyrimidine (MPM), 4,6-dimethylpyrimidine, 4-aminopyrimidine, and quinazoline; hfac = 1,1,1,5,5,5-hexafluoropentane-2,4-dionate], were synthesized and characterized. All of them showed intramolecular ferromagnetic interaction, and the magnetic susceptibilities were analyzed on the basis of the singlet-triplet model, giving 2J/k(B) = 2.2-5.5 K. PM[VO(hfac)(2)](2) crystallized in a monoclinic space group C2/c with a = 34.092(2), b = 6.9783(4), and e = 16.4940(9) Angstrom, beta = 109.104(1)degrees, V = 3707.8(4) Angstrom (3), and Z = 4 for C24H8F24N2O10V2, and MPM[VO(hfac)(2)](2) gave isomorphous crystals. A semiempirical calculation study based on the determined structure suggests the presence of d pi -p pi interaction between vanadium and pyrimidine nitrogen atoms. Ferromagnetic coupling is explained in terms of a spin-polarization mechanism across the pyrimidine bridge. The intermolecular ferromagnetic interaction of PM[VO(hfac)(2)](2) call be interpreted by the contact between the spin-polarized pyrimidine moiety and the oxovanadium oxygen atom in an adjacent molecule.

DOI： 10.1021/ic010730n

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The effect of La substitution and magnetic field on non-Fermi-liquid behaviour in CeRu4Sb12 Reviewed

N Takeda, M Ishikawa

JOURNAL OF PHYSICS-CONDENSED MATTER 13 ( 26 ) 5971 - 5980 2001.7

Language：English Publishing type：Research paper (scientific journal) Publisher：IOP PUBLISHING LTD

CeRu4Sb12 with the filled skutterudite structure exhibits a novel non-Fermi-liquid (NFL) behaviour in the low-temperature specific heat and electrical resistivity at ambient pressure. We investigated the effect of La substitution and magnetic field on the NEL state and found that it can be easily destroyed either by the application of a magnetic field or by a small degree of La substitution. In magnetic fields, CIT becomes strongly depressed and nearly constant below 1 K and rho (T) turns to following a T-2-law, implying that the Fermi-liquid state recovers in high magnetic fields. The type of critical fluctuation is discussed on the basis of the results of magnetic susceptibility, electrical resistivity and specific heat measurements.

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Magnetic Field effect on Non-Fermi Liquid Behaviors in CeRu4Sb12. Reviewed

N. Takeda, M. Ishikawa

PhysicaB 281-282 388 - 390 2000.12

Superconductivity and Magnetic Properties of Filled Skutterudite Compounds RERu4Sb12 (RE=La, Ce, Pr, Nd and Eu). Reviewed

N. Takeda, M. Ishikawa

J. Phys. Soc. Jpn. 69 868 - 873 2000.12

Third-order Magnetic Susceptibility and Quadrupolar Parameter of Kondo-lattice compound Ce3 Pd20 Ge6 Reviewed

J. Kitagawa, N. Takeda, M. Ishikawa, M. Nakayama, N. Kimura, T. Komatsubara

Journal of Physical Society of Japan 69 ( 3 ) 883 - 887 2000.3

Language：English Publishing type：Research paper (scientific journal) Publisher：The Physical Society of Japan (JPS)

We present a report on crystalline-electric-field effects observed in the electrical resistivity and the specific heat of Ce3Pd20Ge6, which are discussed within an energy level scheme of the Γ8 ground state and the Γ7 excited state at 50 K for both inequivalent crystallographic sites of Ce atom.The third-order magnetic susceptibility was deduced from the magnetization measurement in the paramagnetic phase of a single-crystalline sample in magnetic fields applied along [0 0 1] and [1 1 1].In order to explain the temperature dependence of the third-order magnetic susceptibility along [0 0 1], a positive total quadrupolar pair interaction constant of 22 mK is required in addition to a small antiferromagnetic exchange interaction, thereby suggesting ferroquadrupolar ordering with the Γ3 symmetry in this compound.

DOI： 10.1143/JPSJ.69.883

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Jahn-Teller-like phase transition of TmPd3S4 around 200 K Reviewed

J Kitagawa, E Matsuoka, N Takeda, M Ishikawa

PHYSICAL REVIEW B 60 ( 22 ) R15028 - R15030 1999.12

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER PHYSICAL SOC

We report a Jahn-Teller-like phase transition in a synthesized metallic compound, TmPd3S4, of the cubic NaPt3O4 structure type. The transition causes a very large thermal hysteresis in the electrical resistivity between 120 and 230 K and a modulated structure with a modulation vector of about 1/8a* (a*: reciprocal-lattice unit vector) at lower temperatures which was revealed by a low-temperature x-ray powder diffraction. Analyses on the low-temperature specific heat and the magnetic susceptibility suggest that the compound becomes an exchange-induced moment antiferromagnet (T-N=1.1 K) by the nonmagnetic singlet ground state of Tm3+ ions. [S0163-1829(99)51146-6].

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Anisotropic Magnetic Diagram of Ce3Pd20Ge6 with Quadrupolar Ordering Reviewed

J. Kitagawa, N. Takeda, M. Ishikawa, T. Yoshida, A. Ishiguro, N. Kimura, T. Komatsubara

Physica B 259-261 332 - 333 1999.1

Anomalous magnetic properties of CeRu4Sb12 Reviewed

N. Takeda, M. Ishikawa

Physica B: Condensed Matter 259-261 92 - 93 1999

Language：English Publishing type：Research paper (scientific journal) Publisher：Elsevier

We present the temperature dependence of the magnetic susceptibility χ(T), electrical resistivity ρ(T) and low-temperature specific heat C(T) of CeRu4Sb12. χ(T) shows a broad peak around 100 K characteristic to intermediate-valence compounds but the small Weiss temperature of -26 K and ρ(T) suggest that the compound is classified as a Kondo compound. The ground state is very anomalous and non-Fermi liquid behaviors were observed in C/T and ρ(T) at low temperatures. © 1999 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(98)01167-3

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Contrasting Kondo-Lattice Behavior of CeTSi3 and CeTGe3 (T=Rh and Ir). Reviewed

Y. Muro, D. Eom, N. Takeda, M. Ishikawa

J. Phys. Soc. Jpn. 67 3601 - 3604 1998.12

Anisotropic magnetic phase diagram of the Kondo-lattice compound Observation of antiferromagnetic and quadrupolar ordering Reviewed

J. Kitagawa, N. Takeda, M. Ishikawa, T. Yoshida, A. Ishiguro, N. Kimura, T. Komatsubara

Physical Review B - Condensed Matter and Materials Physics 57 ( 13 ) 7450 - 7453 1998

Language：English Publishing type：Research paper (scientific journal)

From the measurement of the specific heat of single crystalline samples of (Formula presented) we have constructed magnetic phase diagrams for a magnetic field up to 4 T, which disclose a pronounced anisotropy along the three principal directions of [100], [110], and [111]. We have found that both the quadrupolar and antiferromagnetic ordering temperatures exhibit distinct directional dependences on the external magnetic field and that new phase transitions evolve in the antiferromagnetic phase as well as in the ordered quadrupolar phase. These facts strongly suggest the existence of a complicated form of anisotropic interaction between the electric quadrupolar moment and the magnetic dipolar moment. The present result is briefly discussed in comparison with the reported one for (Formula presented). © 1998 The American Physical Society.

DOI： 10.1103/PhysRevB.57.7450

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Suppression of Antiferromagnetism by Kondo Effect and Quantum Critical Behavior in CeCoGe3-xSix (0 ≤ x ≤ 3) Reviewed

Duhwa Eom, Masayasu Ishikawa, Jiro Kitagawa, Naoya Takeda

Journal of the Physical Society of Japan 67 ( 7 ) 2495 - 2500 1998

Language：English Publishing type：Research paper (scientific journal) Publisher：Physical Society of Japan

Several pseudoternary compounds of the CeCoGe3-xSix system were studied by magneticsusceptibility, electrical-resistivity and specific-heat measurements. Substitution of silicon for germanium generates the normal chemical pressure and enhances the exchange interaction. The antiferromagnetism in CeCoGe3 is ultimately suppressed around x = 1.2 by the enhanced Kondo effect. Non-Fermi liquid-like behavior has been observed around the critical concentration and an intermediate-valence regime with a very high Kondo temperature of the order of 900 K is followed farther on in the silicon rich region.

DOI： 10.1143/JPSJ.67.2495

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Hydrogen-bonded organic ferromagnet Reviewed

Michio M. Matsushita, Akira Izuoka, Tadashi Sugawara, Tatsuya Kobayashi, Nobuo Wada, Naoya Takeda, Masayasu Ishikawa

Journal of the American Chemical Society 119 ( 19 ) 4369 - 4379 1997.5

Language：English Publishing type：Research paper (scientific journal)

Nitronyl nitroxide derivatives carrying a hydroquinone or a resorcinol moiety 2-(2',5'-dihydroxyphenyl)4,4,5,5-tetramethyl-4,5-dihydro-1H- imidazolyl-1-oxyl-3-oxide (HQNN) and 2-(3',5'-dihydroxyphenyl)-4,4,5,5- tetramethyl-4,5-dihydro-1H-imidazolyl-1-oxyl 3-oxide (RSNN)) have been designed and prepared. These compounds were found to afford hydrogen-bonded crystals. In the case of HQNN, two phases of crystals (α- and βHQNN) were obtained. Of these, the crystal structure of α-HQNN is characterized by the intramolecular hydrogen bond between the o-hydroxy group and the nitronyl nitroxide and by the intermolecular one-dimensional hydrogen-bonded chain between the o- and p-hydroxy groups of the neighboring molecules, respectively. Two of the hydrogen-bonded chains run in parallel, and they are connected by the bifurcated hydrogen bonds formed between the o-hydroxy groups of the facing molecules in the individual chain. The χT value of this crystal increased monotonously with lowering temperature (ST model, J = +0.93 K, Θ= +0.46 K) and turned out to exhibit a ferromagnetic phase transition at 0.5 K. On the basis of the heat capacity data, α-HQNN was found to be a three-dimensional ferromagnet. On the other hand, the crystal of β-HQNN was characterized by the intermolecular hydrogen-bonded chain formed between the hydroxy group at the meta position and the nitronyl nitroxide and by the interchain π-π stacking. The magnetic interaction of β-HQNN was interpreted by the ferromagnetic ST model, and this ferromagnetic interaction (J = +5.0 K) was accompanied by a weak antiferromagnetic interaction (Θ = - 0.32 K) at lower temperatures. Although the structural feature of the crystal of RSNN resembles that of the β-HQNN, it exhibited the antiferromagnetic interaction predominantly (ST model, J = + 10.0 K, Θ = -4.0 K). These magnetic behaviors are consistent with McConnell's theory, when the spin densities at the interacting sites connected by hydrogen bonds are taken into account. Thus, it may be concluded that the hydrogen bond plays a role not only in constructing hydrogen-bonded crystals but also in transmitting spin polarization along the hydrogen bond.

DOI： 10.1021/ja964083o

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Ferromagnetism of Organic Radical Crystals of TEMPO Derivatives. Reviewed

T. Nogami, T. Ishida, M. Yasui, F. Iwasaki, H. Iwamura, N. Takeda, M. Ishikawa

Mol. Cryst. Liq. Cryst. 279 97 - 106 1996.12

Possible quadrupolar ordering in a Kondo-lattice compou Reviewed

Jiro Kitagawa, Naoya Takeda, Masayasu Ishikawa

Physical Review B - Condensed Matter and Materials Physics 53 ( 9 ) 5101 - 5103 1996

Language：English Publishing type：Research paper (scientific journal)

Magnetic and transport properties of the cubic ternary compound (Formula presented)(Formula presented)(Formula presented) are herein reported. The electrical resistivity exhibits the Kondo lattice behavior and a large (Formula presented) coefficient at low temperatures, indicating that this compound is a heavy-electron system with a Kondo temperature of a few degrees Kelvin. The low-temperature specific heat revealed two successive anomalies at (Formula presented) K and (Formula presented) K. The (Formula presented) quartet crystalline-field ground state of Ce ions is conjectured from the thermal variation of magnetic entropy deduced from the specific-heat data. The anomaly at (Formula presented) is probably a result of quadrupolar interaction between (Formula presented) ground states, while the other one at (Formula presented) is due to antiferromagnetic ordering. © 1996 The American Physical Society.

DOI： 10.1103/PhysRevB.53.5101

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Ferromagnetism in Organic Radical Crystal of 4 - (p - Chlorobenzylideneamino) - 2, 2, 6, 6 - tetramethylpiperidin - 1 - oxyl. Reviewed

T. Nogami, T. Ishida, H. Tsuboi, H. Yoshikawa, H. Yamamoto, M. Yasui, F. Iwasaki, N. Takeda, M. Ishikawa

Chemistry Letters. 635 - 636 1995.12

Intra- and inter-molecular ferromagnetic interaction of transition metal complexes containing pyrimidine or pyrazine derivatives Reviewed

Takayuki Ishida, Shin-ichi Mitsubori, Takashi Nogami, Yoshimitsu Ishikawa, Masanori Yasui, Fujiko Iwasaki, Hiizu Iwamura, Naoya Takeda, Masayasu Ishikawa

Synthetic Metals 71 ( 1-3 ) 1791 - 1792 1995.4

Language：English Publishing type：Research paper (scientific journal)

The 1 2 spins of oxovanadium(IV) ions were ferromagnetically coupled with J kB = +1.1∼+2.7 K in the dinuclear complexes L[VO(hfac)2]2 (hfac = hexafluoroacetylacetonate, L = pyrimidine derivatives). Among them, a ferromagnetic transition was observed at about 0.14 K in PM[VO(hfac)2]2 (PM = pyrimidine). The polymeric complex QZ[Cu(hfac)2] (QZ = quinazoline) gave a positive Weiss constant (+0.39 K). The ferromagnetic transition was observed at about 0.12 K. © 1995.

DOI： 10.1016/0379-6779(94)03052-8

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New organic ferromagnets: 4-arylmethyleneamino-2,2,6,6-tetramethylpiperidin-1-oxyl (aryl = phenyl, 4-biphenylyl, 4-chlorophenyl, and 4-phenoxyphenyl) Reviewed

Takashi Nogami, Kensuke Togashi, Hidenori Tsuboi, Takayuki Ishida, Hajime Yoshikawa, Masanori Yasui, Fujiko Iwasaki, Hiizu Iwamura, Naoya Takeda, Masayasu Ishikawa

Synthetic Metals 71 ( 1-3 ) 1813 - 1814 1995.4

Language：English Publishing type：Research paper (scientific journal)

The title radicals were found to be bulk ferromagnets, as indicated by the sharp divergence of the susceptibility. Their transition temperatures were found in the range of 0.2-0.4 K. The X-ray crystal structure analysis of the phenyl, biphenylyl, and chlorophenyl derivatives at room temperature revealed that the crystal consisted of an almost two-dimensional network of the N-O sites. In the case of aryl = 2-naphthyl, metamagnetic behavior was observed below about 0.3 K. © 1995.

DOI： 10.1016/0379-6779(94)03063-C

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New Heavy-Electron System Ce3Pd20Si6 Reviewed

Naoya Takeda, Jiro Kitagawa, Masayasu Ishikawa

Journal of the Physical Society of Japan 64 ( 2 ) 387 - 390 1995

Language：English Publishing type：Research paper (scientific journal)

Magnetic and transport properties of the ternary compound Ce3Pd20Si6 are investigated down to 0.035 k. The temperature dependence of the electrical resistivity indicates that this compound is a new Kondo material. The low-temperature specific heat measurement reveals that C/T is strongly enhanced at low temperatures, reaching as high as 8 J/mole Ce·K2 at 0.2 k. This leads to the conclusion that Ce3Pd20Si6 is one of the heaviest-electron systems. © 1995, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.

DOI： 10.1143/JPSJ.64.387

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Papers - TAKEDA Naoya