Takanari Kashiwagi

University of Tsukuba, Tsukuba, Ibaraki, Japan

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Publications (41)70.51 Total impact

  • S. Kimura · K. Watanabe · T. Kashiwagi · H. Yamaguchi · M. Hagiwara · Z. Honda
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    ABSTRACT: We have performed high-field electron spin resonance (ESR) measurements of the isolated antiferromagnetic dimer system Na2Co2(C2O4)3(H2O)2 by illuminating circularly polarized microwaves at 162 GHz. Different from a usual ESR signal by the magnetic dipole transition, the resonance signal, coming from the direct transition between the singlet and triplet states in this compound, is suggested to show absence of circular dichroism. From this curious behavior, we consider that the direct transition in Na2Co2(C2O4)3(H2O)2 is driven by oscillating electric fields of microwaves. We propose that the spin current mechanism is responsible to induce a finite probability for the electric-dipole-active transition between the singlet and the triplet states in Na2Co2(C2O4)3(H2O)2.
    No preview · Article · Mar 2015 · Applied Magnetic Resonance
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    ABSTRACT: From high field electron spin resonance measurements in illuminating polarized light, we have revealed the existence of electromagnon, i.e., magnon excitation by oscillatory electric fields of light, in the field-induced 1/5-plateau phase of the triangular lattice antiferromagnet CuFeO2. We indicate that peculiar magnon modes, which generate uniform fluctuation of the vector spin chirality at wave vector k = 0, appear in the magnetic ordered phase with a collinear spin structure on triangular lattice. Our experimental results demonstrate that such magnon modes couple with an electric component of light, leading to the emergence of the electromagnon. Moreover, the measurements in circularly polarized light exhibit an anomalous behavior that circular dichroism, which is usually found in magnetic resonance, is absent in the resonance signal of the electromagnon. The microscopic mechanism of the electromagnon in CuFeO2 is also discussed.
    No preview · Article · Aug 2014 · Physical Review B
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    ABSTRACT: We have performed electron spin resonance (ESR) studies of K_{4}^{3+} and (K_{3}Rb)^{3+} nanoclusters incorporated in powder specimens of aluminosilicate sodalite at several microwave frequencies between 9 and 34 GHz. The K_{4}^{3+} and (K_{3}Rb)^{3+} clusters are arrayed in a bcc structure and are known to show antiferromagnetic ordering below the Ne[over ́]el temperatures of T_{N} ≃72 and ≃80 K, respectively, due to the exchange coupling between s electrons confined in the clusters. We have found sudden broadenings of ESR spectra in both samples below T_{N}. The line shape of the spectra below T_{N} is analyzed by powder pattern simulations of antiferromagnetic resonance (AFMR) spectra. The calculated line shapes well reproduce the experimental ones at all the frequencies by assuming a biaxial magnetic anisotropy. We have evaluated extremely small anisotropy fields of approximately 1 Oe indicating that these materials are ideal Heisenberg antiferromagnets. We have also found that the magnetic anisotropy changes from easy-plane type to uniaxial type by changing into a heavier alkali-metal cluster and that the g value shifts to a large value beyond two below T_{N} for K_{4}^{3+} and (K_{3}Rb)^{3+} nanoclusters. These novel features of K_{4}^{3+} and (K_{3}Rb)^{3+} nanoclusters incorporated in sodalite are discussed.
    No preview · Article · Nov 2013 · Physical Review B
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    ABSTRACT: We have performed ESR measurements on the triangular lattice antiferromagnet CuFeO2 to study the detailed frequency and field dependences of its magnon modes, which were recently revealed to be excited by oscillating electric fields. The results of the analysis for the magnon modes based the spin wave theory, and the polarization dependence measurements for the ESR signals are reported.
    No preview · Article · Dec 2012 · Journal of Physics Conference Series
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    ABSTRACT: We have performed high-field multifrequency electron spin resonance (ESR) and high-field magnetization measurements in magnetic fields H of up to 53 T on single crystals of the kagome-lattice antiferromagnet KFe[subscript 3](OH)[subscript 6](SO[subscript 4])[subscript 2]. We have analyzed the magnetization curve and the ESR excitation modes for H∥c by using two kinds of anisotropy origins, the Dzyaloshinsky-Moriya (DM) interactions and the single-ion anisotropy, the former of which is inevitable in a kagome-lattice antiferromagnet. We obtained good agreement between experiment and calculation for the case of the DM interactions. In addition, we have clarified the origin of a field-induced metamagnetic transition observed in the magnetization curve and determined the intraplane and interplane exchanges and the DM interaction parameters.
    No preview · Article · Aug 2012
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    ABSTRACT: We have performed high-field multifrequency electron spin resonance (ESR) and high-field magnetization measurements in magnetic fields H of up to 53 T on single crystals of the kagome-lattice antiferromagnet KFe3(OH)6(SO4)2. We have analyzed the magnetization curve and the ESR excitation modes for H∥c by using two kinds of anisotropy origins, the Dzyaloshinsky-Moriya (DM) interactions and the single-ion anisotropy, the former of which is inevitable in a kagome-lattice antiferromagnet. We obtained good agreement between experiment and calculation for the case of the DM interactions. In addition, we have clarified the origin of a field-induced metamagnetic transition observed in the magnetization curve and determined the intraplane and interplane exchanges and the DM interaction parameters.
    No preview · Article · Mar 2012 · Physical review. B, Condensed matter
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    ABSTRACT: We have performed electron spin resonance (ESR) and magnetization measurements on single crystals of K-Fe-jarosite along the a-axis (in the kagome-plane). We have calculated the resonance branches and the magnetization curve using a spin Hamiltonian including the interlayer exchange and the Dzyaloshinsky-Moriya (DM) interactions. By putting the same parameter values for the analyses along the c-axis (normal to the kagome plane), the calculated results show satisfactory agreement with the experimental ones. As a result, we have successfully explained all the experimental results with one set of the intra- and the inter-plane exchange and the DM interaction parameters.
    No preview · Article · Mar 2012 · Journal of Low Temperature Physics
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    ABSTRACT: In this paper, we report results of high field ESR measurements of the triangular lattice antiferromagnet CuFeO2. From polarization measurements for the ESR signals, we show an appearance of the electromagnon excitation in the field-induced 1/5 plateau phase of this compound.
    No preview · Article · Mar 2012 · Journal of Low Temperature Physics
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    ABSTRACT: We present the results of the magnetization and dielectric constant measurements on untwinned single-crystal samples of the frustrated S=1/2 chain cuprate LiCu2O2. Magnetic phase transitions were observed. A spin-flop transition of the spiral spin plane was observed for the field orientations H∥a, b. The second magnetic transition was observed at H≈15 T for all three principal field directions. This high-field magnetic phase is discussed as a collinear spin-modulated phase, which is expected for an S=1/2 nearest-neighbor ferromagnetic and next-nearest-neighbor antiferromagnetic chain system.
    Full-text · Article · Feb 2012 · Physical review. B, Condensed matter
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    ABSTRACT: We have performed multifrequency electron spin resonance (ESR) measurements of the triangular lattice antiferromagnet CuFeO2, which shows peculiar magnetic ordering and field-induced phase transitions, in high magnetic fields of up to 53 T. Our analysis of the ESR modes and energy dispersion explains the overall behaviors of magnetic excitations in the collinear 4-sublattice phase of this material. We show changes of the exchange interactions due to the lattice distortion of CuFeO2, suggesting strong spin-lattice coupling in this material. In addition, we evaluate the precise value of the magnetic anisotropy in CuFeO2 from the ESR and magnetization measurements. The presence of relatively large second- and third-nearest-neighbor intralayer exchange interactions is also indicated. We discuss that the strong spin-lattice coupling, the large farther neighbor exchange interactions, and the finite axial anisotropy are important to understand the magnetic phase transitions of CuFeO2.
    No preview · Article · Sep 2011 · Physical review. B, Condensed matter
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    ABSTRACT: A novel topologically frustrated pentanuclear cluster helicate [{Cu(II)(μ-L)(3)}(2)Cu(II) (3)(μ(3)-OH)](3+) (L(-)=3,5-bis(2-pyridyl)pyrazolate) has been synthesized and characterized. This cluster has a helical arrangement of ligands around the central metal core. Dzyaloshinsky-Moriya interactions are essential components to observe a gradual magnetization and forbidden transitions of high-field/multi-frequency (HF/MF)-ESR. The origin of the magnetic anisotropy of this compound is influenced by its helical spin structure, and consequently, the Cu(5)-cluster helicate introduces a unique magnetic anisotropy. This observation is a direct evidence of the topological part of the new spin phase in a magnetic system.
    No preview · Article · Sep 2010 · Chemistry - A European Journal
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    ABSTRACT: We have performed multi-frequency ESR measurements on the geometry frustrated triangular lattice antiferromagnet CuFeO2. The observed ESR modes are analyzed based on a mean field theory, taking into account a distortion of the triangular lattice, which was found by recent synchrotron X-ray diffraction measurements.
    No preview · Article · Apr 2010 · Journal of Low Temperature Physics
  • T. Kashiwagi · T. Nakano · A. Hanazawa · Y. Nozue · M. Hagiwara
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    ABSTRACT: We have carried out electron spin resonance (ESR) measurements on powder samples of sodalite loaded with Na at several frequencies between 9.7 and 35GHz and at temperatures between 1.5 and 60K. The ESR absorption spectrum below a Néel temperature TN turns into an asymmetric spectrum with a long tail at low fields from a symmetric one above TN. The line shape of the spectra below TN is analyzed by a powder pattern simulation of the antiferromagnetic resonance spectra with easy-plane anisotropy. The calculated line shape reproduces the experimental one considerably well by assuming a Gaussian distribution of the zero-field energy gap. We have evaluated a small anisotropy field of about 2×10−4T by using the exchange coupling constant calculated from the Weiss and the Néel temperatures. This result indicates that the sodalite loaded with Na is quite an ideal Heisenberg antiferromagnet as expected from the s-electron character of Na clusters and the cubic arrangement of nano-spaces in the sodalite.
    No preview · Article · Apr 2010 · Journal of Physics and Chemistry of Solids
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    ABSTRACT: We report the results of multi-frequency electron spin resonance (ESR) measurements on single crystals of Ni(C5H14N2)2N3(PF6) which is regarded as the one-dimensional Heisenberg antiferromagnet with spin one, namely the Haldane magnet, at very low temperatures down to about 100 mK. We observed the lowest resonance branch below about 500 mK for the field along the chain direction (H||c), which was observed previously only in an inelastic neutron scattering experiment at 30 mK. We compare the resonance branch with that calculated by a phenomenological field theory, and discuss the field dependence and the temperature sensitivity of this ESR branch.
    No preview · Article · Feb 2010 · Journal of Physics Conference Series
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    ABSTRACT: We have developed high-field and multifrequency (HFMF) electron spin resonance (ESR) apparatus for the magnetic fields up to 65T at frequencies up to about 6 THz. In addition to this pulsed field ESR apparatus, we are making a multifrequency ESR apparatus with very high sensitivity in a static field. We report the results of ESR studies on BaCoV2O8 and NiGa2S4, followed by recent developments and future plans of our HFMF ESR apparatus.
    No preview · Article · Dec 2009 · Applied Magnetic Resonance
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    ABSTRACT: The S = 1 quasi-one-dimensional Heisenberg antiferromagnet [Ni(C5H14N2)2N3](PF6), abbreviated as NDMAP, has been studied by electron spin resonance in a magnetic field above the critical field (H c). We studied angular and frequency dependences of spin excitations. The angular dependence of the spin excitations in the vicinity of H c is explained well by a phenomenological field theory, but the agreement between the experiment and the calculation is not satisfactory above 10 T. In high magnetic fields above 15 T, we obtained some characteristic spin excitations which are well explained by conventional antiferromagnetic resonance modes. These results suggest that the spin excitations change from a quantum state to a classical one due to the suppression of quantum fluctuations by high magnetic fields.
    No preview · Article · Dec 2009 · Applied Magnetic Resonance
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    ABSTRACT: Sodium clusters arrayed in aluminosilicate sodalite are known to show antiferromagnetism below the Néel temperature TN of 48 K. We have performed electron spin resonance (ESR) measurements on a powder specimen of this material at an X-band microwave frequency (9.7 GHz) with temperature varying between 4 and 300 K. The ESR spectra show asymmetric broadening below TN, which can be regarded as a powder pattern of the antiferromagnetic resonance (AFMR) signal. From the analysis of the AFMR fields at low temperatures using the exchange-coupling constants evaluated from the magnetic susceptibility, the anisotropy field is estimated to be significantly small at about 1-2 Oe. These results indicate that this material is an ideal Heisenberg antiferromagnet resulting from the character of s-electrons in zeolite cages with a cubic arrangement.
    No preview · Article · Aug 2009 · Journal of the Physical Society of Japan
  • S Kano · K Hisayoshi · T Kashiwagi · T Kida · M Hagiwara · C Uyeda
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    ABSTRACT: Sensitivity to detect diamagnetic anisotropy ΔχDIA of inorganic oxides was improved by increasing intensity of horizontal field from 1.6 T to 5.0 Tesla. The field induced a rotational oscillation of a magnetically stable axis of a sample, which was suspended with a thin fiber. Accurate Δχ values are obtained when restoration torque of the fiber is negligibly small compared to torque due to magnetic anisotropy. Accordingly, Δχ value at a level of 5×10-10 emu/g can be acquired, even if the mass of the sample is relatively small (0.318 g). Necessity of realizing Δχ measurement at low temperature is discussed, which realizes separation of Δχ DIA from a paramagnetic anisotropy caused by isolated magnetic ions.
    No preview · Article · Apr 2009 · Journal of Physics Conference Series
  • C Uyeda · S Kano · K Hisayoshi · T Kashiwagi · T Kida · M Hagiwara
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    ABSTRACT: Technical basis to detect small diamagnetic anisotropy ΔχDIA is established in a method using microgravity μG. Sensitivity of Δχ can be improved by increasing length of measurable period of rotational oscillation of magnetically stable axis with respect to field direction. In order to achieve the above condition, position of the diamagnetic sample should be stabilized in static field area, which was realized by introducing a magnetic circuit with high field homogeneity. Function of a mobile sample stage was effective in minimizing translational motion of sample. Accordingly, magnitude of measurable anisotropy may be decreased to a level of 10-10 emu/g. ΔχDIA of materials with high crystal symmetry, namely hexagonal ice, ZnO, SiC and BaTiO3, can be obtained by the above improvement. Magnetically active property due to magnetic anisotropy may be recognized for almost all the solid materials when sensitivity reaches the above level.
    No preview · Article · Apr 2009 · Journal of Physics Conference Series
  • T Kashiwagi · M Hagiwara · S Kimura · H Miyazaki · I Harada · Z Honda
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    ABSTRACT: The S=1 quasi-one dimensional Heisenberg antiferromagnet Ni(C5H14N2)2N3(PF6), abbreviated as NDMAP, has been studied by electron spin resonance (ESR) in a magnetic field exceeding the critical field (Hc) above which this compound shows a long range order (LRO) at sufficiently low temperatures. Our recently developed ESR apparatus with a dilution refrigerator is utilized to study the spin excitations of NDMAP above Hc for H∥c, because this compound exhibits the LRO below about 1 K. The spin excitation modes above Hc observed below 1 K do not show any difference from those at 1.5 K and the lowest excitation mode observed at 30 mK in the inelastic neutron experiments above Hc was not observed at about 200 mK in this study. Accordingly, the result suggests that the lowest excitation mode is very sensitive to temperature.
    No preview · Article · Mar 2009 · Journal of Physics Conference Series

Publication Stats

211 Citations
70.51 Total Impact Points

Institutions

  • 2010-2015
    • University of Tsukuba
      • Graduate School of Pure and Applied Sciences
      Tsukuba, Ibaraki, Japan
  • 2003-2012
    • Osaka University
      • • Department of Physics
      • • Center for Quantum Science and Technology under Extreme Conditions
      Suika, Ōsaka, Japan
  • 2007
    • Kyoto Institute of Technology
      • Department of Information Science
      Kioto, Kyoto, Japan
  • 2004
    • Yokohama City University
      Yokohama, Kanagawa, Japan