M. Hagiwara

Osaka University, Suika, Ōsaka, Japan

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Publications (250)514.31 Total impact

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    Physical Review B 11/2015; 92(18). DOI:10.1103/PhysRevB.92.180410 · 3.74 Impact Factor
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    ABSTRACT: High field electron spin resonance (ESR) and magnetization measurements reveal the crucial role of the strong spin-lattice coupling to generate the peculiar phase transitions in the chromium spinel oxide CdCr2O4, which possesses a spin-driven Jahn-Teller transition and a field-induced 1/2-magnetization plateau state. From our analysis of the ESR modes and the spin wave dispersion, which was observed from the previous neutron scattering studies, these magnetic properties are shown to originate from the modifications of the exchange interactions due to the lattice distortions. The evaluated exchange constants are examined by the magnetoelastic theory proposed by Penc etal.
    Physical Review B 10/2015; 92(14). DOI:10.1103/PhysRevB.92.144410 · 3.74 Impact Factor
  • A. Okutani · S. Kimura · T. Takeuchi · M. Hagiwara ·
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    ABSTRACT: We have performed high-field multi-frequency electron spin resonance (ESR) measurements of a single crystal of the S = 1/2 quasi one-dimensional (1D) Ising-like antiferromagnet BaCo2V2O8 at 1.5 K in magnetic fields of up to 14 T applied along [110] and [100] directions. Two main ESR branches, which are ascending and descending with increasing magnetic fields, are observed from 400 GHz at zero magnetic field in both cases. The low ESR mode shows a softening near 10 T for H || [100], while no softening was observed below 14 T for H || [110]. This difference in the magnetic excitations may explain the distinct phase diagrams for these two directions.
    Applied Magnetic Resonance 09/2015; 46(9). DOI:10.1007/s00723-015-0655-6 · 1.17 Impact Factor
  • D. Yoshizawa · T. Kida · S. Nakatsuji · K. Iritani · M. Halim · T. Takeuchi · M. Hagiwara ·
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    ABSTRACT: We have performed electron spin resonance (ESR) measurements in the low temperature magnetic-ordered state of polycrystalline samples of CdYb2S4. This material is one of the rare-earth spinel compounds in which Yb3+ ions form the pyrochlore lattice, and consequently, CdYb2S4 possesses anomalous properties caused by geometrical frustration and anisotropic terms. Some ESR signals have been detected, and their resonance fields are well-fitted by linear lines in the frequency vs. magnetic-field plane. One of the ESR modes appears to intersect the origin of this plane, suggesting a nearly gapless feature in the magnetically ordered state of this material. Two additional ESR modes appear above H c = 2.6 T, indicating that there is a field-induced phase transition at H c. Given the nearly gapless feature of CdYb2S4, we expect that the ground state of CdYb2S4 must be either the Palmer-Chalker state or the ψ 2 state.
    Applied Magnetic Resonance 09/2015; 46(9). DOI:10.1007/s00723-015-0651-x · 1.17 Impact Factor
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    ABSTRACT: We explore orbital dynamics in the spin liquid candidate Ba3CuSb2O9 using multi-frequency electron spin resonance. We prepared two high quality single crystals. The crystal with a slight copper deficiency shows a structural phase transition at around 200 K due to the cooperative Jahn-Teller effect, accompanied with orbital ordering. In contrast, the crystal with almost perfect stoichiometry shows no orbital ordering down to the lowest temperature of 1.5 K. Dramatic change in the g-factor anisotropy as a function of frequency and temperature demonstrates orbital quantum fluctuations at a nearly constant time scale of ~ 100 ps below 20 K, evidencing the emergence of an orbital liquid state in this quantum spin liquid compound.
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    ABSTRACT: Crossover phase diagrams in the magnetic field versus temperature (H-T) plane of the nonmagnetic heavy-fermion metamagnets UT2Zn20 (T:Ir, Co) are studied by measuring the magnetic and electronic transport properties. The crossover phase diagrams of UIr2Zn20 and UCo2Zn20 are composed of a low-magnetic-field region (LFR) and a high-magnetic-field region (HFR), which are characterized by magnetic properties and the Hall effect, respectively. The LFR is found to form a closed area in the H-T plane, which is a quite different feature from the conventional uranium heavy-fermion compounds and the first observation in uranium compounds. From the drastic anomaly in the Hall effect at a metamagnetic field of UIr2Zn20, it is found that the metamagnetic behavior in UIr2Zn20 corresponds to a crossover from the heavy-fermion state to the field-induced ferromagnetic or polarized paramagnetic state accompanied by the reconstruction or topology change of Fermi surfaces. In UCo2Zn20, on the other hand, no sign of abrupt change in the electronic state at the metamagnetic field is observed. These contrastive crossover phase diagrams and the electronic state changes at the metamagnetic field are due to the different hybridization strengths between the 5 f electrons of U atoms and the d electrons of Ir and Co atoms, leading to the differences in magnetic correlation and crystalline electric field ground state or the degree of itinerancy of 5 f electrons.
    Journal of the Physical Society of Japan 07/2015; 84(7):074704. DOI:10.7566/JPSJ.84.074704 · 1.59 Impact Factor
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    ABSTRACT: Inelastic neutron scattering is used to study the finite-temperature scaling behavior of the local dynamic structure factor in the quasi-one-dimensional quantum antiferromagnet NTENP ($\text{Ni(N,N'-bis(3-aminopropyl)propane-1,3-diamine)(}\mu\text{-NO}_2\text{)ClO}_4$), at its field-induced Ising quantum critical point. The validity and the limitations of the theoretically predicted scaling relations are tested.
    Physical Review B 07/2015; 92:014412. DOI:10.1103/PhysRevB.92.014412 · 3.74 Impact Factor
  • 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.
    Applied Magnetic Resonance 03/2015; 46(9). DOI:10.1007/s00723-015-0661-8 · 1.17 Impact Factor
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    ABSTRACT: Using X-ray diffraction techniques, we have studied the crystal structure of a copper polynuclear coordination polymer Cu2(pymca)3(ClO4) (pymca = pyrimidine-2-carboxylate), which is found to crystallize as a trigonal crystal system, space group P31m, with the lattice constants a = 9.5904(18) Å and c = 5.9000(11) Å, at temperature T = 150 K. Each pymca ligand connects to two Cu2+ ions, forming a honeycomb network in the ab plane. The T dependence of the magnetic susceptibility of Cu2(pymca)3(ClO4) shows a broad maximum near T = 26K, indicating low-dimensional antiferromagnetic interactions. From the crystal structure and magnetic properties, we conclude that Cu2(pymca)3(ClO4) is a good realization of a spin-1/2 honeycomb lattice antiferromagnet.
    Journal of the Physical Society of Japan 03/2015; 84(3):034601. DOI:10.7566/JPSJ.84.034601 · 1.59 Impact Factor
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    ABSTRACT: A magnetic phthalocyanine based carbon material has been successfully synthesized by using a low energy process that employs highly chlorinated iron-phthalocyanine as building blocks and an alkali metal as a coupling reagent. The X-ray diffraction patterns and XPS spectrum for the reaction products suggest that they consist of amorphouscarbon material that contains uniformly dispersed iron ions. The iron phthalocyanine based carbon material exhibits ferromagnetic properties at room temperature and the ferromagnetic phase transition occurs at TC=490 K.
    01/2015; 40(2):107-110. DOI:10.14723/tmrsj.40.107
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    ABSTRACT: We report on the results of X-ray diffraction (XRD), magnetic susceptibility, and high-field magnetization measurements of oxygen molecules, which are unique magnetic homonuclear diatomic molecules with spin-1, encapsulated in single-walled carbon nanotubes (SWCNTs) with diameters of about 0.8 nm. Antiferromagnetic interactions between neighboring oxygen molecules are expected in SWCNTs, resulting in the formation of a spin-1 one-dimensional Heisenberg antiferromagnet, known as a Haldane magnet. The XRD pattern can be predicted accurately by considering the expected oxygen molecule alignment. The temperature evolution of the magnetic susceptibility and the high-field magnetization curve are typical of those for a Haldane magnet with spin-1. The results indicate that the Haldane state has been realized in a nanospaced material for the first time. This provides an alternative to the conventional condensed matter approach to forming quantum spin systems.
    Journal of the Physical Society of Japan 11/2014; 83(11):113706. DOI:10.7566/JPSJ.83.113706 · 1.59 Impact Factor
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    ABSTRACT: The chromium spinel oxide HgCr2O4 is known to show a peculiar 1/2-plateau in its magnetization curve. The appearance of the magnetization plateau has been interpreted by classical theories, which take into account the magnetoelastic interaction. In this study, we suggest that not only the magnetization curve but also the change in the exchange interaction, which occurs due to lattice distortions during the magnetization process, can be calculated based on the magnetoelastic theory, proposed by Penc et al. We show that the field dependence of the magnetization and the exchange constants, obtained from our previous experiments, agree well with those calculated by the magnetoelastic theory, except for the behaviors prior to the fully polarized phase. This result indicates that an unexpected phase exists just before the saturation of the magnetization in this compound.
    Journal of the Physical Society of Japan 11/2014; 83(11):113709. DOI:10.7566/JPSJ.83.113709 · 1.59 Impact Factor
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    ABSTRACT: We have performed NMR experiments on the quasi one-dimensional frustrated spin-1/2 system LiCuVO$_4$ in magnetic fields $H$ applied along the c-axis up to field values near the saturation field $H_{\rm sat}$. For the field range $H_{\rm c2}<H<H_{\rm c3}$ ($\mu_0H_{\rm c2}\approx 7.5$T and $\mu_0H_{\rm c3} = [40.5 \pm 0.2]$T) the $^{51}$V NMR spectra at $T$ = 380mK exhibit a characteristic double-horn pattern, as expected for a spin-modulated phase in which the magnetic moments of Cu$^{2+}$ ions are aligned parallel to the applied field $H$ and their magnitudes change sinusoidally along the magnetic chains. For higher fields, the $^{51}$V NMR spectral shape changes from the double-horn pattern into a single Lorentzian line. For this Lorentzian line, the internal field at the $^{51}$V nuclei stays constant for $\mu_0 H > 41.4$T, indicating that the majority of magnetic moments in LiCuVO$_4$ are already saturated in this field range. This result is inconsistent with the previously observed linear field dependence of the magnetization $M(H)$ for $H_{\rm c3}<H<H_{\rm sat}$ with $\mu_0H_{\rm sat}=45$T [L. E. Svistov {\it et al}., JETP Letters {\bf 93}, 21 (2011)]. We argue that the discrepancy is due to non-magnetic defects in the samples. The results of the spin-lattice relaxation rate of $^7$Li nuclei indicate an energy gap which grows with field twice as fast as the Zeeman energy of a single spin, therefore, suggesting that the two-magnon bound state is the lowest energy excitation. The energy gap tends to close at $\mu_0H \approx 41$T. Our results suggest that the theoretically predicted spin-nematic phase, if it exists in LiCuVO$_4$, can be established only within the narrow field range $40.5 < \mu_0 H < 41.4$T .
    Physical Review B 10/2014; 90(13). DOI:10.1103/PhysRevB.90.134401 · 3.74 Impact Factor
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    ABSTRACT: We have prepared polycrystalline samples of LaSrRh$_{1-x}$Ga$_x$O$_4$ and LaSr$_{1-x}$Ca$_x$RhO$_4$,and have measured the x-ray diffraction, resistivity, Seebeck coefficient, magnetization and electron spin resonance in order to evaluate their electronic states. The energy gap evaluated from the resistivity and the Seebeck coefficient systematically changes with the Ga concentration, and suggests that the system changes from a small polaron insulator to a band insulator. We find that all the samples show Curie-Weiss-like susceptibility with a small Weiss temperature of the order of 1 K, which is seriously incompatible with the collective wisdom that a trivalent rhodium ion is nonmagnetic. We have determined the $g$ factor to be $g$=2.3 from the electron spin resonance, and the spin number to be $S$=1 from the magnetization-field curves by fitting with a modified Brillouin function. The fraction of the $S$=1 spins is 2--5%, which depends on the degree of disorder in the La/Sr/Ca-site, which implies that disorder near the apical oxygen is related to the magnetism of this system. A possible origin for the magnetic Rh$^{3+}$ ions is discussed.
    Physical Review B 09/2014; 90(14). DOI:10.1103/PhysRevB.90.144402 · 3.74 Impact Factor
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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.
    Physical Review B 08/2014; 90(6). DOI:10.1103/PhysRevB.90.060413 · 3.74 Impact Factor
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    ABSTRACT: We succeed in growing single crystals of SmCd11 by the Cd self-flux method, and clarified the magnetic properties. SmCd11 is an antiferromagnet with a Néel temperature TN1 = 4.7 K, with four successive magnetic transitions at TN2 = 3.5, TN3 = 3.4, TN4 = 2.8, and TN5 = 2.3 K. The magnetization at 1.3 K for \(H\parallel \langle 100 \rangle \) is characteristic, indicating a spin-flip transition at 90 kOe and a canting process of magnetization in magnetic fields up to 300 kOe. From the magnetization, an ordered moment of Sm3+ with the CEF-doublet ground state is estimated to be 0.1 μB/Sm.
    Proceedings of the International Conference on Strongly Correlated Electron Systems (SCES2013); 06/2014
  • Y. Kawasaki · Y. Ideta · Y. Kishimoto · T. Ohno · K. Omura · T. Fujita · S. Kimura · M. Hagiwara ·

    Proceedings of the International Conference on Strongly Correlated Electron Systems (SCES2013); 06/2014
  • Takahito Fujita · Masayuki Hagiwara · Mika Inada · Yukio Yasui · Ichiro Terasaki ·

    Proceedings of the International Conference on Strongly Correlated Electron Systems (SCES2013); 06/2014
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    ABSTRACT: Unconventional high temperature superconductivity as well as three-dimensional bulk Dirac cone quantum states arising from the unique d-orbital topology has been a recent priority research area in physics. In iron pnictide compounds, although transport phenomena arisen from this multiple band Fermi surface are intriguing and scientifically important, they still do not give an adequate matching to neither experimental observations on the band picture nor theoretical calculations and a debate continues. Here we describe a new analytical approach of mobility spectrum, in which the carrier number is conveniently described as a function of mobility without any hypothesis about the number of carriers, on both longitudinal and transverse transport of high quality single crystal Ba(FeAs)$_2$ in a wide range of magnetic field. We show that the major numbers of carriers reside in large parabolic hole and electron pockets with very different topology as well as remarkably different mobility spectra, while the minor number of Dirac carriers resides in both hole- and electron- Dirac quantum states with the largest mobility as high as 70,000 cm$^2$(Vs)$^{-1}$.
    New Journal of Physics 03/2014; 16(9). DOI:10.1088/1367-2630/16/9/093062 · 3.56 Impact Factor
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    ABSTRACT: We present a comprehensive structural study on perovskite-type 6H-Ba3CuSb2O9, which exhibits a spin-orbital short-range ordering on a honeycomb-based lattice. By combining synchrotron x-ray diffraction, electron spin resonance, ultrasound measurement and Raman spectroscopy, we found that the static Jahn-Teller distortion is absent down to the lowest temperature in the present material, indicating orbital ordering is strongly suppressed. We discuss such an unusual state is realized with the help of spin degree of freedom, leading to a spin-orbital entangled liquid state.
    Proceedings of the National Academy of Sciences 03/2014; 112(30). DOI:10.1073/pnas.1508941112 · 9.67 Impact Factor

Publication Stats

2k Citations
514.31 Total Impact Points


  • 1998-2014
    • Osaka University
      • Center for Quantum Science and Technology under Extreme Conditions
      Suika, Ōsaka, Japan
  • 2011
    • Niigata University
      • Department of Physics
      Niahi-niigata, Niigata, Japan
    • Waseda University
      • Department of Applied Physics
      Edo, Tōkyō, Japan
  • 2009
    • Japan Science and Technology Agency (JST)
      Edo, Tōkyō, Japan
  • 1999-2006
    • RIKEN
      Вако, Saitama, Japan
  • 2003-2004
    • Yokohama City University
      Yokohama, Kanagawa, Japan
  • 2002
    • Toyota Physical and Chemical Institute
      Seto, Aichi, Japan
  • 1992
    • Université Paris-Sud 11
      Orsay, Île-de-France, France