M. Sera

Hiroshima University, Hirosima, Hiroshima, Japan

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Publications (232)418.26 Total impact

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    ABSTRACT: Numerical investigations on muon sites in Ce-based Kondo semiconductors, Ce(Ru,Rh)2Al10 were carried out by using the Density Functional Theory. From the view point of simple electrostatic potential calculations, we found all the previously reported muon sites, suggested by di↵erent groups (Kambe S et al. 2010 J. Phys. Soc. Jpn. 79 053708 and Khalyavin D D et al., 2010 Phys. Rev. B 82 100405(R)), can be possibly chosen as muon stopping sites. We also investigated the changes in the potential of the Rh-doped case. We discovered that the electronic potential around the nearest Ru atom to the substituted Rh atom is a↵ected and the potential becomes asymmetric around the nearest Ru ion. Although big changes in hyperfine fields at muon sites have been reported (Guo H et al. 2013 Phys. Rev. B 88 115206), the muon positions estimated from the potential calculations do not change much.
    13th International Conference on Muon Spin Rotation, Relaxation and Resonance, Grindelwald, Switzerland; 12/2014
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    ABSTRACT: Numerical investigations on muon sites in Ce-based Kondo semiconductors, Ce(Ru,Rh)2Al10 were carried out by using the Density Functional Theory. From the view point of simple electrostatic potential calculations, we found all the previously reported muon sites, suggested by di↵erent groups (Kambe S et al. 2010 J. Phys. Soc. Jpn. 79 053708 and Khalyavin D D et al., 2010 Phys. Rev. B 82 100405(R)), can be possibly chosen as muon stopping sites. We also investigated the changes in the potential of the Rh-doped case. We discovered that the electronic potential around the nearest Ru atom to the substituted Rh atom is a↵ected and the potential becomes asymmetric around the nearest Ru ion. Although big changes in hyperfine fields at muon sites have been reported (Guo H et al. 2013 Phys. Rev. B 88 115206), the muon positions estimated from the potential calculations do not change much.
    13th International Conference on Muon Spin Rotation, Relaxation and Resonance, Grindelwald, Switzerland; 12/2014
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    ABSTRACT: The compound NdFe$_2$Al$_{10}$ ($Cmcm$, space group #63) has been studied by both powder and single-crystal neutron diffraction. Below T$_N$ = 3.9 K, the Nd$^{3+}$ magnetic moments order in a commensurate magnetic structure, whose unit cell consists of four orthorhombic unit cells stacked along the $b$ direction. It can be described either as double-$k$ [$\mathbf{k}_1$ = (0, 1/4, 0), $\mathbf{k}_3$ = (0, 3/4, 0)] on the original base-centered orthorhombic lattice or, equivalently, as single-$k$ (wave vector $\mathbf{k}_1$ alone) on the primitive orthorhombic lattice obtained by considering corners and centers of (0 0 1) faces as inequivalent. The intensity refinements point to a structure consisting of (0 1 0) ferromagnetic planes stacked along the $b$ direction, in which the moments are collinear and oriented along the $a$ axis (easy direction according to bulk magnetization measurements). The alternating sequence providing the best refinement turns out to be that which yields the lowest exchange energy if one assumes antiferromagnetic near-neighbor exchange interactions with $J_1 \gg J_2, J_3$. Information is also presented regarding the temperature and magnetic field dependence of the magnetic structure.
    08/2014;
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    ABSTRACT: Kondo semiconductors CeT2Al10 (T = Ru and Os) with the orthorhombic YbFe2Al10-type structure have attracted attentions due to the extremely high Néel temperatures. We have investigated the magnetic properties of NdFe2Al10 with the same structure as CeT2Al10 to obtain information of magnetic interactions in these compounds. From the results of magnetization measurements, it was confirmed that the long range antiferromagnetic order occurs at TN = 3.77(1) K in NdFe2Al10. We have measured 57Fe Mössbauer spectra of NdFe2Al10 in the temperature range from 2.8 to 300 K. All observed Mössbauer spectra can be fitted using one Fe site. The temperature dependence of the refined magnetic hyperfine field below TN cannot be explained by using the Brillouin function with J = 9/2. Furthermore, the Mössbauer spectra in the temperature from TN to 4.2 K indicate magnetic hyperfine fields at the Fe site in the paramagnetic state. These results reveal that there are magnetic fluctuations in the paramagnetic state of NdFe2Al10.
    Proceedings of the International Conference on Strongly Correlated Electron Systems (SCES2013); 06/2014
  • Proceedings of the International Conference on Strongly Correlated Electron Systems (SCES2013); 06/2014
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    ABSTRACT: The magnetoresistance of CeT2Al10 (T = Ru and Os) and the Hall resistivity of CeOs2Al10 have been measured using non destructive pulsed magnets. The longitudinal magnetoresistance of CeRu2Al10 shows a negative magnetoresistance for the magnetic field (H) along the a- and c-axes but shows less field dependence for H||b. These behaviors are probably attributed to the suppression of the conduction electron scattering by the localized moments. On the other hand, the transverse magnetoresistance exhibits a complex H dependence, which cannot be explained simply by a cyclotron motion of the conduction electrons. The longitudinal magnetoresistance of CeOs2Al10 for H||a rapidly decreases with increasing field below ∼10 K, indicating that the semiconducting behavior below ∼15 K at zero field is rapidly suppressed by the magnetic field up to ∼15 T. The Hall resistivity of CeOs2Al10 exhibits a non linear behavior below 4.2 K, which reflects the fact that CeOs2Al10 is a two-carrier system.
    Proceedings of the International Conference on Strongly Correlated Electron Systems (SCES2013); 06/2014
  • Proceedings of the International Conference on Strongly Correlated Electron Systems (SCES2013); 06/2014
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    ABSTRACT: The Γ5u-type antiferro-octupole (AFO) ordered state of Ce0.7La0.3B6, emerging below 1.5 K, has been studied by resonant x-ray diffraction in magnetic fields. We studied in detail what kind of multipole moments are induced by the field in the AFO phase. In a mean-field model for the Γ5u-AFO order within the Γ8 quartet crystal-field ground state, the Γ3g-type antiferroquadrupole (AFQ) is expected to be induced most strongly. However, contrary to this expectation, the main induced moment was the Γ5g-type AFQ, which is the order parameter of the field induced AFQ phase above 1 T.
    Proceedings of the International Conference on Strongly Correlated Electron Systems (SCES2013); 06/2014
  • Proceedings of the International Conference on Strongly Correlated Electron Systems (SCES2013); 06/2014
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    ABSTRACT: In order to investigate the anisotropy of the pressure-induced antiferroquadrupole ordered phase of CeTe, we carried out magnetization measurements under high pressure for three field directions of [001], [110], and [111]. The results show that the transition temperature is the highest for H||[110] and the lowest for H||[111]. This anisotropy is roughly explained by a mean field calculation which assumes Oxy type antiferroquadrupole order. In addition, we carried out resistivity measurements under high pressure to study the Kondo effect. It is shown that the Kondo effect is enhanced by pressure.
    Proceedings of the International Conference on Strongly Correlated Electron Systems (SCES2013); 06/2014
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    ABSTRACT: The CeT2Al10 family of orthorhombic compounds exhibits a very peculiar evolution from a Kondo-insulator (T: Fe) to an unconventional long-range magnetic order (T: Ru, Os). Inelastic neutron scattering experiments performed on single-crystal CeFe2Al10 reveal that this material develops a spin-gap in its magnetic spectral response below ~ 50 K, with a magnetic excitation dispersing from $E = 10.2 \pm 0.5$ meV at the Y zone-boundary point [q = (0,1,0)] to $\approx 12$ meV at the top of the branch. The excitation shows a pronounced polarization of the magnetic fluctuations along a, the easy anisotropy axis. Its behavior is contrasted with that of the (magnonlike) modes previously reported for CeRu2Al10, which have transverse character and exist only in the antiferromagnetic state. The present observation is ascribed to a "magnetic exciton" mechanism invoked to explain a similar magnetic response previously discovered in YbB12.
    01/2014; 89(16).
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    ABSTRACT: The multipole ordered phase in Ce0.7La0.3B6, emerging below 1.5 K and named phase IV, has been studied by resonant x-ray diffraction in magnetic fields. By utilizing diamond x-ray phase plates to rotate the incident linear polarization and a conventional crystal analyzer system, full linear polarization analysis has been performed to identify the order parameters. The analysis shows that the Γ5g(Oyz, Ozx, Oxy) quadrupoles are more induced by the field than the Γ3g (O20 and O22) quadrupoles on the Γ5u (Tx+y +zβ) antiferro-octupole order in phase IV. The problem is that this result is contradictory to a mean-field calculation, which inevitably gives the Γ3g quadrupole as the main induced moment. This result indicates that the Γ5g quadrupole order is close in energy. We consider that a large fluctuation of the Γ5g quadrupole is hidden behind the primary ordering of the Γ5u octupole and that the multipolar fluctuation significantly affects the ordering phenomenon.
    Physical Review B 12/2013; 89(1). · 3.66 Impact Factor
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    ABSTRACT: The magnetic ground state of the Rh-doped Kondo semiconductor CeRu2Al10 [Ce(Ru1−xRhx)2Al10] is investigated with the muon spin relaxation method. Muon spin precession with two frequencies is observed in the x=0 sample, while only one frequency is present in the x=0.05 and 0.10 samples, which is attributed to the broad static field distribution at the muon site. The internal field at the muon site is enhanced from about 180 G in the x=0 sample to about 800 G in the Rh-doped samples, supporting the spin-flop transition as suggested by the magnetization measurement, and the boundary of different magnetic ground states is identified around x=0.03. The drastic change of magnetic ground state by a small amount of Rh doping (3%) indicates that the magnetic structure in CeRu2Al10 is not robust and can be easily tuned by external perturbations such as electron doping. The anomalous temperature dependence of the internal field in CeRu2Al10 is suggested to be attributed to the hyperfine interaction between muons and conduction electrons.
    Physical Review B 09/2013; 88(11). · 3.66 Impact Factor
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    ABSTRACT: We investigated the magnetic properties of the antiferromagnetic (AFM) compound GdT2Al10 (T=Ru and Fe). Although GdRu2Al10 could be understood well as a simple AFM compound, the exchange interaction in GdFe2Al10 is found to be greatly varied with temperature. The magnitude of the AFM exchange interaction is reduced with decreasing temperature. We ascribed its origin to the exchange enhancement of the Fe ion with a decrease of temperature as was observed in YFe2Al10. The ordered moment is found to be along the [011] direction in the bc plane in both compounds from the anisotropic magnetic susceptibility. The origin of the magnetic anisotropy below TN could not be understood by the magnetic dipole interaction, which might come from the AFM order on the zigzag chain.
    Physical Review B 09/2013; 88(10). · 3.66 Impact Factor
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    ABSTRACT: The magnetic ground state of the Rh-doped Kondo semiconductor CeRu2Al10 [Ce(Ru1−xRhx)2Al10] is investigated with the muon spin relaxation method. Muon spin precession with two frequencies is observed in the x=0 sample, while only one frequency is present in the x=0.05 and 0.10 samples, which is attributed to the broad static field distribution at the muon site. The internal field at the muon site is enhanced from about 180 G in the x=0 sample to about 800 G in the Rh-doped samples, supporting the spin-flop transition as suggested by the magnetization measurement, and the boundary of different magnetic ground states is identified around x=0.03. The drastic change of magnetic ground state by a small amount of Rh doping (3%) indicates that the magnetic structure in CeRu2Al10 is not robust and can be easily tuned by external perturbations such as electron doping. The anomalous temperature dependence of the internal field in CeRu2Al10 is suggested to be attributed to the hyperfine interaction between muons and conduction electrons.
    Physical Review B 09/2013; 88(11). · 3.66 Impact Factor
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    ABSTRACT: We have studied the Rh substitution (electron doping) effect in the Kondo semiconductor CeRu2Al10, which orders antiferromagnetically below (T0=27 K), by specific heat C, magnetic susceptibility χ, electrical resistivity ρ, and Hall resistivity ρH measurements of Ce(Ru1-xRhx)2Al10 (x=0.12, 0.2, 0.23, 0.34) single crystals. T0 decreases monotonically with an increase in x. In addition, new anomalies occur at T1˜ 6.5 and T2˜ 3.0 K in all the Rh substitution samples. However, T1 and T2 are almost independent of x. The shape of the anomaly at T0 in χ(T) changes with Rh substitution, which implies the reorientation of the ordered moment. These phenomena indicate that the magnetic properties of CeRu2Al10 are strongly associated with the number of 4d electrons.
    Journal of the Physical Society of Japan 09/2013; 82(9):3702-. · 2.09 Impact Factor
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    ABSTRACT: We have examined the La substitution and its pressure effect on the Kondo semiconductor CeRu2Al10, which shows an unusual antiferromagnetic (AFM) order at T0=27 K with the AFM ordered moment (mAF) parallel to the orthorhombic c axis, not expected from the large anisotropy of the magnetic susceptibility (χ) of χa≫χc≫χb in the paramagnetic state. mAF could not be aligned along the a axis, but could only be in the bc plane. By only 10% La substitution corresponding to a negative chemical pressure effect, the direction of mAF in the AFM ordered phase is changed from the c to the b axis. However, by applying a small pressure of P∼0.3 GPa, this mAF∥b is easily changed to mAF∥c. Thus, the magnetic anisotropy could be easily controlled by tuning the pressure slightly. This indicates that the c-f hybridization dominates the magnetic anisotropy in the AFM ordered state and plays an essential role in the unusual AFM order in CeT2Al10 (T=Ru,Os).
    Physical Review B. 07/2013; 88(4).
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    ABSTRACT: We have investigated the marked change in the magnetic properties of CeRu2Al10 induced by a small amount of Rh substitution [Ce(Ru0.95Rh0.05)2Al10]. The magnetic susceptibility along the a-axis (χa) shows a large decrease with decreasing temperature after showing a sharp peak at T0=24 K and the high field magnetization for the magnetic field along the a-axis exhibits a spin-flop transition at ˜13 T. These indicate that the antiferromagnetic (AFM) order where the AFM moment is parallel to the a-axis takes place, which is consistent with the anisotropy of χa>χc>χb in the paramagnetic region, being different from the AFM order in CeRu2Al10. These results were analyzed by mean field calculation for the two-sublattice model using the crystalline electric field level scheme by Strigari et al. [Phys. Rev. B 86 (2012) 081105]. On the basis of both experimental and calculated results, we conclude that, by a small amount of Rh substitution with one extra 4d electron, the large c--f hybridization along the a-axis, leading to the unusual ground state of CeRu2Al10, is markedly suppressed and the Ce ion in a Rh-substituted sample becomes close to the normal localized magnetic ion.
    Journal of the Physical Society of Japan 05/2013; 82(5):4709-. · 2.09 Impact Factor
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    ABSTRACT: In order to uncover the 4f electron state as a background for the emergence of the novel phase below T0 in CeT2Al10 (T = Ru, Os), the nuclear spin--lattice relaxation rate 1/T1 in the well-localized RKKY system NdRu2Al10 was measured and compared with that in CeRu2Al10. The value of 1/T1 in NdRu2Al10 with TN=2.4 K, which follows de Gennes scaling from TN=16 K in GdRu2Al10, shows a characteristic T-dependence for localized systems, 1/T1=a/(b+cT), with the constants a, b, and c. On the other hand, in CeRu2Al10, 1/T1 at temperatures higher than T*˜ 60 K also follows the same function if the Korringa relaxation is subtracted, indicating that the Ce 4f electron in CeRu2Al10 is in a localized state at least down to T*. Below the characteristic temperature T*, the downward deviation of 1/T1 from the above function might be ascribed to the beginning of Kondo coherence as proposed previously. Further comparison with CeT2Al10 compounds suggests that T* becomes more than 200 K in T = Os and that a coherent Kondo semiconducting state finally emerges in T = Fe.
    Journal of the Physical Society of Japan 02/2013; 82(2):3702-. · 2.09 Impact Factor
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    ABSTRACT: We have performed the investigation of the charge density distribution of CeT2Al10 (T=Ru, Fe) and the crystal structure parameters of LnT2Al10. The lattice parameters of a-, b-, and c-axes exhibit the anisotropic contraction when Ru is replaced by Fe in LnT2Al10, different from the isotropic contraction simply expected from the smaller ionic radius of Fe than Ru. The contraction is larger in the a- and c-axes than in the b-axis. This anisotropic contraction of the YbFe2Al10-type crystal structure originates from the zigzag degree of the zigzag chain formed by T and Al bond along the a- and c-axes are larger than that along the b-axis. The lattice parameters of CeT2Al10 (T=Ru, Fe) exhibit the anisotropic deviation from the lanthanide contraction. The deviation is largest in the a-axis and is very small in the b-axis. Both the characteristic YbFe2Al10-type crystal structure and the anisotropic deviation towards the intermediate valence indicate that the largest c--f hybridization along the a-axis plays the important role and is associated with the unusual antiferromagnetic order in CeT2Al10 (T=Ru, Os).
    Journal of the Physical Society of Japan 02/2013; 82(2):4603-. · 2.09 Impact Factor

Publication Stats

1k Citations
418.26 Total Impact Points

Institutions

  • 2002–2014
    • Hiroshima University
      • • Department of Quantum Matter
      • • Graduate School of Advanced Sciences of Matter
      Hirosima, Hiroshima, Japan
  • 2010
    • Kochi University
      • Graduate School of Integrated Arts and Sciences
      Kôti, Kōchi, Japan
    • Wuhan National High Magnetic Field Center
      Wu-han-shih, Hubei, China
  • 1999
    • Kagoshima University
      Kagosima, Kagoshima, Japan
  • 1985–1999
    • Tohoku University
      • • Institute for Materials Research
      • • Department of Physics
      Sendai, Kagoshima-ken, Japan
  • 1990–1993
    • Nagoya University
      • Department of Material Science
      Nagoya, Aichi, Japan
  • 1989–1991
    • Hokkaido University
      • Division of Physics
      Sapporo-shi, Hokkaido, Japan
  • 1988
    • Aoyama Gakuin University
      Edo, Tōkyō, Japan
  • 1987
    • Université de Toulon
      La Garde-près-Toulon, Provence-Alpes-Côte d'Azur, France