Tatsuya Yanagisawa

Hokkaido University, Sapporo, Hokkaido, Japan

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Publications (94)136.17 Total impact

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    ABSTRACT: Ultrasonic measurements were performed on the cage-structure compound SmBe13. We have investigated the magnetic field-temperature phase diagram of this material by using pulsed magnetic fields. We found that the low-temperature magnetic order is suppressed by a magnetic field of 43 T for H ∥ [001], which is smaller than the estimated value from mean-field approximation assuming the Γ8 quartet crystal-electric-field ground state and simple antiferromagnetic order. We found that the elastic constant C44 shows softening below the ordering temperature and has a local minimum below 7 T. These facts suggest that the low- temperature state is not a simple antiferromagnetically ordered state. In addition, no elastic anomaly due to rattling modes was found in the present measurements.
    No preview · Article · Feb 2016 · Journal of Physics Conference Series
  • Yusei Shimizu · Yoshinori Haga · Tatsuya Yanagisawa · Hiroshi Amitsuka
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    ABSTRACT: Static dc magnetization M(H) measurements were performed for a single crystal of UBe13 down to 0.1 K in magnetic fields up to 80 kOe for H∥〈100〉 and H∥〈110〉. For both field directions, an unusual magnetic anomaly was observed at HMag*∼20–30 kOe in the superconducting mixed state. This anomaly was seen in the thermal-equilibrium-magnetization curves as well as the increasing- and decreasing-field processes of the raw magnetization curves, implying a change of the thermodynamic property at HMag*. Furthermore, the magnetic anisotropy of the superconducting diamagnetic response is found to be significant above HMag*, possibly associated with the anisotropy of the upper critical field Hc2. Considering the suppression of reduced upper critical field h* and the dramatic decrease of Maki parameter κ2 around 0.9Tc, the paramagnetic effect is present in UBe13. The paramagnetic effect in UBe13 could become anisotropic at low temperature below ∼Tc/2. An alternative explanation of the magnetic anisotropy is however that the anisotropy of the nonlinear susceptibility for the heavy electrons in the vortex cores becomes significant below ∼Tc/2.
    No preview · Article · Jan 2016
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    ABSTRACT: We have performed electrical-resistivity measurements under hydrostatic pressures ranging up to 4.47 GPa on the cubic compound CeAg. A pressure-temperature phase diagram has been revised in a high-pressure range above ∼ 2.1 GPa, where the system is known to enter into an unidentified phase through a first-order phase transition. We have found that the electrical resistivity shows a clear kink anomaly below ∼ 4 K in this unknown phase. The anomaly shifts to lower temperature with increasing pressure, and shows a tendency to reach absolute zero at ∼ 6 GPa, suggesting the presence of a pressure-induced quantum critical point around this pressure. We have also observed that a first-order phase boundary line, which separates the phase diagram into two regions of a tetragonal phase and the unidentified phase, seems to terminate in a critical end point located at (PCEP, TCEP) ∼(3.2 GPa , 200 K). This suggests that the crystal symmetry of the unidentified phase above ∼ 2.1 GPa is also tetragonal.
    No preview · Article · Jun 2015 · Journal of Magnetism and Magnetic Materials
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    ABSTRACT: The elastic properties of localized 5f-electron system U3Pd20Si6 were studied by means of ultrasonic measurements under magnetic fields. We have measured elastic constants C11, (C11-C12)/2, C44 and CL110 = CB + (C11-C12)/6 + C44 in order to check a possible contribution of electric quadrupoles on the magnetically ordered phases of this compound for Γ1 ⊕ Γ3, Γ3, Γ5 and Γ1 ⊕ Γ3 ⊕ Γ5 symmetries elastic response, respectively. We discovered that an elastic anomaly, which is accompanied by ultrasonic attenuation maximum of Γ5- symmetry mode, at around T* ~ 16 K in zero magnetic field and shifts to lower temperatures with increasing magnetic fields. Since the T* seems to be continuously connected to the lower boundary of a 'spin-flop' region in the magnetic field-temperature phase diagram of U3Pd20Si6, we conclude that a fluctuation of the spin-system of the 8c-site ion exists even just below TN and couples to elastic wave via magneto-elastic coupling with Γ5-symmetry quadrupoles of U's 5f electron or local charge distributions of the guest U ion.
    No preview · Article · Mar 2015 · Journal of Physics Conference Series
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    ABSTRACT: We performed synchrotron X-ray diffraction measurements on a small single crystal of [GRAPHICS] with approximate dimensions of [GRAPHICS] . A backscattering diffraction set-up (2 [GRAPHICS] ) in combination with a Si(660) monochromator ensures a high instrumental resolution of [GRAPHICS] , where [GRAPHICS] denotes a lattice-plane spacing and [GRAPHICS] is its spread expressed as the full width at half maximum (FWHM). We carefully measured the (550) Bragg peak in the temperature range between 5 and 25K, and found it to show no signature of broadening and splitting when "Hidden Order (HO)" sets in below 17.5K. Temperature variation of the peak position closely follows the behaviour of the known linear thermal expansion coefficient. Detailed analysis of the peak width reveals that the tetragonal fourfold rotational symmetry of [GRAPHICS] is conserved in HO within the experimental accuracy of the orthorhombicity of [GRAPHICS] . We also found that the (550) peak profile exhibits a temperature-independent fine structure, which indicates that the tetragonal [GRAPHICS] -axis lattice parameter of the used crystal is distributed with a FWHM of [GRAPHICS] .
    No preview · Article · Nov 2014 · Philosophical Magazine

  • No preview · Conference Paper · Jun 2014
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    ABSTRACT: Optical anisotropy in a mysterious phase below 17.5 K of URu2Si2 was investigated by means of polarized light microscopy. No contrast was observed to appear in the polarized microscope images of the tetragonal c-plane below 17.5 K; the present experimental results provide no evidence to confirm, within the experimental accuracy, that the tetragonal 4-fold rotational symmetry is lowered to the 2-fold one, forming a multi-domain structure with a single-domain size of a few tens of microns, as suggested by recent measurements of magnetic torque and cyclotron resonance.
    No preview · Conference Paper · Jun 2014

  • No preview · Conference Paper · Jun 2014
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    ABSTRACT: Positive-muon ($\mu^+$) Knight shifts have been measured in the paramagnetic states of Pr$_{1-x}$Nd$_x$Os$_4$Sb$_{12}$ alloys, where $x =$ 0, 0.25, 0.45, 0.50, 0.55, 0.75, and 1.00. In Pr-substituted NdOs$_4$Sb$_{12}$ ($x \le$ 0.75), but not in NdOs$_4$Sb$_{12}$, Clogston-Jaccarino plots of $\mu^+$ Knight shift~$K$ versus magnetic susceptibility~$\chi$ exhibit an anomalous saturation of $K(\chi)$ at $\sim-$0.5% for large susceptibilities (low temperatures), indicating a reduction of the coupling strength between $\mu^+$ spins and $4f$ paramagnetism for temperatures $\lesssim$ 15~K. We speculate that itinerant Pr$^{3+}$ quadrupolar excitations, invoked to mediate the superconducting Cooper-pair interaction, might modify the $\mu^+$-$4f$ ion indirect spin-spin interaction.
    Full-text · Article · Jun 2014 · Physical Review B
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    ABSTRACT: Muon spin rotation and relaxation ($\mu$SR) experiments have been carried out to characterize magnetic and superconducting ground states in the Pr$_{1-x}$Nd$_x$Os$_4$Sb$_{12}$ alloy series. In the ferromagnetic end compound NdOs$_4$Sb$_{12}$ the spontaneous local field at positive-muon ($\mu^+$) sites below the ordering temperature $T_C$ is greater than expected from dipolar coupling to ferromagnetically aligned Nd$^{3+}$ moments, indicating an additional indirect RKKY-like transferred hyperfine mechanism. For 0.45 $\le x \le$ 0.75, $\mu^+$ spin relaxation rates in zero and weak longitudinal applied fields indicate that static fields at $\mu^+$ sites below $T_C$ are reduced and strongly disordered. We argue this is unlikely to be due to reduction of Nd$^{3+}$ moments, and speculate that the Nd$^{3+}$-$\mu^+$ interaction is suppressed and disordered by Pr doping. In an $x$ = 0.25 sample, which is superconducting below $T_c$ = 1.3 K, there is no sign of "spin freezing" (static Nd$^{3+}$ magnetism), ordered or disordered, down to 25 mK. Dynamic $\mu^+$ spin relaxation is strong, indicating significant Nd-moment fluctuations. The $\mu^+$ diamagnetic frequency shift and spin relaxation in the superconducting vortex-lattice phase decrease slowly below $T_c$, suggesting pair breaking and/or possible modification of Fermi-liquid renormalization by Nd spin fluctuations. For 0.25 $\le x \le$ 0.75, the $\mu$SR data provide evidence against phase separation; superconductivity and Nd$^{3+}$ magnetism coexist on the atomic scale.
    Preview · Article · Apr 2014
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    ABSTRACT: Muon spin rotation and relaxation (μSR) experiments have been carried out to characterize magnetic and superconducting ground states in the Pr1-xNdxOs4Sb12 alloy series. In the ferromagnetic end compound NdOs4Sb12 the spontaneous local field at positive-muon (μ+) sites below the ordering temperature TC is greater than expected from dipolar coupling to ferromagnetically aligned Nd3+ moments, indicating an additional indirect RKKY-like transferred hyperfine mechanism. For 0.45≤x≤0.75, μ+ spin relaxation rates in zero and weak longitudinal applied fields indicate that static fields at μ+ sites below TC are reduced and strongly disordered. We argue this is unlikely to be due to reduction of Nd3+ moments, and speculate that the Nd3+-μ+ interaction is suppressed and disordered by Pr doping. In an x =0.25 sample, which is superconducting below Tc=1.3 K, there is no sign of "spin freezing" (static Nd3+ magnetism), ordered or disordered, down to 25 mK. Dynamic μ+ spin relaxation is strong, indicating significant Nd-moment fluctuations. The μ+ diamagnetic frequency shift and spin relaxation in the superconducting vortex-lattice phase decrease slowly below Tc, suggesting pair breaking and/or possible modification of Fermi-liquid renormalization by Nd spin fluctuations. For 0.25≤x≤0.75, the μSR data provide evidence against phase separation; superconductivity and Nd3+ magnetism coexist on the atomic scale.
    No preview · Article · Mar 2014 · Physical Review B
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    Tatsuya Yanagisawa
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    ABSTRACT: This paper reports recent progress of ultrasonic measurements on URu$_2$Si$_2$, including ultrasonic measurements under hydrostatic pressure, in pulsed-magnetic fields, and the effect of Rh-substitution. The observed changes of the elastic responses shed light on the orthorhombic-lattice instability with $\Gamma_3$-symmetry existing within the hidden order and the hybridized 5$f$-electron states of URu$_2$Si$_2$.
    Preview · Article · Dec 2013 · Philosophical Magazine
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    ABSTRACT: We have measured the elastic constant (C11-C12)/2 in URu2Si2 by means of high-frequency ultrasonic measurements in pulsed magnetic fields H || [001] up to 61.8 T in a wide temperature range from 1.5 to 116 K. We found a reduction of (C11-C12)/2 that appears only in the temperature and magnetic field region in which URu2Si2 exhibits a heavy-electron state and hidden-order. This change in (C11-C12)/2 appears to be a response of the 5f-electrons to an orthorhombic and volume conservative strain field \epsilon_xx-\epsilon_yy with {\Gamma}3-symmetry. This lattice instability is likely related to a symmetry-breaking band instability that arises due to the hybridization of the localized f electrons with the conduction electrons, and is probably linked to the hidden-order parameter of this compound.
    Full-text · Article · Nov 2013 · Physical Review B
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    ABSTRACT: The pseudo ternary system Pr1-xNdxOs4Sb12 has been used as a model system to investigate the effect of ferromagnetism (FM) on the unconventional superconductivity (SC) and quantum critical behavior of PrOs4Sb12 [1]. SC in this system disappears near a critical concentration xcr,1˜0.58 and FM appears above xcr,2˜0.33 [1,2]. The new μSR measurements have been performed on samples with x = 0.25, 0.75, and 1. For x = 1 and 0.75, the estimated frozen moments agree with the Nd^3+ CEF ground state moment. For x = 0.25, neither time reversal symmetry breaking nor evidence of freezing of Nd^3+ spins was observed in zero-field μSR measurements, the behavior of which is very different than what is observed for x = 0.45-0.55 [2]. In the SC state, an unexpected linear T dependence of the Gaussian relaxation rate was also found in the transverse field μSR data for x = 0.25, which is different than the plateau in PrOs4Sb12 below 1.3K [3]. [1] Ho, et al., PRB 83, 024511 (2011).[2] Ho, et al., 2010 APS March Meeting, A38.00005 (2010). [3] MacLaughlin et al., PRL 105, 019701 (2010).
    No preview · Article · Mar 2013
  • B. Somsanuk · H. A. Anderson · P.-C. Ho · M. B. Maple · T. Yanagisawa
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    ABSTRACT: The filled skutterudite compound, PrOs4Sb12, displays unconventional superconductivity at a relatively low critical temperature Tc=1.85K. The underlying physics behind this heavy fermion superconducting compound is unknown. To gain better insight into this phenomenon, we studied the effect of ferromagnetism on the unconventional superconductivity of PrOs4Sb12 by using neodymium substituted samples of Pr1-xNdxOs4Sb12. The heat capacities of the samples with x = 1, 0.75, 0.5, and 0.25 were measured using finite heat pulse relaxation calorimetry in a cryocooler system from 11K to 300K. The electronic specific heat coefficient γ of NdOs4Sb12 (estimated from the contributions from conduction electrons, Debye and Einstein lattice modes, CEF effects of rare earth atoms) is found to be ˜60 mJ/K^2-mol, which is much smaller than the previously estimated value γ˜520 mJ/K^2-mol (by using the low temperature specific heat data), but is still relatively large compared to values for simple metals. In addition, the high temperature specific heat of all four samples are approximately the same.
    No preview · Article · Mar 2013
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    ABSTRACT: We have studied anomalous upper critical field Bc2(T) of a single crystal of UBe13 by DC magnetization measurements down to 0.14 K and up to 8 T. We have observed a broad anomaly and a peak effect below Bc2 in magnetization curves. Although a possibility of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state has been proposed as an origin of the unusual upper critical field by previous works, our results have shown that thermal equilibrium magnetization curves reveal no step-like behavior, which could be observed at 1st-order phase transition from a superconducting mixed state to the FFLO state. We have also investigated anisotropy of Bc2 for B || <001> and B || <110>, and found that Bc2 for B || <001< is larger than Bc2 for B || <110> below ~ 0.5 K. These results might indicate that the anomalous upward curvature of Bc2 in UBe13 is related to anisotropy of Bc2 rather than the FFLO state.
    Preview · Article · Dec 2012 · Journal of Physics Conference Series
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    ABSTRACT: We have measured the electrical resistivity of clathrate Ce3Pd20Ge6 under high pressure up to 3.86 GPa in order to investigate pressure effects on two successive phase transitions: O02-type ferroquadrupole order on Ce-8c site at TQ = 1.2 K and antiferromagnetic order on Ce-4a site at TN = 0.75 K. With applying pressure, TQ stays nearly constant at low pressures and gradually decreases above 2 GPa, while TN first increases and then decreases above 2.5 GPa. From these results, critical pressures, where TN and TQ become 0, are roughly estimated to be around 5-6 GPa. In addition, we found that the magnetic resistivity, which is obtained by subtracting the resistivity of La3Pd20Ge6 from that of Ce3Pd20Ge6, exhibits -InT dependence in two different temperature ranges, suggesting presence of two different Kondo temperatures originated in the two crystallographic Ce-sites.
    No preview · Article · Dec 2012 · Journal of Physics Conference Series
  • T. Yanagisawa · H. Saito · Y. Watanabe · Y. Shimizu · H. Hidaka · H. Amitsuka
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    ABSTRACT: Ultrasonic investigations of the elastic constants of non-5f compound ThRu2Si2 were performed in order to highlight possible quadrupolar response in the elastic constants of heavy fermion compound URu2Si2, by using the ThRu2Si2 for backgrounds to subtract the phonon contributions in the elastic constants of URu2Si2. We confirmed that the all-elastic constants of ThRu2Si2 show no elastic anomaly, i.e., increasing monotonically and saturating toward low temperatures, which can be understood regular phonon contributions for the solid states. The background-subtracted (C11-C12)/2 of URu2Si2 keeps decreasing with decreasing temperatures from 300 K, while other share modes C44 and C66 show little change. These contrasts suggest that the Γ3-type quadrupole moment O22 will be still dominant and active in URu2Si2 at low temperatures.
    No preview · Article · Dec 2012 · Journal of Physics Conference Series
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    ABSTRACT: We have performed ultrasonic measurements on single-crystalline URu2Si2 with pulsed magnetic fields, in order to check for possible lattice instabilities due to the hybridized state and the hidden-order state of this compound. The elastic constant (C11-C12)/2, which is associated with a response to the {\Gamma}3-type symmetry-breaking (orthorhombic) strain field, shows a three-step increase at H > 35 T for H || c at low temperatures, where successive meta-magnetic transitions are observed in the magnetization. We discovered a new fact that the absolute change of the softening of (C11-C12)/2 in the temperature dependence is quantitatively recovered at the suppression of hybridized-electronic state and the hidden order in high-magnetic field for H \perp c associated with the successive transitions. The present results suggest that the {\Gamma}3-type lattice instability, is related to both the emergence of the hybridized electronic state and the hidden-order parameter of URu2Si2. On the other hand, magnetic fields H || [100] and [110] enhance the softening of (C11-C12)/2 in the hidden order phase, while no step-like anomaly is observed up to 68.7 T. We discuss the limitation of the localized-electron picture for describing these features of URu2Si2 by examination of a crystalline electric field model in terms of mean-field theory.
    Full-text · Article · Nov 2012 · Journal of the Physical Society of Japan
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    ABSTRACT: We have performed precise dc magnetization measurements for a single crystal of UBe_{13} down to 0.14 K, up to 80 kOe. We observed a magnetic anomaly in the superconducting (SC) mixed state at a field, named H_{Mag}^{*} (∼26  kOe, at 0.14 K), implying that UBe_{13} has a magnetically unusual SC state. We studied the magnetization curves of UBe_{13}, assuming that the H_{Mag}^{*} anomaly originates from (1) and unusual SC diamagnetic response, or (2) a peculiarity of the normal-state magnetization due to vortices in the SC mixed state. The origin of the H_{Mag}^{*} anomaly is discussed.
    No preview · Article · Nov 2012 · Physical Review Letters

Publication Stats

727 Citations
136.17 Total Impact Points

Institutions

  • 2008-2016
    • Hokkaido University
      • • Division of Physics
      • • Graduate School of Science
      • • Creative Research Institution
      Sapporo, Hokkaido, Japan
  • 2005-2010
    • University of California, San Diego
      • Department of Physics
      San Diego, CA, United States
  • 2002-2009
    • Niigata University
      • Graduate School of Science and Technology
      Niahi-niigata, Niigata, Japan
  • 2007
    • Applied Physical Sciences
      Groton, Connecticut, United States