Y. Taguchi

RIKEN, Вако, Saitama, Japan

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Publications (348)

  • [Show abstract] [Hide abstract] ABSTRACT: Competing exchange interactions can produce complex magnetic states associated with spin-induced electric polarizations. With competing interactions on alternating triangular and kagome layers, CaBaCo$_4$O$_7$ (CBCO) may have one of the largest measured spin-induced polarizations of $\sim 1700$ nC/cm$^2$ below its ferrimagnetic transition temperature at 70 K. Powder neutron-diffraction data, magnetization measurements, and spin-wave resonance frequencies in the THz range reveal that the complex spin order of multiferroic CBCO can be described as a triangular array of $c$-axis chains ferromagnetically coupled to each other in the $ab$ plane. Magnetostriction for a set of spin bonds within each chain produces the large spin-induced polarization of CBCO.
    Article · Aug 2016
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    [Show abstract] [Hide abstract] ABSTRACT: The structural, magnetic, and dielectric properties of Pb3Mn7O15 have been investigated using high-quality single crystals. Pb3Mn7O15 adopts a pseudo-hexagonal orthorhombic structure, with partially filled Kagomé layers connected by ribbons of edge-sharing MnO6 octahedra and intercalated Pb cations. There are 9 inequivalent sites in the structure for the Mn ions, which exist both as Mn3+ and Mn4+. Pb3Mn7O15 undergoes an antiferromagnetic transition below TN ~ 67 K, with significant geometric frustration. Neutron powder diffraction on crushed single crystals allowed us to determine the low-temperature antiferromagnetic magnetic structure. We discuss the magnetic interaction pathways in the structure and possible interplay between the structural distortions imprinted by the lone-electron pair of Pb2+ cations and Mn3+/Mn4+ charge ordering.
    Full-text Article · Jul 2016 · Journal of Materials Science Materials in Electronics
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    K. Karube · J. S. White · N. Reynolds · [...] · Y. Taguchi
    [Show abstract] [Hide abstract] ABSTRACT: Skyrmions, topologically-protected nanometric spin vortices, are being investigated extensively in various magnets. Among them, many of structurally-chiral cubic magnets host the triangular-lattice skyrmion crystal (SkX) as the thermodynamic equilibrium state. However, this state exists only in a narrow temperature and magnetic-field region just below the magnetic transition temperature $T_\mathrm{c}$, while a helical or conical magnetic state prevails at lower temperatures. Here we describe that for a room-temperature skyrmion material, $\beta$-Mn-type Co$_8$Zn$_8$Mn$_4$, a field-cooling via the equilibrium SkX state can suppress the transition to the helical or conical state, instead realizing robust metastable SkX states that survive over a very wide temperature and magnetic-field region, including down to zero temperature and up to the critical magnetic field of the ferromagnetic transition. Furthermore, the lattice form of the metastable SkX is found to undergo reversible transitions between a conventional triangular lattice and a novel square lattice upon varying the temperature and magnetic field. These findings exemplify the topological robustness of the once-created skyrmions, and establish metastable skyrmion phases as a fertile ground for technological applications.
    Full-text Article · Jun 2016
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    M. Kriener · T. Nakajima · Y. Kaneko · [...] · Y. Taguchi
    [Show abstract] [Hide abstract] ABSTRACT: Cross-control of a material property - manipulation of a physical quantity (e.g., magnetisation) by a nonconjugate field (e.g., electrical field) – is a challenge in fundamental science and also important for technological device applications. It has been demonstrated that magnetic properties can be controlled by electrical and optical stimuli in various magnets. Here we find that heat-treatment allows the control over two competing magnetic phases in the Mn-doped polar semiconductor GeTe. The onset temperatures Tc of ferromagnetism vary at low Mn concentrations by a factor of five to six with a maximum Tc ≈ 180 K, depending on the selected phase. Analyses in terms of synchrotron x-ray diffraction and energy dispersive x-ray spectroscopy indicate a possible segregation of the Mn ions, which is responsible for the high-Tc phase. More importantly, we demonstrate that the two states can be switched back and forth repeatedly from either phase by changing the heat-treatment of a sample, thereby confirming magnetic phase-change-memory functionality.
    Full-text Article · May 2016 · Scientific Reports
  • [Show abstract] [Hide abstract] ABSTRACT: Magnetic bubbles with winding number S=1 are topologically equivalent to skyrmions. Here we report the discovery of helicity (in-plane magnetization-swirling direction) reversal of skyrmions, while keeping their hexagonal lattice form, at above room temperature in a thin hexaferrite magnet. We have observed that the frequency of helicity reversals dramatically increases with temperature in a thermally activated manner, revealing that the generation energy of a kink-soliton pair for switching helicity on a skyrmion rapidly decreases towards the magnetic transition temperature.
    Article · Apr 2016
  • T. Suzuki · A. Kikkawa · Y. Tokura · Y. Taguchi
    [Show abstract] [Hide abstract] ABSTRACT: We investigated the variation in electronic, thermal, and thermoelectric properties of skutterudite IrSb3 upon filling the voids with alkaline (Na or K) or alkaline-earth atoms (Sr or Ba). Specific heat measurements revealed that the fillers donate electrons with high effective mass, which dominate the electric transport properties of the system. Vibrations associated with the filler additionally contribute to the specific heat, and also scatter phonons efficiently in conjunction with the static disorder, giving rise to the reduced thermal conductivity. The dimensionless thermoelectric figure of merit ZT increases with temperature and electron concentration, and reaches to 0.44 for Ba0.4Ir4Sb12 at 685 K. The observed features for the filled IrSb3 are similar to those of filled CoSb3, indicating that n-type filled skutterudite antimonides have a potential as good thermoelectric materials universally.
    Article · Apr 2016
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    [Show abstract] [Hide abstract] ABSTRACT: We report the experimental observation of longitudinal spin Seebeck effect in a multiferroic helimagnet Ba0.5Sr1.5Zn2Fe12O22. Temperature gradient applied normal to Ba0.5Sr1.5Zn2Fe12O22/Pt interface generates inverse spin Hall voltage of spin current origin in Pt, whose magnitude was found to be proportional to bulk magnetization of Ba0.5Sr1.5Zn2Fe12O22 even through the successive magnetic transitions among various helimagnetic and ferrimagnetic phases. This finding demonstrates that the helimagnetic spin wave can be an effective carrier of spin current. By controlling the population ratio of spin-helicity domains characterized by clockwise/counter-clockwise manner of spin rotation with use of poling electric field in the ferroelectric helimagnetic phase, we found that spin-helicity domain distribution does not affect the magnitude of spin current injected into Pt. The results suggest that the spin-wave spin current is rather robust against the spin-helicity domain wall, unlike the case with the conventional ferromagneticdomain wall.
    Full-text Article · Mar 2016 · APL Materials
  • [Show abstract] [Hide abstract] ABSTRACT: The magnetic phase diagram of a polar ferrimagnet CaBaFe4O7 with a magnetic easy axis has been investigated by measurements of magnetization, specific heat, and magnetoelectricity. A ferrimagnetic transition takes place at TC1=275 K within the orthorhombic phase followed by a second magnetic transition at TC2=211 K. Below TC2, successive metamagnetic transitions occur for magnetic fields applied perpendicular to the easy axis, implying a sequential emergence of magnetic states which are neither collinear nor coplanar. The observation of the static magnetoelectric effect was limited to temperatures below 120 K due to the conducting nature of the crystals at higher temperatures. The magnitude of the ferroelectric polarization shows large changes between the different field-induced magnetic phases. The low-field state is characterized by a large linear magnetoelectric coefficient of αcc=39 ps/m, while a gigantic polarization change of ΔP=850 μC/m2 is observed for μoH=14 T applied along the easy axis.
    Article · Jan 2016
  • Taigen Sase · Hidetaka Onodera · Masashi Uchida · [...] · Yoshio Taguchi
    [Show abstract] [Hide abstract] ABSTRACT: Purpose: The aim of this study was to examine the relationship between stress index (SI) calculated by dividing blood sugar (BS) concentration by serum potassium (K) level at the time of initial examination and both severity and outcome of subarachnoid hemorrhage (SAH). Methods: We retrospectively analyzed 108 patients with SAH. Severity of SAH was assessed using the World Federation of Neurosurgical Societies (WFNS) classification system. The moderate group included patients with WFNS grade I–III, with all other patients classified into the severe group. Outcomes at the time of discharge were assessed using the Glasgow Outcome Scale. Good outcome group included patients with good recovery or moderate disability, while others were classified to the poor outcome group. Biochemical factors evaluated at the initial examination included K, BS, and SI. Results: BS and SI were significantly higher in the severe group than in the moderate group (p<0.01). These indicators were also significantly higher in the poor outcome group than in the good outcome group (p<0.01). Some patients in the moderate group fell into the poor outcome group. In those patients, SI was significantly high. Conclusion: SI was significantly high in patients with severe SAH and in patients with poor outcome. Patients with high SI who are classified into the moderate group might show poor clinical outcomes.
    Article · Jan 2016 · Nosotchu
  • Homare NAKAMURA · Taigen SASE · Daisuke WAKUI · [...] · Yoshio TAGUCHI
    [Show abstract] [Hide abstract] ABSTRACT: Dural arteriovenous fistulas (DAVFs) are generally present in the transverse-sigmoid sinus as well as the cavernous sinus. To date, endovascular surgery has been mainstream; however, direct surgical treatment seems to be primarily limited to anterior skull base DAVFs. We herein report two cases of non-sinus-type DAVF located in the middle cranial fossa that were successfully treated with direct surgery. Both were symptomatic and angiographically classified as Cognard type IV. The first case was referred to our institution because of recurrence of a left middle fossa DAVF seven years after initial treatment with transarterial coil embolization (TAE). Drainer obliteration was performed using the subtemporal approach. The second case had severe headache with prominent clinical features similar to those of a carotid cavernous sinus fistula. TAE was applied to the branches of the right external carotid artery to reduce the flow rate. Drainer obliteration was performed without difficulty using the conventional frontotemporal approach.The cortical vein-draining DAVF, classified as Cognard type III or type IV, presents a high risk of intracranial hemorrhage. When diagnosed, they should be treated completely, as early as possible. The aforementioned drainer obliteration appeared to be the best way to cure the DAVF. Endovascular surgery before direct surgical treatment was effective to reduce shunt flow and to enable an easy access to the shunt point.
    Article · Jan 2016 · Surgery for Cerebral Stroke
  • [Show abstract] [Hide abstract] ABSTRACT: Spin excitations were studied by absorption spectroscopy in CaBaCo4O7 which is a type-I multiferroic compound with the largest magnetic-order induced ferroelectric polarization ({\Delta}P=17mC/m2) reported, so far. We observed two optical magnon branches: a solely electric dipole allowed one and a mixed magnetoelectric resonance. The entangled magnetization and polarization dynamics of the magnetoelectric resonance gives rise to unidirectional light absorption, i.e. that magnon mode absorbs the electromagnetic radiation for one propagation direction but not for the opposite direction. Our systematic study of the magnetic field and temperature dependence of magnon modes provides information about the energies and symmetries of spin excitations, which is required to develop a microscopic spin model of CaBaCo4O7.
    Article · Dec 2015 · Physical Review B
  • [Show abstract] [Hide abstract] ABSTRACT: A series of high-pressure measurements including resistivity, ac and dc magnetic susceptibility, neutron powder diffraction, and synchrotron x-ray diffraction were performed to investigate the crystal structure and electronic states of the itinerant ferromagnet SrCoO3. Two pressure-induced phase transitions were observed at about 1.1 and 45 GPa, corresponding to a spin reorientation and a spin-state transition, respectively, while the cubic crystal structure was stable with pressure up to 60.0 GPa. The origins of these electronic state changes are discussed and rationalized in the light of first-principles calculations.
    Article · Nov 2015 · Physical Review B
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    [Show abstract] [Hide abstract] ABSTRACT: Magnetic skyrmions, swirling nanometric spin textures, have been attracting increasing attention by virtue of their potential applications for future memory technology and their emergent electromagnetism. Despite a variety of theoretical proposals oriented towards skyrmion-based electronics (that is, skyrmionics), few experiments have succeeded in creating, deleting and transferring skyrmions, and the manipulation methodologies have thus far remained limited to electric, magnetic and thermal stimuli. Here, we demonstrate a new approach for skyrmion phase control based on a mechanical stress. By continuously scanning uniaxial stress at low temperatures, we can create and annihilate a skyrmion crystal in a prototypical chiral magnet MnSi. The critical stress is merely several tens of MPa, which is easily accessible using the tip of a conventional cantilever. The present results offer a new guideline even for single skyrmion control that requires neither electric nor magnetic biases and consumes extremely little energy.
    Full-text Article · Oct 2015 · Nature Communications
  • [Show abstract] [Hide abstract] ABSTRACT: We have performed time-resolved (TR) core-level and valence-band angle-resolved (AR) photoemission spectroscopy (PES) to investigate ultrafast dynamics of an electron-doped topological insulator Cu0.17Bi2Se3. The Bi 5d5/2 line was composed of a single peak and exhibited broadening upon both heating and pumping, which we interpreted as a change of phonon temperature (Tp), in the surface region. The electronic dynamics and electron temperature (Te), on the other hand, were determined with near-EF TRARPES. The transient temperature deduced from core-level TRPES shows a similar behavior with Te deduced from near-EF TRARPES. This similar behavior of Tp and Te can be reproduced not by a simple two-temperature model but by a modified one, although we cannot exclude a possibility that core-level broadening also reflects Te.
    Article · Sep 2015 · Physical Review B
  • [Show abstract] [Hide abstract] ABSTRACT: Topologically stable matters can have a long lifetime, even if thermodynamically costly, when the thermal agitation is sufficiently low. A magnetic skyrmion lattice (SkL) represents a unique form of long-range magnetic order that is topologically stable, and therefore, a long-lived, metastable SkL can form. Experimental observations of the SkL in bulk crystals, however, have mostly been limited to a finite and narrow temperature region in which the SkL is thermodynamically stable; thus, the benefits of the topological stability remain unclear. Here, we report a metastable SkL created by quenching a thermodynamically stable SkL. Hall-resistivity measurements of MnSi reveal that, although the metastable SkL is short-lived at high temperatures, the lifetime becomes prolonged (>> 1 week) at low temperatures. The manipulation of a delicate balance between thermal agitation and the topological stability enables a deterministic creation/annihilation of the metastable SkL by exploiting electric heating and subsequent rapid cooling, thus establishing a facile method to control the formation of a SkL.
    Article · Jun 2015
  • Yohtaro Sakakibara · Yoshio Taguchi · Homare Nakamura · [...] · Yoshio Aida
    [Show abstract] [Hide abstract] ABSTRACT: Here, we report a case of dural cavernous angioma. A 54-year-old man presented with headache in his right frontal area for the previous few weeks. Computed tomography(CT)and magnetic resonance imaging revealed a well-demarcated extramedullary mass, 3 x 2.5cm in size, within the subdural space at the right frontal region. The mass was not enhanced on a contrast-enhanced CT scan, and heterogeneously enhanced after administration of Gd-DTPA on magnetic resonance images. Cerebral angiography revealed an avascular mass. Right frontal craniotomy was performed. On surgery, the mass was found to be mainly extramedullar, and partially intramedullar. No adhesion between the mass and the overlying dura was observed. It was removed in an en bloc fashion. The pathological diagnosis was cavernous angioma. The patient's headache was resolved soon after surgery. Cavernous angiomas are usually intramedullar in the subcortical white matter of the cerebral hemispheres;extramedullary cavernous angiomas are rare. Extramedullary dural cavernous angiomas located in the subdural space at the cerebral convexity are extremely rare. They usually present with headache or mass signs, and resemble meningioma radiologically. During surgery they are easily resected with minimal blood loss. Dural cavernous angiomas should be considered in the differential diagnosis of intradural extramedullary mass at the cerebral convexity.
    Article · May 2015 · No shinkei geka. Neurological surgery
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    [Show abstract] [Hide abstract] ABSTRACT: Skyrmions, topologically protected vortex-like nanometric spin textures in magnets, have been attracting increasing attention for emergent electromagnetic responses and possible technological applications for spintronics. In particular, metallic magnets with chiral and cubic/tetragonal crystal structure may have high potential to host skyrmions that can be driven by low electrical current excitation. However, experimental observations of skyrmions have so far been limited to below room temperature for the metallic chiral magnets, specifically for the MnSi-type B20 compounds. Toward technological applications, it is crucial to transcend this limitation. Here we demonstrate the formation of skyrmions with unique spin helicity both at and above room temperature in a family of cubic chiral magnets: beta-Mn-type Co-Zn-Mn alloys with a different chiral space group from that of B20 compounds. Lorentz transmission electron microscopy (LTEM), magnetization, and small angle neutron scattering (SANS) measurements unambiguously reveal the formation of a skyrmion crystal under the application of magnetic field (H<~1 kOe) in both thin- plate (thickness<150 nm) and bulk forms.
    Full-text Article · Mar 2015 · Nature Communications
  • M. Kriener · A. Kikkawa · T. Suzuki · [...] · Y. Taguchi
    [Show abstract] [Hide abstract] ABSTRACT: We present a study on the modification of the electronic structure and hole-doping effect for the layered dichalcogenide WSe_2 with a multi-valley band structure, where Ta is doped on the W site along with a partial substitution of Te for its lighter counterpart Se. By means of band-structure calculations and specific-heat measurements, the introduction of Te is theoretically and experimentally found to change the electronic states in WSe_2. While in WSe_2 the valence-band maximum is located at the Gamma point, the introduction of Te raises the bands at the K point with respect to the Gamma point. In addition, thermal-transport measurements reveal a smaller thermal conductivity at room temperature of W_1-xTa_xSe_1.6Te_0.4 than reported for W_1-xTa_xSe_2. However, when approaching 900 K, the thermal conductivities of both systems converge while the resistivity in W_1-xTa_xSe_1.6Te_0.4 is larger than in W_1-xTa_xSe_2, leading to comparable but slightly smaller values of the figure of merit in W_1-xTa_xSe_1.6Te_0.4.
    Article · Feb 2015 · Physical Review B
  • [Show abstract] [Hide abstract] ABSTRACT: A synchrotron x-ray diffraction study of metal-insulator transitions in W-doped ${\text{VO}}_{2} ({\text{V}}_{1$-${}x}{\text{W}}_{x}{\text{O}}_{2})$ thin films has been carried out. The insulating phase for $x$\le${}0.07$ exhibits cell-doubling with the V dimerization similar to bulk ${\text{VO}}_{2}$, while the insulating phase for $x$\ge${}0.11$ does not. This result suggests that the electronic structure of the $x$\ge${}0.11$ insulators should be different from that of the $x$\le${}0.07$ ones and bulk-insulating phase of ${\text{VO}}_{2}$. The temperature and $x$ dependence of superlattice reflection as observed casts doubt about the direct relationship between the dimerization of V ions and metal-insulator transition. The temperature dependence of the electrical resistivity rather implies the Mott-Anderson localization nature of the insulating phases. X-ray-induced persistent phase transitions are observed at low temperatures in each insulating phase in the vicinity of the boundary to the metallic phase regardless of the difference in the electronic structure. Gradual peak shift suggests that the x-ray irradiation produces nanometer metallic regions.
    Article · Feb 2015 · Physical Review B
  • Homare Nakamura · Tadashi Kudo · Shinji Ohkubo · [...] · Yoshio Taguchi
    Article · Jan 2015 · Spinal Surgery

Publication Stats

5k Citations

Institutions

  • 2013
    • RIKEN
      Вако, Saitama, Japan
  • 1978-2009
    • Tohoku University
      • • Institute for Materials Research
      • • Department of Medical Genetics
      • • Division of Surgery
      Sendai-shi, Miyagi, Japan
  • 1993-2007
    • The University of Tokyo
      • • Department of Applied Physics
      • • Department of Physics
      Tokyo, Tokyo-to, Japan
  • 1996
    • Hokkaido University
      • Division of Physics
      Sapporo, Hokkaidō, Japan