K. Kakurai
Japan Atomic Energy Agency
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Featured researches published by K. Kakurai.
Nature | 2005
Naoshi Ikeda; Hiroyuki Ohsumi; Kenji Ohwada; Kenji Ishii; Toshiya Inami; K. Kakurai; Youichi Murakami; Kenji Yoshii; Shigeo Mori; Y. Horibe; Hijiri Kito
Ferroelectric materials are widely used in modern electric devices such as memory elements, filtering devices and high-performance insulators. Ferroelectric crystals have a spontaneous electric polarization arising from the coherent arrangement of electric dipoles (specifically, a polar displacement of anions and cations). First-principles calculations and electron density analysis of ferroelectric materials have revealed that the covalent bond between the anions and cations, or the orbital hybridization of electrons on both ions, plays a key role in establishing the dipolar arrangement. However, an alternative model—electronic ferroelectricity—has been proposed in which the electric dipole depends on electron correlations, rather than the covalency. This would offer the attractive possibility of ferroelectric materials that could be controlled by the charge, spin and orbital degrees of freedom of the electron. Here we report experimental evidence for ferroelectricity arising from electron correlations in the triangular mixed valence oxide, LuFe2O4. Using resonant X-ray scattering measurements, we determine the ordering of the Fe2+ and Fe3+ ions. They form a superstructure that supports an electric polarization consisting of distributed electrons of polar symmetry. The polar ordering arises from the repulsive property of electrons—electron correlations—acting on a frustrated geometry.
Physical Review Letters | 2001
O. Cepas; K. Kakurai; L. P. Regnault; T. Ziman; Jean-Paul Boucher; Naofumi Aso; Masakazu Nishi; Hiroshi Kageyama; Y. Ueda
The Dzyaloshinski-Moriya interaction partially lifts the magnetic frustration of the spin-1/2 oxide SrCu(2)(BO(3))(2). It explains the fine structure of the excited triplet state and its unusual magnetic field dependence, as observed in previous ESR and new neutron inelastic scattering experiments. We claim that it is mainly responsible for the dispersion. We propose also a new mechanism for the observed ESR transitions forbidden by standard selection rules, which relies on an instantaneous Dzyaloshinski-Moriya interaction induced by spin-phonon couplings.
Journal of the Physical Society of Japan | 2003
Minoru Soda; Yukio Yasui; Toshiaki Fujita; Takeshi Miyashita; Masatoshi Sato; K. Kakurai
Neutron diffraction studies have been carried out on a single crystal of oxygen-deficient perovskite TbBaCo 2 O 5.5 in the temperature range of 7–370 K. There have been observed several magnetic or...
Physical Review Letters | 2005
J. H. Chung; Masaaki Matsuda; Seunghun Lee; K. Kakurai; Hiroaki Ueda; Taku Sato; H. Takagi; K. P. Hong; S. Park
Using elastic and inelastic neutron scattering we show that a cubic spinel, CdCr2O4, undergoes an elongation along the c axis (c > a = b) at its spin-Peierls-like phase transition at T(N) = 7.8 K. The Néel phase (T < T(N)) has an incommensurate spin structure with a characteristic wave vector Q(M) = (0, delta,1) with delta approximately 0.09 and with spins lying on the ac plane. This is in stark contrast to another well-known Cr-based spinel, ZnCr2O4, that undergoes a c-axis contraction and a commensurate spin order. The magnetic excitation of the incommensurate Néel state has a weak anisotropy gap of 0.6 meV and it consists of at least three bands extending up to 5 meV.
Nature Communications | 2012
L. J. Chang; Shigeki Onoda; Y. Su; Ying-Jer Kao; Ku Ding Tsuei; Yukio Yasui; K. Kakurai; Martin R. Lees
In a class of frustrated magnets known as spin ice, magnetic monopoles emerge as classical defects and interact via the magnetic Coulomb law. With quantum-mechanical interactions, these magnetic charges are carried by fractionalized bosonic quasi-particles, spinons, which can undergo Bose–Einstein condensation through a first-order transition via the Higgs mechanism. Here, we report evidence of a Higgs transition from a magnetic Coulomb liquid to a ferromagnet in single-crystal Yb2Ti2O7. Polarized neutron scattering experiments show that the diffuse [111]-rod scattering and pinch-point features, which develop on cooling are suddenly suppressed below TC~0.21 K, where magnetic Bragg peaks and a full depolarization of the neutron spins are observed with thermal hysteresis, indicating a first-order ferromagnetic transition. Our results are explained on the basis of a quantum spin-ice model, whose high-temperature phase is effectively described as a magnetic Coulomb liquid, whereas the ground state shows a nearly collinear ferromagnetism with gapped spin excitations.
Physical Review B | 2011
Shintaro Ishiwata; Masashi Tokunaga; Y. Kaneko; Daisuke Okuyama; Y. Tokunaga; S. Wakimoto; K. Kakurai; T. Arima; Y. Taguchi; Y. Tokura
A helical spin texture is of great current interest for a host of novel spin-dependent transport phenomena. We report a rich variety of nontrivial helimagnetic phases in the simple cubic perovskite
Journal of the Physical Society of Japan | 2006
Minoru Soda; Yukio Yasui; Taketo Moyoshi; Masatoshi Sato; Naoki Igawa; K. Kakurai
{\mathrm{SrFeO}}_{3}
Physical Review B | 2008
J. H. Kim; Seunghun Lee; S. I. Park; M. Kenzelmann; A. B. Harris; J. Schefer; Jae Ho Chung; Charles F. Majkrzak; Masayasu Takeda; S. Wakimoto; S. Park; Sang-Wook Cheong; Masaaki Matsuda; Hiroyuki Kimura; Yasutoshi Noda; K. Kakurai
under magnetic fields up to 42 T. Magnetic and resistivity measurements revealed that the proper-screw spin phase proposed for
Physical Review B | 1999
M. Matsuda; T. Yosihama; K. Kakurai; G. Shirane
{\mathrm{SrFeO}}_{3}
Physical Review B | 2003
A. Oosawa; Masashi Fujisawa; K. Kakurai; H. Tanaka
can be subdivided into at least five kinds of ordered phases. Near the multicritical point, an unconventional anomalous Hall effect was found to show up and was interpreted as due to a possible long-period noncoplanar spin texture with scalar spin chirality.