Browsing by Author "Okamoto, J."

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Electronic structure investigation of a charge density wave coupled to a metal-to-metal transition in Ce3Co4Sn13
(2018-12-18)
Singh, A.
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Huang, H. Y.
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Chin, Y. Y.
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Liao, Y. F.
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Huang, T. C.
We study the electronic structure of the skutterudite Ce3Co4Sn13, which is known to exhibit a charge density wave (CDW) transition, at temperature T-CDW similar to 160 K, coupled to a metal-to-metal transition. We use temperature dependent hard x-ray photoemission spectroscopy (HAXPES) and x-ray absorption spectroscopy (XAS) to investigate the occupied and unoccupied electronic states of Ce3Co4Sn13. The Co 2p and Sn 3p core level spectra show small but finite shifts in binding energy positions across T-CDW while Ce 3d core level spectra do not show any change across the transition. The Ce M-4,M-5-edge XAS spectrum compared with calculations indicate a typical trivalent ionic Ce3+ spectral shape, ruling out Kondo screening in Ce3Co4Sn13. In contrast, the Co L-2,L-3-edge XAS spectrum compared with a calculated spectrum shows evidence for hybridization with neighboring Sn atoms in a trigonal prismatic co-ordination. Temperature dependent XAS across the Co L-2,L-3-edge shows a small shift across T-CDW, consistent with HAXPES results. Detailed XAS measurements as a function of temperature show that the spectral shifts occur with a hysteresis across T-CDW , indicative of a first-order transition. Valence band spectra show a normal Fermi edge above and below T-CDW. The Co 3d states are observed at a binding energy of similar to 2 eV while the Ce 4f states occur as a weak feature within 0.5 eV of the Fermi level. The results suggest an unusual CDW transition coupled to a metal-to-metal transition in Ce3Co4Sn13.
Magnetic ground state and transition of a quantum multiferroic LiCu(2)O(2)
(2008-08-15)
Huang, S. W.
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Huang, D. J.
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Okamoto, J.
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Mou, C. Y.
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Wu, W. B.
Based on resonant soft x-ray magnetic scattering, we report that LiCu(2)O(2) exhibits a large interchain coupling which suppresses quantum fluctuations along spin chains, and a quasi-2D short-range magnetic order prevails at temperatures above the magnetic transition. These observations unravel the fact that the ground state of LiCu(2)O(2) possesses long-range 2D-like incommensurate magnetic order rather than being a gapped spin liquid as expected from the nature of quantum spin-1/2 chains. In addition, the spin coupling along the c axis is found to be essential for inducing electric polarization.
Magnetic order of LiCu2O2 studied by resonant soft x-ray magnetic scattering
(2008-08-01)
Huang, S. W.
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Huang, D. J.
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Okamoto, J.
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Wu, W. B.
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Chen, C. T.
We present results of resonant soft x-ray magnetic scattering measurements on single crystals of LiCu2O2 to address the magnetic order. LiCu2O2 exhibits a long-range magnetic order incommensurate with the lattice, and the modulation vector is (0.5, zeta, 0) in reciprocal lattice units with zeta similar to 0.174, depending upon the temperature. The spin-spin correlation length along the spin chain deduced from the width of momentum scan is larger than 2100 angstrom. The inter-chain correlation length that lies within the ab plane was discovered to be substantial, similar to 690 angstrom. (c) 2008 Elsevier Ltd. All rights reserved.
Multiferroic nanoregions and a memory effect in cupric oxide
(2010-05-01)
Wu, W. B.
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Huang, D. J.
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Okamoto, J.
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Huang, S. W.
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Sekio, Y.
We report the observation of multiferroic nanoregions in cupric oxide, CuO, by means of resonant soft x-ray magnetic scattering. There exists an anomalous memory effect for the direction of the electric polarization in the commensurate-incommensurate magnetic transition that coincides with the ferroelectric transition. Scattering results, incorporated with simulations of diffuse scattering, lead us to propose a scenario that preserved spin handedness in the multiferroic nanoregions is responsible for this memory effect in the magnetically induced ferroelectric properties of CuO.
Orbital ordering of layered manganites from resonant soft X-ray scattering
(2007-03-01)
Chao, K. S.
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Huang, D. J.
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Okamoto, J.
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Lin, H.-J.
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Hsu, C.-H.
We present measurements of Mn L-edge resonant soft X-ray scattering on single-layered manganites with different sizes of cations. Orbital ordering of Pr0.5Ca1.5MnO4 exhibits a stronger three-dimensional character and a dramatically enhanced transition temperature, as compared with those of La0.5Sr1.5MnO4. The c-axis correlation length of orbital ordering in Pr0.5Ca1.5MnO4 is about half of the inplane correlation length. Our results indicate that reduction in one-electron bandwidth and quenched disorder strongly enhances the stabilization of charge-orbital ordering. (c) 2006 Published by Elsevier B. V.
Quasi-two-dimensional d-spin and p-hole ordering in the three-dimensional perovskite La(1/3)Sr(2/3)FeO(3)
(2010-10-22)
Okamoto, J.
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Huang, D. J.
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Chao, K. S.
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Huang, S. W.
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Hsu, C. -H.
Measurements of resonant soft x-ray magnetic scattering reveal anomalous ordering of 3d spins and 2p holes in perovskite La(1/3)Sr(2/3)FeO(3), which is known to exhibit three-dimensional (3D) charge and spin ordering along the (111) direction. Upon cooling, a quasi-two-dimensional phase consisting of ferromagnetic and charge-disproportionated [111] trilayers of Fe(3+)-Fe(5+)-Fe(3+) precedes the development of 3D magnetic ordering at the transition temperature, in sharp contrast to an ordinary transition from the paramagnetic and charge-uniform phase to the antiferromagnetic and charge-disproportionated phase expected according to conventional wisdom.
Quasi-two-dimensional d-spin and p-hole ordering in the three-dimensional perovskite La1/3Sr2/3FeO3
(2010-10-22)
Okamoto, J.
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Huang, D. J.
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Chao, K. S.
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Huang, S. W.
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Hsu, C. -H.
Measurements of resonant soft x-ray magnetic scattering reveal anomalous ordering of 3d spins and 2p holes in perovskite La1/3Sr2/3FeO3, which is known to exhibit three-dimensional (3D) charge and spin ordering along the (111) direction. Upon cooling, a quasi-two-dimensional phase consisting of ferromagnetic and charge-disproportionated [111] trilayers of Fe3+-Fe5+-Fe3+ precedes the development of 3D magnetic ordering at the transition temperature, in sharp contrast to an ordinary transition from the paramagnetic and charge-uniform phase to the antiferromagnetic and charge-disproportionated phase expected according to conventional wisdom.
Symmetry of multiferroicity in a frustrated magnet TbMn2O5
(2007-04-13)
Okamoto, J.
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Huang, D. J.
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Mou, C. -Y.
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Chao, K. S.
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Lin, H. -J.
Based on measurements of soft-x-ray magnetic scattering and symmetry considerations, we demonstrate that the magnetoelectric effect in TbMn2O5 arises from an internal field determined by (S) over right arrow ((q) over right arrow) x (s) over right arrow (-(q) over right arrow) with (S) over right arrow ((q) over right arrow) being the magnetization at modulation vector (q) over right arrow, whereas the magnetoelastic effect in the exchange energy governs the response to external electric fields. Our results set fundamental symmetry constraints on the microscopic mechanism of multiferroicity in frustrated magnets.
Thermally or Magnetically Induced Polarization Reversal in the Multiferroic CoCr(2)O(4)
(2009-02-13)
Choi, Y. J.
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Okamoto, J.
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Huang, D. J.
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Chao, K. S.
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Lin, H. J.
We report the unexpected evolution, with thermal and magnetic-field (H) variations, of the interrelation between the polarization P, magnetization M, and spiral wave vector Q in CoCr(2)O(4), which has a ferrimagnetic conical-spiral magnetic order. For example, P suddenly jumps and changes its sign at the magnetic lock-in transition (T(L)) with thermal variation, or with isothermal variation of H (without changing its direction) at T(L), which surprisingly occurs without change in spiral handedness (i.e., the sign of Q). The presence of multiple spiral sublattices may be behind this unusual behavior.
Thermally or Magnetically Induced Polarization Reversal in the Multiferroic CoCr2O4
(2009-02-13)
Choi, Y. J.
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Okamoto, J.
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Huang, D. J.
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Chao, K. S.
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Lin, H. J.
We report the unexpected evolution, with thermal and magnetic-field (H) variations, of the interrelation between the polarization P, magnetization M, and spiral wave vector Q in CoCr2O4, which has a ferrimagnetic conical-spiral magnetic order. For example, P suddenly jumps and changes its sign at the magnetic lock-in transition (T-L) with thermal variation, or with isothermal variation of H (without changing its direction) at T-L, which surprisingly occurs without change in spiral handedness (i.e., the sign of Q). The presence of multiple spiral sublattices may be behind this unusual behavior.