研究者詳細 - 堀部　陽一

論文 - 堀部　陽一

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Exchange bias in multiferroic RFe <inf>2</inf>O <inf>4</inf> (R = Y, Er, Tm, Yb, Lu, and In) 査読有り

Yoshii K., Ikeda N., Nishihata Y., Maeda D., Fukuyama R., Nagata T., Kano J., Kambe T., Horibe Y., Mori S.

Journal of the Physical Society of Japan 81 ( 3 ) 2012年03月

記述言語：英語掲載種別：研究論文（学術雑誌）

An exchange bias (EB) behavior has been observed for multiferroic RFe 2O 4 (R = Y, Er, Tm, Yb, Lu, and In). The materials with small R 3+ ions (R = Tm, Yb, Lu, and In) exhibit large EB fields (≳1 kOe) below ∼ 100-150 K. This property is rooted in a magnetically glassy state, arising from the competition between ferromagnetic and antiferromagnetic domain interactions. In addition, the EB field tends to be more enhanced for smaller R 3+ ions. Hence, the EB is controlled by the substitution at the R-site in this series. © 2012 The Physical Society of Japan.

DOI： 10.1143/JPSJ.81.033704

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Conduction of topologically protected charged ferroelectric domain walls 査読有り

Wu W., Horibe Y., Lee N., Cheong S., Guest J.

Physical Review Letters 108 ( 7 ) 2012年02月

記述言語：英語掲載種別：研究論文（学術雑誌）

We report on the observation of nanoscale conduction at ferroelectric domain walls in hexagonal HoMnO 3 protected by the topology of multiferroic vortices using in situ conductive atomic force microscopy, piezoresponse force microscopy, and Kelvin-probe force microscopy at low temperatures. In addition to previously observed Schottky-like rectification at low bias, conductance spectra reveal that negatively charged tail-to-tail walls exhibit enhanced conduction at high forward bias, while positively charged head-to-head walls exhibit suppressed conduction at high reverse bias. Our results pave the way for understanding the semiconducting properties of the domains and domain walls in small-gap ferroelectrics. © 2012 American Physical Society.

DOI： 10.1103/PhysRevLett.108.077203

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Ferroelectric and structural antiphase domains in hexagonal RMnO 3 査読有り

Kobayashi K., Koyama T., Horibe Y., Katsufuji T., Cheong S., Mori S.

Materials Research Society Symposium Proceedings 1397 20 - 25 2011年12月

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）

We have investigated characteristic ferroelectric and structural antiphase domain structures in single crystals of hexagonal RMnO3 (R=Y, Ho, Lu, and Yb) by obtaining various electron diffraction patterns, dark-filed images and high-resolution lattice images. In the ferroelectric phase RMnO3 characteristic domain structures consisting of six ferroelectric and structural antiphase domains, which can be identified as the "cloverleaf" pattern, is found in the (110) plane, in addition to the (001) plane, and are inherent to the ferroelectric phase of hexagonal RMnO3. In domain configuration with the cloverleaf pattern in the (110) plane, the structural antiphase boundaries are inclined to be parallel to the [001] direction. © 2012 Materials Research Society.

DOI： 10.1557/opl.2012.448

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Epitaxial growth of topological insulator Bi<inf>2</inf>Se<inf>3</inf> film on Si(111) with atomically sharp interface 査読有り

Bansal N., Kim Y., Edrey E., Brahlek M., Horibe Y., Iida K., Tanimura M., Li G., Feng T., Lee H., Gustafsson T., Andrei E., Oh S.

Thin Solid Films 520 ( 1 ) 224 - 229 2011年10月

記述言語：英語掲載種別：研究論文（学術雑誌）

Atomically sharp epitaxial growth of Bi2Se3 films is achieved on Si(111) substrate with molecular beam epitaxy. Two-step growth process is found to be a key to achieve interfacial-layer-free epitaxial Bi 2Se3 films on Si substrates. With a single-step high temperature growth, second phase clusters are formed at an early stage. On the other hand, with low temperature growth, the film tends to be disordered even in the absence of a second phase. With a low temperature initial growth followed by a high temperature growth, second-phase-free atomically sharp interface is obtained between Bi2Se3 and Si substrate, as verified by reflection high energy electron diffraction (RHEED), transmission electron microscopy (TEM) and X-ray diffraction. The lattice constant of Bi 2Se3 is observed to relax to its bulk value during the first quintuple layer according to RHEED analysis, implying the absence of strain from the substrate. TEM shows a fully epitaxial structure of Bi 2Se3 film down to the first quintuple layer without any second phase or an amorphous layer. © 2011 Elsevier B.V.

DOI： 10.1016/j.tsf.2011.07.033

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Thickness-dependent bulk properties and weak antilocalization effect in topological insulator Bi<inf>2</inf>Se<inf>3</inf> 査読有り

Kim Y., Kim Y., Brahlek M., Bansal N., Edrey E., Kapilevich G., Iida K., Tanimura M., Horibe Y., Cheong S., Oh S.

Physical Review B - Condensed Matter and Materials Physics 84 ( 7 ) 2011年08月

記述言語：英語掲載種別：研究論文（学術雑誌）

We show that a number of transport properties in topological insulator (TI) Bi2Se3 exhibit striking thickness dependences over a range of up to five orders of thickness (3 nm-170 μm). Volume carrier density decreased with thickness, presumably due to diffusion-limited formation of selenium vacancies. Mobility increased linearly with thickness in the thin film regime and saturated in the thick limit. The weak antilocalization effect was dominated by a single two-dimensional channel over two decades of thickness. The sublinear thickness-dependence of the phase coherence length suggests the presence of strong coupling between the surface and bulk states. © 2011 American Physical Society.

DOI： 10.1103/PhysRevB.84.073109

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Multiple-charge modulations in the ferromagnetic insulating state of lightly doped La<inf>1-x</inf>Sr<inf>x</inf>MnO<inf>3</inf> 査読有り

Asaka T., Asaka T., Asaka T., Mori S., Horibe Y., Takenaka K., Yu X., Nagai T., Kimoto K., Kimoto K., Hirayama T., Matsui Y.

Physical Review B - Condensed Matter and Materials Physics 83 ( 17 ) 2011年05月

記述言語：英語掲載種別：研究論文（学術雑誌）

We investigated the texture of charge modulations and behaviors of their domains in the ferromagnetic insulating state of La1-xSr xMnO3 (x=0.125) by low-temperature transmission electron microscopy. We observed simultaneous evolutions of three charge-modulated phases below ∼135 K, close to the charge-ordering-transition temperature T CO∼140 K. The phases form intricate domain structures within one ferromagnetic phase. This indicates that one magnetic state exhibits multiple-charge states. With further decreasing temperature, below ∼40 K, the three charge-modulated phases behave differently from one another. We consider that the behaviors would lead to a phase separation into the ferromagnetic insulating phase and the ferromagnetic metallic one. © 2011 American Physical Society.

DOI： 10.1103/PhysRevB.83.174401

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Magnetic chessboard-type nanodomains in Mn-doped CoFe2O 4 査読有り

Ohno M., Mori S., Togawa Y., Horibe Y.

IOP Conference Series: Materials Science and Engineering 18 ( SYMPOSIUM 6 ) 2011年01月

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）

We examined formation processes of ordered array of two types of rectangular nanorods, characterized as chessboard-type (CB-type) nanodomain structures, by changing the isothermal annealing time at 648 K. Highly organized CB-type nanodomain structures developed through the isothermal annealing treatment from 10 to 730 hours and consequently the CB-type nanodomain structures with ∼50 nm2 in size are formed in samples annealed for 730 hours. From the chemical composition analysis, it is revealed that the two types of rectangular nanorods comprise the coexisting state of one nanorod with composition close to CoFe1.4MnO4 with the cubic structure and another nanorod with composition close to CoFe0.4Mn2O4 with the orthorhombic structure. © Published under licence by IOP Publishing Ltd.

DOI： 10.1088/1757-899X/18/9/092052

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Self-organization, condensation, and annihilation of topological vortices and antivortices in a multiferroic 査読有り

Chae S., Horibe Y., Jeong D., Rodan S., Lee N., Cheong S.

Proceedings of the National Academy of Sciences of the United States of America 107 ( 50 ) 21366 - 21370 2010年12月

記述言語：英語掲載種別：研究論文（学術雑誌）

The interaction among topological defects can induce novel phenomena such as disclination pairs in liquid crystals and superconducting vortex lattices. Nanoscale topological vortices with swirling ferroelectric, magnetic, and structural antiphase relationships were found in multiferroic h-YMnO 3. Herein, we report the discovery of intriguing, but seemingly irregular configurations of a zoo of topological vortices and antivortices. These configurations can be neatly analyzed in terms of graph theory and reflect the nature of self-organized criticality in complexity phenomena. External stimuli such as chemistry-driven or electric poling can induce the condensation and eventual annihilation of topological vortex- antivortex pairs.

DOI： 10.1073/pnas.1011380107

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Direct observation of low-temperature superstructure in spin- and charge-frustrated ferrite YFe<inf>2</inf> O<inf>4-δ</inf> 査読有り

Horibe Y., Ikeda N., Yoshii K., Mori S.

Physical Review B - Condensed Matter and Materials Physics 82 ( 18 ) 2010年11月

記述言語：英語掲載種別：研究論文（学術雑誌）

The low-temperature superstructure of YFe2 O4-δ was carefully investigated by transmission electron microscopy. We found that the unique superstructure at about 100 K is characterized by 1̄ /142/71/14 -type superlattice reflection spots, suggesting the presence of charge-reordering process. The low-temperature high-resolution images clearly show superlattice modulations in Y-O layers as well as Fe-O layers. The modification of intrabilayer charge interactions due to lattice distortions in Y-O layers is discussed to play a crucial role in the stabilization of long-periodic superstructures at low temperatures. © 2010 The American Physical Society.

DOI： 10.1103/PhysRevB.82.184119

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Polarization-modulated rectification at ferroelectric surfaces 査読有り

Wu W., Guest J., Horibe Y., Park S., Choi T., Cheong S., Bode M.

Physical Review Letters 104 ( 21 ) 2010年05月

記述言語：英語掲載種別：研究論文（学術雑誌）

By correlating room temperature conductive atomic force microscopy with low temperature electrostatic force microscopy images of the same sample region, we demonstrate that nanoscale electric conduction between a sharp tip and the surface of ferroelectric HoMnO3 is intrinsically modulated by the polarization of ferroelectric domains. Conductance spectra reveal that the electric conduction is described by polarization-induced Schottky-like rectification at low bias, but dominated by a space-charge limited conduction mechanism at high bias. Our observation demonstrates visualization of ferroelectric domain structure by electric conduction, which may be used for nondestructive readout of nanoscale ferroelectric memories and/or ferroelectric sensors. © 2010 The American Physical Society.

DOI： 10.1103/PhysRevLett.104.217601

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Insulating interlocked ferroelectric and structural antiphase domain walls in multiferroic YMnO 3 査読有り

Choi T., Horibe Y., Yi H., Yi H., Choi Y., Wu W., Cheong S., Cheong S.

Nature Materials 9 ( 3 ) 253 - 258 2010年03月

記述言語：英語掲載種別：研究論文（学術雑誌）

Hexagonal YMnO 3 shows a unique improper ferroelectricity induced by structural trimerization. Extensive research on this system is primarily due to its candidacy for ferroelectric memory as well as the intriguing coexistence of ferroelectricity and magnetism. Despite this research, the true ferroelectric domain structure and its relationship with structural domains have never been revealed. Using transmission electron microscopy and conductive atomic force microscopy, we observed an intriguing conductive cloverleaf pattern of six domains emerging from one pointall distinctly characterized by polarization orientation and structural antiphase relationships. In addition, we discovered that the ferroelectric domain walls and structural antiphase boundaries are mutually locked and this strong locking results in incomplete poling even when large electric fields are applied. Furthermore, the locked walls are found to be insulating, which seems consistent with the surprising result that the ferroelectric state is more conducting than the paraelectric state. These fascinating results reveal the rich physics of the hexagonal system with a truly semiconducting bandgap where structural trimerization, ferroelectricity, magnetism and charge conduction are intricately coupled.

DOI： 10.1038/nmat2632

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Oxygen-deficient effect on charge ordering in spin- and charge-frustrated ferrite YFe2O4-δ 査読有り

Y. Horibe, K. Yoshii, N. Ikeda, and S. Mori

Physical Review B 80 092104 2009年09月

Nanometer-Sized Domain Structures in LuFeMO4 (M = Cu, Co) Revealed by Energy-Filtered Transmission Electron Microscopy 査読有り

Y. Matuso, A. Hirata, Y. Horibe, K. Yoshii, N. Ikeda, and S. Mori

Ferroelectrics 380 56 - 62 2009年09月

Pancakelike Ising domains and charge-ordered superlattice domains in LuFe2O4 査読有り

S. Park, Y. Horibe, Y. J. Choi, C. L. Zhang, S.-W. Cheong, and W. WuMori

Physical Review B 79 180401(R) 2009年05月

Giant magnetic coercivity and ionic superlattice nano-domains in Fe0.25TaS2 査読有り

Y. J. Choi, S. B. Kim, T. Asada, S. Park, W. Wu, Y. Horibe, and S.-W. Cheong,

EUROPHYSICS LETTERS 86 37012 2009年05月

Magnetic and dielectric properties of YbFe2-xMnxO4 (0<x<1) 査読有り

K. Yoshii, N. Ikeda, T. Michiuchi, Y. Yokota, Y. Okajima, Y. Yoneda, Y. Matsuo, Y. Horibe, and S. Mori

Journal of Solid State Chemistry 182 1611 2009年04月

Two Types of Charge Ordering in the Half-Doped Manganites of Bi0.5(Ca,Sr)0.5MnO3 査読有り

Y. Horibe, J.-S. Ahn, P. A. Sharma, S. Mori, C. H. Chen, S.-J. Oh, and S.-W. Cheong

Journal of the Physical Society of Japan 78 044704 2009年03月

Epitaxial checkerboard arrangement of nanorods in ZnMnGaO4 films studied by x-ray diffraction 査読有り

S. M. O'Malley, P. L. Bonanno, K. H. Ahn, A. A. Sirenko, A. Kazimirov, Y. Horibe, T. Asada, M. Tanimura, S. Park, and S. -W. Cheong

Physical Review B 78 165424 2008年10月

Formation of pancakelike Ising domains and giant magnetic coercivity in ferrimagnetic LuFe2O4 査読有り

W. Wu, V. Kiryukhin, H.-J. Noh, K.-T. Ko, J.-H. Park, W. Ratcliff II, P. A. Sharma, N. Harrison, Y. J. Choi, Y. Horibe, S. Lee, S. Park, H. T. Li, C. L. Zhang, and S. -W. Cheong

Physical Review Letters 101 137203 2008年09月

Effect of Oxygen Vacancies on Charge Ordered Structure in YFe2O4-delta 査読有り

S. Mori, S. Shinohara, Y. Matsuo, Y. Horibe, K. Yoshii, and N. Ikeda

Japanese Journal of Applied Physics 47 7595 - 7598 2008年09月

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