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）

In this work, ball-milled iron (Fe)-based nanocrystalline alloy sheets and obtaining platelet particles are used to effectively utilize the end material and apply it to a soft magnetic composite. The instrumental analysis results reveal that, although a microstrain is introduced into the nanocrystalline α-Fe grains in the achieved alloy powder, the amorphous part filled among the grains experiences almost no change. The ball-milling treatment greatly increases the coercive force of the pulverized nanocrystalline sheet. Although the coercive force of the alloy powder decreases after the heat treatment, it remained approximately 10 times higher than that of the heat-Treated alloy sheet without the ball-milling treatment, even after the heat treatment. The magnetic process of the ball-milled and post-Annealed nanocrystalline alloy powder is discussed based on the results of the synchrotron radiation X-ray analysis and transmission electron microscopy with the Lorentz technique.

DOI： 10.1109/INTERMAG50591.2023.10265082

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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）

To realize the effective utilization of the end material and its application to a soft magnetic composite, Fe-based nanocrystalline alloy sheets were ball-milled, and platelet particles were obtained, in this work. Instrumental analyses revealed that although a micro strain was introduced into the nanocrystalline α-Fe grains in the achieved alloy powder, almost no changes were found in the amorphous part filled among the grains. The ball-milling treatment greatly increased the coercive force of the pulverized nanocrystalline sheet. Although the coercive force of the alloy powder decreased after the heat treatment, the coercive force remained to be approximately 10 times higher than that of the heat-treated alloy sheet without the ball-milling treatment, even after the heat treatment. The magnetic process of the ball-milled and heat treated nanocrystalline alloy powder will be discussed in detail in the conference based on the obtained results and Lorentz transmission electron microscopy.

DOI： 10.1109/INTERMAGShortPapers58606.2023.10228768

Scopus

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担当区分：筆頭著者,　責任著者   記述言語：日本語   掲載種別：研究論文（学術雑誌）

<p>遷移金属化合物における自己組織化した異方的ナノ材料は，その物性の多様性と構造制御の観点から注目を集めている．通常，異方的ナノ構造作製のためには，試料作製条件の調整や高温処理が必要である．一方，スピネル型マンガン酸化物におけるナノメートルスケールでのスピノーダル分解を利用したナノ構造作製は，比較的低温での単純な熱処理のみで可能である．本稿では，磁性スピネル(Co,Mn,Fe)₃O₄において行われた研究例を紹介する．本系は遷移金属酸化物にもかかわらず，375℃という低い温度での熱処理によりMn-richな正方晶ナノドメインとMn-poorな立方晶ナノドメインが形成される．これらのナノドメインが複雑に相関し合うことでチェッカーボード型ナノ構造やラメラ型ナノ構造が出現し，磁性に影響を及ぼす．</p>

DOI： 10.11470/oubutsu.91.11_679

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1038/s41467-022-28710-0

DOI： 10.1038/s41467-022-28710-0

その他リンク： https://www.nature.com/articles/s41467-022-28710-0

記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1021/acs.jpcc.1c09324

DOI： 10.1021/acs.jpcc.1c09324

その他リンク： https://pubs.acs.org/doi/10.1021/acs.jpcc.1c09324

記述言語：英語   掲載種別：研究論文（学術雑誌）

The nano-size effects of high-Tc cuprate superconductor La2−xSrxCuO4 with x = 0.20 are investigated using X-ray diffractometry, Transmission electron microscopy, and muon-spin relaxation (µSR). It is investigated whether an increase in the bond distance of Cu and O atoms in the conducting layer compared to those of the bulk state might affect its physical and magnetic properties. The µSR measurements revealed the slowing down of Cu spin fluctuations in La2−xSrxCuO4 nanoparticles, indicating the development of a magnetic correlation at low temperatures. The magnetic correlation strengthens as the particle size reduces. This significantly differs from those observed in the bulk form, which show a superconducting state below Tc. It is indicated that reducing the particle size of La2−xSrxCuO4 down to nanometer size causes the appearance of magnetism. The magnetism enhances with decreasing particle size.

DOI： 10.3390/nano11123450

Scopus

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

Temperature dependence of charge-ordered crystal structures and domain structures in RFe2O4 (R: Y and Lu) was investigated by energy-filtered transmission electron microscopy, combined with conventional transmission electron microscopy. The presence of three-dimensional to two-dimensional charge ordering transition were observed in both YFe2O4 and LuFe2O4 on heating. Furthermore, real-space images obtained with the energy-filtered transmission electron microscopy revealed that YFe2O4 has less anisotropic nanometer-scale charge-ordered domains than LuFe2O4. These findings in RFe2O4 indicate the importance of the interchange interactions between Fe-O bilayers in addition to those within bilayers in the structural phase transitions associated with charge ordering in this system.

DOI： 10.1080/00150193.2021.1984762

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担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1080/09500839.2020.1841915

Kyutacar

記述言語：英語   掲載種別：研究論文（学術雑誌）

© 2020 Elsevier Ltd NbBiCh3 (Ch = S, Se) misfit-layered superconducting single crystals were successfully grown using a CsCl/KCl flux for the first time. The obtained crystals had a well-developed habit parallel to the c-plane with a typical width of 1–2 mm and thickness of 10–40 μm. The superconducting transition temperatures with zero resistivity of NbBiS3 single crystals obtained from the nominal composition of Nb0.9Bi1.2S3 was 0.31 K, and that value of the NbBiSe3 single crystals grown from the stoichiometry composition (NbBiSe3) was 2.3 K. Sharp decreases in electric resistivity and magnetic susceptibility at approximately 3 K suggested a possible superconducting transition temperature of NbBiSe3. The normal-state anisotropy values of grown NbBiS3 and NbBiSe3 single crystals were 2.2–2.4 and 1.5–1.6, respectively.

DOI： 10.1016/j.ssc.2020.114051

Scopus

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担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.35848/1347-4065/abb20f

Kyutacar

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記述言語：英語   掲載種別：研究論文（学術雑誌）

© 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Ultrasensitive and sustainable near-infrared (NIR)-emitting piezoluminescence is observed from noncentrosymmetric and ferroelectric-phase Sr3Sn2O7 doped with rare earth Nd3+ ions. Sr3Sn2O7:Nd3+ (SSN) with polar A21am structure is demonstrated to emit piezoluminescence of wavelength of 800–1500 nm at microstrain levels, which is enhanced by the ferroelectrically polarized charges in the multipiezo material. These discoveries provide new research opportunities to study luminescence properties of multipiezo and piezo-photonic materials, and to explore their potential as novel ultrasensitive probes for deep-imaging of stress distributions in diverse materials and structures including artificial bone and other implanted structures (in vivo, in situ, etc).

DOI： 10.1002/adma.201908083

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

© 2019 Author(s). Distinct nanostructures in (Co,Mn,Fe)3O4 were investigated using X-ray diffraction techniques combined with transmission and scanning transmission electron microscopy, as well as energy dispersive X-ray spectroscopy. The size of the checkerboard nanostructure increased with annealing, followed by the appearance of lamellar nanostructures comprising different types of platelike nanodomains because of nanoscopic spinodal decomposition of Mn and Fe ions. Remarkable local strain relaxation at the nanoscale associated with the domain size is suggested to play an important role in the stabilization of these checkerboard and lamellar nanostructures.

DOI： 10.1063/1.5123780

Kyutacar

Scopus

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

© 2019 American Physical Society. Crystallographic and morphologic features of quadruple and double superstructures in Bi1-xSmxFeO3 with 0≤x≤0.40 were investigated by x-ray powder diffraction and transmission electron microscopy. The presence of a quadruple superstructure accompanied by antiferroic ionic displacements was found near the morphotropic phase boundary between the R3c phase (0<x<0.10) and the Pnma phase (0.25≤x≤0.40). The quadruple superlattice phase coexists with a ferroelectric R3c phase at x=0.15. These superstructures were found to originate from the freezing of multiple phonon modes related to transverse wave ionic displacements. These findings provide further insight towards understanding the complexity of rare-earth-doped BiFeO3.

DOI： 10.1103/PhysRevB.100.024105

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記述言語：英語   掲載種別：研究論文（学術雑誌）

<p>The charged domain walls in ferroelectric materials exhibit intriguing physical properties. We examine herein the charged-domain-wall structures in Ca₃₋<i>_x</i>Sr<i>_x</i>Ti₂O₇ using transmission electron microscopy. When viewed along the [001] axis, the wavy charged domain walls are observed over a wide range (>5 µm). In contrast, short charged-domain-wall fragments (from 10 to 200 nm long) occur because they are intercepted and truncated by the conventional 180° domain walls. These results reveal the unusual charged domain structures in Ca₃₋<i>_x</i>Sr<i>_x</i>Ti₂O₇ and will be useful for understanding their formation process.</p>

DOI： 10.2320/matertrans.MT-MI2019006

CiNii Article

その他リンク： https://ci.nii.ac.jp/naid/130007681964

記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.7566/JPSJ.88.054601

記述言語：日本語   掲載種別：研究論文（学術雑誌）

DOI： 10.11316/jpsgaiyo.74.1.0_1817

CiNii Research

担当区分：筆頭著者,　責任著者   記述言語：日本語   掲載種別：研究論文（学術雑誌）

CiNii Research

記述言語：日本語   掲載種別：研究論文（学術雑誌）

<p>Magnetic properties and mechanical properties of high purity Fe-3 mass%Si alloy by cold crucible levitation melting was investigated. The raw material of the alloy made from electrolytic iron and pure silicon with a purity of 99.99 mass% and 99.999 mass% in amount of impurities excluding Fe and Si were suppressed to 90 ppm or less. In the magnetic property, the iron loss of the alloy was reduced to a third of 35H210, a silicon steel sheet of the same Si composition commercially. This reduction shows the effect of high purity. In the magnetic domain observation, the equal behavior as magnetic properties was observed. In mechanical property, it proved that the high purity Fe-3 mass%Si alloy was easy to draw because the elongation of the alloy was higher than the commercially available silicon steel sheet.</p>

DOI： 10.2320/jinstmet.J2018008

CiNii Article

その他リンク： https://ci.nii.ac.jp/naid/130007492739

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）

DOI： 10.1109/INTMAG.2018.8508412

Scopus

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記述言語：英語   掲載種別：研究論文（学術雑誌）

記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.2320/materia.57.271

CiNii Article

その他リンク： https://ci.nii.ac.jp/naid/130007382152

記述言語：英語   掲載種別：研究論文（学術雑誌）

© 2018, The Korean Physical Society. In this work, a silicate based phosphor doped with divalent and trivalent europium (Eu(2+/3+)) ions have been synthesized by two different synthesis processes, PGMS (propylene glycol modified silane) assisted sol-gel and solid state reaction (SSR) method. The structural, morphological and optical properties were studied in detail. The emission intensity of Li2SrSiO4:Eu3+phosphors synthesized through the PGMS assisted sol-gel increased up to 10 times more than that prepared by SSR method. However, Li2SrSiO4:Eu2+phosphor prepared by PGMS exhibited lower emission characteristics and decreased to one-third of that prepared by SSR. The Eu3+doped Li2SrSiO4synthesized by SSR method using different silicate (Si) sources revealed peculiar optical properties and this is the first kind of its report. The obtained results suggest that the optical properties of Eu(3+/2+)doped in silicate host can be regulated by the alteration of Si source besides sample preparation method. These results open a way to understand the mechanisms responsible for such optical properties and to develop new materials for white LEDs.

DOI： 10.3938/jkps.72.1350

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記述言語：英語   掲載種別：研究論文（学術雑誌）

© 2018 The Japan Society of Applied Physics. Free-standing strontium titanate (SrTiO3/STO) nanoparticles (NPs) were synthesized by the sol-gel method. X-ray diffractometry revealed that the required minimum annealing temperature to synthesize pure and highly crystalline STO NPs was 500 °C. Moreover, morphological observation by field emission scanning electron microscopy showed that the STO NPs have a spherical structure and their size depended on annealing condition. Electrical properties were measured using a low-temperature probing system. Here, an electrode was fabricated by electron beam lithography and the synthesized STO NPs were aligned at the electrodes by dielectrophoresis. The conductance of a sample was proportional to temperature. Two conduction mechanisms originating from hopping and tunneling appeared in the Arrhenius plot.

DOI： 10.7567/JJAP.57.06HE07

Scopus

CiNii Article

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記述言語：英語   掲載種別：研究論文（学術雑誌）

© The Korean Physical Society. All rights reserved. Lithium-strontium-silicate phosphors activated with divalent or trivalent europium ions were synthesized through a conventional solid-state reaction method by using SiO2 with micron-size and nanosize particles as a silicate source. The crystal structures are almost the same in the samples prepared with micron size and nanosize SiO2. However, we newly found that the optical properties of Eu(2+/3+)-activated phosphors depended very much on the size of the particles in the raw SiO2 material adopted as the Si source. The maximal emission wavelength of the Eu2+-doped phosphor prepared with the micron-size SiO2 source was also revealed to be shifted to shorter wavelength by 13 nm as compared to that of Eu2+-doped phosphor prepared with a nanosize SiO2 source.

DOI： 10.3938/NPSM.68.593

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記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.11470/jsapmeeting.2017.2.0_2817

CiNii Research

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）

© 2017 Trans Tech Publications, Switzerland.The simple-perovskite system Bi1-xLaxFeO3 (BLFO) is one of mixed-oxide systems having the multiferroic BiFeO3 as an end material, which shows the ferroelectric and antiferromagnetic orders in its ground state. Because of the paraelectric nature of LaFeO3 as another end material, the ferroelectric-to-paraelectric state change can be expected to occur in the mixed-oxide system BLFO. The interesting feature of BLFO is that there are both the PbZrO3-type and incommensurately modulated (IM) states in the intermediate La-content range between the ferroelectric-R3c and paraelectric-Pnma states. Although the detailed features of these two states have not been understood sufficiently, in this study, we focus on the IM state around x = 0.20, and have investigated the crystallographic features of prepared BLFO samples with 0.15 ≤ x ≤ 0.35, mainly by transmission electron microscopy. It was found that six kinds of superlattice reflections were, for instance, present in the reciprocal lattice of the state at 300 K for x = 0.20, in addition to fundamental reflections due to the cubic simple-perovskite structure. To understand the appearance of these superlattice reflections, we regarded the state as a modulated-structure state in this study. Concretely, the modulated structure was assumed to be characterized by the appearance of both the incommensurate wave with qI = <1/(4+δ) 1/(4+δ) 0>c and the commensurate wave with qII = <1/4 0 0>c in the normal-Imma structure. In addition, the appearance of the two modulation waves could also produce the superlattice reflections at the <1/4 1/4 1/4>c-, <1/2 0 0>c-, and <1/2 1/2 0>c-type positions in the reciprocal lattice. From the comparison with the experimental data obtained in this study, our modulated-structure model seems to be appropriate for the IM state in the vicinity of the PbZrO3-type/IM state boundary.

DOI： 10.4028/www.scientific.net/MSF.879.2222

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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）

© 2017 Trans Tech Publications, Switzerland.In Bi1-xSmxFeO3 (BSFO) having the multiferroic BiFeO3 as an end material, when the Sm content increases from x = 0, it has been reported that the ferroelectric-R3c state is changed into the paraelectric-Pnma state around x = 0.14. The R3c/Pnma state boundary around x = 0.14 can be regarded as a temperature-independent morphotropic-phase boundary (MPB). The notable feature in BSFO is that, in addition to these two states, the antiferroelectric PbZrO3-type state was also found in the vicinity of the MPB. Although the PbZrO3-type state appears as a modulated structure, its detailed features have not been understood yet. We have thus examined the crystallographic features of prepared BSFO samples around x = 0.14, mainly by transmission electron microscopy. The PbZrO3-type state was confirmed to be present in samples with x = 0.15 on the basis of x-ray powder diffraction profiles measured from prepared samples at 300 K. On the other hand, the observation made by transmission electron microscopy indicated that the state for x = 0.15 is characterized by a coexistence state consisting of the ferroelectric-R3c and antiferroelectric PbZrO3-type states. In particular, the crystal structure of the PbZrO3-type state could be identified as a modulated structure with two transverse modulation waves, whose wave vectors are given by qi = [1/2 0 0]o and q2 = [0 1/2 0]o in the orthorhombic-Pnma notation. In addition, eigenvectors of these two transverse waves were also determined to be parallel to the same [001]o direction.

DOI： 10.4028/www.scientific.net/MSF.879.1393

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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）

© 2016 Author(s).The effect of Mn concentration on the formation of nano-domain structures in the spinel oxide (Co,Fe,Mn)3O4 was investigated by electron diffraction, bright-, and dark-field imaging technique with transmission electron microscopy. Large scale phase separation with nano-twin domains was observed in Co0.6Fe1.0Mn1.4O4, in contrast to the highly aligned checkerboard nano-domains in Co0.6Fe0.9Mn1.5O4. Diffusion of the Mn3+ ions with the Jahn-Teller distortions is suggested to play an important role in the formation of checkerboard nano-domain structure.

DOI： 10.1063/1.4961358

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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）

© 2016 Materials Research Society. The multiferroic material YbMnO3 has been reported to exhibit both ferroelectric and antiferromagnetic orders in the ground state. Of these two orders, the ferroelectric order is associated with the P63/mmc-to-P63cm structural transition, which occurs around 1270 K. The interesting feature of the ferroelectric state is that a cloverleaf domain structure with a pseudo-six-fold symmetry is observed in transmission electron microscopy images with the beam incidence parallel to the hexagonal axis. To understand the origin of the formation of the cloverleaf domain structure, we have examined the crystallographic features of the ferroelectric state in YbMnO3 by transmission electron microscopy. In this study, particularly, we adopted the experimental condition that electron beam incidences are perpendicular to the hexagonal axis. It was, as a result, found that there existed various ferroelectric domain structures including the cloverleaf domain structure under the present condition. The notable feature of domain structures found in this study is that each domain structure basically consists of six domains, whose domain boundaries are terminated at one point. Because this feature makes us reminiscent of a discommensurate structure in an incommensurate state, we took high-resolution electron micrographs of areas including domain boundaries. Their analysis indicated that a domain boundary could be identified as a discommensuration with a phase slip of π/3. It is thus understood that the cloverleaf domain structure should be one of domain morphologies for a discommensurate structure, which is related to the break of the translational symmetry.

DOI： 10.1557/adv.2016.154

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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）

© 2016 Materials Research Society. The multiferroic material Bi 1-x Sm xFeO 3 shows ferroelectric and antiferromagnetic properties in the ground state of the Bi-rich side. When the Sm content increases from x = 0 in BiFeO 3 , the (ferroelectric-R3c → paraelectric-Pnma) state change occurs around x = 0.14. According to the previous studies on Bi 1-x Sm xFeO 3 , the state boundary between the R3c and Pnma states can be identified as a morphotropic phase boundary (MPB), which is nearly parallel to the temperature axis in the state diagram. The notable feature of Bi 1-x Sm xFeO 3 is that a remarkable piezoelectric response was also found near the MPB. However, the origin of the remarkable response has not been understood sufficiently. In this study, thus, the crystallographic features in the vicinity of the MPB have been examined by x-ray powder diffraction and transmission electron microscopy. It was confirmed that the R3c and Pnma states were present for 0 ≤ x ≤ 0.15 and for 0.16 ≤ x ≤ 0.30, respectively. In addition to these states, there also existed the PbZrO 3 -type state around x = 0.15, which was identified as a modulated structure. Based on the analysis of the modulated structure, furthermore, it was suggested that the PbZrO 3 -type state could be regarded as a 2q state, which is characterized by two transverse modulation waves with k1 = [1/2 0 0]o and k2 = [0 1/2 0] o in the orthorhombic-Pnma notation.

DOI： 10.1557/adv.2016.155

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記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.2320/materia.55.575

CiNii Article

CiNii Research

その他リンク： http://ci.nii.ac.jp/naid/130005170198

記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1103/PhysRevB.92.220408

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）

CiNii Article

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）

DOI： 10.1016/j.phpro.2015.12.090

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1103/PhysRevLett.113.267602

Scopus

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）

記述言語：日本語   掲載種別：記事・総説・解説・論説等（その他）

記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1021/ja5026134

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1103/PhysRevLett.112.247601

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1080/00150193.2014.890855

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1021/nl404363b

Scopus

記述言語：日本語   掲載種別：研究論文（学術雑誌）

DOI： 10.2320/materia.53.355

CiNii Article

その他リンク： https://ci.nii.ac.jp/naid/130004684512

記述言語：日本語   掲載種別：研究論文（その他学術会議資料等）

DOI： 10.11316/jpsgaiyo.69.2.4.0_681_4

CiNii Article

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記述言語：日本語   掲載種別：研究論文（その他学術会議資料等）

DOI： 10.11316/jpsgaiyo.69.1.4.0_913_2

CiNii Article

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記述言語：英語   掲載種別：研究論文（学術雑誌）

Characteristic behavior and physical properties associated with the vortex domain structure in multiferroic hexagonal manganites RMnO₃（R＝Y, and Ho）have been investigated mainly using transmission electron microscopy and high angle annular dark field scanning transmission electron microscopy. The insulating nature due to peculiar local structures is found at the vortex domain boundaries. In addition, unique 180° <i>charged</i> ferroelectric boundaries originated from the vortex domain formation are discovered, leading to selective boundary conduction related to bound charge screening.

DOI： 10.5940/jcrsj.56.92

CiNii Article

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記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1103/PhysRevB.87.184109

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1103/PhysRevLett.110.167601

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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）

DOI： 10.3938/jkps.62.1077

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1103/PhysRevLett.110.127209

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）

In order to clarify the electronic phase separation consisting of distinct ferromagnetic (FM) metallic and charge-ordered (CO) insulating phases in the colossal magnetoresistive (La, Pr, Ca)MnO3, we have carefully examined the electronic inhomogeneities by Lorentz microscopy, combined with conventional magnetic studies. We discovered the presence of an intermediate FM state characterized by the emergence of nanoscale (10-20 nm) magnetic regions (magnetic nano-droplets) in the intermediate temperature window above the FM transition temperature. The magnetic nano-droplets in fact precede the onset of ferromagnetic long-range order. It is also found that this intermediate state with magnetic nano-droplets is intimately coupled with the presence of the short-range CO regions. © Copyright EPLA, 2012.

DOI： 10.1209/0295-5075/100/67007

Scopus

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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）

Changes in ferroelectric and structural antiphase domain structure by the partial substitution of nonmagnetic Ti4+ ions at the Mn site were investigated carefully by electron diffraction, dark-field imaging, and high-resolution lattice imaging experiments. The ferroelectric and structural antiphase domains are revealed to be mutually interlocked in YMnO 3 and, on the other hand, when x was increased up to x 0:30 in YMn1x TixO 3, the ferroelectric domains disappeared and the size of the structural antiphase domains decreased to approximately 10nm at x 0:30. High-resolution lattice images clearly demonstrate the coexisting state of nanodomains characterized by the modulated structure due to the structural trimerization and the nonmodulated structures. Our experimental results suggest that a partial substitution of Ti4+ ions suppressed the ferroelectric displacement along the [001] direction and the correlation length of the Mn3+ trimerization decreased. © 2012 The Japan Society of Applied Physics.

DOI： 10.1143/JJAP.51.09LE09

Scopus

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記述言語：英語   掲載種別：研究論文（学術雑誌）

We discovered stripe patterns of trimerization-ferroelectric domains in hexagonal REMnO 3 (RE=Ho,Lu) crystals (grown below ferroelectric transition temperatures (T c), reaching up to 1435°C), in contrast with the vortex patterns in YMnO 3. These stripe patterns roughen with the appearance of numerous loop domains through thermal annealing just below T c, but the stripe domain patterns turn to vortex-antivortex domain patterns through a freezing process when crystals cross T c even though the phase transition appears to not be Kosterlitz-Thouless-type. The experimental systematics are compared with the results of our six-state clock model simulation and also the Kibble-Zurek mechanism for trapped topological defects. © 2012 American Physical Society.

DOI： 10.1103/PhysRevLett.108.167603

Scopus

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記述言語：英語   掲載種別：研究論文（学術雑誌）

Using transmission electron microscopy, the anomalies in resistivity and magnetic susceptibility at ∼262K in IrTe 2 are found to accompany the superlattice peaks with q=(1/5,0,-1/5). The wave vector is consistent with our theoretical calculation for the Fermi surface nesting vector, indicating that the ∼262K transition is of the charge-orbital density wave (DW) type. We also discovered that both Pd intercalation and substitution induce bulk superconductivity with T c up to ∼3K, which competes with DW in a quantum critical pointlike manner. © 2012 American Physical Society.

DOI： 10.1103/PhysRevLett.108.116402

Scopus

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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

Scopus

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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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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

Scopus

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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

Scopus

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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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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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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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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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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

Scopus

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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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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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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）

記述言語：日本語   掲載種別：研究論文（学術雑誌）

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）

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）

記述言語：英語   掲載種別：研究論文（学術雑誌）

記述言語：英語   掲載種別：研究論文（学術雑誌）

記述言語：英語   掲載種別：研究論文（学術雑誌）

記述言語：英語   掲載種別：研究論文（学術雑誌）

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）

開催期間： 2014年09月   記述言語：日本語  

開催期間： 2013年12月   記述言語：日本語  

開催期間： 2014年08月   発表言語：英語   講演種別：特別講演   開催地：広島  

開催期間： 2014年07月   発表言語：日本語   講演種別：特別講演   開催地：東京  

対象： 社会人・一般

種別：出前授業

市民カレッジ

対象： 高校生

種別：出前授業

広島県立祇園北高等学校

対象： 高校生

種別：出前授業

福岡県立伝習館高等学校

対象： 高校生

種別：出前授業

福岡県立八女高等学校