Daisuke Shindo

RIKEN, Вако, Saitama, Japan

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Publications (363)822.96 Total impact

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    ABSTRACT: Mechanical control of magnetism is an important and promising approach in spintronics. To date, strain control has mostly been demonstrated in ferromagnetic structures by exploiting a change in magnetocrystalline anisotropy. It would be desirable to achieve large strain effects on magnetic nanostructures. Here, using in situ Lorentz transmission electron microscopy, we demonstrate that anisotropic strain as small as 0.3% in a chiral magnet of FeGe induces very large deformations in magnetic skyrmions, as well as distortions of the skyrmion crystal lattice on the order of 20%. Skyrmions are stabilized by the Dzyaloshinskii-Moriya interaction, originating from a chiral crystal structure. Our results show that the change in the modulation of the strength of this interaction is amplified by two orders of magnitude with respect to changes in the crystal lattice due to an applied strain. Our findings may provide a mechanism to achieve strain control of topological magnetic structures based on the Dzyaloshinskii-Moriya interaction.
    Nature Nanotechnology 06/2015; 10(7). DOI:10.1038/nnano.2015.113 · 34.05 Impact Factor
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    ABSTRACT: Emergent phenomena and functions arising from topological electron-spin textures in real space or momentum space are attracting growing interest for new concept of states of matter as well as for possible applications to spintronics. One such example is a magnetic skyrmion, a topologically stable nanoscale spin vortex structure characterized by a topological index. Real-space regular arrays of skyrmions are described by combination of multi-directional spin helixes. Nanoscale configurations and characteristics of the two-dimensional skyrmion hexagonal-lattice have been revealed extensively by real-space observations. Other three-dimensional forms of skyrmion lattices, such as a cubic-lattice of skyrmions, are also anticipated to exist, yet their direct observations remain elusive. Here we report real-space observations of spin configurations of the skyrmion cubic-lattice in MnGe with a very short period (~3 nm) and hence endowed with the largest skyrmion number density. The skyrmion lattices parallel to the {100} atomic lattices are directly observed using Lorentz transmission electron microscopes (Lorentz TEMs). It enables the first simultaneous observation of magnetic skyrmions and underlying atomic-lattice fringes. These results indicate the emergence of skyrmion-antiskyrmion lattice in MnGe, which is a source of emergent electromagnetic responses and will open a possibility of controlling few-nanometer scale skyrmion lattices through atomic lattice modulations.
    Nano Letters 03/2015; 15(8). DOI:10.1021/acs.nanolett.5b02653 · 13.59 Impact Factor
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    ABSTRACT: Microstructure dependence of magnetic properties of soft magnetic Fe-Si-B-P-Cu nanocrystalline alloys were studied by using in-situ Lorentz microscopy in a transmission electron microscope equipped with a magnetizing system. In particular, we investigated in detail motion of magnetic domain walls in heat-treated Fe85Si12B6P4Cu1 amorphous ribbons. Smooth motion of domain walls was observed for the optimally heat-treated (at 430 °C) nano-crystalline alloy. Pinning of domain walls was observed for higher-temperature-heat-treated (470°C) ribbons. Both ribbons showed a nanocrystalline structure containing α-Fe crystallites of about 15 nm in size. Electron diffraction patterns indicated that the higher-temperature-heat-treated samples contained boride precipitates, which is considered to cause less smooth domain wall motion.
    Journal of Magnetism and Magnetic Materials 02/2015; 375. DOI:10.1016/j.jmmm.2014.08.101 · 1.97 Impact Factor
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    ABSTRACT: Electron holographic vector field electron tomography visualized three-dimensional (3D) magnetic vortices in stacked ferromagnetic discs in a nanoscale pillar. A special holder with two sample rotation axes, both without missing-wedges, was used to reduce artifacts in the reconstructed 3D magnetic vectors. A 1 MV holography electron microscope was used for precisely measure the magnetic phase shifts. Comparison of the observed 3D magnetic field vector distributions in the magnetic vortex cores with the results of micromagnetic simulations based on the Landau-Lifshitz-Gilbert equation showed that the proposed technique is well suited for direct 3D visualization of the spin configurations in magnetic materials and spintronics devices.
    Nano Letters 01/2015; 15(2). DOI:10.1021/nl504473a · 13.59 Impact Factor
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    ABSTRACT: We report the electron holography images of spin configurations in peculiar assemblies of soft magnetic nanoparticles in single-, double-, triple-, or quadruple-sphere geometrical arrangements, in which each particle has a three-dimensional (3D) magnetic-vortex structure. Micromagnetic numerical calculations reveal that the uniqueness of the nanoparticles' 3D vortex structure plays a crucial role in their assembly, especially in terms of the contrasting contributions of the exchange and dipolar interactions to their binding energies. The results represent physical insights into the assembly of 3D-vortex-structure magnetic nanoparticles in different geometrical configurations and offer a practical means of controlling those assemblies.
    Applied Physics Letters 12/2014; 105(23):232402. DOI:10.1063/1.4903741 · 3.30 Impact Factor
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    ABSTRACT: This study reports on the correlation between crystal orientation and magnetic flux distribution of Fe3O4 nanoparticles in the form of self-assembled rings. High-resolution transmission electron microscopy demonstrated that the nanoparticles were single-crystalline, highly monodispersed, (25 nm average diameter), and showed no appreciable lattice imperfections such as twins or stacking faults. Electron holography studies of these superparamagnetic nanoparticle rings indicated significant fluctuations in the magnetic flux lines, consistent with variations in the magnetocrystalline anisotropy of the nanoparticles. The observations provide useful information for a deeper understanding of the micromagnetics of ultrasmall nanoparticles, where the magnetic dipolar interaction competes with the magnetic anisotropy.
    Applied Physics Letters 11/2014; 105(18):183102. DOI:10.1063/1.4901008 · 3.30 Impact Factor
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    ABSTRACT: Investigation of the effect of electron irradiation on ionic liquid (IL) droplets using electron holography revealed that electron irradiation changed the electrostatic potential around the IL. The potential for low electron flux irradiation (0.5×1017 e/m2s) was almost constant as a function of time (up to 180 min.). For higher electron flux irradiation (2×1017 e/m2s), the potential increased exponentially for a certain time, reflecting the charging effect and then leveled off. The IL was found to be changed from liquid to solid state after a significant increase in the electrostatic potential due to electron irradiation.
    Ultramicroscopy 11/2014; 146. DOI:10.1016/j.ultramic.2014.08.003 · 2.44 Impact Factor
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    ABSTRACT: Critical behavior near ferromagnetic transition in EuS and Gd-doped EuS films was studied by magnetization measurement and cryogenic Lorentz microscopy. Ferromagnetic s–f interaction was strongly enhanced by doping 2% Gd. The Curie temperature and critical exponents of the magnetic phase transition for Gd-doped EuS were determined to be 86.3 ± 0.2 K, β = 0.43 ± 0.01, and γ = 1.20 ± 0.05 from the scaling plot, while those for EuS were 14.6 ± 0.1 K, β = 0.39 ± 0.01, and γ = 1.20 ± 0.05. The different universality classes of these materials showed different magnetic domain structures near the Curie temperature: the long-range ferromagnetic ordering based on the mean field model causes the formation of a large domain.
    Applied Physics Express 10/2014; 7(11):113002. DOI:10.7567/APEX.7.113002 · 2.37 Impact Factor
  • Microscopy and Microanalysis 08/2014; 20(S3):276-277. DOI:10.1017/S1431927614003109 · 1.88 Impact Factor
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    Y Murakami · K Niitsu · T Tanigaki · R Kainuma · H S Park · D Shindo
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    ABSTRACT: Direct magnetization measurements from narrow, complex-shaped antiphase boundaries (APBs; that is, planar defect produced in any ordered crystals) are vitally important for advances in materials science and engineering. However, in-depth examination of APBs has been hampered by the lack of experimental tools. Here, based on electron microscopy observations, we report the unusual relationship between APBs and ferromagnetic spin order in Fe70Al30. Thermally induced APBs show a finite width (2-3 nm), within which significant atomic disordering occurs. Electron holography studies revealed an unexpectedly large magnetic flux density at the APBs, amplified by approximately 60% (at 293 K) compared with the matrix value. At elevated temperatures, the specimens showed a peculiar spin texture wherein the ferromagnetic phase was confined within the APB region. These observations demonstrate ferromagnetism stabilized by structural disorder within APBs, which is in direct contrast to the traditional understanding. The results accordingly provide rich conceptual insights for engineering APB-induced phenomena.
    Nature Communications 06/2014; 5:4133. DOI:10.1038/ncomms5133 · 11.47 Impact Factor
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    ABSTRACT: The magnetism of a thin grain-boundary (GB) phase that envelopes the Nd2Fe14B grains in optimally annealed Nd–Fe–B sintered magnets was investigated by electron holography. The phase shift measured from a thin-foil specimen containing a tilted amorphous GB phase (∼3 nm in width) was −0.34 rad, which is substantially smaller than that expected for the nonferromagnetic GB phase of −1.2 rad. Simulations of the phase shift with various magnetization values suggest that the magnetic flux density of the GB phase is ∼1.0 T. The observations imply significant exchange coupling between Nd2Fe14B grains, which can explain the avalanche propagation of magnetization reversal observed in sintered magnets.
    Acta Materialia 06/2014; 71:370–379. DOI:10.1016/j.actamat.2014.03.013 · 4.47 Impact Factor
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    ABSTRACT: This study demonstrates the accumulation of electron-induced secondary electrons by utilizing a simple geometrical configuration of two branches of a charged insulating biomaterial. The collective motion of these secondary electrons between the branches has been visualized by analyzing the reconstructed amplitude images obtained using in situ electron holography. In order to understand the collective motion of secondary electrons, the trajectories of these electrons around the branches have also been simulated by taking into account the electric field around the charged branches on the basis of Maxwell's equations.
    Microscopy and Microanalysis 05/2014; 20(4):1-7. DOI:10.1017/S1431927614000786 · 1.88 Impact Factor
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    ABSTRACT: Skyrmions are nanoscale spin textures that are viewed as promising candidates as information carriers in future spintronic devices. Skyrmions have been observed using neutron scattering and microscopy techniques. Real-space imaging using electrons is a straightforward way to interpret spin configurations by detecting the phase shifts due to electromagnetic fields. Here, we report the first observation by electron holography of the magnetic flux and the three-dimensional spin configuration of a skyrmion lattice in Fe0.5Co0.5Si thin samples. The magnetic flux inside and outside a skyrmion was directly visualized and the handedness of the magnetic flux flow was found to be dependent on the direction of the applied magnetic field. The electron phase shifts φ in the helical and skyrmion phases were determined using samples with a stepped thickness t (from 55 nm to 510 nm), revealing a linear relationship (φ = 0.00173t). The phase measurements were used to estimate the three-dimensional structures of both the helical and skyrmion phases, demonstrating that electron holography is a useful tool for studying complex magnetic structures and for three-dimensional, real-space mapping of magnetic fields.
    Nature Nanotechnology 04/2014; 9(5). DOI:10.1038/nnano.2014.52 · 34.05 Impact Factor
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    ABSTRACT: Precise evaluation of the electrostatic potential distributions of and around samples with multiple charges using electron holography has long been a problem due to unknown perturbation of the reference wave. Here, we report the first practical application of split-illumination electron holography (SIEH) to tackle this problem. This method enables the use of a non-perturbed reference wave distant from the sample. SIEH revealed the electrostatic potential distributions at interfaces of the charged particles used for development in electrophotography and should lead to dramatic improvements in electrophotography.
    Applied Physics Letters 03/2014; 104(13):131601-131601-4. DOI:10.1063/1.4869830 · 3.30 Impact Factor
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    ABSTRACT: We have established a unique technique to fabricate three-dimensional (3D) well-defined transition-metal oxide epitaxial nanostructures. Fabrication of epitaxial spinel ferrite Fe2.2Zn0.8O4 (FZO) nanowall wires with a tunable width down to 20 nm was achieved. Cross-sectional transmission electron microscopy revealed the existence of an epitaxially matched lateral interface between the FZO nanowall wire and the side surface of 3D-MgO substrate. Magnetoresistance measurements showed ferromagnetic properties of the FZO nanowall wire at 300 K. The role of antiphase boundaries on the functionalities of the FZO nanoconfined wire is discussed.
    Applied Physics Express 03/2014; 7(4):045201. DOI:10.7567/APEX.7.045201 · 2.37 Impact Factor
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    ABSTRACT: Advanced split-illumination electron holography was developed by employing two biprisms in the illuminating system to split an electron wave into two coherent waves and two biprisms in the imaging system to overlap them. A focused image of an upper condenser-biprism filament was formed on the sample plane, and all other filaments were placed in its shadow. This developed system makes it possible to obtain precise reconstructed object waves without modulations due to Fresnel fringes, in addition to holograms of distant objects from reference waves.
    Ultramicroscopy 02/2014; 137:7–11. DOI:10.1016/j.ultramic.2013.11.002 · 2.44 Impact Factor
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    ABSTRACT: The magnetic and crystallographic microstructures in Fe2.5Zn0.5O4 (FZO) wires fabricated using nano-imprint lithography, pulsed laser deposition and a molybdenum lift-off mask technique were studied by transmission electron microscopy (TEM). A process using a focused ion beam completely separated the FZO wires from the insulating MgO substrate, and accordingly allowed in-depth TEM studies of the domain structures. Observations using energy-filtered TEM demonstrated good crystallinity of the FZO wires. Both Lorentz microscopy and electron holography studies revealed unexpectedly small magnetic domains (∼100 nm or smaller) due to a significant interaction with antiphase boundaries. The role of antiphase boundaries on the functionalities observed in the constrained wires (e.g., nonlinear I–V characteristics and large magnetoresistance) is discussed on the basis of these microscopic observations.
    Acta Materialia 02/2014; 64:144–153. DOI:10.1016/j.actamat.2013.10.015 · 4.47 Impact Factor
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    ABSTRACT: Crystallographic and magnetic domains produced in a spinel-type compound MnV2O4, which exhibits a type of giant magnetostriction attributed to twin boundary motion, have been studied using transmission electron microscopy techniques. Although MnV2O4 undergoes a displacive cubic-to-tetragonal transformation upon cooling, it does not show a well-defined habit plane (i.e. the plane with a specific index that is favored for minimizing the transformation) due to the small elongation/contraction in the lattice. Electron holography demonstrates a considerable reduction in the magnetic signal by cooling the tetragonal phase to 40 K. Despite the elimination of micrometer-scale ferrimagnetic domains, weak magnetic contrast still remained, indicating small residual magnetic domains in particular portions, such as in the crosshatch of twinning pairs.
    Journal of Alloys and Compounds 11/2013; 577:S731-S735. DOI:10.1016/j.jallcom.2012.02.031 · 3.00 Impact Factor
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    ABSTRACT: The charging effects of microfibrils of sciatic nerve tissues due to electron irradiation are investigated using electron holography. The phenomenon that the charging effects are enhanced with an increase of electron intensity is visualized through direct observations of the electric potential distribution around the specimen. The electric potential at the surface of the specimen could be quantitatively evaluated by simulation, which takes into account the reference wave modulation due to the long-range electric field.
    Microscopy and Microanalysis 08/2013; 19(S5). DOI:10.1017/S1431927613012324 · 1.88 Impact Factor
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    ABSTRACT: The charging effect due to electron irradiation in an electron microscope has been studied so far with incident electrons. Here we report on a new specimen holder to control the charging effect by using electrons emitted from an irradiation port in the holder while maintaining a constant intensity of the incident electron beam. Details of the charging effect, such as electric field variation, are expected to be investigated by electron holography. The new specimen holder was developed by modifying a double-probe piezodriving specimen holder to introduce an electron irradiation port in one of its two arms. As a result, the new modified specimen holder consists of a piezodriving probe and an electron irradiation port, both of which can be controlled in three dimensions, using piezoelectric elements and micrometers. We demonstrate that variations in the charging effect for epoxy resin and surface contamination can be observed by electron holography.
    Journal of electron microscopy 04/2013; 62(4). DOI:10.1093/jmicro/dft021 · 1.63 Impact Factor

Publication Stats

3k Citations
822.96 Total Impact Points


  • 2010–2015
    • RIKEN
      • Center for Emergent Matter Science (CEMS)
      Вако, Saitama, Japan
    • Okinawa Institute of Science and Technology
      Okinawa, Okinawa, Japan
  • 1980–2015
    • Tohoku University
      • • Institute of Multidisciplinary Research for Advanced Materials (IMRAM)
      • • Institute for Materials Research
      • • Department of Chemistry
      • • Department of Physics
  • 2007–2011
    • Osaka Prefecture University
      • • Graduate School of Engineering
      • • Department of Physics and Electronics
      Sakai, Ōsaka, Japan
    • Hokkaido University
      Sapporo, Hokkaidō, Japan
  • 2006
    • Samsung Advanced Institute of Technology
      Usan-ri, Gyeonggi-do, South Korea
  • 2005
    • University of Sydney
      Sydney, New South Wales, Australia
  • 2003
    • Kumamoto University
      Kumamoto, Kumamoto, Japan
  • 1989
    • Purdue University
      ウェストラファイエット, Indiana, United States
    • University of Zurich
      • Institut für Anorganische Chemie
      Zürich, Zurich, Switzerland