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Authors：Ken-ichi Uchida et al.
Published online： 12 December 2016
Press release online (in Japanese)：PDF:735KB
Surface and Interface Research
Authors：Takeshi Seki et al.
Journal：Physical Review B
Published online： 8 December 2016
Press release online (in Japanese)：PDF:353KB
Scientists in Japan have revealed that if a glassy solid possesses a planar (sheet-like) structure, it can exhibit enhanced thermal vibration motion due to the same mechanism known for the planar crystals (two-dimensional crystals), by using large-scale simulations on supercomputers.
"Imagine if we could make a sheet of glass, which has a two-dimensional (2D) planate shape," says Dr. Hayato Shiba, of Tohoku University's Institute for Materials Research (IMR). "In such a confined spatial dimension, a variety of novel phenomena takes place in usual "periodic" systems (crystals, spin systems etc.). This is due to the thermal motion of the constituents taking place on a larger scale because of the limited spatial dimensions."
Such enhanced thermal motion is known to induce new physical phenomena which Shiba, and his research team of Yasunori Yamada (IMR), Takeshi Kawasaki (Nagoya University) and Kang Kim (Osaka University), hope will lead the development of new functional materials and devices necessary for the realization of energy-saving societies.
However, it is still uncertain whether 2D glass, as an "non-periodic" system, exhibits such enhanced thermal motions."Our result indicates that 2D glass can become soft, gradually and forever, as we go to the macroscopic scales. Consequently, the vibration amplitude becomes infinite because of the large-scale motions," says Shiba.
"In other words, such materials might exhibit strong responses to external fields or deformation. The thermal vibration is perfectly different from that in a 3D glass, and it can even alter the fundamental nature of vitrification and glassy phase transition."
In the experiments, 2D glass was experimentally realized using colloidal systems, and can also be realized using other soft and hard materials.
detail1: press release (in Japanese) [PDF:1.6MB]
detail2:Physical Review Letters Website [DOI:10.1103/PhysRevLett.117.245701]
Left and right figures are schematic diagrams of glassy solid in two and three dimensions. Modality of the dynamics of glassy solid in different dimensions is illustrated. In three dimensions, a particle vibrates inside a cage formed by neighboring particles, due to the densely packed condition of the particles, and intermittently goes out of the cage. In two dimensions, long-wavelength vibrational sound waves induce coherent motion of the particles with a large amplitude that can in principle exceed the length scale of particle radii (the aqua colored circle on the left indicates that the caged particle can move a large distance).
Professional development Consortium for Computational Materials Scientists
Authors：Professor Dai Aoki, Professor Hiroyuki Nojiri
20 October 2016
Press release online (in Japanese)：PDF:320KB
Actinide Materials Science
Gold had long been considered a non-magnetic metal. But researchers at Tohoku University recently discovered that gold can in fact be magnetized by applying heat.
They discovered that an electron spin - the origin of magnetism - plays an important role in a material's functionality at a non-constant temperature, where the magnetization and the heat flow interact. A subsequent experiment confirmed, for the first time, that magnetization in gold can be induced by the heat flow driven by a temperature change.
The set up of the experiment was quite simple, involving a bilayer comprising Yttrium iron garnet (YIG), which is an insulator magnet, and a thin film of gold. (Fig below).
In the experiment, the temperature of the YIG side and that of the gold side were kept different to drive a heat flow perpendicular to the bilayer. In addition, a magnetic field was applied in parallel to the heat flow. Under this condition, the Hall voltage*1 was measured in the gold film by in-plane electric current. The Hall voltage showed a clear proportional dependence on the applied temperature gradient.
The team interpreted this Hall voltage as evidence of the evolution of magnetization in the thin gold film due to the heat flow. The Hall voltage was named as a non-equilibrium anomalous Hall effect (nAHE).
"We are excited about the potential of this measurement as a standard method of detecting non-equilibrium magnetization because there's no need for complicated processing and technologies as compared to other highly sensitive magnetometry," says researcher Dazhi Hou. "On top of that, we can detect extremely small magnitudes of magnetization in this measurement. Such small magnetizations is the key to revealing as-yet-unknown useful properties of matters."
"These findings are expected to contribute to the development of innovative spintronics in the use of thermoelectric applications, like energy harvesting, adds Professor Eiji Saitoh, who led the research.
Details of this study were published online on July 26, 2016 in Nature Communications.
This research was achieved as part of JST-ERATO "Spin Quantum Rectification Project" led by Professor Eiji Saitoh.
*1 When passing an electrical current on through a conductor and applying a magnetic field perpendicularly to the direction of the current, an electric voltage will be generated in a direction perpendicular to the current and magnetic field.
detail1: press release (in Japanese) [PDF: 595KB]
detail2:Nature Communications Website[DOI:10.1038/NCOMMS12265]
Hall voltage measurement in the bilayer system under the temperature gradient and external magnetic field perpendicular to the bilayer.
For the innovation of spintronic technologies, Dirac materials, in which low-energy excitation is described as relativistic Dirac fermions, are one of the most promising systems because of the fascinating magnetotransport associated with extremely high mobility. To incorporate Dirac fermions into spintronic applications, their quantum transport phenomena are desired to be manipulated to a large extent by magnetic order in a solid.
We report a bulk half-integer quantum Hall effect in a layered antiferromagnet EuMnBi2, in which field-controllable Eu magnetic order significantly suppresses the interlayer coupling between the Bi layers with Dirac fermions. In addition to the high mobility of more than 10,000 cm2/V s, Landau level splittings presumably due to the lifting of spin and valley degeneracy are noticeable even in a bulk magnet. These results will pave a route to the engineering of magnetically functionalized Dirac materials.
This research was conducted through collaborative research with Tokyo University, Osaka University, RIKEN, High Energy Accelerator Research Organization and IMR. This article carried in Science Advances.
detail1: press release (in Japanese) [PDF:940KB]
detail2: Science Advances Website [DOI: 10.1126/sciadv.1501117]
High Field Laboratory for Superconducting Materials
Laboratory of Low Temperature Materials Science
Mitsubishi Gas Chemical Co., Inc. (MGC), Tohoku University's Advanced Institute for Material Research (AIMR) and Institute for Materials Research (IMR) have developed mass production technology for LiBH4-based solid electrolytes.
These electrolytes are created based on technology developed by Tohoku University, and are suitable as they are flexible and can adhere well to the electrode layer.
There are 2 types of these electrolytes: LiBH4-LiI solid solution and LiBH4-LiNH2 based solid electrolyte. MGC will start supplying the sample of these electrolytes.
For more information on these LiBH4-based solid electrolytes, join MGC at the following conferences.
-nano tech 2016 - The 15th International Nanotechnology
Exhibition & Conference
Dates: January 27 - 29, 2016
Venue: Tokyo Big Sight, Japan
-7th Int'l Rechargeable Battery Expo (BATTERY JAPAN)
Dates: March 2 - 4, 2016