Yoshinobu NAKATANI (仲谷 栄伸)

Offer Organization: Japan Society for the Promotion of Science, System Name: Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B), Category: Grant-in-Aid for Scientific Research (B), Fund Type: -, Overall Grant Amount: - (direct: 13800000, indirect: 4140000)
We show that machine learning can be used to extract material parameters from a single image obtained in experiments. The DzyaloshinskMoriya (DM) interaction and the magnetic anisotropy distribution of thin-film heterostructures, parameters that are critical in developing next-generation storage class magnetic memory technologies, are estimated from a magnetic domain image. Micromagnetic simulation is used to generate thousands of random images for training and model validation. A convolutional neural network system is employed as the learning tool. The DM exchange constant of typical Co-based thin-film heterostructures is studied using the trained system: the estimated values are in good agreement with experiments. Moreover, we show that the system can independently determine the magnetic anisotropy distribution, demonstrating the potential of pattern recognition. This approach can considerably simplify experimental processes and broaden the scope of materials research.

Offer Organization: Japan Society for the Promotion of Science, System Name: Grants-in-Aid for Scientific Research, Category: Grant-in-Aid for Challenging Exploratory Research, Fund Type: -, Overall Grant Amount: - (direct: 3100000, indirect: 930000)
The observation of Skyrmion at room temperature were investigated using ferromagnetic thin films with perpendicular magnetic anisotropy. (1) In the experimental research using Co/Ni multilayer films, it observed the movement of the magnetic domain structures in magnetic wires, however it did not observed the Skyrmions. (2) In the research using numerical simulations, we investigated the nucleation and annihilation conditions of Skyrmions in Co / Ni multilayers and clarified the conditions that the Skyrmion exists stably at room temperature.
As other research, we investigated that (3) the magnitude of the topological Hall effect depending on the magnetization structure in the cross-shaped magnetic wire, and that (4) the changing the magnetic domain structures in the Ni wire on the piezoelectric substrate LiNbO3.

Offer Organization: Japan Society for the Promotion of Science, System Name: Grants-in-Aid for Scientific Research Grant-in-Aid for Specially Promoted Research, Category: Grant-in-Aid for Specially Promoted Research, Fund Type: -, Overall Grant Amount: - (direct: 432500000, indirect: 129750000)
This project established the field of Spin-orbitronics by exploiting the spin-orbit interaction of electrons in solids to form new materials with novel functionalities and find new physics. New approach for designing strong magnetic anisotropy materials, novel way for efficient magnetization control, and new method for controlling spins in antiferromagnets were developed, which will enable development of high speed, energy efficient electronic devices and technological innovations.

Offer Organization: Japan Society for the Promotion of Science, System Name: Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C), Category: Grant-in-Aid for Scientific Research (C), Fund Type: -, Overall Grant Amount: - (direct: 3900000, indirect: 1170000)
Recently a storage system, which uses a magnetic domain wall as an information carrier was proposed, and the domain wall have been studied intensively. Because the domain wall motion velocity is related to the operation speed of the storage system, it is required to obtain the conditions for fast domain wall motion, and to investigate the domain wall motion mechanism. In this research, the effect of the Dzyaroshinskii-Moriya interaction on the domain wall motion induced by a spin current, a magnetic field, and an electric field were investigated by computer simulation, and obtained the conditions for fast domain wall motion, and revealed the domain wall motion mechanism.

Offer Organization: Japan Society for the Promotion of Science, System Name: Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (S), Category: Grant-in-Aid for Scientific Research (S), Fund Type: -, Overall Grant Amount: - (direct: 165700000, indirect: 49710000)
The purpose of this project is to develop novel spin devices that utilize the current-induced spin dynamics in non-uniform spin structure, such as a magnetic domain wall and a magnetic vortex. We succeeded in demonstrating the operation of the spin devices such as domain wall memory and vortex core memory. Furthermore, we obtained unexpected results such as the observation of spin motive force in gyrating vortex core and the modulation of ferromagnetic transition temperature of Cobalt by electric field gating.

Offer Organization: Japan Society for the Promotion of Science, System Name: Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research on Priority Areas, Category: Grant-in-Aid for Scientific Research on Priority Areas, Fund Type: -, Overall Grant Amount: - (direct: 12000000, indirect: -)
This research members are the leaders of each group in A05 "Functions and Control of Spin Currents". We explored principles of control and transformations of various signals and their functions, and proposed new devices and realized their operations. Cooperating with other groups, we studied spin-polarized-current-controlled devices, spin current, microwave and thermal devices, optical spintronics devices, spin-current-induced magnetization reversal devices, and theories and designs. Furthermore, we enhanced exchange of ideas and collaborations. We organized the 6th International Conference on Physics and Applications of Spin Related Phenomena in Semiconductors (PASPS-VI)) in Tokyo, August 2010 (Conference chair : Masaaki Tanaka), and contributed the worldwide advance of this field.

Offer Organization: Japan Society for the Promotion of Science, System Name: Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research on Priority Areas, Category: Grant-in-Aid for Scientific Research on Priority Areas, Fund Type: -, Overall Grant Amount: - (direct: 16600000, indirect: -)
Recently, there are many works relating to the vortex core dynamics by spin current. In this research the mechanism of the vortex core rotation and switching by spin current are investigated by using computer simulation. We also investigate the conditions to use this mechanism for magnetic devices. Because these simulation requires huge amount of the computation time, we propose the method to accelerate the calculation speed by using the graphic processing unit.

Offer Organization: 日本学術振興会, System Name: 科学研究費助成事業 奨励研究(A), Category: 奨励研究(A), Fund Type: -, Overall Grant Amount: - (direct: 900000, indirect: -)
磁性薄膜中に存在する磁壁上の磁化構造であるブロッホラインを情報の記憶単位として用いるブロッホライン記憶装置は、次世代の不揮発性高密度個体記憶装置として現在研究が進められている。情報の書き込み操作であるブロッホライン対の書き込みの操作の一つとして、ブロッホポイント注入法が提案されている。この手法ではまずunwindingな二つのブロッホライン対を生成し、それぞれの内側のブロッホラインを消去することで、windingで安定なブロッホライン対を生成する。内側のブロッホラインの消去過程において、ブロッホポイントの発生が仮定されているが、実験ではブロッホポイントは直接観測することは出来ない。ここでは計算機シミュレーションを行なうことで、ブロッホライン書き込み操作の一部であるブロッホポイントの注入によるブロッホライン対の消滅過程の詳細を求めた。これらの計算は東京大学大型計算機センターのスーパーコンピュータを用いて行なった。計算は三次元の動的計算であるために、その結果として膨大な数値データが得られるが、これを詳細に解析するためには数値の視覚化が必要になる。この作業は研究室のワークステーション上で行なった。数値データと視覚化した画像データは膨大な量になるために、専用のハードディスク装置を購入した。