SATOSHI OKAMOTO

TOHOKU UNIVERSITY

Institute of Multidisciplinary Research for Advanced Materials (IMRAM)

Professor

About

Satoshi Okamoto is a Professor at the Institute of Multidisciplinary Research for Advanced Materials (IMRAM) at Tohoku University. Okamoto lab, established in April of 2020, focuses on research related to high functionality magnetic materials. More specifically, the lab conducts research on methods to control the surface magnetization state of permanent magnets in order to achieve high performance. This includes elucidating and controlling magnetic functions at the nanoscale. Recently, data science approaches have also been integrated into the research process.

Research Disciplines

Materials Science, Magnetic Materials

Featured Presentation

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Title: Three dimensional multimodal analyses on Nd-Fe-B magnet

Keywords: Magnetic material, 3D imaging, Nd-Fe-B magnet

Abstract: Coercivity and hysteresis curve shape are very basic magnetic properties of Nd-Fe-B magnets, but they are still not fully understood. Since they are related to the microstructure of nm-scale grain boundary phase, micrometer-scale main phase grain, and tens micrometer-scale grain alignments. Moreover, they are also strongly related to the magnetization processes of nm-scale nucleation, micrometer-scale domain wall depinning, and tens micorometer-scale domain structure formation. In addition, crystalline orientation of each main phase grain is also an important factor of coercivity and hysteresis curve shape. From these points of view, numerous studies about multiscale microstructure and magnetic domain observations of Nd-Fe-B magnets have been reported so far. Recently, 3-dimensional (3D) visualization techniques of scanning electron microscopy (SEM) and X–ray magnetic circular dichroism (XMCD) microscopy have been developed for 3D-microstructure and magnetic domain structure observations, respectively. And very recently, we successfully demonstrated the combined 3D-magnetic domain structure and microstructure observations of a Tb-Cu infiltrated Nd-Fe-B sintered magnet along the magnetic hysteresis curve with varying the external magnetic field. This was the first observation of the magnetic domain evolution inside the Nd-Fe-B magnet body, and the strong relationship between the magnetic domain evolution and the microstructures was observed. However, the very low signal to noise ratio (SNR) of XMCD signal hinders us from the detailed analysis. Moreover, the complicated microstructures and magnetic domain structures of the Nd-Fe-B sintered magnet also makes the analysis very difficult. Therefore, as a next step, the combined observations of 3D-SEM and 3D-XMCD were employed for a Nd-Fe-B hot-deformed magnet. Since the Nd-Fe-B hot-deformed magnet has a much more uniform microstructure and simple magnetic domain structure, much easier analysis is highly expected. After the elaborate noise reduction processes, very clear magnetic domain evolution was successfully observed. As a result, it is possible to discuss the major domain wall pinning sites and magnetic domain evolution process of the Nd-Fe-B hot-deformed magnet.