The 310th MANA & the 133rd ICYS Joint Seminar

Dr. Hossein Sepehri Amin & Dr. Ming Hu

Date February 1, Friday
Time 15:30-16:30
Place Seminar room #811, 8F, Central Bldg, Sengen Site, NIMS

Download PDF file for seminar info.


Development of high coercivity anisotropic hot deformed Nd-Fe-B magnets

The necessity of developing high coercivity Dy-free Nd-Fe-B magnets for the traction motors of (hybrid) electric vehicles and wind turbines has attracted the interest of researchers to study the coercivity mechanism of Nd-Fe-B type magnets. It is known that the grain size refinement of the Nd2Fe14B phase can enhance the coercivity. Hot-deformed Nd-Fe-B magnets prepared from rapidly solidified powders shows a strongly (001) textured ultra-fine grained structure 1 with the potential to attain a much higher coercivity than that of Nd-Fe-B sintered magnets. However, the reported coercivity of hot-deformed Nd-Fe-B magnets is only 1.6 T 2.

In this work, responsible mechanism for low coercivity of anisotropic hot-deformed Nd-Fe-B sintered magnets will be discussed based on our microstructure studies. Micromagnetic simulation was introduced to understand the microstructure and magnetization reversal correlation of the hot deformed Nd-Fe-B magnets. Micromagnetic simulation results showed that reduction of the saturation magnetization of the grain boundary (GB) phase leads to increase of the nucleation field and coercivity. After nucleation of reversed magnetic domain at the triple junction of the GB phase, reversed domain propagates in a columnar shape followed by lateral propagation. It was found that decrease of the saturation magnetization of the GB phase also increases the pinning strength of the GB phase against magnetic domain wall motion. This can be done by the GB chemistry modification which was demonstrated in hot deformed Nd-Fe-B magnet leading to the coercivity enhancement to a level of 2.3 T.

  1. R. W. Lee, Appl. Phys. Lett. 46, 790 (1985).
  2. K. Khlopkov et al. J. Magn. Magn. Mater. 272-276 (2004) e1937.


Dr. Hossein Sepehri Amin, ICYS-Sengen Researcher, NIMS


Dr. Kazuhiro Hono, Unit Director, Magnetic Materials Unit, NIMS


Templated Synthesis of Nanoporous Materials from Nanostructured Microporous Coordination Compounds

Microporous coordination compounds, including metal-organic frameworks or porous coordination polymers, are widely utilized due to the advantages such as highly porous structure and high specific surface area. Interestingly, microporous coordination compounds can also work as template for making nanoporous materials such as nanoporous metal oxide and carbons. Owing to the initial porous structure of microporous coordination compounds, the obtained nanoporous materials can show high porosity which is welcomed by many applications. Here, we will show several kinds of nanoporous metal oxides and carbons prepared by thermal-decomposition of microporous coordination compounds.


Dr. Ming Hu, ICYS-MANA Researcher, MANA, NIMS


Dr. Yusuke Yamauchi, Independent Scientist, MANA, NIMS