Toward for Improvement of Magnetic Properties in Permanentmagnets
Critical Metal Symposium in Sendai
Abstract
Permanent magnets are widely used in many applications. In this talk, recent progress of a technique for obtaining high coercive Nd-Fe-B magnets and a research for aiming to develop a new-type magnet in our laboratory will be introduced.
Decreasing grain size of the Nd2Fe14B phase is an established method for increasing coercivity of Nd-Fe-B sintered magnets. We decreased the size of jet-milled powder to around 1 m by He jet-milling (He-JM) in Dy-free Nd-Fe-B sintered magnets and obtained high coercivity (0HcJ) of 2 T with (BH)max of around 400 kJm-3. We also succeeded further decrease in the size to 0.3 m by combining HDDR, hydrogen decrepitation (HD) and He-JM. Recently, the effects of annealing and grain boundary diffusion (GBD) process on coercivity were investigated. GBD processed powder showed high 0HcJ of 2.0 T after annealing at 600 oC. From TEM analyses, Nd-rich phase was observed on the surface of the powder.
No material which shows higher magnetic properties than Nd-Fe-B magnets has been found. However, we recently found that Mn-Sn-Co-N alloys show high coercivity comparable to rare earth magnets. The alloy showed high 0HcJ of 1.59 T and two phase microstructure consisting of a perovskite phase and a -Mn phase. TEM observation revealed that many twins were induced in the perovskite phase. It is considered that the microstructure is related to high coercivity.
Decreasing grain size of the Nd2Fe14B phase is an established method for increasing coercivity of Nd-Fe-B sintered magnets. We decreased the size of jet-milled powder to around 1 m by He jet-milling (He-JM) in Dy-free Nd-Fe-B sintered magnets and obtained high coercivity (0HcJ) of 2 T with (BH)max of around 400 kJm-3. We also succeeded further decrease in the size to 0.3 m by combining HDDR, hydrogen decrepitation (HD) and He-JM. Recently, the effects of annealing and grain boundary diffusion (GBD) process on coercivity were investigated. GBD processed powder showed high 0HcJ of 2.0 T after annealing at 600 oC. From TEM analyses, Nd-rich phase was observed on the surface of the powder.
No material which shows higher magnetic properties than Nd-Fe-B magnets has been found. However, we recently found that Mn-Sn-Co-N alloys show high coercivity comparable to rare earth magnets. The alloy showed high 0HcJ of 1.59 T and two phase microstructure consisting of a perovskite phase and a -Mn phase. TEM observation revealed that many twins were induced in the perovskite phase. It is considered that the microstructure is related to high coercivity.
その他特記事項
Some of researches presented in this talk are partially supported by the following projects.（1） NEDO, Japan, Grant-in-Aid for ”Development of technology for reducing dysprosium usage in a rare-earth magnet in Rare Metal Substitute Materials Development Project”, （2） Japan CREST project (Core Research for Evolutionary Science and Technology) in JST (Japan Science and Technology Agency), （3） The Future Pioneering Projects / Development of magnetic material technology for high-efficiency motors” from the Ministry of Economy, Trade and Industry., （4）Elements Strategy Initiative Center for Magnetic Materials (ESICMM).
