Presentation Information
[P2-52]Effect of Sm2Fe17N3 fine powder obtained by jet milling on magnetic properties
*Teruta Inoue1, Yuta Iida1,2, Akihide Hosokawa2, Wataru Yamaguchi2, Yusuke Hirayama2 (1. Niterra Co., Ltd. (Japan), 2. National Institute of Advanced Industrial Science and Technology (AIST) (Japan))
Keywords:
Sm2Fe17N3 powder,particle size,jet milling
1.Introduction
The Sm2Fe17N3 compound is expected as a promising candidate for next generation permanent magnet material because of its high saturation magnetization and coercivity [1] and a high Curie temperature. On the other hand, Sm2Fe17N3 has a problem of insufficient densification due to the limitation of sintering temperature. We have succeeded in improving the densification of Sm2Fe17N3 by using an alloy containing Alkaline earth metal as a sintering aids [2]. With densification, the volume fraction of the main phase increased and magnetic properties were greatly improved. However, further improvement of magnetic performance is needed for social implementation. The magnetic performance of Sm2Fe17N3 sintered magnets is greatly affected by the state of the Sm2Fe17N3 powders to be used for sintering processes. Therefore, we have reported that the magnetic performance was improved by controlling the particle size of the Sm2Fe17N3 powders [3,4]. In this presentation, the effect of particle size distribution on the magnetic performance of Sm2Fe17N3 powders will be reported. The particle size distribution was controlled by reducing the percentage of fine particles of 1µm or less in the Sm2Fe17N3 powders by classification (i.e. sieving) process.
2.Experiment
All processes were performed in a glove box filled with argon atmosphere with the oxygen content below 0.5 ppm. First, a fine Sm2Fe17N3 powder with D50 = 2.5 µm was prepared by jet milling from Sm2Fe17N3 coarse powders of D50 = 30 µm, we attempted to separate fine particles of 1 µm or less in diameter by passing the milled powder through a gas flow classifier (Picoline, Hosokawa micron Ltd.).
3.Results
Fig. 1 shows the measurement results of the magnetic performance of the jet milled powders before and after classification. The Sm2Fe17N3 powder of after classification had higher remanence and the saturation magnetizations since the percentage of fine powder was reduced. In addition, the squareness was improved by about 12%. On the other hand, coercivity decreased by about 17%. By focusing on the fine powder, coercivity was enhanced compared to before classification, while both magnetization and squareness were greatly reduced. The reason for this is that there are more nanograins with a random orientation other than the easy axis of magnetization as the particles become finer, which inhibits the orientation of the particles by external magnetic field as suggested by the FWHM of the XRD peak and the results of microstructural observation by transmission electron microscope.
References
[1] T. Iriyama, K. Kobayashi, N. Imaoka, IEEE Trans. Magn., vol. 28, p.2326-2331 (1992)
[2] Niterra Co., Ltd., AIST, press release “Development of high-density technology for Sm2Fe17N3 permanent magnet” (2024)
[3]A. Hosokawa, W. Yamaguchi, K. Suzuki, K. Takagi, J. Alloys Compounds, vol. 869, Art. no. 159288 (2021)
[4] W. Yamaguchi, A. Hosokawa, K. Takagi, IEEE Trans. Magn., vol. 59, no. 11 (2023)
The Sm2Fe17N3 compound is expected as a promising candidate for next generation permanent magnet material because of its high saturation magnetization and coercivity [1] and a high Curie temperature. On the other hand, Sm2Fe17N3 has a problem of insufficient densification due to the limitation of sintering temperature. We have succeeded in improving the densification of Sm2Fe17N3 by using an alloy containing Alkaline earth metal as a sintering aids [2]. With densification, the volume fraction of the main phase increased and magnetic properties were greatly improved. However, further improvement of magnetic performance is needed for social implementation. The magnetic performance of Sm2Fe17N3 sintered magnets is greatly affected by the state of the Sm2Fe17N3 powders to be used for sintering processes. Therefore, we have reported that the magnetic performance was improved by controlling the particle size of the Sm2Fe17N3 powders [3,4]. In this presentation, the effect of particle size distribution on the magnetic performance of Sm2Fe17N3 powders will be reported. The particle size distribution was controlled by reducing the percentage of fine particles of 1µm or less in the Sm2Fe17N3 powders by classification (i.e. sieving) process.
2.Experiment
All processes were performed in a glove box filled with argon atmosphere with the oxygen content below 0.5 ppm. First, a fine Sm2Fe17N3 powder with D50 = 2.5 µm was prepared by jet milling from Sm2Fe17N3 coarse powders of D50 = 30 µm, we attempted to separate fine particles of 1 µm or less in diameter by passing the milled powder through a gas flow classifier (Picoline, Hosokawa micron Ltd.).
3.Results
Fig. 1 shows the measurement results of the magnetic performance of the jet milled powders before and after classification. The Sm2Fe17N3 powder of after classification had higher remanence and the saturation magnetizations since the percentage of fine powder was reduced. In addition, the squareness was improved by about 12%. On the other hand, coercivity decreased by about 17%. By focusing on the fine powder, coercivity was enhanced compared to before classification, while both magnetization and squareness were greatly reduced. The reason for this is that there are more nanograins with a random orientation other than the easy axis of magnetization as the particles become finer, which inhibits the orientation of the particles by external magnetic field as suggested by the FWHM of the XRD peak and the results of microstructural observation by transmission electron microscope.
References
[1] T. Iriyama, K. Kobayashi, N. Imaoka, IEEE Trans. Magn., vol. 28, p.2326-2331 (1992)
[2] Niterra Co., Ltd., AIST, press release “Development of high-density technology for Sm2Fe17N3 permanent magnet” (2024)
[3]A. Hosokawa, W. Yamaguchi, K. Suzuki, K. Takagi, J. Alloys Compounds, vol. 869, Art. no. 159288 (2021)
[4] W. Yamaguchi, A. Hosokawa, K. Takagi, IEEE Trans. Magn., vol. 59, no. 11 (2023)
