Presentation Information
[O9-3]Particle size effects on degree of alignment in Ba-Cu doped Sm2Fe17N3 sintered magnets
*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,sintered magnet,magnetic alignment
The Sm2Fe17N3 compound is one of prospective candidates for next generation permanent magnets because of its high saturation magnetization and coercivity as well as high Curie temperature [1], but Sm2Fe17N3 has not been sintered densely due to the constraints of decomposition temperature (620°C). Recently, we have developed the novel sintering aid containing alkaline earth metals, which successfully enhanced the volume fraction of main phase and magnetization [2, 3]. Although the energy product could be increased by doping the sintering aid, the magnetic properties should be further improved for practical applications. Then we investigated the factors that could improve the degree of alignment (DOA) of Sm2Fe17N3 anisotropic sintered magnets. Although it has been reported that the DOA in powder tends to decrease when the average particle diameter of Sm2Fe17N3 is near 1 μm [4], few studies have quantitatively evaluated the DOA in sintered magnet. Therefore, in this study, we have investigated the influence of particle diameter on the DOA of Sm2Fe17N3 sintered magnets in details.
The manufacturing process of sintered magnets was carried out in a glove box with the oxygen concentration controlled below 0.5 ppm. Sm2Fe17N3 coarse powder (provided from Sumitomo Metal Mining Co., Ltd.) was pulverized to D50≒1.5 μm (referred to as Powder A, hereafter) and 3.0 μm (Powder B) using jet-milling. Ba-Cu alloy with a eutectic point of 440 °C was selected as a sintering aid. Both pulverized Sm2Fe17N3 powders of A and B were coated with 2 wt.% Ba80Cu20 (at.%) using the magnetron sputtering technique while the powder was stirred. The coated powders were put in the mold made of nonmagnetic WC-FeAl and magnetically aligned with a static magnetic field of 2 T at room temperature. The aligned powders were sintered at 400 – 500 °C for 2 minutes under the vacuum below 0.5 Pa with a pressure of 1200 MPa. The magnetic properties of sintered magnets were evaluated by using VSM (DynaCool, Quantum Design inc.) with the maximum field of 9 T. The DOA of sintered magnets were estimated by measuring the pole-figure around (003) plane using synchrotron X-ray diffraction in Aichi Synchrotron Center.
A relative density of over 90% was obtained for both the sintered magnets of A and B. By measuring the demagnetization curves of sintered magnets, the remanence and the energy product of the sintered magnet B were higher than those of the sintered magnet A, although the sintered magnet B had lower coercivity because of its larger particle size. To discuss the difference in remanence between A and B, the pole figures of sintered magnets were measured. The shape of the pole figures was an ellipse vertically elongated in this paper, which coincides with the actual direction of pressure applied during pressure sintering. In the sintered magnet B, the shape of the high-intensity region of the pole-figure became closer to a circle, suggesting that the alignment degree was improved. The DOA of the sintered magnets A and B were estimated to be 71.9% and 83.6%, respectively from these pole figures. The particle size distribution measurements of the pulverized powder showed that the frequencies of fine particles under 1 μm in the powders of A and B were approximately 30% and 10%, respectively. Therefore, it seems conclusive that the DOA of the Sm2Fe17N3 sintered magnets are dependent on the crystal grain size, and it would be expected that remanence could be further improved by controlling the particle size (and its distribution) of the pulverized powder.
[1] T. Iriyama, K. Kobayashi, N. Imaoka, IEEE Trans. Magn. 28 (1992) 2326-2331.
[2] Niterra Co., Ltd., AIST, press release “Development of high-density technology for Sm2Fe17N3 permanent magnet” (2024)
[3] Y. Iida, A. Hosokawa, W. Yamaguchi, Y. Hirayama, Abstractbooks MMM InterMag 2025, p.97 (2025)
[4] A. Hosokawa, W. Yamaguchi, K. Suzuki, K. Takagi, J. Alloy. Compd. 869 (2021) 159288.
The manufacturing process of sintered magnets was carried out in a glove box with the oxygen concentration controlled below 0.5 ppm. Sm2Fe17N3 coarse powder (provided from Sumitomo Metal Mining Co., Ltd.) was pulverized to D50≒1.5 μm (referred to as Powder A, hereafter) and 3.0 μm (Powder B) using jet-milling. Ba-Cu alloy with a eutectic point of 440 °C was selected as a sintering aid. Both pulverized Sm2Fe17N3 powders of A and B were coated with 2 wt.% Ba80Cu20 (at.%) using the magnetron sputtering technique while the powder was stirred. The coated powders were put in the mold made of nonmagnetic WC-FeAl and magnetically aligned with a static magnetic field of 2 T at room temperature. The aligned powders were sintered at 400 – 500 °C for 2 minutes under the vacuum below 0.5 Pa with a pressure of 1200 MPa. The magnetic properties of sintered magnets were evaluated by using VSM (DynaCool, Quantum Design inc.) with the maximum field of 9 T. The DOA of sintered magnets were estimated by measuring the pole-figure around (003) plane using synchrotron X-ray diffraction in Aichi Synchrotron Center.
A relative density of over 90% was obtained for both the sintered magnets of A and B. By measuring the demagnetization curves of sintered magnets, the remanence and the energy product of the sintered magnet B were higher than those of the sintered magnet A, although the sintered magnet B had lower coercivity because of its larger particle size. To discuss the difference in remanence between A and B, the pole figures of sintered magnets were measured. The shape of the pole figures was an ellipse vertically elongated in this paper, which coincides with the actual direction of pressure applied during pressure sintering. In the sintered magnet B, the shape of the high-intensity region of the pole-figure became closer to a circle, suggesting that the alignment degree was improved. The DOA of the sintered magnets A and B were estimated to be 71.9% and 83.6%, respectively from these pole figures. The particle size distribution measurements of the pulverized powder showed that the frequencies of fine particles under 1 μm in the powders of A and B were approximately 30% and 10%, respectively. Therefore, it seems conclusive that the DOA of the Sm2Fe17N3 sintered magnets are dependent on the crystal grain size, and it would be expected that remanence could be further improved by controlling the particle size (and its distribution) of the pulverized powder.
[1] T. Iriyama, K. Kobayashi, N. Imaoka, IEEE Trans. Magn. 28 (1992) 2326-2331.
[2] Niterra Co., Ltd., AIST, press release “Development of high-density technology for Sm2Fe17N3 permanent magnet” (2024)
[3] Y. Iida, A. Hosokawa, W. Yamaguchi, Y. Hirayama, Abstractbooks MMM InterMag 2025, p.97 (2025)
[4] A. Hosokawa, W. Yamaguchi, K. Suzuki, K. Takagi, J. Alloy. Compd. 869 (2021) 159288.
