Microstructure and Magnetic Properties of Sn added MnBi Bulk Magnets

다국어 초록 (Multilingual Abstract)

Rare-earth free permanent magnets are current emerging issues of industry for the growing market demands. Among the rare-earth free permanent magnets, MnBi has attracted attention for large magnetocrystalline anisotropy constant (K₁ ≈ 1.6 MJ/m³, at 300 K) and unique positive temperature coefficient of coercivity (Hc). The low-temperature phase (LTP) of MnBi exhibits a saturation magnetization (Ms) of 80 emu/g, and the theoretical maximum energy product (BH)max 17.7 MGOe at room temperature. However, it is a challenge to fabricate MnBi bulk magnets while maintaining the superior magnetic properties of the powder, especially to prevent the reduction of Hc from powder to bulk. The effects of Sn adding on the microstructure and magnetic properties of MnBi bulk magnets have been systematically investigated. As kwon, the pure MnBi bulk magnets are challenging to reach high Hc in previous studies, and a few reference works have been reported about research on fabrication of high Hc MnBi bulks by adding the third element. It was found that the Sn-added MnBi bulk magnets show the increased Hc and the improved squareness, apparently related to restructuring the intergranular phase due to Sn element addition. The Hc of MnBi bulk magnet with 3 wt.% Sn reaches 11.6 kOe, which is 35 % higher than that of the pure MnBi magnet. In the sample of 1 wt.% Sn added MnBi bulk magnet, the Hc was elevated to 10.0 kOe, and the maximum energy product (BH)max was recorded of 7.84 MGOe at room temperature. This makes Sn added MnBi bulk magnet a promising candidate for next-generation rare-earth-free bulk magnets.
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