Engineering microstructure to improve coercivity of bulk MnBi magnet

Tang, Wei; Ouyang, Gaoyuan; Liu, Xubo; Wang, Jing; Cui, Baozhi; Cui, Jun

doi:10.1016/j.jmmm.2022.169912

Title: Engineering microstructure to improve coercivity of bulk MnBi magnet

Journal Article · Sun Sep 11 00:00:00 EDT 2022 · Journal of Magnetism and Magnetic Materials

DOI:https://doi.org/10.1016/j.jmmm.2022.169912· OSTI ID:1902756

Tang, Wei ^[1]; Ouyang, Gaoyuan ^[1];

^[1]; Wang, Jing ^[1]; Cui, Baozhi ^[1]; Cui, Jun ^[2]

Critical Materials Institute (CMI), Ames, IA (United States); Ames Lab., Ames, IA (United States)
Critical Materials Institute (CMI), Ames, IA (United States); Ames Lab., Ames, IA (United States); Iowa State Univ., Ames, IA (United States)

MnBi is a candidate material for high-temperature magnets because of its increasing coercivity with increasing temperatures up to 255 °C. However, most efforts in fabricating bulk MnBi magnets have run into the problem of preserving the coercivity (H_cj) of its feedstock powders. About 70% of powder’s H_cj would be lost during the densification process. Our micromagnetic modeling shows that the coercivity mechanism of the MnBi bulk magnet is controlled by nucleation of the reversal magnetization domains, and the large H_cj loss that occurred during the powder consolidation process can be attributed to the inter-grain magnetic coupling. To attain a high H_cj, the grains in the MnBi bulk magnet must be separated with a non-magnetic grain boundary phase (GBP). To validate this GBP hypothesis, we engineered MnBi bulk magnets with two different types of GBP. The first type of GBP was created in-situ by precipitating excessive Bi from the grains; the second type was created ex-situ by coating silicates on the feedstock powders before the consolidation. While both GBP work, the ex-situ approach resulted in a better H_cj due to a more uniform GBP distribution. We report the H_cj loss was reduced from 70% to 15%, and the (BH)max of a warm sintered bulk magnet reached 8.9 MGOe.

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Research Organization:: Ames Laboratory (AMES), Ames, IA (United States)

Sponsoring Organization:: USDOE Office of Science (SC); USDOE Office of Energy Efficiency and Renewable Energy (EERE), Energy Efficiency Office. Advanced Manufacturing Office

Grant/Contract Number:: AC02-07CH11358

OSTI ID:: 1902756

Report Number(s):: IS-J-10,909

Journal Information:: Journal of Magnetism and Magnetic Materials, Vol. 563; ISSN 0304-8853

Publisher:: ElsevierCopyright Statement

Country of Publication:: United States

Language:: English

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