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Title: Optimizing composition in MnBi permanent magnet alloys

Abstract

MnBi is an attractive rare-earth-free permanent magnetic material due to its low materials cost, high magnetocrystalline anisotropy (1.6 × 10 6 J m -3), and good magnetization (81 emu g -1) at room temperature. Although the theoretical maximum energy product (BH) max of 20 MGOe is lower than that of NdFeB-based magnets, the low temperature phase (LTP) of MnBi has a positive temperature coefficient of coercivity, up to 200 °C, which makes it a potential candidate for high temperature applications such as permanent magnet motors. However, the oxygen sensitivity of the MnBi compound and the peritectic reaction between Mn and Bi make it difficult to synthesize into a material with high purity. This challenge is partly offset by adding excess Mn to the alloy, with composition close to Mn 55Bi 45 resulting in the highest saturation magnetization after common processing techniques such as arc melting, casting, melt spinning, and ball milling. In this paper, we report a systematic process which reduces the amount of excessive Mn, while simultaneously providing a large saturation magnetization (M S) of 79 emu g -1 at 300 K in the annealed Mn 52Bi 48 ribbons. We also report excellent magnetic properties in the ball powders,more » resulting in 0.5–5 µm particles with M S of 75.5 emu g -1, coercivity H ci of 10.8 kOe, and (BH) max of 13 MGOe using 9 T applied field at 300 K. A secondary annealing treatment on various ball milled powders increased H ci by up to 21%, and also resulted in an increase in M S up to 78.8 emu g -1.« less

Authors:
 [1];  [1];  [1];  [1];  [2];  [1]; ORCiD logo [2]
  1. Ames Lab., Ames, IA (United States). Division of Materials Sciences and Engineering
  2. Ames Lab., Ames, IA (United States). Division of Materials Sciences and Engineering; Iowa State Univ., Ames, IA (United States). Dept. of Materials Science and Engineering
Publication Date:
Research Org.:
Ames Laboratory (AMES), Ames, IA (United States)
Sponsoring Org.:
USDOE Office of Energy Efficiency and Renewable Energy (EERE)
OSTI Identifier:
1574017
Alternate Identifier(s):
OSTI ID: 1573438
Report Number(s):
IS-J 10072
Journal ID: ISSN 1359-6454
Grant/Contract Number:  
EE0007794; AC02-07CH11358
Resource Type:
Accepted Manuscript
Journal Name:
Acta Materialia
Additional Journal Information:
Journal Volume: 181; Journal Issue: C; Journal ID: ISSN 1359-6454
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; non-rare-earth; permanent magnet; MnBi

Citation Formats

Jensen, Brandt A., Tang, Wei, Liu, Xubo, Nolte, Alexandra I., Ouyang, Gaoyuan, Dennis, Kevin W., and Cui, Jun. Optimizing composition in MnBi permanent magnet alloys. United States: N. p., 2019. Web. doi:10.1016/j.actamat.2019.10.003.
Jensen, Brandt A., Tang, Wei, Liu, Xubo, Nolte, Alexandra I., Ouyang, Gaoyuan, Dennis, Kevin W., & Cui, Jun. Optimizing composition in MnBi permanent magnet alloys. United States. doi:10.1016/j.actamat.2019.10.003.
Jensen, Brandt A., Tang, Wei, Liu, Xubo, Nolte, Alexandra I., Ouyang, Gaoyuan, Dennis, Kevin W., and Cui, Jun. Mon . "Optimizing composition in MnBi permanent magnet alloys". United States. doi:10.1016/j.actamat.2019.10.003.
@article{osti_1574017,
title = {Optimizing composition in MnBi permanent magnet alloys},
author = {Jensen, Brandt A. and Tang, Wei and Liu, Xubo and Nolte, Alexandra I. and Ouyang, Gaoyuan and Dennis, Kevin W. and Cui, Jun},
abstractNote = {MnBi is an attractive rare-earth-free permanent magnetic material due to its low materials cost, high magnetocrystalline anisotropy (1.6 × 106 J m-3), and good magnetization (81 emu g-1) at room temperature. Although the theoretical maximum energy product (BH)max of 20 MGOe is lower than that of NdFeB-based magnets, the low temperature phase (LTP) of MnBi has a positive temperature coefficient of coercivity, up to 200 °C, which makes it a potential candidate for high temperature applications such as permanent magnet motors. However, the oxygen sensitivity of the MnBi compound and the peritectic reaction between Mn and Bi make it difficult to synthesize into a material with high purity. This challenge is partly offset by adding excess Mn to the alloy, with composition close to Mn55Bi45 resulting in the highest saturation magnetization after common processing techniques such as arc melting, casting, melt spinning, and ball milling. In this paper, we report a systematic process which reduces the amount of excessive Mn, while simultaneously providing a large saturation magnetization (MS) of 79 emu g-1 at 300 K in the annealed Mn52Bi48 ribbons. We also report excellent magnetic properties in the ball powders, resulting in 0.5–5 µm particles with MS of 75.5 emu g-1, coercivity Hci of 10.8 kOe, and (BH)max of 13 MGOe using 9 T applied field at 300 K. A secondary annealing treatment on various ball milled powders increased Hci by up to 21%, and also resulted in an increase in MS up to 78.8 emu g-1.},
doi = {10.1016/j.actamat.2019.10.003},
journal = {Acta Materialia},
number = C,
volume = 181,
place = {United States},
year = {2019},
month = {10}
}

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