Optimizing composition in MnBi permanent magnet alloys

Jensen, Brandt A.; Tang, Wei; Liu, Xubo; Nolte, Alexandra I.; Ouyang, Gaoyuan; Dennis, Kevin W.; Cui, Jun

doi:10.1016/j.actamat.2019.10.003

Title: Optimizing composition in MnBi permanent magnet alloys

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Abstract

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 (M_S) 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 M_S of 75.5 emumore »« less

Authors:

Jensen, Brandt A. ^[1]; Tang, Wei ^[1]; Liu, Xubo ^[1]; Nolte, Alexandra I. ^[1]; Ouyang, Gaoyuan ^[2]; Dennis, Kevin W. ^[1];

^[2]

Ames Lab., Ames, IA (United States). Division of Materials Sciences and Engineering
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:: Mon Oct 07 00:00:00 EDT 2019

Research Org.:: Ames Lab., Ames, IA (United States); Iowa State Univ., Ames, IA (United States)

Sponsoring Org.:: USDOE Office of Energy Efficiency and Renewable Energy (EERE)

OSTI Identifier:: 1574017

Alternate Identifier(s):: OSTI ID: 1573438; OSTI ID: 1864011

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.

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                    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.  https://doi.org/10.1016/j.actamat.2019.10.003

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                    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.  https://doi.org/10.1016/j.actamat.2019.10.003.  https://www.osti.gov/servlets/purl/1574017.

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@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         = {Mon Oct 07 00:00:00 EDT 2019},

  month        = {Mon Oct 07 00:00:00 EDT 2019}

}

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