Mechanical and electrical properties of low temperature phase MnBi

Low temperature phase (LTP) manganese bismuth (MnBi) is a promising rare-earth-free permanent magnet material due to its high intrinsic coercivity and large positive temperature coefficient. While scientists are making progress on fabricating bulk MnBi magnets, engineers have begun considering MnBi...

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Bibliographic Details
Published in:Journal of applied physics 2016-01, Vol.119 (3)
Main Authors: Jiang, Xiujuan, Roosendaal, Timothy, Lu, Xiaochuan, Palasyuk, Olena, Dennis, Kevin W., Dahl, Michael, Choi, Jung-Pyung, Polikarpov, Evgueni, Marinescu, Melania, Cui, Jun
Format: Article
Language:English
Subjects:
Applied physics
Arc heating
Bismuth
CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS
Coercivity
Cold pressing
Compressive properties
Electric arc melting
Electrical properties
Electrochemical impedance spectroscopy
Heat treatment
Ingots
Low temperature
Magnetic properties
Manganese
MATERIALS SCIENCE
Microhardness
Motors
Permanent magnets
Physical properties
Positive temperature coefficient
Rare earth elements
Sintering (powder metallurgy)
Spectrum analysis
Temperature
Temperature dependence
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Summary:Low temperature phase (LTP) manganese bismuth (MnBi) is a promising rare-earth-free permanent magnet material due to its high intrinsic coercivity and large positive temperature coefficient. While scientists are making progress on fabricating bulk MnBi magnets, engineers have begun considering MnBi magnets for motor applications. Physical properties other than magnetic ones could significantly affect motor design. Here, we report results of our investigation on the mechanical and electrical properties of bulk LTP MnBi and their temperature dependence. A MnBi ingot was prepared using an arc melting technique and subsequently underwent grinding, sieving, heat treatment, and cryomilling. The resultant powders with a particle size of ∼5 μm were magnetically aligned, cold pressed, and sintered at a predefined temperature. Micro-hardness testing was performed on a part of original ingot and we found that the hardness of MnBi was 109 ± 15 HV. The sintered magnets were subjected to compressive testing at different temperatures and it was observed that a sintered MnBi magnet fractured when the compressive stress exceeded 193 MPa at room temperature. Impedance spectra were obtained using electrochemical impedance spectroscopy at various temperatures and we found that the electrical resistance of MnBi at room temperature was about 6.85 μΩ m.
ISSN:0021-8979
1089-7550
DOI:10.1063/1.4939811