Title: New anisotropic MnBi permanent magnets by field-annealing of compacted melt-spun alloys modified with Mg and Sb

Abstract

A technique has been designed for manufacturing rare-earth-free MnBi-based magnets capable of filling the existing "gap" between the ferrite and rare-earth permanent magnets. Whereas the earlier approaches relied on sintering of fine and easily degrading single-crystal MnBi particles, the new method achieves refinement of the key α-MnBi phase through melt-spinning combined with appropriate alloying. Modification of the MnBi alloys with Mg and Sb generates a high-coercivity nanostructure of the metastable β' phase. A subsequent compaction at 150 °C produces fully dense materials while converting the β' phase into the stable α phase. Lastly, a short annealing at 265–300 °C in a magnetic field of 3 T increases the fraction of the α phase to 97–98% and aligns the c axes of the α crystallites. A maximum energy product (BH)_max of 11.5 MGOe and an intrinsic coercivity Hc of 5.6 kOe have been obtained in a magnet with the nominal composition Mn₅₀Bi_46.5Mg₃Sb_0.5. Because the coercivity increases with temperature, the maximum energy product of this magnet is still as high as 8.9 MGOe at 175 °C. Increasing the Sb content to 1.5 at.% increases the H_c to 9.3 kOe, but at the same time inhibits the development of the texture thus decreasingmore » the (BH)_max. The addition of Mg was found to increase the c lattice parameter of the α phase resulting in an unusually large ratio c/a ≈1.432.« less

Authors:

Gabay, Alexander M. ^[1]; Hadjipanayis, George C. ^[1]; Cui, Jun ^[2]

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+ Show Author Affiliations

1. Univ. of Delaware, Newark, DE (United States)
2. Ames Lab. and Iowa State Univ., Ames, IA (United States)

Publication Date:

Fri Sep 13 00:00:00 EDT 2019

Research Org.:

Univ. of Delaware, Newark, DE (United States); Iowa State Univ., Ames, IA (United States)

Sponsoring Org.:

USDOE Office of Energy Efficiency and Renewable Energy (EERE), Transportation Office. Vehicle Technologies Office; USDOE Office of Science (SC), Basic Energy Sciences (BES)

OSTI Identifier:

1561557

Alternate Identifier(s):

OSTI ID: 1562554; OSTI ID: 1864013

Grant/Contract Number:  

FG02-90ER45413; EE0007794

Resource Type:

Accepted Manuscript

Journal Name:

Journal of Magnetism and Magnetic Materials

Additional Journal Information:

Journal Volume: 495; Journal Issue: C; Journal ID: ISSN 0304-8853

Publisher:

Elsevier

Country of Publication:

United States

Language:

English

Subject:

36 MATERIALS SCIENCE; 75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; metals and alloys; permanent magnets; rapid-solidification; high magnetic fields; magnetic measurements; X-ray diffraction; MnBi