MnBi-based magnets prepared from melt-spun alloys: Effect of $α&nbsp;→&nbsp;β$ phase transformation during field annealing

Gabay, A. M.; Hadjipanayis, G. C.

doi:10.1016/j.jmmm.2020.167340

MnBi-based magnets prepared from melt-spun alloys: Effect of $α → β$ phase transformation during field annealing

Journal Article · Sat Sep 05 00:00:00 EDT 2020 · Journal of Magnetism and Magnetic Materials

DOI:https://doi.org/10.1016/j.jmmm.2020.167340· OSTI ID:1656764

Gabay, A. M. ^[1]; Hadjipanayis, G. C. ^[2]

Univ. of Delaware, Newark, DE (United States); UNIVERSITY OF DELAWARE
Univ. of Delaware, Newark, DE (United States)

The temperature of the annealing treatment applied to the MnBi alloys with the intention to stabilize the α-MnBi “low-temperature” phase – a promising material for the rare-earth-free permanent magnets – is usually kept below the range of the β-Mn_1.08Bi “high-temperature” phase. This work is focused on the investigation of the effects of partial and complete α → β phase transformation in bulk magnetic-field-annealed magnets on their structure and magnetic properties. MnBi alloys modified with In, Mg and Sb were melt-spun, compacted to their full density and then heated in a magnetic field of 30 kOe to temperatures sufficiently high for the beginning of the α → β transformation. A heating of 15 °C/min was used which was immediately followed by cooling at the rate of 7.5 °C/min; the degree of the phase transformation was measured by in situ monitoring of changes in the sample magnetization. In all the studied alloys, the α → β transformation was found to improve the [0 0 1] fiber texture induced by the applied magnetic field, although it simultaneously decreased the coercivity. A partial transformation has resulted in a 11% increase of the maximum energy product for the Mn₅₀Bi₄₉Sb_0.5In_0.5 magnet, to 8.3 MGOe, and a 3% increase for the Mn₅₀Bi₄₆Mg₃Sb_0.5In_0.5 magnet, to 12.8 MGOe. In the latter alloy, the α → β and reverse transformations were found to initially occur in well-defined pockets leading to clusters of large, highly textured α crystallites. In the Mn₅₀Bi_48.5Sb_1.5 magnet, only part of the α phase could be recovered after the transformation, which instead promoted the paramagnetic MnBi_0.9Sb_0.1 phase.

View Accepted Manuscript (DOE)

Research Organization:: Univ. of Delaware, Newark, DE (United States)

Sponsoring Organization:: USDOE; USDOE Office of Science (SC), Basic Energy Sciences (BES)

Grant/Contract Number:: FG02-90ER45413

OSTI ID:: 1656764

Alternate ID(s):: OSTI ID: 2325401

Journal Information:: Journal of Magnetism and Magnetic Materials, Journal Name: Journal of Magnetism and Magnetic Materials Vol. 516; ISSN 0304-8853

Publisher:: ElsevierCopyright Statement

Country of Publication:: United States

Language:: English

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