Abstract
Permanent-magnet materials are one cornerstone of today’s technology, abundant in disk drives, motors, medical equipment, wind generators, and cars. A continuing challenge has been to reconcile high permanent-magnet performance with low raw-material costs. This work reports a Mn-Bi-Sn alloy exclusively made from inexpensive elements, exhibiting high values of Curie-temperature, magnetization, anisotropy, coercivity, and energy product. The samples are produced by field annealing of rapidly quenched Sn-containing MnBi alloys, where the improvement of the magnetic properties is caused by the substitutional occupancy of the 2c sites in the hexagonal NiAs structure by Sn. The substitution modifies the electronic structure of the compound and enhances the magnetocrystalline anisotropy, thereby improving the coercivity of the compound. The energy product reaches 114 kJ/m3 (14.3 MGOe) at room temperature and 86 kJ/m3 (10.8 MGOe) at 200 °C; this value is similar to that of the Dy-free Nd2Fe14B and exceeds that of other rare-earth-free permanent-magnet bulk alloys, as encountered in automotive applications.
Highlights
The samples are produced by field annealing of rapidly quenched Sn-containing MnBi alloys, where the improvement of the magnetic properties is caused by the substitutional occupancy of the 2c sites in the hexagonal NiAs structure by Sn
The structure of MnBi is nontrivial, the ordering or Curie temperature is being a phase-transformation from a lowtemperature phase (LTP) to a high-temperature phase (HTP),29 and its room-temperature magnetocrystalline anisotropy of 1.2 MJ/m3 is relatively low
We have focused on simultaneously improving the anisotropy, coercivity, and energy product of MnBi
Summary
The structure of MnBi is nontrivial, the ordering or Curie temperature is being a phase-transformation from a lowtemperature phase (LTP) to a high-temperature phase (HTP),29 and its room-temperature magnetocrystalline anisotropy of 1.2 MJ/m3 is relatively low. This work reports a Mn-Bi-Sn alloy exclusively made from inexpensive elements, exhibiting high values of Curie-temperature, magnetization, anisotropy, coercivity, and energy product.
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