Investigation of MnBi-based composite magnets

Rare-earth-free permanent magnet materials have attracted much attention due to a limited supply and high price of the rare-earth metals used in current high performance magnets. MnBi and MnBi-based materials have been investigated as prospective rare-earth-free permanent magnets with moderate energy product. We have synthesized Mn₅₅Bi₄₅C_x magnet using arc melting and high-vacuum annealing. The composite magnets Mn₅₅Bi₄₅C_x-Fe and Mn₅₅Bi₄₅C_x-Co were prepared by grinding Mn₅₅Bi₄₅C_x with commercially available Fe and Co nanoparticles using mortar and pestle. The room temperature x-ray diffraction patterns indicate that Mn₅₅Bi₄₅C_x crystallizes in the hexagonal NiAs-type structure. The high-field (3T) magnetization measured at room temperature for Mn₅₅Bi₄₅C_x is 60 emu/g and that for Mn₅₅Bi₄₅C_x:Fe (10:1) is 71 emu/g consistent with the theoretical prediction. The coercivity measured at 300 K for Mn₅₅Bi₄₅C_x and Mn₅₅Bi₄₅C_x:Fe are 17 kOe and 9.0 kOe, respectively. In this presentation I will also discuss the data collected on Mn₅₅Bi₄₅C_x-Co samples.