Modifying magnetic properties of MnBi with carbon: an experimental and theoretical study

Abstract

MnBi and MnBi-based materials have been investigated as prospective rare-earth-free permanent magnets with moderate energy product. One of the main issues with MnBi is the segregation of Bi during materials synthesis reducing net magnetization. We have found that MnBi synthesized in a carbon environment substantially reduces the amount of Bi segregation, improving its saturation magnetization. We have synthesized Mn55Bi45 and Mn55Bi45C samples using arc melting and high-vacuum annealing. The room temperature x-ray diffraction patterns indicate that both Mn55Bi45 and Mn55Bi45C crystallize in the hexagonal NiAs-type crystal structure. The Rietveld analysis of the x-ray patterns shows that the amount of Bi segregation reduces from 16 wt.% for Mn55Bi45 to 5 wt. % for Mn55Bi45C. The high-field (3T) magnetizations measured at room temperature are 61 emu/g and 66 emu/g for Mn55Bi45 and Mn55Bi45C, respectively. In addition, there is a slight increase in the value of the anisotropy constant, namely, 1.6 Merg/cm3 and 2.1 Merg/cm3 for Mn55Bi45 and Mn55Bi45C, respectively. To understand the role of C in enhancing the magnetization of MnBi, we carried out the first-principles calculations of both stoichiometric and nonstoichiometric MnBi alloys, which suggests that the increase of magnetization in Mn55Bi45C is due to the coating of MnBi grains with C.

Enhanced Li-Ion Diffusivity of LiFePO4 by Ru Doping: Ab Initio and Machine Learning Force Field Results

“…It is known that local crystal structure, electronic configuration, and ionic diffusion can be enhanced by surface engineering, for example, coating with carbon, minimizing the particle size at the nanoscale, and doping with suitable dopants . The carbon coating ,− improves the electron conductivity by forming the interparticle charge-conduction layers with enhanced charge mobility.…”