Improving MnAl tetragonal phase stability through doping elements

Permanent magnets are vital in countless commercial applications but the existing high performance magnets use critical rare-earth (RE) elements making them vulnerable to supply chain disruption. This necessitates the exploration of alternative materials. Among the known intermetallic compounds, tetragonal MnAl (phase) is one of the most studied alloys as a potential RE free magnet. However, the phase-MnAl is metastable which can be stabilized using special synthesis procedure. Here we have theoretically investigated the possibility of stabilizing the phase using elemental doping in empty sites. The density functional theory calculation indicates that the phase can be stabilized by doping MnAl with hydrogen, carbon, nitrogen, oxygen or fluorine. However, these increase only magnetization or magnetocrystalline anisotropy (MAE). While the hydrogen and carbon doping increase MAE but decrease magnetization, doping with fluorine increases magnetization but decreases MAE significantly. The doping with oxygen and nitrogen decrease both magnetization and MAE. However, only the carbon doped samples can be synthesized using traditional methods such as arc-melting. We have prepared carbon doped MnAl samples using arc-melting and annealing and the results are consistent with the theoretical prediction. We will discuss both the theoretical and experimental results in this presentation.