Title: Enhancing Phase Stability and Coercivity of MnAl $τ$-L$1_0$ with Fe and Ni Substitutions: \textit{ab initio} and Micromagnetic Modeling

Abstract: The binary manganese aluminium (MnAl) alloy with L$1_0$ crystal structure, which exhibits exceptional magnetic properties, is a promising rare earth element free permanent magnet material. However, according to experimental reports, synthesizing it in a stable bulk form is extremely challenging. Here, we propose and theoretically verify an alternative method of stabilizing the material by partially substituting Mn and Al sites by Fe and Ni and identify its stability, electronic structure, and magnetic properties from density functional theory (DFT) calculations. When considering a fixed ($50\%$)-Ni, the magnetic anisotropy increases with the increasing Fe content, but the trend is opposite in terms of formation energy. The calculated formation energies demonstrate that all the binary and quaternary compositions are stable. Through the analysis of calculated elastic constants and phonon frequencies, we confirm that all compositions are mechanically and dynamically stable. Most importantly, both magnetic moment and magnetic anisotropy constant in $50\%$-Fe substituted composition (equiatomic phase) increases significantly as compared to the MnAl. Predicted coercivity of equiatomic phase is larger than parent compound obtained by combining DFT computed parameters with micromagnetic simulations.