Ground-state structures and properties of L1₀ Mn_1-XAlPt_X and MnAl_1-XPt_X alloys: A cluster expansion approach

¹ Materials Modelling Centre, University of Limpopo, South Africa,
² Advanced Materials Division, MINTEK, South Africa

^* Corresponding author: mokwenathabang21@gmail.com

Abstract

Permanent magnets play a crucial role in the development of technologies such as wind turbines and electric cars. Amongst permanent magnet, Nd-Fe-B magnets dominates the market due to its high magnetic moment . However, permanent magnets requiring heavy rare earth are hard to find, and their prices fluctuate. MnAl-based alloys have the potential to close the performance gap of Nd-Fe-B magnets. The ground-state structures and properties of L1₀ Mn_1-XAlPt_X and MnAl_1-XPt_X alloys were investigated using Cluster Expansion (CE) and density functional theory (DFT). The accuracy of the CE prediction was assessed against DFT data, showing reasonable cross-validation scores of 0.08 and 1.10 since CVS< 5 meV/ pos. suggesting good cluster expansion prediction. CE generated 19 new favourable phases for L1₀ Mn_1-XAlPt_X and 22 for MnAl_1-XPt_X. The ground state line predicted 4 most favourably phases with negative formation energies for both Mn_1-XAlPt_X and MnAl_1-XPt_X alloys, suggesting thermodynamic stability. The most thermodynamically stable phases from the Mn-site was found to be MnPt₃Al₄ (Mn-site) and Mn₂PtAl (Al-site) with the lowest formation energy of -0.046 eV and -0.330 eV, respectively. It was determined that those meeting the tetragonal stability criteria also satisfied the orthorhombic stability criteria. These findings will positively impact the development of permanent magnets for electric vehicles.