Evolution of Intrinsic Magnetic Properties in L1₀ Mn-Al Alloys Doped with Substitutional Atoms and Correlated Mechanism: Experimental and Theoretical Studies

L10 MnAl permanent-magnet alloys are promising candidates to plug the gap in performance and applications between rare-earth permanent magnets and ferrites; doping with a third atom is essential to achieve decent magnetic properties and good L10-phase stability. In this work, the influence of substitutional atoms on intrinsic magnetic properties in L10 MnAl alloys is investigated by combined experimental and theoretical studies. A highly pure L10 phase is synthesized in Mn55Al45-xMx (M = Co, Cu, Ga) alloys by regulation of the heat treatment, on the basis of ternary phase diagrams. It is demonstrated by experimental measurements and calculations that Cu and Co tend to enter 1a (0, 0, 0) sites, where they degrade the intrinsic magnetic properties of the alloys, and Ga prefers the 1d (1/2, 1/2, 1/2) sites, where it improves them. The excess valence electrons of Cu or Co compared with Mn lead to stronger bonding with Al, resulting in the preference of occupying 1a (0, 0, 0) sites. The similar valence-electron structure of Ga compared with Al makes Ga tend to occupy 1d (1/2, 1/2, 1/2) sites. On the basis of this understanding, we propose a strategy of replacing the antiferromagnetic Mn atoms by 3d atoms with fewer valence electrons than Mn, which may effectively enhance the intrinsic magnetic properties. Moreover, the stability of the alloyed L10 phase is investigated; Co is found to degrade the stability of the phase, but the addition of Cu or Ga can stabilize it. These results provide guidance for further performance optimization and composition design of Mn-based rare-earth permanent magnets.