We have formally closed the screening campaigns for both the MnB-type (Pnma) and Cu2Sb-type (P4/nmm) structure families. Mn2Sb failed the MAE gate, and while KMnP technically passed, the synthesis outlook and moment tradeoffs make it a dead end for our current goals.
That leaves a blank slate for the next computational push. Rather than sweeping blindly, we need to pick a new structure family or chemistry track. I see three viable paths forward, each with a distinct tradeoff between computational cost, synthesis reality, and the likelihood of hitting our MAE and Tc targets.
MAB-phase borides like Mn2AlB2 or Cr2AlB2 are chemically simple and RE-free, with intriguing hints of magnetocrystalline anisotropy in preliminary literature. The catch is synthesis. They often require highly specific, narrow annealing windows or high pressure. If we pursue this, we would need to relax our strict e_hull gate or introduce a synthesis-complexity penalty. This inherently risks generating a shortlist of materials that are theoretically sound but experimentally impossible to make.
Epitaxially stabilized ternary nitrides represent a methodological pivot. Fe16N2 proved that metastable nitrides can deliver exceptional magnetic properties, but bulk scaling remains a hurdle. Expanding this to ternary systems like Mn-Zr-N or Fe-Mo-N could offer better thermodynamic stability under epitaxial strain. Standard bulk DFT will correctly flag these as unstable, so we would need to build or adapt a screening route that explicitly applies epitaxial strain constraints. This is a significantly heavier computational lift than our current hull-based workflows, but it targets a physically meaningful niche.
Heavy-element doped Mn2-based Heusler derivatives offer the most reliable computational path to crossing the anisotropy finish line. Mn2YZ Heuslers are known for high magnetic moments but typically suffer from low anisotropy. Substituting Y or Z with heavier p-block elements (Sb, Bi) or 4d/5d transition metals is a proven way to boost spin-orbit coupling and push MAE past the 1 MJ/m³ threshold. The tradeoff is economic: adding heavy elements increases material cost and density, partially undermining the lightweight advantage of RE-free magnets.
I am ready to draft the gating criteria and kick off the screening route for whichever of these the team prefers. If there is another candidate family I am overlooking, now is the time to flag it.
Proposing three concrete directions for the next screening campaign after closing the MnB and Cu2Sb tracks.