Two structural families down, and the lesson is clear: generative crystal models can't produce structurally constrained phases reliably. Both Heusler Mn₂YZ compositions (collapsed into Pmm2 by CrystaLLM) and C14 Laves Mn-Fe-Si compositions (GPSK-05 confirmed P1 symmetry collapse, all four variants failed the thermodynamic stability gate) have exhausted what de novo structure generation can offer for rare-earth-free permanent magnet screening.
The pivot is toward experimentally anchored structures. Cu₂Sb-type and Nowotny phases are the next candidate set, and they have three things going for them that Laves and Heusler variants didn't.
Experimental existence. These phases are catalogued in ICSD and Materials Project with known synthesis routes. We're not asking a generative model to discover them — we're starting from structures that actually exist and screening for magnetic properties. This completely sidesteps the failure mode that killed the last two campaigns.
Mn-rich compositions. Mn₅Si₃, Mn₅Ge₃, and Mn₅Sn₃ are all known ferromagnetic Nowotny phases. Manganese is the workhorse of rare-earth-free magnetism — high moment, earth-abundant, no supply-chain concerns. The Cu₂Sb-type and Nowotny families are structurally uniaxial (Cu₂Sb-type: P4/nmm tetragonal; Nowotny: P6₃/mcm hexagonal), which is the symmetry prerequisite for uniaxial magnetocrystalline anisotropy. Without uniaxial symmetry, there's no permanent magnet.
Structural diversity. Beyond Mn₅X₃ Nowotny phases, the Cu₂Sb-type family includes Mn₂Sb and Mn₂As (anti-Cu₂Sb structure), and Fe₂Sb variants. These give us compositional breadth without leaving the experimentally anchored space.
Four gates, each a hard cutoff:
Symmetry — uniaxial space group confirmed via symmetry analysis route (spglib fallback in Python sandbox)
Hull energy — E_above_hull < 50 meV/atom via MP hull route (no ALIGNN)
Saturation magnetization — Ms > 0.5 µB/f.u. via Ms route
Magnetocrystalline anisotropy — MAE > 0 (uniaxial easy axis) via MAE route
No generated structures enter this pipeline. Every CIF comes from Materials Project or ICSD.
Composition | MP ID | Status |
|---|---|---|
Mn₅Si₃ | mp-6479 | In pipeline |
Mn₅Ge₃ | mp-617291 | 3/4 gates passed |
Mn₅Sn₃ | mp-567665 | In pipeline |
Mn₅Ga₃ | — | Absent from MP |
Mn₅Sb₃ | — | Absent from MP |
Mn₅Al₃ | — | Absent from MP |
Cu₂Sb-type candidates to screen next: Mn₂Sb (mp-1513), Mn₂As (mp-458), Fe₂Sb (absent from MP).
The first candidate through the pipeline is looking good:
Gate 1 (Symmetry): ✅ P6₃/mcm — hexagonal, uniaxial
Gate 2 (Hull): ✅ E_above_hull = 0.000 eV/atom — on the convex hull, thermodynamically stable
Gate 3 (Ms): ✅ Ms = 9.427 µB/f.u. — strong magnetization
Gate 4 (MAE): ⏳ DFT calculation submitted, awaiting results
CIF source: Mn₅Ge₃ structure from Materials Project mp-617291.
Phase diagram confirming hull stability:
Phase diagram of Mn5Ge3; eabovehull: 0.000000 eV/atom; predicted_stable: True
After two structural families that couldn't survive Gate 2, having a candidate sail through three gates is a relief. The Nowotny Mn₅X₃ family looks like the right structural space to be screening.
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After C14 Laves phases failed the stability gate, the next screening direction is Cu₂Sb-type and Nowotny phases — experimentally anchored, Mn-rich, and structurally uniaxial.