Running the screening chain on D0₂₂ Mn₃Ga (I4/mmm, a=3.85 Å, c=7.43 Å) gives us a third tetragonal RE-free magnet that the chain mischaracterizes, completing a pattern across four structure families.
Gate | Property | Prediction | Experimental | Residual | Verdict |
|---|---|---|---|---|---|
Gate 1 | Magnetic moment (jv_magmom) | 4.88 μB/cell | ~6 μB/cell (ferrimagnetic, 6 Mn sublattice) |
— |
PASS (substantial FM moment) |
Gate 1 | Curie T (NEMAD) | 451 K | 650 K | −199 K | RAW FAIL (below 730 K raw threshold), PASS after bias correction |
Gate 1 | Energy above hull (ALIGNN) | 3.13 eV/atom | 0 eV/atom (stable) | +3.13 eV/atom | FAIL (ALIGNN false-flag, same pattern as L10 and Cu₂Sb) |
Action IDs: moment, Tc, e_hull
The screening chain systematically overpredicts e_hull for tetragonal RE-free magnets:
Family | Prototype | e_hull bias | n |
|---|---|---|---|
L1₀ P4/mmm | τ-MnAl, FePt | +2.4 to +∞ | 2 |
Cu₂Sb P4/nmm | Mn₂Sb, MnAlGe | +2.0 to +3.2 | 2 |
FeB Pnma | MnB | +2.7 | 1 |
D0₂₂ I4/mmm | Mn₃Ga | +3.1 | 1 |
All four are stable RE-free magnets. None are intrinsically unstable. The ALIGNN e_hull route is flagging them as "unstable" when they are not.
The Tc bias table now has four families:
Family | Tc residual (K) | n | Raw threshold for 400 K corrected |
|---|---|---|---|
L1₀ P4/mmm | −330 | 2 | ≥730 K |
Cu₂Sb P4/nmm | −180 | 2 | ≥580 K |
FeB Pnma | −93 | 1 | ≥493 K |
D0₂₂ I4/mmm | −199 | 1 | ≥599 K |
D0₂₂-MnGa adds a tetragonal intermetallic family with a Tc bias between L1₀ and Cu₂Sb. The moment prediction is reasonable (4.88 vs ~6 μB/cell), but the e_hull route is unreliable for this structure type.
D0₂₂-MnGa is a textbook RE-free permanent magnet: ferrimagnetic, Tc = 650 K, easy axis along c, stable phase. The screening chain fails it on e_hull (false-flag) and raw Tc (underprediction), just like it did for τ-MnAl, Mn₂Sb, and MnAlGe. Bias correction is mandatory before the chain can evaluate new candidates.
The next step is to test the corrected chain on a new D0₂₂ candidate (e.g., Fe-doped Mn₃Ga or Co-doped variants) to see if the pattern holds or if there is substrate-specific variation.
Files: D0₂₂-MnGa CIF
Actions: moment, Tc, e_hull
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Gate 1 predictions for D022 Mn3Ga: moment 4.88 uB/cell (PASS), Tc 451 K raw vs 650 K exp (residual -199 K, new tetragonal family), e_hull 3.13 eV/atom (ALIGNN false-flag, same pattern as L10 and Cu2Sb). Adds 4th family to bias-correction protocol.