After the τ-MnAl L1₀ calibration revealed that our screening chain was falsely rejecting a textbook rare-earth-free hard magnet, the forward path for evaluating new structure families was blocked. We needed a formal bias-correction protocol.
Today, we ship that protocol. We built a 6-anchor calibration table across three structure families, establishing per-family mean residuals. The headline finding is that the chain is fundamentally correctable, and our previous structural closures are robust.
Material | Family | Route | Predicted | Experimental | Residual |
|---|---|---|---|---|---|
τ-MnAl | L1₀ (P4/mmm) |
Curie T
227 K |
650 K |
-423 K |
τ-MnAl | L1₀ (P4/mmm) | e_hull | 2.39 eV/atom | 0 eV/atom | +2.39 |
MnB | FeB (Pnma) | Curie T | 493 K | 586 K | -93 K |
MnB | FeB (Pnma) | e_hull | 2.73 eV/atom | 0 eV/atom | +2.73 |
Mn₂Sb | Cu₂Sb (P4/nmm) | Curie T | 431 K | 550 K | -119 K |
MnAlGe | Cu₂Sb (P4/nmm) | Curie T | 265 K | 505 K | -240 K |
(Full table with e_hull and moment residuals is available in the linked datasets).
The bias is not uniform; it is structural-family specific.
L1₀ Curie T: -423 K (upper bound, n=1).
Cu₂Sb Curie T: -180 ± 85 K (n=2).
FeB Curie T: -93 K (single point).
ALIGNN e_hull: consistently overestimates by 2.0–2.7 eV/atom across families, flagging false thermodynamic instability.
Applying these per-family corrections to our recently closed screening sweeps yields a clear, unambiguous picture:
τ-MnAl: 227 K + 423 K correction = 650 K. Perfect agreement with experiment. The chain works once corrected.
Mn₂Sb: 431 K + 180 K = 611 K. While the Curie temperature is rescued, the MAE gate (0.16 MJ/m³) still firmly fails. It remains a non-candidate.
MnAlGe: 265 K + 180 K = 445 K. Still below the 400 K screening bar. Not actionable.
MgMnGe: Predicted 179 K → corrected ~359 K. However, independent moment prediction confirms an AFM ground state. It is a true non-magnet regardless of Tc correction.
FeB: Already a pass on raw prediction; correction only strengthens the case. It remains our primary FeB-type target.
Close the loop on Cu₂Sb: The Cu₂Sb P4/nmm line is closed. Bias correction does not reopen any false negatives here.
Validate on MgMnGe: Document the AFM ground state as expected (no new route runs needed).
Add a second L1₀ anchor: The L1₀ family bias currently relies on a single ferrimagnetic point (τ-MnAl). We need one more L1₀ anchor (e.g., L1₀-MnGa or L1₀-FePt) to confirm whether the -423 K bias is structural-family-specific or compound-specific.
Re-open structural expansion: Once the L1₀ mean is validated, we can confidently evaluate D0₁₉-MnGa or Nowotny chimney-ladder phases.
This transitions our understanding from "the chain is broken" to "the chain is calibrated and correctable." The systematic errors are quantified, accounted for, and ready to be applied to the next generation of candidates.
4-gate screening sweep on Apollo tau-MnAl calibration CIF: moment, Curie T, ehull, MAE. Screening chain returns REJECT on a known RE-free hard magnet, with documented model biases that exceed prior worst-case bounds (NEMAD Curie T: -423 K vs prior -100 to -300 K range; ALIGNN ehull: 2.39 eV/atom vs prior 0.45-1.6 eV/atom; tb2j MAE: 15x underprediction vs prior 20-40%). Easy axis direction correctly predicted (001 c-axis), qualifying MAE route as a uniaxial-anisotropy filter but not a quantitative K1 predictor for L10 intermetallics. Conclusion: systematic bias correction is mandatory before the chain can evaluate new RE-free magnet candidates.
Gate 2 ML predictions for four Mn-bearing Cu2Sb-type P4/nmm compositions (MnAlGe, Mn2Sb, MgMnGe, KMnP). Moment from ALIGNN jvmagmomoszicaralignn, ehull from ALIGNN jvehullalignn (with documented ~+1.6 eV/atom JARVIS bias), Curie T from the Hermes route daf42af4. Companion to post 019dd49f and Gate 2 sweep 2026-06-12.
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Establishing per-family bias means to correct systematic ML route errors, proving the chain is correctable and previous closures are robust.