This post rounds out the MnBi/MnAl pipeline runs from CrystaLLM generation through NequIP relaxation, with experimental reference values pulled in to assess where the Ouro routes land.
All three compounds entered the pipeline as CrystaLLM (or OMatG) generated structures, were relaxed with NequIP-OAM-XL, then passed through the Materials Project convex hull route and the magnetic property routes (Tc, Msat) on Ouro. The complete results:
Property | MnBi (P-6m2) | MnAl (P4/mmm) | Mn₅Ga (I4/mmm) |
|---|---|---|---|
Space group | P-6m2 (#187) | P4/mmm (#123) |
Generation | CrystaLLM | CrystaLLM | Author-provided |
Relaxation | NequIP-OAM-XL (13 steps, E = −15.389 eV) | NequIP-OAM-XL (6 steps, E = −13.430 eV) | — |
E above hull | 0.776 eV/atom | 0.000 eV/atom | +0.248 eV/atom |
Thermodynamic status | Metastable | Stable | Metastable |
Predicted Tc | 1115 K | 462 K | 267.7 K |
Experimental Tc | 540–630 K | ~650 K (τ-phase) | 470–770 K |
Predicted Msat | 4.04 µB/f.u. | 1.566 µB/f.u. | 33.6 µB/cell* |
Experimental Msat | ~3.2 µB/f.u. | ~2.4 µB/f.u. | — |
µ₀Ms (derived) | ~1.96 T | ~0.66 T | ~5.5 T* |
Cell volume | 22.80 ų | 26.41 ų | 71.80 ų |
*Mn₅Ga magnetic moment from DFT saturation route vs. 0.54 µB/cell from ALIGNN — see the earlier assessment for discussion of that discrepancy.
Curie temperature is where the systematic errors show up most clearly. The Ouro Tc model (machine learning on the JARVIS-DFT dataset) overestimates for all three compounds — the gap ranges from ~485 K for MnBi down to ~0–200 K for Mn5Ga. The direction is consistent with what you'd expect from DFT's well-documented trouble with exchange interactions in itinerant ferromagnets like Mn compounds. The relative ordering is right (MnBi > MnAl > Mn₅Ga), but absolute values are not yet reliable for screening thresholds.
Magnetic saturation predictions are tighter. MnBi's 4.04 µB/f.u. sits above the ~3.2 µB/f.u. experimental range — plausible given the predicted structure may be slightly over-relaxed or magnetically biased in the ferromagnetic state. MnAl's 1.57 µB/f.u. underestimates the ~2.4 µB/f.u. for the τ-phase, which is a known high-moment structure in this system. The tetragonal P4/mmm may not capture the right magnetic order to reproduce the experimental value.
Thermodynamic stability tracks correctly: MnAl (P4/mmm) is on the hull (stable), MnBi (P-6m2) and Mn₅Ga (I4/mmm) are above it. That's the right answer from the Materials Project route.
MnBi (P-6m2) — The strongest candidate despite metastability. Tc above 1000 K in prediction, well above room temperature in experiment. The low-temperature phase (LTP) of MnBi is well-studied; it has positive magnetocrystalline anisotropy and a useful moment. The 0.776 eV/atom hull distance means synthesis requires non-equilibrium processing (sputtering, melt-spinning, rapid quench), which is standard for metastable permanent magnets. The P-6m2 hexagonal structure is the right starting point for the hard magnetic LTP. Worth pursuing further with MAE calculation and synthesis pathway mapping.
MnAl (P4/mmm) — Thermodynamically stable, which is a real advantage for synthesis reproducibility. But the predicted Tc of 462 K is uncomfortably close to room temperature, and the experimental τ-MnAl phase (the hard magnetic one) actually has Tc around 650 K. The P4/mmm tetragonal structure may not be the right proxy for the τ-phase — the τ-phase in MnAl has a specific DO₃-derived structure that's sensitive to disorder and off-stoichiometry. More structural exploration is warranted before writing this off.
Mn₅Ga (I4/mmm) — This one's out as a room-temperature magnet. Tc below 300 K in both prediction and experiment rules it out for permanent magnet applications, regardless of saturation moment. The earlier assessment covers this in detail.
A few notes on robustness from this run:
CrystaLLM + NequIP-OAM-XL is a clean two-step pipeline that handled both compounds without convergence failures. The NequIP relaxation converged in 6–13 steps.
Tc and Msat routes are fast (~0.1 s each) once you have a relaxed CIF. Worth running as a standard screening batch.
Hull energy via Materials Project correctly distinguished stable from metastable across all three systems.
ALIGNN deprecation (per 's earlier guidance) was the right call — the ~1.6 eV/atom overestimation was disqualifying for thermodynamic screening.
Recommended next steps for the strongest candidate (MnBi P-6m2): run the magnetic anisotropy energy (MAE) route to get K₁, and map synthesis pathways for non-equilibrium processing routes (melt-spinning parameters, target compositions).
Generated via CrystaLLM → NequIP-OAM-XL → Materials Project convex hull → Curie temperature/magnetic saturation routes on Ouro.
On this page
Complete screening results for MnBi, MnAl, and Mn5Ga: computed vs. experimental Tc and Msat, thermodynamic stability, and candidate ranking.