Author-facing protocol note for the Mn–Ge–N vacancy series: what one nitridation series decides, measured parent evidence vs the unmeasured Mn12Ge4N3 hypothesis, and a one-line ask.
In one sentence: this experiment decides whether pulling one nitrogen out of every four (going from Mn3GeN to Mn12Ge4N3) bends the antiperovskite's magnetism into something a magnet could use, or breaks it.
That is the whole question. Everything below is scaffolding for it.
Two things about the parent compound are measured, and they anchor the series:
Mn3GeN is a noncollinear ferrimagnet, with magnetic order persisting from roughly 30 to 500 K and vanishing near the tetragonal-to-cubic transition at about 524 K. That is the neutron-diffraction result of O'Donnell et al., "The crystal and magnetic structures of the nitride antiperovskite Mn3GeN".
The combinatorial synthesis of Mn-Ge-N phases, including nitrogen-deficient members, has been demonstrated by Bauers (MRS Communications 15, 1345 (2025), DOI). The route exists.
Everything about the derivative is hypothesis only. Our model context for Mn12Ge4N3 predicts a saturation magnetization of 736 kA/m and a Curie temperature of 434 K, both computed on an assumed ferromagnetic configuration. Given that the parent is a ferrimagnet, the assumed-FM moment is likely wrong in character, not just in magnitude. A literature sweep on 2026-08-22 confirmed the exact composition Mn12Ge4N3 has no experimental record at all: no synthesis, no magnetometry. The structure itself is sound (a P4/m N-vacancy-ordered superstructure of the antiperovskite, every nitrogen octahedrally coordinated by six Mn at about 2.0 A; it also passes our structure sanity gate), and our Gate 0 verification of the parent Mn3GeN found agreement between an ALIGNN moment prediction and the reported ferrimagnetic moment on the neutron-refined cell. But structure sanity and model predictions are not measurements.
The blind spot, stated precisely: we do not know what the N vacancy (3 vs 4 N per Mn12Ge4 unit) does to the ferrimagnetic ordering, the moment, or the tetragonal distortion. One nitridation series between the two endpoints, plus SQUID M(H) and M(T), closes it.
Six specimens, one precursor family, one magnetometry protocol:
A0, Mn3GeN (N=4): the reference point. Full nitridation, Rietveld-verified phase purity, M(H) to 7 T and M(T) 5-600 K. This is where the series either reproduces the O'Donnell result or fails.
A1-A3 (N=3.75, 3.5, 3.25): graded partial nitridation with mandatory N assay. Each point has a vacancy-driven observable (smooth, monotonic shift in c/a, moment, and ordering temperature) and a failure observable (abrupt phase change, endpoint demixing, secondary Ge or Mn3Ge2).
B, Mn12Ge4N3 (N=3): the vacancy-ordered endpoint. Success means P4/m superstructure reflections in the diffraction pattern AND moment/Tc values that interpolate smoothly from A0. Absent superstructure peaks or a two-phase mixture means N disorder, and the blind spot stays open.
The full synthesis conditions, anneals, purity gates, and per-point decision criteria are in the experiment matrix
This is also an open call: the Mn12Ge4N3 entry on our measured magnetic data call
This protocol was written from the outside, by people who run the models and the verification gates but not the furnaces. So the ask is deliberately small: correct one part of this protocol, or tell us whether the sample series is experimentally realistic. A one-line reply about a wrong anneal temperature, a misjudged N assay, or an unrealistic vacancy-ordering assumption is exactly the contribution we need, and it takes less time than reading most papers.
Credit where it belongs: the measured anchors here are the O'Donnell/Neilson neutron work and the Bauers combinatorial synthesis work. The models and the CIF are ours; the errors in the protocol, if any, are ours too.