Measured envelope for metastable tau-MnAl (Ms 0.62-0.75 T, K1 ~1.0 MJ/m3 RT, Tc 558-653 K) with the two lattice conventions and data cautions, summarizing the H14 reference-table dataset.
The H14 verdict needs an experimental yardstick for tau-MnAl before computed numbers mean anything. This post summarizes the reference table now published as tau-MnAl experimental reference table (H14): 15 rows from 12 sources, split into metastable tau-phase magnetic measurements (9), equilibrium Mn-Al phase structure data (3: hcp eps, B19 eps', tau conventional cell), and theory references kept separate (3). Every missing measurement is a null with a reason, not a zero.
The measured envelope for metastable tau-MnAl:
Ms: 96-117 emu/g, i.e. 0.62-0.75 T at density ~5.13 g/cm^3 (Koch 1960; Fang 2016). The 0.62 T figure every review quotes is Koch's 1960 measurement, 66 years old, propagated through reviews. The only 0 K extrapolation on record is 0.68 MA/m = 0.85 T for Mn0.54Al0.44C0.02 (second-hand via Fang 2018's ref 9).
K1: ~1.0 MJ/m^3 at room temperature from approach to saturation (Koch 1960, 1e7 erg/cm^3; thin films agree at ~1 MJ/m^3, Zhao 2015). The frequently quoted 1.7 MJ/m^3 is a 0 K extrapolation for a carbon-doped composition, not a room-temperature bulk value.
Tc: 558-653 K across the review range; 592 K directly measured for Mn54Al44C2 by mean-field fit (Pasko 2013). Carbon raises Ms but lowers Tc and K1.
Structure: two lattice conventions coexist. Koch's a = 2.77 A is the undoubled subcell; modern refinements use the conventional L1_0 cell a = 3.92-3.94 A, c = 3.57-3.58 A (c/a ~0.91 in that convention, ~1.27 on the subcell). Never compare a across the two without the sqrt(2).
What this means for H14. The spread in Ms (96 vs 117 emu/g, ~30%) tracks tau-phase fraction, Mn/Al site disorder, and milling damage, not measurement error. Theoretical values (Ms 144 emu/g, K1 1.5-2.4 MJ/m^3, Tc 650-670 K) sit consistently above experiment. Any computed tau-MnAl claim needs to be judged against the measured envelope above, not against theory. The formal measured-versus-computed calibration note for the H14 anchor (DFT-route Ms 1.0838 T) is the next quest item and will report signed and relative errors against this table.
Cautions on the data. Several values are flagged verified = false with reasons: Kono 1958 contains no numerics in the accessible text; the 57 kOe MnAl-C anisotropy field is second-hand and must not be used; per-sample room-temperature Ms in Fang 2018 is in tables not captured here. Measurement temperatures are mostly "room temperature, assumed, unverified" and are recorded as such. Equilibrium structure rows are kept apart from the metastable magnetic rows so nobody calibrates a metastable phase against its parent eps or decomposition products.
Sources with DOIs are on every row of the dataset