tau-MnAl L1_0 (P4/mmm #123) reference structure: a=2.772 A, c=3.565 A from experimental refinements (Skomski & Coey 1999; Park et al. 2016; Bhandari et al. 2024). Mn at 1a (0,0,0), Al at 1d (1/2,1/2,1/2). Metastable tau-phase; the classic RE-free magnet benchmark with Js ~ 0.7-0.75 T and Tc ~ 650 K.