Illustration: Alan Stonebraker

Figure 1: Crystal structures and phase diagram of $Ni-Mn-Sn$. The shadowed area in the phase diagram is the region where $Ni-Mn-Sn$, on cooling, first becomes ferromagnetic and later transforms martensitically. (A) The $L21$ structure showing also the relationship with the tetragonal unit cell. (B) Tetragonal ($L10$) unit cell. (C) The tetragonal unit cell viewed from top. (D) The martensitic structure constructed from nanotwinned variants of the $L10$ structure.