Structural instability in new magnetic heusler compounds

The crystal structure and magnetic properties have been determined for a new series of compounds of the form Rh₂TSn. For T = Mn, Ni, or Cu, the room temperature structure is the fully ordered cubic Heusler structure. For T = V, Cr, Fe, or Co, a new structure is observed which is an exceptionally large tetragonal distortion of the Heusler structure (c/a = 1.18?1.27). The appearance of this tetragonal distortion is attributed to an electronic instability of the band Jahn-Teller type.