Fig. 9. Two polymorphic modifications of Gd5Ge4: (a) the Sm5Ge4-type, which supports either the paramagnetic or antiferromagnetic states; and (b) the Gd5Si4-type, which the system adopts when it orders ferromagnetically. Both are layered structures built from nearly identical slabs (one of the slabs is marked by a bracket in (a)) and are related to one another by shear displacements of the neighboring slabs in the directions shown by short arrows near each of the slabs. The numbers above the arrows indicate the magnitude of the displacements. The most drastic difference is observed in the interslab Ge–Ge interactions, with corresponding interatomic distances that vary from 3.62 to 2.62 Å, as marked (from Ref. ).