REGARDING THE ABSENCE OF MAGNETIC ORDER IN QUADRATIC FORMS OF FeS

Tetragonal FeS (a = 3.768 angstrom, c = 5.038 angstrom, group P4/ nmm) has Fe(II) in a tetrahedral environment. Studied by neutron diffraction and Mossbauer effect it does not show any evidence for magnetic ordering at temperatures as low as 1. 7 degrees K. This behavior and the absence of metallic conductivity indicate strong covalency. Heating above 160 degrees C transforms the unstable tetragonal variety exothermically and with a volume contraction into the hexagonal form.