Effects of sulfur vacancies on the crystallographic and spin-rotation transitions of iron sulfide

Sulfur-deficient iron sulfide, ${\mathrm{Fe}}_{1.04}$S, has been studied in comparison with FeS by Mössbauer spectroscopy at various temperatures ranging from 82 to 600 K. It is found that the 4 at. % sulfur vacancy makes the crystallographic α transition from the (NiAs,MnP) structure to a superstructure take place abruptly within 5 K with the superstructure stable up to 410 K. The spin-rotation transition of ${\mathrm{Fe}}_{1.04}$S takes place at 455 K, which is higher by 63 K than that of FeS. The Néel temperature is not affected appreciably by the sulfur vacancy concentration.