An experimental and computational investigation of structure and magnetism in pyrite Co${}_{1-x}$Fe${}_x$S${}_2$: Chemical bonding and half-metallicity

Abstract

Bulk samples of the pyrite chalcogenide solid solutions Co${}_{1-x}$Fe${}_x$S${}_2$ 0 <= x <= 0.5, have been prepared and their crystal structures and magnetic properties studied by X-ray diffraction and SQUID magnetization measurements. Across the solution series, the distance between sulfur atoms in the persulfide (S${}_2^{2-}$) unit remains nearly constant. First principles electronic structure calculations using experimental crystal structures as inputs point to the importance of this constant S-S distance, in helping antibonding S-S levels pin the Fermi energy. In contrast hypothetical rock-salt CoS is not a good half metal, despite being nearly isostructural and isoelectronic. We use our understanding of the Co${}_{1-x}$Fe${}_x$S${}_2$ system to make some prescriptions for new ferromagnetic half-metals.

8 pages including 9 figures