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

TL;DR

This study combines experimental and computational methods to analyze the structure and magnetism of Co$_{1-x}$Fe$_x$S$_2$ pyrite solid solutions, revealing the role of S-S bonding in half-metallicity and guiding the design of new ferromagnetic materials.

Contribution

It provides new insights into the electronic structure and magnetic properties of Co$_{1-x}$Fe$_x$S$_2$, emphasizing the significance of S-S bond length in half-metallicity and proposing design principles for ferromagnetic half-metals.

Findings

S-S distance remains nearly constant across the series.

S-2 antibonding levels pin the Fermi energy.

Hypothetical rock-salt CoS is not a good half metal.

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.