Magnetism Driven by Anion Vacancies in Superconducting $\alpha$--FeSe${}_{1-x}$

Abstract

To study the microscopic electronic and magnetic interactions in the substoichiometric iron chalcogenide FeSe${}_{1-x}$ which is observed to superconduct at x~1/8 up to $T_c$=27 K, we use first principles methods to study the Se vacancy in this nearly magnetic FeSe system. The vacancy forms a ferrimagnetic cluster of eight Fe atoms, which for the ordered x=1/8 alloy leads to half metallic conduction. Similar magnetic clusters are obtained for FeTe${}_{1-x}$ and for BaFe${}_2$As${}_2$ with an As vacancy, although neither of these are half metallic. Based on fixed spin density results, we suggest the low energy excitations in FeSe${}_{1-x}$ are antiparamagnon-like with short correlation length.

arXiv comment6 pages, 5 embedded figures

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