Electronic and magnetic structure of $\alpha$-FeS${\mathrm{O}}_4$

The study of the electronic and magnetic structure of $\alpha$-FeS${\mathrm{O}}_4$ is based on a model which consists of iron surrounded by six S${\mathrm{O}}_4$ tetrahedra forming a ${\left[\mathrm{F}\mathrm{e}{\left(\mathrm{S}{\mathrm{O}}_4\right)}_6\right]}^{-10\mathrm{}}$ cluster; its three-dimensional structure is based on x-ray diffraction data. For many-electron terms of ferrous high-spin compounds derived from semiempirical cluster calculations, we investigate spin-orbit coupling, electric field gradient (EFG), and susceptibility. In particular for the EFG we discuss valence, overlap, and lattice contributions. Within the paramagnetic region of $\alpha$-FeS${\mathrm{O}}_4$ we investigate the orientation of the EFG with respect to the crystallographic frame, the Mössbauer parameters $\Delta E_Q$ and $\eta$, and the susceptibility; we find our results in reasonable agreement with the recent experimental data of Wehner. Within the antiferromagnetic region at 4.2 K we study the influence of the molecular exchange field upon EFG, $\Delta E_Q$, and $\eta$, and we further estimate the orientation of the internal magnetic field ($H_{\mathrm{int}}$) at the iron nucleus with respect to the crystallographic frame. Finally we derive an angle of 27.7° between $H_{\mathrm{int}}$ and the main component of the EFG. Our low-temperature study of $\alpha$-FeS${\mathrm{O}}_4$ agrees with the recent experimental findings of Wehner, but it disagrees with those of Ono and Ito.