Electronic and magnetic structure ofα-FeSO4

Abstract

The study of the electronic and magnetic structure of $\ensuremath{\alpha}$-FeS${\mathrm{O}}_{4}$ is based on a model which consists of iron surrounded by six S${\mathrm{O}}_{4}$ tetrahedra forming a ${[\mathrm{F}\mathrm{e}{(\mathrm{S}{\mathrm{O}}_{4})}_{6}]}^{\ensuremath{-}10}$ 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 $\ensuremath{\alpha}$-FeS${\mathrm{O}}_{4}$ we investigate the orientation of the EFG with respect to the crystallographic frame, the M\"ossbauer parameters $\ensuremath{\Delta}{E}_{Q}$ and $\ensuremath{\eta}$, 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, $\ensuremath{\Delta}{E}_{Q}$, and $\ensuremath{\eta}$, 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\ifmmode^\circ\else\textdegree\fi{} between ${H}_{\mathrm{int}}$ and the main component of the EFG. Our low-temperature study of $\ensuremath{\alpha}$-FeS${\mathrm{O}}_{4}$ agrees with the recent experimental findings of Wehner, but it disagrees with those of Ono and Ito.