Mössbauer parameters of ${}^{57}$Fe substituents in the topological insulator $B{i}_{2}S{e}_3$

Abstract

${}^{57}$Fe Mössbauer spectroscopy can probe several \emph{local} structural, electronic and magnetic properties of Fe-containing systems. However, to establish a direct relationship between these properties and a system's geometric structure, the experimental Mössbauer parameters need to be analyzed \emph{via} electronic structure calculations. Herein, structural, electronic and magnetic effects of iron substituents in the topological insulator $B{i}_{2}S{e}_3$, as uniquely probed by ${}^{57}$Fe Mössbauer spectroscopy, have been determined \emph{via} spin-polarized electronic structure calculations. The iron ion substituents, of \emph{nominal} Fe${}^{3+}(S=5/2)$ oxidation and spin state, are unequivocally shown to substitute Bi${}^{3+}$ sites in epitaxial $B{i}_{2}S{e}_3$ thin-films used for Mössbauer measurements. Concomitant with iron substitution, \emph{localized} structural rearrangements take place whereby the longer Bi-Se bonds of the native system are replaced by significantly shorter Fe-Se counterparts in the Fe-containing system. The resulting distorted-octahedral environment about substituent iron ions gives rise to characteristic Mössbauer parameters (${\delta }_{Fe}\approx$ 0.51 mm/s, $\Delta E_Q\approx$ 0.20 mm/s) which have been calculated in excellent agreement with measured values for Fe-doped $B{i}_{2}S{e}_3$ thin films. Consistent with a substituent Fe${}^{3+}$ ion's \emph{nominal} high-spin electronic configuration ($t_{2g}^{\uparrow \uparrow \uparrow }{e}_g^{\uparrow \uparrow }$), an Fe-centered spin density has been established which, nevertheless, extends towards neighboring Se atoms \emph{via} direct Fe-Se bonding and concomitant Fe(d)-Se(p) hybridization.

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Cited by in corpus (1)

• Magnetic Order in 3D Topological Insulators -- Wishful Thinking or Gateway to Emergent Quantum Effects?