⁵⁷Fe nuclear resonant inelastic scattering of Fe_1.1Te

This study reports results of ⁵⁷Fe Mössbauer spectroscopy and nuclear resonant inelastic scattering (NRIS) in Fe_1.1Te. The Fe-specific partial phonon densities of states (PDOSs) were extracted from the observed spectra. No detectable change at the tetragonal-monoclinic phase transition around 65 K was observed. Therefore the variations in lattice constants and/or distortion in FeTe₄ tetrahedron through the structural transition was minute. From the observed Fe-PDOS, the Lamb-Mössbauer factor was 0.90(3) at 10 K and the Debye temperature was evaluated as 300(10) K. In ⁵⁷Fe Mössbauer spectroscopy, the clear magnetic spittings of spectra were measured below Néel temperature. The obtained values of isomer shifts showed characteristics of Fe²⁺ species and clear difference with the phase transition was observed in temperature dependence of quadrupole splitting (QS). The change of QS must be caused by substantial change of the charge density distribution around the Fe site. This suggests that the band structure or the nature of the Fe-Te bonds becomes highly anisotropic. These results might provide additional information about the respective mechanisms for FeTe_1−xSe_x superconductivity.