Antiferromagnetic Fluctuations in Fe(Se1-xTex)0.92 (x=0.75, 1) Observed by Inelastic Neutron Scattering

Motivated by the discovery of superconductivity in F-doped LaFeAsO, we investigated the magnetic fluctuations in related compounds Fe(Se1-xTex)(0.92) (x = 0.75, 1) using neutron scattering technique. Non-superconducting FeTe0.92 shows it pronounced magnetic fluctuation around vertical bar Q vertical bar approximate to 0.9 angstrom(-1), which is slightly smaller than the magnetic ordering vector vertical bar Q vertical bar approximate to 0.97 angstrom(-1). In a superconductor Fe(Se0.25Te0.75)(0.92), we observed that it magnetic fluctuation is located at vertical bar Q vertical bar approximate to 0.9 angstrom(-1) at low energies and shifts to a higher value of vertical bar Q vertical bar approximate to 1.2 angstrom(-1) at higher energies. The latter value is close to a reciprocal lattice vector Q = (0.5, 0.5, 0.5) or (0.5, 0.5, 0), where the AF fluctuations are observed in other FeAs-based materials. The existence of this common characteristic in different Fe-based superconductors suggests that the AF fluctuations may play an important role in superconductivity.