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

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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 a pronounced magnetic fluctuation around $|Q|\approx 0.9$ Å-1, which is slightly smaller than the magnetic ordering vector $|Q|\approx 0.97$ Å-1. In a superconductor Fe(Se0.25Te0.75)0.92, we observed that a magnetic fluctuation is located at $|Q|\approx 0.9$ Å-1 at low energies and shifts to a higher value of $|Q|\approx 1.2$ Å-1 at higher energies. The latter value is close to a reciprocal lattice vector $\mathbf{Q} = (0.5,0.5,0.5)$ 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.
2009-10-15