Paper detail

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 a related compound Fe(Se1-xTex)0.92 (x = 0.75, 1) using neutron scattering techniques. Non-superconducting FeTe0.92 shows antiferromagnetic (AF) ordering with the ordering vector |Q| = 0.97 A-1 (Q = (0.5,0,0.5)) at TN ~ 70 K and a structural transition between tetragonal and monoclinic phases. In the AF monoclinic phase, the low-energy spectral weight is suppressed, indicating a possible gap formation. On the other hand, in the paramagnetic tetragonal phase, we observed a pronounced magnetic fluctuation around at |Q| ~ 0.92 A-1, which is slightly smaller than the commensurate value. In Fe(Se0.25Te0.75)0.92, which does not show magnetic ordering and shows superconductivity at Tc ~ 8 K, we observed that a magnetic fluctuation is located at |Q| ~ 0.9 A-1 at low energies and shifts to a higher value of |Q| ~ 1.2 A-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 a important role in superconductivity.