Magnetic excitations of Fe1 + ySexTe1 − x in magnetic and superconductive phases

Abstract

We have used inelastic neutron scattering and muon-spin rotation to comparethe low energy magnetic excitations in single crystals of superconductingFe1.01Se0.50Te0.50 andnon-superconducting Fe1.10Se0.25Te0.75. We confirm the existence of a spin resonance in the superconducting phase ofFe1.01Se0.50Te0.50, at an energy of 7 meVand a wavevector of (1/2, 1/2, 0). The non-superconducting sample exhibits two incommensurate magnetic excitations at(1/2, 1/2, 0) ± (0.18, − 0.18, 0) which rise steeply in energy, but no resonance is observed at low energies.A strongly dispersive low energy magnetic excitation is also observed inFe1.10Se0.25Te0.75 close to the commensurate antiferromagnetic ordering wavevector(1/2 − δ, 0, 1/2), whereδ≈0.03. The magnetic correlations in both samples are found to bequasi-two-dimensional in character and persist well above the magnetic (Fe1.10Se0.25Te0.75) andsuperconducting (Fe1.01Se0.50Te0.50) transition temperatures.