Magnetic correlations in the spin-glassy phase of Fe$_{1+\delta }$(Se,Te)

Using elastic and inelastic neutron scattering techniques, we investigated magnetic correlations in Fe$_{1.02}$Se$_{0.3}$Te$_{0.7}$ and Fe$_{1.01}$Se$_{0.15}$Te$_{0.85}$, both of which exhibit spin-glassy (SG) behaviors at low temperatures. Below the phase transition temperature, T$_{SG}$, magnetic Bragg peaks appear at incommensurate wavevector (\textbf{Q}$_{m})$ positions with \textbf{Q}$_{m}$ = (0.46, 0, 0.50). The peaks are broader than the instrumental resolution, indicating short range magnetic ordering. Above T$_{SG}$, strong short range magnetic fluctuations exist around \textbf{Q}$_{m}$ = (0.46, 0, 0.50). The fluctuations have very weak L-dependence, indicating the good two-dimensionality of the magnetic correlations. The location of \textbf{Q}$_{m}$ contrasts with the characteristic wave vector, (0.5,0.5,L), of the magnetic fluctuations observed in the superconducting phase of Fe$_{1+d}$(Se,Te).