Investigation of the spin-glass regime between the antiferromagnetic and superconducting phases in Fe${}_{1+y}$Se${}_x$Te${}_{1-x}$

Abstract

Using bulk magnetization along with elastic and inelastic neutron scattering techniques, we have investigated the phase diagram of Fe${}_{1+y}$Se${}_x$Te${}_{1-x}$ and the nature of magnetic correlations in three nonsuperconducting samples of Fe${}_{1.01}$Se${}_{0.1}$Te${}_{0.9}$, Fe${}_{1.01}$Se${}_{0.15}$Te${}_{0.85}$ and Fe${}_{1.02}$Se${}_{0.3}$Te${}_{0.7}$. A cusp and hysteresis in the temperature dependence of the magnetization for the $x=0.15$ and 0.3 samples indicates spin-glass (SG) ordering below $T_{\mathrm{sg}}=23$K. Neutron scattering measurements indicate that the spin-glass behavior is associated with short-range spin density wave (SDW) ordering characterized by a static component and a low-energy dynamic component with a characteristic incommensurate wave vector of ${\mathbf{Q}}_m=(0.46,0,0.50)$ and an anisotropy gap of $\sim$ 2.5 meV. Our high $\mathbf{Q}$-resolution data also show that the systems undergo a glassy structural distortion that coincides with the short-range SDW order.