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

TL;DR

This study investigates the magnetic phase diagram of Fe$_{1+y}$Se$_x$Te$_{1-x}$, revealing a spin-glass regime with short-range incommensurate SDW order and structural distortions in non-superconducting samples.

Contribution

It provides detailed neutron scattering and magnetization data showing the coexistence of spin-glass behavior, short-range SDW order, and structural distortions in FeSeTe compounds.

Findings

Spin-glass behavior observed below 23K in certain samples.

Short-range incommensurate SDW order with specific wave vector.

Structural distortion coincides with SDW order.

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 $T_{\rm sg} = 23$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 ${\bf Q}_m = (0.46, 0, 0.50)$ and an anisotropy gap of $\sim$ 2.5 meV. Our high ${\bf Q}$-resolution data also show that the systems undergo a glassy structural distortion that coincides with the short-range SDW order.