Correlations in the Fe-Chalcogenide Semiconductor K₅Fe₄Ag₆Te₁₀

Unconventional superconductors such as Fe pnictides and chalcogenides exemplify systems where the interplay between multiple degrees of freedom results in a rich phase diagram. This includes superconductivity, antiferromagnetism, and nematicity and understanding these intertwined phases remains an open question. Here we present a study of K₅Fe₄Ag₆Te₁₀ (KFAT) which displays both nematic and magnetic order, as in Fe-based superconductors, but is a semiconductor with a relatively large magnetic moment which allows critical scattering to be probed reliably and accurately in 3d using neutrons. KFAT displays a superstructure which orders with an incommensurate wavevector. We report neutron diffraction and critical scattering at this incommensurate position allowing the magnetic correlation length to be extracted and the phase transition to be characterized. Links to nematic ordering and correlations will be explored. This provides insight into the microscopic mechanisms in these novel materials not able to be probed accurately in other Fe pnictides due to inherently small magnetic moments.