Tunable ( δ π , δ π )-Type Antiferromagnetic Order in α -Fe(Te,Se) Superconductors

The new $\ensuremath{\alpha}$-Fe(Te,Se) superconductors share the common iron building block and ferminology with the LaFeAsO and ${\mathrm{BaFe}}_{2}{\mathrm{As}}_{2}$ families of superconductors. In contrast with the predicted commensurate spin-density-wave order at the nesting wave vector ($\ensuremath{\pi}$, 0), a completely different magnetic order with a composition tunable propagation vector ($\ensuremath{\delta}\ensuremath{\pi}$, $\ensuremath{\delta}\ensuremath{\pi}$) was determined for the parent compound ${\mathrm{Fe}}_{1+y}\mathrm{Te}$ in this powder and single-crystal neutron diffraction study. The new antiferromagnetic order survives as a short-range one even in the highest ${T}_{C}$ sample. An…