Incommensurate magnetism and structural phase transition in Fe1+yTe

The superconductivity with transition temperature Tc=8 K found in Fe1.01Se ignited interest due to its simple crystal structure. The bulk Fe1+yTe is non-superconducting, but exhibits an antiferromagnetic order that is not driven by the Fermi suface nesting and relatively large ordered moment on the Fe-sublattices. Fe1+yTe also undergoes a structural distortion at low temperatures, and both magnetic and structural transitions can be strongly influenced by tuning parameters such as excess Fe(y) or external pressure. The themodynamic measurements revealed a single first-order transition for Fe1.11Te, whereas two distinct phase transitions have been found for Fe1.13Te. Here we present the results of neutron diffraction experiments on single crystalline Fe1.11Te and Fe1.13Te samples and show that Fe1+yTe display unique interplay of incommensurate magnetism and structural phase transition in comparison to the other parent Fe-superconductors.