Interplay of structure, magnetism, and superconductivity in Se substituted iron telluride with excess Fe.

We investigated the evolution of the temperature-composition phase diagram of Fe(1+y)Te upon Se substitution. In particular, the effect of Se substitution on the two-step, coupled magneto-structural transition in Fe(1+y)Te single crystals is investigated. To this end, the nominal Fe excess was kept at y = 0.