From antiferromagnetism to superconductivity in Fe1+y(Te1-x,Sex) (0d x d 0.20): Neutron powder diffraction analysis

The nuclear and magnetic structure of Fe1+y(Te1-x,Sex) (0d x d 0.20) compounds were analyzed between 2 K and 300 K by means of Rietveld refinement of neutron powder diffraction data. The samples with x d 0.075 undergo a tetragonal to monoclinic phase transition at low temperature, whose critical temperature decreases with the increase of Se content; this structural transition is strictly coupled with a long range antiferromagnetic ordering at Fe site. Both monoclinic phase and long range antiferromagnetism are suppressed for 0.10 d x d 0.20. The onsets of the structural and magnetic transitions remain coincident with the increase of Se substitution. The low temperature monoclinic crystal structure has been revised. Superconductivity arises for x d 0.05, therefore a significant region where superconductivity and long range antiferromagnetism coexist is present in the pseudo-binary FeTe - FeSe phase diagram.