Coexistence of superconductivity and magnetism in Fe1+δ Te1−xSex (x = 0.1, 0.2, 0.28, 0.4 and 0.45)

• Fe1+δ (Te1−xSex) single crystals for x up to 0.45 were synthesized.
• Samples undergo superconducting transitions at around 12–14 K.
• Values of the paramagnetic moment are close to 4 Bohr magnetons.
• μ0Hc(T) curves have positive curvature regions near Tc for H//c axis.

We report on the magnetic and transport properties of the ternary Fe1+δTe1−xSex crystals with nominal Fe excess δ = 0.03–0.04 and x = 0.1, 0.2, 0.28, 0.4, 0.45. The peculiarity of these crystals is the coexistence of superconductivity and magnetism. Susceptibility of all samples follows the Curie–Weiss law at temperatures above approximately 100 K. The values of effective magnetic moment are close to 4 Bohr magnetons for all compositions. Superconducting transition temperature ranges from 12 to 14.5 K with a maximum at around x = 0.3–0.4. For almost all samples the μ0Hc(T) curves have positive curvature regions near Tc when the field is parallel to the c axis.