Coexistence of superconductivity and antiferromagnetism in single crystals A0.8Fe2-ySe2 (A = K, Rb, Cs, Tl/K and Tl/Rb): Evidence from magnetization and resistivity

We measure the resistivity and magnetic susceptibility in the temperature range from 5K to 600K for the single crystals AFe(2-y)Se(2) (A = K-0.8, Rb-0.8, Cs-0.8, Tl0.5K0.3 and Tl0.4Rb0.4). A sharp superconducting transition is observed in low-temperature resistivity and susceptibility, and the fully shielding fraction shows bulk susceptibility for all the crystals, while an antiferromagnetic transition is observed in susceptibility at Neel temperature (T-N) as high as 500K to 540K depending on A. This indicates the coexistence of superconductivity and antiferromagnetism in these intercalated iron selenides. A sharp increase in resistivity arises from the structural transition due to Fe vacancy ordering at temperature slightly higher than T-N. Occurrence of superconductivity in an antiferromagnetic ordered state with so high T-N may suggest new physics in this type of unconventional superconductors. Copyright (C) EPLA, 2011