Coexistence of superconductivity and antiferromagnetism in single crystals A_0.8Fe_2−ySe₂ (A = K, Rb, Cs, Tl/K and Tl/Rb): Evidence from magnetization and resistivity

R. H. Liu, X. G. Luo, M. Zhang, A. F. Wang, J. J. Ying, X. F. Wang, Y. J. Yan, Z. J. Xiang, P. Cheng, G. J. Ye, Z. Y. Li and X. H. Chen^a

Hefei National Laboratory for Physical Science at Microscale and Department of Physics, University of Science and Technology of China - Hefei, Anhui 230026, PRC

^a chenxh@ustc.edu.cn

Received: 16 February 2011
Accepted: 21 March 2011

Abstract

We measure the resistivity and magnetic susceptibility in the temperature range from 5 K to 600 K for the single crystals AFe_2−ySe₂ (A = K_0.8, Rb_0.8, Cs_0.8, Tl_0.5K_0.3 and Tl_0.4Rb_0.4). 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 Néel temperature (T_N) as high as 500 K to 540 K 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.