Superconductivity at 22 K in Ir-doped CaFe_2−xIr_xAs₂ single crystals

Key Laboratory of Applied Superconductivity, Institute of Electrical Engineering, Chinese Academy of Sciences - P. O. Box 2703, Beijing 100190, China

^a ywma@mail.iee.ac.cn

Received: 1 September 2011
Accepted: 5 October 2011

Abstract

In this paper we report superconductivity in single crystals of the new iron-pnictide system CaFe_2−xIr_xAs₂ (x=0, 0.05, 0.10, 0.13) grown by a self-flux solution method and characterized via X-ray, transport and magnetic measurements. The magnetic ordering associated with a structural transition at 160 K present in CaFe₂As₂ is completely suppressed by substitution of Fe with Ir and superconductivity is induced at a critical temperature T_c=22 K in the sample with x=0.13. We also determined the upper critical fields along the ab-plane and c-axis. The anisotropy of the CaFe_2−xIr_xAs₂ superconductors determined by the ratio of H^ab_c2 and H^c_c2 is estimated to be 1.5–2.2. Our results suggest that superconductivity can also be easily induced in the CaFe₂As₂ family by substituting the Fe with Ir, at almost the similar maximum transition temperatures as for Co, Ni and Rh doping.