One-step synthesis of K_xFe_2−ySe₂ single crystal for high critical current density

¹ National Institute for Materials Science - 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan
² JST, Transformative Research-Project on Iron Pnictides (TRIP) - Chiyoda, Tokyo 102-0075, Japan
³ University of Tsukuba - 1-1-1 Tennodai, Tsukuba, Ibaraki 305-0001, Japan

^a OZAKI.Toshinori@nims.go.jp

Received: 14 February 2012
Accepted: 16 March 2012

Abstract

We have established a simple process that allows for the one-step synthesis of K_xFe_2−ySe₂ single crystals, which exhibit high critical current density J_c. The post annealing and quenching technique has improved the homogeneity of as-grown crystals, resulting in full shielding of the external magnetic field. The quenched crystals show a superconducting transition at T_c^onset=32.9 K and T_c^zero=32.1 K. The upper critical fields _{μ 0} H₀₂ (0) for H∥ab and H∥c are estimated to be ∼206 and ∼50 T, respectively. The critical current densities J_c for H∥ab and H∥c reach as high as 1.0×10⁵ and 3.4×10⁴ A/cm² at 5 K. Furthermore, J_c exhibits a high field performance and a significantly weak temperature dependence up to 5 T, suggesting strong pinning. These results demonstrate that K_xFe_2−ySe₂ would be a promising candidate material for practical applications.