Anisotropic superconductivity in Eu(Fe_0.75Ru_0.25)₂As₂ ferromagnetic superconductor

Wen-He Jiao¹, Qian Tao¹, Jin-Ke Bao¹, Yun-Lei Sun¹, Chun-Mu Feng¹, Zhu-An Xu^1,2, I. Nowik³, I. Felner³ and Guang-Han Cao^1,2a

¹ Department of Physics, Zhejiang University - Hangzhou 310027, China
² State Key Lab of Silicon Materials, Zhejiang University - Hangzhou 310027, China
³ Racah Institute of Physics, The Hebrew University - Jerusalem 91904, Israel

^a ghcao@zju.edu.cn

Received: 19 June 2011
Accepted: 8 August 2011

Abstract

We report an unprecedented anisotropic superconductivity in Eu(Fe_0.75Ru_0.25)₂As₂ single crystals. The in-plane resistivity (ρ_ab) and vertical magnetization (M_c) show a superconducting transition at T_SC=23 K with zero resistance and magnetic shielding, respectively. In comparison, the out-of-plane resistivity (ρ_c) does not go to zero, neither does the horizontal magnetization (M_ab) show the shielding against external fields. Magnetization and Mössbauer data indicate that the Eu²⁺ spins order ferromagnetically below 19.5 K with the moments tilted 20^° from the c-axis. Our result suggests spontaneous-vortex phase and/or Fulde-Ferrell-Larkin-Ovchinnikov state in the ferromagnetic superconductor.