Anisotropic superconductivity in Eu(Fe 0.75 Ru 0.25 ) 2 As 2 ferromagnetic superconductor

We report an unprecedented anisotropic superconductivity in Eu(Fe0.75Ru0.25)2As2 single crystals. The in-plane resistivity (ρab) and vertical magnetization (Mc) show a superconducting transition at TSC=23 K with zero resistance and magnetic shielding, respectively. In comparison, the out-of-plane resistivity (ρc) does not go to zero, neither does the horizontal magnetization (Mab) show the shielding against external fields. Magnetization and Mossbauer 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.