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TT: Fachverband Tiefe Temperaturen

TT 10: Poster Session: Superconductivity

TT 10.16: Poster

Montag, 14. März 2011, 14:00–18:00, P4

Superconductivity and local-moment magnetism in Eu(Fe_0.89Co_0.11)₂As₂ — •Shuai Jiang^1,2, Philipp Gegenwart¹, and Guanghan Cao² — ¹I. Physikalisches Institut, The University of Goettingen, Goettingen, Deutschland — ²Department of Physics, Zhejiang University, Hangzhou, China

Here we report the anisotropic measurements of resistivity and magnetization under magnetic fields on a Eu(Fe_0.89Co_0.11)₂As₂ single crystal. We observed a resistivity drop at T_c=21 K, which suggests a superconducting transition. The low-field magnetic susceptibility data also show the evidence of superconductivity. Instead of expected zero-resistance below T_c, a resistivity reentrance appears at 17 K under zero field, coincident with the magnetic ordering of Eu²⁺ moments. According to the temperature and field dependences of anisotropic magnetization, we propose there exists a helical magnetic structure for the Eu²⁺ spins. The external magnetic fields easily changes the helimagnetism into ferromagnetism with fully polarized Eu²⁺ spins, accompanying by disappearance of the resistivity reentrance. Therefore, superconductivity coexists with ferromagnetic state of Eu²⁺ spins under relatively low magnetic field. The magnetic and superconducting phase diagrams are finally finished for magnetic fields parallel and perpendicular to the basal plane.