Combined Study of Structural, Magnetic and Transport Properties of Eu_0.5 Ln _0.5BiS₂F Superconductor*

Superconductivity below 0.3 K and a charge-density-wave-like (CDW-like) anomaly at 280 K were observed in EuBiS2F recently. Here we report a systematic study of structural and transport properties in Eu0.5Ln0.5BiS2F (Ln = La, Ce, Pr, Nd, Sm) by electrical resistivity, magnetization, and specific heat measurements. The lattice constants have a significant change upon rare earth substitution for Eu, suggesting an effective doping. As Ln is changed from Sm to La, the superconducting transition temperature T c increases from 1.55 K to 2.8 K. In contrast to the metallic parent compound, the temperature dependence of electrical resistivity displays semiconducting-like behavior for all the Eu0.5 Ln 0.5BiS2F samples. Meanwhile, the CDW-like anomaly observed in EuBiS2F is completely suppressed. Unlike the mixed valence state in the undoped compound, Eu ions in these rare-earth-doped samples are mainly divalent. A specific anomaly at 1.3 K resembling that in EuBiS2F suggests the coexistence of superconductivity and spin glass state for Eu0.5La0.5BiS2F. Coexistence of ferromagnetic order and superconductivity is found below 2.2 K in Eu0.5Ce0.5BiS2F samples. Our results supplies a rich diagram showing that many interesting properties can be induced in BiS2-based compounds.