Combined Study of Structural,Magnetic and Transport Properties of Eu_(0.5)Ln_(0.5)BiS_2F Superconductor

Superconductivity below 0.3 K and a charge-density-wave-like(CDW-like) anomaly at 280 K were observed in EuBiS_2F recently.Here we report a systematic study of structural and transport properties in Eu_(0.5)Ln_(0.5)BiS_2F(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 semiconductinglike behavior for all the Eu_(0.5)Ln_(0.5)BiS_2F 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 rareearth-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 Eu_(0.5)La_(0.5)BiS_2F.Coexistence of ferromagnetic order and superconductivity is found below 2.2 K in Eu_(0.5)Ce_(0.5)BiS_2F samples.Our results supplies a rich diagram showing that many interesting properties can be induced in BiS_2-based compounds.