In this article,the Sm-doping single crystals Ca_(1-x)Sm_xFe_2As_2(x = 0 ~0.2) were prepared by the Ca As flux method,and followed by a rapid quenching treatment after the high temperature growth.The samples were characterized by structural,resistive,and magnetic measurements.The successful Sm-substitution was revealed by the reduction of the lattice parameter c,due to the smaller ionic radius of Sm^(3+)than Ca^(2+).Superconductivity was observed in all samples with onset T_c varying from 27 K to 44 K upon Sm-doping.The coexistence of a collapsed phase transition and the superconducting transition was found for the lower Sm-doping samples.Zero resistivity and substantial superconducting volume fraction only happen in higher Sm-doping crystals with the nominal x > 0.10.The doping dependences of the c-axis length and onset T_c were summarized.The high-T_c observed in these quenched crystals may be attributed to simultaneous tuning of electron carriers doping and strain effect caused by lattice reduction of Sm-substitution.
We report the discovery and characterization of a novel 112-type iron pnictide Eu Fe As_2, with La-doping induced superconductivity in a series of Eu_(1-x)La_xFeAs_2. The polycrystalline samples were synthesized through solid state reaction method only within a very narrow temperature window around 1073 K.Small single crystals were also grown from a flux method with the size about 100 lm. The crystal structure was identified by single crystal X-ray diffraction analysis as a monoclinic structure with space group of P21/m. From resistivity and magnetic susceptibility measurements, we found that the parent compound Eu Fe As_2 shows distinct anomalies probably due to the Fe^(2+) related antiferromagnetic/structural phase transition near 110 K and the Eu^(2+) related antiferromagnetic phase transition near 40 K.La-doping suppressed both phase transitions to lower temperatures and induced superconducting transitions with a Tc^11 K for Eu_(0.85)La_(0.15) Fe As_2.
Here we report the discovery of superconductivity in the ternary LaRu_2As_2 compound. The polycrystalline LaRu_2As_2 samples were synthesized by the conventional solid state reaction method. Powder X-ray diffraction analysis indicates that LaRu_2As_2 crystallizes in the Th Cr_2Si_2-type crystal structure with the space group I4/mmm(No. 139), and the refined lattice parameters are a = 4.182(6) and c = 10.590(3) . The temperature dependent resistivity measurement shows a clear superconducting transition with the onset T_c(critical temperature) at 7.8 K, and zero resistivity happens at 6.8 K. The upper critical field at zero temperature μ_0H_(c2)(0) was estimated to be 1.6 T from the resistivity measurement. DC magnetic susceptibility measurement shows a bulk superconducting Meissner transition at 7.0 K, and the isothermal magnetization measurement indicates that LaRu_2As_2 is a type-II superconductor.
