The recently discovered(Li_(1-x) Fe_x)OHFe Se superconductor with T c about 40 K provides a good platform for investigating the magnetization and electrical transport properties of Fe Se-based superconductors. By using a hydrothermal ion-exchange method,we have successfully grown crystals of(Li_(1-x) Fe_x)OHFe Se. X-ray diffraction on the sample shows the single crystalline Pb O-type structure with the c-axis preferential orientation. Magnetic susceptibility and resistive measurements show an onset superconducting transition at around T c=38.3 K. Using the magnetization hysteresis loops and Bean critical state model, a large critical current J s is observed in low temperature region. The critical current density is suppressed exponentially with increasing magnetic field.Temperature dependencies of resistivity under various currents and fields are measured, revealing a robust superconducting current density and bulk superconductivity.
The temperature and angle dependent resistivity of Ba(Fe 0.75 Ru 0.25) 2 As 2 single crystals were measured in magnetic fields up to 14 T.The temperature dependent resistivity with the magnetic field aligned parallel to c-axis and ab-planes allow us to derive the slope of dH ab c2 /dT and dH c c2 /dT near T c yielding an anisotropy ratio Γ = dH ab c2 /dT/dH c c2 /dT ≈ 2.By scaling the curves of resistivity vs.angle measured at a fixed temperature but different magnetic fields within the framework of the anisotropic Ginzburg-Landau theory,we obtained the anisotropy in an alternative way.Again we found that the anisotropy(m c /m ab) 1/2 was close to 2.This value is similar to that in Ba0.6K0.4Fe2As2(K-doped Ba122) and Ba(Fe 0.92 Co 0.08) 2 As 2(Co-doped Ba122).This suggests that the 3D warping effect of the Fermi surface in Ru-doped samples may not be stronger than that in the K-doped or Co-doped Ba122 samples,therefore the possible nodes appearing in Ru-doped samples cannot be ascribed to the 3D warping effect of the Fermi surface.
