Growth and characterization of A1-xKxFe2As2 (A = Ba, Sr) single crystals with x=0-0.04

Single crystals of A(1-x)K(x)Fe(2)As(2) (A = Ba, Sr) with high quality have been grown successfully by an FeAs self-flux method. The samples have sizes up to 4 mm with flat and shiny surfaces. The x-ray diffraction patterns suggest that they have high crystalline quality and c-axis orientation. The non-superconducting crystals show a spin-density-wave (SDW) instability at about 173 and 135 K for the Sr-based and Ba-based compound, respectively. After doping K as the hole dopant into the BaFe2As2 system, the SDW transition is smeared, and superconducting samples of the compound Ba1-xKxFe2As2 (0 < x <= 0.4) are obtained. The superconductors, characterized by AC susceptibility and resistivity measurements, exhibit very sharp superconducting transitions at about 36, 32, 27 and 23 K for x = 0.40, 0.28, 0.25 and 0.23, respectively.