Investigation on the flux pinning force and flux pinning mechanism in Ba1-xKxFe2As2 single crystal with Tc = 38.5 K

The discovery of superconductivity in iron-based superconductors by Professor Hosono in Japan in 2008 has triggered off an enormous group of researches the world wide. The iron-based superconductors are regarded as another kind of high-Tc superconductors, which possess lots of merits, such as very high upper critical field (Hc2), high critical current density (Jc), and small crystal anisotropy (), are promising for high field applications. Ba1-xKxFe2As2, as a typical FeAs-122 superconductor, is focused on by both theoretical physicists and material scientists since its discovery. In this paper, we first successfully fabricate Ba1-xKxFe2As2 single crystal. It has an onset transition temperature up to 38.5 K, while its zero resistivity temperature reaches 37.2 K. Both the R-T and M-T data of it show very sharp superconducting transition, and its critical current density at 5 K and self field is over 106 Acm-2 and almost field independent. The flux pinning force and the relative pinning mechanisms in Ba1-xKxFe2As2 are discussed by analyzing the data obtained from the measurements about the R-T and M-H under different conditions. Results indicate that the Ba1- xKxFe2As2 superconductors have very strong intrinsic vortex pinning force, and the vortex potentials (U0) under 9 T field are 5800 K and 8100 K for the H//c and H//ab, respectively. Furthermore, the vortex pinning mechanism is also investigated by analyzing the relationship Jc-B. According to the present results, the flux pinning mechanism should be (l) pinning because of the change of mean free path for electrons induced by nano-size crystallographic defects in Ba1-xKxFe2As2.