Ag Doping Effects in FeSe_0.5Te_0.5 superconductor

抄録

Ag added bulk FeSe_0.5Te_0.5 single crystal like samples Ag_x(FeSe_0.5Te_0.5)_1-x were prepared by solid-state reaction. The x, nominal concentration of Ag, was ranged between 0 and 8%. The pure Ag or Ag compound was not observed in the X-ray diffraction patterns of Ag doped samples. The temperature and magnetic field dependences of magnetizations of prepared samples were measured using a superconducting quantum interference device (SQUID) magnetometer. The T_c was about 14K up to x=4%, but the T_c decreased gradually to 11K above x=5%. The calculated lattice parameter a is approximately constant with Ag addition. On the other hand, the c is nearly constant in the sample of x≤5%, but it decreases rapidly in x≥6%. The x dependence of T_c corresponds to the lattice parameter c. It means that, Ag might replace Fe and partially distorts a tetragonal FeSe_0.5Te_0.5 crystal structure in x>6%. The magnetization decreased with increasing of x, but the fishtail-like humps were observed in the magnetization curves. The maximal J_c(x)/J_c(0) was about 1.5 at x=5% and 5T under the applied magnetic field H perpendicular to the c-axis. The pinning potentials (U₀) were estimated from relaxation measurement of the magnetization at 5K when H was parallel to the c-axis. As a result, the sample of x=5% is considered to be more susceptible to flux creep than the sample of x=0%.