Figure 2

(a) Temperature dependence of magnetization at 5 Oe for Fe_1+yTe_0.6Se_0.4 single crystal annealed at 200°C with increasing time. Changes in T_c and self-field J_c(2 K) with increasing annealing time at (b) 200°C, (c) 400°C. (d) Changes in J_c^2K(0)/J_{c, max}^2K(0) with increasing the annealing time at temperature from 200°C to 400°C.