Fe1.01Se0.38Te0.62 single crystal was successfully grown by self-flux method, and effect of post-annealing technique on structure and superconductivity was also systemically studied. The results show the as-grown sample has an excellent superconductivity with an onset transition temperature Tconset ∼ 14.6 K and a zero resistivity temperature Tczero ∼ 13.4 K. After annealing at 400 °C for 48 h, excess Fe in the post-annealing sample appears with Fe1.06Se0.34Te0.66 formula, and superconductivity was strongly suppressed with Tczero ∼ 8.0 K. The experiments found that excess Fe is located at Fe(2) site with local magnetic moment. According to the Werthamer-Helfand-Hohenberg (WHH) theory, the upper critical fields Hc2 at zero temperature were estimated to be 54.2 T for as-grown sample and 28.2 T for post-annealing sample. Two abnormal drops in DC magnetization are found near 40 K and 125 K for all samples, the one near 40 K may be related to a spin freezing of excess Fe and that near 120 K should be corresponding to the structural transition from tetragonal to monoclinic. This is confirmed by the strain measurement. On the other hand, a kink change of specific heat was also found around 10 K for a post-annealed sample.
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