Size Dependence of Oxygen-annealing Effects on Superconductivity of Fe{1+y}Te{1-x}S{x}

For the Fe-based superconductor Fe{1+y}Te{1-x}S{x}, superconductivity is induced by annealing treatment in oxygen atmosphere, whereas as-grown samples do not show superconductivity. We have investigated the sample-size dependence of O2-annealing effects in Fe1.01Te0.91S0.09. The annealing conditions are fixed to be 1 atm, 200 C, and 2 hours. We have carried out magnetic susceptibility and specific heat measurements in order to evaluate the superconducting volume fraction. We have found that Fe{1+y}Te{1-x}S{x} has an optimal size for the induction of bulk superconductivity by O2 annealing. Our results indicate that O2 annealing is probably effective near the surface of samples over a length of a few tens of micro meters.