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

Abstract

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 O 2 -annealing effects in Fe 1.01 Te 0.91 S 0.09 .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 O 2 annealing. Our results indicate that O 2 annealing is probably effective near the surface of samples over a length of a few tens of micro meters.