Anion height dependence of critical current densities for Fe Te1-x Sex bulk single crystals

Abstract

We have fabricated FeTe1-xSex high quality bulk single crystals. The crystals with different composition of x = 0.375, 0.4, 0.45, 0.46 and 0.475 were prepared by the melting method with two stage heat treatment. The crystal structure and superconducting properties were evaluated. Temperature dependence of magnetization showed that low-T c region exists inside the crystals. Critical temperature T c was the highest value of 14.3 K for the crystal with x = 0.45. Critical current densities J c under the magnetic fields parallel to the c-axis at 4.2 K achieved 1.52 and 0.72 × 105 A / cm2 at 0 T and 5 T respectively for the crystal with x = 0.4. The crystal lattice parameters were examined by Rietveld refinement. The anion height from Fe layer was calculated using the obtained parameters. We investigated the anion height dependence of T c and J c and mentioned an important role of excess Fe about the magnetic flux pinning.