Effect of Sb and Si doping on the superconducting properties of FeSe0.9

Abstract

In the present work, we have studied the effect of doping Sb and Si at the Se-site of FeSe0.9 on the superconducting properties, such as transition temperature (Tc), upper critical field (Hc2) and irreversibility field (Hirr). The polycrystalline samples have been synthesized via two step solid state reaction route with nominal compositions Fe[Se1−x(Sb/Si)x]0.9 (x=0.0, 0.05, 0.10, 0.15 and 0.20). The X-ray diffraction results show the presence of tetragonal α-FeSe phase with the P4/nmm space group symmetry in all the samples. The highest superconducting onset temperatures, Tconset∼9.42Kand9.20K, respectively, for Si and Sb doped samples have been found for x=0.05. The temperature dependence of Hc2(T) and Hirr(T) have been calculated from the magnetoresistance data using the criteria of 90% and 10% of normal state resistivity (ρn) values, respectively. The values of Hc2(0) estimated from Werthamer–Helfand–Hohenberg (WHH) and Ginzburg–Landau (GL) theories are found to follow the same trends and maximum Hc2(0) is found for the composition x=0.10 for both the Si and Sb doped samples. The irreversibility field, Hirr and activation energy, U0 have also been calculated to study the vortex motion behavior of the samples. A clear cut correlation between Hirr and U0 has been found.