Fast suppression of superconductivity with Fe site Ni substitution in   Fe1-xNixSe0.5Te0.5 (x=0.0, 0.01, 0.03, 0.05, 0.07, 0.10 and 0.20) single   crystals
  We report the effect of Ni doping on superconductivity of FeSe0.5Te0.5. The single crystal samples of series Fe1-xNixSe0.5Te0.5 (x=0.0, 0.01, 0.03, 0.05, 0.07, 0.10 and 0.20) are synthesized via vacuum shield solid state reaction route and high temperature heating followed by slow cooling. All the crystals of Fe1-xNixSe0.5Te0.5 series with x up to 0.20, i.e., 20% substitution of Ni at Fe site are crystallized in single phase tetragonal structure with space group P4/nmm. The electrical resistivity measurements revealed that Tc decreases fast with increase of Ni concentration in Fe1-xNixSe0.5Te0.5. Namely the superconducting transition temperature (Tc) being defined as resistivity =0 decrease from 12K to around 4K and 2K for x=0.01 and 0.03 samples respectively. For x=0.05 (5at% Ni at Fe site) though Tconset is observed in resistivity measurements but \r{ho}=0 is not seen down to 2K. For x more than 0.07, neither the Tconset nor Tc\r{ho}=0 is seen down 2K in R-T measurements. It is demonstrated that Ni doping at Fe site in FeSe0.5Te0.5 superconductor suppresses superconductivity fast. The rate of Tc depression is albeit non monotonic. Summarily, a systematic study on suppression of superconductivity with Fe site Ni doping in flux free gown FeSe0.5Te0.5 single crystals is presented in the current communication. 
P.K. Maheshwari, Bhasker Gahtori and V.P.S. Awana
cond-mat.supr-con cond-mat.mtrl-sci