Effect of 3d Metal (Co and Ni) Doping on the Superconductivity of FeSe$_{0.5}$Te$_{0.5}$

Abstract

We report the effect of 3d metal Cobalt (Co) and Nickel (Ni) doping on the FeTe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> Se <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> superconductor with the nominal composition range Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1 - x</sub> M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> Te <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> Se <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> ( M = Co, Ni and x = 0.00, 0.01 0.02, 0.05 , and 0.10). Samples are synthesized through standard solid state reaction route and all are crystallize in single phase tetragonal structure with space group P4/nmm. The lattice parameters ` <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a</i> ', ` <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</i> ' and volume decrease with increase in Co and Ni content, although not monotonically. In fact the ` <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a</i> ' lattice parameter is nearly unaffected for Co doped samples. The superconducting transition temperature ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Tc</i> ) is measured from both DC and AC magnetic susceptibility, which decrease with increase in Ni or Co content. Both Co and Ni suppress <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Tc</i> and drive the system into the normal state. Interestingly, Ni suppresses the superconductivity much faster than the Co. This indicates less effect on in-plane Fe-Se distances and thus reduced disorder in case of Co when compared with Ni substation at Fe site in FeTe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> Se <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> superconductor. It is concluded that in-plane disorder on superconducting Fe-Se and Fe-Se-Se planes directly affects superconductivity in FeTe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> Se <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> superconductor.