Superconductivity of the Bi–Sn Eutectic Alloy

We report on the results of investigations of superconductivity in the Bi–Sn binary alloy with a eutectic concentration of 57 wt % of Bi and 43 wt % of Sn. The temperature and field dependences of the dc magnetization have been measured in the range of 1.8–20 K in magnetic fields of up to 20 kOe using a Quantum Design MPMS3 SQUID magnetometer. A two-stage phase transition with diamagnetism establishment temperatures of 8.55 and 5.1 K has been found. A phase diagram has been built. The coherence length for the first stage has been estimated. The field dependence of the irreversibility temperature has been determined. Positive curvature portions observed in the critical dependences have been interpreted using a model based on the proximity effect.