Superconductivity of the Bi–Sn eutectic alloy

We present results of studies of superconductivity in a binary Bi-Sn alloy of the eutectic composition (57 wt.% Bi, 43 wt.% Sn). Temperature and field dependences of the dc magnetization were measured within a temperature range from 1.8 to 20 K in magnetic fields up to 20 kOe using a Quantum Design MPMS3 SQUID magnetometer. A two-stage phase transition with temperatures of the diamagnetism onset of 8.55 and 5.1 K was observed. A phase diagram was constructed. The coherence length for the first stage was estimated. The field dependence of the irreversibility temperature was found. Critical dependencies showed a positive curvature which was treated within the framework of the proximity effect model.