Iron impurity in Chevrel phases: determination methods and influence on superconductivity

The dependence of critical temperature Tc on pressure P and iron concentration x was measured for FexSnMo6S8. The iron concentration was determined by activation analysis. The variation of Tc(x) is similar to that predicted by Abrikosov and Gorkov (1960). The critical concentration is xcr=0.061 (0.42. at.%). For x=0.04, delta Tc/ delta P is three times higher in absolute value than for x=0 and reaches -3.2*10-4 kbar-1. The variation of Tc(P) is not linear and may be explained by the pressure-enhanced exchange interaction of electrons with the magnetic moment of the impurity atoms.