SUPERCONDUCTIVITY IN TH3NI3SN4

Specific heat, resistivity and ac- and dc-magnetic susceptibility measurements revealed that Th3Ni3Sn4 is a new superconductor with the transition temperature T(c) = 1.38 K. The electronic specific heat coefficient gamma is 31.1 mJ/K2 mol-f.u., the Debye temperature THETA(D) is 255 K and the electron-phonon coupling constant lambda-(ep) is 0.43. The upper critical field Hc2 determined by ac-susceptibility in magnetic fields follows the temperature dependence calculated by Helfand and Werthamer. We conclude that Th3Ni3Sn4 is a BCS-superconductor of type-II with the GL parameter k = 10. Both susceptibility enhancement probably due to spin fluctuation and anomalous temperature dependence of the resistivity suggest that the conduction electron with d-character play an essential role in the superconductivity.