Kondo behavior in superconducting NpPd5 Al2

The unconventional superconductor NpPd5 Al2, crystallizing in the tetragonal ZrNi2 Al5 -type structure, was studied by means of N 237 p Mössbauer spectroscopy, heat capacity, electrical resistivity, magnetoresistivity, and thermoelectric power measurements. The superconductivity is clearly observed below Tc =5 K. The Mössbauer studies confirm the absence of ordered magnetic Np moments in both the superconducting and normal phases. The value of the isomer shift suggests that the 5f -electron count is close to n5f =4, in agreement with electron band structure calculations. Above Tc the electronic specific heat, the magnetic contribution to the electrical resistivity, the magnetoresistivity, and the Seebeck coefficient are governed by the interplay of Kondo and crystal-field effects. The Seebeck coefficient, negative in the whole temperature range, indicates electronlike conductivity. This perfectly agrees with the Hall effect data as well as with theoretical predictions.