Transport and Magnetic Properties of the Superconductor NpPd5Al2

Crystals of the transuranium superconductor ${\text{NpPd}}_{5}{\text{Al}}_{2}$ have been prepared by arc melting stoichiometric amounts of constituent pure metals (Np 99.9%, Pd 99.99%, Al 99.999%). The single crystals (extracted from the batch) were examined by x-ray diffraction, magnetization, resistivity, magnetoresistivity, Hall effect, thermoelectric power, and heat capacity measurements under magnetic fields and at low temperature along the main crystallographic directions. The superconductivity is observed at ${T}_{c}$ $\ensuremath{\sim}5\text{ }\text{K}$. It is intrinsically related to the ${\text{ZrNi}}_{2}{\text{Al}}_{5}$ structure type (space group $I4/mmm$) and independent of the synthesis process. The specific heat measured down to 0.6 K shows that ${\text{NpPd}}_{2}{\text{Al}}_{5}$ is a nonmagnetic strong coupled type II superconductor presenting heavy fermion features $({\ensuremath{\gamma}}_{e}\ensuremath{\sim}190\text{ }\text{mJ}\text{ }{\text{mol}}^{\ensuremath{-}1}\text{ }{\text{K}}^{\ensuremath{-}2})$. The determination of the critical field by electrical resistivity indicates high anisotropic ${B}_{{c}_{2}}$ values: $\ensuremath{\sim}4\text{ }\text{T}$ along [100] and $\ensuremath{\sim}15\text{ }\text{T}$ along [001]. Magnetoresistivity, Hall effect, and thermopower measurements point to strong electronic correlations that could be at the origin of superconductivity in this transuranium intermetallic compound.