Magnetic and electronic properties of the ferromagnetic Kondo-lattice system Np2PdGa3

Intermetallic compounds Lu2PdGa3 and Np2PdGa3 have been found to crystallize in an orthorhombic CeCu2-type structure with the Imma space group. The lattice parameters at room temperature are: a=0.4382(2), b=0.6870(3), and c=0.7593(3) nm for Lu2PdGa3 and a=0.4445(2), b=0.7089(3), and c = 0.7691(3) nm for Np2PdGa3. The electronic ground-state properties of these compounds were established by magnetic, calorimetric, electrical resistivity, magnetoresistance, and Hall coefficient measurements. The experimental data reveal a metallic behavior for Pauli paramagnetic Lu2PdGa3, characterized by Sommerfeld ratio gamma=2.5 mJ/K-2 mol Lu and temperature-independent susceptibility chi(0) similar to 1 x 10(-4) emu/mol. In contrast to the nonmagnetic Lu2PdGa3 reference, Np2PdGa3 behaves as a local-moment ferromagnet with the Curie temperature T-C=62.5(2) K. Low-temperature properties of Np2PdGa3 are characterized by a large Sommerfeld ratio gamma=120(2) mJ/K-2 mol Np and a small Fermi momentum k(F)=0.44 angstrom(-1). The observed features in Np2PdGa3 are well interpreted by assuming competition of three different interactions: Rudermann-Kittel-Kasuya-Yosida (RKKY), crystal electric field (CEF) and Kondo effect, which are represented by respective energies k(B)T(RKKY), Delta(CEF), and k(B)T(K). We argue that Np2PdGa3 is the Np-based ferromagnetic Kondo-lattice system with T-K < T-RKKY approximate to Delta(CEF).