Abstract and subjects
The physical properties including magnetic susceptibility, specific heat, and electrical resistivity of two new plutonium compounds Pu2M3Si5 (M = Co, Ni) are reported. Pu2Ni3Si5 crystallizes in the orthorhombic U2Co3Si5 structure type, which can be considered a variant of the BaAl4 tetragonal structure, while Pu2Co3Si5 adopts the closely related monoclinic Lu2Co3Si5 type. Magnetic order is observed in both compounds, with Pu2Ni3Si5 ordering ferromagnetically at T-C = 65 K then undergoing a transition into an antiferromagnetic state below T-N = 35 K. Two successive magnetic transitions are also observed at T-mag1 = 38 K and T-mag2 = 5 K in Pu2Co3Si5. Specific heat measurements reveal that these two materials have a moderately enhanced Sommerfeld coefficient gamma similar to 100 mJ/mol Pu K-2 in the magnetic state with comparable RKKY and Kondo energy scales.