Magnetic and electronic properties of the antiferromagnet NpCoGa5 -: art. no. 184411

The Np counterpart of the superconducting PuCoGa5 compound, NpCoGa5, has been investigated by magnetization, resistivity, specific heat, and Np-237 Mossbauer spectroscopy measurements. Unlike the plutonium compound, NpCoGa5 does not show any hint of superconductivity down to T=0.4 K but the onset of antiferromagnetic order below T-N=47 K. The magnetization experiments evidence a metamagnetic-like transition (B-c=4.5 T at T=5 K) towards a canted antiferromagnet. The electronic effective mass in NpCoGa5 is moderately enhanced with a Sommerfeld specific heat coefficient gamma=64 mJ mol(-1) K-2, comparable to that of PuCoGa5. An ordered Np moment of 0.84 mu(B) and the occurrence of a Np3+ charge state were inferred from the Mossbauer data. Comparison with NpGa3 suggests a moderate delocalization of the 5f electrons in NpCoGa5. Similarities and differences with the isostructural PuCoGa5 and CeMIn5 compounds are discussed.