MAGNETIC-PROPERTIES OF NPGA3

Polycrystalline samples of NpG3 having the cubic AuCu3-type structure have been examined by magnetization, resistivity and Np-237 Mossbauer measurements. They show that the antiferromagnetic ordering occurring at about 65 K is replaced through a first-order transition by a ferrom agnetic one at 50 K. The saturation Np moment inferred from the hyperf ine field data amounts to 1.56mu(B). The analysis of the isomer shift data for the NpX3 Series allows us to conclude the occurrence of Np3ions and partial 5f delocalization in NpGa3. The value of the Np order ed moment and of the effective paramagnetic moment can be accounted fo r by assuming a GAMMA5 crystal field ground state.