Advanced Science Research Center, Japan Atomic Energy Agency
AnTGa5 (An: Actinides, T: transition metals) have been receiving increasing attention after the discovery of the heavy fermion superconductivity below 19 K in PuCoGa5 . Recently, we extend our research activity in neutron scattering for NpTGa5 (T: Fe, Co, Ni and Rh) compounds in order to get deep insight about the multipolar degree-of-freedom.
We revealed that NpTGa5 exhibits various antiferromagnetic structures of A-, C-, G-type, ferromagnetic ordering and cant magnetism (Fig.1) , which are the reminiscent of manganese perovskites.
The remarkable successive magnetic transition associated with reorientation and considerable increase of magnetic moment found in NpNiGa5 and NpRhGa5 is a signature for the change in the 5f electronic states, where the competing interactions of multipoles are expected to play an important role. We also present recent results of the resonant x-ray scattering experiments on NpNiGa5, which imply the existence of quadrupole ordering. We will sketch out a diverse electronic properties realized in NpTGa5 in terms of the competing magnetic and quadrupolar interactions.
 J.L. Sarrao, et al., Nature 420 (2002) 297.
 N. Metoki, J. Phys. Soc. Jpn., 75 (2006) Suppl. p.24 and references therein.
Fig.1 Rich variety of magnetic structures realized in NpTGa5