Advanced Science Research Center, Japan Atomic Energy Agency
○Fuminori HONDA

AnTGa5 (An: Actinides, T: transition metals) have been receiving increasing attention after the discovery of the heavy fermion superconductivity below 19 K in PuCoGa5 [1]. 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) [2], 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.

[1] J.L. Sarrao, et al., Nature 420 (2002) 297.
[2] N. Metoki, J. Phys. Soc. Jpn., 75 (2006) Suppl. p.24 and references therein.

Fig.1 Rich variety of magnetic structures realized in NpTGa₅