The Importance of the orbital degree-of-freedom in many body itinerant 5 electron system NpTGa

Metoki, Naoto   ; Kaneko, Koji   ; Honda, Fuminori*; Jonen, Shintaro; Yamamoto, Etsuji  ; Haga, Yoshinori   ; Aoki, Dai*; Homma, Yoshiya*; Shiokawa, Yoshinobu*; Onuki, Yoshichika

Systematic neutron scattering study revealed the diverse magnetic properties in NpTGa (T: Fe, Co, Ni, Rh, Pt) with A-, C-, G-type antiferro- and ferromagnetic and canted structure. We found that the successive magnetic transition in NpTGa (T = Fe, Ni, Rh) is an electronic transition between the high- and low-moment states. We argue that the orbital degree of freedom in the itinerant 5 compounds plays an important role for the magnetic properties. A localized model explains the ordering and phase diagram, where the quadrupole order parameter coexists with magnetic dipole in the ground state of NpTGa (T = Fe, Ni, Rh). It means that a localized model is a powerful tool to describe the static property, which is the temporal and spatial average of the fluctuating itinerant system. Our study indicates the existence of the multipole order in itinerant many body 5, where a new theoretical framework is necessary to describe these highly interesting phenomena.