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

遍歴多体5電子系NpTGaにおける軌道秩序の重要性

目時 直人   ; 金子 耕士   ; 本多 史憲*; 浄念 信太郎; 山本 悦嗣  ; 芳賀 芳範   ; 青木 大*; 本間 佳哉*; 塩川 佳伸*; 大貫 惇睦

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

5遍歴反強磁性体NpTGaの磁気構造及び二段転移を中性子散乱によって研究した。その結果、磁気構造及び二段転移が四極子自由度を取り入れた局在モデルによって説明され、遍歴系の静的な秩序に関する局在モデルの有効であることが明らかになった。NpFeGa, NpNiGa, NpRhGaの低温相では反強磁性と四極子秩序の共存が予言されており、格子歪みや超音波,共鳴X線散乱実験などによって、遍歴多体電子系における四極子秩序の存在が確認される必要がある。

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.